저장 및 분석중 도금공정 Cr(VI) 시료의 환원에 관한 연구

Reduction of Hexavalent Chromium Collected on PVC Filter from Electroplating Process during Storage and Analysis

It is known that hexavalent chromium (Cr(VI)) is unstable and can be reduced to a lower valence in air. Therefore, reduction of Cr(VI) in the steps of sampling, storage and analysis will result in underestimation of Cr(VI) level. The purpose of the study is to suggest some appropriate procedures for minimizing the reduction of Cr(VI) during storage and analysis of the air samples collected on PVC filters from pilot electroplating process, and of samples spiked with a plating bath solution from a factory. The average ratio of Cr(VI) recoveries by acid extraction (0.5N H₂SO₄) to those by alkali extraction (2% NaOH/3% Na₂CO₃) in spiked samples was 0.83 ± 0.06. These data indicate that acid extraction can cause the Cr(VI) to be reduced, and Cr(VI) samples on PVC filters should be leached with an alkali solution to prevent from the reduction. Storage time was a significant factor effecting Cr(VI) reduction in samples stored (in vials) at room temperature. The recoveries of Cr(VI) in air samples stored in vial at room temperature were 74% after 1 day, and 56-57% after 3-7 days. The recoveries in spiked samples at the similar condition were 77% after 4 days, 75% after 8 days, and 72% after 17 days. The recovery of Cr(VI) was improved in the air samples by storing them at 4°C (87% after 1 day and 74-83% after 3-7 days). In addition, recovery from the spiked samples stored in vials at 4 °C was higher those stored at room temperature. Thus, it is required that filter sample be stored at 4°C or lower. Storage time was not a significant factor when the Cr(VI) samples were stored in either a 2% NaOH/3% Na₂CO₃ or 0.02M NaHCO₃ solution. Thus, we recommend that Cr(VI) samples from a plating process be stored in a alkali solution to prevent further reduction. In conclusion, this study demonstrates that acid extraction and storage time can lead to a loss of Cr(VI) on PVC filter samples through reduction. These losses will result in an underestimation of Cr(VI) exposure/concentration. we also found that these losses can be minimized by using alkali extraction, by refrigerating the samples during the interim between sample collection and analysis, by minimizing the storage time, and by storing the samples in an alkali solution.