Trace organic compounds method

COMPARISON OP REPRESENTATIVE METHODS FOR THE CONCENTRATION OF TRACE ORGANIC COMPOUNDS IN HATER... 

Recovery of Trace Organic Compounds by the Parfait-Distillation Method... 

The isolation method of solvent extraction has been suggested as a potentially feasible process to concentrate trace organic compounds from finished drinking water (4). One positive attribute of the solvent extraction method is that its performance for any given compound is theoretically predictable from a partition coefficient of a compound between the water sample and an organic solvent. The partition coefficient can be experimentally determined for any solute in any two-phase solvent system (7, 8). Variables of the extraction procedure such as solvent-to-water ratio and the choice of solvents can be adjusted to achieve optimum recovery. 

Besides the classical interlaboratory studies, improvement schemes enable laboratories to develop and validate all steps of new or existing analytical procedure(s) in adequately organised successive exercises. Improvement schemes may be considered as preliminary studies for laboratory or method performance studies or certification of reference materials [5]. Such programmes are very valuable when the analytical procedures include several complex and critical steps, e.g. for the determination of trace organic compounds or chemical species. They require a long term involvement of the organiser and participants, as well as investment of resources. 

The use of subtraction methods for concentrating trace organic compounds in environmental analysis was reviewed by Drugov and Berezkin [148] and by Korol [149]. 

Methods to remove trace organic compounds of all types from aqueous solution (J5, 16, 17) have been studied extensively. One was to deal with pesticide pollution of water supplies by using an oxidant for chemical degradation. Among the many chemical oxidants available, certain ones have shown that they reduce the concentration of organic contaminants—e.g., ozone, chlorine dioxide, chlorine, the peroxides, and potassium permanganate (iS, 19, 20, 21). 

A method of enhancing the response preferentially to trace organic compounds is with a membrane inlet. Typically a poly(dimethylsiloxane) membrane is used... 

Most organic compounds occur at extremely low concentrations in seawater. Their determination involves an extraction/sorption step to increase their concentration levels to the sensitivity range of instrumental analytical methods. Compared with other groups of analytes, the risk of adsorptive losses is most important for trace organic compounds. Hierefore, techniques are preferable which involve direct extraction within the sampler or in situ enrichment onto solid adsorbents. Using very large samplers with a comparably high ratio between volume and internal sampler surface, adsorption losses can be minimized but never excluded entirely. 

Nonetheless, derivatization methods have been successfully employed [56-58,65], most notably via use of the diazonium salt of 4-nitroaniline, For instance, in the study of phenylamide pesticides, no resonance was observed from these colorless compounds however, after derivation to azo dyes, detection limits of (2-4) X 10 M were achieved for monuron, diuron, a-napthylacetamide, and /3-napthylacetamide. Selectivity in distinguishing derivatized products from isomers of monosubstituted phenols (i.e., ortho, meta, and para) has also been shown to be successful, as illustrated in Fig. 8. Moreover, coupling the sensitivity and selectivity of RRS to the well-known spot-test method (qualitatively identifies colorless solutions only by visual identification of the colored products), a more accurate and sensitive characterization method of trace organic compounds is achieved. Such work has been conducted by Nakamura et al. in the characterization and detection of phenols and heterocyclic aromatic compounds on fruit rinds and food preservatives [58]. 

An application of surface-assisted laser desorption-ionization (SALDI) method for practical, ultrahigh sensitivity detection of aromatic amines by GC-MS is reported. The prototype analytical device for trace detection of different organic compounds is created. 

As a possible method of concentrating trace amounts of bioactive organic compounds occurring in the hydrosphere, adsorption properties of various compounds have been explored by employing hydrous metal oxides as the adsorbents. To date, a family of organophosphoms compounds and carbonic acids were adsorbed onto hydrous iron oxide, along with the adsoi ption of monosaccharides onto hydrous zirconium oxide. 

The method of Carius for the determination of chlorine in organic compounds is, of course, absolutely quantitative, but is very tedious, and is scarcely suitable for the detection of very small traces of chlorine, as the weight of oil taken in a Carius determination never exceeds 0 5 grams. 

The most frequently used methods of analyte isolation and concentration for organic compounds involve distillation, extraction auid adsorption techniques. Some typical applications of these techniques and their attendant -advantages and disadvantages for the analysis of trace organic solutes in water are summarized in Table 8.1 [4,26]. These methods will be elaborated on below and in subsequent sections of this chapter. 

A wealth of other data can be obtained from the use of US as an analytical method. Sonoelectrochemical analysis of trace metals [220] and organic compounds [221] has been reported. Ultrasonic atomisation [222] is used in many fields where a dispersion of liquid particles is required. Ultrasonic nebulisation (USN) is used for analysis of organic solutions in conjunction with ICP-AES/MS [223,224] and MIP-AES [225],... 

Probably the most extensive use of particle morphology and microscopy has been in the area of chemical microscopy. With this approach, derivatives of the analyte species are prepared, crystallized, and identified through the morphological characteristics of these derivatives [21]. Most of these applications have been superseded by modem methods of analysis, but the microscopic method can still be used by skilled practitioners for the study of trace quantities of analyte. The literature developed during the heyday of chemical microscopy is too large to be reviewed here, but advances in the field are still chronicled in the Annual Reviews issue of Analytical Chemistry [22]. A substantial review of the optical characteristics of organic compounds is available [23]. 

Chian et al. [69] point out that the Bellar and Iichtenberg [65] procedure of gas stripping followed by adsorption onto a suitable medium and subsequent thermal desorption onto a gas chromatograph-mass spectrometer is not very successful for trace determinations of volatile polar organic compounds such as the low molecular weight alcohols, ketones, and aldehydes. To achieve their required sensitivity of parts per billion, Chian et al. [69] carried out a simple distillation of several hundred ml of sample to produce a few ml of distillate. This achieved a concentration factor of between 10 and 100. The headspace gas injection-gas chromatographic method was then applied to the concentrate obtained by distillation. 

A most important technique which has been developed as an extension of the isotope dilution principle is that of radioimmunoassay (RIA). Analyses by this method employ substoichiometric amounts of specific binding immuno-chemical reagents for the determination of a wide range of materials (immunogens) which can be made to produce immunological responses in animals such as sheep or rabbits. It is possible to combine the specificity of an immunochemical reaction with the extreme sensitivity of radiotracer detection. Analytical methods based upon these principles have achieved wide applicability in the determination of organic compounds at trace levels. 

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