JASMI  Vol.2 No.2 , June 2012
Optimal Sample Preservation and Analysis of Cr(VI) in Drinking Water Samples by High Resolution Ion Chromatography Followed by Post Column Reaction and UV/Vis Detection
ABSTRACT
A recent study by the Environmental Working Group reported the detection of hexavalent chromium (Cr(VI)) in tap water at 31 out of 35 states investigated in the United States. Even though Cr(III) is an essential element for human diet, Cr(VI) is a potential carcinogen. Previous work has clearly identified a linear trend of increasing risk of lung cancer mortality with increasing cumulative exposure to water soluble Cr(VI). Regardless, Cr(VI) is still not regulated or monitored in drinking water in the U.S. There is an existing method (EPA 218.6) for the analysis of Cr(VI), however, this analytical method does not addresses detailed sample preservation techniques and optimization process to achieve lowest detection limit possible. In this study, five buffer solutions with pH of 9 and above were compared to determine the most suitable buffer to preserve Cr(VI) in drinking water samples for an extended period of time. Results showed that the five buffers responded very differently to Cr(VI)-fortified drinking water. The best preserving reagent was found to be Ammonium Hydroxide + Ammonium Sulfate (pH 9.2) and Sodium Carbonate + Sodium Bicarbonate+ Ammonium Sulfate (pH 9.7), whereas a buffer solution with Sodium Hydroxide + Sodium Carbonate (pH 11.5+) resulted in a poor chromatographic resolution. A controlled study with a fortified Cr(III) at 1 ppb was also conducted to ensure no false positive detection of Cr(VI) due to the potential oxidation of Cr(III) during sample storage. The optimal preserving reagent identified from this study was compatible with the existing EPA method 218.6 using ion chroma-tography followed by post column reaction, with a method quantitation limit of 0.020 ppb and matrix spike recovery of ± 10%.

Cite this paper
P. Ezebuiro, J. Gandhi, C. Zhang, J. Mathew, M. Ritter and M. Humphrey, "Optimal Sample Preservation and Analysis of Cr(VI) in Drinking Water Samples by High Resolution Ion Chromatography Followed by Post Column Reaction and UV/Vis Detection," Journal of Analytical Sciences, Methods and Instrumentation, Vol. 2 No. 2, 2012, pp. 74-80. doi: 10.4236/jasmi.2012.22014.
References
[1]   R. F. Cotton and G. Wilkinson, “Advanced Inorganic Chemistry,” 5th Edition, John Wiley and Sons, New York, 1988, p. 680.

[2]   L. M. Calder, in: J. O. Nriagu and E. Nieboer, Eds., Chromium in the Natural and Human Environments, Wiley and Sons, New York, 1988, pp. 215-229.

[3]   S. Beaublen, J. Nriagu, D. Blowes and G. Lawson, “Chromium Speciation and Distribution in Great Lakes,” Environmental Science & Technology, Vol. 28, 1994, pp. 730-736. doi:10.1021/es00053a029

[4]   R. Sutton, In: J. Houlihan, R. Sharp and N. Bruzelius, Eds., EWG Report. Chromium-6 Is Widespread in US Tap Water: Cancer-Causing Chemical Found in 89 Percent of Cities Sampled. http://www.ewg.org/chromium6-in-tap-water

[5]   I. J. Buerge and S. J. Hug, “Kinetics and pH Dependence of Chromium(VI) Reduction by Iron(II),” Environmental Science & Technology, Vol. 31, 1997, pp. 1426-1432. doi:10.1021/es960672i

[6]   S. Comber and M. Gardner, “Chromium Redox Speciation in Natural Waters,” Journal of Environmental Monitoring, Vol. 5, 2003, pp. 410-413. doi:10.1039/b302827e

[7]   V. M. Burns and R. G. Burns, “Mineralogy of chromium,” Geochimica et Cosmochimica Acta, Vol. 39, 1975, pp. 903-910. doi:10.1016/0016-7037(75)90036-8

[8]   J. W. Ball and D. K. Nordstrom, “Critical-Evaluation and Selection of Standard State Thermodynamic Properties for Chromium Metal and Its Aqueous Ions; Hydrolysis Species; Oxides; and Hydroxides,” Journal of Chemical and Engineering Data, Vol. 43, No. 6, 1998, pp. 895-918. doi:10.1021/je980080a

[9]   L. E. Eary and D. Ral, “Kinetics of Chromium (III) Oxidation to Chromium(VI) by Reaction with Manganese Dioxide,” Environmental Science & Technology, Vol. 27, 1987, pp. 1187-1193. doi:10.1021/es00165a005

[10]   Dionex, Application Update 144, “Determination of Hexavalent Chromium in Drinking Water Using Ion Chromatography,” 2003.

[11]   E. J. Arar, J. D. Pfaff and T. D. Martin, “Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography,” Environmental Monitoring Systems Laboratory, U.S.EPA. Revision 3.3, 1994.

[12]   C. C. Zhang “Fundamentals of Environmental Sampling and Analysis,” Wiley and Sons Inc., New York, 2007, p. 212. doi:10.1002/0470120681

[13]   CDPH (California Department of Public Health), “Chromium-6 in Drinking Water Sources: Sampling Results,” California Department of Public Health, Sacramento, 17 February 2009. www.cdph.ca.gov/certlic/drinkingwater/Pages/Chromium6sampling.aspx

[14]   “Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Waste Effluents by Ion Chromatography,” EPA Method 218.6, 1991.

[15]   Metrohm Application Note, AW US6-0134-042009, “Determination of Chromium(VI) in Water, Waste Water and Soils,”

[16]   Metrohm Application Note, AW CH6-1049-102010, “Determination of Chromate in Drinking Water Using New UV Detector”.

 
 
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