Journal of Chromatography A (J Chrom )

Publisher: Elsevier


The Journal of Chromatography A publishes papers on all aspects of separation science including chromatography, electrochromatography, electrophoresis, hyphenated and other multi-dimensional techniques, sample preparation as well as detection methods such as mass spectrometry. Contributions consist mainly of research papers dealing with chromatographic and electrophoretic theory, instrumental developments and their analytical and preparative applications. Section A covers all areas except biomedical sciences and biomedical applications of separation science, which are published in section B: Biomedical Sciences and Applications. Electronic version.

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Publications in this journal

  • [Show abstract] [Hide abstract]
    ABSTRACT: We report for the first time the effect of liophilic mobile phase additives on the mechanism of chiral recognition of basic chiral pharmaceutical on a vancomycin based chiral stationary phase (CSP). Using methanol as the mobile phase and 0.005% formic acid as pH modifier, we evaluated the effect of different concentrations of three types of liophilic anions, formate (HCOO−), nitrate (NO3−), and acetate (CH3COO−), on enantioresolution (Rs), enantioselectivity (α) and retention factor (k) of enantiomers of fluoxetine and atenolol. The effect of liophilic ion types on k followed the Hofmeister series: CH3COO− > HCOO− > NO3−. Increasing concentration from 4 to 20 mM resulted in decreases in Rs and k in accordance to hydrophobicity of the liophilic anion. The effect of temperature or mobile phase composition on enantioseparation was determined at 13 to 40 °C. For both analytes, standard changes in enthalpy (ΔH°) and entropy (ΔS°) were calculated using van’t Hoff plots (ln k against 1/T) to vary from -4.99 to -0.63 kJ/mol and -11.82 to 9.47 J/mol, respectively. The van’t Hoff plots showed that the elution order of the enantiomers of each analyte did not reverse in the temperature range studied. Chiral recognition of the enantiomers of atenolol and fluoxetine in the presence of liophilic ions was enthalpy driven.
    Journal of Chromatography A 09/2014;
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    ABSTRACT: Six new atropisomeric etheroarenes were synthesized by connecting two 2-alkylbenzimidazole fragments via N-N junction. They differ by the substituent nature (methyl, ethyl, propyl, butyl, pentyl and hexyl) of the aliphatic function. The novel atropisomeric compounds were used as chiral probes to study the chromatographic behaviour of the amylose tris(3,5-dimethylphenyl carbamate) (Chiralpak AD-3) chiral stationary phase (CSP) under normal phase mode. The pivotal role of the length and flexibility of the 2,2’-alkyl groups on retention, enantioselectivity and enantiomer elution order was demonstrated by enantioselective HPLC analysis. Additional information on the chiral recognition mechanism was obtained from the evaluation of the correlated thermodynamic data.
    Journal of Chromatography A 09/2014; 1363:128-136.
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    ABSTRACT: An efficient ultra high performance liquid chromatography (UHPLC)–time-of-flight high resolution mass spectrometry (TOF-HRMS) method was elaborated for the determination of hexabromocyclododecane (HBCD) diastereomers in fish samples and compared against UHPLC–Orbitrap-HRMS and UHPLC–triple quadrupole (QqQ) tandem MS (MS/MS) techniques. The TOF-HRMS analyzer was operated at high resolution (>10 000 full width at half maximum (FWHM)) with scanning the m/z range from 600 to 700, to achieve picogram quantitation limits. The effects of various operational parameters on the instrumental response were systematically investigated. Evaluation of the influence of sample clean-up procedure steps on signal suppression effect including removal of the matrix components by means of destructive acidic treatment or non-destructive gel permeation chromatography (GPC), and additional Florisil column chromatography step showed that the analytical response of UHPLC–TOF-HRMS system is much more affected by the presence of matrix components in the final extracts in comparison with UHPLC–Orbitrap-HRMS and UHPLC–QqQ-MS/MS systems. The method was robustly validated and used for the analysis of eel (Anquilla anquilla) samples originating from a Latvian lake. UHPLC–TOF-HRMS showed a suitable performance under the optimized conditions: recoveries for three selected diastereomers in the range of 99–116%; repeatability and intermediate precision expressed as relative standard deviation (RSD) in the ranges of 2.3–7.1% and 2.9–8.1%, respectively. The elaborated method achieved instrumental limits of quantification (i-LOQ) of 0.9–4.5 pg on column that were suitable for the trace analysis of three HBCD diastereomers, corresponding to the method limits of quantification (m-LOQ) of 7.0–29 pg g−1 wet weight (w.w.). The efficiency of UHPLC–TOF-HRMS method was evaluated by comparing the performance characteristics and analytical data from real samples with the validation data and real sample results obtained by applying UHPLC–Orbitrap-HRMS and UHPLC–QqQ-MS/MS techniques for the analysis of HBCD in the same fish samples. Statistical assessment of the experimental data by means of the Fiedman's test revealed that UHPLC–TOF-HRMS, UHPLC–QqQ-MS/MS and UHPLC–Orbitrap-HRMS techniques produced adequate and similar results regarding the HBCD content in fish samples. The presence of HBCD diastereomers was confirmed in all the analyzed eels at concentrations up to 554 pg g−1 w.w. for total HBCD and a diastereomer pattern typical for aquatic biota was observed with strong predominance of α-HBCD. The UHPLC–TOF-HRMS is an appropriate technique for diastereomer-specific quantification of HBCD content in fish samples.
    Journal of Chromatography A 09/2014;
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    ABSTRACT: Diazepam and the structurally related 1,4-benzodiazepin-2-ones tetrazepam, prazepam and flunitrazepam are chiral molecules because they adopt a ground state conformation featuring a non-planar seven membered ring devoid of any reflection-symmetry element. The two conformational enantiomers of this class of benzodiazepines interconvert rapidly at room temperature by a simple ring flipping process. Low temperature HPLC on the Whelk-O1 chiral stationary phase allowed us to separate the conformational enantiomers of diazepam and of the related 1,4-benzodiazepin-2-ones, under conditions where the interconversion rate is sufficiently low, compared to the chromatographic separation rate. Diazepam, tetrazepam and prazepam showed temperature dependent dynamic HPLC profiles with interconversion plateaus indicative of on-column enantiomer interconversion (enantiomerization) in the temperature range between -10°C and -35°C, whereas for flunitrazepam on-column interconversion was observed at temperatures between -40°C and -66°C. Simulation of exchange-deformed HPLC profiles using a computer program based on the stochastic model yielded the apparent rate constants for the on-column enantiomerization and the corresponding free energy activation barriers. At -20°C the enantiomerization barriers, ΔG(≠), for diazepam, prazepam and tetrazepam were determined to be in the range 17.6-18.7kcal/mol. At -55°C ΔG(≠) for flunitrazepam was determined to be in the 15.6-15.7kcal/mol range. The experimental dynamic chromatograms and the corresponding interconversion barriers reported in this paper call for a reinterpretation of previously published results on the HPLC behavior of diazepam on chiral stationary phases.
    Journal of Chromatography A 08/2014; 1363:144-149.
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    ABSTRACT: Gingivitis is a highly prevalent periodontal disease around the worldwide. Porphyromonas gingivalis (P.g), Treponema denticola (T.d) and Tannerela forsythia (T.f) were considered to be three important periodontal pathogens related to gingivitis, and research shows that the counts of periodontal pathogen cells in the patients before, during, and after fixed orthodontic appliance therapy were quite different. We proposed a simple method to extract the periodontal pathogens from the periodontal pocket in this work and demonstrated a new approach to determine periodontal pathogen level based on capillary electrophoresis (CE). After polymerase chain reaction amplification of P.g (197bp), T.d (311bp), and T.f (641bp), it shows that they can rapidly identified by CE within 5min. The peak area in the eletropherogram is linearly related to the concentration of P.g, T.d, and T.f, and the correlation coefficients R(2) corresponding to them are 0.993, 0.993, and 0.956, respectively. According to this linearly relationship, the estimated concentration of P.g, T.d, and T.f in gingival crevicular fluid from one volunteer was inferred to be about 9.90×10(2), 1.48×10(3), and 9.01×10(2)cells/μl, respectively.
    Journal of Chromatography A 08/2014; 1361:286-290.
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    ABSTRACT: The traditional direct bioautography workflow was substantially altered to yield narrow, sharp-bounded effective zones. For the first time, microorganisms quantitatively detected the single effective compounds in complex samples, separated in parallel on a planar chromatogram. This novel effect-directed workflow was demonstrated and optimized for the discovery of endocrine disrupting compounds (EDCs) reacting with the human estrogen receptor down to the femtogram-per-zone range, like 250fg/zone for 17β-estradiol (E2). For application volumes of up to 0.5mL, estrogen-effective compounds could directly be detected in complex samples at the ultratrace level (ng/kg-range). Sharp-bounded, estrogen-effective zones discovered were further characterized by direct elution into the mass spectrometer. HPTLC-ESI-MS mass spectra of (xeno)estrogens were shown for the first time. Owed to the substantially improved zone resolution, compound assignment was reliable and a comparison of the receptor affinities was conducted for six (xeno)estrogens. Also, long-term cell cultivation of the genetically modified yeast was demonstrated on the HPTLC plate. The optimized HPTLC-pYES workflow was proven for real food samples, exemplarily shown for beer. The general applicability of generating sharp-bounded zones was successfully proven by transfer of the fundamentally improved workflow to the Bacillus subtilis bioassay used for discovery of antibiotics in plant extracts. This new era of quantitative direct bioautography in combination with mass spectrometry will accelerate the scientific understanding in a wide application field via the streamlined access to fast and reliable information on effective components in complex samples.
    Journal of Chromatography A 08/2014; 1360:288.
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    ABSTRACT: The interest for environmental fate assessment of chiral pharmaceuticals is increasing and enantioselective analytical methods are mandatory. This study presents an enantioselective analytical method for the quantification of seven pairs of enantiomers of pharmaceuticals and a pair of a metabolite. The selected chiral pharmaceuticals belong to three different therapeutic classes, namely selective serotonin reuptake inhibitors (venlafaxine, fluoxetine and its metabolite norfluoxetine), beta-blockers (alprenolol, bisoprolol, metoprolol, propranolol) and beta2-adrenergic agonist (salbutamol). The analytical method was based on solid phase extraction followed by liquid chromatography tandem mass spectrometry with a triple quadrupole analyser. Briefly, Oasis® MCX cartridges were used to preconcentrate 250 mL of water samples and the reconstituted extracts were analysed with a Chirobiotic™ V under reversed mode. The effluent of a laboratory-scale aerobic granular sludge sequencing batch reactor (AGS-SBR) was used to validate the method. Linearity (R2 > 0.99), selectivity and sensitivity were achieved in the range of 20-400 ng L−1 for all enantiomers, except for norfluoxetine enantiomers which range covered 30-400 ng L−1. The method detection limits were between 0.65 and 11.5 ng L−1 and the method quantification limits were between 1.98 and 19.7 ng L−1. The identity of all enantiomers was confirmed using two MS/MS transitions and its ion ratios, according to European Commission Decision 2002/657/EC. This method was successfully applied to evaluate effluents of wastewater treatment plants (WWTP) in Portugal. Venlafaxine and fluoxetine were quantified as non-racemic mixture (enantiomeric fraction ≠ 0.5). The enantioselective validated method was able to monitor chiral pharmaceuticals in WWTP effluents and has potential to assess the enantioselective biodegradation in bioreactors. Further application in environmental matrices as surface and estuarine waters can be exploited.
    Journal of Chromatography A 07/2014;
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    ABSTRACT: Epinephrine-bonded polymeric monoliths for capillary electrochromatography (CEC) were developed by nucleophilic substitution reaction of epoxide groups of poly(glycidyl-methacrylate-co-ethylenedimethacrylate) (poly(GMA-co-EDMA)) monoliths using epinephrine as nucleophilic reagent. The ring opening reaction under dynamic conditions was optimized. Successful chemical modification of the monolith surface was ascertained by in situ Raman spectroscopy characterization. In addition, the amount of epinephrine groups that was bound to the monolith surface was evaluated by oxidation of the catechol groups with Ce(IV), followed by spectrophotometric measurement of unreacted Ce(IV). About 9% of all theoretical epoxide groups of the parent monolith were bonded to epinephrine. The chromatographic behavior of the epinephrine-bonded monolith in CEC conditions was assessed with test mixtures of alkyl benzenes, aniline derivatives and substituted phenols. In comparison to the poly(GMA-co-EDMA) monoliths, the epinephrine-bonded monoliths exhibited a much higher retention and slight differences in selectivity. The epinephrine-bonded monolith was further modified by oxidation with a Ce(IV) solution and compared with the epinephrine-bonded monoliths. The resulting monolithic stationary phases were evaluated in terms of reproducibility, giving RSD values below 9% in the parameters investigated.
    Journal of Chromatography A 07/2014; 1298:61–67.
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    ABSTRACT: A method based on the coupling of ion chromatography (IC) and electrospray ionization mass spectrometry (ESI-MS) for the separation and determination of thermal decomposition products of LiPF6-based organic electrolytes is presented. The utilized electrolytes, LP30 and LP50, are commercially available and consist of 1mol/l LiPF6 dissolved in ethylene carbonate/dimethyl carbonate and ethylene carbonate/ethyl methyl carbonate, respectively. For the separation method development three ion chromatographic columns with different capacity and stationary phase were used and compared. Besides the known hydrolysis products of lithium hexafluorophosphate, several new organophosphates were separated and identified with the developed IC-ESI-MS method during aging investigations of the electrolytes. The chemical structures were elucidated with IC-ESI-MS/MS.
    Journal of Chromatography A 06/2014; 1354:92-100.
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    ABSTRACT: The last frontier in the chiral stationary phases (CSPs) field for chromatography enantioseparations is represented by homochiral metal organic frameworks (MOFs), a class of organic-inorganic hybrid materials built from metal-connecting nodes and organic-bridging ligands. The modular nature of these materials allows to design focused structures by combining properly metal, organic ligands and rigid polytopic spacers. Intriguingly, chiral ligands introduce molecular chirality in the MOF-network as well as homochirality in the secondary structure of materials (such as homohelicity) producing homochiral nets in a manner mimicking biopolymers (proteins, polysaccharides) which are characterized by a definite helical sense associated with the chirality of their building blocks (aminoacids or sugars). Nowadays, robust and flexible materials characterized by high porosity and surface area became available by using preparative procedures typical of the so-called reticular synthesis. This review focuses on recent developments in the synthesis and applications of homochiral MOFs as supports for chromatography enantioseparations. Indeed, despite this field is in its infancy, interesting results have been produced and a critical overview of the twelve reported applications for gas chromatography (GC) and high-performance liquid chromatography (HPLC) can orient the reader approaching the field. Mechanistic aspects are shortly discussed and a view regarding future trends in this field is provided.
    Journal of Chromatography A 06/2014; 1363:11-26.
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    ABSTRACT: A fast carbohydrate screening platform processible in 96-well format is described. The method is suitable for the determination of various carbohydrates out of complex mixtures as obtained by acidic hydrolysis of carbohydrates polymers. The chromatographic conditions for an efficient separation (12 min) and the derivatization process with 1-phenyl-3-methyl-5-pyrazolone (PMP) were optimized for high resolution separation and simultaneous determination of deoxy-, amino-, anhydro-sugars as well as hexoses, pentoses, dimers, uronic acids and degradation products like furfural and hydroxymethylfurfural (HMF). The potential to quantify with UV- and MS-detector in the same range has been demonstrated for 20 different compounds. Finally, the matrix effects of the hydrolysis were positively evaluated. The micro scale hydrolysis and PMP-derivatization without any extraction or drying steps, both in 96-well format, result in a fast and intuitive sample preparation. In combination with a fast liquid chromatography coupled to UV and electrospray ionization ion trap detection (LC-UV-ESI-MS/MS) for the qualification and quantification of various sugars, dimers and degradation products, this method shows great performance in carbohydrate analysis
    Journal of Chromatography A 05/2014;
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    ABSTRACT: The anti-inflammatory constituents of Ju-Zhi-Jiang-Tang (JZJT), a formula used for thousands of years in China, were identified by LC-MS and pharmacological activity evaluation. In this study, the whole extract of formula was separated into multiple components to facilitate the analytical process. To characterize their contributions to pharmacological activity of formula, activity indexes of constituents were proposed and calculated for the first time, which integrated the chemical and pharmacological information of multiple components. Among the 151 constituents detected in JZJT by LC-Q-TOF-MS and LC-IT-MS, a total number of 108 constituents were identified unambiguously or tentatively, including eighteen potential novel compounds. And, the structures of some constituents were confirmed by NMR. According to their activity indexes, polymethoxy flavones were indicated as the major active constituents responsible for the anti-inflammatory activity of JZJT. To verify the feasibility of activity indexes in predicting the active constituents, nine compounds with positive and negative index values were selected to validate their anti-inflammatory activity in vitro. The results showed that two polymethoxy flavones with higher positive index values, i.e., nobiletin and tangeretin can significantly exert anti-inflammatory effects, while other compounds with negative values did not show any activity. In conclusion, our results indicated the proposed approach might be an efficient and rapid way to identify active constituents of TCM formulae.
    Journal of Chromatography A 05/2014;
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    ABSTRACT: The main di-(2-ethylhexyl) phthalate (DEHP) degradation products, (2-ethylhexyl) phthalate (MEHP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), have been tested. The proposed cost-effective method combines on-line, in-tube solid-phase micro extraction (IT-SPME) in in-valve configuration and capillary liquid chromatography with UV diode array detection (Cap-LC-DAD). Acidification of the samples at pH 3 improved markedly the estimation of MEHP. Aliquots of 4mL of acidified water samples were directly processed. After sample loading, the analytes were desorbed with the mobile-phase and transferred to the monolithic capillary column. Satisfactory linearity and precision, absence of matrix effect and suitable limits of detection (LODs): 0.005, 0.1, 0.1 and 1.5μg/L for MEHP, DEP, DEHP and DBP, respectively have been achieved. The main advantages are speed and the reduction of background signal by minimizing sample preparation. Real water samples have been analyzed.
    Journal of Chromatography A 05/2014;