Capillary batch injection analysis: a novel approach for analyzing nanoliter samples

A significantly miniaturized version of batch injection analysis (BIA) is described. The new technique is based on solution handling by means of a piece of fused silica capillary and is, therefore, termed as capillary batch injection analysis (CBIA). The operation of CBIA is characterized by dispensing nanoliter samples onto the surface of a micro- or minidisk electrode which is immersed in a 1 ml blank solution. The effects of various parameters such as injection volume, capillary outlet/electrode distance, dispensing rate, presence or absence of stirring and capillary/electrode dimensions on the CBIA response are studied and optimized conditions for CBIA operation are derived. Repetitive injections of 188 nl aliquots of hexacyanoferrate(II) are performed with an injection rate of 600 samples/h, with a good precision of the signal height expressed by a relative standard deviation of 1.1% (n=31). Furthermore, CBIA measurements are combined with square-wave voltammetry by recording complete voltammograms during the injection of sub-mu l samples. The enhancement of selectivity is demonstrated by the simultaneous determination of ferrocene and ferrocenemonocarboxylic acid at concentrations ranging from 2.5 x 10(-5) M to 2.5 x 10(-4) M. The square-wave voltammograms of CBIA are nearly identical to those obtained in a large-volume batch experiment. (C) 1998 Elsevier Science B.V.