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At least 883 records · Page 49Linked to original sources
PubMed1989

Simultaneous determination of lactate, pyruvate, and ascorbate in microdialysis samples from rat brain, blood, fat, and muscle using high-performance liquid chromatography.

An isocratic high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of lactate, pyruvate, and ascorbate in tissue and blood, sampled in vivo using the microdialysis technique. The compounds were separated on a silica-based, reversed-phase column or on a resin-based, cation exchange column. The acids were monitored by ultraviolet detection.

Adipose Tissue↗
PubMed1993

Determination of mizolastine, a new antihistaminic drug, in human plasma by liquid-liquid extraction, solid-phase extraction and column-switching techniques in combination with high-performance liquid chromatography.

For the determination of mizolastine (2-[[[1-[(4-fluorophenyl)methyl]-1H-benzimidazol-2-yl]-4- piperidinyl]methylamino]-4(3H)-pyrimidinone, SL 85.0324), a new antihistaminic drug, in human plasma, three methods were developed based on liquid-liquid extraction, solid-phase extraction and column-switching in combination with high-performance liquid chromatography with ultraviolet detection. The liquid-liquid extraction method included a back-extraction step that preconcentrates the drug into a small aqueous volume, resulting in very high sensitivity (0.5 ng/ml of plasma); it can be used in conventional bioanalytical laboratories that do not have sophisticated automatic devices. The solid-phase extraction method is performed by using a robotic system (Benchmate). It is completely automated from the initial sampling to the final injection into the chromatograph. It has a good sensitivity (1 ng/ml of plasma), but requires an expensive apparatus and skilled analysts. The column-switching method is based on a solid-phase extraction performed on-line with chromatographic analysis; it is not completely automatic, because some operations are performed manually. The device required for valve switching is not expensive and can be managed by a simple integrator or a personal computer; it is very easy to use and affords a sensitivity (2.5 ng/ml of plasma) that generally satisfies the needs of pharmacokinetic investigations of mizolastine. The conditions were similar for all the three methods: a C8 type column, an eluent of phosphate buffer and acetonitrile, and a spectrophotometric ultraviolet detector operated at 285 nm.

Autoanalysis↗
PubMed2002

UV-visible derivative spectroscopy under high pressure.

High hydrostatic pressure affects proteins, changing their intra- or intermolecular interactions, conformation and solvation. How to detect these changes? In this paper, via some selected examples, we show the potentiality (but also the limits) of the ultraviolet derivative spectroscopy specially adapted to high pressure experiments.

Animals↗
PubMed1999

Isolation and identification of 4,25-dihydroxyvitamin D2: a novel A-ring hydroxylated metabolite of vitamin D2.

Vitamin D2 is less toxic in rats when compared to vitamin D3. Our laboratory has been involved in research projects which were directed towards identifying the possible mechanisms responsible for the toxicity differences between vitamins D2 and D3 in rats. The present research project was designed to isolate and identify new metabolites of vitamin D2 from serum of rats which were fed toxic doses of vitamin D2. Hypervitaminosis D2 was induced in 30 rats by feeding each rat with 1000 nmol of vitamin D2/day x 14 days. The rats were sacrificed on the 15th day and obtained 180 ml of serum. The lipid extract of the serum was directly analyzed by a straight phase HPLC system. The various vitamin D2 metabolites were monitored by their ultraviolet (UV) absorbance at 254 nm. One of the UV absorbing peaks did not comigrate with any of the known vitamin D2 metabolites. This unknown metabolite peak was further purified by HPLC and was then subjected to UV absorption spectrophotometry and mass spectrometry. The structure assignment of the new metabolite was established to be 4,25-dihydroxyvitamin D2 [4,25(OH)2D2] by the techniques of UV absorption spectrophotometry and mass spectrometry and by the new metabolite's susceptibility to sodium metaperiodate oxidation. At present the biological activity of this unique 'A-ring' hydroxylated vitamin D2 metabolite is not known. As this new metabolite is isolated from the serum of rats intoxicated with vitamin D2, we speculate that 4,25(OH)2D2 may be playing an important role in the deactivation of vitamin D2.

Animals↗
PubMed2000

Determination of spinosad and its metabolites in citrus crops and orange processed commodities by HPLC with UV detection.

Spinosad is an insect control agent that is derived from a naturally occurring organism and is effective on a wide variety of crops, including citrus crops. A method is described for the determination of spinosad and its metabolites in citrus crops and orange processed commodities. The method determines residues of the active ingredients (spinosyns A and D) and three minor metabolites (spinosyn B, spinosyn K, and N-demethylspinosyn D). For dried orange pulp and orange oil, the method has a limit of quantitation (LOQ) of 0.02 microg/g and a limit of detection (LOD) of 0.006 microg/g. For all other sample matrices (whole fruit, edible fruit, juice, and peel), the method has an LOQ of 0.01 microg/g and an LOD of 0.003 microg/g. The analytes are extracted from the various sample types using appropriate solvents, and the extracts are purified by liquid-liquid partitioning and/or solid-phase extraction. All five analytes are determined simultaneously in the purified extracts by reversed-phase high-performance liquid chromatography with ultraviolet detection at 250 nm.

Anti-Bacterial Agents↗
PubMed1991

Quantification of imipenem's primary metabolite in plasma by postcolumn chemical rearrangement and UV detection.

Imipenem (thienamycin formamidine) is an antibiotic active against a broad spectrum of bacteria. Its primary metabolite arises from cleavage of the lactam ring. The metabolite can be formed in-vitro by acid-catalyzed or enzymatic hydrolysis. In animals and man, this metabolite can be generated systemically as well as in the kidneys following the excretion of imipenem into the urine. In man, this dehydropeptidase-catalyzed renal metabolism is minimized by the coadministration of cilastatin, a competitive inhibitor. A specific HPLC assay has been developed to evaluate the disposition of this metabolite in humans having normal or end-stage renal function. The assay employs ion-pair, reversed-phase chromatography, and post-column acid treatment of the analyte for ultraviolet detection.

Chromatography, High Pressure Liquid↗
PubMed1995

Behavior outdoors and its effects on personal ultraviolet exposure rate measured using an ambulatory datalogging dosimeter.

We describe the construction of a small device incorporating a UVB (290-320 nm) sensor that can be worn on the lapel site or waistband and which is electrically coupled to a portable data logger carried in a trouser pocket or worn on a belt. The detector has an approximate cosine-weighted angular response and is linear over a wide dynamic range. It has a spectral sensitivity that follows closely the erythema action spectrum in the UVB region, is less than one order of magnitude greater than this action spectrum in the UVAII region (320-340 nm) and between one to two orders of magnitude greater in the UVAI region (340-400 nm). The instrument has been used to monitor variations in erythemally effective exposure rate that occurred during three outdoor activities with differing weather conditions. Erythemal irradiance incident on the trunk was recorded every 2 s for periods ranging from 1 to 2.2 h. The results demonstrated that behavior outdoors can be a more dominant factor in determining personal exposure than ambient ultraviolet and highlighted the very important role that shade from trees plays in reducing exposure.

Environmental Exposure↗
PubMed1990

Decolouration of the lens pigment in senile nuclear cataract.

Human cataract lens proteins can be bleached by exposure to sodium borohydride (NaBH4), sodium cyanoborohydride (NaCNBH3), or hydrogen peroxide (H2O2). The decolouration resulting from these treatments could be monitored by a change in absorbance at 350 nm. At pH 12 the magnitude of the absorbance change increased in proportion with the severity of the nuclear cataract in the case of NaBH4 and H2O2 treatments, but not in the case of NaCNBH3 treatment. The rate of change in absorbance at 350 nm following exposure to the different reagents was used to evaluate three model systems for senile nuclear cataract. These model systems utilized calf lens proteins which had been tanned by exposure either to 3-hydroxyanthranilic acid, dopa/tyrosinase, or ultraviolet light.

3-Hydroxyanthranilic Acid↗
PubMed1975

Simultaneous assay for six alkaloids in opium, using high-performance liquid chromatography.

A method is described for the quantitative determination of morphine, codeine, cryptopine, thebaine, papaverine, and narcotine in opium by high-performance liquid chromatography. The alkaloids are isolated from a dilute acid extract by adsorption on an Amberlite XAD-2 resin column and eluted first with methanol and then with chloroform-methanol (3+1). After solvent removal by reduced pressure evaporation, the alkaloids are redissolved in chloroform-methanol (3+1). The sample solution, plus brucine as an internal standard, is injected onto a Corasil II column and eluted with hexane that is gradient programmed with a solution of chloroform-methanol-diethylamine (100+300+1). The absorbances of the separated alkaloids are continuously monitored at 254 nm, using a flow-through ultraviolet double-beam photometer.

Alkaloids↗
PubMed1979

Reversed-phase liquid chromatographic separation of 3',5'-cyclic ribonucleotides.

A rapid, reversed-phase "high-performance" liquid-chromatographic separation of the five naturally occurring cyclic ribonucleotides is described. The separation, optimized for the measurement of these compounds in biological samples, is short (25 min), sensitive (50-100 pmol), and requires no sample pre-concentration steps. We also report an alternative isocratic elution mode, optimized for a rapid and selective analysis for adenosine 3',5'-cyclic phosphate. The identity of chromatographic peaks in biological extracts is confirmed by several methods: retention times, co-chromatography with the reference compounds, absorbance ratios, enzymatic peak-shift with cyclic nucleotide phosphodiesterase, and stopped-flow ultraviolet-scanning techniques.

Animals↗
PubMed1989

Thermal denaturation of alpha-crystallin.

Low molecular weight alpha-crystallin, isolated from cow lenses, exhibit irreversible thermal denaturation in solution at 75 degrees C. The heat of denaturation was obtained from a differential scanning calorimetric endothermic peak. A second run on the denatured alpha-crystallin solution showed that the denaturation is irreversible. Viscosimetric study and ultraviolet absorption spectroscopy also indicated irreversible denaturation.

Animals↗