Miniaturisation in flow injection analysis Practical limitations from a theoretical point of view

Introduction Flow injection analysis (FIA) is a well established technique nowadays. One of the interesting features is its low reagent consumption in conjunction with the relatively small sample volumes required. This aspect will become even more important when a further reduction of the dimensions of the systems can be achieved. Technically such a miniaturisation does not present great problems as far as transport conduits or reaction compartments are concerned. Photolithographic techniques developed in chip-technology have reached a remarkable degree of perfection and offer excellent possibilities in this respect. A well known example is the miniature gas chromatograph etched on a silicon wafer of match box size as described by Angel1 et al. ‘. Some years ago RiiiiEka and Hansen213 suggested a similar approach for flow injection manifolds. In their so-called ‘integrated micro conduits’ a large part of the manifold was manufactured by engraving grooves and other parts in a small single block of perspex, also of match box size. However, because of the mechanical engraving technique used, they did not actually reduce the size of the conduits and the major advantage of their design seems to be the diminution of the outer size together with the integration of the various component parts of a manifold in a permanent and rigid position. This contributes significantly to the enhanced repeatability that was experimentally observed. Since lithographic techniques offer the possibility of manufacturing manifolds with smaller dimensions, it is worthwhile to examine the possible problems arising from such a scaling-down. To facilitate further discussions some technological concepts will be introduced first.