Analytical Notes
Agilent Vapor Generation Accessory VGA 77 and VGA 77P User’s Guide 63
Arsenic
NOTE
If arsenic and selenium are both to be determined from the same sample,
determine selenium first, and avoid KI in samples or standards. You can then
determine arsenic after the KI reduction step and any other appropriate treatment
(such as the addition of urea if excess nitric acid is present).
Arsenic in the sample must be in the inorganic form, otherwise
digestion will be necessary.
If digestion is necessary, use acid digestion, ensuring no residual
oxidizing acid is present (see ‘Oxidation States’ on Page 57, or ashing
with an appropriate ashing aid. Simple dry ashing is not
recommended.
Prepare samples in at least 1 M hydrochloric acid.
Ensure that any analyte present as As
V
is reduced to As
III
by the
action of potassium iodide at a concentration of 1% w/v.
Reduction will take about 50 minutes at room temperature. The
reduction can also be carried out at 70 °C in about four minutes;
however you must cool the samples and standards to room
temperature prior to analysis. Since the pumping rate may vary with
solution temperature, the VGA 77 pump will not operate correctly
with hot solutions.
If the reduction step is omitted, and the analyte is retained as As
V
,
the analytical sensitivity is about 20-30% of that obtained for As
III
. If
the original solution contains As
III
, reduction by potassium iodide is
not required.
Reductant container: NaBH
4
0.6% w/v (see also above)
NaOH 0.5% w/v
Acid container: 5 to 10 M HCl
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