Determination of chloroacetic acids using ion chromatography with liquid-phase microextraction preconcentration

Abstract

In order to increase the sensitivity of the ion chromatographic determination of chlorinated acetic acids ( CAAs ) in water, an emulsion microextraction preconcentration was proposed. The emulsification of extractants was performed by the ultrasonic irradiation. Diethyl and methyl tert-butyl ethers were used as extractants. The comparison of extractants showed the advantages of methyl tert-butyl ether: stable aggregation into a separate phase after the dispersion, no loss of extractant at the analysis stages due to volatility. To reduce the detection limits and improve the chromatographic separation of analytes, the organic matrix of the extract was replaced by water. It was achieved by evaporating the extractant at room temperature and dissolving the dry residue in the eluent. Also, this operation eliminated the difficulties associated with the analysis of organic extracts using the ion chromatography with conductivity detector. The absence of loss of the analytes at this stage was experimentally proven. The dependences of the efficiency of microextraction preconcentration on the various process parameters (ultrasonic exposure time, centrifugation time, volume of extractant, salt additive concentration) were established. The detection limits reached were 1∙10 -3 ‒ 8∙10 -3 mg/l, which are 20-600 times lower than the maximum permissible values for CAAs. In addition, the advantages of this preconcentration technique over the published works were the simultaneous removal of interfering impurities, small volume of water samples (4.1 ml) and chromatograph injected volume (50 μl). The relative standard deviation did not exceed 25%. The proposed method was tested by analyzing the samples of tap water. Mono- and dichloroacetic acids were detected, their content did not exceed the MAC values. Keywords : chlorinated acetic acids, ion chromatography, microextraction preconcentration DOI: http://dx.doi.org/10.15826/analitika.2020.24.1.004 R.G. Sirotkin, E.V. Elipasheva, V.A. Krylov, R.E. Grubov, K.A. Lutoshkina National Research Lobachevsky State University of Nizhny Novgorod (UNN) Gagarin pr., 23, Nizhny Novgorod, 603950, Russian Federation