Ultrasensitive determination of selenium in water and food samples by ICP-MS: UiO-66-NH2 for preconcentration and direct slurry hydride generation

Selenium is an indispensable microelement for humans and food is the main source of selenium intake. As one of the best techniques for the determination of selenium, inductive coupling plasma-mass spectrometry (ICP-MS) features some unique advantages, such as wide linear range and high sensitivity. Nevertheless, it still remains a challenge to achieve the accurate and high sensitivity determination of ultra-trace selenium in food samples by ICP-MS owning to the high first ionization energy of selenium and interferences from sample matrices as well as isobaric interferences. In this work, UiO-66-NH2 (metal organic framework, MOF) was fast synthesized by microwave method and employed for the preconcentration of ultra-trace selenium with an adsorption efficiency of nearly 100 %. The selenium-adsorbed MOF was collected by filtration, and then simply converted to slurry for in situ hydride generation (HG) for sensitive detection of selenium by ICP-MS. Various factors affecting the adsorption of selenium by the MOF (including pH, adsorption time, and amount of MOF) together with main parameters of hydride generation (including concentrations of HCl and NaBH4) were carefully evaluated. Experimental results show that effective matrix separation can greatly reduce interference, with an excellent detection limit of 1 ng/L. The practicability and accuracy of this method were successfully confirmed by the determination of trace selenium in several food samples. UiO-66-NH2 (MOF) was used as an effective adsorbent for the preconcentration of selenium prior to direct slurry sampling HG-ICP-MS determination. Direct slurry sampling avoided additional elution procedures and was conducive to eliminating matrix and isobaric interferences. High sensitivity and interference-free determination were achieved for determination of ultra-trace Se in complex food samples.