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Brief introductions to the research articles appearing in the May issues of Analytical Chemistry
Accelerated Articles Faster field analyses The key to successful field analyses is the ability to perform tests quickly, which often means having to analyze a wide range of environmental contaminants simultaneously. Albert Robbat, Jr., and co-workers at Tufts University have made it their goal to develop a system for the simultaneous analysis of polychlorinated biphenyls, pesticides, polycyclic aromatic hydrocarbons, and other organics present in soil samples. They have created data analysis software and built a thermal desorption sample introduction system, which together can quantitatively analyze a wide range of organic compounds in oil-based matrices in 1 mL/min. Yukiko Hirabayashi and co-workers at Hitachi (Japan) modify the SSI interface by placing a multihole plate in front of the mass spectrometer sampling orifice, which reduces the number of solvent molecules introduced into the vacuum region and concomitantly reduces the solvation of analyte ions at higher flow rates. Multiply charged ions with a charge distribution of 11+ to 16+ are analyzed from a 1-uM cytochrome c solution at a flow rate of 1 mL/min without a splitter. ("A Sonic Spray Interface for rhe Mass Analysis of Highly Charged Ions from Protein Solutions at High Flow Rates"; S0003-2700(97)00872-X; p. 1882) Carbonyls yield to LC and MS Both LC and MS techniques pose problems when it comes to measuring carbonyls in air samples. Michael Oehme and colleagues at the University of Basel (Switzerland) and the Norwegian Institute for Air Research combine the LC separation of
carbonyl derivatives with atmospheric pressure chemical ionization MS" in the negative-ion mode for detection. Fragment ions allow identification of carbonyl substructures, and detailed fragmentation pathways are studied. ("Structure Elucidation of 2,4-Dinitrophenylhydrazone Derivatives of Carbonyl Compounds in Ambient Air by HPLC/MS and Multiple MS/MS Using Atmospheric Chemical Ionization in the Negative Ion Mode"; S0003-2700 (97) 00945-1; p. 1979) Iodine determination in food • Iodine is an essential trace element for humans; however, it presents an analytical challenge because of its relatively low natural concentrations. Klaus G. Heumann and Gunther Radlinger of Johannes Gutenberg-University (Germany) describe two different sample treatment methods—extraction by tetramethylammonium hydroxide solution at high temperatures, and complete sample decomposition with perchloric and nitric acids plus microwave assistance—with inductively coupled plasma isotope dilution MS for determining iodine traces in food samples. The detection limit is 8 ng/g using sample weights of 0.8 g; relative standard deviation for concentrations in the microgramper-gram range is 2.8% or less. ("Iodine Determination in Food Samples Using Inductively Coupled Plasma Isotope Dilution Mass Spectrometry"; S0003-2700(97)01308-5) Modeling ion exchange Tetsuo Okada of the Tokyo Institute of Technology (Japan) presents a retention model based on the Stern-GouyChapman electrical double-layer theory for ion-exchange chromatography, which is an extension of earlier studies and describes various experimental facts better than the previous models. The model's efficiency is verified by its ability to predict nonlinear log plots, changes in separation factors, and adsorption isotherms at different salt concentrations. ("Interpretation of Ion-Exchange Chromatographic Retention Based on an Electrical Double-Layer Model"; S00032700(97)00655-0; p. 1692) MEKC at low pH Most applications of micellar electrokinetic chromatography (MEKC) are done in basic solution because of a strong electroosmotic force. James S. Fritz and Weiliang Ding of Iowa State University take the opposite approach and investigate separations of protonated organic bases at pH 2.4 using ethanesulfonic acid and uncoated silica capillaries. A new sulfonated surfactant is also studied. Excellent resolution of a mixture of 19 polycyclic aromatic hydrocarbons and similar compounds and of a mixture of hydrophilic drugs is demonstrated. ("Separation of Neutral Compounds and Basic Drugs by Capillary Electrophoresis in Acidic Solution Using Laurylpoly(oxyethylene) Sulfate as an Additive"; S0003-2700(97) 00883-4; p. 1859) Adsorption vs. absorption Although the correlation between octanol/water partitioning coefficients and solid-phase microextraction coating/water partitioning coefficients has been applied for low-molecular-weight analytes, the correlation fails for analytes with higher molecular • Denotes articles tentatively scheduled for the May 15 issue
weights, such as polychlorinated biphenyls (PCBs). To investigate the relative importance of adsorption and absorption mechanisms, Steven B. Hawthorne and colleagues at the University of North Dakota and Brigham Young University determine PCB partitioning coefficients between poly(dimethylsiloxane) and water. Theyfindthat, when PCB partitioning coefficients are calculated on the basis of surface area, the primary mechanism controlling PCB partitioning from water is surface adsorption. ("Adsorption versus Absorption of Polychlorinated Biphenyls onto Solid-Phase Microextraction Coatings"; S00032700(97)00823-8; p. 1866) Simulating electroosmotic flow Although one-dimensional models are used for studying the influence of the electroosmotic flow profile on separation efficiency, a three-dimensional model is needed to study electroosmotic flow in the complicated geometries of micromachined separation devices. Howard H. Hu and Neelesh A. Patankar of the University of Pennsylvania use a numerical scheme to simulate the electroosmotic injection characteristics of a crosschannel device for CE. Flow induced from the side channels into the injection channel squeezes the streamlines at the intersection, giving a less distorted sample plug. ("Numerical Simulation of Electroosmotic Flow"; S0003-2700 (97) 00846-9; p. .870) Nonionic surfactant analysis Fatty alcohol ethoxylates (FAEs) are important nonionic surfactants used in commercial formulations. Carla Vogt and colleagues at the University of Leipzig (Germany) use CE and HPLC to separate FAEs in technical products and household formulations after derivitization with phthalic anhydride. Peak patterns provide a "fingerprint" of the product and are characteristic of a defined composition. ("Separation of Nonionic Surfactants by Capillary Electrophoresis and High-Performance Liquid Chromatography"; S0003-2700(97)00915-3; p. 1885) Concentrating neutral analytes Because of CE's short optical path length and low injected sample volumes, applications for this technique are limited by low concentration sensitivity. Joselito P. Quirino and Shigeru Terabe of the Himeji Institute of Technology (Japan) describe conditions for the on-line concentration of neutral analytes by fieldenhanced sample injection with reverse migrating micelles for micellar electrokinetic chromatography. Acidic phosphate buffers containing sodium dodecyl sulfate micelles are used as sample solvent and separation solution. A model is provided, and experiments show significant improvements in detector response. ("On-line Concentration of Neutral Analytes for Micellar Electrokinetic Chromatography. 5. Field-Enhanced Sample Injection with Reverse Migrating Micelles"; S00032700(97)01150-5; p. 1893) Dielectrophoretic particle and cell sorter The development of microtools that handle and separate samples in very small volumes remains an analytical challenge. Stefan Fiedler and colleagues at the Humboldt Universitat zu Berlin (Germany) show that forces generated by acfieldsunder conditions of negative dielectrophoresis can be used for these applications. Micrometer-sized latex particles and living mammalian cells are handled in this manner, and particle concentraAnalytical Chemistry News & Features, May 1, 1998 2 9 9 A
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tion and switching are achieved in linearflowsof up to —10 mm/s. ("Dielectrophoretic Sorting of Particles and Cells in a Microsystem"; S0003-2700 (97) 01063-9; p. 1909) HPLC separation of oligonucleotides Synthetic oligonucleotides are used as probes for gene isolation and diagnostics, and a method is needed to test the purity of these probes. Nebojsa M. Djordjevic and co-workers at Novartis Pharma (Switzerland) have developed a fast isocratic HPLC method for the separation of short antisense oligonucleotides and a temperature-programmed method for large oligonucleotides. The isocratic method is sensitive to the organic modifier concentration; a 0.5% change in the mobile phase more than doubled the analysis time. For the larger oligonucleotides, temperature programming decreased the analysis time 75% relative to an isocratic/isothermal run. The methods could be paired with electrospray ionization MS. ("HPLC Separation of Oligonucleotides in Isocratic and Temperature-Programming Mode"; S0003-2700(97)01169-4; p. 1921) Arsenic and short-column LC Chemical speciation of arsenic compounds is under extensive investigation because of the diverse toxicity of arsenic compounds, the differences in metabolism of various arsenic species, and the poorly understood roles of arsenic in biological systems. X. Chris Le and Mingsheng Ma at the University of Alberta (Canada) describe a method that is capable of speciating nanogram per milliliter levels of arsenite, arsenate, monomethylarsonic acid, and dimethylarsinic acid within 3 min. The method is based on LC with a 3-cm guard column and detection of arsenic hydride by atomic fluorescence spectrometry. Detection limits for the four species in urine are 0.4-0.8 ng/mL. ("Short-Column Liquid Chromatography with Hydride Generation Atomic Fluorescence Detection for the Speciation of Arsenic"; S0003-2700(97)01247-X; p. 1926) Zirconia-based stationary phases Ion exchange is a common chromatographic method for separating proteins. Peter W. Carr and Yue Hu of the University of Minnesota describe new zirconia-based polymeric cationexchange stationary phases for HPLC of proteins. In one stationary phase, polyethyleneimine is adsorbed onto porous zirconia particles and cross-linked with 1,4-butanediol diglycidyl ether. In the second stationary phase, poly(acrylic acid) anhydride is both the cross-linker and the stationary phase. These stationary phases are stable under normal separation conditions and up to pH 10. ("Synthesis and Characterization of New Zirconia-Based Polymeric Cation-Exchange Stationary Phases for High-Performance Liquid Chromatography of Proteins"; S0003-2700(97)01024-X; p. 1934) Determining polymer additives The additives in polymers must be identified for quality control and regulatory reasons. Anthony A Clifford and colleagues at the University of Leeds and ICI Technology (both in the U.K.) describe the extraction of Irganox 1010 from polypropylene using high-pressure solvent extraction. Extraction curves for the solvents 2-propanol and acetone fit the "hot ball" model. Diffusion coefficients and activation energies for diffusion are determined for several solvents. In addition, mixed solvents are 300 A
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investigated, which show advantages in some cases. ("Factors Affecting High-Pressure Solvent Extraction (Accelerated Solvent Extraction) of Additives from Polymers"; S0003-2700(97) 01090-1; p. 1943) Rapidly resolving complex mixtures The complete separation of a complex mixture often is not feasible because of the large amount of time typically involved. J. Guiteras and co-workers at Universitat de Barcelona Avgda (Spain) have developed an alternative approach for resolving closely eluting compounds that relies on a multivariate calibration method and three-dimensional data (retention time, emission wavelengths, and fluorescence intensity). Data are rapidly obtained for a mixture of polycyclic aromatic hydrocarbons in water by HPLC with fast-scanning fluorescence spectrometry detection and analyzed by either three-way partial least-squares (tri-PLS) or n factor parallel factor analyses (PARAFAC)) Both methods can predict the concentrations of different compounds in a sample; however, results obtained with tri-PLS were slightly better than those obtained with PARAFAC. ("Three-Way Multivariate Calibration Procedures Applied To High-Performance Liquid Chromatography Coupled with Fast-Scanning Fluorescence Spectrometry Detection. Determination of Polycyclic Aromatic Hydrocarbons in Water Samples"; S0003-2700 (97)00939-6" ;. 1949) Dacthal in soil Although methods exist for determining the herbicide Dacthal and its metabolites in water, rapid methods are needed for measuring it in soils. Jennifer A Field and colleagues at Oregon State University describe a derivatization method in which Dacthal is extracted using supercritical C02, and its metabolites are extracted using subcritical water. Dacthal is extracted in 15 min and the metabolites in 10 min. Sample cleanup is not required and die use of diazomethane is avoided. ("Coupling Supercritical C0 2 and Subcritical (Hot) Water for the Determination of Dacthal and Its Acid Metabolites in Soil"; S00032700(97)01109-8; p. 1956) Determining acidic herbicides in water Conventional methods for measuring acidic herbicides are frequently inefficient and lack analytical precision. Maw-Rong Lee and colleagues at National Chung-Hsing University (People's Republic of China) derivatize acidic herbicides adsorbed on the fiber coating of a solid-phase microextraction device with diazomethane gas. Detection limits by GC/MS are 10-30 ng/L Various degradation compounds are also detected. ("Gas-Phase Postderivatization Following Solid-Phase Microextraction for Determining Acidic Herbicides in Water"; S0003-2700(97) 01153-0; p. 1963) Isolating charged organics from w a t e r Solid-phase extraction has been used for the isolation of environmentally important charged organic compounds from water, but its performance with large numbers of samples or largevolume samples has not been as successful as originally hoped. Tonya R. Dombrowski, George S. Wilson, and E. Michael Thurr man with the U.S. Geological Survey and the University of Kansas investigate anion-exchange and immunoaffinity particle loaded membranes for use in the isolation of charged organics. Recoveries of >90% at flow rates of up to 70 mL/min are ob-
served; a fast-flow immunoaffinity column with antibodies yielded reproducible recoveries at the sameflowrates. ("Investigation of Anion-Exchange and Immunoaffinity Particle-Loaded Membranes for the Isolation of Charged Organic Analytes from Water"; S0003-2700(97)01081-0; p. 1969) Aromatic amines in biological fluids Many aromatic amines are of toxicological concern, and their extensive use in industrial processes warrants close biological monitoring of workers and the general public. Janusz B. Pawliszyn and co-workers at the University of Guelph and the University of Waterloo (both in Canada) report on a headspace solid-phase microextraction technique optimized for extracting and concentrating five target amines from urine, blood, and milk. Combined with GC/MS, the technique can be completed in 15 min with a 5-mL sample, yielding reproducible results with detection limits that range from 0.4 to 7.7 ppb. ("SolidPhase Microextraction of Monocyclic Aromatic Amines from Biological Fluids"; S0003-2700(97)00941-4; p. 1986) Radicals in the air Sarah A. Green and Thomas M. Fllcker of Michigan Technological University have developed a new method for trapping gas-phase radicals by modifying a known solution-phase radical trapping system. Carbon-centered radicals are trapped from gas-phase cigarette smoke and diesel engine exhaust by adsorbing 3-amino-2,2,5,5-tetramethyl-l-pyrrolidinyloxy onto a solid support and passing the gas sample over it. The resulting stable adducts are derivatized, separated by HPLC, and detected fluorometrically. Different suites of radicals are revealed in the two systems, with 22 ± 7 nmol oo radicals per rigarette and 3 ± 1 nmol oo fadicals ser liter ro fiesel lnginn exhaust. ("Detection and Separation of Gas-Phase Carbon-Centered Radicals from Cigarette Smoke and Diesel Exhaust"; S00032700(97)00858-5; p. 2008) Sensitive and robust CE detection • One of the primary reasons that CE has not been widely used for routine trace analyses is the lack of sensitive detection systems. Geoff C. Gerhardt and co-workers at the University of Saskatchewan (Canada) and the Canadian Food Inspection Agency have developed a new end-column detection method for CE that uses square-wave voltammetry (SWV). In contrast with off-column detection techniques, which typically use fragile carbon fiber electrodes and complex decoupling apparatus to separate the high CE voltage from the detection electronics, SWV offers robust and simple detection. A detection limit of 5 x 10"7 M (S/N = 10) is obtained for dopamine, which compares well with the sensitivity of off-column amperometric electrochemical detection. ("Square-Wave Voltammetry Detection for Capillary Electrophoresis"; S0003-2700 (97) 01115-3) Beware of helium head pressure CO2 • To ensure that C0 2 is stored in its liquid state for use in supercritical fluid extraction and chromatography, C0 2 tanks are often pressurized with helium (the liquid phase from the helium head pressure C0 2 [HHPC02] tanks can be transferred to the pump cylinder without having to cool it). Michal Roth of the Academy of Sciences of the Czech Republic has investigated the thermodynamic properties of entrained helium to deter• Denotes articles tentatively scheduled for the May 15 issue
mine its effects on the solubility and retention of naphthalene in SFE and SFC, respectively. He concludes that C02 properties are significantly altered by helium and that HHPC02 should be avoided. ("Helium Head Pressure Carbon Dioxide in Supercritical Fluid Extraction and Chromatography: Thermodynamic Analysis of the Effects of Helium"; S0003-2700(97)01168-2) Dissolved organic carbon method • Dissolved organic carbon (DOC) is a key parameter in the analysis of water quality. Klaus G. Heumann and Jochen Vogl of the Johannes Gutenberg-University (Germany) describe a sensitive and fast determination of DOC in bulk samples and in chromatographically separated fractions by using inductively coupled plasma isotope dilution MS (ICP-IDMS). Detection limits are 0.3 mg/L for bulk analyses and 7 x 10"4 ug/s for transient signals from chromatographic peaks. Simultaneous determination of DOC and heavy metals in separated fractions of complexes with humic substances are made possible by coupling ICP-IDMS with HPLC and using size exclusion chromatography. ("Development of an ICP-IDMS Method for Dissolved Organic Carbon Determinations and Its Application to Chromatographic Fractions of Heavy Metal Complexes with Humic Substances"; S0003-2700 (97) 01283-3) Concentrating proteins for CE analysis • Concentration sensitivity is usually not very high for CE. XingZheng Wu and co-workers at Fukui University and Tokyo Metropolitan University (both in Japan) introduce a simple on-line electrophoretic concentration method for proteins that uses a semipermeable hollow fiber for concentrating the analytes. Protein samples are electromigrated into the hollow fiber. After the analytes have been concentrated, an electric field is applied across the fiber and capillary, and a conventional CE analysis is carried out. When the concentration time is 60 s, CE detection limits for a series of model proteins are lowered by 1000-fold. ("An On-Line Electrophoretic Concentration Method for Capillary Electrophoresis of Proteins"; S0003-2700(97)00911-6) Useful mid-IR data In situ mid-IR monitoring provides useful information on chemical reactions, but the frequency and band shape of spectral absorbances can change as a result of intermolecular forces and temperature. L.-G. Danielsson and colleagues at the Royal Institute of Technology and Astra Production Chemicals (both in Sweden) test data evaluation methods for monitoring the hydrolysis of triethyl phosphonoformate in NaOH using FT mid-IR spectroscopy with an attenuated total reflectance probe. Alternating leastsquares multivariate curve resolution obtains pure component spectra and concentrations, and partial least-squares regression models verify results when possible. ("Evaluation Techniques for Two-Way Data from in Situ Fourier Transform Mid-Infrared Reaction Monitoring in Aqueous Solution"; S0003-2700(97) 01140-2; p. 1726) Environmental DMS measurements The potential link between dimethyl sulfide (DMS) produced by phytoplankton in the ocean and cloud condensation nuclei in Analytical Chemistry News & Features, May 1, 1998 3 0 1 A
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the marine troposphere could have a significant effect on global climate. However, a fast sensor for DMS that could be carried on atmospheric research aircraft and directly measure oceanic DMS fluxes does not exist. Alan J. Hills and colleagues at the National Center for Atmospheric Research and the University of Colorado describe a high-speed sensor for DMS based on a fast chemiluminescent reaction with molecular fluorine. The instrument has a response time of 0.1 s and is highly linear and sensitive. ("Dimethyl Sulfide Measurement by FluorineInduced Chemiluminescence"; S0003-2700(97)00963-3; p. 1735) Free Zn(ll) at picomolar levels Richard B. Thompson and colleagues of the University of Maryland School of Medicine and Duke University Medical Center have developed a new biosensor-based approach to determine free Zn(II) in solution at concentrations in the picomolar to micromolar range. The method involves the binding of a synthetic fluorescent aryl sulfonamide ligand to the human enzyme, apocarbonic anhydrase II. Binding is dependent on the concentration of metal in solution. A significant increase in fluorescence anisotropy is exhibited upon binding, providing an expanded dynamic range for measuring free zinc concentrations. ("Expanded Dynamic Range for Free Zinc Ion Determination by Fluorescence Anisotropy"; S0003-2700(97)01199-2; p. 1749) Temperature influences on vibrational spectra When vibrational spectra are measured on- or in-line for process analytical and control purposes,fluctuationscaused by temperature, pressure, viscosity, and other process variables influence the shape of the spectra in a nonlinear manner. Age K. Smilde and colleagues at the University of Amsterdam (The Netherlands) study the effect of temperature on the predictive ability of multivariate calibration of spectral data from mixtures of ethanol, water, and 2-propanol. Local models are applied to samples of one temperature and global models to samples of different temperatures. ("Influence of Temperature on Vibrational Spectra and Consequences for the Predictive Ability of Multivariate Models"; S0003-2700(97)00992-X; p. 1761) Mapping multiphase domains The coupling of an IR focal-plane array (FPA) detector to a stepscan interferometer has greatly improved FT-IR chemical imaging analysis by combining spectroscopy with visualization. Jack L. Koenig and Sung Joon Oh of Case Western Reserve University report on the use of FT-IR with FPA detection for the characterization of the phase morphology and interfacial regions of cured and uncured polybutadiene/diallyl phthalate blends that exhibit upper critical solution temperature separation behavior. Domain size and structure information are obtained by monitoring C-H, C=0, and C-0 bands of the blend components in the IR region. The average domain sizes of uncured blends are found to increase with aging by coalescence of smaller particles. ("Phase and Curing Behavior of Polybutadiene/Diallyl Phthalate Blends Monitored by FT-IR Imaging Using FocalPlane Array Detection"; S0003-2700(97)01290-0; p. 1768) Answers from phantom data Calibration models for noninvasive glucose monitoring by near-IR are often based on glucose absorbance values that are 302 A
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so small relative to the background absorbance from the tissue matrix that it is difficult to verify the origin of the spectral information. Mark A Arnold and colleagues at the University of Iowa and Ohio University assess the accuracy of predictions for glucose from calibration models built with spectra with no glucose information; that is, they generate a phantom glucose data set in which noninvasive human spectra are simulated and glucose is purposely omitted. The results indicate that nonrandom, time-dependent glucose variations during data collection can produce models that erroneously appear to predict glucose when no glucose information is present. ("Phantom Glucose Calibration Models from Simulated Noninvasive Human NearInfrared Spectra"; S0003-2700(97)01080-9; p. 1773) Toxic phytoplankton blooms Monitoring natural waters for harmful phytoplankton blooms is becoming increasingly important, because of the toxicity and prevalence of these microorganisms. W. H. Nelson and coworkers at the University of Rhode Island have developed a method for detecting species of algae that are capable of producing toxins, such as domoic acid (the compound responsible for an outbreak of food poisoning due to contaminated Prince Edward Island mussels). Fourteen algae clones belonging to four different classes are studied by means of resonance Raman spectroscopy. Excitation wavelengths of 457.9 and 488 nm provide sufficiently distinct spectra to differentiate clones at the algal class level, and principal-component analysis is used to classify sets of similar spectral data. ("Differentiation of Algae Clones on the Basis of Resonance Raman Spectra Excited by Visible Light"; S0003-2700 (97) 01098-6; p. 1782) XRF w i t h TLC Mayumi Ohnishi-Kameyama and Tadahiro Nagata of the National Food Research Institute Gapan) combine TLC and X-ray fluorescence spectrometry without tsing an interfacee Thii seables the direct, nondestructive visualization of elements developed on TLC plates. The method can detect organic compounds, including those with electronegative elements such as phenolic compounds with halogens, which cannot always be measured satisfactorily by other methods. ("An Application of X-ray Fluorescence Spectrometry to the Study of Thin-Layer Chromatography"; S0003-2700(97)01159-l; p. 1916) Bias in multicomponent analysis Spectroscopic data can be used to quantify all components in a mixture provided that its composition is qualitatively welldefined; however, multivariate calibration methods based on Beer's law are susceptible to noise, baseline effects, and spurious peaks, and therefore often lead to biased predictions. Joan Ferre and F. Xavier Rius of the Universitat Rovira i Virgili (Spain) have developed a graphical method to detect bias based on a comparison between the net analyte signal in the test sample and the net analyte signal of the pure analyte spectrum. When an interference is detected by a particular sensor, a moving window approach eliminates the use of that sensor, and a new subset of sensors that minimizes the bias is selected. The method is validated with UV-vis spectra of binary chlorophenol and pesticide mixtures. ("Detection and Correction of Biased Results of Individual Analytes in Multicomponent Spectroscopic Analysis"; S0003-2700(97)00837-8; p. 1999)
