Multianion analysis, miscellaneous methods - Determination of Anions in Natural and Treated Waters - page 715

Chapter 14
Multianion analysis, miscellaneous methods
14.1 Gas chromatography
14.1.1 Non saline waters
14.1.1.1 Carboxylic acids, malonate, hexabenzene carboxylate, octanioate,
octandioate
Olsen et al. [1] determined carboxylic acids by isotope dilution gas chromatography
Fourier transform infrared spectroscopy. The carboxylic acids were first converted to
their methyl esters. Carboxylates studied include malonate, hexabenzene carboxylate,
octanoiate and octandioate.
14.1.1.2 Bromide and iodide
Bromide and iodide occur as trace elements in non saline waters in the concentration
range 10 −4 to 10 −8 M.
For the selective and highly sensitive simultaneous determination of bromide and
iodide Maros et al. [2] suggest a gas chromatographic separation combined with electron
capture detection of the acetone derivatives. The method for iodide determination based
on oxidation with iodate in the presence of acetone followed by an extraction of
iodoacetone with n-hexane gives inaccurate results, especially if other reductive
substances are present that reduce iodate to iodide or iodine. The quantitative oxidation of
iodide and bromide in the presence of acetone to iodo- and bromoacetone can be
performed by chromate and permanganate, without the interference of other reducing
substances. Instead of n-hexane, benzene was found to be more convenient for the
extraction of bromo- and iodoacetone from aqueous solutions, due to the significantly
higher solubilities of these compounds in benzene. The sample preparation for the gas
chromatographic analysis consists of the oxidation of bromide and iodide in the presence
of acetone and of a single-step extraction of the derivatives with benzene.
In this method [2] oxidation of bromide and iodide ions in acidic solutions in the
presence of acetone forms the corresponding acetone derivatives. Iodate was reduced
with thiosulphate prior to the determination. After extraction with benzene the bromo-
and iodoacetone were measured by gas chromatography using electron capture detection.
The bromide and iodide contents of rainwater, drinking water, river water and sea water,
were all determined. The relative standard deviations for bromide at 10 −7 M and for
iodide at 10 −8 M concentration were 1.9% and 3% respectively, using a 10mL sample for
the determination without preconcentration.