A miniature optical emission spectrometric system in a lab-on-valve for sensitive determination of cadmium

A miniature optical emission spectrometric (OES) system is developed by incorporating dielectric barrier discharge (DBD) microplasma as excitation source in a lab-on-valve (LOV) configuration for trace cadmium analysis. The entire system integrates bead injection (BI) sample pretreatment, post-column derivatization, in-situ nebulization and OES detection. Trace cadmium in sample solution is separated and preconcentrated by flowing through a 2-(5-Br-2-pyridylazo)-5-dethylaminophenol (5-Br-PADAP) loaded microcolumn in LOV, followed by elution with 20 μL of 0.1 M hydrochloric acid. The eluate after online derivatization with 5 μL of 0.2 M borate buffer solution containing 7.5% (v/v) ethanol is immediately transported into a pneumatic micronebulizer integrating DBD microplasma for cadmium excitation, and OES is recorded by using a charge coupled device (CCD) spectrometer. As a miniaturized analytical set-up, LOV provides an ideal sample-processing front-end with detection by DBD-OES, while introduction of DBD excitation source in LOV highly improves the analytical performances for trace metal species. With a sample volume of 1.0 mL, a detection limit of 0.06 μg L^-1 and a linear range of 0.2-50 μg L^-1 are achieved for cadmium, along with an enrichment factor of 38. The accuracy of the present system is confirmed by the determination of cadmium in certified reference materials, and further demonstrated by spiking recoveries of cadmium in real water samples.