Capillary electrophoretic determination of ammonia using headspace single-drop microextraction

A new method involving headspace single-drop microextraction (SDME) and capillary electrophoresis (CE) is developed for the preconcentration and determination of ammonia (as dissolved NH3 and ammonium ion). An aqueous microdrop (5 μL) containing 1 mmol/L H3PO4 and 0.5 mmol/L KH2PO4 (as internal standard) was used as the acceptor phase. Common experimental parameters (sample and acceptor phase pH, extraction temperature, extraction time) affecting the extraction efficiency were investigated. Proposed SDME-CE method provided about 14-fold enrichment in about 20 min. The calibration curve was linear for concentrations of NH4+ in the range from 5 to 100 μmol/L (R2 = 0.996). The LOD (S / N = 3) was estimated to be 1.5 μmol/L of NH4+. Such detection sensitivity is high enough for ammonia determination in common environmental and biological samples. Finally, headspace SDME was applied to determine ammonia in human blood, seawater and milk samples with spiked recoveries in the range of 96–107%.