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In AC Research contains brief introductions to the research articles appearing in the April 1 issue of Analytical Chemistry plus a partial listing of articles tentatively scheduled for the April 15 issue. A free updated table of contents is available on the 1st and 15th of every month on the Web (http://pubs.acs.org/ac).
Accelerated Article Polarization sensing Fluorescence sensors can be used in a broad range of applications. Joseph R. Lakowicz and co-workers at the University of Maryland School of Medicine describe a polarization sensor that does not use an electronic detector. Rather, detection relies on visual determination of the polarization. The emissions from a polarized reference fluorophore and an unpolarized sample fluorophore, which responds to the analyte of interest, are transmitted through a dual polarizer and are viewed through a second analyzer polarizer. The analyzer polarizer is rotated until the transmitted intensity of both halves is equal. The compensation angle reveals the sample concentration. The sensor is used to measure pH (with 6-carboxyfluorescein) and the concentration of Rhodamine B in intralipid. ("Polarization Sensing with Visual Detection"; 10.1021/ ac981301i; p. 1241)
Detecting pteridines A new method for detecting pteridines— compounds found in urine, which, at elevated levels, are associated with tumorrelated diseases—has been developed by Yinfa Ma and colleagues at Truman State University and the Chinese Academy of Sciences (People's Republic of China). The technique is based on high-performance CE and laserinduced fluorescence detection. With this technique, the researchers can detect and characterize six pteridines at detection limits below 1 x 10~10 M in nrine eamples from cancer ratients and in control samples. ("Pteridine Analysis in Urine by Capiilary Electrophoresis Using Laser-Induced Fluorescence Detection"; 10.1021/ac981218v; p. 1265)
between the signal and concentration of anti-dsDNA monoclonal antibody in the range 0-300 ug/mL. ("Automated Detection of Anti-Double-Stranded DNA Antibody in Systemic Lupus Erythematosus Serum by Flow Immunoassay"; 10.1021/ ac980899r; p. 1298)
Biomimetic sensors Molecularly imprinted polymers—in which a functional monomer and a cross-linking agent are chemically polymerized in the presence of a template molecule—are gaining in popularity, but their use in biomimetic sensors is just beginning to be explored. Pier Giorgio Zambonin and co-workers at Universita degli Studi (Italy) characterize electrosynthesized poly(o-phenylenediamine) that has been imprinted by glucose and used as the recognition element of a quartzcrystal microbalance biomimetic sensor. The researchers acknowledge some problems, including protein interferences, but find evidence for two types of glucose binding sites. They argue that the study is the first successful application of electropolymerization as a general strategy for preparing molecularly imprinted electrosynthesized polymers. ("Molecularly Imprinted Electrosynthesized Polymers: New Materials for Biomimetic Sensors"; 10.1021/ac980674g; p. 1366)
Identifying gel-separated glycoproteins
Measuring lupus antibodies
Glycosylated proteins often yield poor MALDI peptide maps because of shielding of proteolytic cleavage sites and the presence of modified peptides. Matthias Mann and Bernhard Kiister of the University of Southern Denmark demonstrate that enzymatic removal of N-linked glycans with simultaneous partial (50%) 180-labeling of glycosylated asparagine residues before proteolysis and MALDI peptide mass mapping can overcome these problems. The procedure offers unambiguous identification of glycoproteins that would otherwise require sequencing and enables the identification of N-glycosylation sites with higher sensitivity than previously possible. ("180-Labeling of N-Glycosylation Sites To Improve the Identification of GelSeparated Glycoproteins Using Peptide Mass Mapping and Database Searching"; 10.1021/ac981012u; p. 1431)
Recent studies have revealed that antibodies produced against DNA are associated with systemic lupus erythematosus and several other diseases, making diagnoses difficult. Tadashi Matsunaga and colleagues at Tokyo University of Agriculture and Technology Gapan) use alkaline phosphataseconjugated double stranded (ds) DNA prepared using a commercially available PCR digoxigenin-labeling mix to form a novel analytical substrate for quantifying antibodies in the serum of lupus patients. The assay yields a linear relationship
Identifying nearest-neighbor residues in nucleic acids provides insight into base composition and sequence and is potentially applicable to solving structural problems. James A. McCloskey and Jef Rozenski at the University of Utah describe a new electrospray ionization tandem MS approach that measures precursor-product relationships derived from small-fragment ions produced in the instrument's high-pressure ionization re-
Identifying nearest neighbors with MS
ACS and other publishers have adopted the Digital Object Identifier (DOI) as a unique identifier for articles in print and on the Web. For Analytical Chemistry, the DOI consists of 10.1021/followed by the manuscript number. DOII can be found on the first page oo published articles sad with In AC Research citations. More information on the DOI is available at http://www.doi.org. Please use the DOI when orderrng documents. Analytical Chemistry News & Features, April 1, 1999 231 A
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gion. The researchers demonstrate the technique using modi fied residues in nucleic acids up to 76 bases, ,nd they say ii is applicable to RNA or DNA. ("Determination of Nearest Neigh bors in Nucleic Acids by Mass Spectrometry"; 10.1021/ ac9812431; p. 1454) Bacteria by MALDI MS Catherine Fenselau and Jonathan Bundy at the University of Maryland-College Park use lectins to isolate microorganisms from sample matrixes that may be prohibitive for direct MALDI analysis of phospholipid or other biomarkers. Samples in urine and the physiological buffer can be affinity captured directly on the MALDI probe and readily analyzed with little sample prepa ration. ("Lectin-Based Affinity Capture for MALDI-MS Analysis of Bacteria"; 10.1021/ac981119h; p. 1460) Digestion on the target Ron Orlando and Jennifer Colangelo of the University of Geor gia demonstrate that, under new conditions, exoglycosidase digestions can be performed on a MALDI target at room tem perature in 5-30 min. Oligosaccharide standards are digested with one or more exoglycosidases to show that the enzymes retain their activity and specificity under these new reaction conditions. Primary sequences of carbohydrate chains can be determined in a relatively short amount of time. ("On-Target Exoglycosidase Digestions/MALDI-MS for Determining the Primary Structures of Carbohydrate Chains"; 10.1021/ ac980980u; p. 1479) γ-Carboxyglutamic acid in proteins • David D. Y. Chen and co-workers at the University of British Columbia (Canada) have developed a simple and sensitive CElaser-induced fluorescence method for analyzing y-carboxyglutamic acid (Gla) in proteins, urine, and plasma. The number of Gla residues in three vitamin K-dependent proteins is deter mined by quantifying the amount of fluorescein thiocarbamyl derivative of Gla after alkaline hydrolysis and fluorescein isothiocyanate labeling. Human prothrombin, blood coagulation factor X, and bovine osteocalcin are calculated to have 10.0, 11.0, and 2.1 Gla residues per mole of protein, respectively. ("Analysis of y-Carboxyglutamic Acid Content of Protein, Urine, and Plasma by Capillary Electrophoresis and Laser-Induced Fluorescence"; 10.1021/ac981241g) Mass-sensitive sensor arrays Continuous surveillance of environmen' tal and work-place conditions would pro mote greater safety in companies han dling toxic chemicals. F. L. Dickert and co-workers at the University of Vienna (Austria) describe how mass-sensitive sensor arrays of quartz-crystal microbalances using supramolecular host-guest chemistry are combined with multivariate calibration techniques to measure analytes in the presence of variable air moisture. The system detects xylene isomers with an accuracy of —1% in the range 0-200 ppm. ("Detection of Vol atile Compounds with Mass-Sensitive Sensor Arrays in the Presence of Variable Ambient Humidity"; 10.1021/ac981014e; p. 1338) 232 A
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Determining nicotine In addition to its presence in tobacco smoke, nicotine is also used as a drug, a chemical, and a pesticide. Its determination is important in the tobacco industry and toxicology. Martin M. F. Choi and colleagues at Hong Kong Baptist University and Yangzhou University (both in the People's Republic of China) demonstrate a plasticized polyvinyl chloride) optode membrane incorporated with a valinomycin ionophore, a H+-selective chromoionophore, and lipophilic potassium tetrakis(4-chlororphenyl) borate as a reversible sensing device for the indirect optical determination of nicotine. The recovery of nicotine as its bromoethane derivative is 84-119%. .(Optode Membrane for Determination of Nicotine via Generation of Its Bromoethane Derivative"; 10.1021/ac980838t; p. 1342) Triiodide electrode Mojtaba Shamsipur of Razi University and Ahmad Rouhollahi of Tehran University (both in Iran) describe a triiodide ion-selective electrode based on a charge-transfer complex of iodine with 2,4,6,8-tetraphenyl-2,4,6,8-tetraazabicyclo [3.3.0] octane as a membrane carrier. The electrode has a linear dynamic range of 5.0 x 10"2 to 3.5 x 10"6 M, with a detection limit of 2.0 x 10~6 M. The potentiometric response is independent of pH over the range 4.0-10.5. The electrode can be used for at least 10 months. ("Triiodide PVC Membrane Electrode Based on a Charge-Transfer Complex of Iodine with 2,4,6,8Tetraphenyl-2,4,6,8-tetraazabicyclo [3.3.0] octane"; 10.1021/ ac981077x; p. 1350) Cytochrome c- modified electrode for superoxide dismutase The enzyme superoxide dismutase (SOD) scavenges superox ide molecules and thus has the potential to ameliorate some kinds of organ damage. One technique for measuring SOD ac tivity is to use electrodes coated with cytochrome c and mea sure the current induced after reduction and electrochemical oxidation. F. Lisdat and colleagues at the University of Potsdam and the Max Delbriick Centrum fur molekulare Medizin (both in Germany) have developed a new electrode that uses mercaptoundecanoic acid to immobilize cytochrome c on the gold sur face and to block the surface, preventing other species from interfering with detection. The researchers report that the elec trode is sensitive from 10 to 200 muniis/mL, allowing determi nation down to a few nanograms of SOD, and can complete a measuring cycle in 2-3 min. ("Superoxide Dismutase Activity Measurement Using Cytochrome c-Modified Electrode"; 10.1021/ac980961k;p. 1359) Mercuracarborand-based electrodes Leonidas G. Bachas and co-workers at the University of Ken tucky have developed sensitive and selective liquid/polymeric membrane electrodes for chloride that use [9]mercuracarborand-3 (MC3), a highly preorganized macrocyclic Lewis acid, as the anion carrier. The MC3-based, chloride-sensitive mem brane electrodes are doped with varying amounts of tridodecylmethylammonium chloride and exhibit enhanced potentiomet ric selectivity for chloride over more lipophilic anions, such as perchlorate, nitrate, and thiocyanate. When optimized, the membrane electrodes show a near-Nernstian response toward chloride over a wide concentration range with micromolar de-
tection limits. ("Mercuracarborand 'Anti-Crown Ether'-Based Chloride-Sensitive Liquid/Polymeric Membrane Electrodes"; 10.1021/ac980896e; p. 1371)
Electrospray film deposition Deposition of proteins and other biospecific molecules onto an electrode surface is a common task in fabricating enzyme electrodes and other biochemosensors. Victor N. Morozov and Tamara Ya. Morozova of New York University and the Russian Academy of Sciences investigate electrospray ionization as a method for depositing functionally active protein films on a conductive electrode. Using alkaline phosphatase as a model, the researchers find that enzyme activity is preserved when electrospray deposition is performed at low current and humidity in the presence of disaccharides. ("Electrospray Deposition as a Method To Fabricate Functionally Active Protein Films"; 10.1021/ac9808775; p. 1415)
Infinite-dilution diffusion coefficients As computers become more capable of solving multicomponent transport problems, the need for physical constants on which to base these models increases. Peter S. Fedkiw and David A. Dudek of North Carolina State University describe a technique for measuring the conductivities of dilute solutions in which the distribution of complex ions is systematically varied. The data is statistically regressed to an equation that effectively relates individual ion-diffusion coefficients to solution conductivities. Diffusion coefficients of cuprous cyanide complexes are determined. ("Infinite-Dilution Diffusion Coefficients of Complex Ions from Solution Conductivity Data"; 10.1021/ac981054i; p. 1469)
Cysteine-modified electrodes for copper • Copper (II) sensors made from self-assembled monolayers (SAMs) avoid the problems of surfactant adsorption, but most SAMs have only one type of functional group at their ends, which can limit specificity. Chun-hsien Chen and co-workers at National Sun Yat-Sen University (Republic of China) modify an electrode surface with cysteine for the detection of copper (II). A stable fivemembered ring is formed by the copper(II), cc-amino, and a-carboxy groups. With a preconcentration time of 5 min, the cysteine-modified electrode has a dynamic range of 0.05-5.0 ug/L and a detection limit as low as 25 ng/L. The method measures copper (II) in river water and seawater. ("Application of Cysteine Monolayers for Electrochemical Determination of Sub-ppb Copper(II)"; 10.1021/ac980956g)
Hydrogen-modified GC electrodes • Hydrogenated glassy carbon (HGC) electrodes, which have carbon atoms terminated by C-H bonds, have electrochemical properties (e.g., surface structure, stability, and electrode kinetics) that are significantly different from those of polished glassy carbon (GC) electrodes. Richard L. McCreery and Tzu-Chi Kuo of Ohio State University prepare HGC electrodes by a hot filament technique, in which hydrogen radicals generated from hydrogen gas attack GC electrode surfaces. Raman spectroscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry reveal some important effects of hydrogen termination, including increased resistance to air oxidation. ("Surface Chemistry and Electron-Transfer Kinetics of HydrogenModified Glassy Carbon Electrodes"; 10.1021/ac9807666) • Denotes articles tentatively scheduled for the April 15 issue
CE for chemical warfare degradation products International treaty obligations have created a demand for reliable, rapid, and easily transportable methods for determining chemical warfare agents and their degradation products. Alaa-Eldin F. Nassar and colleagues at Battelle Memorial Institute and Aberdeen Proving Ground use CE with electrokinetic injection, indirect UV detection, and a cationic surfactant to determine methylphosphonic acid and three of its monoacid/monoalkyl esters. Detection limits for the four analytes are as low as 1-2 ug/L for water samples and 25-50 ug/L for aqueous leachates of soil samples. ("Determination of Chemical Warfare Agent Degradation Products at Low-Part-per-Billion Levels in Aqueous Samples and Sub-Part-per-Million Levels in Soil Using Capillary Electrophoresis"; 10.1021/ac980886d, p. 1285) Giving supercritical fluids a little help Supercritical C0 2 does not work well for extracting polar chemicals in soils. Qing X. Li and colleagues at the University of Hawaii-Manoa describe a procedure for extracting pollutants from soil based on pretreating samples with water, Na4EDTA, and methanol. Recoveries are in the range 90-106%. The method quantitatively extracted 2,4-D and its analogues aged in the soil for 2-30 days. Na4EDTA is a good enhancer for extracting 29 analytes representing a wide range of polarity. ("Na4EDTAAssisted Sub-/Supercritical Fluid Extraction Procedure for Quantitative Recovery of Polar Analytes in Soil"; 10.1021/ ac9810157; p. 1309) Gas-phase ammonia detector Estimates of the atmospheric-biospheric budget of ammonia and the total reactive cycling of nitrogen are hampered by a lack of accurate gas-phase measurements of ammonia. Melody Avery Owens and colleagues at the University of MarylandCollege Park describe a photothermal interferometer that detects ammonia using a C0 2 laser-emitting light at 9.22 um. The subsequent collisional heating and expansion leads to a refractive index change, which is detected as a phase shift in one arm of a homodyne interferometer. The instrument's 2a precision is 31 ppt when the signal is integrated for 100 s. ("A Photothermal Interferometer for Gas-Phase Ammonia Detection"; 10.1021/ ac980810h; p. 1391) Arsenic in drinking water Bjoern Klaue and Joel D. Blum of Dartmouth College describe the use of a magnetic-sector inductively coupled plasma mass spectrometer for the determination of arsenic in drinking-water samples, using both standard liquid sample introduction in the high-resolution mode (M/AM = 7800) and hydride generation (HG) in the low-resolution mode (M/AM= 300). High mass resolution ICPMS allows the spectral separation of the wellknown polyatomic ArCl interference; however, sensitivity is compromised (detection limits = 0.3 ug/L). On the other hand, low resolution HG-ICPMS offers superior detection limits in the 0.2-ng/L range and complete ArCl removal even for high-chlorine matrixes. ('Trace Analyses of Arsenic in Drinking Water by Inductively Coupled Plasma Mass Spectrometry: High Resolution versus Hydride Generation"; 10.1021/ac980846+; p. 1408) Analytical Chemistry News & Features, April 1, 1999 233 A
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Toxaphene analysis From the late 1950s to the early 1980s, toxaphene was a widely used insecticide. Because it is a complex mixture, quantification of toxaphene in environmental samples is difficult. Ronald A. Hites and colleagues at Indiana University present an automatic GC/MS method—using electron-capture negative ionization—which is precise and fast. The new method is verified with standard and unknown toxaphene samples contaminated with various amounts of other organochlorine pesticide interferences. ("Automated Toxaphene Quantitation by GC/MS"; 10.1021/ac980906b, p. 1448) Scrubbing with tetraglyme Many of the techniques used for taking air samples have one or more disadvantages. J. R. Troost of American Analyttcal and Technical Services use tetraglyme, a water-soluble organic solvent that was once used in now obsolete EPA methods, as an impingerfluidfor scrubbing a wide variety of volatile organic compounds from air and gas streams. A portion of the tetraglyme is subsequently dispersed into water and analyzed using conventional techniques. Practical quantitation limits of 100 ppbv, with the potential for going lower, are demonstrated. ("An Air to Water Bridge: Air Sampling and Analysis Using Tetraglyme"; 10.1021/ac981316g; p. 1474) Pectinase specificities by tandem MS Pectins often are used in the food industry because of their ability to form gels and stabilize proteins, and they are now being investigated for use in medical applications. Determining the degree and distribution of pectins' methyl ester groups is critical because these factors are related to the function of pectins. Peter Roepstorff and co-workers at Odense University and Danisco Biotechnology (both in Denmark) investigate the specificity of several pectolytic enzymes using collision-induced dissociation in a nanoelectrospray ionization ion trap mass spectrometer. Although quantitative estimates are difficult with mixtures of multiple isomers, the researchers can determine the enzymes' substrate specificities with the method. ("Sequencing of Partially MethylEsterified Oligogalacturonates by Tandem Mass Spectrometry and Its Use To Determine Pectinase Specificities"; 10.1021/ ac981240o; p. 1421) Additive distribution in polymers Time-of-flight secondary ion MS (TOF-SIMS) can distinguish small chemical differences in polymer structures and compositions; thus, TOF-SIMS is being used to detect minor components in polymer systems. M. J. Walzak and co-workers at the University of Western Ontario (Canada), Ford Scientific Laboratories, and Imperial Oil (Canada) use TOF-SIMS to measure the distribution of an antioxidant in linear low-density polyethylene. The parent ion at m/z 599 is too weak to map the distribution, but a fragment ion at m/z 58 could be used. Imaging the concentration of the additive is possible to concentrations as low as 0.1%. ("Detection and Mapping of Chimassorb 944FD Antioxidant Additive in Polyethylene Using TOF-SIMS"; 10.1021/ac980717t; p. 1428) 234 A
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Off-axis nebulizer for ion trap MS The presence of charged residues other than the analyte can degrade the performance of ion trap mass spectrometers. Robert D. Voyksner and Heewon Lee of Research Triangle Institute find that an offfaxis nebullzer positioned at 90-95° ffom the sampling orifice improves the analyte signal and the detection limits in an ion trap mass spectrometer. The detection limit and precision for the determination of dihydroxyvitamin D3 are improved. The LC/MS/MS detection limits are within a factor of 2 from the detection limit determined with a triple quadrupole. The relative standard deviation is less than 8%. ("Improvements in LC/Electrospray Ion Trap Mass Spectrometry Performance Using an Off-Axis Nebulizer"; 10.1021/ac980995s; p. 1441) Itty bitty filters Miniaturization of an analytical system has to include the filter. Fred Regnier and colleagues at Purdue University micromachine solvent and reagent filters into quartz wafers using deep reactive ion etching to create a network of intersecting 1.5 x 10 um channels. When placed at the bottom of reservoirs with a side exit, this network behaves like a lateral percolation filter, with the flow driven by electroosmotic flow. The filters are effective in removing particulates from solvents ranging from dust to cells. ("Microfabricated Filters for Microfluidic Analytical Systems"; 10.1021/ ac981010+; p. 1464) Amino acid order in polymeric surfactants Isiah M. Warner and co-workers at the Louisiana State University investigate the effect of amino acid order on chiral selectivity in polymeric dipeptide surfactants, which can provide crucial information for the design of more efficient surfactants. The microenvironments inside the core of 18 surfactants are investigated with the fluorescence probes pyrene and 6-propionyl-2-(dimethylamino)napthalene. The results lead to a proposed structure of the polymeric dipeptide surfactants in solution, which is tested with two model atropisomers using capillary electrokinetic chromatography. ("Amino Acid Order in Polymeric Dipeptide Surfactants: Effect on Physical Properties and Enantioselectivity"; 10.1021/ ac980461r; p. 1252) Improved microdialysis extraction In microdialysis, analytes diffuse through a semipermeable membrane, and the concentration of the analyte in the outlet perfusionfluidis related to the true sample concentration by the extraction efficiency of the dialysis probe. Julie A. Stenken and Alexander N. Khramov of Rensselaer Polytechnic Institute increase the extraction efficiency by including p-cyclodextrin (|3-CD) in the perfusion fluid as a complexation agent that facilitates transport. The extraction efficiency of ibuprofen is significantly enhanced through different membrane materials, with maximum efficiency occurring when 0.5 w/v% (5-CD is included in the perfusionfluid.A similar effect is not seen for antipyrine, which does not form inclusion complexes with (3-CD. ("En-
hanced Microdialysis Extraction Efficiency of Ibuprofen in Vitro by Facilitated Transport with P-Cyclodextrin"; 10.1021/ ac9811930; p. 1257)
("Supercritical Fluid Extraction and Gas Chromatography/ Mass Spectrometry for the Analysis of Tobacco-Specific Nitrosamines in Cigarettes"; 10.1021/ac9810821; p. 1303)
Selectivity in MEKC Micellar electrokinetic chromatography (MEKC) has expanded the possibilities for CE, but selectivity in MEKC is not yet understood. Morteza G. Khaledi and Mark D. Trone at North Carolina State University study the influence of headgroups using six anionic sodium dodecyl surfactants. The researchers determine that hydrogen bonding has the strongest influence on selectivity, with hydrophobicity also contributing. In addition, the results show that the hydrogen-bond-accepting ability (a coefficient) for a surfactant is proportional to the proton acidity (pKJ of its headgroup. The researchers suggest that the hydrogen-bond-donating ability and the dipolarity of the surfactant systems are the result of water that resides near the micelle surface. ("Characterization of Chemical Selectivity in Micellar Electrokinetic Chromatography: Effect of Surfactant Headgroup"; 10.1021/ac9809736; p. 1270)
Reactive pyrolysis-GC for shellacs The chemical composition of shellac affects its mechanical and thermal properties, which depend on the species of insect that secreted the resin, the type of host tree, and other environmental factors. Analyzing the complex mixture of polyesters to characterize the resin is useful but difficult. Shin Tsuge and colleagues at Nagoya University Furo-cho and Gifu Shellac Manufacturing (both in Japan) have developed a reactive pyrolysis-GC method using tetramethylammonium hydroxide. The technique does not require pretreatment, and permits sensitive determination of terpenic and other acids and of the wax components of the shellac. ("Characterization of Natural Resin Shellac by Reactive Pyrolysis-Gas Chromatography in the Presence of Organic Alkali"; 10.1021/ac981049e; p. 1316)
Designing chiral stationary phases Jean M. J. Frechet and colleagues at the University of CaliforniaBerkeley describe an alternative combinatorial approach in which a chiral stationary phase carrying a library of enantiomerically pure potential selectors (36 L-amino acid anilides) is used to directly screen for enantioselectivity in the HPLC separation of target analytes. The best of the bound selectors is then identified in a few deconvolution steps. The highest selectivity is obtained with L-proline-1-indananilide, which exhibits a values up to 23 under normal phase conditions. ("On-Bead Combinatorial Approach to the Design of Chiral Stationary Phases for HPLC"; 10.1021/ac981143v; p. 1278) Shocking CZE James W. Jorgenson and Katariina Maria Hutterer at the University of North Carolina-Chapel Hill build an ultrahigh-voltage CE system to demonstrate the possibility of extending the applied potential and, thus, the separation power of CE. A commercial 30-kV power supply is extensively modified to provide electrical potentials up to 120 kV; a unique electrical shielding system prevents capillary breakdown and corona or spark discharges. Theoretical plate counts, ranging from 2.7 to 6.1 million plates, are obtained for peptides in a separation run at 120 kV. ("Ultrahigh-Voltage Capillary Zone Electrophoresis"; 10.1021/ac981221e; p. 1293) Analyzing tobacco-specific nitrosamines Siqing Song and David L. Ashley of the Centers for Disease Control and Prevention describe a method for measuring four tobacco-specific nitrosamines (TSNAs). The compounds are extracted by supercritical fluid extraction, purified by a sodium hydroxide wash of the ethyl acetate eluting solvent and by solid-phase extraction, and quantitated with GC/MS. The detection limits are 0.04 ug for Af'-nitrosonornicotine and W-nitrosoanatabine and 0.02 ug for 4-(methylnitrosamino)-l(3-pyridyl)-l-butanone and N'-nitrosoanabine. The method is used to reproducibly measure TSNAs in various cigarette brands. The variation in TSNA levels is greater among different brands than among different packs of the same brand. • Denotes articles tentatively scheduled for the April 15 issue
Novel multilayered stationary phase Chiral separations are necessary for producing safe and effective pharmaceuticals, and chiral chromatography is one of the most common separation methods. Current chiral ligands include cellulose derivatives, synthetic ligands, and proteins such as bovine serum albumin (BSA). K. Saiio and colleagues at Chiba University, Nisshin Flour Milling (both in Japan), Japan Science and Technology, and the Japan Atomic Energy Research Institute have added a multilayered BSA structure on the surface of a porous hollow-fiber membrane. Using the multilayered BSA as the stationary phase, the researchers report separating DL--ryptophan with high resolution and with a separation factor that is independent of the flow rate of the mobile phase. ("High Resolution of DL-Tryptophan at High Flow Rates Using a Bovine Serum Albumin-Multilayered Porous HollowFiber Membrane"; 10.1021/ac9805596; p. 1323) Modeling fullerene retention Isolating and characterizing the different types of fullerenes requires high-efficiency separations. Yves Claude Guillaume and Eric Peyrin of Faculte de Medecine Pharmacie (France) examine the influence of water concentration in a methanol mobile phase on the interaction between fullerenes and a poly(octadecylsiloxane) stationary phase. An enthalpy-entropy compensation analysis reveals that the types of interactions between the fullerenes and the stationary phase are independent of the fullerene structure and mobile-phase composition. Using a geometric model, the increase in fullerene retention with increasing water concentration is found to be caused by the increased effects of surface tension. ("Geometrical Model for the Retention of Fullerenes in High-Performance Liquid Chromatography"; 10.1021/ac9811591; p. 1326) Cold wall temperature effects • A universal calibration method that is transferable from one instrument to the next has been proposed for thermal field-flow fractionation (ThFFF). Systematic experiments to verify the calibration method for a wide range of conditions have shown that the method holds well as long as experimental conditions, such as sample size and cold wall temperature, are the same for each system. Marcus N. Myers and co-workers at the UniverAnalytical Chemistry News & Features, April 1, 1999 235 A
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sity of Utah quantify the effect of cold wall temperature on polymer retention in ThFFF and on the universal calibration constants for the polystyrene-tetrahydrofuran, poly (methyl methacrylate)-tetrahydrofuran, and polyisoprene-tetrahydrofuran systems. ("Thermal Field-Flow Fractionation Universal Calibration: Extension for Consideration of Variation of Cold Wall Temperature"; 10.1021/ac981094m) Sweeping in MEKC • Joselito P. Quirino and Shigeru Terabe of Himeji Institute of Technology (Japan) recently reported on a technique for increasing detection sensitivity in micellar electrokinetic chromatography based on a concentration effect called "sweeping". Essentially, neutral analytes are picked up and accumulated by a pseudostationary phase, such as sodium dodecyl sulfate, and swept into narrow zones when vollage ii applied. The euthors now theoretically examine the dependence of the sweeping phenomenon on analyte charge, retention factor, and electroosmotic flow under a homogeneous electric field. The length of the analyte zone is shown to be solely dependent on the retention factor and the length of the initial zone. ("Sweeping of Analyte Zones in Electrokinetic Chromatography"; 10.1021/ac9810866) High-speed GC with air as a carrier gas • Portable, high-speed capillary GC for directly measuring volatile organic compounds in the environment offers several advantages; but such instruments are still relatively large, in part, because of the need for on-board gas supplies. Richard Sacks and co-workers at the University of Michigan present a model for the operating conditions and performance tradeoffs of a high-speed GC system that uses atmosphericpressure air as the carrier gas and relies on a vacuum pump to draw air and samples through the instrument. The model is validated with a high-speed GC using a cryofocusing inlet and a photoionization detector. ("High-Speed, Vacuum-Outlet GC Using Atmospheric-Pressure Air as Carrier Gas"; 10.1021/ ac981153w)
Water vapor sensor Neal R Armstrong, S. Scott Saavedra, and co-workers at the University of Arizona have developed a water vapor sensor based on a combination of sol-gel processing and planar optical waveguide technologies. The indicator, a porous sol-gel layer doped with erythrosin B, exhibits an increase in absorbance at 514.5 nm in the presence of liquid or gaseous water, which is detected as a decrease in the intensity of the light guided by an integrated optical waveguide. The detection limit is estimated to be
