bluuebunny/crossref_metadata_2025_split huggingface dataset:
A novel approach to the qualitative and quantitative assay of HPTLC plates: Second and fourth derivative recording of spectrophotodensitograms
Authors: Traveset J. , Such V. , Gonzalo R. , Gelpi E. 
Published: May 2005

AbstractOne of the limitations due to lack of resolution for a given pair of analytes in TLC or HPTLC is the need to optimize the system. In Practice this requires time, rerunning of the sample in different developing solvents, and a great deal of expertise on the part of the analyst.In our experience, application of first and second derivative recording techniques to HPTLC facilitates and speeds the whole process, permitting qualitative and quantitative assay of most unresolved spots. Consequently, we have now extended our instrumental capabilities to fourth derivative measurements. For this purpose, we have added a homemade electronic unit in series with the one previously used for first and second order derivatives. Thus, we have been able to evaluate the potential advantages of higher order derivatives for HPTLC analysis of unresolved components in various pharmaceutical products. A comparison of second and fourth order derivative measurements of seriously overlapping HPTLC components in a sample of preservatives used in the pharmaceutical industry suggests that the lower order derivatives might be a better choice in view of the higher accuracy and precision of the corresponding data. This is supported by the results of other applications, such as the assay of a commercial colorant, and a syrup formulation. The observed lack of precision of fourth order measurements stems from the fact that although the second and higher order derivatives produce narrower bandwidths, thus contributing to improved resolution, the signal to noise ratio decreases and satellite peak interactions increase, thus rendering correct discrimination of the fine structural detail of overlapping components more difficult.
Endcapping of high performance liquid chromatography packings derived from silica gel
Authors: Dewaele C. , Mussche P. , Verzele M. 
Published: May 2005

AbstractThe effect of endcapping a reversed phase chromatographic packing material derived from silica gel depends on the degree of derivatization of the phase. The effect can be dramatic for phases with low loading. Whether an octadecylated silica gel has been endcapped or not can be ascertained by chromatographing the pair naphthalene/1‐nitronaphthalene with a water/methanol eluent producing at least k' ≈ 10 for naphthalene. The ratio of the two k' values is 1.4 or higher for an endcapped material, while it is only 1.1 ‐1.2 for a non‐endcapped phase. A similar approach fails to give conclusions of similar utility for octylated silica gels.
Pattern recognition for analysis of cigarette smoke by capillary gas chromatography. Part 1: Total particulate matter (TPM)
Authors: Hsu F. S. , Good B. W. , Parrish M. E. , Crews T. D. 
Published: May 2005

AbstractComplex smoke profiles from fused silica capillary gas chromatography of different cigarette types produce rich information requiring computer and sophisticated statistical analysis to reveal the hidden correlation patterns. In our technique, a Cambridge pad containing total particulate matter (TPM) is extracted with Freon‐11 in a micro‐Soxhlet apparatus. The condenser is maintained at −15°C. After extraction, Freon‐11 is allowed to evaporate under mild conditions. Bis(trimethylsilyl)trifuoroacetamide (BSTFA) is subsequently added to the extract. Trimethylsilylation is completed by maintaining the reaction vessel at 60°C for two hours. A microprocessor‐controlled capillary gas chromatograph with an automatic sampler is used to generate profiles. A link to a host computer provides for transmission of profile reports and access to various statistical and graphic packages. Factor and discriminant analyses are applied to gas chromatographic data from TPM extracts because of their ability in data reduction, pattern extraction and ranking the importance of the gas chromatographic peaks. Some preliminary results from these statistical analyses are discussed.
Correlations between van der Waals volume and retention data of alkylbenzene derivatives in reversed phase micro high performance liquid chromatography
Authors: Jinno K. , Ishigaki A. 
Published: May 2005

AbstractThe structure‐retention relationship in reversed phase micro high performance liquid chromatography has been investigated for substituted alkylbenzene derivatives. The correlation between van der Waals volume and retention data was completely linear and any deviation from this relation might becaused from the overlap volume of substituent alkyl chains. Standard enthalpies of transfer from the mobile to the stationary phase are also proportional to the van der Waals volume of each solute; the results indicate that the mechanism of reversed phase liquid chromatography might involve a solute‐induced volume change in the mobile phase.
Concentration profiles and breakthrough curves in non‐linear chromatography
Authors: Said A. S. , Al‐Nafea M. , Al‐Ali H. , Hamad E. 
Published: May 2005

AbstractThe treatment of the non‐linear isotherm in chromatography by one of the authors [1] is extended to other cases of practical interest. The original paper dealt with the case of an initially thin zone resulting in a Poisson distribution the asymmetry of which is a function of the plate number and the non‐linearity constant. The present work shows that the same relations apply to initially thick zones and to the cases of washing and deposition leading to simple relations for breakthrough curves. For significantly non‐linear isotherms other quasi‐Gaussian distributions can give a better fit.
Dependence of selectivity and resolution upon composition of the binary mobile phase in LSC
Authors: Jaroniec M. , Suprynowicz‐Sieńko D. 
Published: May 2005

AbstractThe recently derived general equation for the capacity ratio has been utilized to study the dependence of selectivity and resolution upon mobile phase composition. This equation accounts for differences in molecular size of solutes and solvents, and for the energetic heterogeneity of the adscrbent surface. Model calculations illustrating the influence of these factors on the selectivity and resolution are presented and discussed.
Femtogram level quantitative determination of nitroglycerin and metabolites in human plasma by GC‐MS negative ion chemical ionization, single ion monitoring
Authors: Settlage J. A. , Gielsdorf W. , Jaeger H. 
Published: May 2005

AbstractRecent developments in the use of negative ion detection in GC‐MS have indicated the potential for highly sensitive analyses for certain compounds. This paper describes the application of the techniques to the assay of Nitroglycerin and its metabolites yielding sensitivity to two femtograms. Because of the low levels of nitroglycerin in biological media such sensitivity is highly desirable if not essential for meaningful measurements. In addition to sensitivity the method is shown to yield extremely good selectivity contributing further to the credibility of quantitative results.
Optimization of a scanning densitometer for fluorescence detection in high performance thin‐layer chromatography
Authors: Butler H. T. , Poole C. F. 
Published: May 2005

AbstractConditions for maximizing resolution and signal‐to‐noise ratios in fluorescence scanning densitometry of separations obtained by high performance thin‐layer chromatography are described. Resolution was found to be independent of most instrument parameters with a small decrease observed at wide slit widths. Signal was found to be markedly dependent on experimental parameters such as slit width, slit height, sensitivity setting, and the time constant of electronic filters. For recording chromatograms a slit width of 1.00 mm, a slit height slightly greater than the spot diameter, a low sensitivity setting (50 mV), electronic filtering, and a scan rate of 24 or 48 mm min−1 are commensurate with minimum recording time and maximum sample detectability without incurring a significant decrease in resolution.
Preparation of reversed‐phase high‐performance thin‐layer plates by in situ reaction with monochlorosilanes
Authors: Ericsson M. , Blomberg L. G. 
Published: May 2005

AbstractThe condition for in situ chemical modification of commercially available thin‐layer plates have been varied and the influence thereof upon reversed phase plate properties has been studied. The reaction variables studied were: average silica pore size, silica water content, use of tri‐ or monochlorosilanes as modifiers, reaction temperature, and addition of base. Coverage and activity of residual silanol groups was studied on modified plates.Desired plate properties are high speed of development in aqueous solvents and low content of active residual silanol groups. Under the conditions tested, the lowest amount of residual silanols was achieved at the expence of the speed of development in aqueous media and vice versa.
Purification of OV‐17 by supercritical fluid fractionation for fused silica capillary gas chromatography
Authors: Barry E. F. , Ferioli P. , Hubball J. A. 
Published: May 2005

AbstractCommercially available OV‐17 was partitioned into a low and a higher molecular weight fraction by supercritical fluid extraction with carbon dioxide. This higher molecular weight fraction is more thermally stable than the original OV‐17 due to its more viscous and gum‐like nature. Based on the growing evidence in the literature that a deactivating agent for fused silica open tubular columns should be compatible with the stationary phase, a precoat of 1,3,5‐trimethyl‐1,3,5‐triphenylcyclotrisiloxane was applied prior to the static coating of high molecular weight OV‐17. Fused silica OV‐17 columns prepared in this fashion are stable up to 300°C.
Evaluation of loop and pump injection systems in preparative liquid chromatography
Authors: Gazda Krystyna , Kowalczyk Jerzy S. 
Published: May 2005

AbstractThe usefulness of pump or loop injectors in preparative liquid chromatography was evaluated. The concentration distribution of samples flowing through a UV detector cell, directly connected to the injector, was recorded at various flow velocities, at various diameters of loop tubing, and using various methods of injection [injection with sample volumes equal to a fraction or total loop volume, etc.]. The most advantageous methods were found to be either use of a loop injector to inject only a fraction of its total volume or use of a pump. Both of these methods ensure a almost rectangular concentration distribution.
Quantitative determination of low concentrations of DHETX m. s. in human plasma by high performance liquid chromatography with fluorescence detection
Authors: Žorž M. , Marušič A. , Smerkolj R. , Prošek M. 
Published: May 2005

AbstractA method is described for separation of low amounts of DHETX m. s. from human plasma, based on extraction and determination by high performance liquid chromatography with fluorimetric detection.
On‐column infrared monitoring for reversed phase liquid chromatography with deuterated solvents
Authors: Fujimoto Chuzo , Jinno Kiyokatsu 
Published: May 2005

AbstractInfrared monitoring was accomplished in reversed phase HPLC on using deuterated solvents. The end of a micro HPLC column was flattend and used as a flow cell for on‐column IR detection. Detection of alkylbenzenes and oil‐soluble vitamins which were separeted on ODS packing with CD3CN/D2O and CD3OD, respectively, was performed at 2940 cm−1.
Improved quantitative capillary GC by the use of CO2 as secondary coolant in cold on‐column injection
Authors: Ogden M. W. , McNair H. M. 
Published: May 2005

AbstractA comparison is made between air and carbon dioxide as secondary cooling gases in cold on‐column injection into capillary columns. Because CO2 is a more effective coolant than air, the injection zone can be kept at a colder temperature, thus preventing loss of sample vapor through the open injector even as the initial oven temperatures because greater than the boiling point of the solvent. Sample loss at these elevated temperatures is shown as a reduction in peak area as functions of column temperature during injection and different injection zone temperatures. The maximum allowable oven temperature during injection is significantly higher when CO2 is used as secondary coolant rather than air.
Reversed‐phase high‐performance thin‐layer chromatography of mono‐, di‐ and trisubstituted bile acid methyl esters
Authors: Iida T. , Yamauchi C. , Chang F. C. 
Published: May 2005

AbstractA comparative study is reported on separation of series of mono‐, di‐, and trisubstituted methyl 5β‐cholanates, which differ only in the position and stereochemistry of hydroxyl or keto groups at position and stereochemistry of hydroxyl or keto groups at positions C‐3, C‐7, and/or C‐12, by reversed‐phase [with chemically‐bonded (C‐18) silica gel] and normal‐phase (silica gel) high‐performance thin‐layer chromatography (HPTLC). Methnol (or acetonitrile)/water systems were employed as mobile phase. Reversed‐phase HPTLC found to be particulary effective for separation of the stereoisomers of di‐ and trisubstituted compounds whereas the less polar monosubstituted isomers are well resolved in normal‐phase HPTLC.
A micro‐volume electron capture detector for use in high resolution capillary column gas chromatography
Authors: Wells G. 
Published: May 2005

AbstractA new design for an electron capture detector cell is described. The cell is compatible with the requirements of high resolution capillary columns and is shown to be useful in applications that require high analysis speed. A unique method of sample introduction reduces the problems of sample loss by adsorption on the surfaces of the cell. Previously reported problems of sample loss by adsorption on active surfaces within the cell when using hydrogen carrier gas are shown to have been eliminated. Examples are shown demonstrating the increased speed of analysis that can be obtained when using hydrogen carrier gas and 100 micron diameter columns.
Determination of biogenic quaternary ammonium compounds on fused silica capillary columns with a splitless injector as a chemical reactor/pyrolysis chamber
Authors: Findeis P. M. , Farwell S. O. 
Published: May 2005

AbstractA conventional splitless injector is used as a pyrolysis chamber or chemical reactor for the N‐demethylation of acetylcholine and other choline esters. The novel uses of 2‐aminoethanol as a N‐demethylation reagent in splitless injection and bonded‐phase fused silica capillary columns in the separation of the tertiary amine derivatives of choline esters are described. A comparison is made between non‐polar and moderately polar fused silica capillary columns in the separation of choline esters.
GC/MS analysis of chlorinated paraffins with negative ion chemical ionization
Authors: Müller Markus D. , Schmid Peter P. 
Published: May 2005

AbstractAlthough chlorinated paraffins (CP) are produced in large amounts (300 000 tonnes per year), little is known about their occurrence in the environment due to the lack of specific and sensitive analytical methods. The present paper describes the GC/MS analysis of different CP's using capillary gas chromatography with on‐column injection and negative ion chemical ionization (NCI) mass spectrometry. Chromatographic resolution of groups of isomers and homologues was obtained. The chromatograms and mass spectra are discussed. The suitability of this method for trace analysis of a CP sample using multiple ion detection (MID) is described.
Analysis of volatile organic compounds in polymers by dynamic headspace and gas chromatography/mass spectrometry
Authors: Jacobsson Sven 
Published: May 2005

AbstractAn experimental method for the analysis of volatile organic compounds in polymers is described. The technique involves dynamic headspace sampling, collection, and concentration of the volatiles in a cold trap, followed by capillary column gas chromatography/mass spectometry. Flow switching is carried out by the Deans switching technique. Four technical polymers used as pharmaceutical packaging materials have been analyzed in order to demonstrate the method.
Large sample injection method (≥ 100 μL) for capillary GC using a commercial thermodesorption unit as injection device
Authors: Kirschmer P. , Oehme M. 
Published: May 2005

AbstractA commercial thermodesorption and cold trap unit can be used as a large sample volume injection device in high resolution gas chromatography. Volumes of more than 100 μl can be injected. More than 97% of solvents, such as hexane, can be removed by a Tenax TA precolumn without any loss of compounds with volatilities comparable to naphthalene. Experimental conditions, recovery rates of polycyclic aromatic hydrocarbons, and the reproducibility of the method are described in detail. The method was successfully applied for the determination of PAH in air particulate matter extracts.
Direct gas chromatographic analysis of halogenated hydrocarbons at the part‐per‐trillion level
Authors: Zlatkis A. , Ghaoui L. , Wang F.‐S. , Shanfield H. 
Published: May 2005

AbstractLarge sample volume on‐column injection (up to 250 μL) of n‐pentane solutions of halogenated hydrocarbons has been employed for the direct measurement of both low‐boiling and high‐boiling compounds in what is essentially a single run. Two‐bonded phase, fused‐silica capillary columns are joined in series, through which the low‐boiling compounds are first chromatographed and detected with an electron capture detector. High‐boiling compounds are then trapped in a section joining the two columns, and subsequently chromatographed in the second column, using the same detector. This procedure permits analysis at the ppt level.
Characterization of OV‐1/FFAP‐mixture coated glass capillary columns used for the separation of free fatty acids
Authors: Pörschmann J. , Welsch T. , Engewald W. , Vigh Gy. 
Published: May 2005

AbstractAs an alternative to acid pretreated UCON and FFAP capillaries for the analysis of wide‐boiling free fatty acid mixtures, OV‐1 : FFAP phase mixtures were used on high‐temperature silylated inert glass capillary columns. The HETP‐carrier gas velocity curves, peak asymmetry factors, coating efficiency, gas phase and stationary phase contributions to the mass transfer resistance were determined for various OV‐1 : FFAP ratios. Mixed‐phase capillaries showed optimum performance at a 2 : 1 OV‐1 : FFAP ratio. The thermal and long‐term stability of OV‐1‐stabilized FFAP columns surpassed those of the UCON and pure FFAP reference column used.
Determination of 1‐nitropyrene by thin‐layer chromatography in a diesel exhaust particulate extract
Authors: Brown K. K. , Poole C. F. 
Published: May 2005

AbstractA method is described for the determination of 1‐nitropyrene in a diesel exhaust particulate extract by thin‐layer chromatography. 1‐Nitropyrene is determined as 1‐aminopyrene after prechromatographic reduction and isolation by solvent partition. The fluorescence response of 1‐aminopyrene is approximately 1000‐fold greater than that of 1‐nitropyrene. The poor fluorescence stability of 1‐aminopyrene on silica gel plates prevents in situ detection by scanning densitometry unless the plates are impregnated with a mixture of 2,6‐di‐tert‐butyl‐4‐methylphenol and Fomblin H‐Vac. A linear response from 1 to 150 ng of 1‐aminopyrene and a detection limit of 1.0 ng were obtained using the impregnated plates. For fourteen samples of a diesel exhaust particulate extract the concentration of 1‐nitropyrene was determined to be 165 μg/g with an RSD = 9.0%. No significant interferences were observed from other nitro‐ or aminopolycyclic aromatic compounds present in the extract.
Optimization of retention time of aromatic acids in liquid chromatography from log P and predicted pKa values
Authors: Hanai T. , Hubert J. 
Published: May 2005

AbstractFor optimization of liquid chromatography separations, several approaches have been reported, among them the use of the hydrophobic fragmental constant, as proposed by Rekker [1]. The fragmental constant is derived from the partition coefficients of various solutes between octanol and water and represents a summation of solubility parameters: van der Waals volume, π ‐ π interactions, hydrogen bonding, etc. With these constants the optimization of reversed phase mode liquid chromatography using octadecyl bonded silica gels as packing was feasible, although large error was found for the eluent with a high concentration of organic modifier or water. This is probably due to the heterogeneous solvation of the surface of the packings and to various solvent effects. In addition, when the acid dissociation constant was known, the retention times of aromatic acids in the ionic form were also predicted using the hydrophobic fragmental constant and the dissociation constant. By comparison of the previous data and a method proposed by Perrin et al. [2] it was possible to predict the dissociation constant of aromatic acids and optimize separation in reversed phase mode liquid chromatography using octadecyl bonded silica gels as packing. Furthermore, an equation for calculating the capacity ratios in a given pH eluent was proposed and the predicted and observed capacity ratios of aromatic acids in several eluents were examined in order to improve the above system.
Determination of tetraiodothyronine in serum by HPLC and electrochemical detection
Authors: Besenfelder E. 
Published: May 2005

AbstractTetraiodo‐L‐thyronine (T4) in human serum was determined by HPLC using a nonphysiological internal standard. For sample preparation, a cation exchange resin, RP‐chromatography on C‐18 or phenylphase, and electrochemical detection (Metrohm 656 or BAS‐LC 4 A) were employed. The mobile phase (0.8 ml/min) was 10 mM H3PO4/CH3OH (40/60 v/v) or 10 mM H3PO4/CH3CN (70/30 v/v, 1.5 ml/min), the voltage applied 800 mV. The coefficient of variation (day to day) was 6.8% (N = 40); concentrations of T4 found were 11 to 20% lower than those obtained by two different commercially available immunoassays.
Analysis of dust and surface swab samples for octachlorodibenzo‐p‐dioxin and heptachlorodibenzo‐p‐dioxins by fused silica capillary GC with EC detection
Authors: Korfmacher W. A. , Rushing L. G. , Nestorick D. M. , Thompson H. C. , Mitchum R. K. , Kominsky J. R. 
Published: May 2005

AbstractA method is described for the analysis of contaminated building dust samples and surface swab samples for octachlorodibenzo‐p‐dioxin (OCDD) and heptachlorodibenzo‐p‐dioxins (HpCDDs). The samples were analyzed by fused silica capillary GC combined with electron capture detection. Analysis was preceded by a short HPLC cleanup step designed to remove polychlorinated biphenyls (PCBs) and other compounds that might interfere. The method was found to work successfully on surface swab and dust samples known to contain PCBs, OCDD, and HpCDDs. The overall recovery of the analysis procedure for OCDD was found to be approximately 80%. The detection limit for the method was sample dependent, but for one typical set of surface swab samples was 0.2 μg/m2 of OCDD.
Preparative HPLC. Part 2. Purification of β‐lactam derivatives using laboratory‐assembled equipment
Authors: Matlin S. A. , Chan L. 
Published: May 2005

AbstractThe capabilities of a preparative chromatograph assembled at moderate cost from commercially available components are examined in relation to the purification of β‐lactam derivatives. It is shown that high efficiency separations can be achieved rapidly, economically, and on a scale sufficient to provide adequate quantities of material for spectroscopic identification and biological testing. In the synthesis of a large batch of aminopropyl silica for preparative HPLC purification of an impure sample of cephacetrile, three different grades of silica were investigated. The material giving the best performance was prepared on a 100 g scale and baseline separations for 0.5 g loadings of the impure cephacetrile were obtained on a 30 cm × 2.2 cm i.d. column. The pure cephalosporin was recovered in high yield by freeze drying of the eluate.