Organic compounds trace level identification

GC on a fused silica capillary column with an MS detector should be used whenever possible for the analysis of organic compounds at trace level in complex mixtures. In fact, it allows the extremely high resolution of GC to be combined with the very high sensitivity and identification power of MS, which makes it possible to determine an analyte at low pg mC levels in the final organic extract. However, GC-ECD is very common for PCB determination since it is both the most sensitive and the less expensive technique for chlorinated compounds (5). PCBs can be separated on a 30-50 m fused silica capillary column with 5% phenyl -95% methylpolysiloxane chemically bonded stationary phase (1). On-column injection is very often used, while several oven temperature programmes have been applied for PCB determinations. The initial temperature is generally 10-15°C lower than the boiling point of the solvent and the final one does not exceed 290-300°C. 

Applications of FAB have been succesfully performed in the characterization of a wide range of compounds (dyes, surfactants, polymers...) but little attention has been devoted to the capabilities of this technique to solve environmental concerns, such as organic pollutants identification in water. The widespread use of surfactants in the environment has required the emplo yment of both sensitive and specific methods for their determination at trace levels. GC/MS and HPLC procedures has been used for the determination of anionic (LAB s) and non ionic surfactants (NPEO) in water (1-4). Levsen et al (5) identified cationic and anionic sirrfactants in surface water by combined field desorption/ collisionally activated decomposition mass spectrometry (FD/CAD), whereas FAB mass spectrometry has been used for the characterization of pine industrial surfactants (6-8). 

Advances in sample extraction and analytical instrumentation now allow the identification of trace levels of pharmaceutical compounds and their metabolites in wastewater effluent, surface and groundwater. Currently there is a need for additional or expanded toxicological studies to determine the effect of a wider range of pharmaceuticals on aquatic and wetland organisms. 

Identification of the diacid butyl esters was conducted by comparing the GC retention times with those of authentic standards. Mass spectra of the organic compounds were also obtained with a GC/MS (ThermoQuest, Trace MS) using a similar GC condition. Duphcate analyses of several filter samples showed that the analytical errors for major diacids were within 10%. Spiked experiments using authentic standards (oxalic, malonic, succinic and adipic acids) in quartz filter showed that recoveries were 77% for oxalic acid and better than 86% for other diacids. Recoveries of glyoxylic acid, pyruvic acid, and methylglyoxal were 88, 72, and 47, respectively (Kawamura and Yasui, in preparation). The procedural blanks showed that contamination levels of the diacids during the analysis were less than 5% of the sample. The data reported here are corrected for the procedural blanks, but not for recoveries. 

Many organic pollutants in water can be analyzed with LC techniques at trace levels. From the different LC methods discussed in this entry, several remarks can be made 1) For routine water monitoring, LC/DAD is the most common detection device used to analyze polar, thermolabile, and non-volatile compounds due to its robustness, high sample throughput, and the possibility of obtaining a UV spectrum that can be used for analyte confirmation 2) LC/FD and ECD are more selective and sensitive than DAD and are especially useful for the monitoring of PAHs, carbamates, and phenols 3) LC/ MS with API sources and different combinations of mass analyzers have become highly robust techniques and the preferred option for the identification, confirmation, and... 

In the shore laboratory, the samples must be handled with the care needed for any trace analysis. It must be remembered that the total amount of organic carbon in seawater is around 1 ppm single compounds are likely to be present at ppb levels. In order to collect enough material even for positive identification of some of the compounds present, the materials must often be concentrated. 

In the modem world, trace analysis plays an important role in such areas as ecology, chemical engineering, food processing, biomedical analysis, and dmg chemistry. Advanced, sensitive, and precise analytical methods allow identification and quantification of different compounds, both organic and inorganic, including macro-molecular complexes. All these methods present very good detection and quantification levels, up to parts per trillion (ppt) or parts per quadrillion (ppq). 

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