Aromatics test, liquid chromatography

Recent studies, including the use of Microtox and ToxAlert test kits [55,56], were carried out for the determination of the toxicity of some non-ionic surfactants and other compounds (aromatic hydrocarbons, endocrine disruptors) before implementation on raw and treated wastewater, followed by the identification and quantification of polar organic cytotoxic substances for samples with more than 20% inhibition. Furthermore, the study of their contribution to the total toxicity was obtained using sequential solid-phase extraction (SSPE) before liquid chromatography-mass spectrometry (LC-MS) detection. This combined procedure allows one to focus only on samples containing toxic substances. 

Certificate of Analysis, Standard Reference Material 869a column selectivity test mixture for liquid chromatography (polycyclic aromatic hydrocarbons), National Institute of Standards and Technology (NIST), Gaithersburg, MD, 1998. Available at http //www.nist.gov/SRM... 

Enzyme immunoassay kits are now available for qualitative field testing or for laboratory screening and semiquantitative analysis of pesticides, herbicides, polychlorinated biphenyls (PCBs), mononuclear and polynuclear aromatic hydrocarbons, pentachlorophenol, nitroorganics, and many other compounds in aqueous and soil samples. Certain analytes may be quantitatively determined as well, with a degree of accuracy comparable to gas chromatography or high performance liquid chromatography determination. The method is rapid and inexpensive. 

Various workers [23-32] have studied the application of high performance liquid chromatography to the determination of PAHs in water samples. Hagenmaier et al. [31] used a reversed phase high-pressure liquid chromatography procedure for the determination of trace amounts of polycyclic aromatic hydrocarbons in water. Different column packing materials were tested, in conjunction with non polar stationary phases of various polarities, for separation efficiency, detection limits and long-term stability. The method was suitable for concentrations as low as 2ng L 1 in a IL sample. Compounds... 

Other test methods are available. Content of benzene and other aromatics may be estimated by spectrophotometric analysis (ASTM D-1017) and also by gas-liquid chromatography (ASTM D-2267, ASTM D-2600, IP 262). However, two test methods based on the adsorption concept (ASTM D-2007, ASTM D-2549) are used for classifying oil samples of initial boiling point of at least 200°C (392°F) into the hydrocarbon types of polar compounds, aromatics, and saturates and recovery of representative fractions of these types. Such methods are unsuitable for the majority of naphtha samples because of volatility constraints. 

The behaviour at normal temperatures against aromatic hydrocarbons (toluene, xylene) corresponds to the case just discussed. At high temperatures ( 80 °C), however, the effect of swelling is irreversible organic solvents can dissolve even a HDPE material under these conditions. This very poor solubility of polyethylene requires special high-temperature equipment in liquid chromatography for the determination of the molecule mass distribution or in viscosity measurement, since these measurements must be performed with a hot test solution. 

Standard Test Method for Fatty Acid Composition by Gas-Liquid Chromatography of Methyl Esters Oils and Oil Acids in Solvent-Redncible Paints Standard Test Method for Analysis of High-Pnrity n-Heptane and Isooctane by Capillary GC Standard Test Method for C8 Aromatic Hydrocarbons by GC... 

Several methods of determination can be used, but two, distillation and gas chromatography are the most popular. Industrial aromatic hydrocarbons are determined by distillation. The temperature is recorded for the initial boiling point, for the sample which has been distilled at 5%, 10%, then at 10% increments up to 90%, then finally at 95%. The temperature should be recorded with precision of 0.1 C. A general test mediod to determine the distillation range of volatile liquids" outlines a similar method of measurement In addition to the measurements at the intervals given above, the temperature of the dry point (distillation temperature of residual quantities) is also recorded. Results must be reported as specified in the method. 

Coal liquids consist of hundreds of individual components and therefore, it is very difficult to identify all the individual components in a sample. The components can be classified as different types such as paraffins, naph-thenics, and aromatics. Because of an MS ability to identify compound-type unique molecular ion fragment patterns, hydrocarbon-type analysis by MS has been practiced for over four decades. ASTM D-2425 specifies a standard test method for hydrocarbon types in middle distillates by MS, with a boiling range of 20 343°C. This is within the boiling range of many CTL process products, so GC-MS has been used for hydrocarbon-type analysis in coal liquids. Initial product separations are conventionally needed for GC-MS-type analysis, such as distillation (ASTM D-86), elution chromatography. 

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