Development and applications of photothermal spectrometry for trace chemical analysis and chromatographic detection

Minren Xu, Marquette University


Based on thermal lens (TL) technique, an ultrasensitive and small volume detection method, a series of instruments have been developed. They are multiple wavelength TL spectrophotometers, TL-circular dichroism (CD) spectropolarimeters and TL-CD detector for high performance liquid chromatography. The multiple wavelength TL spectrophotometer aims to improve the selectivity of this technique. The multiple excitation beams enable this technique to be used for determination of multiple component samples. The absorption ratio at different wavelengths provides finger prints to identify unknown compounds. The two optical configurations, cross beam and collinear beam systems, were employed. A detection limit of 10$\sp{-9}$ M for diaminoanthraquinone, based on 6 mW, 488 nm laser beam modulated at 1.02 Hz and 1 cm pathlength, was achieved for collinear beam system. The TL-CD spectropolarimeters based on different quarter-wave plates, i.e., Fresnel rhomb and Pockels cell were investigated. In the collinear beam system the limit of detection of 1.4 $\times$ 10$\sp{-6}$ in terms of absorbance unit has been achieved. The detection volume was 8 $\mu$L in the cross beam configuration. The spectropolarimeter based on Pockels cell also can be used as a TL-CD detector for HPLC-optical resolution. A detection limit of 7.2 ng was achieved for ($-$) and (+)-tris(ethylenediamine)Cobalt(III) (k$\sp\prime$ = 0.45 and 1.40 respectively) when these two enantiomers were chromatographically resolved. The detector selectively detected chiral species and provided the information on chirality, i.e., positive and negative chromatographic peaks for the pair of enantiomers.

Recommended Citation

Xu, Minren, "Development and applications of photothermal spectrometry for trace chemical analysis and chromatographic detection" (1991). Dissertations (1962 - 2010) Access via Proquest Digital Dissertations. AAI9200162.