Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry

The applicability of capillary electrophoresis (CE) in combination with atm ospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect t o the separation of the analytes and mass spectrometric sensitivity. CE/MS turned out to be an attractive alternative for the determination of h aloacetic acids to existing methods based on GC-ECD. Employing CE/MS deriva tization is not necessary which saves time and avoids possible sources of e rrors. In the present work the sample pre-treatment is performed by liquid- liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and th e: residue is dissolved in methanol and analyzed by CE/MS using a mixture o f 2-propanol/water 80:20 containing triethylamine as the sheath liquid in t he interface. Best results for the separation of all nine possible bromo- a nd chloroacetic acids together with two internal standards are obtained wit h a carrier electrolyte consisting of ammonium acetate/acetic acid in metha nol: to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid con tent is necessary. The method was applied to the determination of haloaceti c acids in real water samples. With optimized CE and MS conditions detectio n limits between 0.3 and 7.6 mu g/L in the original water samples were achi eved, employing a sample volume of 30 mL.