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At least 1,063 records · Page 59Linked to original sources
PubMed1998

Determination of pravastatin in human plasma by high-performance liquid chromatography with ultraviolet detection.

A sensitive high-performance liquid chromatographic (HPLC) method for the quantitation of the HMG-CoA reductase inhibitor pravastatin in human plasma is described. Sample preparation based on reversed-phase solid-phase extraction using triamcinolone acetonide as internal standard (I.S.). The compounds were separated on C18 reversed-phase analytical column and then determined by ultraviolet detection. The recovery of pravastatin from plasma was 69.2+/-6.7% (mean+/-S.D.). The limit of detection for pravastatin in aqueous solution was 0.4 ng, the limit of quantitation in plasma was 2 ng/ml. In a preliminary pharmacokinetic study with two healthy volunteers the t1/2 of pravastatin in plasma was found to be 0.8 and 2.3 h.

Chromatography, High Pressure Liquid↗
PubMed1999

Determination of bile acids in human faecal samples using supercritical fluid extraction and high-performance liquid chromatography.

A supercritical fluid extraction (SFE) method for the extraction of bile acids from faeces is described. HPLC with pulsed amperometric detection was used to examine and confirm the recovery of bile acids. The analytes were extracted within a period of 75 min using supercritical carbon dioxide at a pressure of 34.5 MPa and a temperature of 90 degrees C. In developing this method the following parameters were investigated: temperature, pressure, and extraction time. Two alternative methods of sample preparation were also investigated with a view to reducing the overall analysis time. The method was validated for the major primary and secondary bile acids found in faeces. It was found that the overall mean +/- SD recoveries were 102.1+/-7.92%, 111.6+/-9.91%, 112.1+/-9.92% and 113.7+/-9.92% for dry samples and 108.5+/-15.77%, 110.0+/-7.22%, 115.9+/-11.11% and 106.6+/-9.16% for wet samples with respect to cholic, deoxycholic, chenodeoxycholic and lithocholic acid. The SFE is an alternative to the traditional methods available. The extraction is relatively easy to conduct and does not utilise as much glassware, solvents or time.

Bile Acids and Salts↗
PubMed2001

Isolation and identification of a degradation product in a capsule formulation containing the elastase inhibitor, DMP 777.

An unexpected degradation product, greater than 0.10%, was observed in a DMP 777 capsule formulation stored at 40 degrees C/75% r.h. for 3 months and 25 degrees C/60% r.h. for 2 years. The degradant of interest was prepared in quantity by refluxing the drug substance in dilute acid. A preparative HPLC method was developed to separate the various degradants and to collect each as a separate fraction. Each fraction was analyzed by the analytical HPLC gradient test method to assure positive identification of each peak and to correlate each peak to the original capsule sample. Key isolated degradation products were used for structure elucidation with mass spectrometry and NMR. The major degradant of interest in the capsule formulation was found to be a carboxylic acid resulting from the acid hydrolysis of an amide bond.

Acids↗
PubMed2002

Electrochemically controlled solid-phase microextraction based on conductive polypyrrole films.

Solid-phase microextraction (SPME) fiber coatings based on conductive polypyrrole films were prepared for the electrochemical extraction and desorption of ionic analytes. Simple preparation of each of the PPY extraction coatings on a platinum wire was possible with a constant potential method, but more importantly, cycling of the film between oxidation and reduction potentials facilitated the extraction and desorption of ionic analytes. The analytes were desorbed into a sample aliquot of water and were determined by flow injection analysis using a mass spectrometer. The fiber coatings and the developed electrochemical SPME method were found to be stable and reproducible (RSD < 5%; N = 5) and could be extended to several cations and anions, confirming the versatility of the approach. Preconcentration of the analyte on the fiber was also possible by repeating the processes to increase the amount of analyte extracted.

Letter↗
PubMed2001

Separation, identification, quantification, and method validation of anthocyanins in botanical supplement raw materials by HPLC and HPLC-MS.

A method has been established and validated for identification and quantification of individual, as well as total, anthocyanins by HPLC and LC/ES-MS in botanical raw materials used in the herbal supplement industry. The anthocyanins were separated and identified on the basis of their respective M(+) (cation) using LC/ES-MS. Separated anthocyanins were individually calculated against one commercially available anthocyanin external standard (cyanidin-3-glucoside chloride) and expressed as its equivalents. Amounts of each anthocyanin calculated as external standard equivalent were then multiplied by a molecular-weight correction factor to afford their specific quantities. Experimental procedures and use of a molecular-weight correction factors are substantiated and validated using Balaton tart cherry and elderberry as templates. Cyanidin-3-glucoside chloride has been widely used in the botanical industry to calculate total anthocyanins. In our studies on tart cherry and elderberry, its use as external standard followed by use of molecular-weight correction factors should provide relatively accurate results for total anthocyanins, because of the presence of cyanidin as their major anthocyanidin backbone. The method proposed here is simple and has a direct sample preparation procedure without any solid-phase extraction. It enables selection and use of commercially available anthocyanins as external standards for quantification of specific anthocyanins in the sample matrix irrespective of their commercial availability as analytical standards. It can be used as a template and applied for similar quantification in several anthocyanin-containing raw materials for routine quality control procedures, thus providing consistency in analytical testing of botanical raw materials used for manufacturing efficacious and true-to-the-label nutritional supplements.

Anthocyanins↗
PubMed1998

Quantitative analysis of valence electron energy-loss spectra of aluminium nitride.

The optical properties and electronic structure of aluminium nitride are determined using valence electron energy-loss spectroscopy in a dedicated scanning transmission electron microscope. Quantitative analysis of the experimental valence electron energy-loss spectra to determine the electronic structure encompasses single scattering deconvolution of the valence electron energy-loss spectra to calculate the energy-loss function, Kramers-Kronig analysis of the energy-loss function to reveal the complex dielectric function, transformation of the dielectric function into the optical interband transition strength via optical property relations and finally critical-point analysis of the interband transition strength. The influence of both experimental and analytical parameters on the final result was studied systematically to define and improve the understanding of the methods. To check the reliability of this technique the interband transition strength determined was compared with results of vacuum ultraviolet spectroscopy. Good agreement was found if sample preparation was taken into account. The preparation of the specimen for the transmission electron microscopy has an effect on the electronic structure. Quantitative analysis of valence electron energy-loss spectroscopy, using the methods presented, is an important and capable method to determine the electronic structure of materials and it has the benefit of high spatial resolution.

Journal Article↗
PubMed2001

A new approach of direct sample-digestion before vaporization for determination of a metal in rocks by inductively coupled plasma atomic emission spectrometry.

A new approach to sample digestion, subsequent vaporization and introduction to an inductively coupled plasma (ICP) atomic emission spectrometer was developed for the direct determination of magnesium. To each small sample cuvette made of tungsten, a ground rock sample was precisely weighed. The cuvette was situated on a tungsten boat furnace. Ammonium fluoride solution was added to the cuvette as a chemical modifier. After the on-furnace digestion has been completed, the analyte, magnesium, in the cuvette was vaporized and introduced into the ICP atomic emission spectrometer. Since the powdered samples were wet-digested in the sample cuvettes prior to vaporization, they could be analyzed by using a calibration curve prepared from aqueous standard solutions. This method was applied to the determination of magnesium in several standard reference materials with satisfactory results.

Journal Article↗
PubMed1989

Determination of vitamin D3 in margarines, oils and other supplemented food products using HPLC.

The vitamin D3 content of high fat foods, such as margarines and oils, was determined by liquid chromatography. The method involved sample saponification and an extraction process, in which the purification of the non-saponifiable matter was the critical step. A semi-preparative straight-phase clean up procedure was used to produce an adequately purified sample solution prior to the final analytical quantification step. Vitamin D2 was used as internal standard when estimating the vitamin D3 content. The overall recoveries depended on the fat content of the food sample and varied from 40% for margarines to 80% for low-fat products at a concentration of about 10 micrograms/100 g. The minimum detectable amount was 0.36 ng vitamin D3. The mean relative recovery of vitamin D3 in relation to vitamin D2 was calculated to be 0.97.

Animals↗
PubMed1986

Production and certification of secondary enzyme reference materials (ERMs). Part 2: The need for meaningful protocols that assure photometric accuracy and a well-defined process for value assignment.

A collaborative study to assign values to two enzyme reference materials (ERMs) was performed by 18 laboratories whose spectrophotometers were checked by us, just before the study. We measured the wavelength accuracy and repeatability, the accuracy and linearity of the absorbance curves, the cuvette pathlength, equilibration time, equilibrium temperature, and a few other variables. Five spectrophotometers exhibited a marked wavelength-dependent nonlinearity. Most instruments were rather slow in bringing the sample to the correct temperature and the final temperature was often too high. In the collaborative study, each participant performed the same manual, well-described methods on four occasions in triplicate, using reagents prepared locally. The relation between the photometric checks and the analytical results is discussed, as well as the treatment of outliers and the effects on the variances. Suggestions are made about various facets of collaborative studies. The values assigned to the two ERMs carry a 95% uncertainty interval of +/- 1-4% of the mean.

Alanine Transaminase↗
PubMed1982

A quality assurance programme for quantitative urine analyses.

Eighty-six Australasian laboratories participated in an interlaboratory quality assurance programme for 10 urine analytes. Twelve liquid samples were prepared from commercial lyophilized urine control material and distributed in 3 batches of 4. Use of pre-set acceptability limits for total laboratory error and target values facilitated timely feedback in graphic form. The samples had concentrations which were linearly related; this allowed simple calculation of overall imprecision and bias, graphic feedback of all submitted results, and comparison of performance between laboratories. A number of unsuitable and poor methods were identified. Particular attention must be paid, in future, to more widespread use of appropriate calibration and quality control materials, to avoidance of transcription and calculation errors, and to analysis of urine samples with elevated levels of analyte. Current laboratory performance can meet analytical goals for analyses of urine creatinine, phosphate, urate, and glucose but analysis of urine sodium, potassium, urea, calcium, osmolality, and proteins require a significant improvement.

Humans↗
PubMed1996

Determination of nitrite in human blood by combination of a specific sample preparation with high-performance anion-exchange chromatography and electrochemical detection.

All photometric or HPLC methods described to date have been unable to detect nitrite, a reliable marker of NO synthase activity, in human blood because of its rapid metabolism within the erythrocytes. We now elaborate on method to prevent nitrite degradation during sample preparation which in combination with high-performance anion-exchange chromatography and electrochemical detection allows a sensitive measurement of nitrite. A linear current response in the concentration range of 10-1000 nmol/l nitrite was observed yielding a correlation coefficient of 0.99. In addition, the combination of the electrochemical with a UV detector allowed us to simultaneously quantify nitrate within one analytical run, which is the end product of NO/nitrite metabolism. Basal levels for nitrate and nitrite in human blood were determined with 25 +/- 4 mumol/l and 578 +/- 116 nmol/l (n = 8), respectively and thus were in the same concentration range as expected from NO measurement in saline perfused isolated organs or cultured endothelial cells. Therefore, the presented method may be used to assess activity of endothelial constitutive NO synthase in humans under physiological and pathophysiological conditions.

Biomarkers↗
PubMed2005

Influence of sodium fluoride on the stability of human blood samples and blood gas measurements.

OBJECTIVE: This study aimed to reduce the analytical error associated with measuring oxygen and carbon dioxide partial pressures as well as the pH in arterial blood samples an hour after sample collection. The standard blood sample preparation procedure involving sample cooling down to 0 degrees C is known to have several drawbacks. Therefore, another approach using NaF at room temperature as an inhibitor of metabolic reactions was introduced. DESIGN AND METHODS: Arterial heparin blood samples from six volunteers were distributed over 104 single capillaries prepared with different concentrations of NaF. The capillaries were filled simultaneously and under the same conditions with blood samples, and the blood gas parameters of each sample were measured. Changes in pO2, pCO2, and pH during storage were evaluated with the aid of t test statistics. RESULTS: During the storage period under investigation, fluctuations of the carbon dioxide partial pressure and the pH were low, whereas there was a significant (P < 0.01) decrease of the oxygen partial pressure. This was observed at all NaF concentrations. Depending on the addition of NaF, a significant baseline shift for the time-resolved pH and pCO2 values could be observed. Whereas the partial pressure of carbon dioxide and the pH could be kept stable by adding a defined amount of NaF, the partial pressure of oxygen decreased significantly over 70 min. CONCLUSIONS: The proposed new method can be practically applied to a comparative blood gas study, significantly reducing the blood sample volume required. The application of analytical grade NaF is an improvement compared to previous work because a pH decrease could not be observed.

Blood↗
PubMed2003

State-of-the-art of gas chromatography-based methods for analysis of anthropogenic volatile organic compounds in estuarine waters, illustrated with the river Scheldt as an example.

This review focuses on a number of key procedural steps in the analysis of volatile organic compounds (VOCs) in estuarine waters. The most critical step, from an analytical point of view, is sample preparation. So far, only purge-and-trap and, to some extent, membrane inlet mass spectrometry have successfully been applied in estuarine monitoring of VOCs. The advantages and disadvantages of both techniques are discussed and novel developments are reviewed. Other key elements in VOC analysis and assessment include quality assurance (QA), quality control (QC) and statistical data analysis. This paper gives a brief overview of QA/QC measures of interest in the estuarine monitoring exercise, and provides guidelines for adequate statistical treatment of environmental data. Finally, field measurements of VOCs in estuarine waters are reviewed. Concentrations are reported, and distribution patterns, sources and time-trends are discussed. In addition to data, results of a 3-year monitoring survey (May 1998-November 2000) in the Scheldt estuary are presented.

Belgium↗
PubMed1987

A high-performance liquid chromatographic microassay employing a liquid-solid extraction technique for etintidine in plasma.

This paper describes a new, rapid solid extraction method for the determination of etintidine in plasma. The method employs a semiautomatic sample preparation system. Plasma samples and the internal standard (cimetidine) were applied onto octyl-bonded silica extraction columns. The extraction columns were then subjected to Tris buffer and water wash and were subsequently loaded onto an automatic sample injection system. The contents of the extraction columns were eluted on-line with a mobile phase of acetonitrile:methanol:0.1% ammonium hydroxide (85:10:5, by volume) onto a silica analytical column and detected by UV absorption at 229 nm. The chromatographic condition separates etintidine from some of its metabolites and other endogenous components in plasma. The detection limit for etintidine was 0.02-0.05 microgram/ml when 0.2 ml of plasma was used. This method has been used for the determination of plasma etintidine levels in humans and mice after oral administration of etintidine and was found to be suitable for pharmacokinetic/bioavailability studies of etintidine in humans and animals. The method can also be used for the quantitative determination of cimetidine and certain metabolites of etintidine.

Animals↗
PubMed2001

Determination of BMS-284756, a new quinolone, in mouse serum by high-performance liquid chromatography with fluorescence detection.

A sensitive, simple, and accurate method for determination of BMS-284756, a novel des-F(6)-quinolone antimicrobial agent in mouse serum was developed by HPLC with fluorescence detection. Sample preparations were carried out by protein precipitation with the addition of acetonitrile, followed by evaporation of the acetonitrile to dryness. The resultant residual was then reconstituted in 0.01 M HCl and injected onto a Nucleosil 100 10 microm, C18 25 cm x 4.6 mm analytical column. The mobile phase consisted of acetonitrile-0.01 M NaH2PO4 (20:80, v/v) with 0.01 M tetrabutylammonium hydrogen sulfate. The fluorescence of the column effluent was monitored at an excitation wavelength of 290 nm and an emission wavelength of 418 nm. The assay was shown to be linear from 0.2 to 10.0 microg/ml (R2=0.998). Mean recovery was determined as 95.1%. Inter- and intra-assay precisions were <6% RSD. The HPLC method developed has been applied to determine the pharmacokinetics of BMS-284756 in a murine bacterial infection model.

Animals↗
PubMedDate not supplied

Reporting degree of deacetylation values of chitosan: the influence of analytical methods.

PURPOSE: To investigate and compare the effect of three analytical methods, hydrogen bromide titrimetry (HBr titrimetry), infrared spectroscopy (IR spectroscopy), and first derivative UV-spectrophotometry (FDUV-spectrophotometry) in the determination of degree of deacetylation (DD) of chitosan. METHODS: Three different chitosan samples were selected for the DD quantification employing HBR titrimetry, IR spectroscopy with samples in the forms of KBr disc (at ratios of 1:2 and 1:3) and thin film (concentrations of 0.5 percent and 1 percent), and FDUV- spectrophotometry. RESULTS: The mean DD values of chitosan samples obtained by HBr titrimetry was significantly lower (p < 0.05) compared to IR spectroscopy using film (concentrations of 0.5 and 1 percent) as well as FDUV-spectrophotometry (purified and unpurified samples), but were significantly higher (p< 0.005) than those obtained using IR spectroscopy using KBr disk except for Chit-S2 computed using baseline (a), which were closely comparable (p > 0.05). In the IR spectroscopic method, the DD values differed when computed using different baseline. It can be observed that the values calculated using baseline (b) was generally higher than those calculated using baseline (a). On the other hand, chitosan samples prepared in the form of film might not be significantly affected by the different baseline as no consistent trend was observed. For FDUV-spectrophotometry, the DD values of purified Chit-S2 samples dried using oven and freeze dryer were comparable and not significantly different (p > 0.05). Similarly, no significant difference was observed for unpurified chitosan samples when dried using freeze dryer and oven (p > 0.05). Furthermore, the DD values of the purified and unpurified chitosan samples dried using freeze dryer were not significantly different except for Chit-S2. CONCLUSION: The DD values of chitosan were highly affected by the analytical methods employed. Hence, we proposed that the quantification method for DD should also be stated when reporting the DD value of chitosan sample.

Acetylation↗
PubMed1997

An isotope-dilution gas chromatography-mass spectrometry method for trace analysis of xylene metabolites in tissues.

A gas chromatography-mass spectrometry (GC-MS) method using isotope dilution was developed to measure trace levels of xylene metabolites in brain tissues. The primary metabolites of xylene are dimethylphenol (DMP), methylbenzyl alcohol (MBA), toluic acid (TA), and methylhippuric acid (MHA). The internal standard was a mixture of deuterated DMP-d3, TA-d7, and MHA-d7. DMP-d3 was commercially available and was used as the internal standard for both DMP and MBA. TA-d7 and MHA-d7 were biosynthesized by administering xylene-d10 to rats and collecting their urine. Based on the noise peaks in 10 blank samples, the on-column limits of quantitation (mean +10 SD of noise peaks) were approximately 305, 1220, 545, and 386 pg for DMP, MBA, TA, and MHA, respectively. Analyte detection and recovery tests from brain tissues of control rats were conducted by spiking the tissues with 32 nmol/g of each analyte, together with the deuterated metabolites. The tissues were homogenized, extracted with ethyl acetate, and derivatized by trimethylsilylation. One microliter of the sample was injected into the GC-MS. The recoveries of the analytes were 104 +/- 8%, 80 +/- 9%, 93 +/- 10%, and 92 +/- 11% (mean +/- SD, n = 7) for DMP, MBA, TA, and MHA, respectively. The tissue preparation efficiency, which was indicated by absolute recoveries of internal standards, was approximately 33% for DMP, MBA, and TA and approximately 80% for MHA. No metabolites were detected in untreated control tissues. This simple and sensitive method to simultaneously detect major xylene metabolites in brain tissues could also be used for the analysis of blood and urine samples from workers to monitor p-xylene exposure.

Animals↗
PubMed2005

Separation of proteins with a molecular mass difference of 2 kDa utilizing preparative double-inverted gradient polyacrylamide gel electrophoresis under nonreducing conditions: application to the isolation of 24 kDa human growth hormone.

A method for separating proteins with a molecular mass difference of 2 kDa using SDS-PAGE under nonreducing conditions is presented. A sample mixture containing several human growth hormone (hGH) isoforms was initially separated on a weak anion-exchange column. Fractions rich in 24 kDa hGH as determined by analytical SDS-PAGE were pooled and further separated by cation-exchange chromatography. The fractions pooled from the cation-exchange chromatography contained two hGH isoforms with a 2 kDa molecular mass difference according to SDS-PAGE analysis, 22 and 24 kDa hGH. The 22 and 24 kDa hGH were separated using continuous-elution preparative double-inverted gradient PAGE (PDG-PAGE) under nonreducing conditions. The preparative electrophoresis gel was composed of three stacked tubular polyacrylamide matrices, a 4% stacking gel, a 13-18% linear gradient gel, and a 15-10% linear inverted gradient gel. Fractions containing purified 24 kDa hGH were pooled and Western blot analysis displayed immunoreactivity to antihGH antibodies. PDG-PAGE provides researchers with an electrophoretic technique to preparatively purify proteins under nonreducing conditions with molecular mass differences of 2 kDa.

Chromatography↗