ELEMENT-SELECTIVE TRACE DETECTION OF TOXIC SPECIES IN ENVIRONMENTAL-SAMPLES USING CHROMATOGRAPHIC TECHNIQUES AND DERIVATIVE DIODE-LASER ABSORPTION SPECTROMETRY

Very sensitive laser absorption techniques based on a double-beam sche me with logarithmic processing of the detector signals and wavelength modulation of laser diodes are presented. Detection limits equivalent to 10(-7) absorption per square root of detection bandwidth are obtain ed if sufficient laser power is available and if the absorption is als o subject to additional modulation. The analytical versatility of thes e techniques is demonstrated by quantitative analysis of very low conc entrations of (i) Cr(VI) species in tap water and (ii) chlorinated pol y-aromatics (chlorophenols) in plant extracts, both after chromatograp hic separation. The atomic absorption measurements were performed in a n air-acetylene flame (Cr) and in a low-pressure microwave-induced pla sma (chlorophenols).