In This Issue In search of GC retention times and response factors When identifying and quantifying the components of complex reaction mixtures, standards are needed to determine the response factor for each component; often, however, such standards do not exist. During their investigation of aquathermolysis of organic compounds at high temperatures (for which standards do not exist for many components), Alan R. Katritzky and colleagues of the University of Florida and Mati Karelson of the University of Tartu (Estonia) devised a system of six-parameter equations used to predict response factors and retention times for a large and diverse set of organic compounds. The estimated standard deviations for the retention time and response factor are 4% and 15%, respectively, (p. 1799)
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SFE optimization Interest in the use of supercritical fluid extraction as a replacement method for Soxhlet extraction of organic contaminants from soils and other environmental specimens is increasing because SFE is faster and uses much less organic solvent. However, operating conditions for SFE of pesticides and other contaminants have not been standardized. Susanne Reindl and Frank Hofler of Dionex (Germany) examine the effects of extraction pressure, temperature, fluid volume, cosolvents, flow rate, restrictor temperature, and sample collection method on SFE recovery of a series of PAHs from soil. (p. 1808)
ITP/CZE for determining herbicides To minimize the number of sample-handling steps and to shorten the analysis time, coupling sample preparation with the final separation technique is desirable. Isotachophoresis (ITP) concentrates analytes by removing the matrix constituents; capillary zone electrophoresis (CZE) offers low detection limits. D. Kaniansky of Comenius University (Slovakia) and colleagues demonstrate the effectiveness of ITP/CZE for the determination of trace amounts of paraquat and diquat in water. The detection limit is 1(T9M. (p. 1817)
Eye on wastewater BOD It takes several days to measure the activSPECTROSCOPY ity of aerobic microorganisms in wastewater through tests for biochemical oxygen demand (BOD). Otto Wolfbeis and coworkers at the Karl-Franzens University (Austria) describe the fabrication and use of a fiber-optic microbial optode biosensor to measure oxygen with fluorescence detection. The biosensor, which has typical response times of 5-10 min, gives results that correspond to conventional BOD measurements, (p. 1841)
Balancing sample delivery by laser ablation Laser ablation of solid samples for atomic spectrometry is growing in importance because it requires no sample preparation and may be useful for applications such as field screening of soils at hazardous waste sites. But the sample-to-sample reproducibility of laser ablation is comparatively poor and, thus far, there are few satisfactory ways to normalize the amount of sample introduced into the spectrometer. Arthur D'Silva and colleagues at the U.S. Department of Energy-Ames Laboratory describe the use of a modified piezoelectric quartz crystal microbalance as a mass sensor for aerosol mass measurement to quantitate the laser ablation of a sample, (p. 1911)
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Analytical Chemistry, Vol. 66, No. 11, June 1, 1994 623 A
