Investigations On The Determination Of Trace Heavy Metals By Lab-on-Valve Bead Injection Spectroscopy

The determination of heavy metals is one of the most important tasks in environmental analysis. Currently, atomic absorption spectrometry, atomic fluorescence spectrometry, inductively coupled plasma-mass spectrometry are among the main analytical techniques for the determination of heavy metals. However, modern analytical sciences require not only high sensitivity, precision and analytical throughput, but the miniaturization and automation of analytical instruments have attracted more and more attentions. Especially, field analytical tasks caused by some accidental heavy metals pollution incidents have to be faced. In this respect, the bulky instruments are usually out of choice. Therefore, the development of miniaturized detection system for specific analytical purposes is very important and necessary.In the present dissertation, a miniature analytical system based on a lab-on-valve platform is developed for trace heavy metal analysis by bead injection technique. In the experiment, micro-beads of Sephadex QAE A-25loaded with zincon are automatically introduced into the multipurpose flow cell of the LOV by bead injection operation for selectively capturing target analyte Cu2+. The target analyte Cu2+is separated/preconcentrated on the surface of micro-beads and detected directly by a CCD spectrometer. With a sample volume of2.5mL, a detection limit of3μg L-1and a linear range of10-100μg L-1were obtained for copper, along with a RSD value of2.5%(at the50μg L-1level). The accuracy and practical applicability of the proposed system were validated by analysing certified reference materials, i.e., GBW09101(Human hair), GBW10010(Rice), GBW08608(Trace Elements in Water), and further demonstrated by spiking recovery of copper in a water sample. An approach for the immobilization of a chromogenic reagent on solid phase micro-beads is afterwards performed via a sulfonation reaction. The benzene ring structure exists in various chromogenic reagents, which facilitates the introduction of a sulfonic acid group via sulfonation. Chromogenic reagents ranging from neutral to anionic can be immobilized on Sephadex QAE A-25micro-beads. As a model of application, micro-beads of Sephadex QAE A-25loaded with the chromogenic reagent1-(2-pyridylazo)-2-naphtholsulfonic acid (PAN-S) are employed for the determination of trace cobalt by lab-on-valve bead injection spectroscopy. With a sample volume of1.0mL, a detection limit of8μg L-1and a linear range of20-500μg L-1are obtained for cobalt, along with a RSD value of2.8%(at the200μg L-1level). The accuracy and practical applicability of the present method are validated by analysing a certified reference material of soil GBW07404and vitamin B12injection and mecobalamin tablets, and further demonstrated by spiking recovery of cobalt in two water samples.