Analytical Sciences

Enhanced Desolvation and Improved Deposition Efficiency by Modified Thermospray for the Coupling of HPLC and FT-IR

Mohammad A. MOTTALEB  and Hyo-Jin KIM

Department of Pharmacy, Dongduk Women's University, 23-1 Sungbuk-ku, Seoul 136-714, South Korea

A thermospray interface was modified for the on-line coupling of normal- and reversed-phase high-performance liquid chromatography (HPLC) and Fourier transform infrared (FTIR) spectrometry. An LC/FTIR assembly was used to evaporate the column effluents and the solutes were deposited as a series of individual spots on a stainless-steel moving belt, which continuously transferred the solutes into a diffuse reflectance accessory of FTIR, enabling the identification of deposited solutes by measuring the IR spectrum. A lowered desolvation temperature of reversed-phase HPLC eluents, a higher deposition efficiency, such as 69%, and a reduction of the thermospray capillary voltage were achieved by using a heated gas flow and a heating plate. The thermospray temperature and the distance between the tip of the thermospray tubing and the surface of the belt were shown to influence the area of deposition of spots. A variation of ±1°C could be used for a sensitive and reproducible deposition of Irganox 565 with a relative standard deviation (RSD) of 1.8 to 2.5%. The UV and FTIR chromatograms gave similar features for the HPLC-separated constituents. The interface-derived IR spectra of the constituents showed excellent agreement of the spectral features with those of the standard FTIR spectra, and no thermal degradation was found to occur.

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