Organic compound analysis procedures

Complex matrices such as soil solutions or landfill leachates usually require clean up where interfering compounds are removed prior to organic acid analysis. Procedures used include removal of humin-like substance by passing through special cartridges or precipitation after... 

The continuous advances in instrumental techniques for organic compound analysis enable us to be rigorous in the analysis of carotenoid pigments. The following sections describe the main stages in the procedures of extraction, isolation, identification, and quantification of carotenoid pigments in foods of plant and animal origin. 

In order to detect these elements in organic compounds, it is necessary to convert them into ionlsable inorganie substanees so that the ionic tests of inoiganio qualitative analysis may be applied. This conversion may be accomplished by several methods, but the best procedure is to fuse the organic compound with metallio sodium (Lassalgne s test). In this way sodium cyanide, sodium sulphide and sodium halides are formed, which are readily identified. Thus ... 

Infrared Spectrophotometry. The isotope effect on the vibrational spectmm of D2O makes infrared spectrophotometry the method of choice for deuterium analysis. It is as rapid as mass spectrometry, does not suffer from memory effects, and requites less expensive laboratory equipment. Measurement at either the O—H fundamental vibration at 2.94 p.m (O—H) or 3.82 p.m (O—D) can be used. This method is equally appticable to low concentrations of D2O in H2O, or the reverse (86,87). Absorption in the near infrared can also be used (88,89) and this procedure is particularly useful (see Infrared and raman spectroscopy Spectroscopy). The D/H ratio in the nonexchangeable positions in organic compounds can be determined by a combination of exchange and spectrophotometric methods (90). 

The system of anionic surfactants is another example of organic compounds mixtures. The procedure of their determination is proposed using coordinate pH in two-dimensional spectra of ionic associates anionic surfactants with rhodamine 6G. This procedure was tested on the analysis of surfactant waters and domestic detergents. 

Headspace analysis has also been used to determine trichloroethylene in water samples. High accuracy and excellent precision were reported when GC/ECD was used to analyze headspace gases over water (Dietz and Singley 1979). Direct injection of water into a portable GC suitable for field use employed an ultraviolet detector (Motwani et al. 1986). While detection was comparable to the more common methods (low ppb), recovery was very low. Solid waste leachates from sanitary landfills have been analyzed for trichloroethylene and other volatile organic compounds (Schultz and Kjeldsen 1986). Detection limits for the procedure, which involves extraction with pentane followed by GC/MS analysis, are in the low-ppb and low-ppm ranges for concentrated and unconcentrated samples, respectively. Accuracy and precision data were not reported. 

The analyte must be converted into a volatile compound suitable for mass-spectrometric analysis. Procedures for C, N, and O follow those developed for conventional organic microanalysis— oxidation of organic C to COj, reduction of organic N to N2, and conversion of O2 into CO or COj. In most procedures, cryogenic purification of the products is carried out before mass spectrometry, and both off-line and on-line procedures have been developed. 

Applications APCI-MS is often more widely applicable than ESI-MS to the analysis of classes of compounds with a low molecular weight, such as basic drugs and their metabolites, antibiotics, steroids, oestrogens, benzodiazepines, pesticides, surfactants, and most other organic compounds amenable to El. LC-APCI-MS has been used to analyse PET extracts obtained by a disso-lution/precipitation procedure [147]. Other applications of hyphenated APCI mass spectrometric techniques are described elsewhere LC-APCI-MS (Section 7.33.2) and packed column SFC-APCI-MS (Section 73.2.2) for polar nonvolatile organics. 

GC-C-IRMS instrumentation enables the compound-specific isotope analysis of individual organic compounds, for example, n-alkanes, fatty acids, sterols and amino acids, extracted and purified from bulk organic materials. The principle caveat of compound-specific work is the requirement for chemical modification, or derivatisation, of compounds containing polar functional groups primarily to enhance their volatility prior to introduction to the GC-C-IRMS instrument. Figure 14.7 summarises the most commonly employed procedures for derivatisation of polar, nonvolatile compounds for compound-specific stable isotope analysis using GC-C-IRMS. 

Derivatization of organic compounds has been traditionally used in organic analysis as additional evidence for structural features, to simplify analytical procedures, to improve the sensitivity or accuracy of the analysis, etc. It is worthwhile recalling briefly the requirements for a good derivatizing scheme that were summarized elsewhere in the Functional Group series1 3, because such schemes will be an important part of the analytical chapters. 

The determination of small amounts of organic compounds in complex matrices has long been a difficult analytical problem. If separation procedures are used they frequently need to be complex and are time consuming. By using specific binding reagents, RIA methods avoid such difficulties and facilitate the analysis of many compounds at picogram levels... 

In many cases, extraction of organic compounds requires that the extract be cleaned up before analysis. This may be as simple as centrifugation, but it may also involve concentration or evaporation of the solvent. Another approach is to absorb the analyte of interest on an absorbant and subsequently to extract it into another solvent. This may be necessary to ensure that the extract is compatible with the analytical procedure to be used. 

Keith et al. [36] and Reijnders et al. [37] reviewed applications of gas chromatography-mass spectrometry to sediment analysis. Lopez-Avila et al. [38] investigated the efficiency of dichloromethane extraction procedures for the isolation of organic compounds from sediments prior to gas chromatography-mass spectrometry. The compounds investigated were the 51 priority pollutants listed by the Environmental Protection Agency, USA. 

WAUTERS, E., E.WALRAVENS, E.MUYLLE and G.VERDUYN (1983). An evaluation of a fast sampling procedure for the trace analysis of volatile organic compounds in ambient air. Environm Monitor.Assessm. 3, 151-160. 

Chemical analysis of odorants in ambient air is hampered by the presence of a plethora of volatile organic compounds, which do not contribute to the odour. Nevertheless application of either powerful separation and identification techniques, such as the GC-MS combination, or specific GC-detection or absorption procedures allow qualitative and quantitative determination of odourants. Improvements are under way to achieve the sensitivity necessary for relevant immission concentrations, which go down to 0.1 ppb for some odorants. 

As regards a contaminated soil, this type of analysis may not be possible because the various hydrocarbons cannot be extracted from the sample with equal efficiency. Volatile organic compounds require special procedures to achieve satisfactory recovery from the soil matrix. It thus becomes important to distinguish between those compounds that are considered to be volatile and those that rank as semi- or nonvolatile compounds. 

STL are accredited by the Department of Trade and Industry via the National Measurement Accreditation Scheme (NAMAS). This covers all aspects of laboratory operations, such as organization of the laboratory and methodology, equipment and staff training, quahty-control systems and storage of data. The company acquired the first accreditation in the UK for the analysis of organic compounds by GC-MS. It also operates appropriate procedures to conform with the Department of Health s Good Laboratory Practice (GLP) recommendations. 

In the following discussion, three types of air pollutant analytical data will be examined using principal component analysis and the K-Nearest Neighbor (KNN) procedure. A set of Interlaboratory comparison data from X-ray emission trace element analysis, data from a comparison of two methods for determining lead In gasoline, and results from gas chromatography/mass spectrometry analysis for volatile organic compounds In ambient air will be used as Illustrations. 

The mass spectrometer GC detector has a high degree of compatibility with the purge and trap technique, and GC/MS has been employed widely with this isolation and concentration procedure for the analysis of volatile organic compounds. The mass spectrometer is strongly recommended for samples where there is a possibility of unexpected compounds, and for broad spectrum analyses f 6J of poorly defined samples. 

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