Matrix Isolation Microsampling Procedures in Quantitative Fourier Transform Infrared Spectrometry

Abstract

Techniques for microsampling in infrared spectroscopy by matrix isolation are described. In the matrix isolation of liquid or solid compounds, the sample is vaporized and then diluted with a large excess of a matrix gas; the resulting gaseous mixture is deposited on a cold surface for spectroscopic examination as a solid. Detailed descriptions of the apparatus and procedures employed in the preparation of matrix-isolated samples for qualitative and quantitative analyses by Fourier transform infrared spectrometry are presented. Systems for “microsampling” (detection limits for specific compounds ∼0.5 to 1 μg) and “ultramicrosampling” (detection limits ∼50 to 100 ng) matrix isolation spectroscopy are described. Detection limits and Beer's law behavior for polycyclic aromatic hydrocarbons microsampled by matrix isolation are discussed. The advantages of matrix isolation as a technique for qualitative and quantitative infrared analysis of microsamples are itemized.

Laser-induced fluorescence spectrometry of polycyclic aromatic hydrocarbons isolated in vapor-deposited n-alkane matrices

“…15 K. In the present investigation, we examine the analytical utility of MI fluorescence spectrometry in n-alkane solvents, and we consider the advantages of using dye laser excitation of fluorescence in both alkane and conventional matrices. EXPERIMENTAL Samples were deposited on a gold-plated copper surface, maintained at 15 K, mounted in the head of a closed-cycle helium cryostat ("Spectrim", CTI Cryogenics), by using a Knudsen effusion vacuum sublimation apparatus which has been described previously (2,18,19). After deposition at 15 K, the hydrocarbon matrices were annealed at 145 K for 5 min and were then cooled back to 15 K prior to measurement of fluorescence.…”

Determination of polycyclic aromatic hydrocarbons in unfractionated solid solvent-refined coal by matrix isolation fluorescence spectrometry

“…For MI sample preparation, a conventional Knudsen cell (22) was modified to accommodate solid samples by enlarging the front orifice from 0.5 mm to 4 mm diameter. Samples were codeposited by vacuum sublimation with matrix gas as described previously (17).…”

Matrix Isolation Spectroscopy

“…The sample is contained in a glass Knudsen cell, which is a short piece of 7-mm glass tubing equipped at one end with a vacuum joint and at the other end with a <0.5-mm orifice. Details of Knudsen cell construction will be described elsewhere (10). The Knudsen cell is wrapped with heating wire, the temperature of which is controlled by a variable autotransformer.…”

“…By sequential use of two different Knudsen cell-deposition window systems, it is possible to achieve linear Beer's law behavior in MI FTIR over three decades in analyte concentration (10). Moreover, the linear quantitative ranges of MI fluorescence and FTIR do not totally coincide.…”