METHOD AND APPARATUS FOR ANALYZING ARSENIC CONCENTRATIONS USING GAS PHASE OZONE CHEMILUMINESCENCE

摘要

A practical sequential injection/zone fluidicsbased analyzer that measures waterborne arsenic is capable of differentiating between inorganic As(III) and As(V). The principle is based on generating AsH₃ from the sample in a confined chamber (10) by borohydride reduction at controlled pH, sparging the chamber to drive the AsH₃ to a small reflective cell (70) located atop a photomultiplier tube (50), allowing it to react with ozone generated from ambient air, and measuring the intense chemiluminescence that results. Arsine generation and removal from solution results in isolation from the sample matrix, avoiding the pitfalls encountered in some solution-based analysis techniques. The differential determination of As(III) and As(V) is based on the different pH dependence of the reducibility of these species to AsH₃. At pH < 1, both As(III) and As(V) are quantitatively converted to arsine in the presence of NaBH₄. At a pH of 4 - 5, only As(III) is converted to arsine. In the present form, the limit of detection (S/N = 3) is 0.05 µg/L As at pH = 1 and 0.09 µg/L As(III) at pH ~4 - 5 for a 3-mL sample. The analyzer is intrinsically automated and requires 4 min per determination. In a further embodiment, electrochemical reduction at Cd cathode is used instead of NaBH₄