GC-MS techniques

It was found, that at standard gas-chromatograph sampling of 1 pL of analyte solution the limit of detection for different amines was measured as 0.1-3 ng/ml, or of about 1 femtomole of analyte in the probe. This detection limit is better of published data, obtained by conventional GC-MS technique. Evidently, that both the increasing of the laser spot size and the optimization of GC-capillary position can strongly improve the detection limit. 

What is common to all of these areas is that the relevant number of published GC-GC papers is very small when compared to those concerning single-column and GC-MS methods. While approximately 1000 papers per year are currently published on single-column GC methods and, in recent years, nearly 750 per year on GC-MS techniques, only around 50 per annum have been produced on two-dimensional GC. Of course, this may not be a true reflection of the extent to which two-dimensional GC is utilized, but it is certainly the case that research interest in its application is very much secondary to that of mass spectrometric couplings. A number of the subject areas where two-dimensional methods have been applied do highlight the limitations that exist in single-column and MS-separation analysis. 

Azepine (m/z 93) was first detected and characterized by application of GC/MS techniques to the thermolysis products of 3-[hydroxy(diphenyl)methyl]-3//-azepine.91... 

Acridine-9-carbaldehyde (24%) is one of several products formed from the oxidation of 5//-dibenz[A/]azepine with tert-butyl hypochlorite in dichloromethane at — 70 C.229 The reaction is even more complex in the presence of silver(I) trifluoroacetate, and an analysis of the reaction mixture by GC-MS techniques reveals the presence of eleven products, the major ones being acridine (37%), an unidentified 5//-dibenz[/ ,/]azepinecarbaldehyde (23%) and acridine-9-carbaldehyde (9 %). 

Interpretation Active component A is so stable that a shelf-life in excess of 60 months could be assigned (it is unusual for a pharmaceutical to be approved for more than 5 years). Component B, however, undergoes hydrolysis (this fact has to be independently established, i.e., by GC/MS techniques, or equivalents). (See Fig. 4.26.) The data points cover an incomplete 24-month stability program T - 0, 3, 7, 24). The intercept is at 104.3%, an indication for over-dosing, and the slope is = 0.49 [%/month]. The... 

The GC-MS techniques give much more chemical information than does measurement of only 8-OH-dGua. However, the hydrolysis and derivatization procedures are lengthy and tedious, and may destroy some modified bases, e.g. hydroxymethyluracil (Djuric etal., 1991). It has also been speculated that they might create artefacts, e.g. if the amounts of modified bases increase during the preparation procedures. Data surest that formic acid hydrolysis does not create additional 8-OH-Gua in DNA (Halliwell and Dizdaroglu, 1992) but the question is currently open as to whether the derivatization procedures might do so. 

Polymer extracts are frequently examined using GC-MS. Pierre and van Bree [257] have identified nonylphenol from the antioxidant TNPP, a hindered bisphenol antioxidant, the plasticiser DOP, and two peroxide catalyst residues (cumol and 2-phenyl-2-propanol) from an ABS terpolymer extract. Tetramethylsuccino-dinitrile (TMSDN) has been determined quantitatively using specific-ion GC-MS in extracts of polymers prepared using azobisisobutyronitrile TMSDN is highly volatile. Peroxides (e.g. benzoyl or lauroylperoxide) produce acids as residues which may be detected by MS by methylation of the evaporated extract prior to GC-MS examination [258]. GC-MS techniques are... 

Most dyes, including sulfonated azo dyes, are nonvolatile or thermally unstable, and therefore are not amenable to GC or gas-phase ionisation processes. Therefore, GC-MS techniques cannot be used. GC-MS and TGA were applied for the identification of acrylated polyurethanes in coatings on optical fibres [295]. Although GC-MS is not suited for the analysis of polymers, the technique can be used for the study of the products of pyrolysis in air, e.g. related to smoke behaviour of CPVC/ABS and PVC/ABS blends [263],... 

Quinolizine alkaloids, including sophocarpine, matrine and sophoridine have been determined by GC-MS techniques in kuhuang, a traditional Chinese medicine (GC = gas chromatography) <2005MI967>. Similarly, GC-MS has allowed a phytochemical study of the quinolizidine alkaloids of Genista tenera <2005MI264>. 

The following paragraphs describe some case studies related to procedures based on GC/MS techniques to archaeological and art objects. 

Furthermore, the major disadvantages encountered in GC/MS, i.e. undetectability of synthetic polymers and unpredictable interferences due to their presence, may be avoided using the Py-GC/MS technique. All these aspects strongly suggest how useful, and in some cases fundamental, analytical pyrolysis is in the analysis of complex samples, such as those collected from works of art, to implement and support results obtained with wet chemical pretreatment followed by GC/MS analysis. 

As an alternative, a two-step Py-GC/MS technique can be applied allowing the identification of volatile diterpenoids in the first step and of the polymeric fraction in the second step [33]. The procedure involves an on-line derivatization at 250°C with TMAH, followed by the pyrolysis of the remaining high molecular weight fraction. 

Techniques are available to quantify the generation of smoke, toxic and corrosive fire products using the NBS Smoke Chamber (15), pyrolysis-gas chromatography/mass spectrometry (PY-GC-MS) (J 6), FMRC Flammability Apparatus (2,3,5,17,18), OSU Heat Release Rate Apparatus (13) and the NIST Cone Calorimeter (JJO. Techniques are also available to assess generation of 1) toxic compounds in terms of animal response (19), and 2) corrosive compounds in terms of metal corrosion (J 7). In the study, FMRC techniques and AMTL PY-GC-MS techniques were used. 

The total number of compounds identified using the PY-GC-MS technique varied from 19 for MTL 5 to 39 for MTL 2. 

The analysis of WW samples has been dominated by the use of immunoassays and GC-MS techniques. However, in recent years, LC-MS and LC-MS/MS have gained in popularity, because the above-mentioned preceding hydrolysis step (needed for immunoassay analysis) and derivatization step (needed for GC-MS analysis) are not necessary. 

Quite often a normal electron ionization mass spectrum appears insufficient for reliable analyte identification. In this case additional mass spectral possibilities may be engaged. For example, the absence of the molecular ion peak in the electron ionization spectrum may require recording another type of mass spectrum of this analyte by means of soft ionization (chemical ionization, field ionization). The problem of impurities interfering with the spectra recorded via a direct inlet system may be resolved using GC/MS techniques. The value of high resolution mass spectrometry is obvious as the information on the elemental composition of the molecular and fragment ions is of primary importance. 

The analytes are typically extracted from the biological matrix using solvent extraction or solid phase extraction (SPE). Most analytes require some form of chemical derivatization prior to analysis by GC-MS techniques, whereas with LC-MS-MS no further treatment of the extract is required. The extracts obtained from urine are relatively dirty because of the many endogenous compounds that are present. It is for this reason that the very selective techniques of GC-MS-MS, GC-HRMS, or LC-MS-MS are required to detect some of the prohibited substances that have low detection levels. 

Today, GC-MS (see Section 4.1.1) is a golden standard for detection and quantification of drugs and poisons volatile under GC conditions, whereas nonvolatile compounds require LC-MS (see Section 4.1.2). The GC-MS technique is much more popular for identification purposes than LC-MS, because of the easy availability of the reference mass spectra for many xenobiotics and their derivatives, either in printed or computer form. The most popular libraries are the NIST library, which contains the mass spectra of 130,000 compounds, the Wiley Registry of Mass Spectral Data, which contains 390,000 reference spectra, and the Pfleger-Maurer-Weber library, with 6,300 mass spectra and other data, such as chromatographic retention indexes. 

Sediment and soil samples are homogenized and extracted. Clean-up procedures are required prior to analysis by GC/ECD or GC/MS techniques (Lopez-Avila et al. 1992 Moseman et al. 1977 Saleh and Lee 1978 Tiernan et al. 1990). For sediment, soil, and sludge, recoveries were good (>85%) with sensitivity in the low ppb range (Moseman et al. 1977 Saleh and Lee 1978). Precision is good ( <6% RSD) (Saleh and Lee 1978). Analytical difficulties (unacceptable recovery not detectable using second capillary GC column) were reported (Lopez-Avila et al. 1992 Tiernan et al. 1990). 

Li XH, Meng YZ, Zhu Q, Tjong SC (2003) Thermal decomposition characteristics of poly (propylene carbonate) using TG/fR and Py-GC/MS techniques. Polym Degrad Stab 81 157-165... 

Sulfur can be analyzed by x-ray, GC and GC/MS techniques. Alpha-octacy-closulfur is dissolved in benzene, toluene, or chloroform and analyzed for sulfur by GC using a flame photometric detector or by GC/MS. The characteristic mass ions for its identification are multiples of 32 (i.e. 32, 64, 128, and 256). Sulfur may be identified by mixing a little powder with copper, silver, or mercury at room temperature and identifying the metal sulfide from color change and various instrumental methods. 

The quantitative estimation of species by SEC-GC-MS technique requires a mathematical solution. Two types of approaches for the quantitative estimation can be envisioned. One for the estimation of one or more selected species of interest. The second approach is based on grouping of various species in coal liquids into a few chemical lumps and estimating the quantity of these lumps by using the data derived from the analysis is technique. 

The pyrolysis of 18 polychlorobiphenyls has been studied at 600°C in presence of air, and the polychlorodibenzofurans produced (0.1 to several percent) have been analyzed by GC-MS techniques, although many of the structural assignments are only tentative. Four types of reaction have been uncovered in this process, and they are shown in Scheme 20 for the pyrolysis... 

The technique of mass spectrometry (MS) is itself of no help in the detection of impurities, but in combination with gas chromatography (the GC-MS technique) it would be the method of choice for the identification of impurities. 

An HRTEM study of Zn-Cr Fe oxides using surface-profiling methods in the EM has been reported by Briscoe et al (1984, 1985). Chemical kinetic studies of the oxidation of benzene to maleic anhydride over V-Mo-O catalysts (prepared using 3 V205 Mo03), have been described using GC-MS techniques (Lucas et al 1983). However, microstructural information is limited and there are opportunities for EM studies of these catalyst systems. 

Razskazovskiy et al. employ ESR spectroscopy at low temperatures to investigate electron transfer within brominated DNA [8]. The brominated DNA base electron traps were introduced by bromination of DNA in ice-cooled aqueous solution. The procedure is shown by NMR and GC/MS techniques to modify thymine, cytosine, and guanine, transforming them into 5-bro-mo-6-hydroxy-5,6-dihydrothymine, T(OH)Br, 5-bromocytosine, CBr, and 8-bromoguanine, GBr, derivatives. The bromination products formed in molar ratio close to T(OH)Br/CBr/GBr 0.2 1 0.23 and serve as internal electron scavengers on y-irradiation. Structurally the CBr and GBr are planar, but T(OH)Br is quite nonplanar with the bromine directly above the molecular plane. This disrupts the DNA base stack. Paramagnetic products that result... 

MS techniques, mainly because of its ease of operation, the commercial availability of advanced instrumentation, and the high resolving power of capillary column GC that allows one to carry out specific high-resolution measurement at extremely low levels. The GC-MS techniques are, however, not applicable to all compounds, especially the thermolabile compounds, such as N-nitrosamides, or the nonvolatile NOC. Furthermore, direct HPLC-MS analysis of nonvolatile NOC eliminates the need for derivatization. 

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