bluuebunny/crossref_metadata_2025_split huggingface dataset:
Separation of enantiomers by high performance liquid chromatography using chiral eluents
Authors: Oelrich E. , Preusch H. , Wilhelm E. 
Published: May 2005

AbstractSimple procedures are presented for separating the enantiomers of α‐methyldopa, 5‐hydroxytryptophan, tryptophan, triiodothyronine and thyroxine, which require neither special sorbents nor difficult‐to‐obtain or unstable reagents.The method for α‐methyldopa, 5‐hydroxytryptophan and tryptophan is based on the use of L‐phenylalanine copper complex as the chiral constituent of the mobile phase; LiChrosorb® RP‐18 serves as the stationary phase. The procedure for triiodothyronine and thyroxine is grounded on the L‐proline copper complex as the chiral reagent and LiChrosorb® Si 60 as the stationary phase.In all observed cases, the D‐enantiomer is eluted prior to the respective L‐enantiomer. Chirality inversion of the mobile phase (application of the D‐phenylalanine copper complex) reverses the order of elution; a racemic eluent (DL‐phenylalanine copper complex) leads to no separation. In addition to the enantiomers of α‐amino acids, the enantiomers of α‐hydroxy acids (mandelic acid) can be separated.
Gas‐chromatographic separation of underivatized steroids using a BPhBT liquid crystal stationary phase
Authors: Smith T. R. , Wozny M. E. 
Published: May 2005

AbstractA gas‐chromatographic separation of underivatized steroids is described, in which the liquid crystal N,Ń‐bis(p‐phenylbenzylidene)α,α′‐bi‐p‐toluidine (BPhBT) was used isothermally at 265°C for the stationary phase. The nematic range of this crystal is 247 to 403°C. Use of the BPhBT crystal allowed operations in a temperature range where steroids are volatile and unlikely to display broad elution peaks and long retention times.With columns precoated with 2.5 weight percent of BPhBT, steroids containing minor structural differences in the ring system were readily differentiated. For example, 5‐androsten‐17α‐ethinyl‐3β, 17β‐diol was found to elute more rapidly than its 3‐keto analog, ethisterone. Ethisterone was distinguished readily also from its 19‐nor analog, norethisterone. Additionally, differences in side‐chain functionality and resultant molecular dimensions facilitated the separation of steroids of identical ring structure, as in the comparison of cholesterol with methyl 3β‐hydroxy‐5‐cholenate and 25‐hydroxycholesterol.An enhancement of separation according to the molecular length‐to‐breadth ratio was observed; in general, the larger this length‐to‐breadth ratio, the greater the retention period on the column.
Determination of the isomeric distribution and associated impurities in commercial diethylbenzenes by capillary gas chromatography
Authors: Kuchhal R. K. , Kumar B. , Kumar P. , Gupta P. L. 
Published: May 2005

AbstractA capillary gas chromatographic method for the quantitative analysis of diethylbenzene fractions is described. Estimation of ortho‐, meta‐ and para‐isomers and other C9 and C10 aromatic impurities is covered. The conditions developed involve the use of a capillary column of Carbowax‐1540 (300 feet × 0.01 inch) under isothermal operation. The retention index data for a number of aromatics are presented at four temperatures (90, 100, 110 and 120°C). The method offers a good choice for any level of concentration both for isomers and impurities commonly encountered within a reasonable analysis time.
The Varigrad and similar apparatus in gradient liquid chromatography: A systematic computational approach. Part 1: Theoretical development
Authors: Said A. S. 
Published: May 2005

AbstractDifferent methods for producing a pre‐assigned gradient in liquid chromatography are presented. A systematic approach to the calculations involved is given. The derived equations are mostly Poisson and Poisson summation distributions which are tabulated in the literature. The incremental method of gradient elution developed by Scott has been modified. In the modified apparatus two mixing chambers are used instead of one. This leads to an appreciable decrease in the number of reservoirs needed for the same precision in fitting a desired gradient. The application of the derived equations, together with other Varigrad modifications, will be given in Part 2 of this paper (to be published shortly in this Journal).
Glass capillary SCOT columns by a single‐step coating method
Authors: Chauhan Jasbir , Darbre André 
Published: May 2005

AbstractA single‐step coating method for the preparation of glass capillary SCOT columns is described. It is reproducible and less time‐consuming than the well‐known two‐step coating procedures. Other methods attempted are discussed briefly. Both the flame ionization and electron capture detectors could be used in conjunction with temperature programming. The separations achieved with an “activity mixture”, phenols and phenolic acids, illustrate the resolution obtained. The columns are suitable for quantitative determinations and a comparison is made with a conventional packed column.
Glass capillary gas chromatography with simultaneous flame ionization (FID) and Hall® element‐specific (HECD) detection
Authors: McCarthy L. V. , Overton E. B. , Maberry M. A. , Antoine S. A. , Laseter J. L. 
Published: May 2005

AbstractTwo glass capillary gas chromatographic systems were equipped with inert effluent splitters which allowed simultaneous data acquisition using nonspecific and element‐specific detectors. Simultaneous detection was achieved using the nonspecific flame ionization detector (FID) and the Hall® electrolytic conductivity detector (HECD) operated in either the sulfur‐or the nitrogen‐specific mode. Typical application of the simultaneous detection system as applied to analysis of petroleum residues is briefly described. The Hall electrolytic conductivity detector can be made element specific for halogen‐, sulfur‐, or nitrogen‐containing compounds. Simultaneous detection enhances the information yield from a single sample injection and proves to be a powerful complementary technique when used with computerized gas chromatography/mass spectrometry.
Simultaneous gas chromatographic determination of pirimiphos‐methyl and malathion residues in peanuts, peanut hulls, peanut meats, and peanut oil
Authors: Simonaitis R. A. , Zehner J. M. , Redlinger L. M. 
Published: May 2005

AbstractA gas chromatographic method developed for the simultaneous determination of residues of pirimiphos‐methyl (O‐[2‐(dimethyl‐amino)‐6‐methyl‐4‐pyrimidinyl] O,O‐dimethyl phosphorothioate) and malathion (diethyl mercaptosuccinate S‐ester with O,O‐dimethyl phosphorodithioate), in whole peanuts, peanut hulls, peanut meats, and peanut oil gives good recoveries and has a limit of detection for pirimiphos‐methyl and malathion of 0.04 ppm. Quantitative analysis for the two insecticides with electronic integration was reliable to 0.1 ppm.
Separation of isomeric and nonisomeric monoribonucleotides by isocratic ion pair high performance liquid chromatography
Authors: Al‐Moslih Moslih I. , Dubes George R. , Masoud Asaad N. 
Published: May 2005

AbstractA simple, isocratic, high performance liquid chromatographic procedure is described for the first time for the separation of nine monoribonucleotides using the ion‐pairing technique. An aqueous mobile phase containing 100 mM KH2PO4 and 12.5 mM tetramethylammonium hydroxide as the solvophobic ion, pH 3.9, was used with a reverse phase RP‐18 column. The nine monoribonucleotides studied were separated and eluted in the following order: cytidine‐5′ ‐phosphate, uridine‐5′ ‐phosphate, cytidine‐3′ ‐phosphate, guanosine‐5′ ‐phosphate, uridine‐3′ ‐phosphate, uridine‐2′ ‐phosphate, adenosine‐5′ ‐phosphate, guanosine‐3′ ‐phosphate, and adenosine‐3′ ‐phosphate. Generally the 5′ nucleotides eluted faster than the 3′ and the order of elution within each series was: cytidine, uridine, guanosine, and adenosine. The only nucleotide where three isomers were studied was uridine, and the 2′ eluted later than the 3′. Baseline separation was attained for a mixture containing four 3′ nucleotides and uridine‐2′ ‐phosphate. When the four 5′ nucleotides were chromatographed, baseline separation was also obtained except between cytidine‐5′ ‐phosphate and uridine‐5′ ‐phosphate. The coefficient of variation of the retention characteristics, which reflected day‐to‐day variation, averaged 6.4%.
The dry‐packing of columns in liquid chromatography
Authors: Davies R. D. 
Published: May 2005

AbstractThis contribution comprises two parts, the one covering some variables in the dry‐packing of columns for liquid chromatography, the other the use of an automatic dry‐packer in liquid chromatography. A high‐pressure stainless steel column was dry‐packed using a 20‐44 μm size, irrregularly shaped, silica gel support. It was found that, when support was added in discrete amounts, lateral tapping produced a column of higher efficiency (HETP = 0.69 mm) than was the case for vertical tapping (HETP = 1.37 mm). Simultaneous vertical and lateral tapping produced an intermediate result. Bulk filling of the column followed by tapping was inferior to adding support in discrete amounts. An apparatus constructed to perform the vertical and lateral tapping operations automatically confirmed the above conclusions. It was concluded that commercially available dry‐packing apparatus do not offer the best action for packing an efficient column since they involve predominantly vertical tapping.
Rapid on‐line analysis of low molecular weight hydrocarbons using glass capillary gas chromatography
Authors: Glajch J. L. , Schunn R. A. 
Published: May 2005

AbstractRapid analysis is important for on‐line chromatography. Gaseous or vaporized samples have been injected via heated gas sampling valves of less than 500 μl dead volume. The critical sampling and split problems could be solved by temperature programming. The general analysis described could be successfully used inter alia in scouting reactions.
High‐performance liquid chromatography with continuous gradient elution in screening for unknown metabolites of butoprozine directly in dog bile
Authors: Overzet F. , Drenth B. F. H. , de Zeeuw R. A. 
Published: May 2005

AbstractThis paper describes the screening for metabolites of butoprozine, a new anti‐anginal drug, in dog bile by means of reverse‐phase HPLC. Although it does involve a simple clean‐up step to remove a substantial amount of endogenous bile compounds, this screening method nevertheless avoids extraction of metabolites and thus allows all metabolites to be introduced into the chromatographic system. A single run of 100 minutes from 100% water to 100% methanol in a linear gradient effects adequate separation of the great majority of metabolites without interference from remaining endogenous compounds.Two methods of differentiating between metabolite peaks and endogenous peaks have been worked out. The first one makes use of 14C‐labeled butoprozine by measuring the amount of radioactivity in the column effluent while simultaneously recording the UV absorbance. The second method compares continuous gradient chromatograms of bile recorded before and after butoprozine administration under very similar conditions. The latter method can be applied to both radioactive and non‐radioactive materials.
Gas chromatographic resolution of carbohydrate enantiomers. A new chiral phase for pentoses
Authors: Benecke I. , Schmidt E. , König W. A. 
Published: May 2005

AbstractNew chiral polymers have been prepared by conversion of cyano groups of polysiloxanes XE‐60 and OV‐225 into carboxylic groups and subsequent coupling to give the respective S‐valine‐R‐α‐phenyl‐ethyl amide. In contrast to the corresponding stationary phases with S‐α‐phenylethyl amide groups, which have been used for the resoultion of trifluoroacetylated hexose derivatives, the new phase show high enantioselectivity for pentose and 6‐deoxyhexose derivatives.
A new method for the quantitative analysis of organochlorine pesticides and polychlorinated biphenyls
Authors: Godefroot M. , Stechele M. , Sandra P. , Verzele M. 
Published: May 2005

AbstractA simple method is described for the quantitative determination of organochlorine pesticides and polychlorinated biphenyls (PCB's) in water at the sub‐ppb level. A micro gas‐phase extractor advantageously replaces other preconcentration and purification techniques. The extract is analyzed by capillary gas chromatography without further enrichment. The recovery at the ppb level was nearly 100% for organochlorine pesticides and more than 80% for PCB's. The complete procedure including sample preparation, steam distillation‐extraction, and capillary gas chromatographic analysis is carried out in less than four hours.
Structure elucidation of triglycerides by chromatographic techniques. Part 1: Capillary GC of ozonized triglycerides
Authors: Geeraert E. , De Schepper D. 
Published: May 2005

AbstractStructure determination of triglycerides according to their number of unsaturated fatty acids (N.U.F.A.) is more easily achieved after ozonolysis of their mixtures (fats and oils) than by capillary gas chromatographic analysis of the mixture as such. Analyses performed before and after ozonolysis of cocoa buttel, hazelnut oil, and a mixture of both fats illustrate the potential of this approach to the structure elucidation of triglycerides by chromatographic techniques.
Static coating: An attempt to optimize a straightforward technique involving mechanical closure of the column
Authors: Grob K. , Grob G. 
Published: May 2005

AbstractThe static technique is commonly accepted as the most universal and scientific method of coating. At the same time, however, it is said to be experimentally demanding. Great efforts have therefore been made to render the method easier and safer, resulting in a wealth of recommendations confusing non‐experts. Over a period of two years we have practically applied most of the reported procedures with the aim of studying their practical convenience. We do not doubt that most procedures are comparably suitable in the hands of expert users, i. e. once the initiation efforts have been forgotten, or are otherwise of little interest. We have attempted to describe a method which is specifically suited for easy and quick introduction to beginners. The method is based on mechanical column closure. The principles of the method are discussed, and a comprehensive description of its practical application is given.
Influence of some inorganic salts on the polarity of apolar polymer phases in capillary gas chromatography
Authors: Traitler H. , Rossier M. 
Published: May 2005

AbstractDifferent stationary phases were prepared by mixing a series of inorganic salts with dimethylsiloxane polymer (SE‐30) and then tested by capillary gas chromatography. It was demonstrated that the polarity (as evaluated by measurement of Rohrschneider constants) of the mixed stationary phases, which is inferior or equal to that of a medium‐polar OV‐25 phases, reached even lower values than SE‐30 alone. The influence of NaF, NaCl, NaBr, AgNO3, and other inorganic salts on the polarity of capillaries is reflected by a better resolution and shorter retention time of cis/trans isomers of fatty acid methyl esters (FAMES) as well as positional isomers of triglycerides.
Screening for unknown compounds by HPLC using a multichannel diode array UV‐VIS spectrophotometer: Application to drug metabolism
Authors: Ghijsen R. T. , Drenth B. H. F. , Overzet F. , de Zeeuw R. A. 
Published: May 2005

AbstractThis article describes the use of a multichannel UV‐VIS detector coupled on‐line to an HPLC instrument. Simultaneous measurements of the absorption of a compound over a full range of wavelengths (200–800 nm) makes this almost universal detector a useful tool in screening for unknown compounds. The procedures used to compute so‐called spectro‐chromatograms and to draw pseudo‐three‐dimensional plots are discussed. The experimental examples given include an application to screening for drug metabolites in biological fluids.
Evaluation of a rotary valve/cold trap/reinjection system for capillary columns
Authors: Jacobsson Sven , Berg Sven 
Published: May 2005

AbstractThis paper describes a cold trap/reinjection system for capillary columns which utilizes a flow switching rotary valve. Sample enrichment is performed in a liquid nitrogen‐cooled glass trap attached to the valve. Evaporation of enriched compounds is carried out with the aid of an electric heating coil. Parameters such as cryogenic trapping efficiency, reinjection rates, transference of sample, and adsorption, as well as overall performance, are examined. In addition, a comparison is made between the cold trap/reinjection technique and injection with a gas‐tight syringe.
High resolution HPLC
Authors: Verzele M. , Dewaele C. 
Published: May 2005

AbstractIn order to justify its classification as a “high resolution” technique, HPLC should show an improvement in efficiency by a factor of at least 10, should be easily achievable with separation times of less than 1 h, preferably in the reversed phase mode. This is accomplished by coupling three 25 × 0.46 cm columns packed with 5 μm spherical ROSiL‐C18‐D silica gel. Details of the method and some typical chromatograms are given.
Packing procedure of silica columns for HPLC with aqueous slurries
Authors: Claessens H. A. , Aben G. , Vonk N. 
Published: May 2005

AbstractSuccessful packing of high quality HPLC columns is dependent upon a number of parameters. Especially when using slurry packing techniques, the absence of conglomerates of particles in the slurry and the wettability of the particles are important. The method described in this paper fulfills these conditions, imparting a ξ potential to the 5 and 10 μm silica particles by applying a pH gradient. This results in repulsive forces between the particles and hence leads to a well‐controlled monodisperse situation. Water is used as a slurry and displacement liquid; it combines the advantages of excellent wetting properties and non‐toxicity.
High resolution glass capillary columns for the gas chromatographic analysis of alditol acetates of neutral and amino sugars
Authors: Hudson J. R. , Morgan S. L. , Fox A. 
Published: May 2005

AbstractThe development of improved high resolulation glass capillary columns for separating the alditol acetates of neutral and amino sugars is described. Different capillary column treatments were evaluated for their activity toward amino sugar derivatives and for their effect on the efficiency of the completed column. The simple two‐step procedure of leaching with aqueous hydrochloric acid and dynamic coating with SP‐2330 was found to produce efficient and inert columns.
Mathematics for chromatography. Part I: Concentration distributions and their moments
Authors: Said A. S. , Al‐Ali H. , Hamad E. 
Published: May 2005

AbstractSeveral distributions of interest in chromatography were studied. In each case, the moments up to 4th moment were evaluated and the skew and the excess were deduced. The distributions studied in this article are the normal, continuous Poisson, discrete Poisson, exponentially modified normal, and exponentially modified Poisson distributions.
Peak distortion in chromatography. Part 1: Concentration‐dependent behavior
Authors: Conder J. R. 
Published: May 2005

AbstractAsymmetrical or tailed peaks are a common problem in chromatography. The causes of this distortion are described and classified. Each case is discussed from the point of view of first diagnosing the cause of asymmetry end then dealing with it appropriately; e.g. by removing the cause or, in applications to physicochemical measurement, by using more appropriate measures of retention than the residence time of the peak maximum. The classification of sources of asymmetry applies to both gas and liquid chromatography, allowing information derived from one field to be extended to the other.Part 1 of this review covers nonlinear, concentration‐dependent behavior with and without nonideal band‐spreading. Part 2 will deal with sources of distortion controlled by the kinetics of transport or reaction processes, viz. apparatus effects, incomplete resolution, slow kinetic processes, chemical reaction, and column voids.
Peak distortion in chromatography. Part 2: Kinetically controlled factors
Authors: Conder J. R. 
Published: May 2005

AbstractThe review of the characterization, diagnosis, and treatment of peak distortion begun in Part 1 is concluded. Part 1 dealt with peak distortion caused by nonlinear (concentration‐dependent) chromatographic behavior in the column. The present part covers peak distortion due to either the apparatus, incomplete resolution, slow kinetic processes, reaction on the column, or column voids. All these sources are controlled by the kinetics of transport or reaction processes.
The use of silicon in the preparation of apolar glass capillary columns
Authors: Bertsch W. , Pretorius V. , van Niekerk G. C. 
Published: May 2005

AbstractAs an extention of previous reports, variables affecting the performance of columns modified by silicon deposition have been optimized. The aim of this work was to produce thermostable apolar glass capillary columns regardless of the glass type used and to maintain column performance under stressful conditions. The main parameters studied were the influence of glass type, leaching effects, and silicon layer thickness on column activity. Deactivation and stationary phase conditions were held constant. Both coated and uncoated columns were tested.The thickness of the silicon layer was found to be relatively unimportant. There was no difference whether soft glass or borosiiicate glass was used and leaching before silicon deposition did not influence column activity. Bare silicon surfaces showed considerable activity especially in respect to interactions with free acids and bases.There are indications that the surface consists of silicon oxide and other oxygenated forms of silicon rather than of the element. Treatment of the silicon layers with dilute hydrofluoric acid and the strict exclusion of traces of oxygen and water did not improve the situation. In spite of such specific interactions, silicon surfaces were easily deactivated by heat treatment with polysiloxanes.Silicon surfaces deactivated by baking with octamethyltetrasiloxane at 400°C are inert and temperature stable and show characteristics similar to persilylated surfaces.
Derivatives of cholesterol cinnamate: A comparison of the separations of geometrical isomers when used as gas chromatographic stationary phases
Authors: Heath R. R. , Doolittle R. E. 
Published: May 2005

AbstractFour para‐substituted cholesterol cinnamates were synthesized and evaluated for utility as gas chromatograph (GC) liquid crystal stationary phases. The capability of the phases to separate olefinic geometrical isomers was found to be dependent on the position of the olefinic bond. When unsaturation occurred at positions four carbons or greater from the terminal methyl of the compounds investigated, the relative ability of the phases to separate geometrical isomers was p‐Cl > p‐Me > cholesterol cinnamate > p‐MeO derivative > p‐NO2. When unsaturation occurred at positions four carbons or less from the terminal methyl the relative ability of the para‐derivatives of cholesterol cinnamate to separate geometrical isomers was reversed.
Structure elucidation of triglycerides by chromatographic techniques. Part 2: RP HPLC of triglycerides and brominated triglycerides
Authors: Geeraert E. , De Schepper D. 
Published: May 2005

AbstractThe structure determination of triglycerides by RP HPLC is discussed, and the importance of temperature and mobile phase composition demonstrated. The formation of brominated triglycerides followed by RP HPLC analysis allows rapid determination of cocoa butter equivalents (CBE ) in cocoa butter and chocolate products.