A new study reports the development of a method for the determination of the main toxic arsenic compounds in water samples by capillary electrophoresis coupled to electrospray mass spectrometry.
While arsenic often is considered a synonym for poison, the toxicity of different arsenic compounds varies from harmless to cancerogen. Inorganic arsenic is very toxic and often present in groundwater resources depending on the geochemistry of the aquifer. This has led the European Union and other global organizations to reduce the maximum residue limit for the total arsenic up to 10 μg L−1 in water for human consumption. In order to perform a meaningful risk assessment but also to reduce arsenic contamination levels by adequate water processing, information about the arsenic speciation is mandatory. Most methods for such speciation analysis are based on the use of a senstive element detection system coupled with a separation technique, with HPLC-ICP-MS being the most often used. Since the ICP-MS does not provide any molecular information, the different arsenic species are only identified by their chromatographic retention time by comparison with standards. On the other hand, the ICP-MS often provides compound-idependent element sensitivity, so that quantification of different species is possible with a single standard.
Molecular mass spectrometry such as electrospray mass spectrometry has often been used for the identification of unknown arsenic species but seldom for the quantification of arsenic species. The reason for its limited use is the fact, that the ionization efficiency of different species depends not only on the species but also the matrix, making quantification in complex samples difficult. Also most often ESI-MS cannot compete with ICP-MS for its detection power, calling for a preconcentration procedure, when ultimate detection limits are required.The new study:
Considering these limitations, a spanish researcher from the University of Salamanca has developed a method for the determination of the four main toxic arsenic compounds (iAs(III), i-As(V), MMa and DMA) in water samples by capilarry electrophoresis (CE) coupled to ESI-MS. Separation of the four arsenic species is achieved by CE employing a basic electrophoretic separation medium containing a mixture of hexafluoro-2-propanol (HFIP) and ammonia. Sensitive detection is performed by ESI in negative mode.
Under optimized conditions, the analysis time was less than 6.5 min. Detection limits obtained were below 2 µg/l and the quantification limits were below 6.5 µg/l for all four species. In case that the detection power of the CE-ESI-MS is not sufficient, the water volume of the sample is reduced 50:1 in a rotovap. These conditions are adequate for the arsenic speciation in weakly mineralized water samples.
Thirteen water samples from different locations in the province of Salamanca (W Spain) were analysed. The results obtained showed that CE-ESI(−)-MS could be use as another sensitive approach for the determination of As toxic species, both organic and inorganic.
The original study
Javier Domínguez-Álvarez, Capillary electrophoresis coupled to electrospray mass spectrometry for the determination of organic and inorganic arsenic compounds in water samples
, Talanta, 212 (2020) 120803. DOI: 10.1016/j.talanta.2020.120803
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last time modified: May 13, 2020