Lab-on-Valve Micro Sequential Injection: A Versatile Approach for Implementing Integrated Sample Pre-preparations and Executing (Bio)Chemical Assays

In the last decade, Flow Injection Analysis (FIA) became supplemented by Sequential Injection Analysis (SIA), which, although it inherently entails some limitations as compared to FIA, offers specific advantages, notably in terms of significantly reduced sample and reagent(s) consumption and hence waste generation. Most recently, the Lab-on-Valve (LOV) approach has emerged. Termed the third generation of FIA, the conceptual basis of the LOV is to incorporate all the necessary unit operational manipulations required in a chemical assay, and, when possible, even the detection device, into a single small integrated microconduit, or “laboratory”, placed atop a selection valve. In the lecture emphasis will be placed on the LOV approach. Proven itself as a versatile front end to a variety of detection techniques, its utility will be exemplified by various applications. Particular focus will be directed towards its use as a vehicle for on-line pretreatment of complex sample matrices for determination of trace-level concentrations of metal ions by electrothermal atomic absorption spectrometry (ETAAS) and inductively coupled plasma mass spectrometry (ICPMS) via exploitation of the renewable solid-phase microcolumn concept utilising hydrophobic as well as hydrophilic bead materials. Although ETAAS and ICPMS both are characterised by excellent analytical chemical capabilities, they nevertheless often require that the samples be subjected to suitable pretreatment in order to obtain the necessary sensitivity and selectivity. Either in order to separate the analyte from potentially interfering matrix constituents, or to preconcentrate the analyte material to bring it into the dynamic range of the detector. As will be shown, such pretreatments are advantageously performed in FIA/SIA/LOV manifolds, where all appropriate unit operations can be effected under enclosed and strictly controlled conditions.