Use Of Matrix Isolation Fourier Transform Infrared (FTIR) In Gas Chromatographic Detection

AbstractEarlier work in this laboratory' has shown matrix isolation Fourier transform infraredspectrometry (MI FTIR) to possess several advantages over conventional sampling techniquesfor the qualitative analysis of complex samples. The ability to obtain very sharp spectrausing MI makes it possible to distinguish between very similar compounds, including isomers,present in a sample.Instrumentation to couple capillary column gas chromatography (GC) to MI FTIR has beendeveloped as an alternative to on- the -fly gas -phase GC FTIR measurements. This techniqueallows leisurely study of chromatographic fractions at medium resolution (1 cm-1). A gold - plated disk is cooled to 15K with a closed -cycle helium refrigerator and used to collectcompounds eluting from the GC. Nitrogen is used as both GC carrier gas and matrix material.Beam condensing optics and KRS -5 rods are used to reflect the IR beam from the individualsample deposition surfaces.IntroductionConsiderable interest has developed recently in the use of FTII spectrometry for detec-tion in gas chromatography (GC), as reviewed by Erickson.2 At least two commercial GC -FTIRsystems are available which yield gas phase on- the -fly or vapor phase stopped -flow spectra.A major drawback of the on- the -fly systems is the limited resolution (ca. 4 cm-1) andnumber of FTIR scans (ca. 4) possible in the short time GC effluent is in the beam of thespectrometer. Use of stopped -flow systems results in better spectra, but the chromatographicresolution may be severely degraded if the gas flow is stopped, and other compounds elutingmay be lost if a bypass is used. These experimental limitations result in a practicalrequirement to use sensitive, cooled IR detectors to obtain detection limits of about 100 ngper component.2Matrix isolation is most commonly used as a means of trapping unstable or reactivespecies in order to study them in a leisurely fashion. For a sample which is liquid orsolid at room temperature, matrix isolation involves vaporizing the sample. Accordingly,matrix isolation should be directly applicable to detection in gas chromatography, particu-larly if the same substance is used both as the GC carrier gas and the matrix gas.