Anal Bioanal Chem (2002) 372 : 562–568 DOI 10.1007/s00216-001-1120-y
O R I G I N A L PA P E R
D. Martens · M. Gfrerer · T. Wenzl · A. Zhang · B. M. Gawlik · K.-W. Schramm · E. Lankmayr · A. Kettrup ·
Comparison of different extraction techniques for the determination of polychlorinated organic compounds in sediment Received: 27 August 2001 / Revised: 27 August 2001 / Accepted: 4 September 2001 / Published online: 21 December 2001 © Springer-Verlag 2001
Abstract The performance of various enhanced extraction techniques, such as accelerated solvent extraction, microwave-assisted extraction, Soxhlet extraction, ultrasonic extraction and fluidized-bed extraction for the determination of polychlorinated organic compounds in dry sediment was investigated in two laboratories. The results of the two laboratories were in good agreement. The extraction yields from the batch extraction methods were lower than those from the dynamic techniques. Accelerated solvent extraction, especially, exhibited higher extraction efficiency than the standard procedure, Soxhlet extraction, whereas the results of fluidized-bed extraction were comparable. Keywords Soxhlet extraction · ASE · Microwaveassisted extraction · Ultrasonic extraction · Fluidized-bed extraction · Chlorinated compounds
D. Martens (✉) · A. Kettrup Technical University of Munich, Department of Ecological Chemistry and Environmental Analytical Chemistry, 85350 Freising-Weihenstephan, Germany e-mail:
[email protected] M. Gfrerer · T. Wenzl · E. Lankmayr Technical University of Graz, Institute of Analytical Chemistry, Micro- and Radiochemistry, Technikerstrasse 4/P, 8010 Graz, Austria A. Zhang Nanjing University, School of the Environment, Nanjing, China B.M. Gawlik European Commission, DG Joint Research Center, Institute for Reference Materials and Measurements, 2440 Geel, Belgium K.-W. Schramm · A. Kettrup GSF – National Research Center for Environment and Health, Institute of Ecological Chemistry, Ingolstaedter Landstrasse 1, 85764 Neuherberg, Germany
Introduction Sample pre-treatment is a time-consuming and error-prone step in environmental analysis. Special emphasis has to be given to an accurate choice of extraction techniques and clean-up procedures [1, 2]. In recent years, for the extraction of organic trace compounds from solid matrices, such as soils and sediments, the classic Soxhlet extraction has been replaced by faster, less solvent-consuming and often automated techniques [3, 4]. A selection of these new extraction techniques for sample preparation includes ultrasonic extraction (UE) [5, 6, 7, 8], accelerated solvent extraction (ASE) [1, 6], microwave-assisted extraction (MAE) [1, 4, 5, 8, 9], supercritical-fluid extraction (SFE) [1, 9, 10] and fluidized-bed extraction (FBE) [11, 12, 13]. The extraction procedure itself is a critical step in the analytical cycle: Internal standards are added in solution, while the native analytes are in contact with the solid sample matrix of real world samples for a long time, often resulting in a stronger binding to the matrix. As a result of this different behavior, the extraction efficiency can neither be monitored exactly by use of internal standards nor by the calibration procedure. Therefore, a comparison of different extraction methods is useful. Accurate results can only be achieved by using a homogeneous test material [14]. The homogeneity of certified reference materials (CRMs) is well documented, but these materials are rather expensive for extensive method comparison purposes. A valuable alternative is provided by so-called laboratory reference materials (LRMs). These materials can be prepared according to the same procedure as certified reference materials including homogeneity and stability tests, however, without final certification of the concentration of the individual target compounds. Such a sediment material (S37) was available within the frame of an international environmental research project on the water quality of two Chinese rivers – the Yangtse River and the Liao-He River [15]. The properties of this sediment material from the Yangtse River were well characterized, and the homogeneity and stability of the content of chlorinated compounds were tested [16].
563
Sample aliquots of this sediment were extracted with different methods such as in a Soxhlet apparatus and by ASE, FBE, MAE, and UE. In the present work the result of a comparison of these extraction procedures performed in two laboratories is presented.
the same than the respective between-bottle data. During 7 months a simplified stability study was performed for pentachlorobenzene, hexachlorobenzene, octachlorostyrene, pentachloroanisole, α-hexachlorocyclohexane, 2,4′-DDE, 2,4′-DDD, 4,4′-DDE, 4,4′-DDD as well as for the PCB congeners 28, 52, 101, 138, 153 and 180. Within the limits of measurement variability general stability of the compounds of interest was observed throughout the monitoring period, all data have already been published by Gawlik et al. [16].
Experimental
Reagents and chemicals
The extraction procedures for the comparison were performed in two different laboratories with their own optimized methods. In order to provide a systematic means for the purpose of comparison, the description is divided into ‘method a’ and ‘method b’ if two different procedures were applied for one extraction technique. The same system was used for a characterization of different procedures within the chapters ‘reagents and chemicals’, ‘clean up’, and ‘analysis and quantification’. Besides different extraction solvents, extraction conditions and internal standards, the addition of internal standards was performed at different procedure steps. In methods a and MAE the internal standard was added after extraction, considering extraction efficiencies and possible losses of analytes during extraction, whereas the internal standards were added before extraction in methods b and ASE, considering different extraction efficiencies of freshly added internal standards and stronger matrix-bonded native analytes.
Method a
Sediment sample The extraction experiments were performed using aliquots of the sediment material S37. This sediment material was produced according to the general principles for candidate reference material production except the final certification. Approximately 120 kg of raw material were sampled using a specially designed sampler in tributary of the Yangtse River System (PR China), situated downstream of Nanjing. The wet sediment was sucked to dryness using a large Buchner funnel (i.d. 28 cm), a suction flask (5 L) and a water vacuum pump. The pre-dried material was shipped to the JRC Ispra (Italy) for further processing, such as drying, crushing, sieving and mixing. After a thorough homogeneity study of the bulk, the material was bottled in 50-g portions. A final homogeneity testing between 10 bottles, randomly chosen of the total population, and within one randomly chosen bottle was performed. The coefficients of variation for the within-bottle series were almost
Table 1 Selected ions for MS detection in SIM mode. First ion, quantification ion (in bold); second and third ions: qualifiers
Analyte
Reference compounds were supplied by Dr Ehrenstorfer (Augsburg, Germany) as standard solutions (PCB mix 1 containing the six non-dioxin-like PCBs 28, 52, 101, 138, 153, 180, PCB 209 and octachlorostyrene in iso-octane, PCBz and pesticide-mix 14 containing the rest of the analytes as given in Table 1 in cyclohexane). Acetone, dichloromethane and benzene were purchased from Promochem (Wesel, Germany; purity: Pico grade, for residue analysis). n-Hexane (purity: UniSolv, for organic trace analysis), silica gel (particle size 0.063–0.200 mm, for column chromatography) and anhydrous sodium sulfate were obtained from Merck (Darmstadt, Germany). Diatomite (filter agent) was acquired from Aldrich (Gillingham, UK). Method b Native standard compounds were obtained from Dr. Ehrenstorfer (Augsburg, Germany), PCBz, PCA and OCS as single compounds, the other substances (Table 1) as a mixture. Single isotope-labelled standards (Table 1) and n-nonane (purity: for residue analysis) were purchased from Promochem (Wesel, Germany). The other solvents – n-hexane, acetone and dichloromethane – were supplied by Riedel–de-Haën (Seelze, Germany, purity: pestanal). Silica gel (particle size 0.063–0.200 mm, for column chromatography) and sodium sulfate anhydrous (purity: pro analysis) were acquired from Merck (Darmstadt, Germany). Extraction procedures Soxhlet extraction Method a. For definition of a standard reference procedure, the extraction parameters were chosen according to DIN 38414–20 [17].
Abbr.
m/z (Method a)
m/z (Method b) Analyte
Internal Standard 13C-labelled
Pentachlorobenzene Hexachlorobenzene Octachlorostyrene Pentachloroanisole α-HCH β-HCH γ-HCH 4,4′-DDE 4,4′-DDD PCB 28 PCB 52 PCB 101 PCB 138 Internal Standard (a)
PCBz HCB OCS PCA a-HCH b-HCH g-HCH 4,4′-DDE 4,4′-DDD PCB 28 PCB 52 PCB 101 PCB 138 PCB 209
250, 252, 248 284, 286, 282 308, 310 280, 265 219, 181, 183, 219, 181, 183, 219, 181, 183, 246, 248 235, 237 256, 258 292, 290 326, 328 360, 362 498, 500
250, 252 284, 286 343, 345 265, 263 219, 217 219, 217 219, 217 246, 248 235, 237 256, 258 292, 290 326, 328 360, 362
290, 292
225, 223, 227 225, 223, 227 225, 223, 227 258, 260 268, 270 304, 302 338, 340 372, 374
564 10 g reference sediment S37 were transferred into an extraction thimble (MN 645, 30×100 mm, Macherey–Nagel, Düren, Germany), covered with glass wool (preconditioned for 72 h at 300 °C) and inserted into a 100 mL Soxhlet extractor. The samples were extracted under reflux with 200 mL of n-hexane–acetone 4+1 (v/v) for 24 h. Since extraction thimbles are a potential contamination source, they were extracted before use under reflux in 100 mL Soxhlet extractors with 200 mL n-hexane–acetone 1+1 (v/v) for 4 h. Following extraction, 200 ng of the internal standard PCB 209 were added and the extracts were rotary evaporated to approximately 1 mL. Method b. 10 g aliquots of reference material were accurately weighed into 50 mL glass extraction cartridges with sintered glass frits at the bottom, spiked with 13C-labelled internal standards (each 12.5 ng) and transferred into a 200 mL Soxhlet extractor. Extraction with 300 mL n-hexane–acetone 1+1 (v/v) was performed under reflux for 16 h at a temperature of about 40–50 °C.
weighed into an extraction tube and mixed with 3 g diatomite to enhance the permeability of the solid bed. The specimens were extracted with 50 mL of n-hexane–acetone 4+1 (v/v) for 10 extraction cycles, each held for 8 min. The system was equipped with a temperature sensor for an accurate setting of the heating (85 °C) and cooling (30 °C) temperatures. After extraction the raw extracts were transferred into 100 mL pear-shaped flasks, 200 ng of PCB 209 contained in 20 µL cyclohexane were added and the extracts were concentrated to about 1 mL by means of a rotary evaporator. Method b. 10 g sediment were weighed into the extraction tube and spiked with internal standards (each 12.5 ng). The sample was extracted 10 times with 100 mL n-hexane–acetone (1+1, v/v) for 10 min at a heating temperature of 130 °C and a cooling temperature of 30 °C. The extract was concentrated to 0.5 mL in a rotary evaporator. Ultrasonic extraction
Accelerated solvent extraction ASE was performed using an ASE 200 accelerated solvent extractor (Dionex Corp., Idstein, Germany) equipped with 22 mL stainless-steel extraction cells. 10 g aliquots of S37 were weighed in the extraction cells as follows: The extraction cell was closed at one end, with a frit and an end cap, a cellulose filter (Dionex No. 49458) was placed at the bottom of the extraction cell to prevent cell frit blockage, a quantity of 2 g was placed on top of the filter, internal standards were added (each 12.5 ng), after evaporation of the solvent followed by 8 g sediment and the remaining volume was filled with sea sand (previously conditioned at 600 °C), covered by a second filter and closed with a frit and an end cap. The samples were extracted as follows: extraction solvent: n-hexane– acetone 1+1 (v/v); temperature: 150 °C; pressure: 14 MPa; extraction time: 2×10 min. Microwave-assisted extraction MAE was carried out with a Multiwave extraction system (Anton Paar Physica, Graz, Austria) equipped with a 6-sample tray. A special feature of this system is its integrated pressure and temperature feedback security mechanism [18]. For further security reasons the microwave oven was equipped with an additional gas sensor, which automatically switches off the main power if traces of flammable solvents are detected. Portions of 10 g S37 were weighed into 100 mL perfluoroalkoxy (PFA) polymer extraction vessels and 30 mL n-hexane–acetone 1+1 (v/v) were added. The extraction vessels were closed with Teflon caps and six samples each were simultaneously extracted with the microwave power set to 1000 W for 30 min and the maximum pressure and temperature in the extraction vessels programmed to not exceed values of 3 MPa and/or 130 °C. After a cooling phase of 30 min, the raw extracts were separated from the solid samples by centrifugation (5 min, 300 g) and transferred into 50 mL pear-shaped flasks. The remaining solid was washed twice with about 3 mL of fresh n-hexane and again separated by centrifugation. 200 ng of the internal standard (PCB 209) were added to the combined solutions of raw extract and washing solutions and the extracts were concentrated to about 1 mL by means of a rotary evaporator. Fluidized-bed extraction For the extraction experiments a fexIKA 200 control series extractor introduced in 1997 [11] (IKA-Labortechnik, Staufen, Germany) was used. With the standard configuration of this system four extractions could be carried out simultaneously. Method a. For the extraction of solids each extraction tube was prepared with a fresh polytetrafluoroethylene (PTFE)-filter (47 mm i.d., 10–20 µm, fexIKA). A 10 g aliquot of sediment sample was
Method a. For the experiments described, an ultrasonic bath (Transonic T780, Elma, Singen, Germany) was used. 10 g S37 were weighed into 40 mL eprouvettes with Teflon sealed screw caps and 20 mL of n-hexane–acetone 1+1 (v/v) were added. The eprouvettes were closed and sonicated for 1 h at a temperature of 40 °C. After cooling down to room temperature, the extracts were separated from the solids by centrifugation (5 min, 300 g) and transferred into 50 mL pear-shaped flasks. The remaining solid was washed three times with about 3 mL of fresh n-hexane and again separated by centrifugation. 200 ng of the internal standard (PCB 209) contained in 20 µL cyclohexane were added to the combined solutions of raw extract and washing solutions and the extracts were concentrated to about 1 mL by means of a rotary evaporator. Method b. 10 g of reference sediment were weighed into 100 mL centrifuge tubes, equipped with Teflon sealed caps, and the internal standards were added (each 12.5 ng). Samples were extracted with 45 mL n-hexane–acetone 1+1 (v/v). The extraction was carried out at a temperature of 40 °C for 1 h in an ultrasonic bath (RK-156, Bandelin, Berlin, Germany). To ensure the intermixing, the samples were shaken every 15 min. After extraction, the samples were centrifuged for 10 min (300 g). 20 mL of the clear organic phase were separated and concentrated in a 25 mL pearshaped flask by means of a rotary evaporator to 0.5 mL. Clean up In order to remove polar interferences from the raw extracts, sample clean up by adsorption chromatography on silica gel was performed in both cases. Method a Fresh silica gel (particle size: 0.063–0.200 mm) was activated before use for at least 72 h at 105 °C and was stored at the same temperature as long as not in use to ensure constant activity. Cartridges were prepared by weighing in 1 g silica gel and 1 g Na2SO4 each into empty 6 mL glass extraction cartridges (8 mm i.d.), which were equipped with polyethylene frits at the bottom. The solid bed was conditioned with 50 mL n-hexane and compressed by a stream of N2. The concentrated raw extract and two 1 mL n-hexane–dichloromethane 7+3 (v/v) portions of the washing solutions from the rinsing of the sample vial were applied to the top of the column. The analytes were eluted from the column with a further 10 mL n-hexane–dichloromethane 7+3 (v/v) and collected in a 50 mL pear-shaped flask. The clean solution was concentrated by means of a rotary evaporator, carefully blown to dryness with a gentle stream of nitrogen, taken up in 250 µL of benzene and transferred into a GC-micro vial for measurement. Despite the fact that dichloromethane as well as benzene are risky solvents, they were used because of their favorable properties. Dichloromethane has
565 an appropriate polarity as well as a low boiling point (+40 °C), thus, the mixture of n-hexane–dichloromethane elutes the analytes sufficiently fast from the adsorption column and can also be easily evaporated. This method was originally developed to determine 44 polychlorinated organic compounds. In order to guarantee a short solvent delay during the GC–MS temperature program, benzene (bp 80 °C) was used in 250 µL portions in microvials to reconstitute the residues. Method b 1 g silica gel and 1 g Na2SO4 were weighed into a 6 mL polypropylene cartridge and washed twice with 4 mL n-hexane– dichloromethane 7+3 (v/v). After application of the sample to top of the column, the analytes were eluted with 6 mL n-hexane– dichloromethane 7+3 (v/v) and collected in a 25 mL pear-shaped flask. A volume of 150 µL n-nonane was added and the eluate was concentrated by means of a rotary evaporator to approximately 0.5 mL. Thereafter, the solution was further concentrated under a gentle stream of dry nitrogen to nearly 100 µL. For the purpose of recovery measurement, 10 µL of standard (pentachlorotoluene – 10 ng µL–1) were added and the extract was transferred into a glass micro vial for target compound analysis. Analysis and quantification Analysis was carried out by gas chromatography combined with mass spectrometry (GC–MS) in both methods. Method a GC–MS determination was carried out using a Hewlett–Packard (Waldbronn, Germany) HP6890 gas chromatograph equipped with an HP7683 auto sampler and a split/splitless injector operated in pulsed splitless mode (purge delay: 0.60 min; purge flow: 35.0 mL min–1; pulse pressure: 68.4 kPa). The injector was equipped with a single taper liner packed with a small amount of pesticide-grade glass wool (Supelco, Bellefonte, USA) and maintained at 250 °C. An injection volume of 1 µL was selected for all analyses. The capillary column used was a HP-5MS, 30 m×0.25 mm i.d. and 0.25 µm film thickness. Helium (AGA, Graz, Austria, 5.0) at a constant flow rate of 1.1 mL min–1 was used as carrier gas. The oven temperature program was: 70 °C for 0.50 min ramped at 25 ° min–1 to 170 °C, at 4 ° min–1 to 190 °C, at 10 ° min–1 to 230 °C, at 4 ° min–1 to 270 °C, at 30 ° min–1 to 300 °C and held at 300 °C for 5 min. The gas chromatograph was coupled to an HP5973 massselective detector (electron-impact ionization) operated in singleion monitoring (SIM) mode using the m/z values listed in Table 1. The interface temperature was maintained at 280 °C. The instrument was tuned daily with perfluorotributylamine (PFTBA) using the automatic tune (ATUNE) facility. Calibration was accomplished by internal standardization at 6 concentration levels for the analytes in the range from 15 to 360 pg µL–1. The concentration of the internal standard PCB 209 was kept constant at 800 pg µL–1. In addition, each calibration standard and sample extract was injected in duplicate. Chromatographic peak areas were fitted by linear regression and the correlation coefficients ranged from 0.9992 to 0.9999. Method b GC–MS analysis was performed using an 8000 GC–MS system from Fisons (Rodano, Italy), consisting of a Fisons GC8000, an auto sampler AS800 and a quadrupole mass-spectrometer MD800. The capillary column used was a DB-5 with a length of 30 m, an internal diameter of 0.32 mm and a film thickness of 0.25 µm. The carrier gas used was helium with a constant column head pressure of 50 kPa and an initial flow rate of 1.2 mL min–1. A volume of 1 µL was injected splitless. The following temperatures were used:
Injector temperature was set at 220 °C and the detector interface temperature was maintained at 280 °C. The temperature gradient was: 60 °C for 1 min, ramped at 8 ° min–1 to 140 °C, at 5 ° min–1 to 240 °C, at 12 ° min–1 to 260 °C and held at 260 °C for 3 min. The mass-selective detector was operated in EI–SIM mode using the m/z ions listed in Table 1. 5-Point internal calibration was used in the concentration range from 10 to 500 pg µL–1 for native analytes and a constant concentration of 100 pg µL–1 for internal standards. For statistical calculations and cluster analysis the software package Statgraphics Plus version 3 (Manugistics, Rockville, USA) was used.
Results and discussion In order to identify potential differences of the results obtained from the two laboratories and differing methods, cluster analysis was carried out using the data set as listed in Table 2. The nearest neighbor method using the Euclidean distance was chosen to perform a hierarchical clustering with the aim of recognizing whether the two laboratories build two independent clusters, which would be indicative of incomparable results. The clusters are groups of variables with similar characteristics. To form the clusters, the procedure began with each variable in a separate group. It then combined the two variables which were closest together to form a new group. After re-computing the distance between the group, the two groups then closest together were combined. This process was repeated until only 1 group remained. As can be seen from the dendrogram in Fig. 1, there are very low distances between the investigated extraction techniques and no significant clusters enabling distinction between the laboratories. Despite the fact that the experiments were performed in two laboratories using different GC–MS-equipment, reagents and chemicals as well as their own optimized method for each extraction technique the result is remarkable: The most similar patterns for all analytes, were obtained by the FBE method with the lowest distance, followed by UE and Soxhlet extraction. Only microwave-assisted extraction seems to be somewhat distinguished from the others, although the distance is low too. However, the extraction techniques performed in the two laboratories exhibited statistically similar results for the analyte patterns, despite differences with respect to extraction conditions, internal standards and addition of internal standards before or after extraction. An overview of the results from the analysis of sediment S37 is given in Fig. 2. The numerical values for all extraction experiments and analytes as well as the standard deviation and the precision (relative standard deviation) are presented in Table 2. As can be seen in Fig. 2, lower values were obtained for the more volatile compound PCBz when using method a. For this compound the internal standard might be added before the extraction and, even careful, evaporation to dryness should be avoided. On the other hand for HCB and the HCHs, known as relatively volatile, the values are comparable with those obtained with method b. In order to have an objective means of evaluation, the results from the different extraction procedures are compared with the
1.29±0.13 4.26±0.28 0.18±0.01 0.66±0.05 1.17±0.25 0.85±x 0.89±0.22 2.53±0.13 1.48±0.09 0.14±0.01 0.08±0.01 0.06±0.00 0.06±0.01
10.1 6.5 6.0 7.1 21.4 x 24.4 5.1 6.3 6.9 6.8 6.4 11.2
0.79±0.03 3.74±0.17 0.17±0.02 0.58±0.08 0.73±0.13 0.75±0.10 0.85±0.04 2.17±0.09 1.17±0.08 0.11±0.02 0.08±0.00 0.06±0.01 0.06±0.01
3.3 4.4 13.6 14.2 17.8 13.4 4.6 4.1 6.8 13.3 1.5 14.8 10.6
RSD (%)
Conc. (µg kg–1)
RSD (%) 7.4 1.9 5.3 4.4 3.4 14.1 7.1 4.1 3.6 3.3 4.9 2.7 8.2
Conc. (µg kg–1) 1.02±0.08 3.61±0.07 0.17±0.01 0.55±0.02 0.73±0.03 0.78±0.11 0.87±0.06 2.18±0.09 1.18±0.04 0.12±0.00 0.09±0.00 0.06±0.00 0.05±0.00
0.72±0.03 3.53±0.26 0.22±0.01 0.54±0.07 0.68±0.07 0.78±0.05 0.73±0.08 2.42±0.04 1.25±0.02 0.12±0.01 0.08±0.00 0.07±0.00 0.05±0.00
FBE a
Soxhlet b
Conc.=Concentration, ASE=Accelerated Solvent Extraction, FBE=Fluidized-bed extraction, MAE=Microwave-assisted Extraction, UE=Ultrasonic Extraction, RSD=relative standard deviation
PCBz HCB OCS PCA a-HCH b-HCH g-HCH 4,4′-DDE 4,4′-DDD PCB 28 PCB 52 PCB 101 PCB 138
Conc. (µg kg–1)
Conc. (µg kg–1)
RSD (%)
Soxhlet a
ASE RSD (%) 9.2 8.6 11.6 22.8 23.9 16.8 20.8 9.6 9.8 5.7 0.3 20.7 6.7
Conc. (µg kg–1) 0.59±0.05 3.29±0.28 0.19±0.02 0.48±0.11 0.60±0.14 0.72±0.12 0.75±0.16 1.62±0.15 1.22±0.12 0.07±0.00 0.07±0.00 0.06±0.01 0.06±0.00
RSD (%) 9.7 5.1 2.2 1.7 1.6 7.6 3.6 6.4 6.3 11.9 4.1 7.6 2.7
Conc. (µg kg–1) 0.77±0.07 3.42±0.17 0.19±0.00 0.44±0.01 0.60±0.01 0.61±0.05 0.69±0.03 2.47±0.16 1.30±0.08 0.12±0.01 0.09±0.00 0.07±0.01 0.06±0.00
Conc. (µg kg–1)
RSD (%) 2.2 3.8 23.5 8.0 21.1 15.6 3.8 15.1 6.6 10.2 1.5 2.2 23.6
Conc. (µg kg–1) 0.70±0.02 3.29±0.12 0.16±0.04 0.48±0.04 0.45±0.09 0.53±0.08 0.79±0.03 1.94±0.29 1.11±0.07 0.08±0.01 0.08±0.00 0.06±0.00 0.06±0.01
0.76±0.03 3.11±0.04 0.18±0.01 0.44±0.01 0.49±0.03 0.65±0.20 0.79±0.04 2.03±0.06 1.13±0.01 0.09±0.00 0.08±0.00 0.06±0.00 0.05±0.00
UE b
UE a
3.9 1.2 5.7 1.4 6.5 30.9 5.0 3.1 1.2 1.2 3.5 1.4 1.2
RSD (%)
Analyte identification: PCBz=pentachlorobenzene, HCB=hexachlorobenzene, OCS=octachlorostyrene, PCA=pentachloroanisole, a-HCH=alpha-hexachlorocyclohexane, b-CH= beta-hexachlorocyclohexane, g-HCH=gamma-hexachlorocyclohexane (lindane), x=only one successful quantification
3.9 7.3 5.4 13.1 10.5 6.9 10.4 1.5 2.0 12.1 0.8 5.7 7.9
RSD (%)
MAE
FBE b
Table 2 Concentration (µg kg–1) of polychlorinated organic compounds in the river sediment S37 obtained by different extraction techniques and performed in two laboratories
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Fig. 1 Dendrogram from cluster analysis
results from the Soxhlet extraction as a benchmark technique. The differences between the mean concentrations are given in Table 3. The bold typed data in Table 3 indicate significant differences according t-test and p-values
