Green Analyzer for the Measurement of Total Arsenic in Drinking Water: Electrochemical Reduction of Arsenate to Arsine and Gas Phase Chemiluminescence with Ozone
Publication Type
Original research
Authors
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-O3
GPCL reaction and hence signal intensity increases with
[O3]. Using oxygen to feed the ozonizer produces higher
[O3] 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 μg/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 (r2 ) 0.9999)
and near unity slopes