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At least 883 records · Page 49Linked to original sources
PubMed1993

Determination of trimethoprim in bovine serum by high-performance liquid chromatography with confirmation by thermospray liquid chromatography-mass spectrometry.

A high-performance liquid chromatographic (HPLC) method with a detection limit of 5 ng/ml was developed for the analysis of trimethoprim in bovine serum. Trimethoprim and the internal standard, ormetoprim, under alkaline conditions, were first extracted into dichloromethane and then back-extracted into dilute sulphuric acid (0.15 M) and cleaned-up on a C18 cartridge. Trimethoprim was quantified on a C18 column using a triethylammonium acetate-acetonitrile-methanol (16:3:1, v/v/v) mobile phase at a flow-rate of 1.5 ml/min, with ultraviolet detection at 225 nm. This method was used to verify the accuracy of test responses obtained with the Brilliant Black Reduction test, a rapid screening method, for trimethoprim levels in the serum of steers treated with Trivetrin. Confirmation of the presence of trimethoprim in the sample extract was obtained by thermospray HPLC-mass spectrometry.

Animals↗
PubMed1994

Determination of sertraline and desmethylsertraline in human serum using copolymeric bonded-phase extraction, liquid chromatography and gas chromatography-mass spectrometry.

The determination of the new antidepressant drug sertraline and its main metabolite, desmethylsertraline, in human serum is described. A new solid-phase extraction method employing the dual functionality Clean Screen cartridge is presented followed by reversed-phase liquid chromatographic (LC) analysis. The sample preparation yielded extremely clean extracts and absolute recoveries in excess of 90% for both drugs from human serum. The response of the LC system was linear over the concentration range 0.01-2.5 mg/l for both sertraline and desmethylsertraline with a limit of detection of 0.01 mg/l. A gas chromatographic-mass spectrometric (GC-MS) system is also described should confirmation of the drugs be necessary.

1-Naphthylamine↗
PubMed1994

Determination of the enantiomers of bunolol in human urine by high-performance liquid chromatography on a chiral AGP stationary phase and identification of their metabolites by gas chromatography-mass spectrometry.

A high-performance liquid chromatographic method using a chiral AGP column was developed to screen and determine the enantiomers of bunolol in human urine. The recovery of (+)- and (-)-bunolol from urine was 91.79-95.23% at different concentrations. The coefficients of variation (C.V.) were less than 2.1 and 2.3% for intra- and inter-assays, respectively. Urinary metabolites were detected using GC-MS after derivatization with N-methyl(trimethylsilyl)trifluroacetamide. The influences of pH and modifier on a chiral AGP column were studied.

Adult↗
PubMed1995

Purine enzyme activities in peripheral blood mononuclear cells: comparison of a new non-radiochemical high-performance liquid chromatography procedure and a radiochemical thin-layer chromatography procedure.

Purine enzyme activities are usually assayed by radiochemical procedures and often TLC is part of the separation method. In screening patients with rheumatic diseases, these procedures have shown disadvantages like a relatively large coefficient of variation (C.V.) and time-instability. We describe a non-radiochemical reversed-phase HPLC micro-method with UV detection for measurement of activities of purine 5'-nucleotidase (5'NT; EC 3.1.3.5), purine nucleoside phosphorylase (PNP; EC 2.4.2.1) and hypoxanthine guanine phosphoribosyltransferase (HGPRT; EC 2.4.2.8) in human peripheral blood mononuclear cells (PBMC). The HPLC procedure is compared with the radiochemical TLC procedure by testing both with a 5'NT and a PNP assay. Reproducibility is tested with 14 healthy controls in each procedure. Short-term and long-term time-stability is tested by comparing enzyme activities measured immediately after preparation of the PBMC (week 0) with those found after freezing and storage at -20 degrees C for a maximum of 10 weeks. The HPLC procedure is preferable to the radiochemical TLC procedure because it shows significantly better reproducibility and better time-stability and in addition is non-radiochemical and less time-consuming.

Adult↗
PubMed1996

Determination of 3,4-dihydroxyphenyl glycol in plasma by gas chromatography-mass spectrometry and high-performance liquid chromatography methods.

Several modifications of GC-MS and HPLC methods for plasma level DHPG have been described. The effects of storage temperature and stabilizing agents on DHPG stability have been studied. The stabilizing agent has been found to play a more important role than low-temperature storage in preventing DHPG from decomposition during sample storage. A specific and sensitive GC-MS method (electron impact) has been established using stable isotope-labeled DHPG as an internal standard. HPLC has been improved by modifying the conditions, resulting in a good separation of DHPG and internal standard from solvent front other early eluting compounds. Comparison of the GC-MS and HPLC procedures demonstrates a strong correlation between these two methods.

Aluminum Oxide↗
PubMed1996

Thin-layer chromatography and high-performance liquid chromatography for the assay of fatty acid compositions of individual phospholipids in platelets from non-insulin-dependent diabetes mellitus patients: effect of eicosapentaenoic acid ethyl ester administration.

Eight major phospholipids were separated by a TLC method with a one-dimensional developing system without any pretreatment of the plate and the fatty acids incorporated into each phospholipid class were analysed by an improved HPLC method with a simple elution system, which has advantages with respect to resolution and analysis time. The fatty acid compositions of individual phospholipids in platelets were investigated following administration of ethyl cis-5,8,11,14,17-eicosapentaenoate for more than 13 weeks to patients with non-insulin-dependent diabetes mellitus. The cis-5,8,11,14,17-eicosapentaenoic acid compositions of all phospholipid classes were significantly increased with decreasing platelet aggregation rates after the administration. These results suggested that the present method provides the complete separation of individual phospholipids in sufficient amounts to allow fatty acid analysis on the isolated phospholipid moieties.

Blood Platelets↗
PubMed1996

Determination of delta 9-tetrahydrocannabinol from human saliva by tandem immunoaffinity chromatography--high-performance liquid chromatography.

Smoking or ingestion of cannabis causes cognitive, perceptual and behavioural changes, which are responsive for impaired performance in driving motor vehicles. In this paper a novel liquid chromatographic assay for the selective quantification of delta 9-tetrahydrocannabinol, the major indicator of a present cannabis intoxication in saliva, is described. The method involves a column-switching procedure and requires an extremely simple pre-treatment of the sample. Deproteinized saliva was directly injected into the chromatographic system. The clean-up and enrichment procedure was performed in an immunoaffinity column, followed by the transfer of the antigens to an octysilica analytical column. The immunoaffinity sorbent was obtained by covalent immobilization of specific antibodies on epoxy-activated silica. The mobile phase consisted of methanol-aqueous 0.15 mol/1 NaCl solution (elution programmed) and the analyte was detected by measuring the UV absorption at 220 nm. Using an injection volume of 4.5 ml (dilution 3:2, v/v) the limit of quantification was 20 ng/ml, at a signal-to-noise ratio of 5. Recoveries were estimated to be in the range of 70%. Both intra- and inter- day coefficients of variation were below 5%.

Chromatography, Affinity↗
PubMed2004

Comparison of a three-peptide separation by capillary electrochromatography, voltage-assisted liquid chromatography and nano-high-performance liquid chromatography.

A mixture of three peptides was separated by capillary electrochromatography (CEC), nano-HPLC and voltage-assisted LC. In the latter case the charged analytes migrate through a neutral stationary phase driven by electrophoresis while their interaction with the stationary phase provides the basis for a chromatographic separation. The stationary phases used were poly(glycidyl methacrylate-co-ethylene dimethacrylate)-based monoliths that could be used directly as neutral "C1"-type columns for voltage-assisted LC and nano-HPLC, while their application in CEC became possible after derivatization of the epoxy groups with ionogenic N-ethylbutylamine functions. The separation of the peptide mixture was possible in all three modes. Highest plate numbers and resolutions were obtained under voltage-assisted conditions. The elution order showed dependencies on the charge density but also on the hydrophobicity of the peptides and was different in the three investigated chromatographic modes. The effect of changes in the ionic strength and the organic solvent content of the mobile phase on the resolution and the migration behavior of the peptides was investigated and showed the expected behavior. Voltage-assisted LC is suggested as an alternative to CEC for the separation of charged analytes by electrochromatography.

Chromatography, High Pressure Liquid↗
PubMed2004

Determination of hexanal as indicator of the lipidic oxidation state in potato crisps using gas chromatography and high-performance liquid chromatography.

Hexanal (an oxidative state indicator) formed in the headspace of potato crisps during storage was evaluated using two different procedures. First, solid-phase microextraction, an innovative sampling preparation methodology was used. It consisted on the absorption of analytes directly from samples and subsequent thermal desorption on the gas chromatograph (GC) injector. Then, a reversed-phase high-performance liquid chromatographic technique (HPLC) was employed to quantify hexanal in the form of 2,4-dinitrophenylhydrazone derivative. Methods were evaluated in what concerns to validation parameters such as linearity, repeatibility and detection limit. GC (LOD = 1 ng/ml) method resulted in more sensitive method than HPLC (LOD = 9 ng/ml). The most suitable technique for hexanal measurement was selected.

Aldehydes↗
PubMed2005

Identification and quantification of (polymeric) hindered-amine light stabilizers in polymers using pyrolysis-gas chromatography-mass spectrometry and liquid chromatography-ultraviolet absorbance detection-evaporative light scattering detection.

Direct analysis of polymers containing polymeric hindered amine light stabilizers (HALS) by using pyrolysis coupled to GC-MS is applied successfully for fast and straightforward identification of these HALS additives. Each of the HALS additives shows different pyrolysis gas chromatograms containing characteristic pyrolysis products. As a result, HALS additives with very similar chemical structures, e.g. Chimassorb 944 and Chimassorb 2020, can be distinguished. A HPLC method with both ultraviolet (UV) and evaporative light scattering detection (ELSD) is developed to quantify the various HALS additives in extracts of polymers. The critical factor of the HPLC method is the use of a basic amine, like n-hexylamine, as a solvent additive to facilitate the elution of HALS additives. The various HALS additives can be distinguished according to retention time and peak shape and by using different detection methods. The suitability of the developed methods is demonstrated by the analytical performance of the HPLC method and the identification and determination of the actual content of HALS additives in polyolefines using pyrolysis GC-MS and HPLC. The HPLC method can also be used for the determination of the specific migration of HALS additives from food contact materials.

Amines↗
PubMed2005

Stability of fluorinated surfactants in advanced oxidation processes--A follow up of degradation products using flow injection-mass spectrometry, liquid chromatography-mass spectrometry and liquid chromatography-multiple stage mass spectrometry.

The advanced oxidation process (AOP) reagents ozone (O3), O3/UV, O3/H2O2, and H2O2/Fe2+ (Fenton's reagent) were applied to the anionic and the non-ionic fluorinated surfactants perfluorooctanesulfonate (PFOS) and N-ethyl-N-(perfluoroalkyl)-sulfonyl-glycinic acid (HFOSA-glycinic acid) or N-ethyl-N-perfluoroalkyl sulfonylamido-2-ethanol polyethoxylates (NEtFASE-PEG), their methyl ethers (NEtFASE-PEG methyl ether) and partly fluorinated alkyl-ethoxylates (FAEO) dissolved in ultrapure water. To monitor the efficiencies of destruction samples were taken during the treatment period of 120 min. After sample concentration by C18-solid phase extraction (SPE) and desorption MS, coupled with atmospheric pressure chemical ionisation (APCI) or electrospray interface (ESI) was applied for detection. No elimination of PFOS was observed while HFOSA-glycinic acid and AOP treated non-ionic surfactants were eliminated by oxidation. Degradation products could be detected and identified. So PFOS was observed during HFOSA-glycinic acid oxidation. Polyethylene glycols (PEG) and PEG methyl ethers were generated from non-ionic fluorinated surfactants beside their oxidation products--aldehydes and acids--all identified by tandem (MS-MS) or multiple stage mass spectrometry (MSn). AOP treatment of FAEO blend resulted in a mixture of partly fluorinated alcohols, separated and identified using GC-MS.

Biodegradation, Environmental↗
PubMed2005

Simultaneous resolution of overlapping peaks in high-performance liquid chromatography and micellar electrokinetic chromatography with diode array detection using augmented iterative target transformation factor analysis.

In this paper, augmentation has been applied to data matrices, which originate from hyphenated methods that share the same mode of detection, but use different separation methods, HPLC-DAD and MEKC-DAD. A novel method, wavelength shift eigenstructure tracking (WET), has been proposed for the alignment between the wavelength scale of both detectors. WET proves to be suitable for the detection as well as correction of wavelength shift between both detectors. After correction of the wavelength scale, data obtained on both systems have been augmented and submitted to iterative target transformation factor analysis. Augmented curve resolution provides significantly better estimates of the chromatographic and electrophoretic profiles and spectra than the use of non-augmented curve resolution on HPLC and MEKC data separately. It is particularly useful when the pure fraction of a chromatographic peak is less than 0.10. Finally, the relative weight of MEKC versus HPLC in augmentation may be increased using intensity and noise normalisation. However, since noise normalisation and its accompanying decrease in signal-to-noise ratio leads to a loss of information, and, since intensity normalisation may cause a failure of the augmented curve resolution algorithm, benefits and drawbacks of normalisation should be weighed on a case-by-case basis.

Algorithms↗
PubMed2006

Method development for the determination of residual fluorotelomer raw materials and perflurooctanoate in fluorotelomer-based products by gas chromatography and liquid chromatography mass spectrometry.

The methodology for the determination of perfluorooctanoate (C(7)F(15)COO-, PFO), fluorotelomer alcohols (FTOHs: 6-2, 8-2, and 10-2), perfluorooctyl iodide (PFOI), and 8-2-8 fluorotelomer alcohol ester in complex fluorotelomer-based commercial products has been demonstrated and validated. Sample preparation procedures allowing determination of residual levels of these compounds were developed. The analytes were detected either by LC/MS/MS (PFO), LC/MS (FTOHs), or GC/MS (PFOI, 8-2-8 ester). The methods were validated by investigating the recoveries of analytes spiked at multiple levels to authentic sample matrices. The recoveries generally were between 70 and 130%. The limits of detection were in sub-microg/g range and the limits of quantitation were in the mug/g range. The methods were applied to fluorotelomer-based raw materials and fluorotelomer-based surfactants and polymeric products and represent methods useful for the determination of higher carbon chain length homologs as well.

Alcohols↗
PubMed2006

Characterization and quantification of the hydrocarbons fraction of the subcutaneous fresh fat of Iberian pig by off-line combination of high performance liquid chromatography and gas chromatography.

Hydrocarbons in fresh subcutaneous fat of Iberian pig have been analyzed by GC-MS after fractionation of the unsaponifiable fraction with a new off-line combination of HPLC and GC method. The new method proposed improves the recovery and simultaneous quantification of terpenic hydrocarbons in comparison to the traditional LC method. When necessary and for identification purposes, selective ion monitoring (SIM) was used as acquisition mode in GC-MS. To determine the position of the double bonds in the unsaturated hydrocarbon chain the dimethyl disulfide derivatives (DMDS) were obtained. To elucidate the structure of the branched 1-alkenes the hydrocarbon fraction was submitted to hydrogenation. Thirty-five compounds have been identified, including n-alkanes, n-alkenes, branched (n-1,n-2-dimethyl-1-alkenes) and terpenic hydrocarbons, being the most abundant n-alkenes and n-alkanes of even chain of n-C12-n-C26. Besides the hydrocarbons already described in bibliography, a new diterpenic hydrocarbon, ent-kaurene, have been identified for the first time. The compound reported as Neophytadiene by other authors, has been identified as a 20 atoms hydrocarbon with two double bonds, the 7,11,15-trimethyl-heptadeca-1,4-diene.

Animals↗
PubMed2006

Direct analysis of artemisinin from Artemisia annua L. using high-performance liquid chromatography with evaporative light scattering detector, and gas chromatography with flame ionization detector.

Since the isolation of artemisinin 32 years ago, it has been analyzed by different chromatographic techniques. This work compared the analysis of artemisinin from crude plant samples by GC with flame ionization detection (GC-FID) and HPLC with evaporative light scattering detector (HPLC-ELSD). Data is also presented indicating that GC is suitable for the quantification of two of artemisinin precursors (arteannuin B and artemisinic acid) if a mass spectrometer is available. GC-FID and HPLC-ELSD were chosen because of their low cost compared to other detection methods, their ease of operation compared to HPLC with electrochemical detection, and because neither require artemisinin derivatization. Both GC-FID and HPLC-ELSD provided sensitive (ng level) and reproducible results for the analysis of artemisinin from field plants, with a correlation coefficient of r(2)=0.86 between the two methods. Both methods could be easily adapted to the analysis of pharmaceutical-grade artemisinin.

Artemisia annua↗
PubMed2005

Simultaneous determination of nineteen hallucinogenic tryptamines/beta-calbolines and phenethylamines using gas chromatography-mass spectrometry and liquid chromatography-electrospray ionisation-mass spectrometry.

To investigate the trend of non-controlled drugs of abuse, simultaneous analytical methods were developed using GC-MS and LC-ESI-MS for 8 tryptamines/beta-carbolines, 6 phenethylamines of typically non-controlled substances in Japan, and, additionally, five legally controlled tryptamines and phenethylamines originally found in fungi or plants. Moreover, the proposed methods were applied to analyses of these drugs in 99 kinds of products (a total number of 123 products purchased at adult shops or via the Internet over the past 2 years in Japan), which potentially advertised psychotropic/psychoactive effects. The samples were extracted with methanol under ultrasonication. After centrifugation, the extracts were filtered prior to injections. GC-MS analysis was performed using a DB-5MS capillary column. Regarding the LC-ESI-MS analysis; the separation of the target drugs was optimized on an ODS column in acetonitrile/MeOH (7:3)-10 mM ammonium formate buffer (pH 3.5)/acetonitrile (95:5) by a linear gradient program and a quantitative analysis was carried out by the monitoring of each [M+H]+ in the positive ion mode of ESI-MS. As a result of the analyses using GC-MS and LC-ESI-MS, 5-MeO-DIPT (the synthetic substance known by the street name "Foxy") was found in 8 out of the 99 kinds of products. Additionally, AMT (from brown powder), DMT (from dried plant), harmine and harmaline (from dried plant) were also found in some of the 99 products. These analytical methods could be useful for the investigation of the distribution of the non-controlled psychotropic tryptamines/beta-carbolines and phenethylamines in the market.

Calibration↗