Anions in non saline waters - Determination of Anions in Natural and Treated Waters - page 84

2.4 Arsenate
2.4.1 Spectrophotometric methods
Matsuhara et al. [4 have described a rapid method for the determination of trace amounts
of arsenate (and phosphate) in water by Spectrophotometric detection of their
heteropolyacid-malachite green aggregates following preconcentration by membrane
filtration.
The determination of arsenate is discussed under multianion analysis in section
14.2.2.1.
2.4.2 Flow injection analysis
This technique has been applied to the determination of arsenate in non saline waters [5].
The determination of arsenate is discussed under multianion analysis in section
14.4.1.5.
2.4.3 Atomic absorption spectrometry
Arsenate (and arsenite and phosphate) have been determined in non saline waters by a
technique based on flotation spectrophotometry and extraction—indirect atomic
absorption spectrometry using malachite green as an ion-pair reagent [6].
2.4.4 Polarography
An indirect polarographic method has been used to determine traces of arsenate in
mineral waters [7]. In this method arsenate is converted to uranyl arsenate which is
filtered off and excess uranyl ion is determined by polarography at −3.60V. Phosphates
interfere in this procedure.
Chakraborti et al. [8] determined arsenate by differential pulse polarography on acidic
aqueous solutions containing polyhydroxy compounds such as D-mannitol. Peak heights
measured at −0.55V in a medium containing 2M aqueous perchloric acid and 4.5g
mannitol in a 50ml solution gave linear calibration curves over the range 20-160µg L −l .
Arsenite could be similarly determined at −0.34V or −0.42V with or without mannitol
respectively, the method of measurement at −0.42V being used where arsenite occurred
in the presence of arsenate. Detection limits were approximately 10µg arsenic for both
forms. Examples of results obtained for arsenite and arsenate recovery in a river water
sample are given.
2.4.5 Ion chromatography
This technique has been applied to the determination of arsenate (and sulphite) in non
saline waters [9] and is discussed further under multianion analysis in sections 12.2.2,
12.2.4 and 12.2.5.