Quenched phosphorescence, a new detection method in capillary electrophoresis

The applicability of quenched phosphorescence as a detection mode in capill ary electrophoresis (CE) was explored for a number of analyte classes and b uffer systems. The detection method is based on the quenching of biacetyl p hosphorescence (biacetyl is a constituent of the CE buffer) by the analytes via various mechanisms (energy transfer, electron transfer and, possibly, hydrogen donation) and gives rise to negative peaks in the electropherogram s. A number of buffers in the pH range 4.7-11.5, frequently used in CE, wer e tested for their compatibility with this detection mode. Berate, succinat e, malonate, acetate, and phosphate buffers (pH 4.7-8.5) could be used with out any problems. With a pH of ca. 8.5 or higher the baseline declined with time, while at a pH higher than 9.5 no signal at all was obtained. Obvious ly, the noise on the phosphorescence signal (i.e., the baseline) determines the ultimate analyte detection limits (LODs), The baseline signal-to-noise ratio, usually denoted as the dynamic reserve (DR), was enhanced ca. 25-fo ld compared to direct biacetyl excitation by sensitization of the biacetyl phosphorescence by 1,5-naphthalenedisulfonic acid, and by application of a total emission mirror (TEM). A concentration of 1 x 10(-3) M 1,5-naphthalen edisulfonic acid was found to be optimal. For the buffer systems considered , the DR was typically ca. 300-600 under optimized conditions (noise define d as 1 x sigma). Investigated analytes include naphthalenesulfonic acids (N S), nitrophenols, hydroxybenzoic acids, amino acids, and dithiocarbamates ( DTCs.). For most of these, the LODs were in the 10(-7)-10(-8) M range, whic h is significantly lower than with direct or indirect absorption detection.