|dc.description.abstract||A method using L-cysteine for the determination of arsenous acid (As(III)), arsenic
acid (As(V)), monomethylarsonic acid (MMAA), and dimethylarsinic acid (DMAA) by
hydride generation was demonstrated. The instrument used was a d.c. plasma atomic
emission spectrometer (OCP-AES). Complete recovery was reported for As(III), As(V), and
DMAA while 86% recovery was reported for MMAA. Detection limits were determined, as
arsenic for the species listed previously, to be 1.2, 0.8, 1.1, and 1.0 ngemL-l, respectively.
Precision values, at 50 ngemL-1 arsenic concentration, were f.80/0, 2.50/0, 2.6% and 2.6%
relative standard deviation, respectively.
The L-cysteine reagent was compared directly with the conventional hydride
generation technique which uses a potassium iodide-hydrochloric acid medium. Recoveries
using L-cysteine when compared with the conventional method provided the following
results: similar recoveries were obtained for As(III), slightly better recoveries were obtained
for As(V) and MMAA, and significantly better recoveries for DMAA. In addition, tall and
sharp peak shapes were observed for all four species when using L-cysteine.
The arsenic speciation method involved separation by ion exchange .. high
perfonnance liquid chromatography (HPLC) with on-line hydride generation using the L..
cysteine reagent and measurement byOCP-AES. Total analysis time per sample was 12 min
while the time between the start of subsequent runs was approximately 20 min. A binary .
gradient elution program, which incorporated the following two eluents: 0.01 and 0.5 mM tri.. sodium citrate both containing 5% methanol (v/v) and both at a pH of approximately 9, was
used during the separation by HPLC. Recoveries of the four species which were measured
as peak area, and were normalized against As(III), were 880/0, 290/0, and 40% for DMAA,
MMAA and As(V), respectively. Resolution factors between adjacent analyte peaks of
As(III) and DMAA was 1.1; DMAA and MMAA was 1.3; and MMAA and As(V) was 8.6.
During the arsenic speciation study, signals from the d.c. plasma optical system were
measured using a new photon-signal integrating device. The_new photon integrator
developed and built in this laboratory was based on a previously published design which was
further modified to reflect current available hardware. This photon integrator was interfaced
to a personal computer through an AID convertor. The .photon integrator has adjustable
threshold settings and an adjustable post-gain device.||en_US