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Brief introductions to the research articles in this issue
Accelerated Article Dynamic surface-tension detector Although surfactants are widely found in many consumer products, a commercial instrument suitable for the detection of surfactants in real-time manufacturing processes is not yet available. Lawrence R. Lima, III, Darren R. Dunphy, and Robert E. Synovec of the University of Washington report on the design and characterization of a dynamic surface-tension detector for FIA and LC. The detector optically measures the repeating drop rate from the end of the flow system. The relationship between dynamic surface tension, analyte translational diffusion, and analyte inherent surface activity is examined in relation to the detector signal, (p. 1209)
Enzyme immobilization Do enzymes function differently when they are immobilized on an electrode? Donna Scott and Edmond Bowden of North Carolina State University use rotating disk electrode voltammetry to determine the Michaelis constant and the minimum turnover number for cytochrome c peroxidase adsorbed onto edge-oriented pyrolytic graphite. They discuss evidence that the catalytic reduction of peroxide is a result of the intact enzyme and that the adsorbed enzyme functions for the most part as it would in solution, (p. 1217) DNA intercalation There has been increased interest in studying the intercalation of aromatic residues into the DNA helix. These studies can be used to develop a technology for detecting and quantitating organic carcinogens and toxins. P. C. Pandey and H. H. Weetall of the National Institute of Standards and Technology describe a flow injection system designed for the detection of compounds that intercalate within DNA. A derivative of 9,10-anthraquinone is used as the reference compound for photoelectrochemical detection, (p. 1236) Tellurium traces in biological samples A tellurium-containing antitumor drug designed to be administered at very low doses is driving the need to develop methods for trace determination of the metal in biological specimens. Because tellurium is volatile, AAS methods require low ashing temperatures and added modifiers to achieve reasonable sensitivity. David Herold of the University of California-San Diego and colleagues describe an isotope dilution GC/MS method that uses (4-fluorophenyl) magnesium bro-
mide as a derivatizing agent to determine trace tellurium in urine, plasma, and tissues at low nanogram-per-milliliter concentrations, (p. 1316) Fluorogenic substrates for DNA ELISAs Fluorescent substrates for enzyme-linked immunosorbent assays (ELISAs) are fast replacing radiolabeling of DNA probes in DNA in situ hybridization analyses. However, the high self-fluorescence of nylon membranes used to capture DNA in gel electrophoretic separations and genome library screening procedures has prevented the use of fluorescent substrates for ELISA in these applications. Satoshi Fujita of Aisin Cosmos R&D Gapan) and colleagues evaluate a series of phosphorylated fluorochromes for use as substrates with an alkaline phosphatase-linked fluorescence immunoassay for nylon membrane-bound nucleic acids, (p. 1347) Substitutional stripping Despite low detection limits, stripping voltammetry is of limited usefulness . because the analyte must deposit itself on the electrode. Tsutomu Horiuchi, Osamu Niwa, and Hisao Tabei of Nippon Telephone and Telegraph Gapan) describe substitutional stripping voltammetry, a technique that uses an interdigitated array microelectrode in a sample solution in combination with a macroelectrode in a second cell containing an electroactive species that deposits reversibly on the electrode. The charge generated by the redox cycling reaction of the sample at the interdigitated array is transmitted to the macroelectrode and accumulated by the deposition of metal ion species on the macroelectrode. (p. 1224) Eliminating peroxide from glucose sensors Many glucose oxidase-based glucose sensors rely on the generation of H 2 0 2 for electron transfer. However, peroxide can lower the enzyme activity and the working potential is high enough that the sensor becomes sensitive to vitamin C and acetaminophen, which are often found in patient blood samples. Yoshiyuki Okamoto of Polytechnic University (NY) and colleagues examine the use of non-crosslinked and cross-linked poly (ether amine quinone)s as substitutes for H 2 0 2 in the electron-transfer relay systems for amperometric glucose sensors, (p. 1231) Gold back-extracts mercury for ASV Trace mercury contamination of natural waters is of increasing concern as a health hazard and is often determined by cold vapor AAS and AFS. Jem-Mau Lo and JunDer Lee of the National Tsing Hua University (Republic of China) have developed a differential pulse anodic stripping voltammetry method that uses gold as a back-extracting Analytical Chemistry, Vol. 66, No. 8, April 15, 1994 449 A
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agent in a sample preconcentration step and takes advantage of surplus Au3+ in the solution to generate goldfilmat the working carbon electrode, (p. 1242) MALDI-FTMS of carcinogens Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants that form adducts with DNA, and some isomers show both carcinogenic and mutagenic activity. E. A. Stemmler of Bowdoin College and R. L. Hettich and co-workers at Oak Ridge National Laboratory evaluate five matrices for MALDI-FTMS of four PAH adducts to nucleotides and find that matrix selection can be used to control tiie degree of analyte fragmentation. They demonstrate that MALDI-FTMS produces more structural information than does FABMS or FABMS/MS for the PAH adducts. (p. 1274) Scale-down of thorium dating Measurement of the isotopic ratio of 230 Th/ 232 Th is used along with uranium and thorium concentrations to date geological samples as old as 1.2 million years. However, thermal ionization MS has limited precision for samples with very low 230 Th content. Bryan Fearey of the Los Alamos National Laboratory and colleagues present a continuous-wave resonance ionization MS method that has internal precision comparable to that of the thermal ionization method and has higher detection efficiency, (p. 1286) Modeling isotope peaks On-line methods for compound-specific isotope analysis, important for biomedicine and organic geochemistry, include GC/combustion isotope ratio MS. Keith Goodman and Thomas Brenna of Cornell University compare a Levenberg-Marquardt curve-fitting algorithm with exponentially modified Gaussian (EMG) and Haarhoff-VanderLinde (HVL) functions to investigate the accuracy of each method in modeling overlapping GC/combustion isotope ratio MS peaks. HVL/ EMG or HVL/HVL combinations provide the best fits and are robust and rapid for use in automated fitting, (p. 1294) Derivatization for ESIMS Despite the increasing popularity of electrospray ionization MS, not all types of analytes are amenable to analysis by the technique. J. Martin Quirke, Christopher L. Adams, and Gary J. Van Berkel of Oak Ridge National Laboratory discuss derivatization strategies and reactions for converting alkyl halides, alcohols, phenols, thiols, and amines to "electrospray active" forms of the analyte. The usefulness of the procedures is demonstrated by the specific detection of the major secondary alcohol in oil of peppermint; selective detection of phenols within a mixture of phenols; and identification of primary, secondary, and tertiary amines in cold medicine, (p. 1302) FT-ICRMS with off-resonance excitation Off-resonance excitation of parent ions increases their internal energy for collisionally induced dissociation while controlling their oscillations. Shenheng Guan and Alan Marshall of Florida State University and Markus Wahl of The Ohio State University describe an FT-ICRMS method that uses 450 A
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off-resonance excitation of the precursor ions in combination with axialization of the product ions to reduce radial diffusion loss of the products. They demonstrate significant improvements in detection efficiency, mass accuracy, and mass resolving power for the analysis of the cyclic peptide gramicidin S. (p. 1363) Solid-phase extraction of brine shrimp Ascorbic acid 2-sulfate has been reported as a metabolite of ascorbic acid in humans and in several animal species. André P. De Leenheer and colleagues at the Universiteit Gent (Belgium) evaluate two solid-phase extraction procedures. One uses a reversed-phase ion pair octadecylsilica cartridge, tetrabutylammonium as the counterion, and elution with methanol, and the other uses a diefhylaminopropyl silica cartridge that is eluted with 0.1 M sodium salicylate to investigate the accumulation of ascorbic acid 2-sulfate in brine shrimp cysts. The anion exchange extraction is superior to its ion pair counterpart in terms of recovery, reproducibility, and simplicity, (p. 1330) Engine fuel composition The FIA dye method currently used to determine the composition of jet fuel is time-consuming and generally cannot be used with other types of hydrocarbon fuels such as diesel. Charles W. Sink and Dennis R. Hardy of the Naval Research Laboratory describe an LC separation with differential refractive index detection that does not depend on prior knowledge of the fuel's refractive index and can be extended to other fuels. The technique should also have applications in instances where the identity of the analyte may not be known prior to quantification, such as in environmental analysis, (p. 1334) Determining organic compounds in environmental matrices Growing public concern about the quality of the environment has increased the demand for analytical techniques that can be used to determine organic compounds. Janusz Pawliszyn and co-workers of the University of Waterloo (Canada) describe the development of membrane extraction with a sorbent interface for capillary GC, a technique that combines a hollow fiber membrane with cryofocusing and thermal desorption technologies. Because the membrane module is interfaced directly to the gas chromatograph, analyte loss is minimized. Parameters influencing sensitivity and precision are discussed, and applications are presented, (p. 1339) Oscillating-plasma GC detectors Oscillating-plasma glow discharge cells are being used as detectors for GC. Bryan Cook and Edward Piepmeier of Oregon State University explore the relationships between oscillating frequency, amplitude, and current for these cells as a function of pressure, electrode spacing, and cathode shape to determine a range of useful
operating conditions and to gain insight into cell mecha nisms. They find evidence that the mechanisms controlling frequency and current have significant differences, (p. 1249) Sol-gel planar waveguides Planar integrated optical waveguides have advantages over cylindrical fiber-optic waveguides for some surface character ization applications, with the potential for much higher den sity of total reflections, but they are more difficult to produce with high quality. Scott Saavedra of the University of Arizona and colleagues describe a sol-gel fabrication scheme for the planar waveguides and find that the choice of catalyst strong ly affects the quality of the waveguide surface, (p. 1254)
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Photoactivation spot test for PCBs Cleanup of large areas contaminated with PCBs requires rapid and inexpensivefieldtests, but most of the methods for PCB determinations are complex and require sample pretreatment or derivatization. T. Vo-Dinh and co-workers at the Oak Ridge National Laboratory describe a spot test with fluo rescence detection using UV radiation to photoactivate the derivatization of PCBs by diphenylamine to produce a fluorophore. The method takes 5-10 min and can be used to deter mine PCBs or total chlorine content in soils with part-perbillion detection limits, (p. 1264) Enantiomeric purity of pharmaceuticals Increased restrictions on the enantiomeric purity of pharma ceuticals have resulted in the need for improved analytical techniques to quantitate chiral purity. Kevin M. Spencer and co-workers at EIC Laboratories examined scattered circu larly polarized Raman optical activity (SCP ROA) as a poten tial analytical tool. Their findings show that SCP ROA can be used for quantitative analysis and to simultaneously identify multiple enantiomeric species. This is significant because tradi tional optical activity measurements, such as polarimetry and circular dichroism, are of limited value for mixtures in which the impurities are not quantitatively defined, (p. 1269)
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Viewing the brew Fermentation efficiency depends on the mass concentration, or "density," of cells being used to ferment the reagents. Zhihong Ge, Anna Cavinato, and James Callis of the University of Washington use a fiber-optic bundle for noninvasive near-IR spectroscopy of a glass-walled yeast fermentation vessel to measure cell density from 1 to 60 g/L. Using locally weighted regression to model the data, they find that when the vat is stirred and bubbled at a constant rate, the average standard error of prediction is low. (p. 1354)
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Structural information from GC Most GC detectors respond indiscriminately with regard to molecular structure. Diane L. Smith and Edward H. Piepmeier of Oregon State University describe how an oscillating-plasma glow discharge detector can be used to identify analytes by combining oscillation frequency and average cur rent signals. Principal component analysis is used to deter mine the number of variables necessary to describe the vari ation in the detector's response. Five homologues each of therc-alkanes,1-alkenes, 1-alkynes, 2-ketones, and aldehydes are used to assess differences in response to increasing car bon number, (p. 1323)
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