Abstract

Lead speciation using modified silica capillaries for the introduction of liquid samples to a direct injection nebulizer of an inductively coupled plasma quadrupole mass spectrometer is described and demonstrated. The fused silica capillaries were coated by covalently bonding a cation exchange active organic molecule to the activated capillary surface. The best results were obtained by introducing a bifunctional reagent in a prior step. In this case, a silane reagent was chosen which acted as a methacrylic acid group for further binding. The influence of the chemical modification of the surface of the sample capillary of the DIN on the selective retention of inorganic lead (Pb²⁺) and triethyllead (Et₃Pb⁺) and hence separation and quantification has been investigated. The strong cation exchanger covering has been tested for its stability over a wide pH range (2–9). The interaction of Et₃Pb⁺ with the strong cation exchanger was negligible while the inorganic lead can be selectively retained at pH > 7. Upon flushing with 10⁻² mol L⁻¹ hydrochloric acid, the capillary can be easily regenerated. In order to remove retained inorganic lead several eluents were investigated. Parameters affecting the inorganic and organic lead separation such as sample pH, carrier solution, eluent strength, sample size and flow rate characteristics were studied in addition to optimal DIN-ICP-MS conditions. The detection limits for triethyllead and for inorganic lead were 90 and 200 ng L⁻¹ respectively, i.e., absolute detection limits of 0.3 and 0.6 pg respectively. In order to demonstrate the capability of the technique for the analysis of an environmental matrix, a sample of artificial rainwater was analysed.