No description available.

No description available.

No description available.

No description available.

No description available.

The current US Environmental Protection Agency (USEPA) maximum contaminant level (MCL) for total chromium of 100 ppb is under revision to consider a specific level for Cr(VI), which has a proposed MCL of 10 ppb in California. Cr(VI) is a suspected carcinogen, and interconverts with the other most commonly found chromium species, Cr(III). To regulate and further understand the behavior of Cr(VI) in water systems, appropriate sample preservation methods are essential for accurate measurements. The ammonia buffer (recommended by EPA) was proven to be the most effective preservation when a holding time of 14 days is considered. Apart from proper Cr(VI) preservation, sampling at an appropriate site is important for determining the public's exposure to Cr(VI). The proposed MCL for Cr(VI) in the state of California will be monitored at the entry point of distribution systems. To the extent that Cr(VI) is formed in the distribution system or in water contacting plumbing, measurements at the treatment plant might not reflect consumer exposure at the tap. Cr(VI) can be released to drinking water from Cr present in stainless steel alloys. At the maximum residual disinfectant level (MRDL), Cr(VI) formation decreased in the order chlorine dioxide > chlorine > chloramine. Less Cr(VI) was released from stainless steel at lower pH in the presence of chlorine, but the opposite trend was observed for chlorine dioxide. Stainless steels with a higher chromium content tended to release more Cr(VI). / Master of Science

No description available.

Ion chromatography coupled with a conductivity detector was used to investigate the analysis of Cr(III) and Cr(VI) in aqueous samples. An IC methodology for Cr(III) was developed using a cation column and an eluent containing tartaric acid, ethylenediamine, and acetonitrile at pH 2.9. The detection limit of this method can reach 0.1 ppm level with good precision. Several operational parameters were evaluated during the regular use of the method. Comparison of the IC method with AA method showed good agreement between the two methods. The anion exchange column was used for Cr(VI) determination. The best results were obtained with an eluent containing sodium gluconate, borate buffer, glycerin, and acetonitrile. The retention time for the Cr207 2 - sample was 11 min. and the calibration curve was linear between 1.0 and 100 ppm.

Digitized by Kansas Correctional Industries

In order to assess the benefit or toxicity of chromium in dietary supplements, trivalent chromium and hexavalent chromium must be measured and verified with mass balance (sum of both species equaling total chromium). This is necessary because dietary supplements report trivalent chromium, an essential trace element, as an ingredient, but hexavalent chromium, a toxic carcinogen, may also be present. Because trivalent chromium is stable in acidic conditions and hexavalent chromium in alkaline conditions, interconversions between species occur and increase the difficulty of quantification. Therefore, EPA Method 3060A was first performed to extract hexavalent chromium. Then, EPA Method 3052 was performed on the residue to digest the remaining trivalent chromium. Speciated Isotope Dilution Mass Spectrometry (SIDMS) with Ion-Exchange Chromatography-Inductively Coupled Plasma-Mass Spectrometry (IC-ICP-MS) was used to account for interconversions as well as determination of trivalent and hexavalent chromium concentrations in the studied samples. Mass balance indicated that the analyzed supplements contained hexavalent chromium ranging from 0 to 16% of the total chromium content. / Bayer School of Natural and Environmental Sciences / Environmental Science and Management (ESM) / MS / Thesis