SUMMARY


Hydride generation atomic absorption
spectrometry (HGAAS) is a sensitive and
selective method for the determination of
As(T) and arsenic(III); however, it is subject
to metal interferences for acid mine waters.
Antimony(III) and Sb(V) interfere with the
HGAAS As(T) determination when the molar
ratios of Sb(III) and Sb(V) exceed 4 and 2,
respectively. Low As(III) recoveries occurred
when the molar ratios of metals to As(III)
were: Cu(II) greater than 120, Fe(III) greater
than 70, Cr(VI) greater than 2, Cd greater
than 800, Sb(III) greater than 3, Sb(V) greater
than 12, or Se(IV) greater than 1. Samples
could not be diluted to an As(III)
concentration (As(III) less than 20 μg/L)
below which these interferences were absent.
Copper(II) and Fe(III) are of primary concern
because water generated from acid mine
drainage potentially contains high
concentrations of Cu(II) and Fe(III).
Separation of Fe(III) and Cu(II) from the
sample while maintaining the existing
As(III)/As(T) ratio can be achieved using
cation exchange.
Some acid mine waters contain high
Fe(III) and Cu(II) and accurate measurements
of As(III) is problematic without removing
the Fe(III) and Cu(II) prior to hydride
generation. Proper sample collection and
preservation are critical to maintain the
existing As(III/V) ratio prior to the analysis.
Filtering samples through a 0.1 μm filter,
acidifying with HCl to a pH less than 2, and
storing in an opaque bottle at 4°C inhibits
changes in the As(III)/As(T) ratios for up to
15 months after sample collection.

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