In This
Issue
Brief introductions to the research articles in this issue
Measuring Na and Κ within human erythrocytes BIOANALYTICAL The ability to recognize minute changes in cells in the early stages of disease or carcinogenesis can lead to early diagno sis and more effective treatment. Ed ward S. Yeung and Nai-Ho Cheung of Iowa State University describe an ap proach to single-cell chemical analysis that involves pulsedlaser vaporization followed by monitoring of the atomic emis sion produced. By using a modified sheath-flow arrangement, detection of 8 fg of Na is possible with one laser pulse. The correlation between Na and Κ content in cells is weak. By using Poisson statistics, one can obtain single-cell information even when multiple cells are vaporized with each laser pulse, (p. 929) Disposable clinical sensing strips Disposable enzyme electrodes, such as dry-reagent sensor strips used by diabetics to monitor blood glucose levels, are extremely attractive for routine clinical use. Joseph Wang and Qiang Chen of New Mexico State University describe a new approach for fabricating amperometric enzyme strips that relies on the entrapment of glucose oxidase and lactate oxi dase within the microdisk pores of commercial screen-printed composite electrodes. The resulting strips offer highly selec tive sensing coupled with high sensitivity that results from the array character and large microscopic area. (p. 1007)
Improving DNA separations Pulsed-field gel electrophoresis is an effective technique for separating megabase-length DNA fragments in agarose slab gels. Michael J. Navin, Tracey L. Rapp, and Michael D. Mor ris of the University of Michigan report that the separation of DNA fragments can be improved through the use of variable frequency modulation in capillary electrophoresis. They find that the mobilities of the fragments are primarily a function of capillary power dissipation (i.e., temperature), regardless of whether a dc or modulated driving source is used, but that the separation efficiency depends on the presence of an ac field component and on the frequencies included in the modu lation protocol, (p. 1179) Studying the action of a cardiac antiarrhythmic agent Danny K. Y. Wong of Macquarie University (Australia) and co-workers have studied the pharmacochemical aspects of the cardiac antiarrhythmic agent, amiodarone, which is toxic and causes frequent side effects. The exact electrophysiologic mechanism of the action of amiodarone on cardiac tissues is unknown, as is the distribution of the drug through organs and tissues. Wong and co-workers use conductometric and spectroscopic methods to examine the interaction of amio darone as a possible electron donor with several small mole cules of biological importance (p. 1198).
ELECTROANALYTICAL Simplified surface plasmon DNA by CE resonance The ability to analyze DNA with high sensitivity, speed, and Existingfiber-optic-basedsurface plasthroughput is important to the success of the Human Genome . mon resonance instruments, designed Project. Hideki Kambara and colleagues at Hitachi (Japan) with thin-film-covered prisms, have a have developed a gel capillary-array electrophoresis system limited range of refractive index mea with real-time fluorescence detection that can be used to read surement and can't be used to monitor nucleic acid bases at a speed of 200/h. Multiple sheath flows aqueous systems with refractive in surround the 20 capillaries with buffer solution to prevent dexes of 1.33-1.35. William J. H. Bender, Raymond E. Dessy, DNA band diffusion in the gel-free irradiated region. The de Mark S. Miller, and Richard 0. Claus of Virginia Polytechnic tection limit for fluorophore-labeled DNA is 10"13 M. (p. 1021) Institute and State University describe the construction and operation of afiber-opticchemical microsensor for surface plasmon resonance with directly deposited thin films and anaTrace enzyme detection in single cells lytes. (p. 963) A combination of on-column enzyme reaction with laserinduced fluorescence detection is making it possible to use CE to separate and measure the activity of trace enzymes in a Shedding light on kinetic controversy single red blood cell. Qifeng Xue and Edward S. Yeung of Ferrocene has been used for more than 40 years to ascertain Iowa State University use NAD+ as a substrate for lactate de electrochemical behavior at electrodes; however, there are hydrogenase (LDH) isoenzymes in a rapid on-column reac discrepancies in the compound's kinetic constants. Geoffrey tion and separation method that produces the fluorophore N. Kamau of the University of Nairobi (Kenya) and James F. NADH in peaks corresponding to the activity of the separated Rusling of the University of Connecticut and colleagues re isoenzyme bands. Possible uses of the method include assess port on their studies offilmformation during die oxidation of ment of cell aging, liver disease, cancer metastasis, and other ferrocene at platinum electrodes. Results indicate that the physiological conditions in which LDH activity plays a role, extent offilmformation is affected by the type of solution (p. 1175) used and electrode size (micro versus macro), (p. 994) Analytical Chemistry, Vol. 66, No. 7, April 1, 1994 387 A
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Hot and cold running enzyme electrode The use of redox polymers as electron mediators in enzyme electrodes has always involved a compromise between the need for the polymer to be hydrophilic to support the redox enzymes and the problem of its being too water soluble. Noboru Oyama and colleagues of the Tokyo University of Agriculture and Technology (Japan) describe the preparation and performance of a glucose oxidase-based glucose sensor using a redox polymer whose water solubility depends on the temperature of its surroundings. The technique may be useful for creating renewable electrodes that operate at higher temperatures and can be cleaned by washing off the polymer coating in cold water after one use. (p. 1002) Shutting out acetaminophen noise Acetaminophen, one of the most commonly taken over-thecounter pain relievers, interferes strongly with peroxide-producing reactions. Its presence in a sample can wreak havoc with the performance of amperometric biosensors that depend on the generation of H 2 0 2 to produce a signal, such as those used for blood glucose monitoring. George Wilson of the University of Kansas and colleagues have developed a composite membrane that screens out acetaminophen and improves the performance of a glucose biosensor, (p. 1183) Building a better electrode with foam Porous electrodes operating in both amperometric and coulometric modes have been successfully used in HPLC applications. Cells incorporating reticulated vitreous carbon have been effective, but the high surface areas of carbonized polyacrylonitrile (PAN) foams should allow improvements in electrolysis efficiencies at higher flow rates using an electrode of reduced length and diameter. Stephen G. Weber and Brian K. Davis of the University of Pittsburgh describe a carbonized PAN foam-based coulometric cell that supports high conversion coefficients at reasonable flow rates, (p. 1204) Isotope dilution MS of vanadium Interferences from titanium and chromium limit the capability of isotope dilution MS to measure vanadium isotopic ratios at the natural levels found in seMASS SPECTROMETRY rum and foodstuffs. Jack D. Fassett and co-workers at the National Institute of Standards and Technology evaluate the capability of resonance ionization MS and thermal ionization MS to compensate for interferences from chromium and titanium. Measurements obtained with resonance ionization MS are more specific but less precise than those obtained by thermal ionization MS. (p. 1027) Surface analysis via quantitative static SIMS Recent progress in the quantitative study of static SIMS data of organic compounds has shown that it is possible to obtain information about molecular structure and bonding on films with submonolayer to monolayer coverage. Joseph A. Gardella, Jr., and Jian-Xin Li of the State University of New York at Buffalo describe a modified method that uses both integration and curve-fitting procedures to elucidate the secondary ion formation mechanism and to quantify small changes in
the surface chemistry of the Langmuir-Blodgett films of octadecylamine on polycrystalline silver, (p. 1032) Tandem MS and SID Surface-induced dissociation (SID) of molecular ions has been studied as the method for ion fragmentation in tandem MS. Luke Hanley of the University of Illinois-Chicago and colleagues use methane thiolate adsorbed on Ag(lll) to investigate molecular ion beam damage. Pyridine ions are found to significantly damage the methane thiolate at energies of 32 and 64 eV. Despite this modification, little change is seen in the SID spectra, (p. 1038) Geology and isotope dilution MS Because of differences in valence and chemical affinity between Pa and U, substantial chemical fractionation occurs during geologic processes. The resultant disequilibrium between 231Pa and 235U provides a means to date these processes. David A. Pickett of Los Alamos National Laboratory and colleagues demonstrate a method to measure 231Pa, the longest lived intermediate in the 235U series. The method allows determination of as little as a few tens of femtograms of 231 Pa with an uncertainty of ±1%. Measurements of 231Pa/235U can be used to date marine carbonates, bones, and scavenging rates in deep-sea sediments, (p. 1044) FTMS of hydrocarbons Catalytic hydrogénation of perdeuterated aromatic species generates selectively deuterated hydrocarbon species. Ben S. Freiser and co-workers at Purdue University demonstrate that transition metal ion chemical ionization used in conjunction with FTMS holds promise as a simple, qualitative, and potentially quantitative method for determining isotopolog and isotomer distributions in partially deuterated cyclic hydrocarbons. Compared with high-resolution NMR spectroscopy, the method requires less sample, easily detects compounds at low concentrations, and is less difficult to interpret, (p. 1050) LC/ESI-MS of peptides Electrospray ionization MS of tryptic peptides usually produces an abundant doubly-charged ion from which the mass of the peptide can be determined. The assignment of mass can be confusing if a singly- or triply-charged ion is the only ion present. Robert J. Anderegg of Glaxo Research Laboratories and Gitte Neubauer of Imperial College (U.K.) describe the addition of submillimolar amounts of sodium acetate to the mobile phase during LC/ESI-MS to encourage the formation of sodium replacement ions, the spacing of which allows unambiguous determination of the charge state of the ion, and thus the mass of the peptide, (p. 1056) Emissions analyzer Analyzing vehicle exhaust is difficult because it contains many components with wide ranges of constantly varying concentrations. C. Weickhardt, U. Boesl, and E. W. Schlag of the Technische Universitat Miinchen (Germany) demonstrate resonance-enhanced multiphoton ionization using pulsed lasers with time-of-flight MS for time-resolved detection of pollutants in vehicle exhaust. Time resolution is < 100 ms, sensitivity is 1 ppm, and precision is 10%. Parameters are determined for 25 pollutants, and results from a real exhaust sample are presented, (p. 1062). Analytical Chemistry, Vol. 66, No. 7, April 1, 1994 389 A
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Neural networks and pyrolysis MS Pyrolysis MS is a powerful technique for the characterization of microbial systems. To obtain quantitative information from pyrolysis spectra, Royston Goodacre, Mark J. Neal, and Douglas B. Kell of the University of Wales (U.K.) apply partial least-squares regression, principal components regression, and artificial neural networks to predict concentration in mixtures of lysozyme and glycogen, DNA or RNA and glycogen, and bacteria. Neural networks provide the most accurate information, (p. 1070) Optimizing cloud point extractions Only a limited amount of work has been devoted to investigating the experimental parameters that affect the extraction efficiency and preconcentration factor of surfactant-mediated phase separations, also known as cloud point extractions. Willie L. Hinze and Raymond P. Frankewich of Wake Forest University report on the effects of temperature, pH, surfactant hydrophobicity, equilibrium temperature and time, ionic strength, and analyte concentration. They conclude that the optimized cloud point approach is a viable, attractive alternative extraction technique for acidic and basic organic compounds in an aqueous matrix, (p. 944)
SEPARATIONS
Turning up the pressure on CE Some analytes are so close in structure and electrophoretic mobility that even 2D CE doesn't separate them. High-performance ID modifications such as increasing the applied potential or manipulating the electroosmotic flow can increase Joule heating and can be difficult to control during a long analysis. Christopher T. Culbertson and James W. Jorgenson of the University of North Carolina-Chapel Hill describe a flow-counterbalanced method for CE that uses large pressures to retard the flow of analytes in the capillary and permits the separation of analytes with electrophoretic mobility differences as small as 10"7 cm 2 /s. (p. 955) Analyzing flow injection peaks A general derivation for FIA peak shapes has eluded theoreticians, and extracting information from the peaks has been addressed largely by empirical methods. As part of their work to develop computer-controlled automated FIA systems, A. P. Wade and co-workers at the University of British Columbia (Canada) describe the representation of flow injection response curves by a generalized Fourier expansion in Gram and Daguerre polynomials. Both series are found to be sensitive to changes in peak shape and able to represent important features in flow injection time domain signals, (p. 971) Improved scrubbing Reduced sulfur compounds play an important role in the global atmospheric sulfur cycle by transporting biogenic sulfur from the ocean to the atmosphere. Cecilia Persson and Caroline Leek of the University of Stockholm (Sweden) demonstrate improved sulfur sampling capability using a scrubber made of cotton wadding and a Nation drier. Analyses were performed using GC with a flame photometric detector. Precision is better than ±3% for dimethyl sulfide and ±5% for carbon disulfide and dimethyl disulfide, (p. 983)
Improving precision and accuracy in CZE Although CZE is a highly efficient separation method for qualitative purposes, there is a lack of confidence in the technique with respect to quantitative analysis because of problems concerning precision and accuracy. Joachim Leube and Odette Roeckel of Hoffman-La Roche (Switzerland) improved accuracy and precision for CZE with electrokinetic injection by using a matrix-corrected peak area combined with calibration by regression with one internal standard. Intraassay precision and accuracy are improved by factors up to 12 and 6.5, respectively, (p. 1090) Saving time and solvents with microwaves Evaluating new sample preparation techniques that minimize solvent use is part of an ongoing EPA program. Viorica LopezAvila and co-workers at the Midwest Research Institute and EPA report that microwave-assisted extraction of stable organic compounds from soil samples seems to be a viable alternative to conventional sample preparation procedures such as Soxhlet and sonication extraction. The microwave technique requires less time and less solvent for extraction. Up to 12 samples can be extracted simultaneously in a few minutes, (p. 1097) Bonding, sample introduction, and column geometry on a chip J. Michael Ramsey and co-workers at Oak Ridge National Laboratory address three aspects of microchip electrophoresis devices. Bonding of the substrate and cover slip is accomplished by hydrolyzing the surfaces and then joining and annealing them. Two sample introduction techniques, pinched and floating sample loading, are evaluated. Pinched sample loading is found to be superior with regard to temporal stability and plug length. A serpentine column geometry is evaluated, and though band-broadening phenomena are measurable, it does not appear to be a severe problem when field strength is < - 200 V/cm. (p. 1107) Separations on a chip Microfabricated chemical instruments show great promise both for the laboratory and as chemical sensors. J. Michael Ramsey and co-workers at Oak Ridge National Laboratory describe a glass microchip device for free solution electrophoresis. Micromachining allows four channels to be joined at an intersection with essentially no dead volume. For a separation length of 0.9 mm, electrophoretic separations with baseline resolution are achieved in < 150 ms with an electric field strength of 1.5 kV/cm and an efficiency of 1820 plates/s. For a separation length of 11.1 mm, 18,600 plates-per-second efficiency is achieved, (p. 1114) Adjusting the retention window in MECC Micellar electrokinetic capillary chromatography using high electricfieldstrengths and open-tubular, fused-silica capillaries filled with surfactant-rich electrolyte solutions is well suited for the separation of neutral and charged species. Joel T. Smith, Wassim Nashabeh, and Ziad El Rassi of Oklahoma State University address the need for micellar phases with adjustable retention windows by introducing and evaluating charged micelles in situ. A series of Ar-D-gluco-ALmethylalkanamide surfactants in the presence of borate ions at alkaline pH are evaluated, (p. 1119) Analytical Chemistry, Vol. 66, No. 7, April 1, 1994 391 A
In This Issue Oligosaccharides by CE Despite their increasing importance in medical science, biotechnology, and the food industry, oligosaccharides in mixtures have been poorly characterized because of their complex structures. Milos Novotny and co-workers at Indiana University describe the separation of complex oligosaccharide mixtures using open-tubular CE with fluorescent detection. Efficiencies of more than 1 million plates are achieved, facilitating resolution of branched oligosaccharides, (p. 1134) CE using formamide Using nonaqueous media in CE would extend the applicability of the technique, because researchers would have a wider range of dielectric constants, polarities, densities, viscosities, and acid-base chemistries. Rachhpal S. Sahota and Morteza G. Khaledi of North Carolina State University describe their work using formamide as a solvent in CE. Higher electrolyte concentrations and electricfieldstrengths are achieved, and the linearity between the current and applied voltage is improved. The implications of using other nonaqueous media are also discussed, (p. 1141) Comparing FFF, HDC, and SEC When selecting a method to characterize the molecular mass distribution of polymers, resolving power and separation speed are the most crucial factors to consider. Johan C. Kraak of the University of Amsterdam (The Netherlands) and colleagues establish a general framework for the theoretical comparison of these two characteristics for thermal FFF, packed and open-tubular hydrodynamic chromatography, and SEC. For each technique a dimensionless parameter is defined that includes the basic variables affecting retention, and the capabilities of each method are compared, (p. 1147) Determining organotin compounds with SFE and GC The environmental impact of certain organotin compounds can be significant because many are highly toxic to aquatic life. Josep M. Bayona and co-workers at CID-CSiC (Spain) describe a procedure that incorporates in situ derivatization, SFE with carbon dioxide, and GC separation with flame photometric detection for determining butyl- and phenyltin in sediments. The method minimizes sample handling steps, decreases analysis time, and reduces solvent use. (p. 1161) The dyes have it Although UV absorption is a common method of detection for nucleic acid capillary gel electrophoresis, laser-induced fluorescence offers better detection limits. Michael D. Morris and Yongseong Kim of the University of Michigan describe the effects of bis- and mono-intercalating dyes on the capillary electrophoretic separation of double-stranded DNA in buffers containing (hydroxypropylmethyl) cellulose, (p. 1168) Extractive hydrogénation Mohammad Itani and Roger W. Giese describe extractive hydrogénation as a preparation procedure for biological samples. The sample is subjected to intense hydrogénation in the presence of water and an excess of a palladium/carbon catalyst. The catalyst is then extracted with an organic solvent; the extract is ready for analysis by GC with a flame ionization detector or electron impact MS. The method brings a broad
variety of organic samples into the scope of GC/electron impact MS computerized spectral libraries, (p. 1189) Chemometrics and QC SPECTROSCOPY To supply customers with high-quality products, manufacturers must apply QC measures during all phases of production, rather than only checking the final product. However, this must be done quickly without slowing down production. Hans R. Keller, Jiirgen Rottele, and Hermann Battels of Ciba-Geigy Ltd. (Switzerland) apply Monte Carlo simulation methods to two sets of spectroscopic data taken from industrial environments to demonstrate their use as a screening method. The quality can be predicted on the basis of noise, spectra, calibration concentration, and the number of calibration samples, (p. 937) Chemiluminescence and chemometrics For linear systems in which the species behave independently, resolving chemiluminescent components in a mixture can be accomplished by several methods. For nonlinear multicomponent systems, curve-fitting methods are used. Aurora Navas Diaz and José Antonio Gonzalez Garcia of the Universidad de Malaga (Spain) use the least-squares P-matrix method for multicomponent kinetic analysis to determine protocatechuic and caffeic acids. Good agreement is obtained between theoretical and experimental results, (p. 988) Air analysis using laser spectroscopy Most surface analysis methods require that the sample be in a vacuum, making it difficult to analyze compounds on solution surfaces. Teiichiro Ogawa and colleagues at Kyushu University (Japan) describe a laser two-photon ionization technique for determination of aromatics on the surface of water in ambient air. The method is applicable to use in polar solvents, in which direct photoionization methods are difficult to apply; the detection limit for pyrene is 9 pptr, close to the detection limit that can be obtained in hexane solution, (p. 1012) IRRAS of silicon wafers IR reflection absorption spectroscopy can produce IR spectra in sampling situations in which transmission spectroscopy is impossible, such as in situ spectroscopy offilmson thick substrates. Interpretation of such spectra is complicated, however, by interference fringes. James W. Taylor and colleagues at the University of Wisconsin describe a method that uses the information provided by these fringes to obtain the thickness and complex RI of thefilmin regions of little or no absorption in photoresistfilmson silicon substrates, (p. 1015) Assay for oxidized vitamin C The blood and tissue concentrations of dehydroascorbic acid (DHA), the oxidized form of vitamin C, may play a role in diabetes and may interact with cholesterol. But DHA, unlike the reduced form of vitamin C, doesn't absorb well in the UV-vis region and is difficult to determine in the presence of its more abundant cousin. Esther Schweinzer and co-workers at the University of Vienna (Austria) have developed a methanol derivatization method for determining micromolar concentrations of DHA without ascorbate interference in a spectrophotometric kinetic measurement assay, (p. 1086) Analytical Chemistry, Vol. 66, No. 7, April 1, 1994 393 A
