A Universal Approach for Selective Trace Metal Determinations via Sequential Injection-Bead Injection-Lab-on-Valve (SI-BI-LOV) Using Renewable Reagent-loaded Hydrophobic Beads

A new sample pretreatment approach is presented for selective and sensitive determination of trace metals via electrothermal atomic absorption spectrometry (ETAAS) based on the principle of bead injection (BI) with renewable reagent-loaded hydrophobic beads in a Sequential Injection-Lab-on-Valve (SI-LOV) mode.

The methodology uses poly(styrene-divinylbenzene) beads containing pendant octadecyl moieties (C18-PS/DVB), which are pre-impregnated with a selective organic metal chelating agent prior to the automatic manipulation of the beads in the microbore conduits of the LOV unit. By adapting this approach, the immobilization of the most suitable chelating agent can be effected irrespective of the kinetics involved, optimal reaction conditions can be used for implementing the chelating reaction of the target metal analyte with the immobilized reagent, and an added degree of freedom is offered in selecting the most favourable elution mode in order to attain the highest sensitivity.

Cr(VI) is used as model analyte to demonstrate the potential of the SI-BI-LOV scheme, in which 1,5-diphenylcarbazide (DPC) is pre-impregnated on the beads, the surface of which serves as the active microzone. It is shown that the bead material can endure very high acidity which is a prerequisite for the reaction.

On-line sample pH adjustment prevents alteration of the original distribution of the chromium species, while assuring fast rates for the DPC-Cr(VI) reaction. The proposed procedure was successfully applied for the determination of trace levels of Cr(VI) in natural waters of variable cpmpexity. Furthermore, it was validated by the determination of total chromium in a NIST standard reference material (NIST 1640, natural water) after Cr(III) oxidation.