Total-effluent gas chromatography-mass spectrometry

Abstract

Calif. 94720A GC-MS system which allows introduction of a total GC effluent of up to 20 ml/min directly into the ion source of a mass spectrometer is described. The effect of flow rate on ion source and analyzer pressures, overall sensitivity, and resolving power of the system are evaluated. It has been shown that 10_1°-10_11 gram/sec sample flow rates are obtained for cholesterol trimethylsilyl ether at helium flow rates of 1-7 ml/min. Within that flow rate range, only a 12% reduction in mass spectrometer resolving power was noted. The system has been shown to be suitable for a wide range of molecules from low molecular weight gases to high molecular weight steroid and carbohydrate derivatives.Since the original work of James and Martin ( 7), the application of gas-liquid chromatography to the separation and identification of components of complex mixtures of organic materials has increased enormously. A wide variety

Introduction to Gas Chromatography/High Resolution Mass Spectrometry

“…As normally defined, the mass resolution, R, at 10% valley separation of two equal mass peaks is given by 7. KIMBLE Gas Chromatography/High Resolution Mass Spectrometry 125 R = Μ/ΔΜ (4) where M is the nominal mass and ΔΜ is the accurate mass difference for the two mass peaks ( Figure 2). The time difference, At, between the maxima of these two peaks can be determined from the rate of change of mass with time (from equation 2) giving -M dM = -5** .…”

“…e ' t/T · dt which approximates to τ for small values of ΔΜ and At. Dividing by equation (2) gives AM -At M ~T~ and using equation (4), this reduces to At = "I (5) From symmetry considerations, the time difference, At, between the peak maxima is equal to the time taken to scan across one of these peaks between the points which are at 5% of the maximum peak height ( Figure 2). Thus, if τ and At are known, then the resolution can be calculated for each single peak throughout the mass range.…”

“…As with any successful technique, many improvements have been incorporated in recent years in order to provide the maximum amount of information that can be derived from a GC/MS analysis. Significant developments include the use of: a) glass capillary columns (1)(2)(3), for minimized surface effects and increased chromatographic resolution; b) direct interfacing of capillary columns to the mass spectrometer ion source (4)(5)(6)(7), to reduce sample losses in a molecular separator and to preserve chromatographic resolution by elimi nating large-volume connectors; c) high pressure ionization methods (e.g., chemical ionization, [8][9][10][11][12][13][14], to provide complementary in formation to assist in the interpretation of electron impact spectra; d) improved computer techniques, for automated data acquisition, data handling (15)(16)(17), spectrum recognition (18)(19)(20)(21)(22)(23) and interpretation (24)(25)(26).…”

Techniques in gas chromatography/chemical ionization mass spectrometry

“…This type of interface has been used in several laboratories in conjunction with capillary columns with flows of 0.4 to 4 ml/min (STP) of He being taken directly into an open mass spectrometer source (12)(13)(14)(15). One instrument with a very high capacity pumping system has been reported to handle 20 ml/min (STP) of He (16). In all of these systems the pressures in the mass spectrometers are reported to be very low, essentially comparable to conventional electron impact conditions, and the spectra are considered to be produced by electron impact (El) only.…”

Gas chromatography

“…A flame photometric detector was coupled to a capillary column and used to detect trace amounts of sulfur compounds (315). By using highspeed differential pumping of the source and analyzer of a mass spectrometer, helium flow rates in the range 0.1 ml/min can be tolerated in the direct coupling of a capillary column gas chromatograph to a mass spectrometer without special interfacing (382), and oxygenated steroids and triterpenoids in the C27 to C32 range may be analyzed.…”