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Biomedical subjects

E Roets

Publications and source records attributed to E Roets.

At least 73 records · Page 4Linked to original sources
PubMed1996

Evaluation of liquid chromatography methods for the separation of ampicillin and its related substances.

Two laboratories collaborated to examine the selectivity of four isocratic liquid chromatography (LC) methods for the separation of ampicillin and its related substances. The United States Pharmacopeia (USP) assay method gave the best selectivity. Similar selectivity was obtained on C18 columns as well as on C8 and poly(styrene-divinylbenzene) copolymer columns. A resolution test using cefradine was proposed to replace the test with caffeine prescribed by the USP. Based on the USP method, a gradient LC method was developed for the analysis of related substances in ampicillin. This LC method has been proposed for assay and purity control in the ampicillin monographs of the European Pharmacopeia.

Ampicillin↗
PubMed1996

Investigation of the reaction mechanism of the mercurimetric determination of benzylpenicillin.

The assay of different penicillins in the European Pharmacopoeia was carried out by mercurimetric titration with potentiometric determination of the end-point. The consecutive formation of reaction products during titration was followed by reversed-phase liquid chromatography (LC) and ultraviolet detection. In one experiment the titration was carried out with 14C-labeled benzylpenicillin and the reaction was followed with LC coupled to radiochemical detection. The identity of the intermediates and final reaction products was deduced from their retention times in comparison with reference products obtained by independent chemical transformation of benzylpenicillin. This allowed one to define for the first time the complete reaction scheme. This involves the isomerization of the natural penicilloic acid followed by decarboxylation, which has not been reported previously. At the end of the titration, only benzylpenilloaldehyde and a 1:1 complex of mercury and penicillamine were present in the solution.

Chromatography, Liquid↗
PubMed1996

Interlaboratory study of the analysis of ampicillin by liquid chromatography.

A liquid chromatographic method for the analysis of ampicillin was examined in a collaborative study involving seven laboratories. The method included an isocratic part, which is used in the assay. The isocratic part is similar to the assay method for ampicillin of the US Pharmacopeia XXIII Revision. When the isocratic part is combined with gradient elution, the method is suitable for purity control. Six samples of ampicillin (anhydrous, trihydrate and sodium salt) with varying purity were analysed. The main component and related substances were determined. An analysis of variance proved the absence of consistent laboratory bias. The laboratory-sample interaction was significant. Estimates of the repeatability and reproducibility of the method, expressed as standard deviations of the result of the determination of ampicillin, were calculated to be about 0.9 and 1.1 respectively.

Ampicillin↗
PubMed1996

Capillary zone electrophoresis of minocycline.

A method is described for analysis of the tetracycline antibiotic minocycline using capillary zone electrophoresis. Potential impurities are 4-epiminocycline, 6-deoxy-6-demethyltetracycline, 7-didemethylminocycline, 7-monodemethylminocycline and 9-minocycline. Method development was undertaken with a mixture consisting of minocycline and its related substances mentioned above. Using a fused silica capillary, the type of buffer and its pH and concentration were investigated. In all cases 1 mM EDTA was added to prevent metal ion complexation. Instrumental parameters such as capillary temperature and applied voltage were optimised. The effects of the sample solvent and of organic modifiers in the buffer were also investigated. The following method is proposed: capillary: fused silica, l = 38 cm, L = 44 cm, 50 microns i.d.; buffer: 25 mM sodium tetraborate, 1 mM EDTA at pH 11.75; voltage, 13 kV; temperature, 15 degrees C; UV detection performed at 254 nm. Relative standard deviations, linearity, LOD and LOQ are reported and compared with those of liquid chromatography.

Anti-Bacterial Agents↗
PubMed1996

The interference of penicilloic acids with Karl Fischer titration of penicillins.

Phenoxymethylpenicilloic acid monohydrate was titrated with 12 different brands of Karl Fischer reagent. It was shown that only the four pyridine-containing reagents gave correct results for water content, providing that the sample solution was cooled in an ice bath or that the delay time of the amperometric end-point determination was 10 s instead of 30 s, as prescribed by the European Pharmacopoeia. The other reagents always gave results, which were too high. When these reagents were used to titrate the water in sodium amoxicillin, sodium carbenicillin or sodium ticarcillin the same conclusions could be drawn with regard to the accuracy of the results, the usefulness of the reagents and the reaction conditions. These penicillins may contain up to 9% penicilloic acids. The maximum relative error obtained with pyridine-free reagents was about 50% for ticarcillin. It has been confirmed that penicilloic acids interfere with Karl Fischer titration of water and that this interference is greatly dependent on the brand of reagent and on the reaction conditions.

Indicators and Reagents↗
PubMed1995

Isolation of decomposition products of tylosin using liquid chromatography.

Decomposition products of tylosin A were isolated using open column chromatography and preparative liquid chromatography. Two decomposition products, formed in slightly alkaline medium, were identified as epimers of tylosin A aldol, one of which has been described previously. Another decomposition product was formed on exposure of a tylosin A solution to light. Isomerization of the double bond between C12-C13 takes place, resulting in the formation of the hitherto unreported isotylosin A.

Carbohydrate Sequence↗
PubMed1995

Determination of the relative amounts of the B and C components of neomycin by thin-layer chromatography using fluorescence detection.

The determination of the relative amounts of the B and C components of neomycin sulphate by thin-layer chromatography using silica gel plates from Whatman as the stationary phase is described. The mobile phase consisted of methanol-20% (m/v) sodium chloride solution (15:85). Fluorescence detection was performed after derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole. The influence of different parameters on the separation was investigated. A number of commercial samples was analysed using this method and the results were compared with results obtained with ion-exchange chromatography and ninhydrin colorimetric detection, which is the official method prescribed by the European Pharmacopoeia. The described method is much easier to perform than the official method.

4-Chloro-7-nitrobenzofurazan↗
PubMed1995

The influence of ageing on muscarinic receptors, beta-adrenoceptors and adenylate cyclase activity in the bovine lung.

Muscarinic and beta-adrenoceptors were identified in airway epithelium, smooth muscle and lung parenchyma from Holstein-Friesian calves and cows and were characterized with [3H]quinuclidinyl benzilate and [3H]dihydroalprenolol, respectively. The muscarinic receptor density in the smooth muscle of cows (Bmax = 4803 +/- 245 fmol/mg protein) was 33% greater (p < 0.01) than in calves. Low receptor numbers were detected in the epithelium and parenchyma. In both calves and cows, the density of epithelial beta-adrenoceptors was twice as high as in smooth muscle and parenchyma. The quantity of beta-adrenoceptors in the tracheal epithelium (Bmax = 994 +/- 83 fmol/mg protein) and smooth muscle (Bmax = 492 +/- 41 fmol/mg protein) in cows was respectively 37% (p < 0.001) and 35% (p < 0.01) lower than in calves. Adenylate cyclase (AC) assays indicated that the basal and the (-)-isopropylnoradrenaline- (ISO-) stimulated cAMP production were not significantly different between the calves and cows. After stimulation with NaF, significantly higher cAMP production was found in all tissues from cows. Significant correlations were found between absolute AC responses to NaF and beta-adrenoceptor density in epithelium (r = -0.75, p < 0.001) and smooth muscle (r = -0.63, p < 0.01). It seems that, in older animals, the production of cAMP is independent of the number of receptors, indicating the presence of fully active compensatory mechanisms.

Adenylyl Cyclases↗
PubMed1995

Assay and purity control of minocycline by thin-layer chromatography using UV and fluorescence densitometry--a comparison with liquid chromatography.

A thin-layer chromatography (TLC) method using UV and fluoresecence densitometry is described for the assay and purity control of minocycline (MC). With a mobile phase dichloromethane-methanol-water (57:35:8, v/v/v) and a silica gel thin-layer, previously sprayed with 10% m/v sodium edetate adjusted to pH 9.0, 4-epiminocycline and 7-didemethylminocycline were well separated from MC and from each other, 7-monodemethylminocycline and 6-deoxy-6-demethyltetracycline (6-DODMTC) were not separated from each other and were only partially separated from minocycline. 6-DODMTC was selectively determined by fluorescence densitometry, while quantification of other impurities and the assay of MC were performed by UV densitometry. Results obtained with qualitative TLC were compared with those obtained by a liquid chromatography (LC) method using a poly(styrene-divinylbenzene) copolymer stationary phase. The correlation coefficient for TLC and LC results was > 0.999. For TLC the relative standard deviation for the assay of MC at 1.25 mg ml-1 was < 3.0% (n = 4), while for LC it was < 1.0% (n = 4).

Anti-Bacterial Agents↗
PubMed1995

Study of the stability of tylosin A in aqueous solutions.

The decomposition of the 16-membered ring macrolide antibiotic tylosin A in aqueous buffers has been investigated in the pH range 2-13, by means of a liquid chromatographic assay with ultraviolet detection at 280 nm. In acidic medium, tylosin A is converted into tylosin B, while in neutral and alkaline medium, tylosin A aldol is formed together with a number of polar decomposition products of unknown identity. The decomposition kinetics have been studied as a function of the type and concentration of the buffer, ionic strength, pH and temperature.

Anti-Bacterial Agents↗
PubMed1995

Relationship between numbers of alpha 2- and beta 2-adrenoceptors on blood cells of bulls and milkability of their daughters.

Milk yield and milking time were measured on one occasion for several daughters (n = 6-44) from 16 bulls at morning milkings. Blood from the bulls was collected, and platelets and mononuclear leucocytes were isolated. The alpha 2-adrenoceptors on platelet membranes were identified by binding of [3H]rauwolscine, whereas for the determination of beta 2-adrenoceptors on intact mononuclear leucocytes, [3H]CGP-12177 was used. It was found that mean milk flow rate was highly correlated (P < 0.001) with the alpha 2-adrenoceptor densities on blood platelets. No correlation was found with the beta 2-adrenoceptors on mononuclear leucocytes. It is concluded that estimation of the alpha 2-adrenoceptors on blood platelets from bulls could eventually be used to investigate milking characteristics of cows, and might be useful in the future as a marker in genetic studies.

Animals↗
PubMed1995

Effects of Staphylococcus aureus mastitis after endotoxin application on milk yield and composition during subsequent lactation of guinea-pigs.

The effects of Staphylococcus aureus mastitis on milk yield and composition throughout subsequent lactation in lactating guinea-pigs and the role of endotoxin pretreatment on these phenomena were investigated. Primiparous lactating guinea-pigs were intramammarily inoculated with sterile saline (group 1), S. aureus strain UC 6097 (group 2), or with S. aureus UC 6097 after endotoxin pretreatment (group 3). Clinical signs and survival rate were monitored. During the second lactation, daily milk yield was measured and milk composition was determined. In primiparous inoculated guinea-pigs, moderate (group 3)-to-severe acute mastitis (group 2) was produced. During subsequent lactation, milk yield in the control group peaked on day 5 and then decreased. Concentrations of Na+ and Cl- in milk, and concentrations of fat, gradually increased, but lactose and K+ decreased. After an early decrease, NAGase in milk increased towards the end of lactation. Except for higher NAGase concentrations in group 3, milk yield and composition during the second lactation did not differ significantly between the mastitis and the control groups. Endotoxin pretreatment only plays a role in the determination of the severity of the infection.

Animals↗
PubMed1994

Quantitative analysis of quaternary ammonium antiseptics using thin-layer densitometry.

A thin-layer chromatography method for quantitative analysis of quaternary ammonium antiseptics is described. Silanized silica gel was used as the stationary phase. The mobile phase consisted of methanol-25% (m/v) sodium acetate solution-acetone (65:35:20). The method is able to separate the chain homologues of benzalkonium chloride, cetylpyridinium chloride and cetrimide. Detection was performed using a colour reaction with potassium triiodide solution. The different homologues were quantified using UV densitometry at 400 nm. A number of commercial samples was analysed using this method. From the results it appears that it is worthwhile to have a limit test for the composition of quaternary ammonium antiseptics in pharmacopoeial monographs, the more so as the antibacterial activity depends on it.

Acetates↗
PubMed1994

Isolation and structural elucidation of an impurity of cefradine.

An impurity of unknown identity was isolated from commercial cefradine by liquid chromatography on poly (styrene-divinylbenzene) with HOAc (0.01 M)-CH3CN (94:6, v/v) as the mobile phase. The structure was elucidated as 4',5'-dihydrocefradine using nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). The structure was confirmed by comparison with the chromatographic retention characteristics and photodiode-array detected ultraviolet spectrum of the synthetic compound and with its infrared, NMR and MS spectra. The presence of 4',5'-dihydrocefradine in cefradine has not been described previously.

Cephalexin↗
PubMed1993

Quantitative analysis of tylosin by column liquid chromatography.

A column liquid chromatographic method suitable for the quality control of tylosin A is described. The determination can be carried out on different C8 or C18 columns, using a mobile phase containing acetonitrile, 0.2 M tetrabutylammonium hydrogensulphate, 0.2 M phosphoric acid and water. The flow-rate is 1 ml/min and detection is performed at 280 nm. The method shows good selectivity towards the major components tylosin A, B, C and D and demycinosyltylosin. Minor degradation products, mainly observed in solutions, are also separated. The compositions of several standards are compared and results for a number of commercial samples are presented.

Calibration↗
PubMed1993

A comparative study of LC methods for analysis of cefradine.

A comparative study of two isocratic liquid chromatographic methods for the analysis of cefradine is described. The first method is prescribed by the European Pharmacopoeia for the assay of cefradine, using classical alkyl bonded phase (C18) as the stationary phase. Poor reproducibility of the selectivity towards cefradine and its related substances was observed when this method was used and none of the C18 columns examined was able to separate cefradine completely from its potential related substances under the prescribed LC conditions. On the other hand, the second method, which uses poly(styrene-divinylbenzene) as the stationary phase, shows good selectivity even when using columns from different manufacturers and of different age. Four bulk samples of cefradine were analysed following both methods and the results were compared.

Cephalexin↗
PubMed1993

Quantitative analysis of cefradine by liquid chromatography on poly(styrene-divinylbenzene).

A method is described for isocratic analysis of cefradine by liquid chromatography on a poly(styrene-divinylbenzene) column (PLRP-S, 250 x 4.6 mm i.d.) at 50 degrees C. Cefradine is separated from its related substances using a mobile phase of acetonitrile-0.02 M sodium 1-octanesulphonate-0.2 M phosphoric acid-water (14.5:10:5:up to 100, v/v/v/v). The flow rate was 1.0 ml min-1 and UV-detection was performed at 254 nm. The method was employed for the quantitative analysis of reference substances, bulk samples and pharmaceutical dosage forms.

Acetonitriles↗