Determination of hexavalent chromium

Using ammonium pyrrolidine dithiocarbamate/methyl isobutyl ketone, hexa-valent chromium is extracted from a solution containing potassium hydrogen phthalate and determined by atomic absorption. 

Dissolve 0 g potassium hydrogen phthalate (CgH KO/ji) and 4 g sodium hydroxide (NaOH) in 500 ml water. 

Dissolve 1.0 g ammonium pyrrolidine dithiocarbamate (APDC) in water and make up to 100 ml. 

Treat with 1.0 ml buffer solution and 0.5 ml APDC solution and mix. 

Separate off organic phase and determine its chromium content by means of atomic-absorption analysis or the graphite tube technique. 

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Wang J, Ashley K, Marlow D, England EC, Carlton G. Field method for the determination of hexavalent chromium by ultrasonication and strong anion-exchange solid-phase extraction. Anal. Chem. 1999 71 1027-1032. 

Wang J, Ashley K, Kennedy ER, et al. 1997a. Determination of hexavalent chromium in industrial samples using ultrasonic extraction and flow injection analysis. Analyst 122(11) 1307-1312. 

The APDC—MIBK extraction system is widely used to determine a variety of metals in water. In both the U.K. [6, 7] and the U.S.A. [8] it is the standard method for the determination of lead and cadmium in water. It is also used as a standard method [8] in the determination of hexavalent chromium. In order to determine total chromium, trivalent chromium is oxidised to hexavalent chromium by bringing the sample to the boil and adding sufficient potassium permanganate solution (0.1 N) dropwise to give a persistent pink colour while the solution is boiled for 10 min. 

The choice of the sorbent is dictated by the characteristics of both the analytes and their potential interferences. The sorbents most frequently employed here are silica, alkylsilane-modified silica (bonded phases), alumina, porous polymers (with and without ion-exchange groups) and carbon-based materials. One typical application is a method for the determination of hexavalent chromium in soils [10] using the on-line system depicted in Fig. 4.9. After USAL, the analytes in the leachate were directly determined or preconcentrated depending on their concentration. Concentration was performed by on-line solid-phase extraction using a laboratory-made minicolumn packed with a strong anion-exchange resin. The absolute limits of detection were 4.52 and 1.23 ng without and with preconcentration, respectively. 

Figure 4.9. On-line coupling of USAL and detection with (B) and without (A) an intermediate preconcentration-clean-up step for the determination of hexavalent chromium in soil. AS — acid stream, D — debubbler, DPC — diphenylcarbazide, DS — detection system, FC — flow cell, IV — injection valve, L — leachant, LC — leaching chamber, MC — mixing coil, PL — propagating liquid, PP — peristaltic pump, PC — reaction coil, SAEC — strong anion-exchange column, S / — switching valve, UP— ultrasonic probe, 1/1/— waste and 1/1/6 — water bath. (Reproduced with permission of the Royal Society of Chemistry, Ref [10].)...

Chromotropic acid was applied as a reagent for ultraviolet spectrophotometric determination of hexavalent chromium in water [10]. 

Chromium(vi). This inorganic pollutant can be determined by a whole range of analytical techniques, e.g. FAAS, ICP-AES/MS or XRF. However, in this situation the requirement is to determine a particular oxidation state of chromium. While not mentioned specifically in the list of analytical techniques above, a method does exist for the spectrophotometric determination of hexavalent chromium based on extraction with a chelating agent (see Chapter 5 for details). 

The application of the semi-deterministic approach, described in Chapter 2 and applied before in this chapter, can be used for the determination of hexavalent chromium. Exceptionally, the optical pathlength is 50 mm for this application because of the regulation compliance constraint. Contrary to the previous determination (nitrate, sulphide, hypochlorite, etc.), this application must take into account the pKa value (about 5.8) of the dichromate in equilibrium with chromate ... 

Thomas DH, Rohrer JS, Jackson PE, Pak T and Scott JN (2002) Determination of hexavalent chromium at the level of the California Public Health Goal by ion chromatography. J Chromatogr A 956 255-259. 

For the determination of hexavalent chromium (at concentrations > 0.01 mg 1 ) a photometric method with diphenylcarbazide (CgHg-NH-NH-CO-NH-NH-CgHj) is used (red-violet colour). Absorbance is measured directly or after extraction into amyl alcohol at a wavelength of 540 nm (green filter) [19, 41]. 

Gilliom RJ, Helsel DR (1986) Estimation of distributional parameters for censored trace level water quality data. 1. Estimation techniques. Water Resour Res 22 135-146 Goldoni M, Caglieri A, Poli D, Vettori M, Corradi M, Apostoli P, Mutti A (2006) Determination of hexavalent chromium in exhaled breath condensate and environmental air among chrome... 

Concentration by evaporation is possible, if concentrations are low. A method of extraction for the determination of total chromium and for the determination of hexavalent chromium is described below. 

B) Determination of hexavalent chromium using diphenyl carbazide... 

Figure 2 Ion chromatograms of chromate in drinking waters (A) unspiked sample, (B) sample spiked with 0.2pgl Cr(VI). (Reprinted with permission from Thomas DH, Rohrer JS, Jackson PE, Pak T, and Scott JN (2002) Determination of hexavalent chromium at the level of California public health goal by ion chromatography. Journal of Chromatography A 956 255-259 Elsevier.)...

ICP-OES, along with ICP-MS and X-ray fluorescence (XRE), is used for the analysis of the materials in electronic equipment. The EU has established directives on the disposal of waste electrical and electronic equipment (WEEE) and the restriction of the use of hazardous substances (RoHS) in electronic equipment sold in, into, and out of the EU. The maximum allowable quantities in electrical equipment of the following hazardous substances are 0.1% by weight for Pb, hexava-lent chromium (CrVI), mercury, and polybrominated biphenyl and polybrominated diphenyl ethers (PBDEs) and 0.01% by weight for Cd. Pb, Hg, Cd, and total Cr can be measured by ICP-OES, while the determination of hexavalent chromium requires a separation step in order to determine the oxidation state. This can be done using a hyphenated instrument, described in the following. Total bromine can also be measured by ICP-OES, but the determination of the PBDEs is generally done by GC-MS, described in Chapter 12. The WEEE/RoHS requirements have led many instrument manufacturers to have an installed method template for such analyses in their software. 

Besides the common inorganic anions (F , CU, Br, NOa , P04 , and S04 ) and cations (Na, K, NH4", Mg " ", and Ca " "), chromate and arsenite are of primary concern because of their greater toxicides as compared to chromium(III) and arsenate, respectively. Hexavalent chromium is a toxic form of chromium that must be monitored in manufacturing wastes. Ion chromatography with postcolumn addition of diphenylcarbazide is probably the most specific and sensitive method available for the determination of hexavalent chromium. 

US EPA Method 7199 Determination of hexavalent chromium in drinking water, groundwater and industrial wastewater effluents by ion chromatography and US... 

Comparison of the determination of hexavalent chromium by ion chromatography coupled with ICP-MS or with colorimetry. Presentation at the Plasma Winter Conference on Plasma Spectrochemistry 1992, San Diego, CA,... 

Arar, E. J., Long, S. E., Martin, T. D., and Gold, S. (1992). Determination of hexavalent-chromium in sludge incinerator emissions using ion chromatography and inductively coupled plasma mass spectrometry. Environ. Sci. Technol. 26(10), 1944. 

The technique is not viable for elements low in the periodic table (from fluorine downward) although there is research into the use of X-ray fluorescence for fluorine and boric oxide. To this end, a method has been developed for the determination of B2O3, which allows either a wet chemical or inductively coupled plasma (ICP) finish, the latter being based on methods for the pottery industry. Another wet (colorimetric) method for the determination of Hexavalent chromium has also been produced. Finally, in the area of black and nitride ceramics, a series of standards is appearing that allow their characterization using a mixture of X-ray fluorescence. X-ray diffraction, and special chemical speciation methods. 

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