Preconcentration and Speciation of Chromium(III) in Waters by Using 5-Palmitoyl-8-Hydroxyquinoline Immobilized on a Nonpolar Adsorbent. Hayati Filik.
Microchim. Acta 140, 205–210 (2002) DOI 10.1007/s00604-002-0909-5
Original Paper Preconcentration and Speciation of Chromium(III) in Waters by Using 5-Palmitoyl-8-Hydroxyquinoline Immobilized on a Nonpolar Adsorbent Hayati Filik Department of Chemistry, Faculty of Engineering, I_ stanbul University, Avclar, 34850 I_stanbul, Turkey Received December 20, 2001; accepted May 22, 2002; published online September 12, 2002 # Springer-Verlag 2002
Abstract. A method for the quantitative separation and preconcentration of trace amount Cr(III) in real samples has been developed. It is based on the sorption of Cr(III) ions onto a column of Amberlite XAD-2 resin functionalized with 5-palmitoyl-8-hydroxyquin oline reagent. The resin was used for speciation and preconcentration of chromium because this functionalized resin is selective for Cr(III) ions. The effect of pH, flow-rate, sorption capacity, reusability and effect of various metal cations and salt anions on the sorption on to the resin were investigated. The sorption is quantitative in the pH range of 4.5–7.0, and Cr(III) ion was desorbed by using hydrochloric acid. The amount of metal ion in the eluate was determined by a flame atomic absorption spectrometer. Total chromium was obtained by an efficient reduction of Cr(VI) to Cr(III) by hydroxylamine. The procedure has been applied to the determination and speciation of chromium in lake water, and in the chromium-plating baths. Key words: Chromium; speciation; amberlite XAD-2; 5-palmitoyl8-hydroxyquinoline; water.
Chromium exists in three oxidation states in natural water. The characteristic oxidation states are 2 þ , 3 þ , 6 þ , represented in acidic solution by Cr2 þ (chro(chromic), and Cr2 O7 2 (chromous), Cr3 þ (dichromate) and in basic media found as Cr(OH)2, CrO2 (chromite), and CrO4 2 (chromate). The chromous ion, Cr2 þ , is rapidly oxidized to Cr3 þ in aqu-
eous solution by air. The three Cr valencies have different toxicologic potentials. Further, within each valency group, toxicity varies according to solubility. Thus whereas chromic acid, H2CrO4, in which Cr is 6 þ , is highly corrosive and toxic, Cr2 þ and Cr3 þ salts, including Cr2O3 are described a far lower order of toxicity. Na2CrO4, a highly soluble Cr compound, in which Cr is also hexavalent, also has a low order of toxicity but the corresponding insoluble chromates of Ca, Pb, and Zn are suspected human lung carcinogens. Chromium(III), for example, is considered an essential micronutrient at the trace levels for humans and animals to maintain normal glucose metabolism. In particular, Cr(VI) is considered to be the more toxic form in biological systems [1]. Toxic chromium enters the environment from industrial effluent or waste-disposal sources, such as wastewater from steel works, electroplating, and tanning industries. Traces of chromium may also enter drinking-water supply systems [2]. It is therefore necessary to control and to measure the level of the two species in wastewater, natural water and drinking water. The determination of the various species of Cr must be carried out immediately following the sampling. In the usual method for the speciation of chromium species, the Cr(VI) concentration is first determined spectrophotometrically at 540 nm as a complex with 1,5-diphenylcarbazide. After the oxidation of Cr(III) to Cr(VI) with suitable oxidants, such as ammonium peroxodisulfate, the total amount of
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Cr(VI) is determined again [3, 4]. For this purpose, various methods are used, and these methods include coprecipitation with metal hydroxides [5–7], solvent extraction [8, 9], electrochemical separation [10, 11], solid-phase extraction [12, 13], ion exchange [14], and adsorption [15], which have been widely used for the preconcentration and separation method of the mixtures of the two oxidation states. Retention of Cr(VI) has been achieved using columns with melamine-formaldehyde [16], melamine–urea–formaldehyde [17], sodium dodecylsulphate-coated alumina microcolumns [18], C18 bonded silica reversed phase sorbent with diethyldithiocarbamate as complexing agent [12]. Cr(III) can be retained selectively using the chelating resin polyaminophosphonic acid (PAPhA) [14], immobilized quinoline-8-ol or iminodiacetate functional groups (Muromac A-1) [19], columns with macroporous resin after complexation with quinolin-8-ol [20], S.cerevisiae immobilized on sepiolite [21]. Simultaneous retention of chromium species can be carried out with activated alumina microcolumns [12, 22], methyltrioctilammonium chloride loaded silica gel columns [20], Dowex 1-X 8 anion-exchange resin columns [24, 25]. In other methods, employed for the speciation of Cr(VI) and Cr(III) two different sorbent have been used. For Cr(VI) retention an Eurospher 100-C18, and for Cr(III) retention a potassium hydrogen phthalate modified C18 column have been used [26]. An AG MP1 anion resin has been used to retain Cr(VI) and Chelex 100 ion exchange resin to retain Cr(III) [27]. 8-Hydroxyquinoline reacts with Cr(III) more rapidly than other ligands [20]. At the same time 8hydroxyquinoline (oxine) and oxine type chelating resins are selective for Cr(III) ions and do not retain Cr(VI) ions [19, 20]. In previous works, 5-palmitoyl8-hydroxyquinoline (P.Ox) (Fig. 1) [28, 29] functionalized Amberlite XAD-2 chelating resin column was
H. Filik
used to preconcentrate and separate Ga(III) from Al(III) and for the speciation of Ga(III) [30, 31]. This paper describes the quantification of the two valency states of chromium Cr(III) and Cr(VI). A double column procedure was used for preconcentrating Cr(III) and Cr(VI) from synthetic and real samples. By reducing Cr(VI) to Cr(III) in a separate sample, chromium was measured as total Cr and in this way, both species were quantified. The method was successfully applied to the selective determination of Cr(III) and Cr(VI) in lake water and in the electroplating-industry wastewater samples. Experimental Reagents and Solutions All chemicals were of analytical-reagent grade and obtained from E. Merck. A standard solution of 1000 mg=L Cr(III) was prepared from Cr(III) chloride hexahydrate in 0.5 M hydrochloric acid. A solution of 1000 mg=L Cr(VI) was prepared by dissolving 2.8290 g of K2Cr2O7 in 1 L of distilled water. From these solutions, other diluted standard solutions were prepared on a daily basis. Both solutions were standardized by the iodometric method [32]. The pH adjustments were made with acetate (0.2 M) buffers. The dilute solution of HCl (up to 4 M) was used as eluant. An aqueous solution of 5% (w=v) hydroxylamine was used as reducing reagent, (prepared fresh daily). Amberlite XAD-2-P.Ox chelating resin was synthesized as described earlier [30, 31]. Unless stated otherwise, all the reagents were of analytical-reagent grade. The resin bead was let to swell in 1:1 alcohol–water before usage. The glassware used was cleaned by soaking overnight in aqueous HNO3 (1:1), and then rinsing with distilled water several times. Instruments Atomic absorption spectrometric measurements were made with an atomic absorption spectrometer of Varian SpectrAAFS 220 using an air–acetylene flame. A Hitachi 220 A UV-visible spectrophotometer was used for photometric measurements. The pH values of the solutions were measured by a Metrohm E-512 pH-meter using the full range of 0–14. A mechanical shaker with a speed control ability was used for batch equilibration. The column experiments were performed by using a 10 mm in diameter pyrex glass column partly filled with 5 g of functionalized resin. Recommended Procedure
Fig. 1. 5-Palmitoyl-8-hydroxyquinoline (P.Ox)
The procedure described is based on the finding that the retention of cationic Cr(III), but not anionic Cr(VI) was possible with an Amberlite-XAD-2-P.Ox chelating resin. A double column procedure was used for preconcentrating Cr(III) and Cr(VI) from synthetic and natural water samples. The void volume of the column is 1.0 50 cm. The glass column with a height of 8 cm was packed with a 5 g of Amberlite XAD-2-P.Ox resin and the resin was treated with a 20 mL of 2 M HCl and washed with distilled water until the resin was acid free. The water sample solution (100 mL) containing up to 0.5 mg=mL of chromium ion adjusted to an optimal pH of 4.5 (using acetate buffer) was passed through the first column at a flow
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Preconcentration and Speciation of Chromium(III) in Waters rate of 5 mL min 1. Then the resin in the first column was washed with buffer solution at appropriate pH and, the Cr(III) retained was eluted with hydrochloric acid solution. The reduction of Cr(VI) to Cr(III) procedure was based on that reported by Isshiki et al. and Pasullean et al. [19, 20]. The effluent solution of the first column was evaporated at appropriate volume (80 mL). Then 2 mL of 2 M HCl was added to 80 mL of effluent or a sample solution, it followed by adding of 1 mL of 5% hydroxylamine. The solution was left at room temperature for at least 20 min. After reduction of Cr(VI) to Cr(III), the pH was readjusted to 4.5 with acetate buffer and the volume made up to 100 mL with distilled water. The solution was passed through the second column. The originally present Cr(III) and Cr(VI) after reduction was retained by the first and second columns respectively. The chromium retained in each column was eluted with 20 mL of 2 M HCl and analyzed by FAAS. The used resins were washed with water until being neutral again prior to next use.
Results and Discussion Cr(III) and Cr(VI) Sorption as a Function of pH The effect of the pH of chromium solution on the retention of Cr(III) and Cr(VI) onto the column has been investigated separately. To determine the optimum pH range for the sorption of each chromium valencies, two sample solutions having pH in the range of 1.0–8.0 were passed through two different columns packed with Amberlite XAD-2-P.Ox. The pH of the solutions were adjusted in a range of 1.0–8.0 by using hydrochloric acid and acetate buffer solutions. Then 100 mL solution containing 0.5 mg=mL of Cr(III) and Cr(VI) ion solutions were passed through the column at constant flow rate 5 mL min 1. The retained ions from the resin can be desorbed with a 20 mL of 2 M HCl. Cr(III) and Cr(VI) have been determined in the eluate by FAAS. The graph of retention as a function of pH is shown in Fig. 1. The maximum retention of Cr(III) occurs in acidic media, in the pH range of 4.5–7.0. At pH lower than 4.5, Cr(III) was not chelated quantitatively and the decrease in response at higher pH was probably due to the formation of hydroxides. It was confirmed that Cr(VI) was not retained at all in the pH range of 1.0–8.0 as shown in Fig. 1. The Flowrate and Eluent Acid Concentration The degree of Cr(III) sorption on Amberlite XAD-2P.Ox was studied by varying the flow rates of the solution. The water sample containing 0.5 mg=mL (100 mL) of Cr(III) was adjusted to an optimal pH value (4.5). Thereafter they were passed through an Amberlite XAD-2-P.Ox. loaded column at a flow rate
varying between 1 and 10 mL min 1. The retained Cr(III) from the resin column was eluted with 20 mL of 2 M HCl (recovery >98%), the desorption percentage decreased remarkably when the acid volume was
