影響六價鉻環境採樣分析之因素

Evaluation of Analytical Method for Airborne Hexavalent Chromium

本實驗之目的在探討六價鉻在PVC 濾紙上不同時間之穩定性，並加入不同量之二氧化錳，以觀察不同時間對六價鉻之還原作用，同時比較單酸與混合酸對PVC 濾紙六價鉻之萃取效率；瞭解不同加熱時間與溫度對六價鉻之萃取效率，以期作為未來環境中採集及分析六價鉻元素方法之參考。鉻酸之分析方法係參考行政院勞工委員會分析公告參考方法，結果為六價鉻標準品的檢量線之濃度範圍由0.04 μg/mL 到 2μg/mL，六價鉻檢量線之斜率﹐會隨著標準溶液貯存時間增加而有降低的趨勢。而六價鉻在PVC 濾紙的萃取效率隨著貯存時間增加而降低；若超過24 小時其萃取效率約為80%，當添加愈多量二氧化錳在PVC 濾紙時， 則六價鉻濃度會隨貯存時間增加而有降低現象，硫酸對PVC 濾紙上六價鉻的萃取效率與混合酸（H2SO4, HClO4 and HNO3）並無明顯之差異，在100℃以下時六價鉻在PVC 濾紙萃取效率，會隨著貯存時間及溫度的增加而增加；但若超過100℃時則其萃取效率﹐會隨著貯存時間及溫度的增加而減少。因此﹐建議在分析六價鉻時應注意在PVC 濾紙上六價鉻之穩定度，及其它可能干擾因素，以免影響六價鉻分析之準確度。

The purpose of this study was to evaluate the stability of hexavalent chromium (Cr(VI)) on PVC filters and investigate how different factors such as acids, manganese dioxide, time and temperature affect the Cr(VI) recovery efficiency from PVC filters. Analytical methods used for the determination of Cr(VI) followed the recommendations published by Taiwan’s Institute of Occupational Safety and Health (IOSH). A calibration curve was set up and showed the Cr(VI) ranged from 0.04 μg/mL to 2 μg/mL. Both the slope of the calibration curve and recovery efficiency increased with storage time. As more manganese dioxide (MnO2) was added to the filter, extraction efficiency of Cr(VI) decreased as storage time increased. Sulfuric acid and mixed acids were used to extract chromium on PVC filters and recover efficiencies were 87% and 82%, respectively. As temperatures fell below 100℃, the extraction efficiency of chromium was nearly 100%. With temperatures over 100 ℃for a period of one hour, Cr(VI) concentrations decreased to a non-detectable level. The authors conclude that many factors can affect the determination of Cr(VI) collected on PVC filters and special care must be taken in order to ensure accurate results.