Choice of fluorescence wavelengths for the determination of trace amounts of chlorine by graphite furnace laser-excited molecular fluorescence spectrometry of indium monochloride

Abstract

New excitation and detection wavelengths were explored in an attempt to improve the sensitivity of laser-excited molecular fluorescence spectrometry (LEMOFS) in a graphite tube furnace for the determination of chlorine through indium monochloride molecular fluorescence. Fluorescence spectra of the A-, B- and C-band systems of indium monochloride, excited at 267.21 nm, were obtained, and the sensitivities were compared. The most sensitive excitation/detection scheme, was found to be 267.2 nm/269 nm, where the detection wavelength was within the same, C-band, electronic transition, as the excitation wavelength, but with a different vibrational transition. To the knowledge of these workers, this was the first recorded analytical use of a vibrational transition within the same electronic transition for LEMOFS. The vibrational transitions of the fluorescence spectra were spectroscopically well resolved. A detection limit of 10 pg for chlorine was achieved, which was a 50-fold improvement over our experiments carried out at wavelengths used by other workers. Unfortunately, the best detection limit of these previous researchers at their wavelengths could not be reproduced by us. As a result, the detection limit reported here is no better than the best previously reported detection limit, which remains an improvement of two orders of magnitude over molecular absorption spectrometry of indium monochloride. The effects of metal ions and non-metal ions were studied. Chlorine was determined in two biological standard reference materials obtained from the National Institute of Standards and Technology. Vaporization matrix effects were observed and removed by dilution. By use of simple aqueous calibration, the results obtained for the two reference samples were in good agreement with the non-certified reference values of chlorine.