Green Analyzer for the Measurement of Total Arsenic in Drinking Water: Electrochemical Reduction of Arsenate to Arsine and Gas Phase Chemiluminescence with Ozone

We describe matrix-isolated, reaction chemistry based measurement of arsenic in water down to submicrograms per liter levels in a system that requires only air, water, electricity, and dilute sulfuric acid, the bulk of the latter being recycled. Gas phase chemiluminescence (GPCL) measurement of arsenic is made in an automated batch system with arsenic in situ electroreduced to arsine that is reacted with ozone to emit light. The ozone is generated from oxygen that is simultaneously anodically produced. Of 22 different electrode materials studied, graphite was chosen as the cathode. As(V) is reduced much less efficiently to AsH3 than As(III). Prereducing all As to As(III) is difficult in the field and tedious. Oxidizing all As to As(V) is simple (e.g., with NaOCl) but greatly reduces subsequent conversion to AsH3 and hence sensitivity. The rate of the AsH3-O-3 GPCL reaction and hence signal intensity increases with [O-3]. Using oxygen to feed the ozonizer produces higher (O-3) and substantial signal enhancement. This makes it practical to measure all arsenic as As(V). The system exhibits an LOD (S/N = 3) for total arsenic as As(V) of 0.36 mu g/L (5 mL sample). Comparison of total As results in native and spiked water samples with those from inductively coupled plasma mass spectrometry (ICPMS) and other techniques show high correlation (r(2) = 0.9999) and near unity slopes.