In AC
Research
tion-limited laser excitation, and a high-efficiency photon detec tor. They report that because of an unlimited excitation throughput and a low background level, the technique allows fluorescence detection of single rhodamine molecules with an S/N of ~ 10 in 1 ms, which approaches the theoretical limit set by fluorescence saturation. ("Real-Time Detection of Single Molecules in Solution by Confocal Fluorescence Microscopy"; AC950164B; p. 2849)
Watching it dissolve Traditional pharmaceutical dissolution testing of tablets has fo cused on removing sample aliquots for analysis at certain time intervals. D. S. Walker and colleagues at East Carolina Univer sity and Burroughs Wellcome demonstrate a seven-channel fiber-optic UV-vis spectrograph for in situ real-time monitor ing of dissolution testing. The active ingredients studied span the range from 30 to more than 750 mg/tablet. ("UV-Visible Spectral Dissolution Monitoring by In Situ Fiber-Optic Probes"; AC950258L; p. 2858)
Determining comonomer type using melt-state MAS NMR Although solution-state 1!C NMR is often used for identifying and quantitating the branching features of a polyolefin, it re quires that the polymer must be soluble in an appropriate sol vent and suffers from relatively low sensitivity. Galen R. Hat field and co-workers at W.R. Grace & Co. and Himont USA use melt-state 1JC NMR with magic-angle spinning and dipolar de coupling to determine comonomer type and content in polyolefins. The melt-state approach yields comonomer contents that are in good agreement with those obtained via solution-state NMR. ("Melt-State 13C MAS NMR Determination of Comono mer Type and Content in Ethylene/a-Olefin Copolymers"; AC950214C; p. 3082)
Determining platinum group elements in auto catalysts• The economic value of platinum group elements (Pt, Pd, Rh, Pb) used in catalytic converters has created a significant recycling industry, with the value of the recycled catalyst dependent on accurate chemical assay of these elements. E. S. Beary and P. J. Paulsen of the National Institute of Standards use ICPMS for the high-accuracy determination of Pt, Pd, Rh, and Pb in two used automobile catalysts. They use isotope dilution quantifica tion for Pb, Pt, and Pd, and internal standard quantification for Rh. ("Development of High-Accuracy ICP Mass Spectrometric Procedure for the Quantification of Pt, Pd, Rh, and Pb in Used Auto Catalysts"; AC950272Y)
Detecting aromatics using SERS* Surface-enhanced Raman scattering (SERS) at rough-metal films or particles is a promising tool for chemical sensors because of its ability to easily detect submonomolecular layers of organic sub stances adsorbed at metal surfaces. Wieland Hill and colleagues at the Institut fur Spektrochemie und Angewandte Spektroskopie (Germany) and Texas Christian University demonstrate that chemical modification of rough silver surfaces by p-tert-hu\si\calix[4]arenetetrathiol produces a substrate for SERS that reversibly complexes with aromatics from aqueous solutions. ("De tection of Aromatics in Aqueous Solution by Surface-Enhanced Raman Scattering by Substrates Chemically Modified with p-tertButylcalix [4] arenetetrathiol"; AC950335C) 520A
Analytical Chemistry, September 1, 1995
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