CCQM KEY COMPARISON K75 DETERMINATION OF TOXIC METALS IN ALGAE
Prepared by A. Shakhashiro1, A. Toervenyi1, S. Gaudino2, S. Rosamilia2, M. Belli2 1
G. C. Turk3
IAEA Environment Laboratories, Austria.
Environmental Metrology Unit, Istituto Superiore per la Protezione e la Ricerca Ambientale, Rome, Italy.
2
National Institute for Standards and Technology, USA.
3
DRAFT B
Seibersdorf February 2010
EDITORIAL NOTE The use of particular designations of countries or territories does not imply any judgment by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA. page ii
FOREWORD
The IAEA is a signatory of the Mutual Recognition Arrangement (CIPM, 1999), which was drawn up by the International Committee for Weights and Measures, under the authority given to it in the Meter Convention. The objectives of the International Committee for Weights and Measures Mutual Recognition Arrangement are to establish the degree of equivalence of national measurement standards maintained by National Metrology Institutes, to provide for the mutual recognition of calibration and measurement certificates issued by the National Metrology Institutes, and to provide governments and other parties with a secure technical foundation for wider agreements related to international trade, commerce and regulatory affairs. Within the frame of mutual cooperation between the IAEA and the BIPM, this key comparison and pilot study were organized under the auspices of the Inorganic Analysis Working Group of the at the Consultative Committee for Amount of Substance (CCQM). The scope of the study was the determination of toxic metals in the IAEA-450 algae candidate reference material. The study is additionally being used as a demonstration of “core-capabilities” that participants use as a mean to provide evidence for their Calibration and Measurement Capabilities (CMC) claims, and as such participants were asked to report in parallel to the National Institute of Standards and Technology in the USA on core capabilities demonstragted during the study. The study was classed as a Key Comparison K75 with a parallel Pilot Study P118 with the larger scope. The present report will be referenced in the key comparisons database (KCDB) of the International Bureau of Weights and Measures. Details are given in this report on methodologies applied in this international comparison and its results. The study was piloted by the Chemistry Unit of the Terrestrial Environment Laboratory in Seibersdorf (Austria) and the IAEA officer responsible for its coordination was A. Shakhashiro of the IAEA Environment Laboratories.
TABLE OF CONTENT
1.
INTRODUCTION................................................................................................... 2
2.
PARTICIPATING INSTITUTES ........................................................................... 3
3.
SAMPLES AND INSTRUCTION TO PARTICIPANTS ...................................... 5
3.1.
MATERIAL ..................................................................................................... 5
3.2.
HOMOGENEITY STUDY .............................................................................. 5
3.3.
INSTRUCTIONS TO PARTICIPANTS ......................................................... 6
4. 4.1. 5.
METHODS OF MEASUREMENT ........................................................................ 7 APPLIED ANALYTICAL PROCEDURES.................................................... 7 RESULTS AND DISCUSSION ........................................................................... 13
5.1.
GENERAL ..................................................................................................... 13
5.2.
ASSESSMENT OF CORRELATION BETWEEN REPORTED RESULTS AND DIGESTION MIXTURES USED...................................... 14
5.3.
ASSESSMENT OF MOISTURE CONTENT CORRECTION FACTOR ........................................................................................................ 15
5.4.
CALCULATION OF THE REFERENCE MASS FRACTION VALUES AND ASSOCIATED UNCERTAINTIES .................................... 15
5.5.
EQUIVALENCE STATEMENTS................................................................. 21
5.6.
METROLOGICAL TRACEABILITY .......................................................... 23
6.
DEMONSTRATED CORE-CAPABILITIES ...................................................... 25
7.
CONCLUSIONS ................................................................................................... 26
ACKNOWLEDGEMENT ....................................................................................................... 26
1.
INTRODUCTION
The determination of mass fraction of toxic elements and especially platinum emitted from automobile catalytic converters in the air is a critical factor in assessing air quality and the potential impact of possible pollutants. Air is in fact one of the main pathways for human exposure to toxic elements. Biomonitors, such as lichen and algae, are examples of environmental samples that have been widely used by the scientific community to assess and monitor the level of environmental pollution. For this purpose, the IAEA-450 algae material containing heavy metals and platinum at low level was prepared by IAEA Seibersdorf Laboratories in collaboration with the Italian National Institute for Environmental Protection - ISPRA (former APAT). During the April meeting in 2009 of the Inorganic Analysis Working Group (IAWG) of the CCQM it was agreed to organize a key comparison K75 for Pt and Ni and a parallel pilot study P118 for As, Cd, Cr, Hg, Ni, Pb and Pt using this algae material. It was also planned and agreed to use the results of this study as a practical demonstration of a CCQM comparison that makes use of the “core-capabilities” utilized by participants as a mean of providing evidence for Calibration and Measurement Capabilities (CMC) claims. The results of this demonstration will help to guide the CCQM in its quest to develop more efficient and effective mechanisms for supporting CMC claims. The matrices prepared by the participants and agreed by IAWG are included in Appendix I. This part of the study was piloted and reported by NIST, which is leading this aspect of the study. Additionally, this study has been designated as the third IAWG Feasibility Study. For this purpose Ni and Pt were designated as case study measurands among the measured ones in the CCQM-K75 and P118 studies. Appendix II shows the technical protocol and reporting forms used in this study.
page 2
2.
PARTICIPATING INSTITUTES
13 institutes were registered in the Key Comparison CCQM-K75. Table 1 lists the participating NMIs sorted by the order of the date of receipt of the request for registration in the study. Table 1. List of participating National Metrology Institutes # 1
Institute Institute full name number
3
Country
Contact person
Measurand
USA
Gregory C. Turk
Ni, Pt
Germany
Jochen Vogl
Ni, Pt
China
Wang Jun
Ni, Pt
Germany
Detlef Schiel
Ni, Pt
Japan
Kazumi Inagaki
Ni, Pt
United Kingdom
Rebeca SantamariaFernandez
Ni, Pt
GOV LAB HK
Hong Kong
W F Tong
Ni
KRISS
Korea, Republic of
Euijin Hwang
Ni
NIST
National Institute for Standards and Technology BAM
2
3
4
4
7
8
Bundesanstalt für Materialforschung und – prüfung NIM-PRC
National Institute of Metrology PTB
Physikalisch-
Technische Bundesanstalt NMIJ/AIST
5
9
6
10
7
12
8
9
13
14
National Institute of Advanced Industrial Science and Technology LGC
Laboratory of the Government Chemist Government Laboratory Korea Research Institute of Standards and Science NRCC
National Research Council of Canada
Canada
Lu Yang,
Ralph Sturgeon
Ni, Pt
# 10
11
12
13
Institute Institute full name number 15
16
17
18
CMQ-F
Centro De Metrologia Química, Fundacion-Chile TUBITAK UME
National Metrology Institute of Turkey NMISA
National Metrology Institute of South Africa INMETRO
Instituto Nacional de Metrologia,Normalização e Qualidade Industrial
All participating institutes reported their results.
page 4
Country
Contact person
Measurand
Chile
Gabriela Massiff
Ni, Pt
Turkey
Oktay Cankur
Ni, Pt
South Africa
S.M. Linsky
Brazil
A. Barzev
Thiago de Oliveira Araujo
Ni, Pt
Ni
3.1. Material
3.
SAMPLES AND INSTRUCTION TO PARTICIPANTS
Two batches of unicellular microalgae (Scenedesmus obliquus) were grown in an outdoor bioreactor by the Institute of Microbiology, Academy of Sciences of the Czech Republic, Trebon. One batch was grown on standard nutrient solution (natural contamination level), the second batch was grown on a nutrient solution containing elevated levels of As, Cd, Cr, Hg, Ni, Pb, and Pt. After harvesting, the thickened suspension was stored in a cooled tank from which it was continuously fed to a spray drier. Thereafter, in order to adjust the Pt mass fraction to the level of environmental pollution in road dust, the two algal materials were mixed in a ratio of 1:100 (high Pt: low Pt). Using high purity methanol according to the procedure proposed in [1], slurries of the two algae materials were produced and merged under constant stirring in 200 g batches. After 72 hours drying at 60 °C, the dry material was homogenized using a Turbula shaking device for 8 hours. Then the 200 g batches were merged and homogenized at ISPRA Laboratories (Rome, Italy). The particle size distribution was determined by laser light scattering technique and found to be less than 100 µm. The bulk material homogeneity was tested before bottling. The material was bottled and tested for homogeneity. 3.2. Homogeneity study The homogeneity of bulk materials at all stages was checked prior to further processing or mixing. The bulk material was dispensed in high quality plastic bottles at 10 g each. Thereafter, the bottles were gamma irradiated at the IAEA’s laboratories. For within and between bottles homogeneity studies 10 bottles of the IAEA-450 algae material were randomly selected from 971 bottles. Three test portions of 0.2 g were taken from each bottle for the analysis. The test portions were digested using microwave assisted digestion method. The digested algae samples and reagent blanks were analyzed using ORC-ICP-MS (Agilent) for As, Cd, Cr, and ICP-MS (Perkin Elmer) for Ni and Pb. Quantification was achieved against aqueous calibration. Results were obtained for As and Cr using the reaction cell. A procedure for the determination of low level platinum in algae material using reverse ID-ICP-MS (Perkin Elmer) was applied. No aqueous calibration was used and measurement results were traceable to SI units. Prior digestion, all algae test portions were spiked with 20 µl of 100 µg/l enriched 195Pt spike solution. The quantification of the Pt mass fractions was achieved following the established procedure based on 194Pt/195Pt isotopic ratio measurements in blank, sample, natural Pt standard, Pt spike and RID solutions. Mercury was analyzed at 20 mg level using a direct mercury analyzer (DMA) instrument. The standard uncertainty associated with the between bottles heterogeneity was calculated using the formulas stated in ISO Guide 35 [2]. The results of single ANOVA calculation and applying the formula for estimation of the uncertainty originated from between bottles heterogeneity u ∗bb are reported in Table 2.
u *bb =
MS within 2 4 n ν MSw ith in
(1)
Where: MS within
Mean square (ANOVA) of within bottles.
ν MS within
Degree of freedom of mean square of within bottles.
u ∗bb n
Uncertainty originated from between bottles heterogeneity. Number of observations.
TABLE 2. ESTIMATED BETWEEN-BOTTLES UNCERTAINTY OF THE STUDIED ANALYTES IN THE IAEA-450 ALGAE MATERIAL
Method
ORC-ICP-MS
ICP-MS
RID-ICP-MS
DMA
Measurand
Cr
As
Cd
Pb
Ni
Pt
Hg
ubb* (%) n=30
1.86
1.19
0.98
1.05
1.64
0.71
0.89
The homogeneity study results reported in Table 2 shows that the sample’s quality fits for the purpose of this comparison. 3.3. Instructions to participants Each participant had received two labeled and trackable bottles (10 g) of the algae material along with a cover letter indicating for each participant a user name and password to log-in and report the results. The participants were asked to thoroughly mix the samples before processing and to analyze the algae with minimum test portion of 200 mg. The technical protocol and example of the reporting forms used in this study are shown in Appendix II. For dry mass factor determination, the participants were requested to take an independent test portion (minimum 0.5 g) for drying at 80 °C for at least 4 hours. The participants were requested to report their results as a mean value of 5 independent measurements with corresponding standard uncertainty expressed in mg/kg based on dry mass using a dedicated on-line reporting web based application The participants were asked to report the measurement results combined standard uncertainty (1 sigma level) where all major individual sources of uncertainty have been identified and taken into account. Summary of the analytical procedure including the sample dissolution and calibration methods was also requested to be reported on-line. The samples were shipped on 15 May 2009 and the initial target date for results reporting was set to 30 September 2009 and then extended to 15 October 2009 to compensate for delays due to summer vacation.
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4.
METHODS OF MEASUREMENT
The methods of measurement were left free to be selected by the participating institutes. From the type of the sample and level of platinum concentration, it was found that ID-ICP-MS method was the best method for determining a low level of elements in algae.
The most used analytical techniques were: HR-ICP-MS, ICP-QMS, ID-ICP-MS, and INAA. The digestion method mostly used was microwave assisted digestion. The information on the amount of test portions taken for analysis, the percentage of moisture content and the limit of detection are given in Tables 4 and 5 in section 5. 4.1. Applied analytical procedures
Certain NMIs provided some details on their analytical procedure; a summary of the reported technical details of the applied procedures is reported below. NIST
NIST reported that Ni and Pt were determined using ID ICP-MS with Microwave Assisted Digestion. Five sub-samples were taken from the K75 bottle at approximately 0.3 g of each sample were accurately weighed by difference into a cleaned quartz microwave vessel via a transfer funnel, and spiked with accurately weighed aliquots of 62Ni (approximately 3 µg/g), and 194Pt (approximately 0.2 µg/g), followed by the addition of 6.9 g of hydrochloric acid, and 2.4 g of nitric acid. The heating program consisted of the application of 600 W continuous power for ten minutes followed by 1000 W for twenty minutes. The vessel temperatures reached approximately 230 ºC, at a pressure of approximately 70 bar. Two control materials; consisting of two sample aliquots from a single bottle of SRM 1515 (Apple Leaves) were prepared in a similar manner to the samples. Following digestion, the mixture was evaporated down to approximately 0.5 mL at 120 ºC. The contents were then centrifuged. ICP-MS measurements were made using a Thermo X7 instrument operated in conventional (non CCT) mode. A sample uptake rate of 0.5 mL/min., and spray chamber temperature of 3 ºC were used. Nickel isotopes m/z 60 and m/z 62 were measured using a dwell time of 10 ms for each isotope. Platinum isotopes m/z 194 and m/z 195 were measured using a dwell time of 10 ms on each isotope. Isotope ratio measurements were made using peak jumping data acquisition with one point per peak. Five blocks of data each 30 seconds in duration were acquired per sample, and the 60Ni/62Ni and 194Pt/195Pt isotope ratios used for computations. Measured ratios were corrected for mass bias and detector dead-time (37 ns). Instrument mass bias correction was achieved by measuring nickel (SRM 3136) and platinum (SRM 3140) standard solutions of natural composition, and using these to carefully calibrate one of the spike calibration mixes. The calibrated spike calibration mixes were re-measured periodically throughout the analysis and used to correct the analytical samples and blanks for any instrument mass bias drift. Corrections were applied by assuming any drift to be linear with time. NIST reported that calibration was performed using the working 62Ni and 194Pt isotopic spike solutions were calibrated by reverse isotope dilution using high-purity primary standards (SRM 3136, Nickel Standard Solution, Lot number 00612, certified concentration 9.738 ± 0.022 mg/g, and SRM 3140 Platinum Standard Solution, Lot number 00615, certified concentration 9.98 ± 0.03 mg/g). For each standard, two separate stock solutions were prepared by gravimetric serial dilution. Two spike calibration mixtures were prepared from each of these solutions, generating four spike mixtures, and these were measured using ICPMS, under the same conditions as the samples.
The NIST reported value using ID ICP-MS for Ni and Pt is 0.8126 and 0.0760 mg/kg respectively. The expanded measurement result uncertainty is 0.0255 and 0.0092 mg/kg for Ni and Pt respectively (approximately 95 % confidence interval). In addition, NIST reported a second result for Pt using RNAA method. According to NIST the comparator neutron-activation analysis method was used in conjunction with postirradiation radiochemical separations (RNAA), following established irradiation and counting procedures of samples, controls, and standards appropriate to the analytical task. NIST reported that commercial high-purity Pt metal foil was used to prepare the calibration standard solution by dissolving a piece of Pt foil in a mixture of HCl and HNO3. The irradiations were carried out for 6 h in the RT-1 pneumatic facility of the NBS Research Reactor at the NIST Center for Neutron Research. The procedure for the radiochemical determination of Pt uses the activation reaction 198 Pt(n,γ)199Pt(β-)199Au, where the intermediate species, 199Pt (t1/2 = 0.5133 h), is short-lived compared to the daughter nuclide, 199Au (t1/2 = 3.139 d), used for quantification. The protocol of Zeisler and Greenberg (1988) was employed in the present work, with the small modification that the HF and HCl rinses of the precipitated Au were omitted since no silicate or rare earth element residues were observed in the samples. Quality control samples were prepared from SRM 3140 Platinum Standard Solution (Lot No. 000615). The NIST reported value using RNAA is 0.0785 mg/kg and the standard measurement result uncertainty is 0.0008 mg/kg. NIST reported an uncertainty budget with estimated individual uncertainty components for both analytical methods. According to the rules for Key Comparisons where more than one technique is used for the determination of the same measurand, the combined result is used to calculate the Key Comparison Reference Value and degrees of equivalence. Therefore NIST reported the Pt result as a combined value from both analytical methods RNAA and ID ICP-MS. BAM
BAM used a different method for sample digestion comparing to other NMIs, it was reported by BAM that the sample dissolution was performed using quartz vessels in a high pressure asher (HPA) at 320°C and 130 bar. To separate Ni from the matrix, a cation exchange resin AG 50W (matrix: 0.5 mol/L HCl and 80% acetone, Ni: 3 mol/L HCl) was used; while Pt was separated as chloro-complex by anion exchange resin AG1 X8; then the resin was digested after washing. NMI-PRC
NMI-PRC reported that the sample was completely digested with HNO3 using microwave digestion method. The analytical method blank was treated in the same way as samples. The blank level recorded was less than 1ppb and 10 ppb for Pt and Ni respectively. The final results were corrected by subtracting the method blank. All measurements of the isotopic ratios were performed by Q-ICP-MS (Agilent 7500ce). The result of the calibration of the spike was calculated according to validated formulas. Ni and Pt mass fractions were measured using double isotope dilution mass spectrometry (IDMS). Primary assay standards were first used to calibrate concentrations of the enriched isotope 194Pt and 61Ni. Then, the calibrated enriched isotopes were used as spikes to determine the amount content of Pt and Ni in CCQM- K75 sample, respectively.
page 8
In order to keep blank contribution and contamination small, sub-boiled acids and sub-boiled water were used. Dry-mass correction was done according to the method provided in the technical protocol. NMI-PRC reported an uncertainty budget with estimated individual uncertainty components. PTB
PTB reported details of the analytical procedure applied. For Ni and Pt digestion, PTB used a mixture of 3 mL 65% subboiled HNO3 and 9 mL 30% ultra pure HCl and a microwave MLS ETHOS-1600 to perform the digestion for duration of 1 h at 210 °C. The solutions were evaporated to dryness using MLS microwave evaporation rotor at 450 hPa and 90 °C. The residues were re-dissolved in 5 mL 1 mol/L ultra pure HCl using an ultrasonic bath within 10 min. The pH of the solution was adjusted to pH=8.5. Then a nickel selective resin Eichrom was used to separate the nickel from the matrix. The nickel was stripped from the column with 1.5 ml of a 3 mol/L HNO3. The solution then was filtered using a syringe filter (PTFE, 0.45 µm) into the PP auto-sampler vials and measured after adding 3.5 mL water. For platinum, the residues were redissolved in 5 mL 1% ultra pure HCl using an ultrasonic bath within 10 min. The solution then was filtered using a syringe filter (PTFE, 0.45 µm) into autosampler vials and measured. HR-ICP-MS Finnigan2, Thermo Fischer Scientific was used for the measurement applying double IDMS method with spike isotopes 60Ni and 198Pt. The reference spike mixtures underwent the same procedure (digestion, separation, dilution) as the samples to avoid an additional method blank determination. NMIJ/AIST NMIJ/AIST reported that a microwave assisted digestion was used using a mixture of HNO3, HCLO4 and HF. No further details on the digestion method were provided. The Ni and Pt measurement was performed using the double isotope dilution ICP-MS method. The ICP-MS used was Agilent 7500c. The cell gas condition for Ni was He: 4 mL/min. The condition for Pt was He: 0.5 mL/min. The ICP-SFMS used for checking the spectral interference for Ni was ELEMENT2 with middle resolution mode (resolution >4000). NMIJ/AIST reported that the dry mass factor correction was evaluated according to the technical protocol provided by the IAEA. NMIJ/AIST reported also details of the uncertainty components considered in the measurement results uncertainty budget which is calculated using the spread-sheet method. LGC
LGC reported that the material (bottle no 43) was agitated to ensure homogeneity. Aliquots of 0.50-0.60 g were taken and appropriate amounts of 61Ni spike and196Pt spike were added to each sample prior to digestion using a closed vessel microwave digestion system (quartz vessels, Multiwave 2000, Anton-Paar). A mixed acid digest was applied; 3 mL HNO3 (Ultra pure, Romil, UK) and 2 mL H2O2 (Super Purity, Romil) followed by 1 mL HCl (Ultra pure, Romil) after the digestion program. After cooling, the samples were diluted to approx. 35 g with high purity water (18.2 M cm, Elga Maxima, UK). LGC reported that the standards used in the determination of Ni and Pt were purchased from NIST (Gaithersburg, USA). The SRM 3136 (lot number 000612) has a certified concentration of Ni of 9738 ± 22 µg/g traceable to SI. A primary standard of Pt was purchased from NIST, SRM3140 (lot number 000615) has a certified concentration of Pt of 9980 ± 30 µg/g traceable to SI. A 61Ni enriched isotope spike was obtained as metal from AEA (Harwell, Oxfordshire, UK) and dissolved in HNO3. A 196Pt enriched isotope spike was obtained as metal from Oakridge National Laboratories (Tennessee, USA) and dissolved in HCl.
A single element Pt standard at 992.1 µg/g (lot 72-072214B, Alfa Aesar, Johnson Matthey, UK) and a single element Ni standard at 981 µg/g (lot C530467, Romil) were used as instrumental quality control check standards. Additionally, a certified reference material, namely NIST SRM1547 Peach Leaves, was used as a digestion recovery check for Ni (0.69 ± 0.09 µg/g). No suitable matrix reference material was available for Pt. Regarding the instrumentation used, LGC reported that the analysis was carried out using an Agilent 7500ce ICP-MS operating in standard mode (no collision cell gases) for Pt, and in gas mode (He) for Ni. Samples were introduced into the plasma via a Micromist® quartz concentric nebuliser and a Scott type double pass spray chamber cooled to 2°C. Each analysis comprises 10 x 100 replicate ratio measurements of the 60Ni/61Ni and 62Ni/61Ni ratios for Ni analyses; 195Pt/196Pt and 194Pt/196Pt ratios for Pt analyses. KRISS
KRISS reported the use of microwave assisted digestion for both As and Ni with digestion mixture of HNO3 and H2O2. For Ni measurement, isotope dilution mass spectrometry was used by KRISS. The isotope ratios of 60Ni and 62Ni were measured. The measuring instrument used was ELEMENT2 ICP-MS (Thermo SCIENTIFIC Inc.) with medium resolution (>4000) for Ni and high resolution (>10000) for As to avoid spectral interferences. For quality control and method validation, KRISS used the reference material Codfish tissue (NMIJ CRM 7402a). NRCC
NRCC reported that ID ICP-MS analytical procedure was applied using a PerkinElmer SCIEX ELAN 6100 (Thornhill, Ontario, Canada). NRCC described the applied analytical procedure as the following: Samples were prepared in a class-10 or class-100 clean room environment. Six 0.25g sub-samples of the CCQM-K75 algae were weighed into individual pre-cleaned Teflon digestion vessels. After the addition of suitable amount of enriched 61Ni and 198Pt standard solutions, 2ml of HNO3, 6 ml of HCl and 1 ml of HF were added. Three sample blanks were also prepared concurrently but with the addition of only 10 % of the amount of enriched isotope standard used in the samples. The vessels were then sealed and heated in a Milestone Microwave Labstation microwave oven for digestion. After cooling, the caps were removed and rinsed. The contents were transferred into polypropylene tubes and placed on a hot block in a class-10 fume hood and heated at 85oC until near dryness. The residues were dissolved in 0.25 ml HNO3 and 0.5 ml HCl and diluted to 25 ml for determination of Pt. For determination of Ni, 10 ml aliquots of the above solutions were pipetted into clean 15 ml plastic bottles, to which 0.25 ml of aqueous ammonia and 5 ml 0.5 M ammonium acetate buffer at pH 5.5 were added. The solutions were passed through a Toyopearl AF-Chelate 650M iminodiacetate resin column for matrix separation prior to ICP-MS determination. The reference/spike isotope pair used was 60Ni/61Ni and 195Pt/198Pt. Samples were introduced into ICP-MS and intensities of Ni and Pt isotopes obtained from a blank solution of 1% HNO3 and 2% HCl for Pt and a 2% HNO3 for Ni were subtracted from all samples and standards. Four measurements were made on each sample solution to obtain mass bias corrected 60Ni/61Ni and 195Pt/198Pt ratios from which Ni and Pt concentrations were derived. For dry weight determination, separate sub-samples of 0.5 g each were taken and dried in an oven at 80oC for 5 hours.
page 10
CMQ-F
CMQ-F reported that the microwave digestions were used as samples treatment method. Five portions of CCQM-K75 algae material were digested independently. A CEM MARS XP-1500 Microwave oven equipped with 12 vessels was used. CMQ-F reported that 0.4 grams of CCQM algae sample were accurately weighed into the microwave vessels using an analytical scale. Six grams of ultra pure nitric acid were added to the sample, and the mixture was left to stand for 12 hours at room temperature for predigestion. Vessels were then sealed and subjected to the microwave oven program. After this step, vessels were cooled to room temperature. Then, they were opened and a mixture of ultra pure hydrogen peroxide and hydrofluoric acid were added to the samples. Samples were then subjected to a second step of microwave digestion. For the digestion of Pt HNO3, H2O2 and HClO4 were used. After microwave digestion, samples were evaporated on a hot plate until ~1 ml was left and taken to their final mass (~35 g) with a 2% of HNO3 solution, by accurately weighing in an analytical scale. Reagents blanks were prepared and subjected to the same treatment as samples, and the values obtained during measurements of these blanks were taken into account when calculating the concentration of the samples. Moisture in CCQM samples was determined in three replicates, following the directions included in the technical protocol. The moisture obtained for the CCQM-algae sample was 3.57%. Ni measurements were performed by ICP-MS, using a collision cell in Helium mode to eliminate polyatomic interferences. Pt measurements were performed by ICP-MS using Normal Mode. NIST SRMs were used as calibration standards and for the standard additions measurement technique for all measurements: Ni (SRM-3136 Lot N°000612); Pt (SRM-3140 Lot N°000615). Calibration standard solutions were prepared by successive gravimetric dilutions of the corresponding SRM. The concentrations of Ni and Pt in CCQM K75 and QC samples were determined by the standard additions methods. Samples were spiked with a known amount of a Standard Solution containing the corresponding metal at levels of 2x and 3x (where x represents the unknown concentration of the metal in the samples). From regression of the responses versus the additions, the concentration of each metal in the samples was calculated. Rhodium was used as an Internal Standard for all metals analyzed by ICP-MS. CMQ-F reported the equation used for uncertainty estimation based on GUM-Supplement 1 guidelines. TUBITAK UME
TUBITAK UME reported that a microwave assisted digestion was used for both Ni and Pt with a digestion mixture of HNO3, HCl and H2O2. Standard addition calibration has been used in the measurement. Standards have been prepared in sample matrix. Tomato leaves SRM 1573a has been used for quality control of Ni results. HR-ICP-MS and ICP-QMS were used for measuring the mass fractions of Ni and Pt.
NMISA
NMISA reported the use of Microwave assisted digestion with HNO3, HCl, HF in case of Pt and HNO3, HF and H2O2 for Ni. Double Isotope Dilution ICP-MS was used as a measuring technique. Sample and Standard blends were prepared gravimetrically adding appropriate spikes of 61Ni and 195Pt. Primary standard material used Ni: NIST SRM, Lot no. 3136 and Pt: NIST SRM 3140, Lot No. 000615. BCR 482: Lichen was used as a quality control material. NMISA reported that the following components of uncertainty sources which were taken into consideration in the estimation of measurement results uncertainty: Counting statistics (ratio measurements, mass bias correction), dry mass correction, blank correction, weighing, calibration and digestion. INMETRO
INMETRO reported analytical results produced by digestion of the algae using a microwave assisted digestion method with a mixture of HNO3 and H2O2 was used for Ni determination. INMETRO reported also that external aqueous standard solutions were used for calibration to attain quantitative values. The calibration standards used were prepared from NIST SRM 3136 (Ni-60). Intermediate solutions and the calibration standards were prepared by gravimetric dilution. The range of the curve and the dilution of the sample were set according to the concentration of the sample and the linearity of the response of the instrument to Ni. To validate the method NIST SRM 1643e was used.
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5.
RESULTS AND DISCUSSION
5.1. General 23 measurement results were reported for the CCQM Key Comparison K75 from 13 NMIs. The reported results sorted by laboratory code were compiled and presented in Table 3, in Tables 4 and 5 the reported results are compiled and sorted for Platinum and Nickel. TABLE 3. REPORTED RESULTS IN CCQM-K75
Institute code
Institute name
3
NIST
4
BAM
7
NIM
8
PTB
9
NMIJ-AIST
10
LGC
12
GOV-LAB
14
NRCC
15
CMQ-F
16
TUBITAKUME
13
KRISS
17
NMISA
18
INMETRO
Measurand
(mg/kg)
Reported standard uncertainty (mg/kg)
Digestion method
Measurement method
MWAD
1
Pt
0.07725
0.00196
Pt
0.0719
0.0004
HPA
ID-ICP-MS
Pt
0.0735
0.0007
MWAD
ID-ICP-MS
Pt
0.07155
0.00057
MWAD
2
Pt
0.0727
0.0007
MWAD
2
Pt
0.076
0.004
MWAD
ID-ICP-QMS
Ni
0.797
0.02
MWAD
ID-ICP-QMS
Pt
0.0727
Ni Ni Ni Ni Ni Ni
Ni Ni
0.8126 0.821 0.779 0.793 0.826 0.800
0.0127
0.0058 0.015 0.023 0.012
0.018
MWAD HPA
MWAD
ID-ICP-MS
ID-ICP-MS ID-ICP-MS
ID-ICP-MS
MWAD
2
MWAD
2
MWAD
ID-ICP-QMS
0.82236
0.00512
MWAD
0.815
0.011
MWAD
0.0015
Combined
2
ID-ICP-MS ID-ICP-MS ID-ICP-MS
ID-ICP-MS
MWAD
ID-ICP-QMS ICP-QMS
ID-ICP-QMS
Pt
0.069
0.003
MWAD
Pt
0.076
0.003
MWAD
Pt
0.07835
0.00085
MWAD
2
Ni
1.011
0.017
MWAD
ICP-QMS
Ni Ni
Ni
Combined: ID-ICP-MS with RNAA, 2 Double ID ICP-MS 3 Combined with ICP-QMS NR: Not reported HPA: High pressure asher MWAD: Microwave assisted digestion 1
Reported value
0.805 0.908
0.8331
0.033 0.055
0.0141
MWAD
ICP-QMS 3
MWAD
3
MWAD
2
HR-ICP-MS HR-ICP-MS ID-ICP-MS ID-ICP-MS
TABLE 4. REPORTED RESULTS FOR PLATINUM CCQM-K75 Reported Lab value Institute name code (mg/kg) 3 NIST 0.07725 4 BAM 0.0719 7 NIM 0.0735 8 PTB 0.07155 9 NMIJ/AIST 0.0727 10 LGC 0.076 14 NRCC 0.0727 15 CMQ-F 0.069 16 TUBITAK-UME 0.076 17 NMISA 0.07835 TABLE 5. REPORTED RESULTS FOR NICKEL CCQM-K75 Reported Lab value Institute name code (mg/kg) 3 NIST 0.8126 4 BAM 0.821 7 NIM 0.779 8 PTB 0.793 9 NMIJ-AIST 0.826 10 LGC 0.800 12 GOV-LAB 0.797 13 KRISS 0.82236 14 NRCC 0.815 15 CMQ-F 0.805 16 TUBITAK-UME 0.908 17 NMISA 0.8331 18 INMETRO 1.011
NR: Not reported page 14
u(xi) (mg/kg)
U(xi) (mg/kg)
K
0.00196 0.0004 0.0007 0.00057 0.0007 0.004 0.0015 0.003 0.003 0.00085
0.00356 0.0008 0.0014 0.0012 0.0013 0.007 0.003 0.006 0.006 0.0017
2.57 2 2 2 2 2 2 2 2 2
Test portion mass
Moisture content
Limit of detection
(g) 0.273 0.450 0.370 0.250 0.350 0.500 0.250 0.450 0.500 0.250
(%) 5.1 5.057 4.2 3.0 4.5 4.5 3.78 3.57 5.01 3.919
(mg/kg) NR 0.00003 0.000001 NR 0.00008 0.001 0.0002 0.003 NR NR
u(xi) (mg/kg)
U(xi) (mg/kg)
K
Test portion mass
Moisture content
Limit of detection
0.0127 0.0058 0.015 0.023 0.012 0.018 0.02 0.00512 0.011 0.033 0.055 0.0141 0.017
0.0255 0.012 0.031 0.045 0.024 0.037 0.04 0.010 0.022 0.066 0.11 0.0282 0.034
2 2 2 2 2 2 2 2 2 2 2 2 2
(g) 0.316 0.500 0.479 0.250 0.350 0.500 0.500 0.200 0.250 0.400 0.500 0.250 0.250
(%) 4.74 5.057 4.2 3.0 4.9 4.5 2.58 3.98 3.78 3.57 5.01 3.919 2.397
(mg/kg) NR 0.0008 0.000003 NR 0.0005 0.01 0.002 NR 0.003 0.040 NR NR 0.000003
5.2.Assessment of correlation between reported results and digestion mixtures used All NMIs used microwave assisted digestion method except BAM used a high pressure asher. However, nine different digestion mixtures were used as indicated on Figures 1 and 2. The type of digestion mixture was denoted by a bold blue number. It can be seen that HNO3 was used by all NMIs in addition to one of the acids HCl, HClO4, HF. Only four NMIs used the oxidant H2O2. From Figures 1 and 2 and reported results it can be observed that there is not a correlation between the digestion mixture used and the reported result. All digestion mixtures used were equally performing for the analysed element in this specific matrix. 5.3. Assessment of moisture content correction factor During the autumn 2009 meeting of the CCQM IAWG in Rio de Janeiro, it was agreed that a thorough investigation of correlation between results and moisture content reported results should be performed. To address this request and based on the reported information by the participating NMIs, it was found that all of the NMIs used the prescribed method for the moisture content determination in the comparison technical protocol. It is self explanatory that different moisture content results could be reported as the air humidity could vary in different laboratories and in different days in the same laboratory. The reported moisture content results ranged between 3.0-5.1% as shown in Figures 1 and 2. From these figures it can be seen that it is difficult to find a correlation between the moisture content results and reported results. PTB, BAM and NMIJ/AIST reported different moisture content results between 3-5%, but platinum measurement results were in a very good agreement and showed no effect due to variations in determination of moisture content. Moreover, the correlation factor of a linear regression of the reported results sorted in ascending order for both Pt and Ni, shown in Figures 3 and 4, is around 10 times higher than the correlation factor of the corresponding moisture content results which indicates the very low probability of a correlation between the moisture content results and the reported analytical results. 5.4. Calculation of the reference mass fraction values and associated uncertainties In order to evaluate the degree of equivalence of the results using relative bias, a reference value of the mass fraction has to be calculated for each element as a consensus value from the reported results. To assess the differences caused by the type of the applied statistical approach in deriving the consensus value and its uncertainty, four different statistical quantifiers namely: arithmetic mean, median, mean value according to algorithm A [3] and mixture model-median (MM-median) [4] were used and compared. The last three approaches are based on robust statistics. To estimate the standard uncertainty associated with the reference value of the mass fraction, four statistical estimators were used namely: standard deviation, adjusted median of absolute
deviations MADe, algorithm A standard deviation S(Alg. A) [3] and the mixture modelmedian based standard deviation S(MM-median) [4]. The results of each calculation are shown in Table 6. As it can be seen from Table 6, a good agreement was observed between the consensus values calculated as an arithmetic mean and using other robust approaches for both Ni and Pt.
Therefore, it is proposed to consider the median as the key comparison reference value
(KCRV) and the uncertainty derived from MADe according to formula (2) as the KCRV associated standard uncertainty (u) and the key comparison expanded uncertainty KCRU is calculated as per formula (3), the KCRV and KCRU of both analytes are listed in Table 7. It should be noted that all reported measurement results were included in the calculation of the KCRV and KCRU.
u = 1 .25 *
MAD e n
(2)
U = 2*u
(3)
MAD e = ( median i (| X i − median j ( X j ) |)) / 0.674
(4)
Where: u: standard uncertainty
MADe: Adjusted median of absolute deviations according to formula (4), which is an estimate of standard deviation based on the Median Absolute Deviation(MAD), for a standard normal distribution. n: number of observations U: KCRU expanded uncertainty k=2.
To appreciate the level of discrepancy between the robust and arithmetic consensus values, both values for each element were shown in the Figures 1 and 2. The red and black bold lines represent the median and arithmetic mean of the reported data respectively, and the dashed lines represent the expanded uncertainty according to formula (3). In each Figure, different colours were used to indicated the analytical techniques used for the reported measurement results while the expanded measurement results uncertainties (k=2) were denoted by a black vertical line. TABLE 6. RESULTS OF CALCULATION OF THE CONSENSUS VALUES AND ITS DISPERSION Measurand
Arithmetic Mean
Standard deviation
(mg/kg)
Median
MADe
Alg. A mean
(mg/kg)
S(Alg. A)
MMmedian
(mg/kg)
S(MMmedian)
(mg/kg)
Ni n=13
0.8325
0.0619
0.8150
0.0222
0.8165
0.0256
0.8180
0.0240
Pt n=10
0.0739
0.0029
0.0731
0.0033
0.0739
0.0033
0.0731
0.0035
All reported measurement results were considered in the calculation of the consensus values.
page 16
TABLE 7. RESULTS OF CALCULATION OF THE KCRV AND KCRU Measurand
KCRV
(Median)
MADe
MADe
(mg/kg)
u(KCRV)
(%)
U(KCRV)
U(KCRV)
(mg/kg)
(%)
Ni (K75) n=13
0.8150
0.0222
2.7
0.0077
0.0154
1.9
Pt (K75) n=10
0.0731
0.0033
4.5
0.0013
0.0026
3.6
Median
ID ICP-QMS/ID ICP-MS
HR ICP-MS
ID ICP-MS&RNAA
Mean
Median – U
Median+U
ICP-QMS
Expanded uncertainty k=2
3-4% 3-4%
5%
4-5%
3-4%
6
9
3-4% 4-5%
5%
5.1% 3-4%
0.09 0.08 0.07
3
4
4
1
5
5
4
9
NMISA
Pt mass fraction (mg/kg)
0.1
NIST
–
0.06 0.05
TUBITAKUME
CCQM-K75
LGC
NIM
NRCC
NMIJ/AIST
BAM
PTB
CMQ-F
0.04
Figure 1. CCQM-K75, Platinum measurement results in algae The blue bold numbers denote the digestion mixture used in sample dissolution: 1- HNO3
2- HNO3, H2O2
3- HNO3, H2O2, HClO4 4- HNO3,HCl
5- HNO3,HCl, H2O2
6- HNO3, HClO4, HF
7- HNO3, HF
8- HNO3, H2O2, HF 9- HNO3, HF, HCl
The values in percentage shown in a yellow oval denote the moisture content mass fraction expressed in percentage.
page 18
Median
ID ICP-QMS/ID ICP-MS
HR ICP-MS
Median – U
Median+U
ICP-QMS
Expanded uncertainty k=2
2-3% 3-4% 3-4% 2-3% 3-4% 3-4% 5%
3-4%
5%
4
3
3-4% 3-4% 3-4%
5%
0.95 0.85
0.65
1
3
8
4
9
3
2
7
NMIJ-AIST
0.75
KRISS
Ni mass fraction (mg/kg)
1.05
Mean
5
4
2
INMETRO
TUBITAK-UME
CCQM-K75
NMISA
BAM
NRCC
NIST
CMQ-F
LGC
GOV-LAB
PTB
NIM
0.55
Figure 2. CCQM-K75, Nickel measurement results in algae The blue bold numbers denote the digestion mixture used in sample dissolution: 1- HNO3
2- HNO3, H2O2 3- HNO3,HCl
4- HNO3, , HCl, H2O2
5- HNO3,HCl, HF
6- HNO3, HClO4, H2O2
7- HNO3, HClO4, HF 8- HNO3, HF
9- HNO3, H2O2, HF The values in percentage shown in a yellow oval denote the moisture content mass fraction expressed in percentage.
Moisture content
y = 0.0008x + 0.0682 2 R = 0.9053
NIMThailand
NMISA
NIST
TUBITAKUME
LGC
VNIIM
GOV-LAB
NIM
NRCC
NMIJ/AIST
BAM
PTB
y = 0.0005x + 0.0373 2 R = 0.0826 LNE
0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02
CMQ-F
Pt [mg/kg], moisture content g/g
Pt
NMI
Figure 3. Pt measurement results sorted by ascending order versus moisture content results
1.22
Moisture content
y = 0.0118x + 0.746 2 R = 0.7354
1.02 0.82 0.62 0.42
INMETRO
LNE
NIMTHAILAND TUBITAKUME
NMI
NMISA
KRISS
BAM
NRCC
NIST
CMQ-F
LGC
GOV-LAB
PTB
0.02
NMIJ-AIST
y = 0.0007x + 0.3876 2 R = 0.0016
0.22 NIM
Ni [mg/kg], moisture content g/10g
Ni
Figure 4. Ni measurement results sorted by ascending order versus moisture content results
page 20
5.5. EQUIVALENCE STATEMENTS The equivalence statements have been calculated according to the BIPM guidelines. The degree of equivalence (and its uncertainty) of a reported result by a National Metrology Institute compared to the KCRV is calculated according to the following formulas 5 and 6:
d i = ( xi − xref )
U (d i ) = 2 ∗ u ( xi ) 2 + u ( x ref ) 2
(5)
Where: xi is the reported value (i = 1 to n), x ref . is the Key Comparison Reference Value (KCRV),
di is the difference between the reported value and the KCRV ( xi − xref ) , u ( xi ) is the reported measurement result standard uncertainty, u ( x ref ) is the standard uncertainty associated with x , ref
U(di) is the expanded uncertainty (k = 2) of the difference di at a 95% level of confidence. The equivalence statements for CCQM-K75 are given in Tables 8 and 9.
TABLE 8. EQUIVALENCE STATEMENT OF PLATINUM FOR CCQM-K75 Difference Reported Reported standard unc. value Lab Institute name di xi u ( xi ) code (mg/kg) (mg/kg) (mg/kg) 3 4 7 8 9 10 14 15 16 17
NIST BAM NIM PTB NMIJ/AIST LGC NRCC CMQ-F TUBITAK-UME NMISA
0.07725 0.0719 0.0735 0.07155 0.0727 0.076 0.0727 0.069 0.076 0.07835
0.00196 0.0004 0.0007 0.00057 0.0007 0.004 0.0015 0.003 0.003 0.00085
0.00415 -0.0012 0.0004 -0.00155 -0.0004 0.0029 -0.0004 -0.0041 0.0029 0.00525
U(di) (mg/kg) 0.00470 0.00272 0.00295 0.00284 0.00295 0.00841 0.00397 0.00654 0.00654 0.00311
di/U(di) 0.882 -0.441 0.135 -0.546 -0.135 0.345 -0.101 -0.627 0.443 1.690
(6)
. TABLE 9. EQUIVALENCE STATEMENT OF NICKEL FOR CCQM-K75 Difference Reported Reported standard unc. value Lab Institute name di xi u ( xi ) code (mg/kg) (mg/kg) (mg/kg) 3 4 7 8 9 10 12 13 14 15 16 17 18
page 22
NIST BAM NIM PTB NMIJ-AIST LGC GOV-LAB KRISS NRCC CMQ-F TUBITAK-UME NMISA INMETRO
0.8126 0.821 0.779 0.793 0.826 0.800 0.797 0.82236 0.815 0.805 0.908 0.8331 1.011
0.0127 0.0058 0.015 0.023 0.012 0.018 0.02 0.00512 0.011 0.033 0.055 0.0141 0.017
-0.0024 0.0060 -0.0360 -0.0220 0.0110 -0.0150 -0.0180 0.0074 0.0000 -0.0100 0.0930 0.0181 0.1960
U(di) (mg/kg) 0.0297 0.0193 0.0337 0.0485 0.0285 0.0392 0.0429 0.0185 0.0269 0.0678 0.1111 0.0321 0.0373
di/U(di) -0.081 0.311 -1.068 -0.454 0.386 -0.383 -0.420 0.398 0.000 -0.148 0.837 0.563 5.251
5.6. METROLOGICAL TRACEABILITY In order to demonstrate the metrological traceability of the reported results of Ni and Pt in the CCQM K75, the participating NMIs provided information on the calibration method and calibration standards used as shown in Tables 10 and 11. Table 10: Calibration method and standards used for Ni determination in algae NMI
Calibration method Calibration standards for Ni
NIST
ID
SRM 3136
BAM
ID
BAM-Y11 Primary Ni
NIM-PRC
ID
61
PTB
ID
SRM 986 Nickel (isotopic)
NMIJ/AIST
ID
JCSS (Japanese calibration service system) grade standard solution traceable to NMIJ primary Ni
LGC
ID
SRM 3136, Lot No. 000612
GOV-LAB
Standard Addition
SRM 3140, Lot No. 000615
KRISS
ID
KRISS Ni Primary reference materials with certified concentrations of 1000.43±0.67 mg/kg (lot No. HS081003B-6) and 1014.27±0.67 mg/kg (lot No. MS080930B-7), 62Ni enriched isotope from ISOTEC Inc.
NRCC
ID
Reverse spike against natural abundance high purity Ni standard characterized at NRC using in-house ISO-17025 accredited GD-MS laboratory
CMQ-F
Standard addition
SRM 3136, Lot No. 000612
TUBITAK-UME
Standard addition
Ni Single Element Solution (LN: 426809) characterized by TUBITAK-UME using SRM 3136, Lot No. 000612
NMISA
ID
SRM 3136
INMETRO
External calibration
SRM 3136
NIM CRMGBW 08618 Nickel in water
Ni enriched isotope was obtained from CIAE China.
Table 11: Calibration method and standards used for Pt determination in algae NMI
NIST BAM
Calibration method
ID for Q-ICPMS
External calibration for RNAA ID
Calibration standards for Pt SRM 3140, Lot No. 000615 High purity metal foil BAM Primary Pt
NIM primary assay standard solution which is dissolved from an accurately known amount of high purity Pt.
NIM-PRC
ID
PTB
ID
BAM Primary Pt
NMIJ-AIST
ID
SRM 3140, Lot No. 000615
LGC
ID
SRM 3140, Lot No. 000615
NRCC
ID
Reverse spike against natural abundance high purity Pt standard characterized at NRC using in-house ISO-17025 accredited GD-MS laboratory
CMQ-F
Standard addition
SRM 3140, Lot No.000615
TUBITAK-UME
Standard addition
ICP-MS-68A Solution C Multi Element Solution (Lot No. 619124) traceable to SI through NIST SRM 3100 series. The material is later characterized by TUBITAK UME using SRM 3140, Lot No. 000615
NMISA
ID
SRM 3140, Lot No. 000615
page 24
Pt enriched isotope was obtained from Oakridge National Laboratory, USA. 194
6.
DEMONSTRATED CORE-CAPABILITIES
CCQM K75 is the first Key Comparison organized by the IAWG to employ a system of CoreCapabilities for inorganic chemical analysis. This system has been developed over the last several years as part of a strategy to improve the efficiency and effectiveness of Key Comparisons to support CMC claims. Using this system new CMC claims can be supported by describing which Core-Capabilities are required to provide the claimed measurement service and then referencing Core-Capabilities that were successfully demonstrated by participation in Key Comparisons. This is the first Key Comparison to report which CoreCapabilities have been demonstrated based on the experience of the analysts participating in the study. Compilations of the Core-Capabilities required for successful provision of NMI measurement services for inorganic chemical analysis have been developed over the last several years by the IAWG at their semi-annual meetings. They are organized in tabular form according to the primary instrumental methodology employed. The system includes a three-level degree of difficulty scale for each Core-Capability. The tables of Core-Capabilities were agreed upon by the IAWG prior to the commencement of CCQM K75. Participants in CCQM K75 received Core-Capability forms together with the samples. They were instructed to review the lists of Core-Capabilities prior to beginning the analysis and to make note of, and document, Core-Capabilities that they felt were being demonstrated in the course of performing the analysis. They were instructed to select a level-of-difficulty that they felt was demonstrated for each Core-Capability and to justify the selection of higher degrees of difficulty. The completed Core-Capability forms were submitted by the participants along with their measurement results. At the autumn 2009 meeting of the IAWG in Rio de Janeiro compilations of the submitted Core-Capability forms submitted by the participants were presented and discussed. Consensus opinions regarding demonstrated Core-Capabilities and the associated degrees of difficulty were decided upon. Appendix I lists the agreed upon demonstrated Core-Capabilities for CCQM K75, including the degrees of difficulty, and a brief justification for the higher degrees of difficulty.
7.
CONCLUSIONS
The key comparison CCQM-K75 was successfully organized. The participating NMIs demonstrated a high level of measurement capabilities and technical competence in analysing nickel and platinum at a low level of concentration in environmental sample such as algae. The between-laboratories reproducibility standard deviation for nickel and platinum was 1.9% and 3.6% respectively, which reflects an excellent agreement of between-laboratories measurement results. The ratio between the bias and its expanded uncertainty for nickel and platinum was below 2.0 for all reported results except in one case.
This study was a practical demonstration of a CCQM comparison to use the “corecapabilities” utilized by participants as a mean of providing evidence for Calibration and Measurement Capabilities (CMC) claims for Ni and Pt. The matrices prepared by the participants and agreed by IAWG were complied and presented in Appendix I.
Based on this CCQM international key comparison, the measurement capability of the NMIs which participated in the CCQM-K75 has been demonstrated in determination of Pt and Ni in algae matrix. ACKNOWLEDGEMENT The contact persons, analysts and NMIs responded to this study and contributed their efforts to the K75 key comparison, as listed below, are highly appreciated and acknowledged. Institute
Contact person and/or analysts
NIST
G. C. Turk, D. Cleveland, S. E. Long, B. E. Tomlin
BAM
NIM-PRC PTB
NMIJ/AIST LGC
GOV LAB HK
J. Vogl, M. Koenig
W. Jun, C. Wei, Z. Jao D. Schiel, O. Rienitz K. Inagaki
R. Santamaria-Fernandez, S. Hill, S. Merson, R. Hearn W. F. Tong
KRISS
E. Hwang, K. S. Lee,
CMQ-F
G. Massiff
NRCC
L. Yang, R. Sturgeon
TUBITAK UME
O. Cankur, N. Tokman and E. Uysal
INMETRO
T. O. Araujo, M. Rocha, L. Reis, T. Aranso, R. Sena, M. Mello, M. Christina
NMISA
S. M. Linsky, A. Barzev
The efforts of A. Trinkl (IAEA) in information technology support and T. Benesch (IAEA) in logistics support are highly appreciated. Special thanks to Dr. M. Sargent the Chairman of the IAWG/CCQM and Dr. R. Hearn for reviewing the draft report.
page 26
REFERENCES [1]
SHAKHASHIRO, A., GONDIN DA FONSECA AZEREDO, A. M., SANSONE, U., FAJGELJ, A., Matrix Materials For Proficiency Testing: Optimization of a Procedure for Spiking Soil With Gamma-Emitting Radionuclides, Anal Bioanal Chem, DOI 10.1007/s00216-006-0772-z, August 2006.
[2]
INTERNATIONAL STANDARDS ORGANZATION, ISO Guide 35: Reference materials - General and statistical principles for certification, Geneva, Switzerland, (2005).
[3]
INTERNATIONAL ORGANIZATION 13528:2005, Annex C.
[4]
DUEWER, D, L, A Robust Approach for the Determination of CCQM Key Comparison Values and Uncertainties, Paper presented at the 10th meeting of the CIPM Consultative Committee for Amount of Substance - Metrology in Chemistry, Sevres, France, (2004). www.bipm.info/cc/ccqm/allowed/10/ccqm0415.pdf.
FOR
STANDARDIZATION,
ISO
APPENDIX I: TABLES OF DEMONSTRATED CORE-CAPABILITIES CCQM K-75, Trace Metals in Algae Analyte: Ni Methodology: ICP-MS (without isotope dilution) Participating Institutes: CMQ-F, TUBITAK UME, INMETRO Core Capability
Institutes Demonstrating
Degree of Difficulty
Explanation
contamination control and correction
All
Moderate
The concentration of Ni in the sample was low enough and the potential for Ni contamination in reagents, containers, and the laboratory high enough that special care needs to be taken to avoid contamination.
digestion/dissolution of organic matrices
All
Moderate
Some issues with undissolved silicates were encountered requiring extra treatments.
calibration of analyte concentration
All
Low
signal detection
All
Moderate
digestion/dissolution of inorganic matrices volatile element containment pre-concentration vapor generation matrix separation liquid chromatographic separation gas chromatographic separation
page 28
The low concentration combined with degraded signal/noise resulting from
Core Capability
Institutes Demonstrating
Degree of Difficulty
correction or removal of isobaric/polyatomic All interferences
Moderate
correction or removal of matrix-induced signal All suppression or enhancement
Low
detector dead-time correction
Low
All
Explanation techniques used to deal with polylatomic interferences increased the difficulty of this measurement Interference was observed from CaO.
29
Demonstrated Inorganic Core Capabilities CCQM K-75, Trace Metals in Algae Analyte: Ni Methodology: ID-ICP-MS Participating Institutes: NIST, BAM, NIM-PRC, PTB, NMIJ/AIST, LGC, GOV LAB HK, KRISS, NRCC, NMISA
Core Capability
Institutes Demonstrating
Degree of Difficulty
Explanation
contamination control and correction
All
Moderate
The concentration of Ni in the sample was low enough and the potential for Ni contamination in reagents, containers, and the laboratory high enough that special care needs to be taken to avoid contamination.
digestion/dissolution of organic matrices
All
Moderate
Some issues with undissolved silicates were encountered requiring extra treatments.
BAM, PTB, NIST, NRCC
Low
All
Low
digestion/dissolution of inorganic matrices volatile element containment pre-concentration vapor generation matrix separation liquid chromatographic separation gas chromatographic separation spike equilibration with sample
page 30
Core Capability
Institutes Demonstrating
Degree of Difficulty
Explanation
Moderate
The low concentration combined with degraded signal/noise resulting from techniques used to deal with polylatomic interferences increased the difficulty of this measurement
correction or removal of isobaric/polyatomic All interferences
Moderate
Interferences were observed from CaO, ArNa, ArMg, and Fe. Various techniques were employed to remove or correct for these interferences.
detector deadtime correction
All
Low
mass bias/fractionation control and correction
All
Low
spike calibration
All
Low
signal detection
All
31
Demonstrated Inorganic Core Capabilities CCQM K-75, Trace Metals in Algae Analyte: Pt Methodology: ICP-MS (without isotope dilution) Participating Institutes: CMQ-F, TUBITAK UME Core Capability contamination control and correction
digestion/dissolution of organic matrices
Institutes Demonstrating
Degree of Difficulty
All
Low
All
Moderate
calibration of analyte concentration
All
Low
signal detection
All
Moderate
Explanation
Some issues with undissolved silicates were encountered requiring extra treatments. An optimized mixture of HCl and HNO3 was required to bring and keep Pt in solution.
digestion/dissolution of inorganic matrices volatile element containment pre-concentration vapor generation matrix separation liquid chromatographic separation gas chromatographic separation
correction or removal of isobaric/polyatomic All interferences page 32
Low
Concentration of Pt is low.
Core Capability
Institutes Demonstrating
Degree of Difficulty
correction or removal of matrix-induced signal All suppression or enhancement
Low
detector deadtime correction
Low
All
Explanation
33
Demonstrated Inorganic Core Capabilities CCQM K-75, Trace Metals in Algae Analyte: Pt Methodology: ID-ICP-MS Participating Institutes: NIST, BAM, NIM-PRC, PTB, NMIJ/AIST, LGC, NRCC, NMISA Core Capability contamination control and correction
digestion/dissolution of organic matrices
Institutes Demonstrating
Degree of Difficulty
All
Low
Explanation
Some issues with undissolved silicates were encountered requiring extra treatments. An optimized mixture of HCl and HNO3 was required to bring and keep Pt in solution.
All
Moderate
BAM, PTB
Low
spike equilibration with sample
All
Moderate
Difficulties associated with full dissolution of Pt affects the spike equilibration.
signal detection
All
Moderate
Concentration of Pt is low.
digestion/dissolution of inorganic matrices volatile element containment pre-concentration vapor generation matrix separation liquid chromatographic separation gas chromatographic separation
correction or removal of All isobaric/polyatomic page 34
Low
Institutes Demonstrating
Degree of Difficulty
detector deadtime correction
All
Low
mass bias/fractionation control and correction
All
Low
spike calibration
All
Low
Core Capability
Explanation
interferences
35
APPENDIX II: TECHNICAL PROTOCOL AND REPORTING FORMS
page 36
Att.
Atoms For Peace Wagramer Strasse 5, P.O. Box 100, A-1400 Wien, Austria Phone: (+43 1) 2600 • Fax: (+43 1) 26007 E-mail:
[email protected] • Internet: http://www.iaea.org In reply please refer to: Analytical Quality Control Services Dial directly to extension: (+431) 2600 728 226 E-mail:
[email protected] • Internet: http://www.iaea.org/programmes/aqcs
Seibersdorf, 2009-03-15
CCQM Key Comparison K75 and Pilot Study P118 Toxic metals in algae Dear Participant,
With reference to your participation in the CCQM Key Comparison K-75 and Pilot Study P-118 on the determination of toxic metals in algae, please find enclosed a set of samples together with the relevant protocol. Determination results and estimated standard combined uncertainties should be reported using the reporting forms (F-01 to F-04). These forms can be accessed via the IAEA website at URL: http://curem.iaea.org/iaea_cu_/ Your user name is: xxxx Your password is : xxxx
You can find full reporting instructions on the main page of the website. The target date for result reporting is the 30 of September 2009.
You are kindly requested to print the final results report generated by the system as a PDF file after submission of your results, sign the first page and send the report by fax or e-mail as your valid results to: e-mail:
[email protected], Fax: +43 1 2600 728 226
The received copy of your results report will constitute your valid results for this study and will be used as the definitive source of information to confirm your results transferred to the on-line data base and to accept any claim in case of data transfer errors. If you do not send the printed report the data entered via the website will be considered as the official results and in this case it will not be possible to ask for any corrections after the results submission target date.
Sincerely yours,
M-12/Rev. 4 (Oct. 04)
Abdulghani Shakhashiro 37
CCQM Key comparison K75 and Pilot Study P118 Toxic metals in algae Technical Protocol 1. Background
In recent years, an increasing number of papers dealt with the environmental impact of platinum group elements (PGE) emitted from automobile catalytic converters. To study the bioavailability of these elements which are present at ultra-low concentrations in the biological matrices, thoroughly evaluation of the CMC of NMIs is required. Biomonitors, such as lichen and algae, are examples of environmental samples that have been widely used by the scientific community to monitor environmental pollution. For this purpose, beside IAEA-392 and IAEA 413 another algal material containing heavy metals and platinum at low level was prepared by IAEA Seibersdorf Laboratories in collaboration with the Italian National Institute for Environmental Protection - ISPRA (former APAT).
2. Material
Two batches of unicellular microalgae (Scenedesmus obliquus) were grown in an outdoor bioreactor by the Institute of Microbiology, Academy of Sciences of the Czech Republic, Trebon. One batch was grown on standard nutrient solution (natural contamination level), the second batch was grown on a nutrient solution containing elevated levels of As, Cd, Cr, Hg, Ni, Pb, and Pt. After harvesting, the thickened suspension was stored in a cooled tank from which it was continuously fed to a spray drier. Thereafter, the two bulk materials were gamma irradiated at the IAEA’s laboratories to avoid a bacterial deterioration and tested for homogeneity. Thereafter, in order to adjust the Pt mass fraction to the level of environmental pollution in road dust, the two algal materials were mixed in a ratio of 1:100 (high Pt: low Pt). Using high purity methanol, slurries of the two algae materials were produced and merged under constant stirring in 200 g batches. After 72 hours drying at 60 °C, the dry material was homogenised using a Turbula shaking device for 8 hours. Then the 200 g batches were merged and homogenised at ISPRA Laboratories. The particle size distribution was determined by laser light scattering technique and found to be less than 100 µm. The bulk material homogeneity was tested before bottling. The material was bottled and tested for homogeneity by analyzing As, Cd, Cr, Hg, Ni, Pb and Pt in 10 bottles at 3 replicates from each bottle. The material homogeneity was tested for a test portion of 200 mg (Hg was tested at 20 mg level). 38
3. Measurands
Participants are requested to perform 5 independent measurements on 5 different test portions to determine the mass fraction of the elements they have selected in the registration phase. Potential Analytes and expected mass fraction in (mg/kg) Pt (0.1) Cr (3.0) Ni (1.0) Cd (0.1) Hg (0.1) Pb (1.0) As (0.1)
4. Choice of method/procedure.
Participants may use any validated analytical procedure of their choice. 5. Test sample handling
Participants are asked to thoroughly mix the sample before processing and to analyze the sample with minimum test portion of 200 mg.
For moisture content determination, an aliquot (minimum 0.5 g) of the sample must be taken for drying at 80 °C for at least 4 hours. 6. Reporting of results
The mean value of 5 independent measurements and its associated uncertainty should be expressed and reported in mg kg-1 based on dry mass. Uncertainty should be reported as the combined standard uncertainty (1 sigma level) where all major individual sources of uncertainty have been identified and taken into account. Full details of the analytical procedure including the sample dissolution and calibration methods. Participants will be asked to provide information about their metrological traceability (calibration standard certificate). Target date for results reporting is 30 September 2009.
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On-line Results reporting forms CCQM-Key comparison K75 and pilot study P118 Toxic metals in algae Results and uncertainties reporting form (F-02) Moisture content [%]:…………………………………… Bottle Number ……….. As
Analytical results Mass fraction [mg/kg] based on dry mass
Total combined standard uncertainty* at
Test
portion [mg]
1σ level
Cd Cr Hg Ni Pb Pt * Standard uncertainty of individual determination expressed in (mg/kg) (see uncertainty quantification sheet)
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Bottle number: …………..
CCQM-Key Comparison K75 and pilot study P118 Toxic metals in algae Combined Uncertainty Estimation Form (F-03)
1- Please describe your approach for evaluation of uncertainty components and give the formula used for calculation of the expanded uncertainty. 2- You are kindly asked to list the sources of uncertainties included in the estimation of the combined standard uncertainty. Kindly indicate, by putting “X” in the appropriate box, which uncertainty components were considered in your estimation of the combined uncertainty for each analyte Element Unc. components
As
Cd
Cr
If not enough space please add separate sheets to this page.
Hg
Ni
Pb
Pt
CCQM-Key Comparison K75 and pilot study P118 Toxic metals in algae Reporting Form 04 Information on analytical method (should be repeated each analyte) This questionnaire is an integral part of the study and is addressed to the person performing the analysis. The answers will be considered together with the analytical results. 1. What was the basis of the choice of your method? − from open literature, ISO, National standard without changes
Please indicate the reference:
with modifications in-house method −
how long has this procedure been used in your laboratory? (Years):
2. What is your personal experience with this method? < 1 year
1 - 3 years
> 3 years
occasionally
rarely
3. Do you perform this type of measurement: regularly
4. What Analytical Quality Control tools are used in your laboratory? − control charts for reagent blank reference materials control sample Other please specify: − −
independent check of calculations proficiency tests
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DESCRIPTION OF QUALITY CONTROL PROCEDURE Use of blanks, CRM, Control samples, duplicate, replicate, spike sample and control charts. DESCRIPTION OF THE ANALYTICAL PROCEDURE Kindly give a short description of your method including sample treatment and separation method where applicable. 1. Digestion procedure: Non-destructive Dry ashing Wet digestion Microwave assisted digestion Open-hot plate digestion Fusion High pressure asher Other please specify: Acids used
HNO3
ml:
HCl
ml
HF
ml:
H2SO4
ml:
HClO4
ml:
H2O2
ml:
Other please specify:
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MEASUREMENT TECHNIQUE: Non Destructive ED-XRF
WD-XRF
TR-XRF
INAA PIXE Other, please specify
Destructive Flame-AAS for analytes : Graphite furnace AAS for analytes : Hydride generator for analytes : ICP-OES for analytes : Q-ICP-MS for analytes : HR-ICP- MS for analytes : ASV for analytes : Other, please specify
_____________________________________________________________________________________________________________
CALIBRATION METHOD
_________________________________________________________________________________________________________________
Please provide details of the calibration method. Calibration procedure and calibration standard solution (source) traceability
_____________________________________________________________________________________________________________
______________________________________________________________________________________________________________
REFERENCE MATERIALS USED FOR QUALITY CONTROL
_________________________________________________________________________________________________________________
Please specify which reference materials were used for quality control or method validation purposes.
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