bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of ethers and alcohols in reformulated gasolines by gas chromatography/atomic emission detection
Authors: Diehl J. W. , Finkbeiner J. W. , di Sanzo Frank P.
Published: May 2005

A GC method for the determination of oxygenated additives in reformulated gasolines (RFG) is described. The method uses on‐column injection and atomic emission selective detection of oxygenates using the 777 nm NIR emission line. Detection limits are approximately 10 ppm oxygen. Results compared well with other techniques, such as GC/FTIR.
HRGC separation of PCB congeners
Authors: Larsen Bo Richter
Published: May 2005

High resolution gas chromatography has greatly changed the field of polychlorinated biphenyl (PCB) analysis. From a rough estimation of the total PCB concentration on packed column GC, the development of commercially available fused silica capillary columns in the late 1970s and early 1980s has advanced the analysis of PCBs to a point where they can be accurately measured as separated congeners. The state‐of‐the‐art of PCB analysis in the 1990s is routine isomer‐specific analysis with multi‐column techniques using long (<50 m) narrow (> 0.25 mm) columns. A broad spectrum of commercially available stationary phases have been completely characterized with regard to their PCB elution profiles.
Retention properties of a cyanopropylsiloxane‐bonded silica‐based sorbent for solid‐phase extraction
Authors: Seibert Donna S. , Poole Colin F.
Published: May 2005

The characteristic kinetic and retention properties of a silica‐based cyanopropylsiloxane‐bonded sorbent for solid‐phase extraction are described. Abraham′s solvation parameter model is used to characterize the contribution of individual intermolecular interactions to retention under liquid chromatographic and sample processing conditions with aqueous methanol mixtures as the mobile phase. The main features governing retention by the sorbent are the solute's size and hydrogen‐bond basicity; interactions of a dipole type are not significant when aqueous methanol solutions are employed as the mobile phase. Compared to typical silica‐based octadecylsioxane‐bonded sorbents the greater difficulty of forming a cavity in the solvated cyanopropylsiloxane‐bonded sorbent more than offsets the more favorable dipole‐type and solute hydrogenbond base interactions of the cyanopropylsiloxane‐bonded sorbent. It is shown that there are no practical circumstances for which a cyanopropylsiloxane‐bonded sorbent would be more useful than a typical ODS sorbent for the isolation of organic non‐electrolytes from water by solid‐phase extraction.
Application of hyphenated techniques to the chromatographic authentication of flavors in food products and perfumes
Authors: Casabianca Hervé , Graff Jean‐Bernard , Jame Patrick , Perrucchietti Christiane , Chastrette Maurice
Published: May 2005

This work presents two techniques for testing for the adulteration of flavors. One uses multidimensional gas chromatography on cyclodextrin derivatives to separate chiral compounds, the other uses isotope ratio mass spectrometry coupled with gas chromatography to determine stable isotope ratios. Applications to fruits and plants for the food and perfume industry are introduced.
HRGC‐MS and HPLC‐MS identification of new ketosterols in an extract of wheat straw
Authors: Chaves das Neves Higuinaldo J. , Gaspar Elvira M. M. S.
Published: May 2005

An ethereal extract of wheat (Triticum aestivum) straw with a positive biological assay for allelopathic activity, has been analyzed by HRGC. By means of HRGC‐MS the extract composition was assessed as a complex mixture of organic acids and sterolic compounds. The sterolic fraction was subsequently separated and further studied by HRGC‐MS and HPLC‐MS. Among the thirty seven components identified, some described for the first time in wheat straw, two new ketostero's were characterized by means of their MS spectra. The potential of the particle‐beam (PB) interface in HPLC‐MS studies of unknown mixtures is exemplified and compared with that of HRGC‐MS.
An evaluation of solid‐phase microextraction for analysis of volatile organic compounds in drinking water
Authors: Nilsson Torben , Pelusio Fabio , Montanarella Luca , Larsen Bo , Facchetti Sergio , Madsen Jørgen Øgaard
Published: May 2005

Solid‐phase microextraction (SPME) has been applied to the quantitative analysis of 60 volatile organic compounds (VOCs) in drinking water. Equilibration curves for the partitioning of the VOCs between the fiber coating and fortified water obtained at 20, 50, and 80 °C are found between the theoretical curves for completely agitated and non‐agitated samples. Two important factors for the amount adsorbed by the SPME fiber coating are the extraction time and the fiber coating/water distribution coefficient, KFW. Both depend on the sample temperature, but in a counteracting manner: Increasing the temperature shortened the equilibration times, especially for the heavier VOCs, but also lead to lower KFW values, and consequently a lower sensitivity of the method. KFW values are determined for 33 of the VOCs at 40, 60, and 80°C and the heats of adsorption,–ΔH, are calculated. The nature of the adsorption is found to be exothermic which explains the decreasing sensitivity of the method with increasing temperature. Detection limits were typically from 20 ng/l to 200 ng/l, except for the very light VOCs with which detection difficulties were encountered. For all of the VOCs the linear range extended from the lowest concentration at which they were actually detected to at least 5 mg/l. The precision, 3% average standard deviation when an internal standard was used, was satisfactory for most quantitative routine analysis. SPME was also applied to head‐space (HS) analysis of drinking water through the coupled equilibrium between water/head‐space/fiber coating. HS‐SPME is demonstrated to have shorter equilibration times than SPME directly from the water and equal sensitivities, except for the very light VOCs. Water samples from a drinking water plant contaminated in the low μg/l range with 1,1,1‐trichloroethane, trichloroethene and tetrachloroethene were analyzed. There seems to be a reasonable agreement between results obtained by SPME and purge & trap. It is concluded that SPME has a great potential for drinking water analysis.
Determination of lactulose and mannitol in urine by HRGC
Authors: Relva Angela M. S. , das Neves Higuinaldo J. Chaves , Ferreira Margarida A.
Published: May 2005

Alteration of intestinal permeability towards compounds like sugars is an indication of abnormalities observed in some diseases. Measurement of the dual sugar absorption of lactulose and mannitol is a non‐invasive test of intestinal permeability. The use of this test is however limited by difficulties in the analysis of sugars in urine at low concentrations. In this study we have developed an analytical procedure for quantitative assay of the lactulose–mannitol pair in urine by high resolution gas chromatography. The minimum detectable amounts are 7.5 pg for lactulose and 4.4 pg for mannitol. The calibration curves are linear in the range of 100–6400 mg L−1. Recoveries are within the range 86–102 % for mannitol and 84–105 % for lactulose.
Characterization of polymers by multi‐step thermal desorption/programmed pyrolysis gas chromatography using a high temperature PTV injector
Authors: van Lieshout Mark H. P. M. , Janssen Hans‐Gerd , Cramers Carel A. , Hetem Martin J. J. , Schalk Huub J. P.
Published: May 2005

Thermal treatment hyphenated with gas chromatography is a versatile and powerful tool in the study of polymer characterization. An inexpensive system where thermal treatment at different temperatures occurs inside a Programmable Temperature Vaporization injector (PTV) is described. The samples investigated, commercial plastics, are complex mixtures that contain several polymers and additives. These plastics as well as their pure constituents are subjected to multi‐step thermal treatment. The individual chromatograms of the various constituents of the polymeric sample are correlated with those of the final material in order to identify additives (thermal desorption) and degradation products (pyrolysis). Results obtained with the new method indicate the interesting potentials of the technique for the characterization of polymer compositions. Reproducibility of absolute and relative peak areas has been considered and found to be acceptable. The absence of a heated transfer line and switching valves, which are always present in conventional set‐ups, eliminates the risk of losses of high molecular weight components. Further advantages of the technique proposed are simplicity, versatility, and its inexpensive nature.
Gas‐chromatographic headspace analysis of phenol and cresols in soils by direct acetylation
Authors: Llompart‐Vizoso Maria P. , Lorenzo‐Ferreira Rosa A. , Cela‐Torrijos Rafael
Published: May 2005

A quick, simple and selective procedure has been developed for the determination of phenol, o‐cresol, m‐cresol, and p‐cresol in soil samples. The method is based on the gas chromatographic headspace analysis of phenols as acetate derivatives. These acetates were prepared directly in the wetted soil samples by acetic anhydride in the presence of KHCO3˙ With this procedure sample handling is reduced to a minimum as desorption and derivatization of the analytes are developed from the wetted samples inside the vial of the head space sampler.

The acetate esters were analyzed using a 60 m × 0.56 mm DIIDP capillary column (di‐isodecyl‐phthalate), using 2‐chlorophenol as an internal standard. The detection limit was between 0.03–0.08 μg g−1 for the different species considered. Soil samples having carbon contents lower than 5 % can be analyzed by the proposed procedure.
A four factor simplex optimization of a serially coupled open tublar columns gas chromatographic system
Authors: Bakeas Evangelos B. , Siskos Panayotis A.
Published: May 2005

Optimization of a gas chromatographic system with two capillary columns coupled in series in a single oven for the linear temperature programmed separation of a mixture of C1C10 hydrocarbons has been carried out using the simplex optimization method. The following four selectivity parameters were optimized: the initial temperature of the oven; the initial hold time; the temperature programmed rate; and the pressure at the mid‐point of the system. The optimization procedure was monitored by the Cp criterion.
Use of vancomycin as chiral selector in capillary electrophoresis. Optimization and quantitation of loxiglumide enantiomers in pharmaceuticals
Authors: Fanali Salvatore , Desiderio Claudia
Published: May 2005

Vancomycin has been used as chiral selector for the enantiomers separation of D, L‐loxiglumide, a new drug proposed for the treatment of gastrointestinal pathology. The chiral selector, dissolved at very low concentration in the running buffer, filled only part of the capillary (polyacrylamide coated) and allowed chiral resolution in less than 12 min using a 50 mM phosphate buffer at pH 6. The partial separation technique allowed to obtain a detection limit of 0.5 μg/ml for each enantiomer avoiding the drop in sensitivity due to the strong UV absorption of vancomycin when present in the detector path. The effects of vancomycin concentration and buffer pH on enantiomers resolution have been studied in order to find the optimum experimental conditions for the chiral purity control of drug. The optimized method, using the internal standard, showed good reproducibility for both migration times and normalized peak area ratio and for linearity. Under the studied operating conditions it was possible to detect 0.2 % (w/w) of L‐loxiglumide as a chiral impurity. Analysis of pharmaceutical preparations of D‐loxiglumide did not reveal the presence of the impurity (L‐isomer).
Retention index system, adsorption characteristics, and structure correlations of polycyclic aromatic hydrocarbons in fuels
Authors: Elizalde‐González María P. , Hutfließ Markus , Hedden Kurt
Published: May 2005

Part of this work focuses on temperature programmed retention index assessment of 70 polynuclear aromatic hydrocarbons (PAHs) using a methylsilicone capillary column. The use of the retention index presented here offers a good possibility of identifying and determining PAHs in the mass range discussed and to apply such conditions to the analysis of fuel deposits. Retention indices and vaporization enthalpy data of PAHs are linearly related to the molecular total energy. This paper describes also a gas‐chromatographic study of the adsorption of some PAHs on Carbopack.
Gas chromatographic determination of some glycol ethers and glycol ether acetates by FID, O‐FID, and MS detection. Preliminary applications in simultaneous monitoring of these chemicals in biological matrices
Authors: Giachetti Claudio , Zanolo Giovanni , Verga Giuseppe R. , Perovanni Fabio , Assandri Alessandro
Published: May 2005

Twelve compounds, commonly used as industrial solvents and belonging to the chemical class of glycol ethers and glycol ether acetates, were investigated. Several analytical conditions, applied to single or connected capillary columns of different length and polarity coating and connected to FID, O‐FID and MS detection systems, were assayed. Tests on heptafluorobutyryl derivatives were also attempted to improve the analytical sensitivity. The aims were to establish gas chromatographic methods suitable for analysis of reference standard compounds and to verify their applicability to biological matrix analysis for pharmacokinetic and toxicological studies, since these chemicals have been shown to be hazardous in laboratory animals and are presumed to be dangerous in man.
Studies on cryogenic trapping of solutes during chromatographic elution in capillary gas chromatography
Authors: Marriott Philip J. , Kinghorn Russell M.
Published: May 2005

Cryogenic trapping of solutes leads to narrowing of the chromatographic band. By placing the trap at the end of a capillary column, it is possible to study the effectiveness of the trap in terms of producing a sharpened elution profile. The trap may be heated by supplementary heating, but here convective heating from the GC oven is employed simply by turning off the cryogenic coolant. It is estimated that it takes about 50 s for the trap to heat up sufficiently to allow trapped solute to be remobilized, although this depends upon the oven temperature and thermal mass of the trap. It can also be shown that the more volatile solutes mobilize faster from the trap in this particular mode of operation. The recovery of trapped components shows that there is essentially quantitative trapping, and the solutes are trapped just at the leading edge of the trap.
Screening of four beta‐blockers and codeine in urine by on‐line coupled RPLC‐GC with on‐line derivatization
Authors: Hyötyläinen Tuulia , Pilviö Riitta , Riekkola Marja‐Liisa
Published: May 2005

On‐line coupled reversed phase liquid chromatography‐capillary gas chromatography (RPLC‐GC) was used in the separation of four derivatized beta‐blockers and codeine in urine. Sample clean‐up was accomplished in the LC part and compounds were separated in the GC part. After the LC column the aqueous phase was switched to organic solvent by on‐line liquid‐liquid extraction and the two phases were separated in a sandwich‐type phase separator. The organic extract was then transferred to a loop‐type LC‐GC interface. Beta‐blockers were derivatized on‐line in the interface before GC analysis. Concurrent eluent evaporation was used during the introduction of the sample fraction, and excess of solvent vapors was removed via an early vapor exit. The sample pretreatment was minimal; the only manual pretreatment step was the filtration of the urine sample.
Pressure drop effects on selectivity and resolution in packed column supercritical fluid chromatography
Authors: Lou Xianwen , Janssen Hans‐Gerd , Snijders Henri , Cramers Carel A.
Published: May 2005

The influence of pressure drop on retention, selectivity, plate height and resolution was investigated systematically in packed supercritical fluid chromatography (SFC) using pure carbon dioxide as the mobile phase. Numerical methods developed previously which enabled the prediction of pressure gradients, diffusivities, capacity factors, plate heights and resolutions along the length of the column were used for the model calculations. The effects of inlet pressure and supercritical fluid flow rate on selectivity and resolution are studied. In packed column SFC with pure carbon dioxide as the mobile phase, the pressure drop can have a significant effect on resolution. The flow rate is shown to have a larger effect than generally realized. The calculated data are shown to be in good agreement with the experimental results. Finally, the variation of the chromatographic parameters along a 5.5 meter long model SFC column is illustrated. The possibilities and limitations of using long packed columns in SFC are discussed. It is demonstrated that long columns with large plate numbers do not necessarily yield better separations.
On‐line coupling of liquid chromatography and capillary gas chromatography for the determination of a trace pyrethroid insecticide in fruit extracts
Authors: Modeste Fabrice , Caude Marcel , Devaux Philippe
Published: May 2005

The following paper presents a fast, selective, sensitive, and automated procedure for the residue analysis of the pyrethroid insecticide acrinathrin in various fruit samples by on‐line combination of Liquid Chromatography (LC) with capillary Gas Chromatography (GC) and an Electron‐Capture Detector (ECD). The loop‐type interface and Fully Concurrent Solvent Evaporation (FCSE) were chosen due to their ease of use and low volatility of acrinathrin. Commercially available LC diol columns with small internal diameters (2.1 mm) provided the selectivity required for the separation of the solute from matrix components and permitted the transfer of fraction volumes up to 500 μl into the retention gap, located inside the gas chromatograph. Optimization of the operating conditions with standard solutions showed the influence of the GC initial transfer temperature on the response of acrinathrin and the quantitative nature of the transfer was established by liquid scintillation counting. The linearity and precision were studied with the aid of calibration plots, whereas quantitative recoveries of the analyte (at least 95 %) were determined in spiked fruits. Compared to the corresponding off‐line technique, the on‐line approach allows us to reach lower detection limits (ppb level when 20 μl LC injections are performed) with excellent repeatability between 0.6 and 6.6 %. Moreover, the integrated analytical set‐up is robust, less time‐consuming and subsequently brings a marked improvement in the sample preparation step of complex biological matrices. Finally, the versatility of the system renders it highly suitable for the determination of other similar pyrethroids in order to develop a multiresidue method.
Determination of low molecular weight aliphatic amines by HPLC in environmental water samples
Authors: Djozan Dj. , Faraj‐Zadeh M. A.
Published: May 2005

A high resolution liquid chromatographic method is described for determination of low molecular weight (LMW) aliphatic amines in environmental waters. The analytes after isolation are derivatized by fluram and separated with isocratic elution on octyl (C8) column, followed by fluorimetric detection in 395/495 nm. Different isolation procedures such as octadecylsilane (ODS) and strong cation exchanger (SCX) solid phase extraction (SPE) cartridges and Amberlite CG‐120 resin were evaluated. The quantitative characteristics such as recovery, linear dynamic range, correlation coefficient, limit of detection (LOD), and relative standard deviation (RSD) are presented. Using this method, aliphatic amines were analyzed in rain and tap water as well as in waste water.
Enantiomeric separation of acidic drugs by capillary electrophoresis using a combination of charged and uncharged β‐cyclodextrins as chiral selectors
Authors: Fillet Marianne , Bechet Isabelle , Schomburg Gerhard , Hubert Philippe , Crommen Jacques
Published: May 2005

High resolution could be achieved for the enantiomers of acidic drugs, namely, sulindac, fenoprofen, ketoprofen, warfarin, and hexobarbital, in a buffer of pH 3 by the simultaneous addition of uncharged and charged β‐cyclodextrin derivatives. The interaction of the analytes with the anionic sulfobutyl ether β‐cyclodextrin provides the analytes with an adequate electrophoretic mobility whereas the interaction with various neutral β‐cyclodextrins generates high enantioselectivity. Five neutral cyclodextrins, the native β‐cyclodextrin, as well as methyl‐, dimethyl‐, trimethyl‐ and hydroxypropyl‐β‐cyclodextrin, were tested to enhance the enantioselectivity of the electrophoretic system. High resolution values and the shortest analysis times for the five drugs tested were achieved in a buffer made of 100 mM phosphoric acid adjusted to pH 3 with triethanolamine and containing dimethyl‐ or trimethyl‐β‐cyclodextrin in addition to sulfobutyl ether β‐cyclodextrin.
On‐line solid‐phase extraction‐thermal desorption‐gas chromatography with ion trap detection tandem mass spectrometry for the analysis of microcontaminants in water
Authors: Louter Arjan J. H. , Van Doornmalen Jacco , Vreuls Jolan J. , Brinkman Udo A. Th.
Published: May 2005

An improved set‐up for solid‐phase extraction with thermal desorption coupled on‐line to gas chromatography (SPETD‐GC) is presented. It includes a newly designed liner for a programmable temperature vaporizer (PTV) and an improved water elimination system. The SPETD procedure now includes a washing step with HPLC‐grade water to prevent degradation of analytes due to interaction with remaining sample constituents. The system was used to analyze surface and tap water samples over a 4‐month period. No decrease of chromatographic or trace‐enrichment performance was observed, and a liner packed with Tenax GR could be used for at least 150 analyses. The SPETD module was coupled to GC with ion‐trap detection for mass spectrometric (MS) and MS/MS detection. The linearity and repeatability of the procedure for several pesticides which were tested in the 0.5–10 μg/1 range were fully satisfactory (1 μg/1, RSD range 5–11%; n = 5). When using sample volumes of 0.1 ml only, detection limits were as low as 0. 1‐0.2 μg/1. As an example, the confirmation and quantification of a suspected pesticide in a real‐life sample using electron impact and positive chemical ionization in both the MS and MS/MS mode is shown.
Isolation and determination of toxic congeners of polychlorinated biphenyls in environmental samples
Authors: Huang Eleanor B. , Poole Gray , Chiu Chunh
Published: May 2005

A Method has been developed for the separation and enrichemen of there non‐ortho, eight mono‐ortho, and di‐ortho substituted polychlorinated biphenyls (PCBs) from Aroclor formulations and environmental samples. The fractionation is accomplished using high performance liquid chromatography (HPLC) with a 2‐(1‐pyrenyl)ethyldimethylsilysily silca column. GC‐MSD with an optimized temperature program was used for quantitation, Hexane, pentane, cyclohexane, iso‐octane, and 2‐propanol were tested as a mobile phase for the isolation of the thirteen target PCBs in a Aroclor 1242, 1254, and 1260 (1:1:1) misture, Pentane at room temperature with a slow rate of 0.7 ml/min is the condition of choice. The average recovery of thirteen target PCBs spiked in the Aroclor mixture is 99.5% with an average relative standard deviation of 4.5%. The average method detection limit is 8pg/μl. Targer PCBs in the reference solis, incinarator ash, and sediment samples were measured.
Initial bandwidth resulting from splitless and solid phase microextraction gas chromatographic injections
Authors: Snow Nicholas H. , Okeyo Pius
Published: May 2005

The initial width of the injected solute bands is a major determinant of the final measured peak width. While the individual processes contributing to this intial width have been observed and described qualitatively by many authors, little attention has been focused on their quantitative relationship. Using solid phase microextraction (SPME) and splitless injections of a hydrocarbon test mixutre the contributions to overall peak variance in SPME and splitless injections can be separated and quantitated. In SPME, it is seen that thermal focusing or rapid desorption must serve to provide focused bands. In splitless, thermal fucusing and solvent effects provide focusing. Variance contributions for each of these are calculated and shown.
Characterization and monitoring of amitraz degradation products in honey
Authors: Jiméanez Juan Joséa , Bernal Joséa Luis , Del Nozal María Jesús , Toribio Laura , Atienza Julián
Published: May 2005

Capillary gas chromatography in combination with atomic emission and electron impact‐chemical ionizaion mass spectrometry detectors have been used to detect amitraz degradation products in honey storage, characterize their structure, and evaluate their occurrence over a 100 day peroid. To this end, honey samples were extracted with an 8:2 v/v n‐hexane/acetone mixture. Amitraz was found to be rapidly decomposed into five related compounds, of which N‐(2,4‐dimethylphenyl)formamide was the most abundant and persistent.
Oral malodor, assessed by closed‐loop, gas chromatography, and ion‐trap technology
Authors: Claus Dirk , Geypens Benny , Ghoos Yvo , Rutgeerts Paul , Ghyselen Jenny , Hoshi Keika , Delanghe Geertrui
Published: May 2005

A method is described for the analysis of volatile organic compounds in saliva and tongue coating samples. The techniue is based on an off‐line preconcentration step by means of a closed‐loop trapping system followed by gas chromatography‐ion trap detection. With the closed‐loop technique, the volatile organic compounds(VOCs) are released from the matrix and trapped on an adsorbent without interference of water. The VOCs are released from the adsorbent into the gas chromatograph by thermdesorption. After separation, identification of the compounds is performed by ion trap technology.

By this technique 82 compounds could be demonstrated in saliva and tongue coating samples. The technique is also used to demonstrate the formation of volatile bacterial fermentation compounds when a protein substrate is added to tongue coating samples. It is considered a very promising tool in further research on oral malodor.
The characterization and quantitation of sulfur‐containing compounds in (heavy) middle distillates by LC‐GC‐FID‐SCD
Authors: Beens Jan , Tijssen Robert
Published: May 2005

A modified sulfur chemiluniinescence detector (SCO) has been interfaced to a HPLC‐HRGC hyphenated system. This combination enables the full characterization and quantitation of the sulfur containing compounds in (heavy) middle distillate oil fractions (boiling range 150–450°C). The system is suited to identify and determine the various groups of orgaiio‐sulfur structures such as: thiols + sulfides + thiophencs, benzothiophenes, dibenzothiophenes and benzo‐naphthothiophenes. Within these groups a separation according to boiling point is accomplished. Therefore it allows the separation, identification and quantitation of a number of individual species, especially those which are refractory to hydrodesulfu‐rization (HDS), such as 3‐methyl‐benzothiophene, 4‐methyl‐dibenzothiophene and ‐J,6‐dimethyl‐dibenzothiophene. The analysis of these groups and specific compounds is the key in understanding the kinetics of the chemistry involved in HDS. The complete instrumental set‐up is fully automated by computer control. To suppress possible interferences and quenching of the sulfur response of the SCL from (large amounts of) hydrocarbons, it is aligned above the adapted flame ionization detector (FID) of the GC. This renders a sensitivity of the SCO for sulfur of 2 pg. s−1, which corresponds to a minimum detectable level for individual sulfur species in oil fractions for the complete system of 1 ppm (mg. kg−1) sulfur. Its linear dynamic range exceeds 105, which means that also untreated, high sulfur containing feedstocks can be analyzed directly. The selectivity of sulfur to carbon of the modified SCO exceeds 106. A number of HDS feedstocks and desulfurized products of different desulfurization levels have been analyzed with the system. From the analysis results the behavior of the refractory compounds in HDS can now be followed closely.
Detection of volatile organic sulfur compounds in water by headspace gas chromatography and membrane inlet mass spectrometry
Authors: Ojala Marja , Ketola Raimo , Mansikka Timo , Kotiaho Tapio , Kostiainen Risto
Published: May 2005

Two gas chromatographic methods, GC‐FID (flame ionization detection) and GC‐ELCD (electrolytic conductivity detector) are compared in tlie analysis of volatile organic sulfur compounds (VOSCs) in water samples with a membrane inlet mass spectrometry (MIMS) technique. Carbon disulfide, ethanethiol, dimethyl sulfide, ethyl‐methyl sulfide, thiophene, and dimethyl disulfide were used as test compounds. Linear dynamic ranges were found to be two decades with the GC‐ELCD method and four decades with the GC‐FID and MIMS methods. Detection limits were at low (μg/1 levels with the two gas chromatographic methods and clearly below μg/1 level with the MIMS method. Analysis of one sample takes 40 min with the gas chromatographic methods and five minutes with the MIMS method. The selectivity was good, especially with the GC‐ELCD and the MIMS method. In addition, quantitative results obtained with spiked water samples by the three methods are compared.
Methodological aspects of headspace SPME: Application of the retention index system
Authors: Schäfer Brit , Hennig Peter , Engewald Werner
Published: May 2005

The applicability of the retention index system to hcadspacc solid phase microextraxtion (HS–SPME) was investigated. In headspace SPME, the two equilibria gas phase/matrix and fiber coating/gas phase have to he considered. In this paper the equilibrium fiber coating/gas phase is discussed separately to characterize it more detailed and to investigate several methodical aspects. Therefore, the different distribution constants Kfiber/gas of n‐alkanes, which were used for reference compounds, were related to their Kováts retention indices. The validity of the derived linear relationship log Kfiber/gas versus retention index I is demonstrated for various examples. This relation is helpful for the assessment of distribution constants of substances not available and for the choice of a suitable fiber coating. Furthermore, quantification of analytes in the gas phase can be done without authentic substances.
Supercritical fluid extraction of oxindole alkaloids from Uncaria tormentosa
Authors: Lopez‐Avila Viorica , Benedicto Janet , Robaugh Dave
Published: May 2005

Supercritical fluid extraction of oxindole alkaloids from Uncaria Tormentosa is described. The extraction was performed with supercritical carbon dioxide alone and with supercritical carbon dioxide modified with 10% metanol, and the extracts were analyzed by GC/MS and HPLC/MS.
Determination of inosine 5′‐monophosphate and guanosine 5′‐monophosphate in pig feed by capillary zone electrophoresis
Authors: Liu Huwei , Qi Shize , Zhang Yingnan , Huang Aijin , Sun Yiliang
Published: May 2005

A capillary zone clectrophoresis method was developed for the determination of IMP and GIMP, commonly used as flavor enhancers in poultry feed, in a real sample of complex composition. A baseline separation of inosine 5′‐monophosphate and guanosine 5′‐monophosphate was achieved within 10 min and the other components in the sample did not interfere with the separation. Quantitative results obtained from pig feed samples are presented. The separation conditions and experimental reproducibility are also discussed.
Effect of temperature, collection mode, and modifier on the supercritical CO2 extraction of dicofol residues from fish samples
Authors: Lanças Fernando M. , Galhiane Mário S. , Rissato Sandra R. , Barbirato Marco A.
Published: May 2005

Toxicity evaluation of Dicofol to Astyanax bimaculatus schubarti, a characteristic fish species living in tropical rivers and lakes was carried out through LC50 – 96 Hours. These experiments were performed under laboratory controlled conditions with atmospheric air flow and dilution water at 25°C in the static mode, supercritical fluid extraction (SFE) with pure CO2 and CO2 modified with hexane and methanol were used at 50, 70, 80, and 100°C and 300 atm. Several collection modes were studied to extract Dicofol from fish samples. The extraction efficiencies were directly comparedd with those obtained after 8 h of Soxhlet extraction using the same clean‐up with Florisil and analysis by HRGC/ECD and HRGC/MS as a confirmatory analytical technique. The SFE recoveries at temperatures lower than 80°C were typically lower than soxhlet recoveries; however a temperature increase enhanced the efficiency of SFE. The results showed that under certain conditions, supercritical fluid gave higher extractio power (extracted 11 % more pesticide), shorter extraction time, and lower solvent consumption than Soxhlet, thus affording an excellent alternative to the conventional method for extracting Dicofol from fish sample.
A new method for sorptive enrichment of gaseous samples: Application in air analysis and natural gas characterization
Authors: Baltussen Erik , Janssen Hans‐Gred , Sandra Pat , Cramers Carel A.
Published: May 2005

A new method for the preconcentration of trace components from gaseous samples is described. The system is based on enrichment of the solutes on a packed bed of 100% polydimethylsiloxane (PDMS) particles followed by thermal desorption and GC analysis. It was demonstrated that breakthrough volumes for packed PDMS traps can be calculated from theoretical equations. The PDMS material exhibits excellent thermal stability even after 200 consecutive runs. Additional advantages of packed sorbent beds over conventional adsorbent materials include high inertness, the absence of displacement effects and a reduced affinity for water. The practicality of the system was demonstrated by the analysis of air and natural gas using the system described here, components in the range of octane to benso[a] pyrene could be quantitatively trapped and thermally desorbed at mild temperatures. With the present set‐up the detection limit is in the order of 0.1 ng/m3 (MSD detector).
Current measurement of nonaqueous solvents: Applicatons to capillry electrophoresis and electrochromatography
Authors: Lister Ashley S. , Dorsey John G. , Burton D. Edward
Published: May 2005

The solvents acetonitrile, methanol, N, N‐dimethylformamide, dimethyl sulfoxide, formamide, and deionized water were investigated for their ability to support current flow without added electrolyte. Using open tubular capillary electrophoresis, currents were measured to be in the nanoampere (10−9 A) range for all solvents but formamide (10−6 A). Comparisons with flow data showed no clear relationship between current and electroosmotic flow. Packed capillary columns (3‐μm ODS) were used for separations using both pure solvent and hydrophobic dyes showed mild retention in pure ACN. A 16 polynuclear aromatic hydrocarbon (PAH) standard soluton was separated in 80/20 ACN/H2O with reduced plate heights (h) between 2.8 and 3.1 for retained species. A separation of nine androstenediones was achieved using a 70/30 MeOH/H2O mobile phase.
Packed column SFC of gas oils part I: Hydrocarbon group separation using pure carbon dioxide
Authors: M'Hamdi Rachid , Thiéabaut Duduer , Caude Marcel
Published: May 2005

In this paper, the critical application of the ASTM method to hydrocarbon group separation in gas oils using conventional packed column SFC coupled to FID is described. Resolution of model compounds is studied using a recent commercial apparatus and the chromatographic conditions such as pressure, temperature, and density of the mobile phase and the nature of the stationary phase after FID detection conditions have been selected to give the best sensitivity. Three gas oils differing in composition (ratio arimatic/non‐aromatic hydrocarbons)have been selected to evaluate the method for separation of the non‐aromatic hydrocarbon group from mono‐, di‐, and polyaromatic hydrocarbons groups (sub‐aromatic groups).

The ASTM requiements for this analysis are very easy to obtain in adsorption chromatography. However, in adsorption or normal phase chromatography, SFC results cannot be perfect either for the quantification of aromatic and non‐aromatic hydrocarbon fractions because there is still an overlap between the two groups (the separation is better in adsorption chromatography than in normal phase chromatography) or for sub‐aromatic fractionation (the separation is better in normal phase chromatography than in adsorption chromatography); combination of both separation techniques only improves the sub‐aromatic group fractionation. Thus, further enhancement of resolution for group and sub‐group separation is needed.
Temperature effects on supercritical carbon dioxide extractions of hydrocarbons from geological samples
Authors: Jafféa Rudolf , Gong Yumin , Furton Kenneth G.
Published: May 2005

The extraction of aliphatic and aromatic hydrocarbons from New Albany Shale by supercritical carbon dioxide at different extraction temperatures is described. The main goal of this work was to determine the effect of the temperature on the extraction process (i.e. relative extraction rate and efficiency). The data suggest that temperature changes of 20 and 40 degrees for the relatively moderate extraction temperatures tested (55, 75, and 95°C), can have significant effects on both relative extraction rates and yields. While lower molecular weight aromatics presented exponential extraction profiles, similar to those of the aliphatic hydrocarbons, higher molecular weight aromatics, such as the phenanthrenes, showed a linear extraction profile. This behavior cannot be explained by solubility differences in the supercritical fluid alone, and are, therefore, most likely based on differences in the speciation of the hydrocarbons within the sample matrix. Extractions at elevated temperatures (300°C) resulted in significant increments in the relative recoveries of all compounds, but particularly for the aromatic hydrocarbons. This may be caused by structural rearrangement of the sample matrix with subsequent release of trapped hydrocarbons and possibly by C‐S and S‐S bond breakage.
Comparison of mathemical methods for the calculation of retention indices at high temperature in gas chromatography
Authors: Didaoui L. , Touabet A. , Meklati B. Y.
Published: May 2005

The retention indices of three homologous series (2‐alkanones, 1‐alkanols, cycloalksanones) have been determined at high temperature by the application of two new adaptation methods: A multiparametric least‐squares regressions iterative method based on the dertermination of the adjusted retention times and a cubic interpolation directly using the uncorrected retention times without dead time correction. The two methods were applied to two types of columns. The first group includes eight packed columns (seven OV polymethylphenylsiloxane and Apolane‐87 stationary phases), while the second includes five glass capillary columns (four methyl‐silicons with different film thicknesses and Apolane‐87 stationary phases). The retention indices obtained with a multiparametric and a cubic interpolation methods were compared with each other and with those calculated by Grobler's, Guardino's, Kaiser's and Kovàts' methods. The influence of coating, film thickness, and temperature on them was investigated.
Comparision of varuious bulk fluids and modifiers as near‐crtical mobile phases on a polymeric column using linear solvatio energy realationships
Authors: Blackwell John A. , Stringham Rodger W.
Published: May 2005

Linear solvation energy realationships (LSERS) were used to qunatitatively compare the relative contributions of dipolarity/polarizability, hydrogen bonding, and other types of intermolecular interactions to retention and selectivity using various bulk moblie phase component. Using experimental condition which differ only by the compostion of the bulk moble phase component, the factors which cause selctivity to differ between HPLC, subcritical fluid chromatography and supercritical fluid charomatography were decovoluted. Heptance‐based HPLC mobile phases showed superior selectivities towards analytes which differ in hydrogen bond donating ability, gas‐to‐hexadecane partion coefficint and dipolarity/ploarizability. subcritical fluid chromatography with HFC‐134a (1, 1, 1, 2‐tetrafluoroethane) as the bulk fluid produced superior seclectivities for which differ in hydrogen bond accepting ability and execess molar refraction properties. Many of these factors showed temperature dependences which act to attenuate or accenture the particular intermolcular interaction.
Capillary electrophoresis with post‐column addition of terbium and sensitized lanthanide‐ion luminescence detection for the determination of diflunisal and salicylic acid
Authors: Milofsky Robert , Bauer Eve
Published: May 2005

A detection scheme based on the Post‐column addition of terbium followed by sensitized luminescence detection has been developed. Two model Compounds‐ saliculic acid and diflunisa‐ were separated by capillary electophoresis in an alkaline phosphate buffer. A Solution containing terbium and CTAB was added post‐column via a “home‐built” reactor resulting in the rapid fromation of the strongly luminescent terbium‐salicylic acid and terbium‐diflunisal complexes in a reaction capillary. Following complexationn in the reaction capillarty, the 325 nm line from a HeCd laser was used to excite the analytes which efficiently transfer their energy to terebium. Resuulant luminescence of terebium was liner of 2 orders of magnitude. This novel and practical system enables the detection of micromolar concentrations of diflunisal and salicylic acid‐ a 10 fold improvement over UV absorbance detection in the same system. Post‐column addition of terbium also eliminates the problems associated with strong adsorption of the lanthanide ion to the silica walls of the separation capillary and the formation of metal‐ligand complexes with different coordination numbers.
Analysis of tinuvin 1577 polymer additive in edible oils using on‐line coupled HPLC‐GC
Authors: Baner Albert L. , Guggenberger Andreas
Published: May 2005

An application of automated on‐line HPLC‐HRGC is described for direct analysis of edible oils for migrated polymer additives. The sample preparation, separating the additive from the oil triglycerides, is carried out using normal phase HPLC. The fraction of the eluent containing the additive is automatically transferred to a HRGC where a second and final separation of the additive from minor oil components takes place. The method compares well with off‐line separation methods. Migration data for Tinuvin 1577 from PET and PC polymers as well as an unspecified experimental polymer is given. The advantages and disadvantages of using different edible oils as food simulants are discussed.
A reversed phase high‐performance liquid chromatography method for determination of cephalexin in human plasma
Authors: Pecavar Anika , Šmidovnik Andrej , Milivojevic Dušan , Prošek Mirko
Published: May 2005

A reversed‐phase HPLC method for the analysis of cephalexin (7‐[(aminophenylacetyl)amino]‐3‐methyl‐8‐oxo‐5‐thia‐1‐azabicyclo[4.2.0]oct‐2‐ene‐2‐carboxylic acid) by isocratic separation is described. A comparison is made between the ultrafiltration land the extraction procedure developed in our laboratory. The extraction procedure, based on the deproteinization of plasma with perchloric acid followed by the extraction with dichloroethane and separation of cephalexin on a reversed phase column, gave better recovery. Quantitative validation of our method has been performed by an external standard technique. The relative standard deviations were between 1.1 and 1.9% in the within‐day assay and between 1.2 and 2.2% in the inter‐day assay. The limit of detection was 0.14ug/ml and the limit of quantification was 0.28ug/ml. This method is rapid, sensitive, simple, and reproducible. The LC MS/MS technique was successfully used for identification and quantification of cephalexin in human plasma samples.
A design approach to the structural analysis of interleukin‐2
Authors: Ciardelli T. L. , Landgraf B. , Gadski R. , Strnad J. , Cohen F. E. , Smith K. A.
Published: May 2005

A semi‐synthetic protein design approach has been employed for the structural investigation of a putative helical region at the C‐terminus of Interleukin‐2. With crystallographic or NMR derived conformational data as yet unavailable, we have relied only on primary sequence information and computer‐assisted modelling to direct the analysis. By employing both chemical peptide synthesis and recombinant DNA methods, the C‐terminus of IL‐2 was modified according to a strategy designed to stabilize helical secondary structure. A semi‐synthetic protein incorporating 12 simultaneous amino acid replacements was constructed, which possessed potentiated biological activity and displayed a far UV circular dichroism spectrum comparable to a hybrid protein with the authentic sequence. By comparison, another hybrid protein containing a C‐terminal region designed to contain helix breaking residues was totally devoid of bioactivity. These findings provide evidence that the modelling method correctly identified a helix necessary for the formation of a bioactive tertiary fold. Moreover, by employing semi‐synthesis it was possible to circumvent the difficulties associated with the preparation, purification and analysis of multiple recombinant proteins, and also to avoid the unreliability of total chemical synthesis for proteins greater than 100 residues.
Theoretical analysis of compartmented coupling in linear enzyme systems
Authors: Brooks S. P. J. , Storey K. B. , Suelter C. H.
Published: May 2005

Exact equations which describe the kinetic patterns of enzyme/enzyme complexes, when compartmented coupling occurs between them, are presented. Compartmented coupling refers to the creation of a local environment in which the concentration of an intermediate, shared by two enzymes, is higher than its solution concentration. This result in a higher coupling enzyme activity, a condition reflected in a shorter transition time for the system. In this paper, equations are presented which allow experimenters to quantitate the effect of compartmented coupling in terms of changes in the apparent Km and Vmax values. The equations presented in this paper are more exact than those previously derived since they do not incorporate first order assumptions before derivation.