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At least 811 records · Page 45Linked to original sources
PubMed1998

Optimization of a hydrophobic solid-phase extraction interface for matrix-assisted laser desorption/ionization.

Matrix-assisted laser desorption/ionization (MALDI) probe surfaces derivatized with octadecanethiol (C18) can be used as hydrophobic solid-phase extraction devices to isolate and desalt biopolymers directly on the probe surface. Using quantitative MALDI, it was possible to determine the approximate amount of peptide that bound to C18 surfaces and thus to calculate a surface density. It was determined that the amount of peptide bound at the probe surface was independent of the analyte concentration in the immersion solution (from high- to sub-ng ml-1 concentrations), but rather was dependent on the immersion time of the surface as it was exposed to the analyte. The capacity of C18-derivatized probes to bind biopolymers in fixed amounts frees the analyst from the necessity for adjusting analyte concentration through multiple step procedures such as serial dilution or vacuum drying. This time savings result in an overall increase in the efficiency of the MALDI technique.

Cytochrome c Group↗
PubMed2006

Study on the decomposition of 2-chloroethylnitro- sosulfamides (CENS) in serum using HPLC on-line solid phase extraction.

In this paper we have investigated the kinetic decomposition of 2-chloroethylnitrososulfamides (CENS) in fetal calf serum. The study was monitored by on-line solid phase extraction linked to RP-LC-MS. We demonstrated that CENS are less stable in fetal calf serum than in aqueous buffer at pH 7.4 and 37 degrees C. Moreover, we have shown that partition coefficient of CENS can be correlated to the kinetics decomposition, and we observe that the stability is better for lipophilic CENS. The different metabolites after decomposition have been tentatively identified by RP-HPLC-MS. This study indicates the formation of several metabolites resulting from a mechanism of decomposition more complex than in aqueous phosphate buffer, nevertheless, leading to the same main products.

Animals↗
PubMed2005

Qualitative and quantitative analysis of active flavonoids in Flos Lonicerae by capillary zone electrophoresis coupled with solid-phase extraction.

Flavonoids are an important bioactive group in the commonly used herbal medicine Flos Lonicerae. A new method of capillary zone electrophoresis (CZE) coupled with solid-phase extraction (SPE) was developed for simultaneous assay of flavonoid aglycones and glycosides in Flos Lonicerae. Optimum CZE separation was achieved with a background electrolyte (BGE) solution consisting of 80 mM boric acid and 20 mM phosphate acid, adjusted to pH 8.1, with 15% acetonitrile (v/v) added, and applying a separation voltage of 28 kV. The SPE method was used for pretreating the complex matrix of botanical materials and good reproducibility was obtained when avicularin was used as internal standard. Linearity of the method was excellent with correlation coefficients (r2) in the range of 0.9995-0.9999 and detection limits were lower than 0.6 microg/mL for the four flavonoids. The obtained recoveries varied between 93 to 104% while the relative standard deviations (RSDs) were below 4.4% (n=3). The developed CZE method was successfully used for the separation of eight flavonoids and the quantification of the four flavonoids in five species of Flos Lonicerae.

Animals↗
PubMed1994

High-performance liquid chromatographic and megabore gas-liquid chromatographic determination of levetiracetam (ucb L059) in human serum after solid-phase extraction.

For monitoring drug levels of the new potential anticonvulsant drug levetiracetam (ucb L059) in human serum, two assay methods were developed and compared. A solid-phase extraction procedure was followed by either reversed-phase HPLC separation and UV-detection or GLC separation using cold on-column injection on a megabore column and nitrogen-phosphorous detection. Absolute recovery of the drug exceeded 97%. Precision and accuracy values for the 16.0 micrograms/ml quality control sample were 2.4% and 101 +/- 5% (n = 10), respectively, for the GLC method. Precision and accuracy values for the 12.1 micrograms/ml quality control sample were 1.0% and 100 +/- 1% (n = 7), respectively, for the HPLC method. Agreement between both methods was excellent (r = 0.993). Both methods are suitable for pharmacokinetic studies and therapeutic drug monitoring as well. Serum level data for levetiracetam in a patient on chronic antiepileptic medication are presented.

Autoanalysis↗
PubMed1994

Determination of chlorinated phenols and cresols in human urine using solid-phase extraction and gas chromatography.

A method is described for the isolation, derivatization, separation and determination of chlorinated phenols and cresols in urine. After acid hydrolysis, solid-phase extraction on Separcol SI C18 was used. Quantification was based on the internal standard method using 2,6-dibromophenol. Before GC determination the isolated compounds were derivatized with pentafluorobenzyl bromide. The separation of interfering substances followed on a Ekosorb column using elution with dichloromethane-toluene (15:85). The recovery of the method ranged from 72.3 +/- 9.9 to 109.9 +/- 6.3% and the limit of determination varied from 0.0005 to 0.002 micrograms ml-1. Using this method, 52 persons from occupationally and non-occupationally exposed groups were examined for the presence of chlorinated compounds in urine. The levels of chlorinated phenols and cresols were several times higher in the group of occupationally exposed workers, especially for 2,4-dichlorophenol.

Chemical Industry↗
PubMed1994

Determination of diltiazem and its main metabolites in human plasma by automated solid-phase extraction and high-performance liquid chromatography: a new method overcoming instability of the compounds and interference problems.

An automated sample preparation method, based on solid-phase extraction (SPE) was developed on an ASPEC-Gilson device and combined with HPLC for the determination of diltiazem and three of its metabolites in human plasma (N-desacetylmonodesmethyldiltiazem, N-monodesmethyldiltiazem, O-desacetyldiltiazem). A 1-ml volume of plasma is diluted with 0.5 ml of 0.1 M ammonium dihydrogen phosphate and the sample is automatically loaded onto a SPE silica (C18) column (100 mg); the column is flushed with two different solvents, then eluted with 0.5 ml of a 0.1 M ammonium dihydrogen phosphate-acetonitrile mixture (20:80, v/v) containing 0.06% of triethylamine. The eluate is evaporated to dryness and the residue reconstituted with a suitable solvent and injected onto a C8 silica column connected to a UV detector (lambda = 238 nm). This method overcomes problems caused by the partial instability of diltiazem and metabolites in human plasma during analysis. There is no chromatographic interference from endogenous compounds. The limits of quantitation (LOQ) are 2.5 and 2 ng ml-1 for diltiazem and the metabolites in human plasma, respectively. Linearity between concentrations and detector response for diltiazem and metabolites ranged from 10-200 and 5-100 ng ml-1 in human plasma, respectively. The method has been validated.

Acetylation↗
PubMed2004

Simultaneous solid-phase extraction of acidic, neutral and basic pharmaceuticals from aqueous samples at ambient (neutral) pH and their determination by gas chromatography-mass spectrometry.

Seven polymeric solid-phase extraction (SPE) sorbents were evaluated with regard to their ability to extract acidic, neutral and basic pharmaceuticals and estrogens simultaneously from water at neutral pH. Highest recoveries (70-100%) for the majority of the analytes were obtained with styrene-methacrylate and styrene-N-vinylpyrrolidone co-polymers. The latter one (Oasis HLB) was chosen for further refinement of an extraction method for the quantitative determination of acidic and neutral drugs in surface water samples at detection limits below 1 ng/l. A sequential elution protocol was applied for clean-up and separation of the extracted analytes into fractions suitable for further compound specific processing. The neutral analytes as well as the acidic compounds after derivatisation were quantified by GC-MS. Caffeine, ibuprofen, its metabolites and diclofenac were detected in river water samples in the 1-100 ng/l range.

Chromatography, High Pressure Liquid↗
PubMed2004

Sensitive determination of erdosteine in human plasma by use of automated 96-well solid-phase extraction and LC-MS/MS.

A sensitive and selective method for quantitation of erdosteine in human plasma was established by use of 96-well solid-phase extraction (SPE) and liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI/MS/MS). Plasma samples were transferred into 96-well OASIS HLB extraction plate using an automated sample handling system and the drugs were eluted with methanol. The eluents were then evaporated and reconstituted with mobile phase. All sample transfer and SPE was automated through the application of both the Perkin-Elmer MultiPROBE II HT and TOMTEC Quadra 96 workstation. Compounds were separated on a C18 column with 1 mM ammonium acetate-acetonitrile (80:20, pH 3.2), as mobile phase at a flow rate of 0.3 ml/min. The limit of quantitation (LOQ) was 0.2 ng/ml, using a sample volume of 0.2 ml for the analysis. The reproducibility of the method was evaluated by analyzing three at 14 quality control (QC) levels over the nominal concentration range from 0.2 to 5000 ng/ml. The intraday accuracy was found to range from 99.6 to 105.0% with precision (% RSD) of less than 4.76% at five QC levels. The interday accuracy was found to range from 95.0 to 100.5% with precision of less than 5.26% at five QC levels. Erdosteine produced a protonated precursor ion ([M+H]+) at m/z 250, and a corresponding product ion at m/z 204. Internal standard (letosteine) produced a protonated precursor ion ([M+H]+) at m/z 280 and a corresponding product ion at m/z 160. The high sample throughput of the method has been successfully applied to a pharmacokinetic study of erdosteine in human plasma.

Adult↗
PubMed2001

New polymeric sorbent for the solid-phase extraction of chlorophenols from water samples followed by gas chromatography-electron-capture detection.

A polymeric material, polyaniline, was employed as a new sorbent for solid-phase extraction (SPE) of some environmental pollutants from water samples. Chlorophenols were extracted from aqueous samples by SPE using 120 mg polyaniline and determined by gas chromatography with electron-capture detection. The acetate esters of these phenols were formed by the direct addition of acetic anhydride to the organic extractant in the presence of K2CO3. Different conditions were applied to obtain higher retaining capacity and breakthrough volumes. The results compared with those obtained by other groups. The RSD for a river water sample spiked at sub-ppb level was lower than 10% (n = 3) and detection limits were between 3 and 110 ng(-1).

Chlorophenols↗
PubMed2002

Combination of supported liquid membrane and solid-phase extraction for sample pretreatment of triazine herbicides in juice prior to capillary electrophoresis determination.

A possibility of a combination of supported liquid membrane (SLM) and solid-phase extraction (SPE) for the determination of atrazine at microgram level in different type of fruit juices is presented. In comparison to SPE extraction from juice samples, the application of SLM-SPE enrichment provides much cleaner extracts and the possibility of lowering the limit of detection as low as 30 microg/l. However, it was also shown that by appropriate manipulation of SLM extraction conditions mainly flow-rate of donor phase and volume ratio between donor and acceptor phase, the level of detection can be further decreased to 10 microg/l. The results suggest that the application of SLM extraction prior to SPE is an alternative method for atrazine enrichment from complicated liquid matrices and could be used as routine method for the clean-up of such samples.

Atrazine↗
PubMed2001

Trace determination of 1-octacosanol in rat plasma by solid-phase extraction with Tenax GC and capillary gas chromatography.

1-Octacosanol is the major component of policosanol, a new natural lowering-cholesterol agent. A sensitive solid-phase extraction with a Tenax GC capillary gas chromatography method for determining the proportion of this fatty alcohol in plasma after its denaturation with trichloroacetic acid was developed. The trimethylsilyl ether derivative of the target analyte obtained from the organic extract showed excellent chromatographic properties and was detectable in the low nanogram range (1 ng/ml). Adequate separation from plasma's extract was achieved with a fused-silica capillary column (30m x 0.25 mm I.D.) with SPB-5 (0.5 microm film thickness) and operated with temperature programming from 100 to 200 degrees C at 40 degrees C/min and from 200 degrees C increased at 10 degrees C/min to 320 degrees C, then held for 30 min, the carrier gas flow-rate (argon) was 1 ml/min. Quantification was performed by the internal standard method using 1-hexacosanol. The reliable relative retention parameters and the mass response factors values, and their confidence levels, ensure a proper GC sensitivity, necessary for the determination of the alcohol being analyzed. The method was evaluated to a concentration range from 6 to 47.6 ng/ml of plasma obtaining recoveries from 95 to 98%. The correlation between the theoretical concentration values and the corresponding experimental values was appropriate (gamma=0.9718 x -0.0915; r2=0.9998). The method showed a good within-day (RSD=4.3%) and between-day (RSD=6.0%) precision according to the acceptance criteria (<10%). This procedure was successfully applied to the study of 1-octacosanol in rat plasma samples after a single oral administration (40 mg/kg) of policosanol.

Animals↗
PubMed1997

High-performance liquid chromatography determination of praziquantel enantiomers in human serum using a reversed-phase cellulose-based chiral stationary phase and disc solid-phase extraction.

A sensitive HPLC method for the quantification of praziquantel enantiomers in human serum is described. The method involves the use of a novel disc solid-phase extraction for sample clean-up prior to HPLC analysis and is also free of interference from trans-4-hydroxypraziquantel, the major metabolite of praziquantel. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OJ-R) under isocratic conditions using a mobile phase consisting of 0.1 M sodium perchlorate-acetonitrile (66:34, v/v) at a flow-rate of 0.5 ml/min. Recoveries for R-(-)- and S-(+)-praziquantel enantiomers were in the range of 84-89% at 50-500 ng/ml levels. Intra-day and inter-day precisions calculated as R.S.D. were in the ranges of 3-8% and 1-8% for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.2-5% and 0.3-8% ranges for both enantiomers, respectively. Linear calibration curves were in the concentration range 10-600 ng/ml for each enantiomer in serum. The limit of quantification of each enantiomer was 10 ng/ml. The detection limit for each enantiomer in serum using a UV detector set at 210 nm was 5 ng/ml (S/N=2).

Antiplatyhelmintic Agents↗
PubMed1997

High-performance liquid chromatographic analysis of ondansetron enantiomers in human serum using a reversed-phase cellulose-based chiral stationary phase and solid-phase extraction.

A stereospecific HPLC method was developed for the assay of R-(-)- and S-(+)-ondansetron enantiomers in human serum. The method involves the use of solid-phase extraction for sample clean-up and is also free of interference from 6-hydroxyondansetron, 7-hydroxyondansetron and 8-hydroxyondansetron, the three major metabolites of ondansetron. Chromatographic resolution of the enantiomers was performed on a reversed-phase cellulose-based chiral column (Chiralcel OD-R) under isocratic conditions using a mobile phase consisting of 0.7 M sodium perchlorate-acetonitrile (65:35, v/v) at a flow-rate of 0.5 ml/min. Recoveries at 200 ng/ml levels were more than 90% for both ondansetron enantiomers. Intra-day and inter-day precisions calculated as R.S.D.s were in the 0.3-5% and 2-8% ranges for both enantiomers, respectively. Intra-day and inter-day accuracies calculated as percent error were in the 0.3-11.5% and 0-3% ranges for both enantiomers, respectively. Linear calibration curves were obtained for each enantiomer in serum in the concentration range 15-750 ng/ml. The limit of quantitation of each enantiomer was 15 ng/ml. The detection limit for each enantiomer in serum using UV detection at 210 nm was 7 ng/ml (S/N=2).

Antiemetics↗
PubMedDate not supplied

Analysis of gabapentin in serum and plasma by solid-phase extraction and gas chromatography-mass spectrometry for therapeutic drug monitoring.

A simple method for the determination of gabapentin (Neurontin) is described. The method uses solid-phase extraction by disk column and derivatization followed by gas chromatographic-mass spectrometric analysis. The single-step derivatization with MTBSTFA produces a t-BDMS derivative of both the carboxylic and amine moieties of the molecule. Each step of the procedure was optimized to assure reliable performance of the method. The assay limit of detection was 0.1 microg/mL with a linear range from 1.0 to 35 microg/mL. Within-run (n = 3) and between-run (n = 40) coefficients of variation were less than 8.2 and 15.9%, respectively. The method has proven reliable in routine production for more than a year, producing clean chromatography with unique ion fragments, consistent ion mass ratios, and no interferences. Statistical analysis of the gabapentin concentrations measured in 1020 random specimens over a 2-month period showed a mean concentration of 6.07 microg/mL with a standard deviation of 5.28.

Acetates↗
PubMed1997

Improved separation and determination of phospholipids in animal tissues employing solid phase extraction.

Separation of five glycerophospholipids having different polar groups, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylglycerol (PG) and cardiolipin (CL), was investigated by means of solid-phase extraction (SPE) cartridges. First, the phospholipids were retained in an aminopropyl-bonded phase (NH2) cartridge and subsequently eluted as neutral (PC and PE) and acidic (PS, PG and CL) glycerophospholipid fractions. Secondly, a combination of silica gel (SI) cartridge and NH2 cartridge was employed to separate five glycerophospholipids. The polarity of the eluent was responsible for neutral glycerophospholipid separation. Concerning acidic glycerophospholipids, the separation of PG and CL from PS depended mainly on the pH of the eluents, and the separation of PG and CL was affected by the solvent, depending on eluent polarities. Favorable recovery (not less than 95%, for five authentic phospholipids, 10-100 micrograms each) and repeatability (sigma = 2.3 for 10 micrograms ranges) were attained by the present method. This method of separation was applicable to the analysis of phospholipids in biological samples.

Animals↗
PubMed2006

Determination of a series of quinolones in pig plasma using solid-phase extraction and liquid chromatography coupled with mass spectrometric detection Application to pharmacokinetic studies.

A simple and sensitive liquid chromatography (LC) method was developed for the simultaneous determination of eight quinolones in pig plasma samples. The following two methods of detection were used: ultraviolet (UV) and mass spectrometry with electrospray ionization (ESI/MS). Sample preparation consisted of solid-phase extraction (SPE) on Strata X cartridges prior to the analysis by LC/UV or LC/ESI/MS. The recovery, linearity, limit of detection (LOD) and limit of quantification (LOQ), precision and accuracy of the method were evaluated using spiked pig plasma samples. The suitability of the method for pharmacokinetic studies was evaluated by determining the concentrations of enrofloxacin (ENR) and ciprofloxacin (CIP) also in pig plasma, after administration of 200mg of enrofloxacin per kilogram of fodder during 5 consecutive days.

Animals↗
PubMed2005

Determination of atorvastatin and metabolites in human plasma with solid-phase extraction followed by LC-tandem MS.

The aim of the present study was to develop a chromatographic method for the analysis of atorvastatin, o- and p-hydroxyatorvastatin (acid and lactone forms) in human plasma after administration of atorvastatin at the lowest registered dose (10 mg) in clinical studies. Sample preparation was performed by solid-phase extraction and was followed by separation of the analytes on an HPLC system with a linear gradient and a mobile phase consisting of acetonitrile, water and formic acid. Detection was achieved by tandem mass spectrometry operated in the electrospray positive ion mode. Validation of the method for the compounds for which reference compounds were available (acid forms of atorvastatin, o- and p-hydroxyatorvastatin) showed linearity within the concentration range (0.2-30 ng/ml for atorvastatin acid and p-hydroxyatorvastatin acid, and 0.5-30 ng/ml for o-hydroxyatorvastatin acid) (r2 > or = 0.99, n = 5 for all analytes). Accuracy and precision (evaluated at 0.5, 3 and 30 ng/ml for atorvastatin, p-hydroxyatorvastatin and 1, 3 and 30 ng/ml for o-hydroxyatorvastatin) were both satisfactory. The detection limit was 0.06 ng/ml for atorvastatin and p-hydroxyatorvastatin, and 0.15 ng/ml for o-hydroxyatorvastatin. The method has been successfully applied in a clinical study where atorvastatin, o- and p-hydroxyatorvastatin (both acid and lactone forms) could be detected in a 24-h sampling interval after administration of the lowest registered dose of atorvastatin (10 mg) for one week.

Atorvastatin↗