Preparation of a high pH-resistant AAPTS-silica coating and its application to capillary microextraction (CME) of Cu, Zn, Ni, Hg and Cd from biological samples followed by on-line ICP-MS detection

In this work, a novel sol–gel coating of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AAPTS)-silica was prepared for capillary microextraction (CME) of trace Cu, Zn, Ni, Hg and Cd followed by on-line ICP-MS detection. This organic–inorganic hybrid coating was in situ created on the inner walls of fused silica capillary using a sol solution containing tetramethoxysilane (TMOS) as a precursor, AAPTS as a co-precursor, ethanol as the solvent and cetyltrimethylammonium bromide (CTAB) as the template. The structure of the capillary coating was characterized by IR, SEM and TEM. Various experimental parameters affecting capillary microextraction of the target analytes have been investigated carefully, and the optimized extraction conditions were established. It was found that the AAPTS-silica coating with a terminal functional group of –NH–CH2–CH2–NH2 exhibited a high selectivity towards the selected metal ions. With a consumption of 1.0 mL sample solution and 80 μL eluent, the detection limits (3σ) were found to be 1.8, 11.8, 1.1, 3.3 and 1.4 pg mL−1 for Cu, Zn, Ni, Hg and Cd, respectively. A sampling frequency of 14 h−1 and an enrichment factor of 12.5 were obtained under the optimized experimental conditions. The relative standard deviations (RSDs) for the target analytes were less than 3.6% (C = 1 ng mL−1, n = 7, sample volume = 1 mL). Two certified reference materials of NIES No.10-c rice flour and BCR-CRM 278 mussel flesh were analyzed to validate the proposed method, and the determined values were in good agreement with the certified values. The developed method had also been applied to the determination of trace target elements in human hair, serum and urine, and the recoveries for the spiked samples were in the range of 89.2–101.8%. The AAPTS-silica coated capillary showed an excellent pH resistance and could be used for more than 120 times without decreasing adsorption efficiency.