Influence of a stacking phenomenon on the results of Hadamard transform capillary electrophoresis

Advantageous features (enhanced sensitivity and low baseline noise) of the multiplex measuring procedure, the Hadamard transform capillary electrophoresis (HT-CE), are experimentally demonstrated and critically discussed. To perform a perfect multiplex experiment in CE, sample species need to be dissolved in the background electrolyte medium and have very low concentration. The mismatch of electric conductivity resulting from a sample dissolved in water or in a separation buffer diluted with water will lead to sample stacking and corrupting the anticipated outcome. The multiplex measurements were carried out with benzyltriethylammonium bromide, resorcinol and 3,5-dihydroxybenzoic acid in the phosphate buffer, 511 sample/buffer injections were performed into the capillary according to the pseudorandom binary sequence. The averaged electropherogram of the single injection was calculated from the detection signal with the aid of the Fourier transform. The results illustrate the detrimental effect of sample matrix dilution with water and the effect of increased initial sample concentration on the multiplex measurement in CE. Multiplex advantage, in theory possible in the HT-CE, can be obtained at low concentration levels feasible with laser induced fluorescence and optically gated sampling. To achieve successful multiplex measurements with the UV detector, the single injection signal should be approximately at the baseline noise level.