bluuebunny/crossref_metadata_2025_split huggingface dataset:
A CP‐MAS NMR study of some deactivation methods in capillary gas chromatography
Authors: Rutten G. , van de Ven A. , de Haan J. , van de Ven L. , Rijks J. 
Published: May 2005

AbstractThe effect of temperature, water content, and the type of reagent on the silylation of fused silica capillaries was studied by 29Si and 13C CP‐MAS NMR. Fumed silica (Cab‐O‐Sil M5), which is essentially a highly dispersed vitreous quartz with a surface comparable to that of fused silica capillary columns, was selected as a model material.Hexamethyldisilazane (HMDS) and 1,2‐diphenyl‐1,1,3,3‐tetraphenyldisilazane (DPTMDS), which were used as silylation reagents, yielded trimethyl‐ and dimethylphenylsilyl surface groups respectively at lower temperatures (< 350°C and <250°C respectively). At higher temperatures, increasingly more dimethylsilyl groups are formed, with the silicon bound to two oxygen atoms. This process occurs for DPTMDS at a considerably lower temperature than for HMDS. The formation of silyl groups on the surface and the disappearance of hydroxyl groups are followed independently. The 13C NMR and GC‐MS of the reaction products showed that with DPTMDS, the formation of two Si‐O‐Si links is accompanied by a loss of phenyl groups rather than of methyl groups.After the Cab‐O‐Sil had been dried over P2O5, the formation of these double links occurred for HMDS only at temperatures above 460°C and for DPTMDS at 400°C. Thus we concluded that water supplies oxygen atoms for double Si‐O‐Si links (possibly crosslinks) necessary for efficient deactivation. This may explain the less successful silanization of fused silica capillaries because their water content is lower than that of glass capillaries.
Changes in peak width and concentration at the inlet and outlet of a chromatographic column
Authors: Conder J. R. 
Published: May 2005

AbstractThe original plate model of chromatography is extended to the sorption process occurring at the column inlet and the desorption process at the column exit. At the column inlet it is shown that sufficiently wide feed bands undergo no change in concentration but a fall in band width, i.e., the volume of mobile phase occupied by the solute band is reduced. The reduction factor is (1 + k) where k is the mass distribution ratio (capacity factor). Narrower bands suffer partial reduction in both band width and concentration. On desorption at the outlet, however, the change is always in band width and not concentration. A perfect detector registers the true concentration‐time profile of the band in the column if the solute mass fraction in the stationary phase is below 10−3 at the column outlet. The risks of stripping the stationary phase at high solute concentrations in analytical and preparative or production gas chromatography are compared.
Factors affecting the reversed‐phase liquid chromatographic separation of polycyclic aromatic hydrocarbon isomers
Authors: Wise S. A. , Sander L. C. 
Published: May 2005

AbstractReversed‐phase liquid chromatography (LC) on C18 stationary phases provides excellent selectivity for the separation of polycyclic aromatic hydrocarbons (PAH). Recent studies have shown that several factors affect selectivity for the LC separation of PAH including phase type (monomeric or polymeric), pore diameter and surface area of the silica substrate, and surface density of the C18 ligands. In this paper the separation of eleven PAH isomers of molecular weight 278 is used to further illustrate the effect of stationary phase characteristics and shape of the solute (length‐to‐breadth ratio, L/B) on retention and selectivity. Only polymeric C18 phases with a high C18 surface coverage provided separation of all eleven isomers and the elution order of these isomers generally followed increasing L/B values. The effect of solute nonplanarity on reversed‐phase LC retention was investigated on both monomeric and polymeric phases using a series of planar and nonplanar PAH pairs. For each solute pair, the nonplanar solute eluted earlier than the planar solute, the largest selectivity factors being observed on the C18 phase with the highest percent carbon load. Based on these studies, a model is proposed to describe the retention of PAH on polymeric C18 phases.
Immobilized stationary phases on the basis of polyethylene glycol
Authors: Horká M. , Kahle V. , Janák K. , Tesařik K. 
Published: May 2005

AbstractThe preparation of the immobilized stationary phase based on Carbowax 20 M is described. Bifunctional isocyanates were used for cross‐linking. The properties of the prepared stationary phase were studied.
Analysis of mono‐, di‐, and triglycerides by capillary supercritical fluid chromatography
Authors: White C. M. , Houck R. K. 
Published: May 2005

AbstractThe separation of mixed mono‐, di‐, and triglycerides by capillary supercritical fluid chromatography is described. The separations were performed at low operating temperatures, using a carbon dioxide mobile phase, a conventional flame ionization detector, and two different stationary phases, DB‐5 (95% dimethyl‐(5%)‐diphenylpolysiloxane) and DB‐225 (50% cyanopropyl‐methyl‐(50%)‐methylphenylpolysiloxane). Because the separations were performed at low operating temperatures, no thermal degradation of the glycerides was observed. Even under these mild operating conditions, trinervonin, a triglyceride having a molecular weight over 1100 amu, was readily eluted. When rapid pressure programming of the carbon dioxide mobile phase was employed, trinervonin was eluted in less than two minutes. On DB‐5, the mono‐, di‐, and triglycerides eluted in order of increasing molecular weight. A graph of t′r (on DB‐5) versus molecular weight is linear. When DB‐225 was used as the stationary phase, triglycerides eluted in the order of increasing unsaturation. Thus, the order of elution on DB‐225 was tristearin, triolein, trilinolein, and trilinolenin.
Modified flame ionization detector for the analysis of large molecular weight polar compounds by capillary supercritical fluid chromatography
Authors: Richter B. E. 
Published: May 2005

AbstractThe modifications made to a flame ionization detector (FID) to facilitate the detection of large molecular weight polar compounds analyzed by capillary supercritical fluid chromatography are described. Some specific examples are given to demonstrate that polar compounds can be effectively eluted using deactivated fused silica capillary columns and supercritical carbon dioxide at 40°C.
The application of gradient saturation in unidimensional planar chromatography of polar lipids. Part 1: Presentation of the HPTLC system
Authors: Kolarovic L. , Traitler H. 
Published: May 2005

AbstractA thermostated HPTLC system was assembled to test the influence of gradient chamber saturation upon resolution of polar lipids chromatographed on boric acid‐impregnated silica gel plates. Inexpensive mixtures of nonacidic (14 component peaks) and acidic (8 component peaks) lipids were prepared from soya lecithin by a simplified procedure involving DEAE‐Sephadex liquid column chromatography to monitor performance of the system using a readily available reference material. The system requires ca. 5 min chamber presaturation after which the polar lipids are chromatographed in less than 30 min. Retention times (tR) as well as peak area % values of all component peaks and measured by scanning photodensitometry to demonstrate the influence of different modes of chamber saturation upon the resolution of polar lopids.
Column switching applied to capillary gas chromatography/fourier transform infrared spectroscopy
Authors: Smith S. L. 
Published: May 2005

AbstractA dual oven gas chromatograph incorporating a micro, mechanical switching valve has been interfaced to an FTIR spectrometer. With this system, each oven can be operated with independent temperature control. Complete choice of the columns' type and capacity gives flexibility in the separation prior to spectroscopic evaluation. An application which demonstrates some of the advantages of column switching in GC/FTIR is presented. Minor sample components have been successfully analyzed by heart‐cutting the appropriate section of the separation from a high to a low capacity column. In this way, the dynamic range of the technique is effectively increased while an efficient chromatographic inlet to the FTIR is maintained.
Modified GC‐phases for the enantiomeric separation of optically active compounds: Crosslinking experiments with polymeric chiral compounds
Authors: Schomburg G. , Benecke I. , Severin G. 
Published: May 2005

AbstractCrosslinking experiments for immobilization of the well‐known chiral stationary phases XE 60‐L‐valine‐(S)‐ and XE 60‐L‐valine‐(R)‐α‐phenylethylamide within capillary columns have been successfully carried out. Crosslinking was also obtained with mixtures of the chiral compound acrylyl‐L‐valine‐(S)‐α‐phenylethylamide and the polyethylene glycol Carbowax 20M. Immobilization of 75% to 90% was achieved by crosslinking the polymeric chiral phases, but sometimes up to 100% of these phases remained within the columns after the usual subsequent solvent treatment. The crosslinking of Carbowax 20M with acrylyl‐L‐valine‐(S)‐α‐phenylethylamide led to a chiral polymer of a polarity different from that of the common siloxane type chiral phases.
Analysis of light hydrocarbons (C2C6) at PPT levels by high resolution gas chromatography
Authors: Schmidbauer N. , Oehme M. 
Published: May 2005

AbstractAn analytical technique is described which allows the determination of C2C6 hydrocarbons in the ppt‐range from up to 21 air samples after removal of air humidity. Preconcentration is carried out on a two stage cryotrap system. The compounds are separ ated on a temperature‐programmed capillary coated with Al2 O3. Detection limits (S/N 2:1) of 1.5 to 5 ppt were obtained for air samples from the Arctic. The reproducibility of the method was about 3% at the 50–100 ppt level. Practical problems are discussed in detail.
Analysis of essential oils by direct sampling from plant secretory structures and capillary gas chromatography
Authors: Bicchi C. , D' Amato A. , Frattini C. , Nano G. M. , Cappelletti E. , Caniato R. 
Published: May 2005

AbstractIt is of fundamental importance to know the true composition of the essential oil produced by the secretory structures of a plant, both from a biogenetic and a chemotaxonomic point of view. This paper considers a method which combines direct sampling with on‐column CGC and studies the oils directly from the secretory structures: some examples are given (Humulus lupulus L., Tagetes erecta L., and Tagetes patula L.). For each plant, the composition of the distilled oil is compared to that obtained by direct sampling, and a photograph of the secretory structures taken by electroscanning microscopy is given.
Dicholorbenzyl alkyl ether homologs as retention index markers and internal standards for the analysis of environmental samples using capillary gas chromatography
Authors: Wells D. E. , Gillespie M. J. , Porter A. E. A. 
Published: May 2005

AbstractA homologous series of 2,4‐dichlorobenzyl alkyl ethers (DCBEs) have been synthesized and purified for use as retention index calibrants and internal standards. They are stable, sensitive to ECD and FID and ideal for GC‐MS, with base peaks at m/z 159/161. The retention index calibration against the n‐alkanes for a linear temperature program (LTP) series is given and recommendations made for the most suitable members of the DCBE series for use as internal standards in organochlorine (OC) residue analysis.
On‐line multidimensional chromatography using packed capillary liquid chromatography and capillary gas chromatography
Authors: Cortes H. J. , Pfeiffer C. D. , Richter B. E. 
Published: May 2005

AbstractThe introduction of selected fractions from a liquid chromatograph into a gas chromatograph has been described; however, analyses were performed by off‐line experiments requiring collection and reinjection of the separate fractions or by on‐line procedures where disadvantageously, only a fraction of the separated peak or a well resolved component in a mixture could be introduced into a gas chromatograph. This disadvantage is overcome by the apparatus and method described in this paper, which utilizes a multidimensional chromatography system employing a high efficiency, packed capillary LC column coupled on‐line to a capillary gas chromatograph.The liquid chromatograph (so designed) can act as a highly efficient clean‐up or chemical class fractionation step prior to introduction into the gas chromatograph, significantly reducing sample preparation times in many applications. Thus minor components in a complex matrix can be determined without prior sample clean‐up, an example of which is the determination of polychlorinated biphenyls in a complex hydrocarbon matrix.
Liquid crystal stationary phases for gas chromatography and supercritical fluid chromatography
Authors: Rokushika S. , Naikwadi K. P. , Jadhav A. L. , Hatano H. 
Published: May 2005

AbstractNovel monomeric and polymeric liquid crystalline compounds were synthesized as stationary phases for gas chromatography (GC) and supercritical fluid chromatography (SFC). Monomeric liquid crystalline compounds were used in packed column gas chromatography for the separation of isomeric aromatic compounds and insect sex pheromones. Liquid crystalline polymers possess long nematic ranges and a uniform coating was easily achieved in glass and fused silica capillaries, which could stand temperatures up to 250°C in GC and pressures of 200 MPa at 160°C in SFC. The columns provide excellent selectivity and resolution for fused ring aromatic compounds such as the isomers anthracene and phenanthrene or triphenylene and chrysene.
Practical applications of open tubes in liquid chromatography
Authors: Engelhardt H. , Lillig B. 
Published: May 2005

AbstractThe practical applications of open tubes in liquid chromatography as separation columns and as reactors for post column derivatization are discussed. With present technology, the potential efficiency of open tubular columns cannot be fully exploited. As reactors in post column derivatization, these tubes offer many advantages if knitted or stitched to enhance radial mass transfer. The application of open tubes with diameters between 0.12 mm and 0.6 mm as reactors in the selective and sensitive detection of amino acids is demonstrated.
A fast procedure to immobilize polyethylene glycols in glass capillary columns
Authors: Russo M. V. , Goretti G. C. , Liberti A. 
Published: May 2005

AbstractPolyethylene glycols can be immobilized in glass capillary columns by a new procedure involving covering the glass walls with a layer of graphitized carbon black and by flowing a mixture of the stationary phase and dicumyl peroxide. After curing and conditioning the column is ready for use. Excellent performance is reported for Carbowax 20 M and high molecular weight glycols. For other glycols the immobilized layer is less stable and can be washed out.
On the efficiency of capillary columns coated with medium polarity thick films
Authors: David F. , Proot M. , Sandra P. 
Published: May 2005

AbstractThe efficiency of FSOT columns coated with thick films of polyphenylmethylsiloxane was theoretically and experimentally compared to thin apolar and medium polar coatings and to thick apolar coatings. Experimental hū and TZū plots clearly demonstrate the enormous loss in chromatographic efficiency of thick films of medium polar siloxane stationary phases. The low diffusion coefficient in the liquid phaese is responsible for this behavior. The influence of the temperature and the nature of the solute on the efficiency was also studied.
Enzyme activity determination by radio gas chromatography on capillary columns
Authors: Herkner K. , Schaupal R. , Goedl U. 
Published: May 2005

AbstractAndrogen 5α‐reductase from the foreskin of 48 boys in prepubertal age was analyzed by evaluation of the apparent Km‐and Vmax‐ values after tissue incubation. Reaction rates were calculated after determination of specific radioactivity of distinct metabolites, by comparison to the radioactivity of the precursor. Reaction products were separated by radio gas chromatography on capillary columns. The chromatography system was based on multicolumn equipment with column switching facilities and a variable splitter at the outlet of the separation column. A radioactivity monitor (gas proportional counter) was used for measurement of radioactivity in the column effluents. An electron capture detector was used for mass detection of steroid acyl derivatives.
Packed columns vs. wall coated open tubular columns in quantitative analyses of polychlorinated biphenyls
Authors: Kominar R. J. , Onuska F. I. , Terry K. A. 
Published: May 2005

AbstractThis article describes and critically evaluates a complete method for the quantitation of PCB in sediment samples. The extraction and clean‐up procedure is described. Packed column and capillary column results are compared. Capillary column quantitation yields lower values for total PCB loading. Preferences for capillary column quantitation are discussed and explained. Capillary quantitation is based on the combination of an external Aroclor standard and an internal decachlorobiphenyl standard for normalizing data. In light of the recent report of synthesis of all 209 PCB congeners a suggestion is made to use these as absolute standards to establish a bank of primary standard Aroclors.
Temperature programmed retention indices: Calculation from isothermal data. Part 2: Results with nonpolar columns
Authors: Curvers J. , Rijks J. , Cramers C. , Knauss K. , Larson P. 
Published: May 2005

AbstractThe procedure for calculating linear temperature programmed indices as described in part 1 has been evaluated using five different nonpolar columns, with OV‐1 as the stationary phase. For fourty‐three different solutes covering five different classes of components, including n‐alkanes and alkyl‐aromatic compounds, both isothermal and temperature programmed indices were determined. The isothermal information was used to calculate temperature programmed indices. For several linear programmed conditions accuracies better than 0.51T‐units were usually obtained. The results are compared with published procedures.It is demonstrated that isothermal retention information obtained on one column can be transferred to another column with the same stationary phase but different column dimensions and/or phase ratio. The temperature programmed indices calculated in this way also have an accuracy better than 0.51T‐u.The temperature accuracy and precision of the GC‐instrumentation used was of the order of 0.1°C. All calculations can be run with a Basic‐programmed microcomputer.
Preparation of polysiloxane stationary phases for capillary column chromatography: A New methoxyphenyl phase
Authors: Bradshaw J. S. , Adams N. W. , Johnson R. S. , Tarbet B. J. , Schregenberger C. M. , Pulsipher M. A. , Andrus M. B. , Markides K. E. , Lee M. L. 
Published: May 2005

AbstractContemporary methods for the synthesis of alkyl‐ and arylsubstituted polysiloxane stationary phases are reviewed. A new, moderately polar phase containing the 3‐(4‐methoxyphenyl)‐propyl group is reported.
Preparation of inert and high‐temperature stable apolar and medium polar glass‐capillary columns using OH‐terminated polysiloxane stationary phases
Authors: Blum W. 
Published: May 2005

AbstractCoating intensively leached silica surfaces with OH‐terminated phases provides a new way of producing, by simple means, columns with substantially increased inertness and thermostability. In addition, their separation efficiency is found to be typically higher than that of columns with traditional coatings. The underlying basic effect is a condensation process between terminal silanol groups of the phase and residual silanols, of the glass surface, thus producing the mentioned inertness. Moreover, the surface‐bonded molecules are immobilized without addition of a radical generator. If required, crosslinking can also be effected using a volatile azo compound. No vinyl groups are required for this additional immobilization process. The paper discusses all processes involved, and gives detailed working directions for the following medium polar phases. OV‐1701‐OH, OV‐31‐OH (new, 17% cyanopropyl), OV‐61‐OH, and OV‐17‐OH, and the apolar phases PS‐347.5 and PS‐086. There is no doubt so far that the principle of terminal silanol groups is applicable to all silicone phases, and may replace the traditional endcapped stationary phases in the future.
Coupled HPLC‐capillary GC – state of the art and outlook
Authors: Grob K. , Schilling B. 
Published: May 2005

AbstractHPLC fractions involving eluents of low to intermediate polarity can be introduced into capillary GC using the retention gap technique. Partial or complete solvent evaporation during sample introduction reduces the length of, or almost eliminates, the zone in the column inlet (retention gap) flooded by the introduced liquid, allowing introduction of larger HPLC fractions and/or use of shorter retention gaps. The corresponding techniques are reviewed. The retention gap technique is poorly suited for water‐containing HPLC eluents (reversed phase HPLC) and fails completely if HPLC eluents contain, e.g., buffer salts. Various techniques for extracting such HPLC eluents are considered, preference being given to extraction into GC stationary phases from where solutes are thermally desorbed into the GC separation column. Limiting factors are diffusion of solutes within the liquid phase to be extracted and retention power of the extraction tubes.
Deactivation of fused silica capillary columns with cyanopropylhydrosiloxanes
Authors: Markides K. E. , Tarbet B. J. , Schregenberger C. M. , Bradshaw J. S. , Lee M. L. , Bartle K. D. 
Published: May 2005

AbstractA method is described for surface deactivation and modification of fused silica capillary columns with a cyanopropyl‐containing reagent. The deactivation procedure involved a dehydrocondensation reaction between a bis(cyanopropyl)methylhydropolysiloxane reagent and surface silanol groups at an optimum temperature of only 250°C. Actual critical surface tension measurements were made using the capillary rise method. Excellent deactivation for acidic and basic compounds at the low ng level, and wettability for nonpolar and polar polysiloxane stationary phases were obtained. A procedure was developed to remove acidic impurities that are present in polar stationary phases.
Determination of glibenclamide in human serum by HPLC
Authors: Nieder M. , Dilger C. , Jaeger H. 
Published: May 2005

AbstractThe antidiabetic drug glibenclamide can be reliably quantitated in human serum with high performance liquid chromatography. The serum is buffered and extracted with toluene. The organic solvent is evaporated, the residue dissolved in the mobile phase and an aliquot sampled automatically and chromatographed. UV‐detection at 229 m allows a lower limit of quantitation of 5 ng/ml. Precise handling of exact volumes facilitates external calibration. Statistical data for imprecision and inaccuracy are given and illustrate reliable quantification. Application of the method to experimental and clinical pharmacokinetic studies with specific problems is illustrated.