LC-thermospray

An LC-thermospray MS assay was used for the determination of FZD in porcine tissue. Frozen pulverized tissue was homogenized with MeOH McIlvaine buffer, and the supernatant was extracted with dichloromethane. The organic layer, evaporated and reconstituted in... 

Leachate samples from industrial landfills were analysed by LC-NMR and LC-thermospray (TSP)-MS with emphasis on organic acids [12], After removal of the neutral and basic components by pre-extraction with methylene chloride,... 

Table 6.4 Aromatic carboxylic and sulfonic acids identified in a leachate sample by LC - thermospray-MS. Reprinted from Benfenati, E., Pierucci, P., Fanelli, R., Preiss, A., Godejohann, M., Astratov M., Levsen, K. and Barcelo, D., J. Chromatogr., A, 831, 243-256, copyright (1999) with permission of Elsevier Science. 

An initial analysis of urine from the two accidental casualties reported above, using LC-thermospray/... 

There are a few analytical methods for pirlimycin. The method of Homish et al. uses acidified acetonitrile as extractant for both tissues and milk, followed by a solvent partition and C18 SPE. Final determination is by RP-LC-thermospray MS. The method of Martos et al. uses acetonitrile for extraction followed by a simple defatting step with hexane prior to determination by LC-ESI-MS/MS. 

Vitamin D and its metabolites can be detected on the basis of their native UV absorption (Amax = 264 nm) or after conversion to isotachysterols (Amax = 301 nm). However, because of the inherent poor selectivity and sensitivity of this approach quantitation is mostly performed offline by a radioligand assay. Several metabolites have also been determined in plasma by LC-thermospray MS. 

Narrow-bore h.p.l.c.(0.22 mm id, 3 or 5 /im silica particles)-e j.-m.s. with gradient elution has been applied to glucose, sucrose, myo-inositol. and the cyanogenic glucoside dhurrin. Reversed-phase h.p.Lc.-thermospray m.s. and m.s.-m.s. has been used to identify and determine desulphogluco-sinolates derived from plant material. ... 

Applications of h.p.Lc. - thermospray m.s. techniques to the analysis of natural iridoid glycosides, four components of the aminoglycoside gentamicin complex, urinary metabolites of... 

Cs-Ci6 alkylpolyglycosides Bench-scale biodegradation media Water SPE on C 8 cartridge (MeOH elution) sludge Freeze-dry, MeOH and 98 2 MeOH/12 M HCl extraction, extracts neutralized, freeze-dry, and concentrated by SPE on Ci (MeOH elution) FIA-thermospray MS and LC-thermospray MS 202... 

In many applications in mass spectrometry (MS), the sample to be analyzed is present as a solution in a solvent, such as methanol or acetonitrile, or an aqueous one, as with body fluids. The solution may be an effluent from a liquid chromatography (LC) column. In any case, a solution flows into the front end of a mass spectrometer, but before it can provide a mass spectrum, the bulk of the solvent must be removed without losing the sample (solute). If the solvent is not removed, then its vaporization as it enters the ion source would produce a large increase in pressure and stop the spectrometer from working. At the same time that the solvent is removed, the dissolved sample must be retained so that its mass spectrum can be measured. There are several means of effecting this differentiation between carrier solvent and the solute of interest, and thermospray is just one of them. Plasmaspray is a variant of thermospray in which the basic method of solvent removal is the same, but the number of ions obtained is enhanced (see below). 

The LC/TOF instmment was designed specifically for use with the effluent flowing from LC columns, but it can be used also with static solutions. The initial problem with either of these inlets revolves around how to remove the solvent without affecting the substrate (solute) dissolved in it. Without this step, upon ionization, the large excess of ionized solvent molecules would make it difficult if not impossible to observe ions due only to the substrate. Combined inlet/ionization systems are ideal for this purpose. For example, dynamic fast-atom bombardment (FAB), plas-maspray, thermospray, atmospheric-pressure chemical ionization (APCI), and electrospray (ES)... 

LC can be combined with all kinds of mass spectrometers, but for practical reasons only quadrapolar, magnetic/electric-sector, and TOP instruments are in wide use. A variety of interfaces are used, including thermospray, plasmaspray, electrospray, dynamic fast-atom bombardment (FAB), particle beam, and moving belt. 

Mass speetrometry has been used to eharaeterize mieroeystins using the method of fast-atom bombardment (FAB) ionization and MS/MS. Anatoxin-a has been analysed by MS in eombination with gas ehromatography in bloom and water samples, and in benthie eyanobaeterial material and stomaeh eontents of poisoned animals.Reeently, liquid ehromatography (LC) linked to MS has been employed to analyse mieroeystins, where FAB-MS and atmospherie-pressiire ionization (API-MS) have been used, and anatoxin-a, where thermospray (TSP-MS) was iised. ... 

Phenylurea herbicides (urons). Dinocap, Dinoseb, Benomyl, Carbendazim and Metamitron in Waters [e.g. determination of phenylurea herbicides by reverse phase HPLC, phenylurea herbicides by dichloromethane extraction, determination by GC/NPD, phenylurea herbicides by thermospray LC-MS, Dinocap by HPLC, Dinoseb water by HPLC, Carbendazim and Benomyl (as Carbendazim) by HPLC], 1994... 

He then joined the Central Research Establishment of the Home Office Forensic Science Service (as it then was) at Aldermaston where he developed thermogravimetry-MS, pyrolysis-MS, GC-MS and LC-MS methodologies for the identification of analytes associated with crime investigations. It was here that his interest in LC-MS began with the use of an early moving-belt interface. This interest continued during periods of employment with two manufacturers of LC-MS equipment, namely Kratos and subsequently Interion, the UK arm of the Vestec Corporation of Houston, Texas, the company set up by Marvin Vestal, the primary developer of the thermospray LC-MS interface. 

Ionization methods that may be utihzed in LC-MS include electron ionization (El), chemical ionization (Cl), fast-atom bombardment (FAB), thermospray (TSP), electrospray (ESI) and atmospheric-pressure chemical ionization (APCI). 

In summary, it can be said that prior to the development of the thermospray interface there were an increasing nnmber of reports of the analytical application of LC-MS [3] bnt in this present anthor s opinion, based on a nnmber of years of using a moving-belt interface, the technique could not be considered to be routine . The thermospray interface changed this and with the commercial intro-dnction of the combined APCI/electrospray systems in the 1990s the technique, for it now may be considered as a true hybrid technique, has reached maturity (although this should not be taken as a suggestion that there will be no further developments). 

The advantages and disadvantages of this type of interface, particnlarly in comparison to the moving-belt interface which was available at the same time, are listed below. This was one of the first LC-MS interfaces to be made commercially available and, although used in a number of laboratories, its development was halted premamrely by the introduction of the thermospray interface (as we shall see later). 

The thermospray interface overcame many of the problems enconntered with the moving-belt and direct-liquid-introdnction interfaces and with the advent of this, LC-MS became a routine analytical tool in a large number of laboratories. This was reflected in the fact that this was the first type of interface made available commercially by the majority of the mannfacturers of mass spectrometers. 

A thermospray system is shown schematically in Figure 4.6. This consists of a heated capillary through which the LC eluate flows, with the temperature of this capillary being carefully controlled to bring about around 95% vaporization of the liquid. The vapour so produced acts as a nebulizing gas and aids the break-up of the liquid stream into droplets. 

Figure 4.6 Schematic of a thermospray LC-MS interface. From applications literature published by Vestec (Applied Biosystems), Foster City, CA, and reproduced with permission.

The introduction of the thermospray interface provided an easy-to-use LC-MS interface and was the first step in the acceptance of LC-MS as a routine analytical technique. It soon became the most widely used LC-MS interface of those available in the mid to late 1980s. 

Electrospray ionization occurs by the same four steps as listed above for thermospray (see Section 4.6). In contrast to thermospray, and most other ionization methods nsed in mass spectrometry, it shonld be noted that electrospray ionization nnnsnally takes place at atmospheric pressure. A similar process carried out under vacuum is known as electrohydrodynamic ionization and gives rise to qnite different analytical results. This technique has not been developed into a commercial LC-MS interface and will not be considered further. 

In this book, a number of different LC-MS interfaces have been described, where some of these have been included primarily from an historical standpoint. Currently, the most widely used interfaces are, undoubtedly, the electrospray and APCI interfaces and it is these that will be concentrated upon (a search of the Science Direct database [1] for 2001 nsing the term thermospray , previously the most widely used interface, yielded only one paper). 

See footnote cto Table3 LC/PB/MS = hquid chromatography/particle beam mass spectrometry LC/APcl/ESl-MS/MS = liquid chromtography/atmospheric pressure chemical ionization/electrospray ionization tandem mass spectrometry LC/FTIR = Fourier transform infrared LC/TSP-MS/MS = liquid chromatography/thermospray tandem mass spectrometry LC/TSP-MS = liquid chromatography/thermospray mass spectrometry. 

As with GC, the combination of MS and MS/MS detection with LC adds an important confirmatory dimension to the analysis. Thermospray (TSP) and particle beam (PB) were two of the earlier interfaces for coupling LC and MS, but insufficient fragmentation resulted in a lack of structural information when using TSP, and insufficient sensitivity and an inability to ionize nonvolatile sample components hampered applications using PB. Today, atmospheric pressure ionization (API) dominates the LC/MS field for many environmental applications. The three major variants of API... 

The mass spectra of mixtures are often too complex to be interpreted unambiguously, thus favouring the separation of the components of mixtures before examination by mass spectrometry. Nevertheless, direct polymer/additive mixture analysis has been reported [22,23], which is greatly aided by tandem MS. Coupling of mass spectrometry and a flowing liquid stream involves vaporisation and solvent stripping before introduction of the solute into an ion source for gas-phase ionisation (Section 1.33.2). Widespread LC-MS interfaces are thermospray (TSP), continuous-flow fast atom bombardment (CF-FAB), electrospray (ESP), etc. Also, supercritical fluids have been linked to mass spectrometry (SFE-MS, SFC-MS). A mass spectrometer may have more than one inlet (total inlet systems). 

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