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Chromatografy Methods for Environmental - Ando D.J.

Ando D.J. Chromatografy Methods for Environmental - Wiley publishing , 2003. - 265 p.
Download (direct link): chromatography2003.pdf
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Methods for Environmental Trace Analysis
Table 5.5 Examples of arsenic compounds found in environmental samples
Compound Formula
Arsenious acid; arsenite; As(rn)“ HAsO2
Arsenic acid; arsenate; As(v)“ H3AsO4
Monomethylarsonic acid (MMAA)“ H2(CH3 )AsO3
Dimethylarsinic acid (DMAA)“ H(CH3)2AsO2
Arsenobetaine (AsB) (CH3)3As+CH2COOH
Arsenocholine (AsC) (CH3 )3As+CH2CH2COOH
“Compounds forming gaseous species: As(iii) and As(v) form AsH3; MMAA forms monomethylarsine, CH3AsH2; DMAA forms dimethylarsine, (CH3)2AsH.
Figure 5.13 Procedure used for organoarsenical extraction - ‘Method 1’ [18]: HPLC-ICP-MS, high performance liquid chromatography-inductively coupled plasma-mass spectrometry; MMAA, monomethylarsonic acid; DMAA, dimethylarsinic acid. Note: original extraction procedure based on that of Beauchemin et al. [19].
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Figure 5.14 Procedure used for organoarsenical extraction - ‘Method 2’ [18]: HPLC-ICP-MS, high performance liquid chromatography-inductively coupled plasma-mass spectrometry; MMAA, monomethylarsonic acid; DMAA, dimethylarsinic acid. Note: original extraction procedure based on that of Crews et al. [20].
range of toxicities, e.g. As(III) is toxic. In fish tissue, the main form of arsenic is arsenobetaine, which is non-toxic. A variety of methods exist for the extraction, clean-up and subsequent analysis of arsenic species in samples. Two specific methods used for the extraction and subsequent analysis of arsenic species in fish tissue are shown in Figures 5.13 and 5.14. Often, the extracts are analysed by using combined chromatography separation with atomic spectroscopic detection. While a search of the scientific literature will identify a variety of approaches and procedures that have been applied, a recent review highlights the main separation techniques [21]. A summary of the methods used for the determination of organoarsenicals in fish tissue is given in Table 5.6.
SAQ 5.4
By reference to Table 5.6, can you identify any similarities between the different extraction methods used for organoarsenical determination from sediments?
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Methods for Environmental Trace Analysis
Table 5.6 Summary of the various methods used for organoarsenical determination in fish tissue [22]
Extraction technique“ Separation technique6 Detection“
1 g of sample ultrasonically extracted with Cation-exchange, followed ICP-AAS
water/methanol (1:1 (vol/vol)). Extract by post-column hydride
evaporated, followed by SPE clean-up generation with NaBH4 after UV irradiation
2 g of sample ultrasonically extracted with Anion-exchange, followed QFAAS
water/methanol (1:1 (vol/vol)). Extract by post-column hydride
evaporated, followed by silica column generation with NaBH4
clean-up after UV irradiation
2 g of sample extracted with water GC, followed by post-column hydride generation with NaBH4 after UV irradiation QFAAS
1 g of sample ultrasonically extracted with HPLC followed by ICP-AES
water/methanol (1:1 (vol/vol)). Extract post-column hydride
evaporated, diluted with water and filtered generation with NaBH4
1 g of sample extracted with HPLC (anion-exchange), QFAAS
water/methanol (1:1 (vol/vol)) by stirring. followed by post-column
Extract evaporated, diluted with water hydride generation with
and filtered, followed by SPE NaBH4
1 g of sample ultrasonically extracted with HPLC (anion-exchange), QFAAS
water/methanol (1:1 (vol/vol)). Extract followed by post-column
evaporated, diluted with water and filtered hydride generation with NaBH4
1 g of sample ultrasonically extracted with water/methanol (1:3 (vol/vol)). Extract evaporated, diluted with water and filtered (SPE) HPLC (ion-pair) ICP-MS
1 g of sample ultrasonically extracted with water/methanol (1:1 (vol/vol)). Extract evaporated, diluted with water and filtered HPLC (anion-exchange) ICP-MS
0.5 g of sample extracted using mechanical stirring with 0.1 g trypsin and ammonium bicarbonate (pH 8) HPLC (anion-exchange) ICP-MS
1 g of sample microwave-extracted with water. Extract filtered HPLC (anion-exchange) ICP-MS
150 mg of sample ultrasonically extracted with methanol/methane (5:2 (vol/vol)) and back-extracted into water. Extract evaporated HPLC (caton-exchange) ICP-MS
a SPE, solid-phase extraction.
6UV, ultraviolet; GC, gas chromatography; cGC, capillary gas chromatography.
“ICP-AAS, inductively coupled plasma-atomic absorption spectroscopy; QFAAS, quartz-fUrnace atomic absorption spectroscopy; ICP-AES, inductively coupled plasma-atomic emission spectroscopy; ICP-MS, inductively coupled plasma-mass spectrometry.
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5.6.4 Chromium
Trivalent chromium (Cr(III)) is an essential element for man as it is involved in glucose, lipid and protein metabolism. In contrast, hexavalent chromium (Cr(vI)) is a potent carcinogen. It is therefore essential to be able to distinguish between these two different oxidation states of chromium. A variety of methods exist for the extraction and subsequent determination of Cr(vi). A specific method for the extraction of Cr(vI) from soluble, adsorbed and precipitated forms of chromium compounds in soils, sludges, sediments and similar materials is shown in Figure 5.15. Among the methods suitable for the analysis of Cr(vi) is a colorimetric method based on diphenylcarbazide (Figure 5.16). This method is suitable for the determination of Cr(vi) within the range 0.5-50 mgl-1. Interferences from molybdenum and mercury (up to 200 mgl-1 can be tolerated) are possible at low concentrations of Cr(vi); interference is also possible from vanadium (concentrations up to 10 x Cr(vi) can be tolerated). A calibration curve is generated by serial dilution of a 50 mgl-1 Cr(vi) stock solution prepared from potassium dichromate (dissolve 141.4 mg of potassium dichromate (K2Cr2O7) in reagent water and dilute to 1 l) and then following the same procedure as used for the sample (see Figure 5.16). A search of the scientific literature will undoubtedly identify a range of procedures for the extraction and separation of chromium species. A recent review, however, highlights the current methods used for the determination of chromium species in solution [25].
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