Norman E. Hoffman

Injection of eluites in solvents stronger than the mobile phase in reversed-phase liquid chromatography

Abstract A study was made of the distortion and multiplication of peaks that occur when an eluite is injected dissolved in a solvent that is significantly stron

Gas chromatography of some urinary acid metabolites related to phenylketonuria.

Abstract A rapid accurate method for the determination of o -hydroxyphenylacetic acid, β-phenyllactic acid, and phenylpyruvic acid has been developed for the analysis of phenylketonuric urine. A semiquantitative measure of the amount of p -hydroxyphenylpyruvic acid is obtained simultaneously. The method uses ethyl acetate extraction of acidified urine, trimethylsilylation of the residue from ethyl acetate evaporation, and gas chromatography of the trimethylsilyl derivatives on a SE-30 column. Normal alkanes are used as internal standards.

A SENSITIVE GAS CHROMATOGRAPHIC METHOD FOR THE DETERMINATION OF LACTIC ACID.

Abstract A gas chromatographic method for the determination of lactic acid in blood and organ perfusates has been developed. The method offers speed and simplicity of analysis while retaining the higher sensitivity of the chemical method.

Determination of cyclophosphamide in whole blood and plasma by reversed-phase high-performance liquid chromatography

A rapid, simple, and sensitive reversed-phase high-performance liquid chromatographic determination of the cytostatic drug cyclophosphamide in whole blood and plasma has been developed. The pre-chromatography isolation of the drug involves salting-out of acetonitrile with simultaneous extraction of cyclophosphamide from whole blood and plasma. A short column packed with 5-micron reversed-phase octadecylsilane (ODS) spherical particles was used with an isocratic elution of 5 mM potassium phosphate (pH 6.80)-acetonitrile (80:20, v/v). The cyclophosphamide was monitored at 190 nm and 0.40-0.002 a.u.f.s. At a flow-rate of 1.0 ml/min, the retention time of cyclophosphamide was ca. 9 min. The completion time for the assay was less than 20 min and the assay had a detection limit of 0.30 microgram/ml. This method was used to determine the stability of cyclophosphamide in plasma at room temperature and at -10 degrees C.

Separating Ability of Some Polar Mobile Phases in Reverse Phase High Performance Liquid Chromatography

Abstract Homologous series of n-alkanes, n-alcohols, ethers, esters, amides and ketones were studied as solutes. Methanol, acetonitrile, ethanol, dioxane, 2-propanol and tetrahydrofuran were mobile phases. Spherisorb ODS columns with light and heavy octadecyl coatings were used. Methanol and acetonitrile were found to be the most selective solvents for reverse phase separation. The polar amides, alcohols, and ketones behaved differently from nonpolar solutes in acetonitrile mobile phases. Results were interpreted with the solvophobic theory.

Association between plasma high density lipoprotein cholesterol and antipyrine metabolism in alcoholics.

Seven patients entering an alcoholic detoxification and treatment unit exhibited elevated levels of plasma high density lipoprotein cholesterol (HDLC) and enhanced metabolic disposal of antipyrine. Following a 2-week abstinence treatment, the HDLC levels were reduced by 28% (from 64 to 47 mg/100 ml) and the t 1/2 of antipyrine was extended from 12.4 to 13.7 hours. The extent of the HDLC reduction correlated with the antipyrine t 1/2 changes (r = -0.753, P = 0.05).

Gas chromatographic determination of urinary methylmalonic acid

Abstract A method for the determination of methylmalonic acid in urine has been developed. The method consists of essentially two operations: ( 1 ) A separation of methylmalonic acid from most of the urinary components by ion-exchange chromatography. ( 2 ) A gas chromatographic determination of methylmalonic acid by the technique of decarboxylation and chromatography of the monocarboxylic acid formed. Other malonic acids are used as internal standards in the gas chromatographic analysis.

High-performance liquid chromatographic determination of fusidic acid in plasma

Fusidic acid was determined in plasma by a high-performance liquid chromatographic method. Fusidic acid was extracted from plasma with acetonitrile that was salted out with ammonium sulfate. Prior to salting out cadmium sulfate was mixed with the acetonitrile-plasma mixture to help remove interfering constituents. A 150 mm X 4.6 mm column packed with 5-microns cyanopropyl stationary phase was used for chromatography. The mobile phase was acetonitrile-20 mM sodium dihydrogenphosphate (pH 3.50) (39:61, v/v). An ultraviolet-visible detector was set at 204 nm. The presence of water in the injection solvent had a significant effect on the fusidic acid peak height. A number of clinically important acquired immunodeficiency syndrome drugs did not interfere with the fusidic acid determination. The relative standard deviation varied between 0.99 and 7.8%. A limit of detection of 200 ng/ml was obtained for a 80-microliters injection.

An HPLC Method for Measuring 5-Fluorouracil in Plasma

Abstract 5-Fluorouracil in plasma was determined by extraction with methyl isobutyl ketone, evaporation of the ketone, and reverse phase high performance liquid chromatography of the evaporation residue. With UV detection at 280 nm the lower limit of detection is 10.0 ng/ml and interfering peaks eliminated. The method is highly reproducible.

Teratogenic evaluation of terpenoid derivatives.

Abstract Eight terpenoid derivatives with juvenile hormone activity were tested for teratogenicity. Three of the derivatives were teratogenic when administered to mice as a single intraperitoneal injection of 1 mg/gm on either day 9 or day 10 of pregnancy. However, intubation at 5 mg/gm of the two most teratogenic derivatives resulted in one of the derivatives marginally increasing the incidence of abnormal embryos above peanut oil-intubated controls; the other intubated derivative was without adverse affect. Of the remaining five compounds, two with high juvenile hormone activity were without teratogenic effect when injected at 1 mg/gm. Since teratogenic effects were observed only at a dose above likely exposure levels and by a route of administration not possible in the environment, support is provided for the potential use of terpenoid derivatives in the control of insect pests.