bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative structure‐retention relationships in reversed‐phase liquid chromatography using several stationary and mobile phases
Authors: Vonk Erik C. , Lewandowska Katarzyna , Claessens Henk A. , Kaliszan Roman , Cramers Carel A. 
Published: July 2003

AbstractQuantitative Structure‐Retention Relationships (QSRRs) have been employed to study retention mechanism of Reversed‐Phase Liquid Chromatography (RPLC). Two C18 and two C8 columns were used with mobile phases containing methanol, acetonitrile, and tetrahydrofuran in concentrations ranging from 40 to 90 (v/v)% in water. QSRR equations derived are generally characterized by a satisfactory quality of fit, although missing data or a low average retention can decrease the goodness‐of‐fit. In agreement with literature the most important retention descriptors appeared to be the analyte's molecular volume and its hydrogen‐bond accepting basicity, but also the polarity/polarizability, hydrogen‐bond donating acidity, and excess molar refraction showed statistical significance in several cases. Relatively small, but significant differences between the two C18 stationary phases were observed. The differences between C8 and C18 column types were more pronounced. The influence of the mobile phase on regression coefficients is more difficult to interpret, because of adsorption of mobile phase constituents by the stationary phase. However, the importance of this partitioning of water and modifier is illustrated by the practically identical trends in b values for the three modifiers studied, while the trends in v values are significantly different. Principal component analysis of the QSRR regression coefficients demonstrated the prevailing role of the mobile phase for chromatographic properties of the RPLC systems studied as compared to the stationary phase.
Investigation of factors influencing the performance of open‐tubular stationary phases in capillary electrochromatography
Authors: Freitag Ruth , Constantin Stéphane 
Published: July 2003

AbstractSilica‐based, open‐tubular capillary columns bearing C8‐moieties were produced by the sol gel approach. The influence of experimental conditions adjusted during the preparation of the stationary phase on the performance of the resulting capillary column were investigated in terms of the plate height, the resolution, and the capacity factors, taking the separation of three non‐charged polyaromatic hydrocarbons (naphthalene, phenanthrene, pyrene) as example. Acetone served as EOF marker. The optimal synthesis protocol was then used to prepare columns for an analogous investigation of the chromatographic parameters, namely the mobile phase composition, the applied voltage and temperature, as well as the column length, thickness, and inner diameter on the performance of the capillary columns.
Fast comprehensive two‐dimensional gas chromatography (GC×GC) using 50‐μm ID second‐dimension columns
Authors: Adahchour Mohamed , Tas̨öz Ayla , Beens Jan , Vreuls René J. J. , Batenburg A. Max , Brinkman Udo A. Th. 
Published: July 2003

AbstractUp till now, comprehensive two‐dimensional gas chromatography has suffered from the serious disadvantage that the first‐dimension separation has to be operated both at sub‐optimum flow and at slow temperature programming rates to enable the required number of modulations across a first‐dimension peak. Consequently, the separation efficiency of the first‐dimension is (far) below optimum and the overall analysis times become longer than necessary. This problem can be solved by selecting a short 50‐μm ID second‐dimension column, and combining it with a standard long 250‐μm ID first‐dimension column. Compared with conventional GC×GC set‐ups, an over 3‐fold reduction of the analysis time was reached in the present study without sacrificing resolution; to the contrary, a substantial increase of the peak capacity was obtained.
Determination of drugs used in advanced breast cancer by capillary gas chromatography of pharmaceutical formulations
Authors: Berzas Juan J. , Rodríguez Juana , Contento Ana M. , Cabello Maria P. 
Published: July 2003

AbstractA capillary gas chromatographic method with flame ionisation detection (FID) has been developed for the analysis of Tamoxifen, Anastrozole, and Letrozole in their pharmaceutical preparations, using Clomipramine as the internal standard in order to achieve quantification. Optimal conditions were investigated: column head pressure (110 kPa), injector and detector (FID) temperatures (both 325°C), time and temperature for the splitless step (0.75 min and 70°C), volume injected (2 μL), and an oven temperature program providing analysis times shorter than 8 minutes. The principal aspects of the validation method are examined and discussed. A test of the ruggedness of this method was carried out using the Plackett‐Burman fractional factorial model with a matrix of fifteen experiments. Detection limits of 17.0, 9.6, and 30.6 μg L–1 were obtained for Tamoxifen, Anastrozole, and Letrozole, respectively. This method is simple, rapid, and sensitive; it was tested on the analysis of pharmaceutical preparations, achieving recoveries between 98.8% and 100.3%.
Highly efficient separation of dsDNA fragments on glass chips by using an ultralow viscosity sieving matrix
Authors: Wang Hui , Qin Jianhua , Dai Zhongpeng , Wang Li , Bai Jiling , Lin Bingcheng 
Published: July 2003

AbstractA novel protocol has been established to separate dsDNA fragments with high efficiency on glass chips by using an ultralow viscosity sieving matrix with added glucose. Low‐molecular‐weight hydroxypropylmethylcellulose (HPMC), with a viscosity nearly equivalent to that of water, was used to electrophoretically separate fluorescent intercalator‐labeled double‐stranded DNA (dsDNA) fragments on microfluidic glass chips. In comparison with conventional sieving protocols, low‐molecular‐weight HPMC as sieving matrix could result in reduced running cost and analysis time, in addition to a comparable separation efficiency of dsDNA fragments. In this paper, the addition of glucose was investigated to enhance the separation of DNA in the lowest viscosity polymer evaluated. The effect of staining dye and field strength were also evaluated. At an applied electric field strength of 200 V/cm, satisfactory resolution of the PBR322/HaeIII DNA marker could be achieved within 4 min by using 2% HPMC‐5 with 6% glucose added. Coelectrophoresing PCR product along with ϕX174/HaeIII DNA sizing marker was also demonstrated by using the ultralow viscosity HPMC‐5 solution on a glass chip.
LC method for the simultaneous determination of R‐timolol and other closely related impurities in S‐timolol maleate: Optimization by use of an experimental design
Authors: Djang'eing'a Marini Roland , Chiap Patrice , Boulanger Bruno , Dewe Walthère , Hubert Philippe , Crommen Jacques 
Published: July 2003

AbstractA liquid chromatography (LC) method using cellulose tris(3,5‐dimethylphenylcarbamate) (5 μm) as chiral stationary phase (CSP) and a mixture of hexane, 2‐propanol, and diethylamine as mobile phase was developed for the simultaneous determination of R‐timolol and other potential related substances in S‐timolol maleate samples. An experimental design was elaborated in order to test the effects of the different selected factors. Three factors were studied simultaneously, namely the concentrations of 2‐propanol and diethylamine as well as the column temperature. The effects of these factors were evaluated statistically. Optimal LC conditions were then deduced by applying a multicriteria decision making approach, namely Derringer's desirability function, for the responses of interest. The developed LC method was compared to the European Pharmacopoeia method and was applied to the determination of R‐timolol and other related substances in several samples of S‐timolol maleate from different sources.
High performance centrifugal partition chromatographic separation of alkaline earth metal ions with bis‐2‐ethylhexylphosphinic acid
Authors: Nagaosa Yukio , Wang Tao 
Published: July 2003

AbstractThe mutual separation of Ca(II), Mg(II), Sr(II), and Ba(II) was studied by high performance centrifugal partition chromatography using 0.16 M bis‐2‐ethylhexylphosphinic acid in heptane as a stationary phase. Two‐step elution of the four metal ions loaded was accomplished with aqueous chloroacetic acid mobile phases (pH 6.50 and 5.30). Ethanol (5%) was added to the pH 6.50 mobile phase for the separation of Sr(II) and Ba(II). The chromatographic conditions were 2,136 partition channels, 800 rpm rotational speed, and 1.5 cm3/min flow rate. The elution curve was obtained by monitoring the absorbance of each metal complex post‐labeled with a chromogenetic agent.
Cyclodextrin derivatives in GC separation of racemates with different volatilities. Part XIX: Thermodynamic aspects of enantioselective GC separation of some volatiles with γ‐cyclodextrins 2,3‐substituted with methyl and acetyl groups
Authors: Bicchi Carlo , Brunelli Claudio , Cravotto Giancarlo , Rubiolo Patrizia , Galli Mario , Mendicuti Francisco 
Published: July 2003

AbstractThe thermodynamic parameters involved in the enantiomer separation of two homologous series of γ‐lactones (C6–C8 and C10–C12) and a group of structurally related monoterpenoids with a p‐menthane skeleton (menthol, i‐menthol, neo‐menthol, neo‐i‐menthol, menthone, i‐menthone, and 3‐oxo‐1,8‐cineole) are determined to investigate how inverted substitution in positions 2 and 3 of the cyclodextrin ring with methyl and acetyl groups influences the enantioselectivity of 2‐O‐methyl‐3‐O‐acetyl‐6‐O‐t‐hexyldimethylsilyl‐γ‐cyclodextrin and 2‐O‐acetyl‐3‐O‐methyl‐6‐O‐t‐hexyl‐dimethylsilyl‐γ‐cyclodextrin. The thermodynamic results show that the methyl and acyl groups, in positions 2 and 3 respectively, act complementarily to increase enantioselectivity and that the relative configuration of the stereogenic centres in the selectands influences enantiomer separation.
Extraction of polycyclic aromatic hydrocarbons and organochlorine compounds from water: A comparison between solid‐phase microextraction and stir bar sorptive extraction
Authors: Popp Peter , Bauer Coretta , Hauser Barbara , Keil Petra , Wennrich Luise 
Published: July 2003

AbstractThe enrichment of semi‐volatile compounds from water using solid‐phase microextraction (SPME) and stir bar sorptive extraction (SBSE) was compared. The investigations (analysis of PAHs and organochlorine compounds) were performed to compare SPME‐GC/MS and SBSE‐thermodesorption‐GC/MS. Additionally, SPME fibres and stir bars were desorbed in a small volume of solvent and analysed by HPLC with fluorescence detection. This method was applied to PAHs. SBSE is more robust and under the given conditions (extraction from a 10 mL sample, 1 h exposure time of fibres and stir bars) enables higher recoveries (20.1–97.2%) for the compounds investigated than SPME (recoveries of 6.3–51.6%). Detection limits between 0.1 and 4.5 ng/L were calculated for the SPME‐GC/MS combination, whereas the SBSE‐GC/MS combination enabled detection limits between 0.05 and 1.0 ng/L. Coupled to HPLC, the detection limits of the PAHs investigated were found to range between 1.0 and 10.0 ng/L (SPME) or between 0.3 and 2.0 ng/L (SBSE). The advantage of SPME is that the procedure can be completely automated, which is not possible when combining SBSE with GC or LC.
Capillary zone electrophoresis of phenol and methylphenols at high pH in methanol
Authors: Porras Simo P. , Kuldvee Ruth , Jussila Matti , Palonen Sami , Riekkola Marja‐Liisa 
Published: July 2003

AbstractCapillary zone electrophoresis of phenol and its three methyl‐substituted derivatives (cresols) was investigated in water and methanol as solvents for the electrolyte. In water the acid strengths of o‐cresol and p‐cresol are too similar to allow their capillary zone electrophoretic separation. In pure methanol the differences in acid strength are amplified and all three cresols and phenol were clearly separated with use of pH 13–14 buffers prepared from maleic acid. The dependence of electrophoretic mobilities on pH in MeOH was investigated, and a slight difference was observed between theoretically calculated mobilities and measured mobilities. Maleate background electrolytes provided highly repeatable separations of the analytes. High pH medium in methanol appears to be a good choice for capillary zone electrophoretic separation of weak acids with similar acidity in water. The effective separation of 2,4‐xylenol and 2,6‐xylenol was also demonstrated.
High performance liquid chromatography determination of 4‐nonylphenol, 4‐tert‐octylphenol, and their short ethoxyl chain polyethoxylates in water samples using a microporous membrane liquid‐liquid extraction sample pretreatment technique
Authors: Liu Jing‐fu , Liang Xia , Jiang Gui‐bin , Cai Ya‐qi , Zhou Qing‐xiang , Liu Guo‐guang 
Published: July 2003

AbstractMicroporous membrane liquid‐liquid extraction (MMLLE) sample pretreatment, coupled with reversed‐phase high performance liquid chromatography with fluorescence detection (HPLC‐FLD) was proposed for the determination of alkylphenols (APs), including 4‐nonylphenol (4‐NP) and 4‐tert‐octylphenol (4‐t‐OP), and their short ethoxyl chain polyethoxylates (SEC‐APEOs) in environmental aqueous samples. After MMLLE, 4‐NP, 4‐t‐OP, and SEC‐APEOs were trapped in hexane used as acceptor. The hexane with enriched analytes was purged to dryness with nitrogen gas. Methanol (0.6 mL) and then water (1.4 mL) were added to dissolve the residue and the analytes were subsequently focused onto a C18 precolumn prior to injection onto the analytical column for separation and detection by reversed‐phase HPLC‐FLD. The proposed procedure permits convenient determination of APs and SEC‐APEOs, which have similar endocrine activity and appear as a single peak in reversed‐phase HPLC. The detection limits for 4‐NP and 4‐t‐OP were 0.1 and 0.05 μg/L, respectively. Four samples including tap water, river water, and effluent from a sewage treatment works water were analyzed by the proposed method and the recoveries at 0.5 μg/L spiked level were in the range of 74–110%.
Separation of diastereomers of flavanone‐7‐O‐glycosides by capillary electrophoresis using sulfobutyl ether‐β‐cyclodextrin as the selector
Authors: Aturki Zeineb , Sinibaldi Massimo 
Published: July 2003

AbstractA method was developed for the separation of diastereomers of flavanone‐7‐O‐glycosides by capillary electrophoresis using sulfobutyl ether‐β‐cyclodextrin (SBE‐β‐CD) in the background electrolyte. The effect of the concentration of the CD additive, buffer pH, and organic modifier on the migration times and resolution for five flavanone glycosides (naringin, hesperidin, neohesperidin, narirutin, and eriocitrin) was studied. Baseline separations of these compounds as pairs of diastereoisomers were achieved with 20 mM tetraborate buffer at pH 7 containing 5 mg/mL of SBE‐β‐CD and 10% (v/v) of methanol. The developed method was used for the qualitative analysis of the diastereomeric composition of the major flavanone glycosides in different citrus juices. The ability of SBE‐β‐CD to discriminate flavanone enantiomers was also investigated.
Factors affecting microporous membrane liquid‐liquid extraction
Authors: Kuosmanen Kati , Lehmusjärvi Marja , Hyötyläinen Tuulia , Jussila Matti , Riekkola Marja‐Liisa 
Published: July 2003

AbstractThe effect of different factors on the extraction yield in microporous membrane liquid‐liquid extraction (MMLLE) was studied in this work. The factors were the extraction temperature, mixing of the donor and acceptor solvents, state of the acceptor (stagnant or flowing), solvent set‐up in the membrane unit (organic phase on top or bottom), adsorption of the analytes into the membrane material, and the membrane pore size. The effect of temperature, as it was mediated through the other factors, was of particular interest. Increase in the extraction temperature improved the extraction yields substantially: for naphthalene the extraction yield increased from 14.3% to 17.7% and for benz[a]anthracene from 0.4% to 11.1% when the temperature was raised from 20°C to 80°C. The diffusion coefficients, which were determined with a chromatographic band broadening method, were also clearly increased with temperature: the average diffusion coefficient obtained for naphthalene in water at ambient temperature was 7.92×10–10 m2/s, while at 70°C it was 2.19×10–9 m2/s. The most vigorous mixing of the solvents was obtained with counter‐currently flowing acceptor phase and water on top in the membrane block. The adsorption to the membrane material compared with theoretical 100% extraction yield ranged from 0.5 to 5.4% at 80°C when no acceptor phase was present.
Determination of organophosphate ester plasticisers in blood donor plasma using a new stir‐bar assisted microporous membrane liquid‐liquid extractor
Authors: Jonsson Ove B. , Nilsson Ulrika L. 
Published: July 2003

AbstractA new stir‐bar assisted microporous membrane liquid‐liquid extractor (MMLLE) was used for clean‐up of organophosphate esters in blood plasma. The plasma sample was stirred on one side of a planar membrane while the receiving organic phase was continuously pumped on the other side. Recoveries for eight different organophosphate esters were between 30 and 89% and relative standard deviations between 1.2 and 15%. The method limits of detection, when extracting 5 g plasma and analysing the extract with gas chromatography and nitrogen phosphorus detector, were between 0.2 and 0.9 ng g–1 plasma at S/N = 3. The extraction efficiency in terms of analyte mass transfer per time unit through the membrane was shown to be much higher for stir‐bar assisted MMLLE compared to the more commonly used flow‐cell type of membrane extractor. Blood donor plasma collected with three different types of whole blood collection bag system was analysed with respect to organophosphate ester plasticisers. In plasma from one type of bag system, triphenyl phosphate (TPhP) and 2‐ethylhexyl diphenyl phosphate (EHDPP) were detected at concentrations of 0.053–0.13 μg g–1 and 0.73–1.2 μg g–1 plasma, respectively. The main source of the organophosphate esters was found to be the whole blood collection bag system, with some parts containing EHDPP at concentrations of approximately 60 μg g–1. In plasma collected with the other two types of bag systems, no detectable levels of organophosphate esters were found.
Capillary gas chromatographic determination of Tamoxifen in the presence of a number of antidepressants in urine
Authors: Rodríguez Juana , Berzas Juan J. , Contento Ana M. , Cabello Maria P. 
Published: July 2003

AbstractA capillary gas chromatographic method with flame ionisation detection is described for the determination of Tamoxifen in association with the antidepressants Fluoxetine, Fluvoxamine, and Clomipramine, using Anastrozole as the internal standard. Optimal conditions were investigated: column head pressure (110 kPa), injector and detector temperature (230°C and 250°C, respectively), time and temperature of the splitless step (1.25 min and 80°C), injected volume (2 μL), and oven temperature programme. This provided analysis times of under 11 minutes. Good results were obtained for different aspects including stability of the solutions, linearity, accuracy, and precision. Detection limits between 2.4 and 12 μg L–1 were obtained for all the studied compounds. A ruggedness test of the method was carried out using the Plackett‐Burman fractional factorial model with a matrix of fifteen experiments. The method which has been developed is easy, rapid and sensitive and has been used to determine Tamoxifen, Fluoxetine, Fluvoxamine, and Clomipramine present at clinically relevant levels in urine. Before GC‐FID determination, it was necessary to apply a simple extraction preconcentration step to the urine using a C18 cartridge with methanol as eluent.
Determination of prednisolone, naphazoline, and phenylephrine in local pharmaceutical preparations by micellar electrokinetic chromatography
Authors: Gallego José María Lemus , Pérez Arroyo Julián 
Published: July 2003

AbstractA new, rapid, and simple method is described and used to resolve and quantify mixtures of prednisolone, naphazoline, and phenylephrine. The determination was accomplished by micellar electrokinetic chromatography (MEKC) using a fused‐silica capillary (57 cm×75 μm ID). The separation was carried out at 25°C and 30 kV, using a 5 mM phosphate‐5 mM borate buffer adjusted to pH = 8.2, 40 mM sodium dodecylsulfate (SDS) as background electrolyte. Under these conditions, the run time was 6.6 min and the limits of quantification were about 0.4 mg/L for every component. Repeatability and reproducibility studies showed no significant differences at 95% confidence level. Application of multivariate calibration regression spectrophotometric methods (PLS‐1, PLS‐2, and PCR) clearly demonstrated, especially in the case of PLS‐1, the high resolving powder of these techniques if all possible interferences are suppressed. MEKC has been used for quantifying these compounds in different pharmaceutical products and the method gave good results compared with spectrophotometry. The pharmaceutical preparations do not require any separation steps when analysed by the two procedures described.
Chiral gas chromatography for the determination of 1,2‐O‐isopropylidene‐sn‐glycerol stereoisomers
Authors: Dröge Melloney J. , Bos Rein , Woerdenbag Herman J. , Quax Wim J. 
Published: July 2003

AbstractA stereospecific gas chromatography (GC) method using a (6‐O‐t butyldimethylsilyl‐2,3‐di‐O‐methyl)‐β‐cyclodextrin as the chiral stationary phase has been developed and validated for the determination of the enantiomers of 1,2‐O‐isopropylidene‐sn‐glycerol (IPG), an important chiral synthon, in kinetic resolution experiments. After liquid‐liquid extraction with ethyl acetate, the enantiomers of R‐(–)‐IPG and S‐(+)‐IPG and their corresponding butyrate‐ and caprylate esters were baseline separated using this chiral GC method. The method was accurate, reproducible, specific, and precise and recoveries of at least 77% were accomplished. The detection limits for IPG and its esters were 0.6 ng and 0.1 ng, respectively. The application of this method was demonstrated by a kinetic resolution experiment using the lipase A of Bacillus subtilis.
Chemometrics in capillary electrophoresis. Part A: Methods for optimization
Authors: Sentellas Sònia , Saurina Javier 
Published: July 2003

AbstractThis paper reviews the application of chemometric techniques to optimise capillary electrophoresis separations. The optimization of the electrophoretic conditions should not be understood merely as an independent study of the influence of each variable on the resolution. In many cases, simultaneous optimization of several experimental variables may be required. Furthermore other important aspects such as analysis time, precision, and detection limits should also be considered as responses for a proper optimization. Other important chemometric tasks dealing with data analysis are reviewed in Part B (see S. Sentellas and J. Saurina, Chemometrics in capillary electrophoresis. Part B: Methods for data analysis).
On‐line conversion and determination of aspirin using a flow injection–capillary electrophoresis system
Authors: Chen Hong Li , Fan Liu Yin , Chen Xing Guo , Hu Zhi De , Zhao Zheng Feng , Hooper Martin 
Published: July 2003

AbstractA novel, rapid, and simple capillary electrophoresis (CE) method has been developed for the determination of aspirin by on‐line treatment with alkali. Such on‐line reaction with 0.20 mol/L NaOH solution for 2.5 min at 45°C automatically and reproducibly converts aspirin into its hydrolysis product salicylic acid. Analysis is carried out in less than 12 min after conversion of aspirin in a flow injection (FI) system coupled to a CE instrument via a split‐flow interface cell, and a sampling frequency of 9 h–1 is achievable. The on‐line conversion method has been used to determine aspirin in four commercial pharmaceutical preparations, and the results are satisfactory.