Kelly L. Norton

Performance characteristics of a real-time direct deposition supercritical fluid chromatography-Fourier transform infrared spectrophotometry system

Abstract In this paper, real-time, on-line measurements of direct deposition capillary supercritical fluid chromatography-Fourier transform infrared spectra of subnanogram quantities of analytes is demonstrated for the first time. The minimum identifiable quantity for caffeine (a strong infrared absorber) obtained with this interface was 600 pg (injected) and 1–10 ng for weaker absorbers. Spectra over the entire mid-infrared region of compounds separated with a mobile phase of carbon dioxide modified with two percent methanol were able to be measured. The interface shows linear behavior over two orders of magnitude for both the area under a strong absorption band in the infrared spectra versus injected quantity and for the area under a peak from the functional group chromatogram versus injected quantity.

Comparison of direct deposition and flow-cell gas chromatography-Fourier transform infrared spectrometry of barbiturates

Comparison of flow-cell and direct deposition (DD) interfaces between gas chromatographs (GC) and Fourier transform infrared (FT-IR) spectrometers is reported. Seven barbiturates were separated on fused-silica GC capillary columns. Infrared spectra of the separated barbiturates were measured in real-time by either a Hewlett-Packard infrared detector (flow-cell) interface or a Digilab Division of Bio-Rad Tracer (DD) interface. Without losing chromatographic resolution, the DD GC-FT-IR interface gave both detection limits and minimum identifiable quantities nearly two orders of magnitude lower than the flow-cell GC-FT-IR interface.

A unified approach to the chromatography/FT-IR interface

Most previous interfaces between a Chromatograph and an FT-IR spectrometer have been applicable to only one type of chromatograph-gas, liquid, or supercritical fluid. In this paper, the similarities and differences between various chromatography/FT-IR interfaces are described, and an interface which should be equally applicable to all three types of chromatography is proposed. In each case, the mobile phase is eliminated while the eluting components are condensed in a small area on a moving substrate. The spectra are then measured using an FT-IR microscope. The methods by which the mobile phase is eliminated depend on the nature of the chromatography, while the infrared sampling technique is determined by the nature of the substrate. The relative merits of transmission, reflection-absorption, diffuse reflection, and diffuse transmission spectrometry are discussed.

Recent advances in the hyphenation of chromatographs and FT-IR spectrometers☆

Abstract A common approach to measuring on-line infrared spectra of species eluting from gas, supercritical, and high performance liquid chromatographs is described. The eluites are deposited as very small spots on a moving ZnSe window and are passed through a microbeam of a Fourier Transform infrared spectrometer shortly after deposition. Identifiable spectra can be obtained from subnanogram quantities of each analyte. Spectra measured in this way are very similar to KBr-disk reference spectra.

Comparison of Direct-Deposition Supercritical Fluid and Gas Chromatography/Fourier Transform Infrared Spectra to Condensed-Phase Library Spectra

Comparisons of spectra from direct-deposition (DD) capillary gas chromatography (GC) and supercritical fluid chromatography (SFC)/Fourier transform infrared (FT-IR) measurements of two quinones with C2 symmetry axes and several barbiturates to spectra from condensed-phase libraries of the corresponding compounds are reported. The best spectral search results were obtained when the eluites were deposited on an amorphous substrate, such as ZnSe. A small number of polar, hydrogen-bonding compounds were found to align with each other or with a crystalline substrate. Different crystalline forms of some polymorphic analytes can also yield ambiguous identifications. These effects produce enough differences in the DD GC/FT-IR and SFC/FT-IR spectra to cause occasional incorrect identifications when the spectra are searched against KBr-disk library spectra.

Chapter 6 SFC/FT-IR Measukements Involving Elimination of the Mobile Phase

Publisher Summary This chapter describes two distinct methods of implementing the interface between chromatographs and Fourier transform infrared (FT-IR) spectrometers. In the first method, the column effluent is passed through a suitable flow-cell while in the second the mobile phase is continuously eliminated and the eluites are deposited on an appropriate substrate prior to the measurement of the infrared spectrum. Both of these approaches have been applied to the supercritical fluid chromatography Fourier transform infrared (SFC/FT-IR) interface. Off-line and on-line DD SFC/FT-IR measurements are also explained in the chapter. The chapter also illustrates several important features of DD SFC/FT-IR. Firstly, the technique is equally applicable to separations effected on capillary or 1-mm that is, packed columns using modified or unmodified mobile phases. Secondly, on-line data can be obtained after making quite minor modifications to a commercial DD GC/FT-IR interface. Thirdly, the minimum quantity of any analyte that can be identified in real time using this technique is a few hundred picograms for strongly absorbing compounds such as acenaphthenequinone. DD SFC/FT-IR is expected to become an important tool for chemists involved in the analysis of samples containing trace amounts of organic compounds that are too nonvolatile to be separable by gas chromatography.

Advantages And Disadvantages Of A Chromatographic/FT-IR Interface Based On Mobile Phase Elimination

Interfaces between chromatographs and FT-IR spectrometers based on mobile phase elimination and eluite deposition are usually more sensitive than flow cell methods. In the GC/FT-IR 1,2 and SFC/FT-IR314 interfaces developed by our group, the eluites are deposited in a small area (<0.04 mm2) on a moving infrared transparent window (usually ZnSe) and their spectra are measured using an FT-IR microscope. One advantage that has been ascribed to this technique is the ability to use standard condensed phase spectral libraries for spectral searching.5 In this paper, the results of a systematic study are described in which SFC/FT-IR spectra are compared to libraries of condensed phase reference spectra. The particular analytes that were investigated were chosen to probe several possible sources of variation between SFC/FT-IR spectra and reference spectra of the same compounds prepared as KBr disks.