Determination of Inorganic Arsenic (III) and Arsenic (III Plus V) Using Automated Hydride‐Generation Atomic‐Absorption Spectrometry

A simple method was developed to analyze aqueous inorganic arsenic in the µg L −1 range using automated hydride‐generation atomic‐absorption spectrometry. Total inorganic arsenic, As(III plus V), was determined by reducing As(V) to As(III) using KI then generating the hydride in 6 M HCl. Arsenic (III) was determined by generating the hydride at pH 4.0 to 4.5 using an oxalate buffer. Detection limits for the As(III plus V) and As(III) analytical methods were less than 0.4 µg As L −1 . Arsenic(V) was calculated by difference. Spiking of actual sample solutions with As(III) and As(V) showed the procedure to be accurate on solutions with initial pH values ranging from 2.7 to 9.8 and As(III)/As(V) ratios ranging from 1:4 to 4:1. Recoveries of As were within 1.5 µg As L −1 of added amounts ranging from 10.0 to 40.0 µg As L −1 , and standard deviations of triplicate analyses were within 0.4 µg As L −1 . Automated hydride generation allowed analysis at a rate of 53 samples per h, a significant rate increase over traditional batch hydride generators. Spontaneous oxidation of As(III) to As(V) was observed on spiked samples mixed 3 h before analysis.