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Mobile Phase Composition (mobile + phase_composition)

Distribution by Scientific Domains

Chemistry	92%

Selected Abstracts

Capillary electrochromatography with monolithic silica column:,I.

ELECTROPHORESIS, Issue 3 2003
Preparation of silica monoliths having surface-bound octadecyl moieties, applications to the separation of neutral, charged species, their chromatographic characterization
Abstract Monolithic silica columns with surface-bound octadecyl (C18) moieties have been prepared by a sol-gel process in 100 ,m ID fused-silica capillaries for reversed-phase capillary electrochromatography of neutral and charged species. The reaction conditions for the preparation of the C18-silica monoliths were optimized for maximum surface coverage with octadecyl moieties in order to maximize retention and selectivity toward neutral and charged solutes with a sufficiently strong electroosmotic flow (>,2 mm/s) to yield rapid analysis time. Furthermore, the effect of the pore-tailoring process on the silica monoliths was performed over a wide range of treatment time with 0.010 M ammonium hydroxide solution in order to determine the optimum time and conditions that yield mesopores of narrow pore size distribution that result in high separation efficiency. Under optimum column fabrication conditions and optimum mobile phase composition and flow velocity, the average separation efficiency reached 160,000 plates/m, a value comparable to that obtained on columns packed with 3 ,m C18-silica particles with the advantages of high permeability and virtually no bubble formation. The optimized monolithic C18-silica columns were evaluated for their retention properties toward neutral and charged analytes over a wide range of mobile phase compositions. A series of dimensionless retention parameters were evaluated and correlated to solute polarity and electromigration property. A dimensionless mobility modulus was introduced to describe charged solute migration and interaction behavior with the monolithic C18-silica in a counterflow regime during capillary electrochromatography (CEC )separations. The mobility moduli correlated well with the solute hydrophobic character and its charge-to-mass ratio. [source]

A sequence optimization strategy for chromatographic separation in reversed-phase high-performance liquid chromatography

AICHE JOURNAL, Issue 2 2010
Xueling Du
Abstract A sequence optimization strategy combining an artificial neural network (ANN) and a chromatographic response function (CRF) for chromatographic separation in reversed-phase high-performance liquid chromatography has been proposed. Experiments were appropriately designed to obtain unbiased data concerning the effects of varying the mobile phase composition, flow-rate, and temperature. The ANN was then used to simultaneously predict the resolution and analysis time, which are the two most important features of chromatographic separation. Subsequently, a CRF consisting of resolution and analysis time was used to predict the optimum operating conditions for different specialized purposes. The experimental chromatograms were consistent with those predicted for given conditions, which verified the applicability of the method. Furthermore, the proposed optimization strategy was applied to literature data and very good agreement was obtained. The results show that a strategy of sequential combination of ANN and CRF can provide a more flexible and efficient optimization method for chromatographic separation. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Influence of mobile phase composition on the high-performance liquid chromatographic/electrospray ionization mass spectrometric analysis of 11-nor-9-carboxy-,9 -tetrahydrocannabinol (THC-COOH) and its glucuronide in urine

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2004

[source]

Methacrylate ester-based monolithic columns for nano-LC separation of tocopherols in vegetable oils

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 17-18 2010
María Jesús Lerma-García
Abstract The separation and determination of tocopherols (Ts) in vegetable oils by nano-LC chromatography with UV,vis detection using lauryl methacrylate ester-based monolithic columns has been developed. The separation of Ts was optimized in terms of mobile phase composition on the basis of the best compromise among efficiency, resolution and analysis time. Using a mobile phase composed of ACN/methanol/water, an excellent resolution between Ts was achieved within 18,min. The LODs were lower than 0.26,,g/mL, being repeatability values of retention time and peak area below 0.15 and 3.1%, respectively. The method was applied to the quantification of Ts and tocotrienols present in several vegetable oils from different botanical origins. [source]

Comparison of HPLC enantioseparation of substituted binaphthyls on CD-, polysaccharide- and synthetic polymer-based chiral stationary phases

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2010
Lucie Loukotková
Abstract Retention and enantioseparation behavior of ten 2,2,-disubstituted or 2,3,2,-trisubstituted 1,1,-binaphthyls and 8,3,-disubstituted 1,2,-binaphthyls, which are used as catalysts in asymmetric synthesis, was investigated on eight chiral stationary phases (CSPs) based on ,-CD, polysaccharides (tris(3,5-dimethylphenylcarbamate) cellulose or amylose CSPs) and new synthetic polymers (trans -1,2-diamino-cyclohexane, trans -1,2-diphenylethylenediamine and trans -9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-11,12-dicarboxylic acid CSPs). Normal-, reversed-phase and polar-organic separation modes were employed. The effect of the mobile phase composition was examined. The enantiomeric separation of binaphthyl derivatives, which possess quite similar structures, was possible in different enantioselective environments. The substituents and their positions on the binaphthyl skeleton affect their properties and, as a consequence, the separation system suitable for their enantioseparation. In general, the presence of ionizable groups on the binaphthyl skeleton, substitution with non-identical groups and a chiral axis in the 1,2, position had the greatest impact on the enantiomeric discrimination. The 8,3,-disubstituted 1,2,-binaphthyl derivatives were the most easily separated compounds in several separation systems. From all the chiral stationary phases tested, cellulose-based columns were shown to be the most convenient for enantioseparation of the studied analytes. However, the polymeric CSPs with their complementary behavior provided good enantioselective environments for some derivatives that could be hardly separated in any other chromatographic system. [source]

Determination of pKa values of nonsteroidal antiinflammatory drug-oxicams by RP,HPLC and their analysis in pharmaceutical dosage forms

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2009
Ebru Cubuk Demiralay
Abstract In this study, pKa values were determined by using the dependence of the capacity factor on the pH of the mobile phase for four ionizable substances, namely, tenoxicam, piroxicam, meloxicam, and naproxen (I.S.). The effect of the mobile phase composition on the ionization constant was studied by measuring the pKa at different ACN concentrations, ranging from 30 to 40%. The adequate condition for the chromatographic determination of these compounds in pharmaceutical dosage forms was established based on the different retention behaviors of the species. An octadecylsilica Nucleosil C18 column (150×4.6 mm, 5 ,m) was used for all the determinations. The chromatographic separation of oxicams was carried out using acetonitrile (ACN)/water at 35% v/v, containing 65 mM phosphoric acid and UV detection at a wavelength of 355 nm. The method developed was successfully applied to the simultaneous determination of these drug compounds in laboratory-prepared mixtures and their commercial pharmaceutical dosage forms. Each analysis requires no longer than 12 min. [source]

HPLC enantioseparation of ,2 -homoamino acids using crown ether-based chiral stationary phase

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 7 2009
Róbert Berkecz
Abstract RP high-performance liquid chromatographic methods were developed for the enantioseparation of eleven unusual ,2 -homoamino acids. The underivatized analytes were separated on a chiral stationary phase containing (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as chiral selector. The effects of organic (alcoholic) and acidic modifiers, the mobile phase composition and temperature on the separation were investigated. The structures of the substituents in the ,-position of the analytes substantially influenced the retention and resolution. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers. [source]

Pharmaceutical analysis by supercritical fluid chromatography: Optimization of the mobile phase composition on a 2-ethylpyridine column

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2008
Claudio Brunelli
Abstract The separation of neutral, acidic, and basic pharmaceuticals with diverse physicochemical properties by packed column supercritical fluid chromatography (pSFC) on a 2-ethylpyridine column (25 cm×4.6 mm id, 3 ,m particles) is presented. The optimization strategy involved separations at 100% methanol (MeOH) and at 50% MeOH/50% ACN while keeping the peak symmetry additives formic acid (FA) and isopropylamine (IPA) at constant levels of 0.25% v/v. By plotting the adjusted retention times as a function of the MeOH/ACN ratio, an optimal modifier ratio composition of 65% MeOH/35% ACN was found. The total set of 26 neutral, acidic, and basic pharmaceuticals was analyzed and the optimal composition experimentally verified. This mobile phase composition is currently used in pharmaceutical method development and open-access generic screening environments. [source]

Development and validation of a stereoselective HPLC method for the determination of the in vitro transport of nateglinide enantiomers in rat intestine

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 12 2007
Srinivas Maddi
Abstract A simple stereoselective high performance liquid chromatographic method was developed for the determination of the in vitro transport of the enantiomers of nateglinide (N -(trans -4-isopropylcyclohexyl-carbonyl)-phenylalanine) in the rat intestine using a Chiralcel OJ-RH column (150×4.0 mm, 5 ,m). The effects of the mobile phase composition, pH, the flow rate, and the temperature on the chromatographic separation were investigated. The enantioseparation was achieved at 33°C using a mobile phase containing 100 mM potassium dihydrogen phosphate, pH 2.5, and ACN (32:68 v/v) delivered at a flow rate of 1 mL/min. The analytes were monitored at 210 nm and linearity (r >0.99) was obtained for a concentration range of 0.5,50 ,g/mL. The LOD and LOQ were 0.2 and 0.5 ,g/mL for the R -enantiomer and 0.2 and 0.8 ,g/mL for the S -enantiomer, respectively. Both, the intra- and interday accuracy and precision of the calibration curves were determined. The method was successfully applied to estimate the in vitro passage of the enantiomers and the racemate of nateglinide in duodenum, jejunum, and ileum of rats. Generally, higher concentrations of nateglinide and the S -enantiomer were observed when the racemate was administered compared to administration of the individual enantiomers of nateglinide. [source]

High-performance liquid chromatographic resolution of 1-(1,4-benzodioxane-2-formyl)- piperazine enantiomers after chiral derivatization

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2005
Zhiqiong Chen
Abstract Chiral separation of racemic mixtures is of the greatest importance to the pharmaceutical industry, as the isomers of a given racemate may exhibit substantially different pharmacological effects, not to mention possibly differing toxicity behaviour. A novel chiral separation method is developed for the determination of 1-(1,4-benzodioxane-2-formyl)piperazine (BFP) enantiomers. The indirect resolution is performed by applying precolumn derivatization with the chiral reagent 2,3,4,6-tetra- O -acetyl-,-D-glucopyranosyl isothiocyanate (GITC). The resulting diastereoisomers are separated on a reversed-phase ODS column with methanol-potassium dihydrogen phosphate (0.02mol/L, 50:50) as mobile phase. UV detection is at 250 nm. The effect of mobile phase composition upon resolution and analysis time is investigated. Two diastereoisomers show nearly base-line separation under optimal chromatographic conditions. The presented study provides a simple and accurate method for the enantiomeric quality control and the optical purity assay of BFP. [source]

A theoretical explanation for the retention mechanism of ion exclusion chromatography

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2003
Bronis, aw K. G
Abstract Ion Exclusion Chromatography is classically used for the separation of weak acid anions. Dilute strong acids (e.g. sulphuric or perchloric acid) or just water are used as eluents. To increase the exclusion effect, strong cation exchangers, characterized by high concentration of functional groups, are applied. The inner column volume of commercially available columns is increased by increasing their size in comparison to traditional ones (usually 300×7.8 mm ID). The description of the retention mechanism of this technique implicitly assumes that both mobile and stationary phases are typical aqueous solutions, and their dielectric constants are thus equal. This equality implies the equality of solute dissociation constants in both phases. Another implicit assumption is that the dead- and inner volumes of the column are constant, and independent of the mobile phase composition. The present paper shows that stationary and mobile phases are generally characterized by different physicochemical parameters. Thus, they cannot be considered as regular aqueous solutions. Additionally, we show that weak cation exchanger resins, which are characterized by a relatively small concentration of the functional groups, and weak acid based buffers can also be used in IEC. This would expand the possible applications of this method and enable, for example, the separation of strong acids (anions). The influence of ionic strength on the retention and dead- and inner column volumes is also discussed. Finally we also briefly describe the retention mechanism of Electrostatic Ion Chromatography. [source]

Stationary and mobile phases in capillary electrochromatography (CEC)

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2003
Jan Jiskra
Abstract This review describes the state of the art of capillary electrochromatography (CEC). Properties of and interactions between stationary and mobile phases applied in CEC are described and discussed; developments in stationary phases, partly also monolithic stationary phases, are reviewed. Special attention is paid to the comparison of the behaviour of stationary and/or mobile phases under CEC versus HPLC conditions with respect to variables such as particle and pore size of the stationary phase, mobile phase composition, and temperature. These issues are discussed throughout the paper. A number of applications in CEC is presented as well. [source]

Investigation of factors influencing the performance of open-tubular stationary phases in capillary electrochromatography

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 9-10 2003
Ruth Freitag
Abstract Silica-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. [source]

Phospholipids in liquid chromatography/mass spectrometry bioanalysis: comparison of three tandem mass spectrometric techniques for monitoring plasma phospholipids, the effect of mobile phase composition on phospholipids elution and the association of phospholipids with matrix effects

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2009
Yuan-Qing Xia
Because plasma phospholipids may cause matrix effects in bioanalytical liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods, it is important to establish optimal mass spectrometric techniques to monitor the fate of phospholipids during method development and application. We evaluated three MS/MS techniques to monitor phospholipids using positive and negative electrospray ionization (ESI). The first technique is based on using positive precursor ion scan of m/z 184, positive neutral loss scan of 141 Da and negative precursor ion scan of m/z 153. The second technique is based on using class-specific positive and negative selected reaction monitoring (SRM) transitions to monitor class-representative phospholipids. The third technique, previously reported, utilizes in-source collision-induced dissociation (CID)-based positive SRM of m/z 184,,,184. We recommend the all-inclusive technique 1 for use in qualitative assessment of all classes of phospholipids and technique 2 for use in quantitative assessment of class-representative phospholipids. Secondly, we evaluated the elution behaviors of the plasma phospholipids under different reversed-phase mobile phase conditions. The phospholipid-eluting strength of a mobile phase was mainly dependent on the type and amount (%) of the organic eluent and the strength increased in the order of methanol, acetonitrile and isopropyl alcohol. Under the commonly used gradient and isocratic elution schemes in LC/MS/MS bioanalysis, not all the phospholipids are eluted off the column. Thirdly, we investigated the association between phospholipids and matrix effects in positive and negative ESI using basic, acidic and neutral analytes. While the phospholipids caused matrix effects in both positive and negative ESI, the extent of ionization suppression was analyte-dependent and was inversely related to the retention factor and broadness of the phospholipids peaks. The lysophospholipids which normally elute earlier in reversed-phase chromatography are more likely to cause matrix effects compared to the later-eluting phospholipids in spite of the larger concentrations of the latter in plasma. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Comparison of negative ion electrospray mass spectra measured by seven tandem mass analyzers towards library formation

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2008
ina Volná
A library of negative ion electrospray ionization mass spectra and tandem mass spectra (MS/MS) of sulfonated dyes has been developed for fast identification purposes. The uniform protocol has been elaborated and applied to the measurements of more than 50 anionic dyes. Three collision energies are selected in our protocol which ensures that at least one of them provides a suitable ratio of product ions to the precursor ion. The robustness is investigated with altered values of tuning parameters (e.g. the pressure of the nebulizing gas, the temperature and the flow rate of drying gas, and the mobile phase composition). The results of the inter-laboratory comparison of product ion mass spectra recorded on seven different tandem mass spectrometers (three ion traps, two triple quadrupoles and two hybrid quadrupole time of flight instruments) are presented for four representative anionic dyes , azo dye Acid Red 118, anthraquinone dye Acid Violet 43, triphenylmethane dye Acid Blue 1 and Al(III) metal-complex azo dye. The fragmentation patterns are almost identical for all tandem mass analyzers, only the ratios of product ions differ somewhat which confirms the possibility of spectra transfer among different mass analyzers with the goal of library formation. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Effect of chemically bonded stationary phases and mobile phase composition on , -blockers retention in RP-HPLC

BIOMEDICAL CHROMATOGRAPHY, Issue 3 2009
Boguslaw Buszewski
Abstract The effects of stationary and mobile phase on retention of 18 , -adrenolytic drugs (, -blockers) have been studied. Four ,deactivated surface' stationary phases (polar-embedded or end-capped) were examined. Special attention was drawn to the cholesterolic (SG-CHOL) and alkylamide (SG-AP) stationary phases, and their application for analysis of the compounds. The retention of analyzed substances was also examined in terms of mobile phase composition. Sixteen different configurations of mobile phases were prepared, all based on methanol and acetonitrile with ammonium acetate and ammonium formate. The difference in retention between ammonium formate and acetate water solutions, and peak shape changes related to the addition of triethylamine (TEA), were investigated. Principal component analysis was used to find the similarities between stationary phases. Polar-embedded phases synthesized on the same sorbent possess very similar properties. All phases based on silica gel compared with the monolithic column also showed similarities in retention of , -blockers. The addition of TEA to the mobile phase did not influence strongly the retention, and analysis of asymmetry factors showed only a little peak broadening for a few compounds on the monolithic column. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A validated HPLC method with electrochemical detection for simultaneous assay of 5-aminosalicylic acid and its metabolite in human plasma

BIOMEDICAL CHROMATOGRAPHY, Issue 5 2005
Giancarlo Palumbo
Abstract A high-performance liquid chromatographic method was developed, validated and applied to the simultaneous determination of 5-aminosalicylic acid (5-ASA) and its acetylated metabolite (acetyl-5-ASA) in human plasma. The method involves liquid,liquid extraction with methanol followed by isocratic reversed-phase chromatography on a Kromasil KR100 C18 column with electrochemical detection. The recovery, selectivity, linearity, precision and accuracy of the method were evaluated from spiked human plasma samples. The effects of mobile phase composition, buffer concentration, mobile phase pH and concentration of organic modi,ers on retention of 5-ASA, acetyl 5-ASA and internal standard were investigated. Limits' of detection were 5 ng/mL for 5-ASA and 10 ng/mL for acetyl-5-ASA, respectively. The method can be used for supporting therapeutical drug monitoring and pharmacokinetic studies. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Preparation and Evaluation of a Novel Cellulose Tris(N-3,5-dimethylphenylcarbamate) Chiral Stationary Phase

CHINESE JOURNAL OF CHEMISTRY, Issue 1 2008
Jin GE
Abstract A novel cellulose tris(N -3,5-dimethylphenylcarbamate) (CDMPC) chiral stationary phase (CSP) was prepared by coating CDMPC on TiO2/SiO2, which was prepared by coating titania nanoparticles on silica through a self-assemble technique. At first, 2-hydroxyl-phenyl acetonitrile and , -phenylethanol were separated on this new CSP to evaluate the chiral separation ability. Then, two pesticides, matalaxyl and diclofop-methyl were separated. The influence of the mobile phase composition on the enantioselectivity was discussed, and the repeatability and stability of the CSP were studied too. [source]

High-performance liquid chromatographic chiral separation of ,2 -homoamino acids

CHIRALITY, Issue 9 2009
Zoltán Pataj
Abstract Reversed-phase high-performance liquid chromatographic methods were developed for the separation of enantiomers of eleven unnatural ,2 -homoamino acids on chiral stationary phases containing macrocyclic glycopeptides (teicoplanin-containing Chirobiotic T and T2) or the macrocyclic peptide teicoplanin aglycone (Chirobiotic TAG) as chiral selectors. The effects of the organic modifier, the mobile phase composition, temperature, and the structures of the analytes on the separations were investigated. Separations were carried out at constant mobile phase compositions in temperature range 7,45°C and the changes in enthalpy, ,(,H°), entropy, ,(,S°), and free energy, ,(,G°), were calculated. The ,,(,G°) values obtained on the three columns indicated that Chirobiotic TAG, without sugar units, may promote the interactions of the enantiomers of ,2 -homoamino acids with branched alkyl or aryl side-chains, whereas for ,2 -homoamino acids with alkyl side-chains Chirobiotic T and T2 seem to be more favorable. The elution sequence was determined in some cases and was observed to be R < S. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source]

Direct enantioselective HPLC monitoring of lipase-catalyzed kinetic resolution of tiaprofenic acid in nonstandard HPLC organic solvents,

CHIRALITY, Issue 8 2008
Ashraf Ghanem
Abstract The first straightforward lipase-catalyzed enantioselective access to enantiomerically enriched tiaprofenic acid as a versatile method in chiral separation of racemates is demonstrated. The latter was directly monitored by enantioselective HPLC using a 3,5-dimethylphenylcarbamate derivative of cellulose-based chiral stationary phase namely Chiralpak IB (the immobilized version of Chiralcel OD). Non-standard HPLC organic solvents were used as diluent to dissolve the "difficult to dissolve" enzyme substrate (the acid) and as eluent for the simultaneous enantioselective HPLC baseline separation of both substrate and product in one run without any further derivatization. The existence of a non-standard HPLC organic solvent (e.g., methyl tert -butyl ether) in the mobile phase composition is mandatory to accomplish the simultaneous enantioselective HPLC baseline separation of both substrate and product. Chirality, 2008. © 2008 Wiley-Liss, Inc. [source]

Effective HPLC resolution of [4]heterohelicenium dyes on chiral stationary phases using reversed-phase eluents

CHIRALITY, Issue 8 2007
Claudio Villani
Abstract [4]Heterohelicenium cations 1a,c adopt a twisted helical structure that renders them chiral. They are configurationally stable and their enantiomers have been resolved, for the first time, by HPLC on Chiralcel OD-RH and Chirobiotic TAG chiral stationary phases (CSPs). Chiral cations 1a,c have been resolved by HPLC using water-based eluents containing KPF6 as additive. The elution order of the analyte enantiomers was determined by on-line CD detection, and was found to be opposite on the two CSPs. The effect of mobile phase composition and analyte structure on retention and enantioselectivity was investigated. Chirality 19:601,606, 2006 © 2006 Wiley-Liss, Inc. [source]

Comparative HPLC enantioseparation of ferrocenylalcohols on two cellulose-based chiral stationary phases

CHIRALITY, Issue 5 2007
Angela Patti
Abstract The direct HPLC enantiomeric separation of several ferrocenylalcohols on the commercially available Chiralcel OD and Chiralcel OJ columns has been evaluated in normal-phase mode. Almost all the compounds were resolved on one or both chiral stationary phases (CSPs) with separation factor (,) ranging from 1.06 to 2.88 while the resolution (Rs) varied from 0.63 to 12.70 In the separation of the ,-ferrocenylalcohols 1a,e and the phenyl analogues 2a,e, which were all resolved except 1c, a similar trend in the retention behavior for the two series of alcohols was evidenced and the selectivity was roughly complementary on the two investigated CSP. For three ferrocenylacohols, chosen as model compounds, the influence of the mobile phase composition and temperature on the enantioseparation were investigated and additional information on the chiral recognition mechanism were deduced from the chromatographic behavior of their acetylderivatives. Chirality, 2007. © 2007 Wiley-Liss, Inc. [source]

Sensitivity improvement of circular dichroism detection in HPLC by using a low-pass electronic noise filter: Application to the enantiomeric determination purity of a basic drug

CHIRALITY, Issue 2 2007
Marie Lorin
Abstract The quality control of chiral drugs requires the determination of their enantiomeric purity. Nowadays, circular dichroism (CD) spectroscopy is gaining increasing importance in pharmaceutical analysis because of the commercially available CD detector in liquid chromatography. The separation of the two enantiomers of a basic drug (efaroxan) was achieved by high performance liquid chromatography using an amylose-derivated column with both UV and CD detections. A baseline-resolved separation (resolution: 5) was obtained after optimization of the mobile phase composition with hexane-ethanol-diethylamine (90:10:0.05; v/v/v). The use of a commercial low-pass electronic noise filter of the CD signal has improved the signal-to-noise ratio by a factor twelve and allowed the quantitation of each enantiomer in the 1.25,300 ,g ml,1 concentration range. The CD linear calibration curve, expressed in terms of stereoisomer height ratio versus concentration ratio, was plotted over the 0.4,6% range. A correlation coefficient greater than 0.999 was obtained by least-squares regression and the limit of detection for the distomer/eutomer ratio was estimated at 0.14%. Although the method validation showed good repeatability on the retention times (RSD < 0.9%), on the peak height ratios (RSD < 8.7%) of each enantiomer only up to 99.2% enantiomeric purity was achieved. Chirality, 2006. © 2006 Wiley-Liss, Inc. [source]

Capillary electrochromatography with monolithic silica column:,I.

Mixed-mode chromatography/isotope ratio mass spectrometry,

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2010
James S. O. McCullagh
Liquid chromatography coupled to molecular mass spectrometry (LC/MS) has been a standard technique since the early 1970s but liquid chromatography coupled to high-precision isotope ratio mass spectrometry (LC/IRMS) has only been available commercially since 2004. This development has, for the first time, enabled natural abundance and low enrichment ,13C measurements to be applied to individual analytes in aqueous mixtures creating new opportunities for IRMS applications, particularly for the isotopic study of biological molecules. A growing number of applications have been published in a range of areas including amino acid metabolism, carbohydrates studies, quantification of cellular and plasma metabolites, dietary tracer and nucleic acid studies. There is strong potential to extend these to new compounds and complex matrices but several challenges face the development of LC/IRMS methods. To achieve accurate isotopic measurements, HPLC separations must provide baseline-resolution between analyte peaks; however, the design of current liquid interfaces places severe restrictions on compatible flow rates and in particular mobile phase compositions. These create a significant challenge on which reports associated with LC/IRMS have not previously focused. Accordingly, this paper will address aspects of chromatography in the context of LC/IRMS, in particular focusing on mixed-mode separations and their benefits in light of these restrictions. It aims to provide an overview of mixed-mode stationary phases and of ways to improve high aqueous separations through manipulation of parameters such as column length, temperature and mobile phase pH. The results of several practical experiments are given using proteogenic amino acids and nucleosides both of which are of noted importance in the LC/IRMS literature. This communication aims to demonstrate that mixed-mode stationary phases provide a flexible approach given the constraints of LC/IRMS interface design and acts as a practical guide for the development of new chromatographic methods compatible with LC/IRMS applications. Copyright © 2010 John Wiley & Sons, Ltd. [source]