Behari Jai Raj, Prakash Rajiv
Analytical Chemistry Department, Industrial Toxicology Research Centre, P.O. Box 80, M.G. Marg, Lucknow 226001, UP, India.
Chemosphere. 2006 Mar;63(1):17-21. doi: 10.1016/j.chemosphere.2005.07.073. Epub 2005 Oct 6.
Analysis of arsenic in water is important in view of contamination of ground water with arsenic in some parts of the world including West Bengal in India and neighboring country Bangladesh. WHO has fixed the threshold for arsenic in drinking water to 10ppb (microg/l) level, hence the methodology for determination of arsenic is required to be sensitive at ppb level. Atomic absorption spectrophotometry with vapour generation assembly (AAS-VGA) is well known technique for the trace analysis of arsenic. However, total arsenic analysis [As(III)+As(V)] is very crucial and it requires reduction of As(V) to As(III) for correct analysis. As(III) is reduced to AsH3 vapours and finally to free As atoms, which are responsible for absorption signal in AAS. To accomplish this the vapour generation assembly attached to AAS has acid channel filled with 10 M HCl and the reduction channel with sodium borohydride. Further sample can be reduced either before aspiration for analysis, using potassium iodide (KI) or the sample can be introduced in the instrument directly and KI can be added in the reduction channel along with the sodium borohydride. The present work shows that samples prepared in 3 M HCl can be reduced with KI for 30 min before introduction in the instrument. Alternatively samples can be prepared in 6 M HCl and directly aspirated in AAS using KI in VGA reduction channel. The latter methodology is more useful when the sample size is large and time cycle is difficult to maintain. It is observed that the acid concentration of the sample in both the situations plays an important role. Further reduction in acid concentration and analysis time is achieved for the arsenic analysis by using modified method. Analysis in both the methods is sensitive at ppb level.
鉴于世界上一些地区（包括印度西孟加拉邦及其邻国孟加拉国）的地下水受到砷污染，对水中砷进行分析很重要。世界卫生组织已将饮用水中砷的阈值定为10 ppb（微克/升）水平，因此测定砷的方法需要在ppb水平上具有灵敏性。带蒸汽发生装置的原子吸收分光光度法（AAS-VGA）是一种众所周知的砷痕量分析技术。然而，总砷分析[As(III)+As(V)]非常关键，为了进行正确分析，需要将As(V)还原为As(III)。As(III)被还原为AsH3蒸汽，最终还原为游离的As原子，这些原子是AAS中吸收信号的来源。为实现这一点，连接到AAS的蒸汽发生装置的酸通道中填充有10 M HCl，还原通道中填充有硼氢化钠。此外，样品可以在吸入进行分析之前，使用碘化钾（KI）进行还原，或者可以直接将样品引入仪器中，并且可以在还原通道中将KI与硼氢化钠一起加入。目前的工作表明，在3 M HCl中制备的样品可以在引入仪器之前用KI还原30分钟。或者，可以在6 M HCl中制备样品，并在VGA还原通道中使用KI直接吸入AAS中。当样品量很大且难以维持时间周期时，后一种方法更有用。可以观察到，在这两种情况下样品的酸浓度都起着重要作用。通过使用改进的方法，在砷分析中实现了酸浓度和分析时间的进一步降低。两种方法的分析在ppb水平上都是灵敏的。
