Gas chromatography-mass spectrometry GC-MS

It is of primary importance to find the optimum operating conditions for GC 

Analytes condense at the entrance of the column and are subsequently separated based on their molecular mass and polarity. 

These properties determine analyte volatility and, as a result, the residence times in the stationary (liquid) phase (usually an organosilicon oil) and the gaseous mobile phase (usually He). 

More volatile components elute first as they are carried through the column by the carrier gas at lower temperatures. 

Increasing the oven temperature enables the transfer of compounds with higher boiling points from the stationary phase into the vapor phase and their elution from the column. 

FIGURE 2.2 Separation process on a fused silica capillary GC column. 

In principle one could monitor a GC effluent with a nondestructive detector like a TCD, pass it on through a suitable interface, and acquire and print out the mass spectra of peaks as they are eluting. With fast digital data converters and the speed and power of modern desktop PCs, it is better to simply acquire mass spectral data as a continuous sequence of spectra or selected mass fragment signals as the GC run proceeds. A data file in computer memory consists of a sequence of MS scans ordered by retention time. There are three main modes of acquiring and employing such data files  

This powerful, versatile technique can be used to obtain a significant amount of compositional information on plastic samples. It is particularly useful in identifying minor components of the sample such as the stabiliser, antistatic agent and, where appropriate, the crosslinking system. 

It can also be used to investigate the polymer fraction within a sample when the instrument is fitted with a pyrolysis unit set at around 600 °C. 

The technique also plays a role in failure diagnosis by being able to provide information on odours, and 

There are a variety of ways that the sample or fractions of the sample (e.g., an extract) can be analysed by GC-MS. These include static headspace, dynamic headspace, solution injection and pyrolysis. 

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Confirmation of the identities of nitrosamines generally is accompHshed by gas chromatography—mass spectrometry (gc/ms) (46,87). High resolution gc/ms, as well as gc/ms in various single-ion modes, can be used as specific detectors, especially when screening for particular nitrosamines (87) (see Analytical LffiTHODS Trace and residue analysis). 

The combined techniques of gas chromatography/mass spectrometry (gc/ms) are highly effective in identifying the composition of various gc peaks. The individual peaks enter a mass spectrometer in which they are analyzed for parent ion and fragmentation patterns, and the individual components of certain resoles are completely resolved. 

Identification of stmctures of toxic chemicals in environmental samples requires to use modern analytical methods, such as gas chromatography (GC) with element selective detectors (NPD, FPD, AED), capillary electrophoresis (CE) for screening purposes, gas chromatography/mass-spectrometry (GC/MS), gas chromatography / Fourier transform infra red spectrometry (GC/FTIR), nucleai magnetic resonance (NMR), etc. 

When the gas chromatograph is attached to a mass spectrometer, a very powerful analytical tool (gas chromatography-mass spectrometry, GC-MS) is produced. Vapour gas chromatography allows the analyses of mixtures but does not allow the definitive identification of unknown substances whereas mass spectrometry is good for the identification of a single compound but is less than ideal for the identification of mixtures of... 

In gas chromatography/mass spectrometry (GC/MS), the effluent from a gas chromatograph is passed into a mass spectrometer and a mass spectrum is taken every few milliseconds. Thus gas chromatography is used to separate a mixture, and mass spectrometry used to analyze it. GC/MS is a very powerful analytical technique. One of its more visible applications involves the testing of athletes for steroids, stimulants, and other performance-enhancing drugs. These drugs are converted in the body to derivatives called metabolites, which are then excreted in the... 

Gas chromatography/mass spectrometry (GC/MS) is the synergistic combination of two powerful analytic techniques. The gas chromatograph separates the components of a mixture in time, and the mass spectrometer provides information that aids in the structural identification of each component. The gas chromatograph, the mass spectrometer, and the interface linking these two instruments are described in this chapter. 

Gardner impact, 243 Gas chromatography/mass spectrometry (GC/MS) analysis, 304 Gaymans, Reinoud J., 135 Gel coats, 30... 

FIG. 18 Determination of alkanesulfonates with thin-layer chromatography (TLC) and gas chromatography-mass spectrometry (GC-MS) clean-up procedure. 

The data in Table I are also significant in terms of the type of analysis to determine the presence of NDMA. In all cases analysis was done using gas chromatography coupled with a Thermal Energy Analyzer, a sensitive, relatively specific nitrosamine detector (12). Further, in six of the studies, the presence of NDMA in several samples was confirmed by gas chromatography-mass spectrometry (GC-MS). The mass spectral data firmly established the presence of NDMA in the beer samples. 

PLC is used for separations of 2 to 5 mg of sample on thin-layer chromatography (TLC) plates (0.25-nun layer thickness) or high-performance TLC (HPTLC) plates (0.1-mm thickness). In these instances, the method is termed micropreparative TLC. The isolation of one to five compounds in amounts ranging from 5 to 1000 mg is carried out on thicker layers. PLC is performed for isolation of compounds to be used in other tasks, i.e., further identification by various analytical methods, such as ultraviolet (UV) solution spectrometry [1] or gas chromatography/mass spectrometry (GC/MS) [2], obtaining analytical standards, or investigations of chemical or biological properties [3]. 

To identify the volatile components, gas chromatography-mass spectrometry (GC-MS) is still the method of choice. A comparison of the GC fingerprints of B. carter a and B. serrata reveals the different composition of the volatile fractions (Figure 16.1). Common monoterpenes, aliphatic, and aromatic compounds of olibanum are, e g., pinene, limonene, 1,8-cineole, bomyl acetate, and methyleugenol (Figure 16.2). 

Characterization of various types of damage to DNA by oxygen-derived species can be achieved by the technique of gas chromatography-mass spectrometry (GC-MS), which may be applied to DNA itself or to DNA-protein complexes such as chromatin (Dizdaroglu, 1991). For GC-MS, the DNA or chromatin is hydrolysed (usually by heating with formic acid) and the products are converted to volatile derivatives, which are separated by gas chromatography and conclusively identified by the structural evidence provided by a mass spectrometer. Stable isotope-labelled bases may be used as internal standards... 

When pushed to the limit by overriding human health concerns, residue chemists have achieved detection limits of Ippt (Ingkg ) or even into the low ppqr (1 pg kg ) range. An example at the 1 ppt level is provided by methods for 2,3,7,8-tetrachlorodibenzodioxin (TCDD) in milk and TCDD in adipose tissue. Eor relatively clean matrices such as water and air, preconcentration on solid-phase adsorbents followed by GC or gas chromatography/mass spectrometry (GC/MS) can provide detection limits of 1 ng m and less for air (examples in Majewski and Capel ) and 1 ngL and less for water (examples in Larson et A summary of units of weight and concentration used to express residue data is given in Table 1. 

The requirements regarding commodities which are difficult to analyze are also not very clear. The listed crops do not cause difficulties in each kind of determination [e.g., brassica or bulb vegetables in gas chromatography/mass spectrometry (GC/MS)]. On the other hand, different species of the same crop may have different interference peaks, which may or may not affect quantitation. Presumably, the easiest approach is to perform additional validations, even if the final extracts are not difficult to analyze. In the author s experience, validations should generally include hops and tobacco, if the pesticide is used in these crops. 

To determine the residue levels of dinitroaniline herbicides, GC/NPD or GC/ECD is used in general. An aliquot of GC-ready sample solution is injected into the gas chromatograph under the conditions outlined below. Further confirmatory analysis is carried out using gas chromatography/mass spectrometry (GC/MS) in the selected-ion monitoring (SIM) mode. 

The development of new fiber coatings in the near future should further improve the specificity of SPME and overcome some of the observed matrix effects. Quantification by stable isotope dilution gas chromatography/mass spectrometry (GC/MS) may assist in improving analytical performance. Along with the possible application of micro LC and capillary LC columns to in-tube SPME, the development of novel derivatization methods and the potential for the analysis of fumigant pesticides, SPME appears to be a technique with a future in the analysis of pesticide residues in food. 

Several determination methods such as GC, HPLC, gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) are used for the analysis of neonicotinoid residues. The applications of GC/MS and LC/MS are of increasing importance. The application of HPLC to the determination of neonicotinoids residues is limited, especially when metabolites (such as acetamiprid and nitenpyram) can be easily determined by GC after derivatization. 

Air is sampled through a glass-fiber filter disk for 6 h at a rate of 2 L min. The filter is placed in a vial containing acetonitrile and the vial is heated at 70 °C for 40 min. After cooling, the vial is ultrasonicated for 15 min. An aliquot of the acetonitrile is filtered and analysed by gas chromatography/mass spectrometry (GC/MS). 

Gas chromatography/mass spectrometry (GC/MS) Gas chromatograph equipped with a split/splitless injector, autosampler, DB-5 MS fused-silica column, 15 m x 0.25-mm i.d., 0.25-qm film thickness and mass-selective detector... 

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