Chromatographic interfaces

The main characteristics of sector mass spectrometers are shown in Table 6.29. Magnetic sector mass spectrometers are often considered more difficult to operate than QMS and ToF-MS the high-voltage source is more demanding to chromatographic interfacing. For figures of merit, see Table 6.27. 

FTICR-MS is capable of powerful mixture analysis, due to its high mass range and ultrahigh mass resolving power. However, in many cases it is still desirable to couple a chromatographic interface to the mass spectrometer for sample purification, preconcentration, and mixture separation. In the example given above, DTMS under HRMS conditions provides the elementary composition. Apart from DTMS, PyGC-MS can be performed to preseparate the mixture of molecules and to obtain the MS spectrum of a purified unknown. Direct comparison with the pure reference compound remains the best approach to obtain final proof. 

Table 7.24 Sample types in relation to chromatographic interfaces, ionisation methods and mass spectrometers...

Sample classes Chromatographic interfaces Ionisation methods Mass spectrometers"... 

Development and application of various chromatographic interfaces to infrared spectrometers have been reviewed [167], more particularly also for SFC-FTTR [167,372,383,384] and on-line cSFC-FTIR [385], Taylor and Calvey [386] have reviewed high-pressure flowcell cSFC-FTIR and pSFC-FTTR. Griffiths et al. [374] reviewed SFC-FTTR involving elimination of the mobile phase. 

Recently, the focus has been placed especially on the chromatographic interface as a means for improving bioanalytical efficiency and novel advantages on samples preparation (and separation) related to the fact that they are generally the rate limiting steps in drug development process. 

Henry, M.C., Wolf, L.K., and Messmer, M.C., In situ examination of the structure of model reversed-phase chromatographic interfaces by sum-frequency generation spectroscopy, J. Phys. Chem. B, 107, 2765, 2003. 

Wirth, M.J. and Swinton, D.J., Single-molecule probing of mixed-mode adsorption at a chromatographic interface. Anal. Chem., 70, 5264, 1998. 

A schematic diagram of the automatic system is shown in Fig. 4.7a. The sample -to-gas-chromatograph interface and requirements for the injection of a hquid mixture onto a gas chromatographic column from a flowing stream present the greatest problem, in contrast to sample transfer and dilution techniques in automatic analysis, which are well documented. 

The pyrolysis products of expls in tandem with GC/MS served as indirect identification of contaminant expls in the environment. The pyrolysis products generated, which are indicative of the parent molecule, are separated by GC and identified by MS (Ref 108). Red water produced by the sellite purification of crude TNT was analyzed by GC/MS for potentially useful organic compds, 2,4-DNT, 3- and 5-sulfonic acids (Ref 124). The enhanced detection of TNT vapors was achieved by pre-concn on a metal surface, and flash-desorbed onto a chromatograph interfaced with a quadrupole MS (Ref 76). Vapors of TNT, acetone, toluene, cyclohexanone, and an organosilicon were detected and identified by GC/MS (Ref 78). Various reports were surveyed to determine which methods, including GC/MS, aire potential candidates for the detection of traces of TNT emitted from military land-mines (Ref 80) The vapors collected from Comp B were analyzed by GC/MS besides the TNT and RDX, H20, N20, C02, plus several unidentified compds, were detected (Ref 79). By the use of GC, isomeric impurities in the vapor, as well as solid phase of TNT, were resolved and identified by MS (Refs 61,62 115)... 

Samples of fatty acid esters were analyzed with a gas chromatograph interfaced with a mass selective detector (Model QP 5050A Shimadzu) using a capillary column PE-5 (20 m x 0.18 mm x 0.25 mm). The following... 

We hope that this manuscript will encourage flavor chemists to understand and better utilize the modern techniques available in mass spectrometry. In particular we believe these desorption techniques and associated chromatographic interfaces to be especially useful for the is of food derived peptides, amino acids, polyhydroxypyrazines and other polar or high molecular weight components of caramelization and Maillard reactions. 

Figure 1.1 Snapshot of a reversed-phase liquid chromatographic interface. Tethered Ci8 chains are leftmost, displayed as ball-and-stick. The water/methanol mixture mobile phase, 10% methanol by volume, is on the right terminated by a fluid interface with vapor. Three-site model methanol molecules are also displayed as ball-and-stick, but the water molecules are wires only. (See Clohecy, 2005.)...

Clohecy, J., Computer Simulation of Liquid Chromatographic Interfaces. Ph.D. thesis. Cincinnati University of Cincinnati (2005). 

Data acquisition from the different types of chromatograph interfaced to the system... 

The analysis was carried out on a Perkin-Elmer 3920B gas chromatograph interfaced to a modified Bendix model 12 time-of-flight mass spectrometer with a variable split between a flame ionization detector and the source of the mass spectrometer. The separation was made on a 15.2 m x 0.51 mm SCOT column coated with OV 17 and temperature programmed from 100°-250°C at 4°C min. ... 

The GC-MS computer system consists of a Perkin-Elmer 990 gas chromatograph interfaced to a Hitachi RMU-6L mass spectrometer which is in turn interfaced to an IBM 1802 computer. The details of this hardware and associated software have been published previously (2). The HRMS system consists of a DuPont Instruments 21-llOB mass spectrometer and a D. W. Mann comparator interfaced to the IBM 1802 computer. Details on this system are available elsewhere (3). Both mass spectrometers were operated at 70 eV ionizing energy. 

The extracts are analysed using a Finnigm 9610 gas chromatograph interfaced to a Finnigan 4023 quadropole mass spectrometer and a Super Incos, NOVA 4xdata system with a 70 MB disc drive. Mass spectra is recorded with 1 scan per 0,6 sec in full scan mode (35-400 amu). The mass spectrometer is operated in the electron impact mode at 70e V. The analysis is performed using a 30m DB-5 fused silica capillary colunm with 0,25 pm film thickness (J W Scientific, Inc.). The iigector temperature is kept at 270°C, the interface oven at 250°C and the ion source at 270°C. The oven is initially held at 30°C for 5 mm and increased 4°C per minute to 300°C and kept there for 10 minutes. 

Chromatographic interfaces — Interfaces have been developed for GC, LC, and CE, and have achieved wide application. 

First, the system deviates from ideality as there is a finite rate of mass transfer of solute molecules across the chromatographic interface. The contribution to the overall HETP arising from this kinetic control of the sorption-desorption process increases with increasing mobile phase flow-rate. 

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