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Biomedical subjects

D R Newkirk

Publications and source records attributed to D R Newkirk.

At least 19 recordsLinked to original sources
PubMed1982

Evaluation of three methods for recovery of sulfamethazine metabolites from swine tissue.

Recent investigations have clearly established the presence of desaminosulfamethazine (I), N4-acetylsulfamethazine (II), and N4-D-glucosyl sulfamethazine (III) in the tissues of swine which have been dosed with sulfamethazine (V). N4(1-Deoxy-D-glucuronyl) sulfamethazine (IV) has frequently been found in the urine and feces of animals. These metabolites have generally not been investigated in current sulfamethazine methods; therefore, it is not clear to what extent they might be measured by these procedures. Metabolites I, II, III, and IV were synthesized and characterized by several chemical and physical measurements. These metabolites and their parent, V, were added to swine tissue and recoveries were measured by a gas-liquid chromatographic (GLC), a colorimetric, and a gas chromatographic/mass spectrometric method with electron ionization-selected ion monitoring (GC/MS EI-SIM). With modifications of the gas chromatographic parameters, the GLC method can quantitate compounds, I, II, and V simultaneously. If a hydrolysis step is added, all 3 methods can quantitate compound II as V and, in addition, the GC/MS EI-SIM and colorimetric methods can quantitate III as V. In none of these methods do metabolites I, II, III, or IV interfere in the determination of V.

Animals↗
PubMed1981

High pressure liquid chromatographic determination of cholesterol in foods.

A high pressure liquid chromatographic method that uses the benzoate ester of cholesterol has been developed for the measurement of cholesterol in foods. A 300 x 3.9 mm id muBondapak C18 column and a variable wavelength ultraviolet detector are used with a 100% methanol mobile phase. Amounts as low as 10 ng cholesterol benzoate can be detected. The results from the analyses of a variety of foods are given and compared with results from gas-liquid chromatographic analyses. The comparison of the 2 chromatographic techniques is favorable.

Cholesterol↗
PubMed1977

Gas-liquid chromatographic determination of cholesterol and other sterols in foods.

A gas-liquid chromatographic (GLC) method, using the butyryl esters of sterols, has been developed for the measurement of cholesterol, stigmasterol, sitosterol, and campesterol in foods. An immobile phase of 1% SE-30 coated on 100-120 mesh Gas-Chrom Q packed in a 6 inch X 4 mm id glass column operated at 255 degrees C was the most satisfactory of 7 column packings evaluated. Extraction with chloroform-methanol gave 98.7% recovery with a coefficient of variation of 1.8% for cholesterol added to a variety of foods. When cholesteryl palmitate was added to vegetable oil and the butyryl derivative was prepared, followed by GLC analysis, the recovery was 99.3% with a coefficient of variation of 0.9%. Amounts as low as 1 mg/100 g food can be detected with a precision of 2.5%. The results of the analysis of a variety of foods for cholesterol, campesterol, sitosterol, and stigmasterol are given.

Cholesterol↗