| 1. |
- Adeyemi, David, et al.
(författare)
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Electrospun Nanofibers Sorbents for Pre-Concentration of 1,1-dichloro-2,2 bis-(4-chlorophenyl)ethylene with Subsequent Desorption by Pressurized Hot Water Extraction
- 2011
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Ingår i: Chromatographia. - : Springer Science and Business Media LLC. - 0009-5893 .- 1612-1112. ; 73:9-10, s. 1015-1020
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Tidskriftsartikel (refereegranskat)abstract
- Electrospun polystyrene (PS) nanofibers (130-500 nm) incorporating a potassium salt of imidazole-1-carbodithioate were evaluated as potential sorbents for the pre-concentration of a model organochlorine pesticide; 1,1-dichloro-2,2bis-(4-chlorophenyl)ethylene (DDE). The efficiencies of DDE (0.25-1.0 mu g L-1) adsorption by the nanofiber sorbent followed by desorption employing pressurized hot water extraction (PHWE) were investigated and monitored using gas chromatography with electron capture detection (GC-ECD). Parameters such as time, temperature and pressure of extraction, sample volume, DDE concentration and sorbent mass were optimized. The maximum adsorption of DDE (0.50 mu g L-1) on electrospun PS and carbodithioate incorporated PS nanofibers was at 43.7 and 94.6%, respectively, in 20 min. Incorporation of carbodithiote doubled the adsorption efficiency of PS and achieved LOD of 0.000234 mu g L-1 for DDE. The optimal DDE desorption on the PHWE system was 93.8% in 10 min. It would seem that the use of electrospun nanofibers as sorbent material with subsequent desorption by PHWE has great potential and thus warrants further investigations. This approach as it uses water as an extraction solvent for an organochlorine pesticide provides an opportunity to eliminate organic solvents, especially for procedures aimed at monitoring organic pollutants in the environment.
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| 2. |
- Gyllenhaal, Olle, et al.
(författare)
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Evaluation Conditions for SFC of Metoprolol and Related Amino Alcohols on Hypercarb (Porous Graphitic Carbon) with Respect to Structure–Selectivity Relations
- 2010
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Ingår i: Chromatographia. - : Springer Science and Business Media LLC. - 0009-5893 .- 1612-1112. ; 71:1-2, s. 7-13
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Tidskriftsartikel (refereegranskat)abstract
- Mobile phase chromatographic conditions for the selective separation of metoprolol from related amino alcohols have been evaluated using Hypercarb as support and carbon dioxide with addition of methanol as mobile phase. The objective for the presented study was to show the unique ability of the porous graphitized carbon surface to separate closely structurally related substances. Experimental results, using Hypercarb and “chromatographic normal phase conditions” (SFC), are presented with focus on how to control retention and to improve peak performance. A high concentration of basic aliphatic amine additive was required in order to elute the amine analytes as symmetrical peaks. N,N-Dimethyloctylamine was preferred over triethylamine since the retention was markedly shorter though the selectivity and resolution were virtually the same. The selectivity can be optimized by altering the temperature of the column. A high selectivity was demonstrated between metoprolol and two homologues with one and two extra methylene groups inserted between the secondary nitrogen atom and the carbon atom with a hydroxyl group attached. The mobile phase flow rate effect the column efficiency only to a minor extent as the steepness of the van Deemter curve for metoprolol was virtually flat in the range studied: 0.5–3.0 mL min−1.
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| 3. |
- Jastrebova, Jelena, et al.
(författare)
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Comparison of UPLC and HPLC for Analysis of Dietary Folates
- 2011
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Ingår i: Chromatographia. - : Springer Science and Business Media LLC. - 0009-5893 .- 1612-1112. ; 73, s. 219-225
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Tidskriftsartikel (refereegranskat)abstract
- Ultra performance liquid chromatography (UPLC) using small sub-2 mu m particles and high performance liquid chromatography (HPLC) were compared for separation and determination of the most common dietary folates; 5-methyltetrahydrofolate, tetrahydrofolate, 5-formyltetrahydrofolate, 10-formylfolic acid and folic acid. Two UPLC columns-Acquity BEH C(18) and Acquity HSS T3, and two HPLC columns with similar surface chemistry-Xbridge C(18) and Atlantis d18 were tested. When using UPLC, the signal-to-noise ratio could be improved by a factor of 2-50 for different folate derivatives and the run time could be reduced fourfold without sacrificing separation efficiency. The applicability of UPLC to real food samples was demonstrated
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| 4. |
- Saleh, Aljona, et al.
(författare)
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Digestion of Enolase and Carbonic Anhydrase as Model Proteins for Therapeutic Proteins in Blood Plasma with Immobilized Thermolysin and Quantification of Some of the Peptides by LC/LC-MS/MS
- 2014
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Ingår i: Chromatographia. - : Springer Science and Business Media LLC. - 0009-5893 .- 1612-1112. ; 77:1-2, s. 59-74
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Tidskriftsartikel (refereegranskat)abstract
- There is a need for fast method development in the early drug discovery phase of therapeutic proteins. Thermolysin has not been used for quantification of proteins in blood plasma earlier. It is a thermostable protease which permits the use of high temperatures for fast hydrolysis of proteins. Model proteins were digested with immobilized thermolysin on agarose gel. Protein-specific peptides were selected for quantitation and quantified based on stable isotope dilution. Protein digests of blood plasma were cleaned and separated using an automated LC/LC-MS/MS system. Essential digestion parameters that influence thermolysin hydrolytic activity were optimized for high peptide yield. The validated methods were selective, linear, precise and accurate with a limit of detection of 2 nM for both proteins. The proposed strategy for method development could be valuable for quantification of proteins in blood plasma samples. The study underscores and discusses important features of the enzymatic digestion and chromatographic separation.
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| 5. |
- Sibiya, P., et al.
(författare)
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Hollow-Fibre Liquid-Phase Microextraction for the Determination of Polycyclic Aromatic Hydrocarbons in Johannesburg Jukskei River, South Africa
- 2013
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Ingår i: Chromatographia. - : Springer Science and Business Media LLC. - 0009-5893 .- 1612-1112. ; 76:7-8, s. 427-436
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Tidskriftsartikel (refereegranskat)abstract
- A simple, rapid and environmentally friendly hollow-fibre liquid-phase microextraction (HF-LPME) technique was developed for the quantitative determination of polycyclic aromatic hydrocarbons (PAHs) in aqueous samples. GC-MS was then used as the method of analysis. The HF-LPME technique involves extraction of PAHs from a 20-mL sample containing 20 % acetonitrile as a modifier. The PAHs were extracted into a 5-cm hollow fibre filled with heptane as organic solvent. At a stirring speed and extraction time of 600 rpm and 30 min, respectively, the acceptor solvent was then collected to be analysed. Parameters that affect the extraction efficiency were optimised in order to achieve high enrichment of the analytes. In order to evaluate the practical applicability of the HF-LPME technique, the performance of the method was compared to solid-phase extraction using spiked deionised water and real water samples. The obtained concentration enrichment factors ranged from 48 to 95 for HF-LPME and 81-135 for SPE, depending on the individual PAH. The detection limit ranged from 23 to 95 ng L-1 for HF-LPME and 20-52 ng L-1 for SPE. Water samples from the Johannesburg area, South Africa, were analysed using both extraction methods and the results were in good agreement. The relative standard deviations were less than 12 % for both methods. In this comparison, SPE was found to give high concentration enrichment factors and recovery, whereas faster and cheaper analyses were achieved with HF-LPME. The concentration of PAHs found could be arranged in the following order: phenanthrene > acenaphthene > fluoranthene > naphthalene > pyrene.
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| 6. |
- Sroka-Markovic, Janina, et al.
(författare)
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Development of an HPLC Method for Determination of Related Impurities in Prilocaine Substance
- 2012
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Ingår i: Chromatographia. - : Springer Science and Business Media LLC. - 0009-5893 .- 1612-1112. ; 75:7-8, s. 329-336
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Tidskriftsartikel (refereegranskat)abstract
- Development of a reversed phase high performance liquid chromatographic method for determination of six related impurities in prilocaine substance is reported. The test of related impurities in European Pharmacopoeia (Ph. Eur.) cannot meet the demands with the chromatographic parameters given, therefore different types of chromatographic systems and eight columns have been evaluated in the present study. A new method with a Hypercarb column was developed and validated. This method fulfils the demands in the Ph. Eur., and the validation shows that the method is selective, reproducible, linear, accurate and robust with sufficient limits of detection (0.001-0.004% of 2.5 mg prilocaine mL(-1)) and quantification (0.002-0.009% of 2.5 mg prilocaine mL(-1)).
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