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Biomedical subjects

D W Fink

Publications and source records attributed to D W Fink.

35 records · Page 2Linked to original sources
PubMed1980

Determination of avermectins in plasma at nanogram levels using high-performance liquid chromatography with fluorescence detection.

An analytical method is described for the determination of the avermectins in plasma based upon high-performance liquid chromatography of fluorescent derivatives of these compounds. The analyte is isolated by adsorption chromatography on Florisil, dehydrated in an acetic anhydride-pyridine mixture, and the fluorophore is further separated by chromatography on silica gel in advance of introduction into a reversed-phase system. This method, which can be applied to samples containing as little as 0.2 ng drug per ml, has an accuracy of 5% mean relative error and a precision of 8% relative standard deviation. A study and discussion of several factors which affect the analytical reaction are included.

Animals↗
PubMed1980

Fluorometric determination of thiazole-containing compounds.

Fluorescence spectroscopy was applied to the development of sensitive analytical methods for the determination of thiazole and several congeners that contain substituted thiazole rings. Treatment to yield thionine, previously used spectrophotometrically to measure thiazole and fluorometrically only for sulfur determinations in inorganic systems, is further characterized and illustrated with the determination of the antibiotic thiopeptin. This method is selective for submicrogram quantities of thiazole rings in the presence of fused-ring derivatives and reduced analogs. It has a precision of +/- 2% RSD (n = 11) at the 15-ng/ml thiazole concentration level with a signal-to-noise ratio of 3:1. For thiopeptin, this method has an accuracy of 5% mean relative error (n = 8) over the 5--20-ppm range in medicated feed.

Animal Feed↗
PubMed1979

High pressure liquid chromatographic determination of arprinocid in feed.

Arprinocid [9 - (2 - chloro - 6 - fluorophenylmethyl)-9H-purin-6-amine] is determined in feed by high pressure liquid chromatography with a silica column and ultraviolet detection. The drug is extracted from the feed into chloroform in the presence of pH 7 phosphate buffer, transferred to 0.1N HCl, and separated from interfering substances by partitioning with hexane. The acidic solution is neutralized, and the analyte is extracted into chloroform for injection into the chromatograph. This procedure has been applied to feeds containing 0.0030--0.0090% arprinocid with a precision of less than 5% relative standard deviation at the 0.0060% formulated concentration level. The results of this chromatographic procedure also correlate with those from a colorimetric analysis.

Adenine↗
PubMed1978

Difference spectrophotometric determination of p-hydroxybenzoic acid in presence of its esters.

A difference spectrophotometric analytical method was developed for the selective determination of p-hydroxybenzoic acid in the presence of its alkyl esters without prior separation. Based on the spectral shift to a shorter wavelength accompanyint carboxyl dissociation, the procedure measures as little as 2% of this acid in mixtures with the alkyl ester preservatives and has an accuracy of 2% mean relative error over the 0.16-12.0 microgram of p-hydroxybenzoic acid/ml range.

Hydroxybenzoates↗
PubMed1978

Facile separation of sulfonamides from their degradates by liquid--liquid extraction.

Regulation of acidity for protonation of the free N4-amine can provide for the selective liquid--liquid extraction isolation of a sulfonamide from its degradation products. This principle is applied for the stability-indicating determination of sulfacetamide in the presence of sulfanilamide, sulfaquinoxaline in feed, and sulfabromomethazine in dosage forms. In solution, sulfabromomethazine can exhibit photodecomposition to sulfamethazine. The mean relative errors of the these methods and the precision, represented by relative standard deviations, are each typically less than 2%.

Animal Feed↗
PubMed1978

Colorimetric determination of arprinocid in feed.

An analytical method has been developed for the determination of arprinocid (9-(2-chloro-6-fluorophenylmethyl)-9H-purin-6-amine) in feed, based upon measurement of the absorbance of the diazo chromophore formed from a product of zinc reduction of the drug in acidic solution. The analyte is extracted from the feed into chloroform in the presence of a pH 7 phosphate buffer and isolated by adsorption chromatography on alumina, followed by partitioning between hexane and 0.15M HCl. The reduction product in the aqueous phase is then treated for colorimetric measurement. This procedure has been applied to determining 0.0010--0.0080% arprinocid in feed with a precision of less than 5% relative standard deviation near the middle of this concentration range. Of 32 feed additives examined, only zoalene and sulfamethazine were serious interferences. A study and discussion of several factors, e.g., reaction time, pH, and amount of zinc metal, that affect the analytical reactions are also included.

Absorption↗
PubMed1978

Further studies on the colorimetric determination of ronidazole in feeds.

A previously published colorimetric method for determining ronidazole, (1-methyl-5-nitro-imidazol-2-yl)methyl carbamate, can be used as an analytical technique for measuring the stability of this drug in medicated feeds. Although the color reaction per se is not selective, elution profiles of ronidazole and its demonstrated hydrolytic degradation product, 1-methyl-2-hydroxymethyl-5-nitroimidazole, show that the chromatographic separation used in the sample preparation efficiently isolates the drug from the degradation product. No interference was found in feeds containing 0.010% ronidazole and up to 0.010% degradation product.

Animal Feed↗
PubMedDate not supplied

Determination of ivermectin in medicated swine feeds at the 2 ppm concentration level.

An analytical method has been developed that is applicable to the determination of Ivermectin in medicated feeds at the 2 ppm concentration level. It is based upon liquid chromatographic analysis with a reverse-phase column and ultraviolet detection. After the drug is extracted from the feed into methanol, an analytical sample is prepared by the consecutive use of column chromatography on alumina and solid-phase extraction on Sep-Pak C18 and silica cartridges. This procedure has been applied to the concentration range 0.50-3.0 ppm of Ivermectin in feed with an accuracy of +/- 2% mean relative error and a precision of +/- 2% relative standard deviation at the 2 ppm concentration level.

Animal Feed↗
PubMedDate not supplied

Liquid chromatographic determination of ivermectin in feed.

An analytical method for determining ivermectin in feed at 0.50-3 ppm is presented. The method is based on liquid chromatographic measurement after sample preparation by adsorption chromatography on alumina and solid-phase extraction. Two complete, final, finished medicated feeds and the corresponding control feeds used in their preparation were analyzed. Recoveries from feeds fortified at 50-150% of the 2 ppm ivermectin use concentration also were determined. Mean recoveries from replicate analyses ranged from 90 to 100%, and coefficients of variation (CVs) were less than 4.5%. No significant interferences were found in control feeds. The pooled distribution of individual analytical results (n = 100) gave a mean recovery of 100%, a recovery range of 90-111%, and an overall CV of 5.5%. Resolution of the total variance into its 2 components gave a within-laboratory CV of 4.1% and a between-laboratory CV of 3.4%. There was no significant difference in recoveries among laboratories, days, concentrations, and feed base or between fortified and medicated feeds (P > 0.2).

Animal Feed↗