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 scheme 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 obtained if sufficient laser power is available and if the absorption is also subject to additional modulation. The analytical versatility of these techniques is demonstrated by quantitative analysis of very low concentrations of (i) Cr(VI) species in tap water and (ii) chlorinated poly-aromatics (chlorophenols) in plant extracts, both after chromatographic separation. The atomic absorption measurements were performed in an air-acetylene flame (Cr) and in a low-pressure microwave-induced plasma (chlorophenols).