Showing papers in "Journal of Chromatographic Science in 1997"

Mass Spectral Characterization of p-Nonylphenol Isomers Using High-Resolution Capillary GC—MS

Abstract: High-resolution gas chromatographic (GC) analyses of p-nonylphenol at selected oven temperatures have achieved resolution of 22 para-isomers. Separation is accomplished through the use of a 100-m capillary GC column exhibiting over 400,000 theoretical plates. Coupling this GC analysis to a mass spectrometer has resulted in discrete mass spectra that more accurately characterize this important group of isomers. Analysis of the spectra indicates the presence of five distinct groups of isomers. Group designations are presented based on the substitution of the alpha-carbon on the alkyl chain. This data, in conjunction with model mass spectra, elucidate the structures of p-nonylphenol isomers. Quantitative analysis using high-resolution GC with a flame-ionization detector is also presented. Fourier transform infrared analysis confirms ortho- and para-phenolic substitution. Examination of the infrared fingerprint region provides an unequivocal confirmation of phenolic substitution.

Hyphenated Liquid Chromatographic Method for the Determination of Colistin Residues in Bovine Tissues

Abstract: A selective and sensitive high-performance liquid chromatographic (HPLC) method has been developed for the measurement of colistin residues in milk and in four bovine tissues (i.e., muscle, liver, kidney, and fat). The sample treatment consists of protein precipitation using 10% (w/v) trichloroacetic acid, solid-phase purification on C18 cartridges, and precolumn derivatization of colistin with ortho-phthalaldehyde and 2-mercaptoethanol in borate buffer (pH 10.5). This latter step is performed automatically, and the resulting reaction mixture is injected into a switching HPLC system including a precolumn and an analytical column packed with end-capped LiChrospher RP18 (5 microns). Washing the precolumn and final elution onto the analytical column are conducted using acetonitrile-0.01M phosphate buffer (pH 7.0) mixtures with respective proportions of 65:35 and 68:32 (v/v). Detection is carried out by spectrofluorometry (excitation wavelength, 340 nm; emission wavelength, 440 nm). The retention times of the derivatives corresponding to the two main components of colistin (i.e., polymyxins E2 and E1) are approximately 14 and 18 min, respectively. The structural study of the derivatives corresponding to polymyxins E1 and E2 is carried out by HPLC coupled with electrospray mass spectrometry; data obtained confirms that the derivatization process occurs with the five amino groups of the analytes. Selectivity is obtained in the HPLC system versus other coadministered anti-infective drugs (beta-lactams, aminoglycosides, tetracyclines, and sulphonamides) and endogenous compounds. Quantitation is performed using the sum of the peak areas of polymyxin E1 and polymyxin E2 derivatives. Testing linearity affords correlation coefficients greater than 0.990 for calibration curves in the range of 10-500 microL/L for milk, 50-1000 micrograms/kg for muscle and fat, and 100-1000 micrograms/kg for kidney and liver. Relative standard deviation values are less than 10% at a concentration of 25 micrograms/L in milk and 100 micrograms/kg in tissues (six replicates); recoveries are higher than 60%.

Determination of Amino Acids in Green Beans by Derivatization with Phenylisothiocianate and High-Performance Liquid Chromatography with Ultraviolet Detection

Abstract: A high-performance liquid chromatographic method for the determination of primary and secondary amino acids in green beans is described. Hydrochloric acid hydrolysates of 15 representative samples of bean proteins are derivatized with phenylisothiocianate, and the resulting phenylthiocarbamyl derivatives are separated on a reversed-phase column by gradient elution with sodium acetate buffer and acetonitrile-water (60:40 [v/v]) and detected by ultraviolet detection at 254 nm. Recoveries range from 93.5 to 97.5%, method precision (relative standard deviation) ranges from 1.26 to 3.98%, and detection limits range from 8.11 to 13.3 pmol/μL.

Detection of Tricyclic Antidepressants in Whole Blood by Headspace Solid-Phase Microextraction and Capillary Gas Chromatography

Abstract: A simple method for the extraction of four tricyclic antidepressants from whole blood by headspace solid-phase microextraction (SPME) is presented. The whole blood samples contain four drugs (amitriptyline, chlorimipramine, imipramine, and trimipramine) and are heated at 100°C in a septum-capped vial in the presence of distilled water and NaOH solution; a polydimethylsiloxane-coated SPME fiber is exposed to the headspace of the vial to allow adsorption of the drugs before capillary gas chromatography (GC) with flame-ionization detection. The headspace SPME-GC produces intense peaks for each drug with very little background noise. Recoveries of the four drugs by the present method are 5.3-12.9%. The calibration curves for the drugs show linearity in the range of 31-1000 ng/0.5 mL The detection limits of each drug are 16-25 ng/0.5 ml. Imipramine is detectable from rat blood 5 h after oral administration of imipramine (500 mgAg body weight); the concentration is 1.44 ± 0.209 μg/mL.

Poly(diallyldimethylammonium chloride) as a cationic coating for capillary electrophoresis

Abstract: A novel cationic polymer coating that exhibits a fast anodal electroosmotic flow (EOF) has been developed for capillary electrophoresis. In the first approach, poly(diallyldimethylammonium chloride) is chemically bonded onto the interior capillary wall; in a second approach, the polymer is physically adsorbed onto the inner wall of the capillary. Capillaries modified by both approaches exhibit an anodal EOF in the pH range of 2.2-8.8, with a relatively pH-independent EOF (approximately -5.5 × 10 -4 cm2/V s) over the pH range of The application of the novel EOF-reversed phase is demonstrated by the improved separation of basic proteins and beta-adrenergic blocking drugs. Separation efficiencies ranging from 50,000 to 200,000 plates per meter are observed for proteins. The relative standard deviation (RSD) of migration times for multiple injections of test proteins is less than 0.65%. The reproducibility of capillary synthesis is 2.3% RSD for capillaries synthesized on three different days. The lifetimes of both the bonded and physically coated capillaries exceed 40 h of continuous use at 240 V/cm at pH 4.

Chromatographic Analysis of Water and Wine Samples for Phenolic Compounds Released from Food-Contact Epoxy Resins

Abstract: Food-contact epoxy resins can release phenolic compounds such as phenol, m-cresol, bisphenol F, bisphenol A, 4-tert-butylphenol, bisphenol F diglycidyl ether (BFDGE), and bisphenol A diglycidyl ether (BADGE) into foodstuffs. A validated high-performance liquid chromatographic method with fluorometric detection is described for the simultaneous analysis of these compounds in wine and mineral water. Sample preparation by solid-liquid extraction enables detection limits of 2.5 μg/L in wine and 0.25 μg/L in mineral water to be achieved. Recovery rates are close to 100%, except for BFDGE and BADGE (around 60% in wine and 75% in mineral water).

Simple Analysis of Diphenylmethane Antihistaminics and Their Analogues in Bodily Fluids by Headspace Solid-Phase Microextraction—Capillary Gas Chromatography

Abstract: Thirteen antihistaminic drugs and their analogues are tested for their extraction by headspace solid-phase microextraction from human whole blood and urine. Their determination is made by using capillary gas chromatography with flame ionization detection. Relatively high recoveries are obtained for terodiline, diphenhydramine, diphenylpyraline, and orphenadrine in urine; but the recoveries in blood extracts are 4–51 times lower than those in urine extracts for all drugs. Benactyzine and piperilate are not suited for the extraction method. The calibration curves are drawn for four drugs spiked to whole blood and for eleven drugs spiked to urine; excellent linearity is confirmed for the drugs. The detection limits for the drugs are 76–473 ng/mL in blood and 13–186 ng/mL in urine. Diphenhydramine is determined for whole blood obtained from a male subject who had received oral administration of 30 mg diphenhydramine–HC1150 min before the sampling; the concentrations of the drug are 0.12 and 1.22 μg/mL for blood and urine, respectively.

Characterization of flavonoids in extracts from four species of Epimedium by micellar electrokinetic capillary chromatography with diode-array detection.

Abstract: A micellar electrokinetic capillary chromatographic (MEKC) method with diode-array detection is developed for the characterization of pharmacologically active flavonoids in extracts prepared from Epimedium brevicornum, E. hunanense, E. coactum, and E. truncatum. The pK a values of icariin, epimedin B, and epimedin C are determined by spectrophotometry. Optimal separation of icariin, epimedin B and C, and eight other compounds is achieved by determining pK a values and by systematically optimizing electrolytic and instrumental parameters. The repeatability of analyses and the reliability of identifications are evaluated by the marker technique. Calculated for relative migration times of flavonoids in the extracts, the repeatability of the analyses varies from 0.7 to 6.4% (nine replicates). For migration indices calculated with two markers, however, the repeatability almost falls below 0.5%. The distribution of the flavonoids is found to differ both qualitatively and quantitatively among the four species. The MEKC technique appears to provide a powerful tool for the identification and quality control of plant drugs and for phytotaxonomic investigations.

Derivatization Solid-Phase Microextraction Gas Chromatographic—Mass Spectrometric Determination of Organic Acids in Tobacco

Abstract: Isovaleric, valeric, hexanoic, benzoic, phenylacetic, 3-methylvaleric, heptanoic, octanoic, and nonanoic acids are converted to their methyl esters and quantitated for flue-cured tobacco grades of increasing stalk position using derivatization headspace solid-phase microextraction (SPME) with selected ion monitoring mode mass spectrometry. Qualitative analysis of the headspace of tobacco derivatized with methanolic hydrochloric acid using a 65-pm Carbowax-divinylbenzene SPME fiber indicates selectivity for relatively nonpolar volatile and semivolatile organic acid methyl esters. By contrast, direct exposure of an 85-μm polyacrylate SPME fiber to derivatives followed by GC-MS analysis provides the capability to evaluate significantly more polar organic acid methyl esters such as malic acid dimethylester and citric acid trimethylester.

Effect of Extraction Conditions and Modifiers on the Supercritical Fluid Extraction of 88 Pesticides

Abstract: Supercritical fluid extraction (SFE) conditions for multiresidue analysis of pesticides are evaluated using diatomaceous earth (Celite) spiked with 88 pesticides (16 organochlorine, 33 organophosphorus, 8 pyrethroid, 12 carbamate, and 19 other pesticides). The SFE parameters considered are CO2 density, CO2 flow rate, extraction temperature, static and dynamic extraction times, trap temperature, and addition of modifier. SFE without modifier is insufficient to extract polar pesticides from fortified Celite. The addition of water to Celite is most effective in enhancing the recoveries of pesticides. Methanol is also an effective modifier, but the recovery of captafol, captan, phosmet, and chinomethionat decreases as time goes on after the addition of methanol. The best obtained conditions of SFE (2.0 g sample) are as follows: 0.40 mL of water as a modifier, 0.70 g/mL CO2 density, 50°C extraction temperature, 2.0 mL/min CO2 flow rate, 3.0 min of static extraction, and 20.0 min of dynamic extraction. The extracted pesticides are collected on an octadecylsilane trap at 30°C. Quantitative analysis of the 88 pesticides is performed by gas chromatography—mass spectrometry using the selected ion monitoring mode. Recoveries from fortified Celite are greater than 90% for 79 pesticides and greater than 70% for the other pesticides, except acephate, methamidophos, and propamocarb. The relative standard deviations of the recoveries are less than 5% for almost all of the pesticides.

An Alternative Method for the Calculation of Equivalent Chain Length or Carbon Number of Fatty Acid Methyl Esters in Gas Chromatography

Abstract: The carbon number or equivalent carbon number (ECN) of fatty acid methyl esters (FAMEs) separated on a 30-m x 0.32-mm-i.d. Omegawax 320 capillary column is calculated directly from the retention data. When the described equation is used to identify FAMEs in a mixture of FAMEs from rambutan and para-rubber seed oils, the calculated ECN values are very close to the widely accepted equivalent chain length values described in the literature. Hence, the equation can probably be used as an identification tool for FAMEs.

Speciation of Nitrogen Compounds in Gasoline and Diesel Range Process Streams by Capillary Column Gas Chromatography with Chemiluminescence Detection

Abstract: This paper describes the development of a gas chromatographic method that uses nitrogen-specific detection based on chemiluminescence. A highly sensitive nitrogen-specific detector (Antek 705D) coupled to a Hewlett-Packard gas chromatograph is optimized to speciate nitrogen compounds in gasoline and diesel range process streams. Under optimized conditions, the nitrogento-carbon selectivity is greater than 106. The nitrogen chemiluminescence detector (NCD) provides a uniform response to different classes of nitrogen compounds and can detect concentration of individual components down to 100 ppb nitrogen. The detector's linear response in a range of 0.2 to 54 ppm nitrogen for an individual nitrogen component is established using several aliphatic and aromatic nitrogen-containing compounds. Gasoline and diesel range streams containing any level of total nitrogen can be analyzed after appropriate dilution so that each nitrogen component is below 50 ppm. In addition to the nitrogen speciation, total nitrogen can simultaneously be determined with reasonable accuracy using the NCD system. The repeatability and accuracy of the nitrogen quantitation is found to be within 7% at the 95% confidence level based on six to seven measurements. cess relatively inexpensive, heavy, and low-quality feed stocks containing large quantities of nitrogen and other heteroatoms' compounds. In order to obtain the desired product quality and also to understand the effect of nitrogen compounds during cat­ alytic processes, it is beneficial to speciate nitrogen compounds that are present in various process streams. A few attempts (1–5) have been made to identify some of the nitrogen compounds in the petroleum streams. However, in these studies, nitrogen compounds were analyzed after being concentrated using different laborious techniques such as acidtreatment extraction, ion-exchange chromatography, etc. The results of these studies are not quantitative because some of the nitrogen compounds were either not extracted or were lost during the extraction. The concentrated fractions were analyzed by gas chromatography (GC) using different detectors or gas chromatography-mass spectrometry (GC-MS). The most commonly used nitrogen detectors are Hall detec­ tors and nitrogen-phosphorus detectors (NPD). Hall detectors

Subcritical Fluid Extraction of Stevia Sweeteners from Stevia rebaudiana

Abstract: In this paper, the extraction of steviol glycosides in Stevia rebaudiana, including stevioside, rebaudioside A, rebaudioside C, and dulcoside A by subcritical fluid extraction (SubFE) is investigated. A simple, efficient SubFE method is developed. The extraction conditions (extraction phase composition, extraction time, etc.) are optimized. An extraction efficiency of more than 88% is obtained using methanol as a modifier. Determination of stevioside in the leaves of Stevia rebaudiana is performed by using the SubFE method developed and capillary electrophoresis.

Liquid Chromatographic Determination of Vitamin C in Aquatic Organisms

Abstract: A reversed-phase ion-pair liquid chromatographic method using electrochemical detection and internal standardization with isoascorbic acid (IAA) is described for the determination of ascorbic acid (AA) and dehydroascorbic acid (DHAA) in aquatic organisms. Several extractants are compared with regard to recovery and stability of AA and DHAA, including 5% metaphosphoric acid (MPA)-0.54mM ethylenediaminetetraacetic acid (EDTA), 1 % acetic acid (Hac)-1 mM EDTA, 1 % Hac-0.1 % MPA-1 mM EDTA, 2mM homocysteine-1 mM EDTA, and water-methanol (70:30, v/v) containing 0.7mM EDTA. The two nonacidic extractants afford insufficient protection of AA (water-methanol-EDTA) or DHAA (homocysteine-EDTA). High ionic strength acidic mixtures (e.g., 5% MPA) may be associated with a negative drift in the retention times of AA and IAA. Hac (1 %)-EDTA (1 mM) yields lower recovery except when supplemented with MPA. A mixture of 1 % Hac-0.1 % MPA-1 mM EDTA is useful in extracting AA from the brine shrimp Artemia, Brachionus, fish eggs, fish larvae, and postlarvae of shrimp as part of its routine high-performance liquid chromatographic determination in these matrices.

Liquid Chromatographic Analysis of Amphetamine and Related Compounds in Urine Using Solid-Phase Extraction and 3,5-Dinitrobenzoyl Chloride for Derivatization

Abstract: A chromatographic method for the analysis of amphetamine and related compounds in urine using 3,5-dinitrobenzoyl chloride (3,5-DNB) as a labeling reagent is presented. This assay is based on the employment of solid-phase extraction (SPE) cartridges for sample cleanup and derivatization. Experimental conditions are optimized for the simultaneous derivatization of ephedrine, norephedrine, pseudoephedrine, beta-phenylethylamine, amphetamine, methamphetamine, and 3-phenylpropylamine. The derivatives formed are separated in a LiChrospher 1000 RP18 (125 x 4-mm i.d., 5-microns film thickness) analytical column using a water-acetonitrile gradient elution and detected at 254 nm. Derivatization in C18 SPE disks is found to be the best option for analysis of urine samples; this method provides analyte conversions that are about 85-102% of those obtained by the analogous solution derivatization. Because the 3,5-DNB reagent is a strong pi-acid, the described method can be used in combination with a Pirkle-type donor column for chiral analysis. The practicality of the described approach is illustrated by determining amphetamine enantiomers using a Supelcosil LC-(S)-naphtylurea (250 x 4.6-mm i.d., 5-microns film thickness) column and a mobile phase of n-hexane-acetonitrile-ethyl acetate. Under these conditions, good linearity and reproducibility are observed over the 0.5-10 micrograms/ml concentration range; the limit of detection is 50 ng/mL.

Simultaneous Solid-Phase Extraction and Gas Chromatographic—Mass Spectrometric Determination of Hemoglobin Adducts from Tobacco-Specific Nitrosamines and Aromatic Amines

Abstract: A new method for the simultaneous determination of hemoglobin adducts from aromatic amines and tobacco-specific nitrosamines (TSNA) is described. After mild base-catalysed hydrolysis releasing aromatic amines and the TSNA adduct 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB), the extraction, cleanup, and concentration are performed by a one-step procedure using C18 cartridges. Determination in the picograms per gram of hemoglobin range by gas chromatography-mass spectrometry with negative chemical ionization requires a separate derivatization procedure with pentafluoropropionic anhydride and pentafluorobenzoylchloride for aromatic amines and HPB, respectively. The method is shown to be quantitative, reproducible, and applicable to the determination of hemoglobin adducts from monocyclic and bicyclic aromatic amines as well as TSNA in smokers and nonsmokers.

Chromatographic ion-exchange simultaneous separation of arsenic and selenium species with inductively coupled plasma-mass spectrometry on-line detection

Abstract: The high-performance liquid chromatographic (HPLC) simultaneous separation of arsenite, arsenate, monomethylarsonic acid, dimethylarsinic acid, selenite, and selenate is studied. The dependence of the retention times of these species on the pH of the mobile phase and on the concentration and chemical composition of buffer solutions (acetate, carbonate, and phosphate) is investigated using a Merck Polyspher IC AN2 and a Hamilton PRPX100 anion exchange column. With a flame atomic absorption spectrometric detector (FAAS) and arsenic or selenium concentrations of at least 100 mg/L, the best simultaneous separation of these species is achieved on the PRP-X100 column using 0.015M ammonium phosphate buffer at pH 8.5, a 1-mL/min flow rate, and a 20-min analysis time. In a second study, these separation conditions are optimized by using an inductively coupled plasma-mass spectrometric (ICP-MS) detector. The use of a 12.5mM ammonium phosphate buffer adjusted to pH 8.5 with ammonia and a flow rate of 1.5 mL/min is found to be optimal for HPLC-ICP-MS studies with the PRP-X100 column. The analysis time is about 16 min; absolute detection limits are estimated in the range of 11-21 pg for arsenic species and 200 and 417 pg for SeIV and SeVI, respectively. Reproducibility ranges from 2.1 to 3.2%, and the linearity is verified in the 0-200-ng/mL range.

A new procedure for the specific high-performance liquid chromatographic determination of hydroxyproline.

Abstract: A procedure suitable for a selective high-performance liquid chromatographic (HPLC) analysis of the imino acid hydroxyproline in the presence of a large excess of amino acids is proposed. To deaminate the amino acids, the well-known reaction with nitrous acid is exploited. The N-nitroso derivatives of imino acids obtained are extracted in ethyl acetate, denitrosated by hydrobromic acid, and treated with dabsyl-chloride. The final HPLC separations are carried out on a reversed-phase column in a rapid isocratic run. The use of the cis isomer of hydroxyproline as an internal standard allows good reproducibility. As an application of the described method, the hydroxyproline content in samples containing collagen and an excess of bovine serum albumine (up to 20:1) is determined.

Analysis of Biodesulfurization Products Using Solid-Phase Extraction

Abstract: Alkylated dibenzothiophenes (DBTs) are not efficiently desulfurized by the conventional hydrodesulfurization (HDS) process, and thus they remain targets for deeper desulfurization of HDS-treated oil. Microbial degradation systems are expected to convert these heterocyclic sulfur compounds to inorganic sulfur (sulfate or sulfite). For screening and characterization of the potentially useful desulfurizing microbes, it is very important to analyze microbial metabolites of these DBTs. For this purpose, highly sensitive methods of analysis and efficient concentration are required because there would be only small amounts of the metabolites in microbial culture media. A sample preparation technique based on solid-phase extraction (SPE) was studied to separate DBT metabolites from an organic matrix such as gas oil. Our results demonstrate that the metabolites with polar functional groups such as 2-hydroxybiphenyl or ο,ο'-biphenol produced by a desulfurizing microbe (Rodococcus erythropolis) can be efficiently separated from the organic matrix and concentrated quantitatively by SPE. Moreover it has been proven that the combination of SPE with gas chromatography-mass spectrometry or gas chromatography-atomic emission detection analysis can be successfully used for detailed characterization of gas oil treated by desulfurizing biocatalysts. gency of sulfur emission standards is increasing around the world. In this respect, biological desulfurization systems have recently attracted attention for their potential advantages com­ pared with HDS. There are several reasons for this: they work at low temperatures and under low pressure, require no addi­ tion of hydrogen gas, and possibly degrade organosulfur com­ pounds, which are considerably resistant to HDS treatment (3-5). Dibenzothiophene (DBT) has been used as the model compound to represent the organosulfur material present in

Direct Measurement of Total trans- and cis-Octadecenoic Fatty Acids Based on a Gas-Liquid Chromatographic Class Separation of trans-18:1 and cis-18:1 Fatty Acid Methyl Esters

Abstract: A gas-liquid chromatographic (GLC) class separation is described whereby the contents of total trans- and cis-octadecenoic fatty acids can be obtained for relatively simple samples such as margarines and for more complicated food mixtures and biological specimens. The method is an adjunct to the standard process commonly used for quantitating the general fatty acid profile of a sample (extraction of lipids, preparation of methyl ester derivatives of fatty acids, GLC separation on Carbowax-20M capillary columns). There is no incremental work beyond the addition of one chromatographic run on a cyanosilicone capillary column at 242°C that lasts only 20-25 min. The chromatograms provide a composite trans peak and a composite cis peak with sufficient resolution between them to provide direct estimation of total trans- and cis-octadecenoic fatty acids. A concurrent analysis for the general profile of fatty acids in an unknown (using Carbowax20M columns) is included with every analysis for trans content to check for internal consistency and for general quality control.

Liquid Chromatographic Determination of Cocaine, Benzoylecgonine, and Cocaethylene in Whole Blood and Serum Samples with Diode-Array Detection

Abstract: An extraction with Bond Elut Certify solid-phase extraction (SPE) columns is developed for the isolation of cocaine, benzoylecgonine, and cocaethylene from whole blood and serum followed by reversed-phase liquid chromatography with diode-array detection. Two internal standards (2'-methylbenzoylecgonine and 2'-methylcocaine) with close structural resemblance to benzoylecgonine (a carboxylic acid) and to the two esters, cocaine and cocaethylene, are used in the analytical procedure. A thorough evaluation of this SPE and a comparison with different liquid-liquid extractions clearly show the superiority of the SPE. A linear response (correlation coefficient greater than 0.998) over a broad concentration range (0.025-5.0 micrograms/mL) is obtained. The sensitivity, specificity, precision (coefficients of variation less than 4.9% for within-day reproducibility and less than 5.3% for total reproducibility), and accuracy of the method are excellent for each analyte. Forensic blood samples from people suspected of cocaine abuse are analyzed and show the usefulness of the method, even for degraded postmortem samples.

A Study of the Behavior of Polar and Nonpolar Solid-Phase Microextraction Fibers for the Extraction of Maillard Reaction Products

Abstract: Aqueous solutions of Maillard reaction products are analyzed using nonpolar and relatively polar solid-phase microextraction (SPME) fibers. The behavior of the polydimethylsiloxane (nonpolar) and carbowaxdivinylbenzene (CWDVB, polar) fibers toward these solutions over a concentration range of 0.005-50 ppm is described. Both fibers demonstrate a marked tendency to selectively adsorb the more highly alkyl-substituted components relative to their comparable proton-substituted counterparts. The CWDVB fiber is found to be more selective for the more polar Maillard reaction products. By employing SPME, gas chromatography, selected ion monitoring (SIM), mass selective detection, and a relatively short exposure time of 10 min, a detection limit in the range of unit parts per billion is established for the fibers. The addition of NaCl to the aqueous solutions significantly increases the amounts of adsorbed components. A linear response between average analyte SIM area counts and analyte concentration over the range of 0.005-0.50 ppm is demonstrated for many of the components.

Determination of the Enantiomers of Mianserin and its Metabolites in Plasma by Capillary Electrophoresis After Liquid—Liquid Extraction and On-Column Sample Preconcentration

Abstract: Capillary electrophoresis has drawn considerable attention in the past few years, particularly in the field of chiral separations because of its high separation efficiency. However, its routine use in therapeutic drug monitoring is hampered by its low sensitivity due to a short optical path. We have developed a capillary zone electrophoresis (CZE) method using 2mM of hydroxypropyl -B- cyclodextrin as a chiral selector, which allows base-to-base separation of the enantiomers of mianserin (MIA), desmethylmianserin (DMIA), and 8-hydroxymianserin (OHMIA). Through the use of an on-column sample concentration step after liquid-liquid extraction from plasma and through the presence of an internal standard, the quantitation limits were found to be 5 ng/mL for each enantiomer of MIA and DMIA and 15 ng/mL for each enantiomer of OHMIA. To our knowledge, this is the first published CE method that allows its use for therapeutic monitoring of antidepressants due to its sensitivity down to the low nanogram range. The variability of the assays, as assessed by the coefficients of variation (CV) measured at two concentrations for each substance, ranged from 2 to 14% for the intraday (eight replicates) and from 5 to 14% for the interday (eight replicates) experiments. The deviations from the theoretical concentrations, which represent the accuracy of the method, were all within 12.5%. A linear response was obtained for all compounds within the range of concentrations used for the calibration curves (10-150 ng/mL for each enantiomer of MIA and DMIA and 20-300 ng/mL for each enantiomer of OHMIA). Good correlations were calculated between ((R) + (5))-MIA and DMIA concentrations measured in plasma samples of 20 patients by a nonchiral gas chromatography method and CZE, and between the (R)- and (S)-concentrations of MIA and DMIA measured in plasma samples of 37 patients by a previously described chiral high-performance liquid chromatography method and CZE. Finally, no interference was noted from more than 20 other psychotropic drugs. Thus, this method, which is both sensitive and selective, can be routinely used for therapeutic monitoring of the enantiomers of MIA and its metabolites. It could be very useful due to the demonstrated interindividual variability of the stereoselective metabolism of MIA.

High-Performance Size Exclusion Chromatography Using Enhanced-Fluidity Liquid Mobile Phases

Abstract: One of the most effective ways to improve the resolution of size exclusion chromatography (SEC) is to decrease band broadening by lowering the mobile phase viscosity. In this study, the use of enhanced-fluidity liquid mixtures of tetrahydrofuran (THF)-liquid CO2 for the separation of polystyrene standards by SEC under room temperature and moderate pressure conditions was investigated. By adding low viscosity liquid CO2 to THF, the mixtures had markedly lower viscosities than THF. As a result, higher efficiency and a shorter analysis time were obtained. When a mixture with 40 mol % CO 2 and 60 mol % THF was used as the mobile phase, the pressure drop across the column decreased by 38% compared with the drop obtained using 100% THF as the mobile phase. KamletTaft solvatochromic parameters π* and β were used to measure the solvent strength of the THF-CO 2 mixtures. A solvent strength similar to that of pure THF was observed when up to 50 mol % CO2 was added to THF. No notable deviation in the SEC calibration curve was observed when up to 40 mol % CO 2 was used. However, as a consequence of diminished solvent strength, significant adsorption of solutes to the stationary phase was detected when more than 50 mol % CO 2 was used.

High-Performance Liquid Chromatographic Separation of Corticoid Alcohols and Their Derivatives: A Hydrolysis Study Including Application to Pharmaceuticals

Abstract: Several reversed-phase high-performance liquid chromatographic methods for the baseline separation of some glucocorticoid alcohols and their derivatives (esters and acetals) have been developed. These methods involve fluorocortisone and fluorocortisone acetate, triamcinolone and triamcinolone acetonide, dexamethasone and dexamethasone phosphate, 21-hydroxydeflazacort and deflazacort, betamethasone and betamethasone valerate using deoxycorticosterone or methylprednisolone as an internal standard, a Hypersil C 18 column, several mobile phases containing acetonitrile, and ultraviolet detection. These sensitive methods are used for a further hydrolysis study in an aqueous medium using standard solutions, which allowed the simultaneous monitoring of glucocorticoid derivatives and their hydrolysis products. In this study, the main variables that can affect the hydrolysis (pH and temperature) are also studied. Several applications to pharmaceuticals containing glucocorticoids are also reported.

Determination of Volatile Acids in Tobacco, Tea, and Coffee Using Derivatization-Purge and Trap Gas Chromatography-Selected Ion Monitoring Mass Spectrometry

Abstract: Short-chain organic acids from agricultural products are simultaneously extracted and derivatized using methanolic hydrochloric acid Acetic, isobutyric, butyric, isovaleric, valeric, hexanoic, 3-methylvaleric, heptanoic, and nonanoic acids are quantitated using purge and trap gas chromatography with selected ion monitoring mode mass spectrometry Flue-cured, burley, and oriental tobacco varieties are compared based on their volatile organic acid content Commercial coffee, tea, and three cigarette brands are analyzed, and their differences are evaluated to demonstrate the utility of this technique for natural product analysis

Dependence of Chromatogram Peak Areas Obtained by Curve-Fitting on the Choice of Peak Shape Function

Abstract: Seven different chromatographic peak shape functions are evaluated for use with nonlinear least-squares curve-fitting for asymmetric peak area measurements. The four-parameter functions that are evaluated are unable to adapt to peaks exhibiting substantial tailing, which results in peak area underestimates. Peak tailing is more readily represented by using six- and eight-parameter functions; however, the use of these more flexible functions can result in peak area overestimation and inaccuracies for overlapping peaks. The exponentially modified Gaussian function is advocated for general purpose chromatogram curve fitting because it adapts to extended peak tailing better than the other four-parameter functions evaluated and provides better reproducibility when large digitization intervals are employed or when poor initial curve-fitting parameters are chosen than the six- and eight-parameter functions that were evaluated.

Liquid Chromatographic Sample Cleanup Coupled On-Line with Gas Chromatography in the Analysis of Beta-Blockers in Human Serum and Urine

Abstract: An on-line coupled reversed-phase liquid chromatographic-gas chromatographic (LC-GC) method with minimal manual sample preparation is developed for the analysis of metoprolol, oxprenolol, propranolol, timolol, and codeine (as an internal standard) in human serum and urine. The method is based on a loop-type interface and concurrent eluent evaporation technique. On-line liquid-liquid extraction (LLE) is used to extract the analytes from aqueous eluent to organic solvent before injection onto the GC, and the two phases are separated with a sandwich-type phase separator. The LC is used for cleanup, and the GC is used for the final separation and detection of the analytes. Total analysis time is less than 45 min, which is much less than those of traditional analysis methods. Recoveries in LC cleanup and on-line LLE are excellent. A marked increase in the recoveries with on-line LLE is obtained by heating the aqueous eluent and the extraction coil. Linearity and repeatability of the method are good for both serum and urine, and the limits of quantitation for the analytes are 18-44 ng/mL.

Trends in Capillary Electrophoresis: 1997

Abstract: This article is intended to present an overview of developments in the field of capillary electrophoresis (CE) and its application to the analysis of micro-environments. Instrumental developments in injection and detection methods and the separation chemistries are outlined. Emphasis is placed on methods and means that have significantly improved the capability of CE. Subsequently, several selected applications to the exploration of microenvironments such as CE-based sensors, CE on microchip, and single cell analysis are described. The recent advancements in these areas are highlighted.

Research associated with the development of EPA method 552.2

Abstract: The work presented in this paper entails the development of a method for haloacetic acid (HAA) analysis, Environmental Protection Agency (EPA) method 552.2, that improves the safety and efficiency of previous methods and incorporates three additional trihalogenated acetic acids: bromodichloroacetic acid, chlorodibromoacetic acid, and tribromoacetic acid, which are not included in the previous two methods, standard method 6251B and EPA method 552.1. The final procedure includes a microextraction coupled with derivatization by acidic methanol. All nine possible brominated and chlorinated HAAs are detectable at concentrations of less than 1 pg/L. The objective of this paper is to describe the various approaches that were explored, the conclusions that were drawn from the associated studies, and the reasoning behind the changes that were incorporated into EPA method 552.2