Comparison of Solvent Elimination Systems for the Analysis of Dyes and Pesticides by High-Performance Liquid Chromatography Fourier Transform Infrared Spectrometry

Abstract

Two systems have been compared for the on-line production of infrared spectra of compounds separated by high-performance liquid chromatography (HPLC). System 1 had a thermospray interface to evaporate the mobile-phase solvents and deposit the solutes onto a moving stainless steel belt, for direct analysis by reflection–absorption IR spectrometry. In system 2, the column effluent was split 1:6 and pumped through an ultrasonic nebulizer. The spray was desolvated at reduced pressure in a heated transfer tube and the solutes deposited onto a ZnSe window for direct analysis by transmission IR spectrometry. When system 1 was used for the analysis of reactive dyes, eluent containing ammonium acetate caused a large background spectrum, as a film of unknown composition was formed on the surface of the stainless steel belt. An alternative procedure, without ammonium acetate, was developed with a mixed-mode column containing C18 and cation exchange particles, but variable retention times were obtained. System 2 could be used satisfactorily with eluents containing ammonium acetate, and it produced dye spectra of better resolution than those obtained with system 1. When the dyes were examined under a microscope, the material on the ZnSe window was more uniform and more evenly distributed on a narrower track than were the deposits on the stainless steel belt. Consequently, the peak shape of the IR chromatograms was better with system 2, and a lower detection limit was achieved for reactive blue 74 (9 ng). When mixtures of the pesticides metolcarb and carbofuran were analyzed, a thermospray temperature of 196 °C was required to desolvate the effluent from the HPLC column in system 1. At this temperature, thermal degradation of the pesticides occurred, and no spectrum was recorded from the belt surface. However, with system 2, deposition of the pesticides was achieved at 90 °C, without degradation, and IR spectra/chromatograms were obtained. Overall, the study showed that the infrared chromatograph (IRC) was the more efficient and flexible interface for HPLC Fourier transform infrared (FT-IR) spectrometry.

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

“…Detailed descriptions of the interface have been given elsewhere. [15][16][17][18] The column effluents were transferred to the thermospray interface assembly, which was surrounded by a heated nitrogen gas stream supplied by two channels at 5 l min -1 from each channel, which continually flowed down to the thermospray capillary tubing (125 µm i.d. × 1.5 mm o.d.)…”

“…The success or failure of the technique almost exclusively depends on the interface performance. In general, flow cells [1][2][3] and solvent elimination [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] procedures have been used for the interfacing of HPLC to FTIR. Although more convenient, the usefulness of the flow-cell procedure is limited because the aqueous-based mobile phase, commonly used in reversed phase (RP)-HPLC, strongly absorbs IR radiation in many areas of the IR spectrum, resulting in a loss of sample spectral information.…”

“…15 This hyphenated technique was recently employed to analyze linear alkylbenzene sulfonates 16 and reactive dyes. 17,18 Although the use of a heated gas flow at a rate of 6 l min -1 reduced the thermospray temperature, 15 deposition problems, thermospray capillary blockage, a loss of resolution in FTIR chromatograms, [15][16][17] and peak splitting 18 were experienced. To keep these problems in mind, we further revised, or developed, glass thermospray by introducing another heated gas flow channel and a heating plate underneath the deposition belt to enhance the eluent evaporation and to improve the resolution in the FTIR detection chromatograms, respectively.…”

Application of an HPLC-FTIR Modified Thermospray Interface for Analysis of Dye Samples

“…19 This coupled technique was employed to analyze the linear alkylbenzene sulfonate, 20,21 river-water residues, 22 polystyrene samples 23 and pesticides. 24 Because HPLC-FTIR can provide functional-group features, 19,20 it may also provide complementary information to HPLC-MS for dyes. It was of interest to access whether the provided functional-group features by FTIR could give sufficient information to explain the reasons for the different chromatograms given by the formulated and purified reactive dyes.…”

“…In the HPLC-FTIR thermospray interface, some problems were also experienced concerning the use-phase modifiers in the HPLC eluent. [19][20][21][22][23][24][25] In order to analyze dye samples by HPLC-FTIR thermospray, a small-gradient HPLC method has been developed. 25 This paper describes the applicability of an HPLC-FTIR modified thermospray interface for dye analysis.…”