Hexavalent-chromium (18540299) (CrVI) was determined in workplace samples using ultrasonic extraction and flow injection analysis (FIA). CrVI was extracted from standard solutions and simulated samples and retained on an ion exchange resin via ultrasonic extraction in alkaline solution. CrVI was separated from trivalent- chromium (CrIII) and other cations on a strong anion exchange resin using a slightly basic ammonium-sulfate buffer solution. Prior to FIA with ultraviolet/visible (UV/VIS) detection, the eluate was acidified with hydrochloric-acid and mixed with the 1,5- diphenylcarbazide complexing reagent. Breakthrough of CrVI from the anion exchange resin and recovery of CrVI were examined by separating, eluting, and analyzing solutions of various buffer strengths spiked with CrVI and CrIII. CrVI breakthrough increased with increasing ammonium-sulfate concentration. For workplace samples, a buffer solution containing 0.05 molar (M) ammonium- sulfate and 0.05M ammonium was needed for the efficient extraction and reduced breakthrough of CrVI. Over 95% of the CrVI was eluted from the anion exchange resin using 5 milliliters of the buffer solution containing 0.1M ammonium and 0.5M ammonium-sulfate. The presence of CrIII did not affect CrVI recovery. Using standard and sample solutions, the relative standard deviations (RSDs) for FIA analysis varied between 1.5 and 4.5%. The detection limit of FIA with UV/VIS detection equaled 0.11 nanograms. Simulated workplace samples spiked with CrVI and CrIII solutions of known concentrations and certified reference materials were separated and analyzed. CrVI recoveries ranged from 93.8 to 95.6% for samples spiked with 25 to 40 micrograms of CrVI. CrIII present in the samples was not oxidized to CrVI. The RSDs varied from 3.2 to 7.6%. The technique was also applied to the measurement of CrVI in several real workplace samples. The authors conclude that ultrasonic extraction with FIA allows for the efficient, sensitive, and accurate determination of CrVI in workplace samples.
NIOSH-Author; Analytical-methods; Analytical-instruments; Analytical-chemistry; Hexavalent-chromium-compounds; Metals; Sample-preparation; Ultraviolet-spectrometry; Ion-exchange-chromatography; Laboratory-techniques; Chemical-analysis;
Author Keywords: Hexavalent chromium; ultrasound; base extraction; anion exchange; flow injection; industrial hygiene