Mass spectral interfaces

Several detection systems are utilized in CE for the analysis of nucleoside and nucleotide mixtures. The performances of UV-visible absorption, conductance, electrochemical, a- P radiochemical and fluorescence detectors and mass spectral interfacing have been compared recently. Although UV-visible absorption is generally considered as not very sensitive, low limits of detection (LODs) of 8x10 mol 1 have been reported for purine metabolites using this method. The conductivity technique suffers from poor sensitivity. Electrochemical detection has a higher sensitivity, but its usefulness is limited by the fact that only electroactive species can be detected. Detection by mass spectrometry (MS) leads to poor sensitivity and implies expensive instrumentation. Radiochemical detection has been applied to a- P-labeled thymidine, cytidine, and adenosine... 

Gas chromatography is a most favourable case for interfacing to a mass spectrometer, as the mobile phases commonly used do not generally influence the spectra observed, and the sample, being in the vapour phase, is compatible with the widest range of mass-spectral ionisation techniques. The primary incompatibility in the case of GC-MS is the difference in operating pressure for the two hyphenated instruments. The column outlet in GC is typically at atmospheric pressure, while source pressures in the mass spectrometer range from 2 to... 

In chromatography-FTIR applications, in most instances, IR spectroscopy alone cannot provide unequivocal mixture-component identification. For this reason, chromatography-FTIR results are often combined with retention indices or mass-spectral analysis to improve structure assignments. In GC-FTIR instrumentation the capillary column terminates directly at the light-pipe entrance, and the flow is returned to the GC oven to allow in-line detection by FID or MS. Recently, a multihyphenated system consisting of a GC, combined with a cryostatic interfaced FT1R spectrometer and FID detector, and a mass spectrometer, has been described [197]. Obviously, GC-FTIR-MS is a versatile complex mixture analysis technique that can provide unequivocal and unambiguous compound identification [198,199]. Actually, on-line GC-IR, with... 

Searches through more than one data base in combination would be very desirable. For example, one often possesses mass spectral and nmr data for an unknown and it would be very useful to be able to identify any compounds that match these data in a single search. Work is going on in this area do interface programs so that this approach can be tested. In another development, it is expiected that the CONGEN programs developed for the DENDRAL project [30] will be merged into CIS within the... 

With the advent of the practical API-based LC-MS interfaces, the high specificity of mass spectral analysis permitted a radical decrease in the amount of analytical time invested (sample preparation, injection, chromatography) prior to final detection (Hsieh et al., 2006 Maurer, 2007). Although SRM detection as the final step in LC-MS analysis can incorporate several stages of specificity (Chapter 3), some form of sample preparation/extraction is still performed to remove unwanted... 

LC-ARC-MS is a novel radiochemical detection system that is designed to detect samples with very low levels of radioactivity (Lee et al., 2000 Lee, 2003). Similar to the conventional flow through radiochemical detection method, LC-ARC is an in-line detection technique that allows real-time display of metabolite peaks. LC-ARC can either be set up as a stand-alone system or be coupled with a mass spectrometer to become LC-ARC-MS. Thus, the combination of ARC and MS enhances the sensitivity of peak detection and also provides mass spectral information for structural elucidation of metabohte(s). Other interfaces, coupled with the LC-ARC system, are also available for example, LC-ARC/RD-MS/FC is a system of LC-ARC which couples with a radiochemical detector (RD), a mass spectrometer, and fraction collector (FC) (Lu et al., 2002). 

For this work, a 5 meter x 50 micron ID fused silica column, coated with a 0.25 micron polydimethylsiloxane film was introduced directly into the source chamber through the transfer line normally used for GC/FTMS. A restrictor was created at the end of the column by using a microflame to draw out the end of a 1 meter portion of deactivated but uncoated column to an inside diameter of approximately one micron. Details of the instrumentation used for SFC have been described elsewhere [19]. With the SFC interface in place, pressures in the source chamber were approximately 5 x 10 5 torr. Despite this high source cell pressure, we were able to obtain relatively high quality mass spectral data with analyzer side detection at 5 x 10"7 torr. 

The on-line interfacing of capillary isoelectric focusing with Fourier-transform ion cyclotron resonance-mass spectrometry (FTICR-MS) was shown to be effective for separating minor components of protein mixtures for on-line mass spectral analysis [62-64],... 

An interfaced data system is required to acquire, store, reduce and output mass spectral data. 

New detection systems will be developed for increased sensitivity which will place increased demands on prechromatographic sample treatment. Although many of the proposed liquid chromatographic/mass spectrometric interfaces have shown promise using model compounds (B3, B4, Bll, B22, C2, C6, H17, K4, S3, S29, S30), their routine use for on-line characterization is not yet practical. Similar problems have been encountered with liquid chromatographic/infrared detection (K3S, K36, T3). Detection systems such as electrochemical or radioactivity detectors will find increased use for the selective analysis or spectral characterization of eluting compounds (K24, Ml, Y3, Y4). 

These chromatographic examples demonstrate the utility of PLOT columns for the resolution of the various chemical constituent fractions of shale oil and their compatibility with interfaced IR and mass spectral peak identification. The major advantage of the higher column peak capacity of the PLOT columns makes the latter measurements more feasible particularly for the minor components in the chromatogram. 

Figure 3. Mass spectral characterization of neburon via the moving belt interface top, under methane Cl conditions bottom, under ammonia Cl conditions.

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