Flow injection and sequential injection: The optimal solutions for executing appropriate on-line separation and preconcentration schemes for detection of trace-level concentrations of metals in complex matrices by ICPMS

Despite its excellent analytical chemical capacity, ICPMS (and also ETAAS), nevertheless, often requires suitable pretreatment of the sample material to facilitate the desired sensitivity and selectivity of measurement. Either because of the presence of potentially interfering matrix constituents, or because the analyte material, in addition to suitable separations, needs to be subjected to preconcentration. Such pretreatments schemes are advantageously performed in flow injection (FI) or sequential injection (SI) manifolds, where all unit operations can be effected on-line and under enclosed and strictly controlled conditions. Various separation/preconcentration procedures are feasible, such as liquid-liquid extraction encompassing back-extraction into an aqueous solution, (co)precipitation with collection in knotted reactors, adsorption on columns packed with hydrophophilic or hydrophobic materials, hydride generation, or the use of ion-exchanger packed reactors. Apart from hydride generation, where the analyte is converted into a gaseous species, the common denominator for these approaches is that the analyte material finally is contained within a well-defined small volume of eluate, which then is introduced into the analytical instrument. While the graphite tube of the ETAAS can accommodate merely up to 50 l of solution, yet might tolerate organic but preferably should be subjected to inorganic eluates, the ICPMS has potentially a larger volumetric capacity yet cannot accept organic solvents as these adversely will impair its performance. In the lecture, selected examples of separation/preconcentration FI/SI-procedures for the determination of trace levels of metals will be presented, particular emphasis being placed on the use of the novel “lab-on-valve” (LOV) concept.