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896 A Analytical Chemistry, Vol. 66, No. 18, September 15, 1994
In This Issue method is convenient, no calibration of the method has been re ported at the required level of accuracy. Norman V. Klassen, David Marchington, and Heather C. E. McGowan of the Na tional Research Council of Canada report the calibration of the I3 method against titrations by permanganate with a standard uncertainity of 0.5%. They have also extended the sensitivity of the permanganate titration, which has traditionally been ~3 μΜ H202 when observed visually, to 0.3 μΜ H202 by titrating to the visible endpoint, then determining the excess permanganate by optical absorption, (p. 2921) Improving productivity with expert systems The need for higher productivity has prompted research that will lead to the development of totally automated, unattended instru ment analysis. Martin J. Stillman, Shabari Lahiri, and Bill Yuan of the University of Western Ontario (Canada) expand on their previous work to develop an interconnected set of expert sys tems that permits automated analysis byflameatomic absorp tion analysis. They describe the development of two programs that carry out instrument control, automated sample handling, and data measurement and allow the analytical system to recog nize the failure of data values to meet quality control standards in real time. The researchers report that the critical steps in real time corrective control of analytical measurements are obtain ing measured data values that reflect the instantaneous condi tion in the sample chamber and modeling the measured data val ues in terms of analyte quality, (p. 2954) Screening heavy metals with laser spectroscopy Because of concern overtiieirrole as pollutants, heavy metals in soils, sand, and sewage sludge samples are studied using timeresolved optical emission spectrometry from laser-induced plasma. Israel Schechter of the Israel Institute of Technology and co-workers from the Technical University of Munich (Ger many) and the Max Planck Institute for Quantum Optics (Ger many) describe this fast screening detection system designed for on-line in situ analysis. Various factors that affect the detec tion limits and the quality of the analysis (such as aerosol pro duction, crater formation, size effects, timing effects, laser inten sities, and humidity) are investigated. To improve reproducibil ity of elemental analysis, a special data analysis program that implements principal component regression calibration is used. The computer program provides good calibration plots and detection limits in the 10 μg/g range, (p. 2964) Variable-temperature DRIFTS Diffuse reflectance FT-IR spectroscopy (DRIFTS) is often used to study solid samples such as organic materials, catalysts, and inorganic substances and has recently been used to obtain infor mation on solid-state structural changes caused by heating. Robert L. White and Rong Lin of the University of Oklahoma study the effect of sample temperature on interferograms and reflectance spectra obtained using a room-temperature deuterated triglycine sulfate pyroelectric detector and a liquid nitrogen cooled mercury-cadmium-telluride photoconducting detector. They report that modulated sample emittance, which destruc tively interferes with the FT-IR source interferogram, becomes significant at high sample temperature. Unless this emittance is optically blocked, it distorts the voltage output from both types of detectors, (p. 2976)
