bluuebunny/crossref_metadata_2025 huggingface dataset:
Capillary electrophoresis separation of heterocyclic nitrosoamino acid‐conformers at sub‐ambient temperatures
Authors: Janini George M. , Muschik Gary M. , Issaq Haleem J.
Published: May 2005

The separation of a selected group of naturally occurring, heterocyclic nitrosoamino acids was achieved by capillary zone electrophoresis and the resolution of the syn and anti conformers improved as the temperature was lowered to 5 °C. The double peaks observed for each nitrosoamino acid are probably caused by the slow kinetics of conformational isomerism. The experimental setup consisted of a P/ACE 5510 electrophoresis system, a 57 cm polyacrylamidecoated capillary, and a 10 mM phosphate buffer, pH 7.2, containing 2 mM of 3‐(N‐N‐dimethylmyristylammonio)propanesulfonate (DMMAPS) and 0.1% Tween 20. Our study shows that (a) the lower the temperature, the greater the resolution and the longer the migration times; and (b) different nitrosoamino acid conformers were resolved at different temperatures because of differences in the rate of isomerization. For example, the conformers of N‐nitrosothiazolidine‐4‐carboxylic acid were partially resolved at 30 °C while those of N‐nitrosoproline were well resolved at the same temperature.
Liquid trapping after supercritical fluid extraction with modified carbon dioxide
Authors: Thompson P. G. , Taylor Larry T.
Published: May 2005

A polarity test mix consisting of acetophenone, N,N‐dimethylaniline, naphthalene, 2‐naphthol, and n‐tetracosane was spiked onto sand and extracted with carbon dioxide modified with acetonitrile, methanol, or toluene. The extracts were collected in chloroform, hexane, methanol, or a mixed collection solvent consisting of equal parts chloroform‐hexane‐methanol. The mixed collection solvent which showed excellent recoveries for pure CO2, had the worst recoveries of all the collection solvents with modified CO2. Overall hexane was the best collection solvent studied for these analytes under these extraction conditions.
Direct coupling of capillary supercritical fluid chromatography with double‐focusing high resolution mass spectrometry
Authors: Bücherl T. , Eschler M. , Gruner A. , Palibroda N. , Wolff E.
Published: May 2005

An integral restrictor interface with jet separator for coupling capillary column supercritical fluid extraction – supercritical fluid chromatography with high resolution mass spectrometry (SFE‐SFC‐MS) has been built and used for the analysis of a fatty acid ester, and of polymer additives with a wide range of masses. The mobile phase used was supercritical carbon dioxide; a flame ionization detector (FID) was used in parallel with the mass spectrometer. Different SFC‐MS interface operating conditions, e.g. temperature, restrictor position, flow rate, and sample transfer conditions were optimized to obtain good sensitivity and separation for these applications. In addition, the sensitivity of measurements performed with the direct insertion probe and by SFC‐MS interface have been compared.
Analysis of atmospheric sulfur gases by capillary gas chromatography with atomic emission detection
Authors: Swan Hilton B. , Ivey John P.
Published: May 2005

The atomic emission detector (AED) has been found to be a sensitive and selective instrument for analysis of atmospheric sulfur gases by capillary gas chromatography. It was possible to determine atmospheric dimethyl sulfide at concentrations below 0.3 nmol/m3 typical of the remote marine environment in winter. Sample analyses from the Australian Baseline Air Pollution Station, Cape Grim, are used to illustrate this.

In comparison with other sulfur‐specific detectors previously used for this work, the AED has been found to exhibit the best combination of specificity and sensitivity. A configuration comprising a series of valves, gas calibration loops, and a cryogenic trap prior to the GC‐AED was used for sample analysis. Standard addition of sulfur hexafluoride was found to assist determination of carbonyl sulfide, as it could be used to take into account the magnitude of signal quenching from coeluting gases. The AED was also found to be a selective detector for the direct injection of water‐soluble dimethyl sulfide oxidation products.
Identification of sterene compounds produced during the processing of edible oils
Authors: Mennie Darren , Moffat Colin F. , McGill Alister S.
Published: May 2005

Samples of maize, rapeseed, soyabean, sunflower, and palm oils, collected at different stages in their respective refining processes, have been analyzed for the presence of dehydrated sterols (sterenes). A total of fifteen compounds were detected. Four have been characterized using model systems designed to investigate their formation. Their elemental composition, and that of the other eleven sterenes, was determined by high resolution mass spectrometry and structures assigned to a further six compounds. These included the ‐3,5‐, ‐2,5‐, ‐4,6‐,‐3,5,22‐, and ‐4,6,22‐ sterenes. Sterenes were not present in crude or alkali neutralized oils. Bleaching introduced a maximum concentration of 5 μg g−1 of total sterenes into the edible oils. Deodorization is the dominant stage in sterene production resulting in a maximum total concentration of 163 μg g−1. This increased concentration arises due to dehydration of the sterols and considerable isomerism of the sterenes.
On‐line recording of 13C/12C ratios and mass spectra in one gas chromatographic analysis
Authors: Meier‐Augenstein Wolfram
Published: May 2005

An isotope ratio mass spectrometer and an ion trap mass spectrometer have been coupled in parallel to one gas chromatograph. Using this arrangement both the 13C/12C ratio and the mass spectrum of a given compound can be measured simultaneously under identical gas chromatographic conditions. Although column connection fittings are employed to split the capillary eluate, chromatographic performance was barely impaired. Development of the system has been monitored by recording δ13C values of the constituents of Grob test mixture no. 2. The accuracy and reliability of system performance has also been tested.
Stereochemical differentiation and simultaneous analysis of 3‐, 4‐, and 5‐hydroxyalkanoic acids from biopolyesters by multidimensional gas chromatography
Authors: Kaunzinger Astrid , Podebrad Frank , Liske RÜDiger , Maas Birgit , Dietrich Armin , Mosandl Armin
Published: May 2005

The direct enantioselective analysis of 3‐, 4‐, and 5‐hydroxy fatty acids from biological material has been achieved by enantioselective multidimensional gas chromatography (enantio‐MDGC) with heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐butyldimethylsilyl)‐ or (2,3‐di‐O‐acetyl‐6‐O‐tert‐butyldimethylsilyl)‐β‐cyclodextrin as chiral stationary phase. All the bacteria investigated produced polyesters of enatiomerically pure (R) configured compounds.
A study of the compositional variation of the essential oil of ylang‐ylang (Cananga odorata Hook Fil. et Thomson, formagenuina) during flower development
Authors: Stashenko Elena E. , Torres William , Morales Jairo René Martinez
Published: May 2005

Volatile secondary metabolites from Colombian ylang‐ylang flowers were obtained by combined steam distillation ‐ solvent extraction. The samples were analyzed by high resolution gas chromatography with flame ionization, nitrogen/phosphorus, or mass spectrometric detection. The chemical composition of the oils extracted from flowers at different stages of development differed both qualitatively and quantitatively. The generation of total volatile metabolites, light oxygenated compounds in particular, increased markedly during flower maturation. In this work the quality of the ylang‐ylang essential oils was studied as a function of flower maturity.
Evaluation of the performance of various universal and selective detectors for sulfur determination in natural gas
Authors: Tuan Hai Pham , Janssen Hans‐Gerd M. , Cramers Carel A. , Kuiper‐van Loo Ellen M. , Vlap Harm
Published: May 2005

In the present contribution, the performance of a number of commercially available selective and universal detectors that can be used in the analysis of sulfur components in natural gas is evaluated in terms of sensitivity, selectivity, reproducibility, quenching effect, stability, and compound dependence of the sulfur response. Investigated detectors include the sulfur chemiluminescnce, the flame photometric, the electron capture, the mass spectrometric, the thermal conductivity, and the flame ionization detector. The sulfur chemiluminescence detector was found to have the best overall performance, e.g., low picogram amounts of sulfur can be detected accurately and the linear dynamic range is more than five orders of magnitude. After careful optimization, the sulfur response of this detector was found to be almost compound independent. All other detectors, including the flame photometric and the electron capture detector, have more or less compound dependent responses.
A further study on the chiral separation power of a soluble neutral β‐cyclodextrin polymer
Authors: Ingelse Benno A. , Everaerts Frans M. , Sevcik Juraj , Stransky Zdenek , Fanali Salvatore
Published: May 2005

Enantiomeric separation of some basic compounds, namely selegiline, amphetamine, and clenbuterol, was studied by capillary electrophoresis using an uncharged β‐cyclodextrin polymer added to the background electrolyte at pH 2.5. Both complexation and resolution were influenced by the concentration of the chiral polymer confirming our previous results obtained in our earlier work for a wide number of pharmaceutical compounds. In this further study, we examined the influence of different organic additives to the background electrolyte on the enantioselectivity of the chiral selector, also using an extended number of analytes. In most cases, the use of an organic additive resulted in a decrease of resolution. However opposite to that, in some cases, e.g. ephedrine, the organic solvent proved to be essential to achieve enantiomeric resolution. Furthermore the influence of the capillary temperature on the resolution of the analytes was evaluated. Increase of temperature had a deleterious effect on the resolution of the enantiomers. For ephedrine, however, relatively high temperature (50 °C) proved to be advantageous, for the resolution of the optical isomers.
Determination of hydroxycarbamates in aqueous matrices by direct derivatization and GC‐MS analysis in chemical ionization mode
Authors: Vincenti Marco , Minero Claudio , Lago Stefania , Rovida Costanza
Published: May 2005

A rapid and effective procedure, developed for the determination of polar compounds in water, has been applied to hydroxycarbamates. In few minutes, it is possible to perform a catalyzed derivatization of such compounds directly in the aqueous medium, using n‐hexyl chloroformate. Extraction with n‐hexane and injection into a benchtop GC‐MS system are the only two further steps to complete the analysis. Chemical ionization proved to be more effective than electron impact to produce valuable mass spectra in terms of selectivity and sensitivity. Linear quantitative responses were demonstrated over a two‐order‐of‐magnitude range. The minimum detectable concentration was 3 ppb for acetohydroxamic acid and 10 ppb for hydroxyurethane, obtained from Po river water samples spiked with the two hydroxycarbamate standards.
Identification of volatile (micro) biological compounds from household waste and building materials by thermal desorption–capillary gas chromatography–mass spectroscopy
Authors: Wilkins Cornelius Kendall , Larsen Kjeld
Published: May 2005

Volatile compounds from biodegradable household waste and infected building materials have been studied by dynamic or equilibrium headspace sampling and concentration on Tenax TA followed by thermal desorption and HRGC‐MS. Equilibrium headspace sampling was also used to study vegetables stored for 14–18 days at ambient temperature. Over 200 compounds were tentatively identified. The concentration of organic sulfur compounds from garden waste was high enough to contribute to respiratory problems of waste handling personnel. Nitriles, alkyl nitro compounds, and alkyl nitrates were isolated from radish and carrot samples at low concentrations (10–50 ppb). Air monitoring in waste handling working environments may be required to ensure the safety of personnel. Branched aliphatic aldehydes, carboxylic acids, esters, and 2‐alkanones were found in the headspace of the infected building materials, indicating that volatile compounds may be useful for detection of microbial growth in buildings.
GLC‐MS analysis of the fatty acids of the seed oil, triglycerides, and cyanolipid of Paulliania elegans (Sapindaceae) – a rich source of cis‐13‐eicosenoic acid (paullinic acid)
Authors: Spitzer Volker
Published: May 2005

The fatty acids of the total lipids, triglycerides, and the cyanolipid of Paullinia elegans (Sapindaceae) have been analyzed as their methyl esters and 4,4‐dimethyloxazoline derivatives by gas chromatography‐mass spectrometry. It was shown that the gas chromatographic separation of the oxazoline derivatives was sufficient to ensure the correct identification of the monoenic fatty acid positional isomers. Stereochemistry of the double bonds has been confirmed by infrared and 13C‐nuclear magnetic resonance (NMR) spectroscopy. cis‐13‐Eicosenoic Acid (Paullinic acid) (44.4%) and cis‐11‐octadecenoic acid (cis‐vaccenic acid) (19.8%) were found to be the main components beside other monoenoic acid positional isomers. The cyanolipid of P. elegans was identified as 2,4‐dihydroxy‐3‐methylenebutyronitrile derivative by IR, 1H‐NMR, 13C‐NMR spectroscopy and was quantified by 1H‐NMR spectroscopy (71.4%).
Microwave extraction in analytical chemistry of pollutants: Polychlorinated biphenyls
Authors: Onuska Francis I. , Terry Ken A.
Published: May 2005

The microwave energy produced by a high intensity microwave oven was used to extract polychlorinated biphenyls (PCB) from water samples. This static method was compared with liquid‐liquid extraction to determine the optimum and limiting conditions in extraction processes. The sample size and sample container shape determine the temperature profiles in the sample. Using a 500 mL sample size, the detection limit is in the low ng/L range when an electron capture detector is employed.
Solvent‐assisted supercritical fluid extraction for the isolation of semivolatile flavor compounds from the cinnamons of commerce and their separation by series‐coupled column gas chromatography
Authors: Miller Kenneth G. , Poole Colin F. , Chichila Tina M. P.
Published: May 2005

Solvent‐assisted supercritical fluid extraction is superior to Soxhlet extraction, solvent extraction at reflux, and simultaneous setam distillation solvent extraction for the isolation of semivolatile compounds from the cinnamons of commerce. Optimized extraction conditions are described using carbon dioxide at 300 atm and 70°C to extract 0.5 g of powdered cinnamon mixed with 4.5 g of anhydrous sodium sulfate to which 1.0 ml of acetonitrile was added at the start of the sequential 30 min static and 30 min dynamic extraction. The semivolatile compounds were collected by solvent trapping in ethyl acetate and analyzed directly by series coupled‐column gas chromatography after filtration and partial solvent evaporation. Twenty‐one compounds identified by mass spectrometry were quantified in twenty‐four samples of cinnamon and cassia purchased in Sri Lanka, Korea, United Kingdom, and the United States of America. True cinnamon is easily distinguished from cassia by the presence of eugenol, absence of δ‐cadinene, much lower amounts of coumarin, and larger amounts of benzyl benzoate. Principal component analysis using the relative composition of the twelve major semivolatile compounds provides a clear distinction between true cinnamon and cassia as well as useful interspecies differences which can be used for further classification.
Sampling and gas chromatographic analysis of volatile organic compounds in hot and extremely humid emissions
Authors: Knobloch Thomas , Engewald Werner
Published: May 2005

Adsorptive enrichment on hydrophobic adsorbents, thermal desorption, and capillary gas‐chromatographic analysis have been used to determine volatile organic compounds in extremely humid stack‐gas emissions from the residential burning of brown‐coal briquets. One hundred and fifty two compounds were identified and quantified. Quantitative emission factors were determined for the identified individual compounds in relation to the amount of the fuel used. These factors enable a first assessment of the pollution of the city of Leipzig with volatile organic compounds resulting from the burning of indigenous lignite.
Separation of tetracycline and its related substances by capillary zone electrophoresis
Authors: Van Schepdael Ann , Saevels Jan , Lepoudre Xavier , Kibaya Rukia , Gang Ni Zhi , Roets Eugèn , Hoogmartens Jos
Published: May 2005

Tetracycline was separated from its main impurities 4‐epitetracycline, anhydrotetracycline, 4‐epianhydrotetracycline, chlortetracycline, and demethyltetracycline by capillary electrophoresis. Systematic method development was performed in which following parameters were consecutively optimized: type and pH of the buffer, buffer concentration, type and concentration of organic modifier, voltage and temperature. Qualitative and quantitative aspects of the method are compared with liquid chromatography.
Characterization and identification of the mucilage extracted from orchid bulbs (Bletia campanulata) by high temperature capillary gas chromatography (HT‐CGC)
Authors: Peña Araceli , Capella Santiago , González Carolusa
Published: May 2005

The aim of this work was to develop an analytical method by High Temperature Capillary Gas Chromatography (HT‐CGC) to characterize and identify the presence of tzauhtli, orchid mucilage, in works of art. During the pre‐Hispanic and colonial period, tzauhtli was used as an adhesive for paper and feathers, as well as paint binder, and was one of the components of the paste used to model corn stalk sculptures. The mucilage was extracted with hot water from orchid bulbs (Bletia campanulata) and lyophilized. The free sugars from the mucilage were analyzed by CGC after derivatization. The polysaccharide of the mucilage was characterized after its partial acid hydrolysis by HT‐CGC analysis of the oligosaccharides obtained. The proposed chromatographic method allows the identification of different mucilages in works of art. This contribution is the first report of the oligosaccharides from the hydrolysis of the mucilage extracted from orchid bulbs (Bletia campanulata).
Automated optimization of split ratio in capillary gas chromatography
Authors: Nishikawa Y. , Miyoshi S. , Shyoji M. , Braun G.
Published: May 2005

An electronic gas‐flow controller system called Advanced Flow Control (AFC), which controls not only carrier gas pressure at the column inlet but also the total gas flow including the split flow, was designed and evaluated. BASIC programming of repetitive analyses of standard mixtures under varied split ratios and pressure programs allowed automated optimization of those conditions for the desired column loading and resolution between adjacent peaks.
Separation of twenty‐one naphthalene sulfonates by means of capillary electrophoresis
Authors: Kok Steven J. , Koster Emile H. M. , Gooijer Cees , Velthorst Nel H. , Brinkman Udo A. Th. , Zerbinati Orfeo
Published: May 2005

The production and use of naphthalene sulfonates can easily cause pollution of surface and other types of waters. In the present study, capillary electrophoresis in combination with UV absorption detection was used to separate 21 amino‐ and hydroxy‐substituted naphthalene sulfonates which included multiple isomeric compounds. The influence of various parameters such as pH (which turned out to be extremely important), temperature of the surrounding air flow, and the use of buffer additives (micelles, cyclodextrins, organic modifiers) was studied. Complete separation of all analytes including the isomers, was achieved in two runs with a 50 mM boric acid/borate buffer, containing either 100 mM sodium dodecylsulfonate or 15% acetonitrile. The limits of detection obtained for the individual compounds typically were 20μgI−1. River water samples spiked at this concentration level could be analysed using a simple three‐step sample clean‐up procedure.
HPLC—UV determination of pesticide residues at 0.01 ppm in apple and pear pulp used for baby food
Authors: Bicchi Carlo , Balbo Cristina , Binello Arianna , D'Amato Angelam
Published: May 2005

Two distinct methods are described for determination of residues of ethiofencarb and triforine, and of diflubenzuron, teflubenzuron, and triflumuron at the 0.01 ppm level in apple and pear pulp used for baby food;recoveries are above 50%. Diflubenzuron, teflubenzuron, and triflumuron are extracted with a 1:1 mixture of dichloromethane and acetone, and the extracts are cleaned by SPE using C18 as stationary phase and methanol as mobile phase. Ethiofencarb and triforine are extracted with dichloromethane, and the extracts cleaned using the same stationary phase but a 1:1 mixture of acetonitrile and water as mobile phase. Analysis of both groups of pesticides is by isocratic HPLC—UV at 210 nm using an RP‐18 column and acetonitrile‐water as mobile phase.
Gas chromatographic separation of the stereoisomers of organophosphorus chemical warfare agents using cyclodextrin capillary columns
Authors: Smith J. Richard , Schlager John J.
Published: May 2005

The synthesis of the organophosphorus nerve agents sarin, tabun, and cyclohexyl methylphosphonofluoridate (GF) produces a mixture of two stereoisomers except for soman where four stereoisomers are produced. Significant differences exist in the reported toxicity and AChE inhibition rates of the various stereoisomers. This makes the ability to distinguish between the different stereoisomers desirable. Five different derivatized cyclodextrin stationary phases developed for gas chromatography were tested for their ability to resolve the nerve agent stereoisomers using a gas chromatograph interfaced to an atomic emission detector. Of the five columns that we examined, only the 2,6‐di‐O‐pentyl‐3‐O‐trifluoroacetyl or 2,6‐di‐O‐pentyl‐3‐O‐butyryl γ‐cyclodextrins were able to successfully resolve all four soman stereoisomers. The elution order for each column was determined using solutions of isolated soman stereoisomers. Enantiomers of sarin, tabun, and GF were resolved with varying degrees of success on the different cyclodextrin stationary phases. Only the butyryl γ‐cyclodextrin was able to separate the enantiomers of all four of the nerve agents examined in this study. The capacity (k) and selectivity (α) factors were determined for each of the chemical warfare agents successfully separated. The TNO Prins Maurits Laboratory in the Netherlands has previously developed several different chromatographic methods to resolve the stereoisomers of soman, sarin, and tabun. The advantage of the method described here is that commercially available cyclodextrin gas chromatography columns were used to resolve the stereoisomers, thereby facilitating rapid and routine analysis of organophosphorus nerve agents.
A new method for the chiral HRGC assay of L‐2‐hydroxyglutaric acid in urine
Authors: das Neves Higuinaldo J. Chaves , Noronha João Paulo , Rufino Helena
Published: May 2005

L‐2‐Hydroxyglutaric aciduria is a recently discovered inherited neurometabolic disease for which diagnostic identification of the right enantiomer is required. A method is described where alkyl esters of both L‐and D‐2‐hydroxyglutaric acids are prepared without side lactonization. Esterification is achieved at room temperature by reaction with appropriate alkyl chloroformates. This method avoids lactonization, in contrast to esterification with alcohols in acidic media or with diazomethane. The identity of the derivatives is established by HRGC‐FTIR and HRGC‐MS. Chiral HRGC separation with capillaries coated with 1(R)‐trans‐N‐N'‐1,2‐cyclohexylenebisbenzamideoligodimethyL‐siloxane and with a cyclodextrin is compared. The method is adequate for quantitative determinations.
Determination of cholesterol in fat and muscle of pig by HPLC and capillary gas chromatography with solvent venting injection
Authors: Maraschiello Ciriaco , Díaz Isabel , Regueiro José A. García
Published: May 2005

Two methods for determination of cholesterol in fat and muscle of pig were evaluated: extraction with chloroform:methanol (2:1, v/v) followed by saponification (method 1) and direct saponification (method 2). HPLC and GC were used to determine cholesterol concentrations. GC analysis was performed with a capillary column of 100 μm using a PTV injector in the modes of cold split and solvent venting. Cholesterol was analyzed without derivatization. Both methods of extraction did not present significant differences (p > 0.01). Sample analysis by GC with solvent venting injection and HPLC showed the lowest % r.s.d. but GC in the cold split mode allowed to obtain a shorter analysis time. Cholesterol concentrations obtained by HPLC were not statistically different from the results obtained by GC with solvent venting injection and were slightly lower than those previously reported. Cholesterol concentrations in fat and muscle tissues respectively ranged from 52 to 77 mg/100 g and from 55 to 65 mg/100 g.
Retention in SFC at high density
Authors: Shen Yufeng , Hung Hongxin , Zhou Liangmo
Published: May 2005

The elucidation of the detailed mechanism of retention in supercritical fluid chromatography (SFC) is a complex problem, especially for high‐density supercritical fluid mobile phases. Martire and Boehm developed a theory of SFC retention based on a statistical thermodynamic treatment, and introduced a density‐squared equation for retention in SFC: In k = a + b/T + cρ + dρ/T + eρ2/T. In this paper the systems n‐alkane‐polydimethylsiloxane‐CO2 and n‐carboxylic acid methyl ester‐polydimethylsiloxane‐CO2 have been treated using the method introduced by Martire and Boehm. In the ranges of reduced temperature from 1.079 to 1.293 and reduced SF mobile phase density from 0.705 to 1.632, two problems were discovered in the treatment of SFC retention behavior by the method of Martire and Boehm: (1) the experimental value of the site of CO2 in the lattice field, ra, of the two systems was ca 0.9, which is obviously different from the theoretical values of 3.6 or 5.4; and (2) the difference between experimental and calculated retention values increased with increasing SF mobile phase density. The minimum in SFC retention predicted by Martire and Boehm was not observed. On the basis of some assumptions and the experimental data, the following retention equation was derived: In k = a + b/T + cρ + dρ/T + eρ2/T + fρ3/T + gρ4/T. This equation was consistent with the experimental data and can conveniently be used to explain other SFC retention behavior.
The advantage of dual‐column approach and retention indices combined with refined reporting in gas chromatographic drug screening
Authors: Rasanen Ilpo , Ojanperä Ilkka , Vartiovaara Juhani , Vuori Erkki , Sunila Pekka
Published: May 2005

A dual‐column gas chromatographic retention index method was evaluated for the toxicological screening for basic drugs in autopsy blood samples. The dual‐column approach with DB‐5 and DB‐1701 capillary columns doubles the Identification Power of the corresponding single column methods. The long‐term intralaboratory variation of the dialkylfluoroaniline series based retention indices of drugs in blood ranged from 0.03% to 0.2% which was generally better than that obtained using the relative retention time. Novel software is described for the processing and reporting of the dual‐column chromatographic data in analytically useful form. Besides retention data, the response factors served as an additional identification factor.
HRGC/FID/NPD and HRGGC/MSD study of Colombian ylang‐ylang (Cananga odorata) oils obtained by different extraction techniques
Authors: Stashenko Elena E. , Prada Nubia Quiroz , Martínez Jairo R.
Published: May 2005

Steam distillation (SD), simultaneous distillation‐solvent extraction (SDE), and supercritical (CO2) extraction (SFE) were used to isolate volatile secondary metabolites from fresh, totally mature flowers of Colombian ylang‐ylang (Cananga odorata). The various extracts were analyzed by capillary chromatography (DB‐1, DBWAX, 60 m columns) using FID, NPD or MSD (EI, 70 eV). Kováts indexes, mass spectra, or standard substances were employed for compound identification. 51, 70, and 73 compounds at concentrations above 100 ppb were detected in the SD, SDE, and SFE extracts, respectively. The main constituents of these extracts were linalool (20.7, 28.0, and 16.5%), germacrene‐D (10.1, 3.1, and 20.3%) benzyl benzoate (14.1, 2.9, and 3.9%), benzyl acetate (9.6, 17.0, and 6.2%), caryophyllene (3.1, 2.9, and 3.9%), and p‐methylanisole (6.8, 6.1, and 2.7%). 85% of the composition of SDE extracts was represented by oxygenated compounds. Heavy hydrocarbons (Cn >20) and fatty acids were found only in the SFE extracts, which also had a higher content of nitrogenated compounds (phenylacetonitrile, 4‐methylbenzaldoxime, indole, 2‐phenyl‐nitroethane, and methyl anthranilate) and sesquiterpenes (43% vs 19.5% in SD and 8.1% in SDE) and 1.5 – 2 times lower concentration of monoterpenes and light oxygenated compounds than the SD (49.7%) and SDE (64.5%) extracts.
Capillary electrophoresis determination of six bioactive constituents in San‐huang‐hsieh‐hsin‐tang
Authors: Sheu Shuenn‐Jyi , Lu Chyong‐Fang
Published: May 2005

A capillary electrophoretic method for simultaneous determination of six bioactive ingredients (berberine, palmatine, baicalin, sennoside B, emodin, and sennoside A) in the Chinse herbal formula San‐huang‐hsieh‐hsin‐tang was established. A carrier composed of aqueous buffer solution (50 mM sodium cholate, 15 mM sodium dihydrogen phosphate, and 4.25 mM sodium borate)‐acetonitrile (3:2) was found to be the most suitable electrolyte for this separation. Contents of these constituents in a non‐pretreated methanol‐water extract of San‐huang‐hsieh‐hsin‐tang sample could be easily determined within 20 min. The effects of borate, cholate, and organic modifier (acetonitrile) concentration of the carrier on the migration behavior of the solutes were also studied.
Separation of neutral and basic enantiomers by cyclodextrin electrokinetic chromatography using anionic cyclodextrin derivatives as chiral pseudo‐stationary phases
Authors: Tanaka Yoshihide , Yanagawa Mayumi , Terabe Shigeru
Published: May 2005

Separations of neutral and basic racemates were performed using five different anionic cyclodextrin (CD) derivatives as chiral selectors, viz. carboxymethylated β‐CD, β‐CD phosphate sodium salt, sulfobutyl ether β‐CD sodium salt, carboxymethylated γ‐CD, and γ‐CD phosphate sodium salt. For the separation of neutral racemates, an untreated fused silica capillary was employed and various neutral racemates were successfully separated. Since the pH of the buffer affected the electroosmotic flow (EOF), the resolution was improved by changing the buffer pH. A polyacrylamide coated capillary was employed for the separation of basic racemates to suppress EOF and to prevent adsorption of cationic analyte on the capillary surface. By choosing an appropriate type and concentration of anionic CD, about 40 basic racemates were successfully separated. Some rough binding constants of basic analytes with an anionic β‐CD were measured to discuss the optimum concentration of the CD. The migration direction was dependent on the binding constants and the concentration of the CD. The analyte strongly bound to the anionic CD migrated towards the anode but the weakly bound one moved towards the cathode. Anionic γ‐CDs were also very useful for the separation of basic enantiomers. Five neutral CDs were employed as chiral selectors to compare selectivity between charged and neutral CDs, and eleven racemates could only be resolved using anionic CDs. The separation of some basic racemates in human plasma was also described. The direct injection of plasma samples was possible for some enantiomers that did not interact strongly with plasma proteins.
On‐line solvent evaporator for coupled LC systems: Further developments
Authors: Moret Sabrina , Grob Konrad , Conte Lanfranco S.
Published: May 2005

An on‐line solvent (eluent) evaporator is used for reconcentrating a fraction from a first LC column before introduction into a second LC separation step, possibly involving another mobile phase. For pentane and pentane containing 10 % of dichloromethane, evaporation rates of 1 ml/min were achieved. On evaporating a volume of 6 ml, 2‐ethylnaphthalene was retained to more than 75%. Separation of aliphatic and polyaromatic hydrocarbons in a linseed oil is shown as an application.
The determination of volatile organic compounds in soils using solid phase microextraction with gas chromatography‐mass spectrometry
Authors: James Kevin J. , Stack Mary A.
Published: May 2005

Solid phase microextraction (SPME) was applied in the development of a protocol for the analysis of a number of target organic compounds in landfill site samples. The selected analytes, including aromatic hydrocarbons, chlorinated hydrocarbous, and unsaturated compounds, were absorbed directly from a headspace sample above a soil layer onto a fused silica fiber. Following exposure, the fiber was thermally desorbed in the injection port of the gas chromatograph and eluted compounds were detected using a mass selective detector. The stability and sensitivity of the extraction technique were examined at five temperatures (22–60°C) using a 100μm polydimethylsiloxane fiber. Calibrations, using soil samples spiked with selected solvents (0.5–30 μg/g), were linear; trichloroethene (r2 = 0.992) and benzene (r2 = 0.998). SPME was applied to the examination of a municipal landfill where 8 sites were sampled, at three depths, resulting in the detection of xylene (maximum 2.8 μg/g) and a number of other non‐target organic contaminants.
High temperature (70°C) size exclusion chromatography of petroleum waxes with RI and FID detection
Authors: Carbognani Lante
Published: May 2005

Molecular weight distribution of solid petroleum waxes is a key parameter for the general characterization of these materials. Particular interest concerns extremely large components, typically present in oil distillation residua, and solid deposits found in oil production facilities. Molecular weight distributions of oil waxes were determined in this work by high temperature size exclusion chromatography. Separations were carried out with two different eluents, namely toluene and ortho‐dichlorobenzene and two detection systems, these being a differential refractive index and a flame ionization detector. Toluene proved to be the best choice when combined with flame ionization detection. Better uniformity of response was the greatest advantage achieved by this approach. The experimental set up permitted analysis of samples containing molecules with up to 138 carbon atoms. Burning properties of very large molecules, isomerism affecting calibration, and signal asymmetry when flame ionization detection was adopted were three issues still requiring additional efforts to understand and to improve analysis accuracy.
Environmental applications of capillary gas chromatography coupled with atomic emission detection — a review
Authors: Pedersen‐Bjergaard Stig , Greibrokk Tyge
Published: May 2005

Environmental applications of capillary gas chromatography coupled with atomic emission derection (GC‐AED) have been reviewed with emphasis on both the commercial and laboratory‐built systems. Attention was focused on (1) element‐selective detection of non‐metallic as well as metallic pollutants, (2) identification of contaminants, and (3) sample preparation considerations.
Complete PCB congener distributions for 17 aroclor mixtures determined by 3 HRGC systems optimized for comprehensive, quantitative, congener‐specific analysis
Authors: Frame George M. , Cochran Jack W. , Bøwadt Søren S.
Published: May 2005

Three HRGC systems (1: 30m DB‐XLB capillary with MS‐SIM detection; 2: 60m DB‐XLB capillary with full‐scan, ion‐trap MS detection; and 3: Parallel dual‐column DB‐17 and series‐coupled HP5/HT5 with ECD detection) were used to completely characterize multiple lots of 8 different‐numbered Aroclor mixtures by quantitative calibration against 9 solutions containing primary standards of all 209 PCB congeners. Despite lower absolute sensitivity and more Aroclor congener coelutions than the dual‐column ECD system, the MS systems enabled measurement of more congeners per Aroclor since their greater linear response range did not require dilution of samples and standards. Pairs of different lots of Aroclors 1248 and 1254 displayed markedly different proportions of congeners, and the 1254 pair displayed strong differences in the extent of ortho‐chlorine substitution. The tables of congener weight percent distributions among Aroclors are more comprehensive and quantitatively precise than those of prior publications. However, the limitations of single‐level calibration precluded measurement of all congeners to the ±10% accuracy desirable for establishing these Aroclors as secondary standards for comprehensive, quantitative congener‐specific PCB analysis.
Adulteration or natural variability? enantioselective gas chromatography in purity control of essential oils
Authors: König Wilfried A. , Fricke Christiane , Saritas Yücel , Momeni Behdad , Hohenfeld Gerhard
Published: May 2005

The potential of enantioselective capillary gas chromatography with modified cyclodextrins as chiral stationary phases for authenticity control is demonstrated for a selection of economically important essential oils. Adulteration can be easily detected in cases where enantiomerically pure constituents are present in natural oils. In cases of (naturally) varying enantiomeric compositions of chiral constituents, enantioselective gas chromatography may prove insufficient.
Analysis of carbamate pesticides by micellar electrokinetic chromatography
Authors: Rossi Massimo , Rotilio Domenico
Published: May 2005

Capillary elcctrophoresis (CE) was used for the qualitative and quantitative analysis of eleven compounds of the carbamate, thio‐carhamate, and dithiocarbamate classes of pesticides. Micellar elec‐trokinetic chromatography (MEKC) was employed for the separation of these substances. The analysis was performed using an uncoated fused silica column, in borate buffer containing SDS and 10% methanol at basic pH, and UV detection at 230 nm. The addition of methanol to the buffer increased the separation and affected intrinsic migration of analytes. The working standard solutions were prepared in acetonitrile/water 50:50. Although these compounds are structurally different, with a large spectrum of chemical properties, such as polarity and solubility, good separation and sensitivity were obtained. Moreover, good recovery of car‐bamates was obtained from tap‐water using a styrene‐divinylben‐zene polymer column with the solid phase extraction (SPE) technique.
Matrix‐induced peak enhancement of pesticides in gas chromatogrtaphy: Is there a solution?
Authors: Erney D. Ronald , Pawlowski Tina M. , Poole Colin F.
Published: May 2005

In this study, it is shown that calibration solution prepared in control matrix extrix extract can be used to compensate for matrix‐induced chromatographic response enhancement observed for certain pesticedes. This phenomenon is characterized by enhanced chromatographic response for certain pesticides in the presence of matrix du to reduced analyte loss during injection. Unacceptably high recoveries are seen for affected pesticides when maatrix‐free solutions are used for reference and calibration. The effects of matrix concentration on overall enhancement and linear response were determined. When used as reference standards for the determination of recovery, matrix‐standard solutions were found to provide acceptable recoveries for pesticides subject to matrix‐induced chromatographic response enhancement along with other pesticides. General guidelines are presented for using matrix‐standard calibration solutions in pesticide residue analysis.
Hyphenation of gas chromatography and resonance‐enhanced laser mass spectrometry (REMPI‐TOFMS): A multidimensional analytical technique
Authors: Zimmermann Ralf , Boesl Ulrich , Heger Hang‐Jörg , Rohwer Egmond R. , Orthner Erla K. , Schlag Edward W. , Kettrup Antonius
Published: May 2005

Analysis of environmental samples usually requires time consuming sample preparation and clean‐up procedures prior to instrumental detection. Faster analysis requires an enhanced instrumental selectivity in order to reduce the necessary clean‐up effort. In this context we present a novel concept for coupling gas chromartography/mass spectrometry (GC‐MS) with high resolution UV spectoscopy to increase selectivity. We use UV‐laser induced, resonance‐enhanced multi‐photon ionization (REMPI)as a compound specifie ion source for time‐of‐flight mass spectrometry (TOFMS). The REMPI ionization involves the UV absorption spectroscopy into the ionization process as an aditional analytical dimension. The heart of the GC‐REMPI‐TOFMS coupling is a specially designed valve, which repetitively (20 Hz) expands the chromatographic eluent as short supersonic jet gas pulses (≈ 150 μs duration) into the vacuum of the mass specrtrometer. The sample molecules are cooled down to temperatures of 10‐40 K within the jet expansion. Under these conditions, UV absorption spectriscopy (i.e. REMPi spectroscopy) becomes highly compound selective, even able to distinguish isomeric compounds. The ions formed by REMPI ionization are mass analyzed in the TOFMS. Thus the GC‐REMPI‐TOFMS coupling presented here is actually a three‐dimensional analytical instrument, providing gas chromatographic (retention time) as well as mass spectrometric (molecular mass) and UV ‐spectroscopic (excitation laser wavelength) selectivity. In combination with gas phase sampling and concentration techniques for semi‐volatile organic air pollutants based,e.g., on silicone rubber traps the GC‐LAMS technique can be a powerful tool for fast environmental target analysis,e.g. for industrial emission control purposes.
The variation of carrier gas viscosities with temperature
Authors: Hinshaw John V. , Ettre Leslie S.
Published: May 2005

After describing simplified equations exspressing the temparature dependency of the viscosity of carrier gases (helium, nitrogen and hydrogen ) relative to a base value, absolute relationships based on the kinetic theory of gases are discussed. Comparative data obtained using various calculation methods are given and are compared to measured values. Based on the kinetic relationshipsm, of viscosity. Finally, the influence of pressure on the viscosity is also briefly discussed. As a supplement, Viscosity data are tabulated for the three gases in the range of 0°C to 400°C in increments of 2 K, calculated using the kinetic relationships.
On‐line determination of organophosphorus pesticides in water by solid‐phase microextraction and gas chromatography with thermionic‐selective detection
Authors: Lopez‐Avila Viorica , Young Richard , Beckert Werner F.
Published: May 2005

This paper describes the extraction of 49 organophosphorus pesti‐cides (OPPs) from water samples using solid‐phase microextraction (SPME). Three fibers, including a 15‐μm XAD‐coated fiber, a 85‐μm polyacrylate‐coated fiber, and a 30‐μm polydimethylsilox‐ane‐coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate‐coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD‐ and polyacrylate‐coated fibers. With some exceptions, the XAD‐ and polyacrylate‐coated fibers performed better than the PDMS‐coated fiber. The superiority of the XAD‐nd polyacrylate‐coated fiber. The superiority of the XAD‐ and polyacrylate‐coated fibers over the PDMS‐coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber.
Determination of acyclovir in plasma by high performance liquid chromatography with UV detection. Method development and method validation
Authors: Šmidovnik A. , Wondra Alenka Golc , Prošek Mirko
Published: May 2005

A HJPLC method for the determination of acyclovir in plasma is described. The method is simple and sensitive enough for bioequiva‐lence studies, where a large number of plasma samples with low acyclovir concertration are involved. The procedure is based on the deproteinization of plasma with perchloric acid and separation of acyclovir on a Hypersil ODS Column at pH 5.6 with UV detection. The calibration standards are linear up to at least 4000 ng/mL and the limit of quantification is 10 ng/mL.
Separation of basic proteins and peptides by capillary electrophoresis using a cationic surfactant
Authors: Ding Weiliang , Frit James S.
Published: May 2005

Incorporation of a low concentration of cetyltrimethylammonium bromide (CTAB) in the running electrolyte is shown to dynamically coat the silica capillary and to reverse the direction of electroosmotic flow. The CTAB coating prevented interaction of proteins with the capillary surface and enabled sharp peaks to be obtained in the electropherograms. A systematic study of experimental parameters demonstrated the importance of selecting a suitable buffer electrolyte and an appropriate pH. Excellent separations were obtained for five proteins, three enkephalins, and six dipeptides with an efficiency of approximately 500,000 theoretical plates per meter. The method developed is very simple to perform and was found to give excellent reproducibility.
Solid phase extraction of organophosphorus, triazine, and triazole‐derived pesticides from water samples. A critical study
Authors: Báez Maria E. , Rodriguez Manuel , Lastra Olga , Contreras Paola
Published: May 2005

A critical study using C18 SPE columns for the determination of organophosphorus, triazine, and triazole‐derived pesticides, nap‐ropamide, and amitraz is presented. The type of sorbent, sorbent mass, flow rate in the extraction process, sample concentration of the different compounds, sample volume, pH, and ionic strength were evaluated. Special emphasis was placed on the evaporation step of eluates prior to GC determinations and on prefiltration of sample waters. Pesticide recovery is linear over a wide range of concentrations for most of compounds under study. Under general extraction conditions losses can be expected for amitraz, pro‐metryn, prometon, dimethoate, penconazole, and propiconazole. At 100 ng L−1, enhanced responses are produced for mevinphos, simazine, malathion, triadimefon, methidathion, and phosmet, which can be attributed to matrix effects. At basic pH, recovery of prometon, prometryn, and penconazole are improved. Low flow rates and high ionic strength enhance the recovery of prometon and prometryn. For phosmet, the influence of sample volume was established. Likewise, the influence of sorbent quantity was established for phosmet and dimethoate. Losses during the evaporation step were observed for mevinphos, dimethoate (> 50%), penconazole, propiconazole, and prometon (30%). Prefiltration of sample waters did not cause significant variations in the whole process of extraction. Impurities arising from the sorbent materials were not detected.