Interfacing technique

There is no single LC-MS interface that is ideally suited for all compounds of interest to analytical chemists. It is evident that LC-APCI-MS and LC-PB-MS are currently the LC-MS methods most frequently used for polymer/additive analysis. The two techniques are compared in Table 7.69. When PB and API interfacing techniques are used, much more structural information can be obtained, and unambiguous identification... 

In the analysis of surfactants by MS in combination with interfacing techniques that were able to handle liquids, the FIA—MS and LC—MS methods performed by the API technique have become a powerful tool. No other analytical approach at that time was able to provide as much information as that obtainable with MS and MS-MS. The analysis of surfactants, even in complex mixtures on the one hand, is facilitated... 

The liquid-liquid free interface diffusion (FID) method, in which protein and precipitant solutions are carefully superimposed and left to slowly mix diffusively, was least used in the past due to handling difficulties. However, in the last 4 years the free interface technique has experienced a revival for both screening and optimization procedures. The... 

Mass spectrometry is a valuble tool with which an abundancy of structural information may be obtained from a minute amount of material. Capillary electrophoresis may be interfaced with mass spectrometry by electrospray ionization [124-126] or continuous-flow, fast-atom bombardment methods [127,128]. Several reviews discuss applications of the interfacing techniques, and address the attributes and disadvantages associated with these methods [129,130]. Critical parameters involved in the optimization of CE-electrospray ionization mass spectrometry analysis have been reviewed as well [131],... 

Since PLOT columns, although applied in other areas (8,19), have received little attention in the shale oil field, a number of applications in different areas will be considered. Their ready laboratory preparation makes the evaluation of novel stationary phases straightforward and their sample level compatibility with such interfaced techniques as vapor-phase IR makes them very attractive. 

D. Puig, D. Barcelo, I. Silgoner, M. Grasserbauer, Comparison of three different LC-MS interfacing techniques for the determination of priority phenolic compounds in water, J. Mass Spectrom., 31 (1996) 1297. 

Coupling mass spectrometry (MS) to capillary electrophoresis provides detection and identihcation of amino acids, peptides, and proteins based on the accurate determination of their molecular masses [15]. The most critical part of coupling MS to CE is the interface technique employed to transfer the sample components from the CE capillary column into the vacuum of the MS. Electrospray ionization (ESI) is the dominant interface which allows a direct coupling under atmospheric pressure conditions. Another distinguishing features of this soft ionization technique when applied to the analysis of peptides and proteins is the generation of a series of multiple charged, intact ions. 

Compared with gas chromatographs, it is more difficult to interface liquid chromatographs with mass spectrometers because the analytes are dissolved in a liquid rather than a gas. As discussed previously, several interface techniques have been developed for coupling a liquid chromatograph to a mass spectrometer, which has allowed HPLC-MS and HPLC-MS/MS to be successfully applied to a wide range of compounds. In theory as long as a compound can be dissolved in a liquid, it can be introduced into an HPLC-MS system. Thus polar and nonpolar analytes and large molec-... 

The introduction of the thermospray interface in the mid to late 1980s provided the first efficient LC-MS connecting technique. With the relatively new interface techniques of electrospray interface and the complementary atmospheric pressure chemical ionization interface (APCI), the full potential of the LC-MS system can now be achieved. 

These interface techniques for connecting the HPLC with the MS-system are very sensitive for most of the substances of interest to the flavour industry. Therefore, HPLC-MS coupling techniques have become an increasingly powerful tool for quality control of flavourings, especially for the analysis of complex mixtures like process flavourings or contaminants present in such complex mixtures. New developments in the area of mass detection systems, such as time-of-flight (ToF) mass analysers and tandem mass spectrometry systems or the features of matrix-assisted laser desorption ionization (MALDI) techniques, may enhance the analytical capabilities of these systems in the near future [16, 17, 28-31 ]. 

Three LC-MS interfacing techniques were compared. When using the thermospray (TSP) interface, [M — H] or [M - - CHsCOO]" were obtained as the main ions. APCI and ion spray (ISP) interfaces gave [M — H] at 20-30 V as the main ion. Calibration graphs were linear from 1 to 100 ng for each compound with repeatability values of 15-20%. Instrumental LOD for APCI were 3-180 ng in full scan and from 0.001-0.085 ng in SIM mode. Instrumental LOD for ISP and TSP were larger by approximately one order of magnitude . 

Nishimura, S. et al., Zeta potential measurement of muscovite mica basal plane-aqueous solution interface by means of plane interface technique, 7. Colloid Interf. Sci., 152, 359, 1992. 

The so-called plane interface technique is a modiflcation of the electroosmotic method, in which submicrometer particles are used as probes to visualize the osmotic velocity proflle close to an interface. The method allowed precise determination of the potential at mica, qnartz, sapphire, and fused-silica snrfaces as a function of The attempF to apply the plane... 

Another interfacing technique that has stimulated significant interest in recent years involves the interfacing of CE with API/MS (124-130). In this technique, charged compounds are separated under the influence of a high electric field in small-diameter capillary tubes filled with buffer. Efficient separations, short anal-... 

Figure 8.21. Two interface techniques used for DTA-MS by Aspina et ai. (79). Interface ( ) is continuous inlet system with bypass (b) membrane separator. 

Numerous additional advances in GC/MS occurred throughout the last decade. Mass spectrometers have now become almost routine, reliable instruments. Improvements in design of both sector and quadrupole instruments is today reflected in greater spectral resolution and sensitivity parameters. Versatility of the GC/MS combined instruments has been dramatically improved by better interfacing techniques and an increased use of capillary columns. The chemical ionization methods have become important for work with relatively unstable molecules there is a significant rationale for their increasing use in biochemical research. 

---