SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A new method for the determination of phospholipid fatty acids in biological samples, combination of solid-phase extraction (SPE) and fast gas chromatography (GC) was developed. Its application to human plasma and human erythrocytes showed to be robust and reliable for quick and correct identification in routine analysis.
The combination of capillary electrophoresis (CE) and mass spectrometry (MS) with solid-phase extraction (SPE) has been used for the identification of nicotine and eight of its metabolites in urine. The recovery of cotinine from cotinine-spiked urine, by C18 SPE, was found to be 98%. Smokers urine (200 ml) was preconcentrated 200-fold via SPE prior to analysis. The sample stacking mode of CE, when compared to capillary zone electrophoresis, was shown to improve peak efficiency by 132-fold. The combination of hydrodynamic and electrokinetic injection was studied with sample stacking/CE/MS. The on-column limits of detection (LOD) of nicotine and cotinine, by this technique, were found to be 0.11 and 2.25 microg/ml, respectively. Hence, LODs of nicotine and cotinine in urine after 200-fold preconcentration were 0.55 and 11.25 ng/ml, respectively.
This communication describes the invention and further development of the first 96-well solid-phase extraction system and the original purposes to which it was put. We also describe the adaption of this system for bioanalysis of pharmaceutically active small molecules and the needs underlying it. The system has become a world-wide standard for high-throughput bioanalysis and has been extended by others to include, for example, disk-phase extraction and supported liquid-liquid extraction, as well as 384-well systems. The factors that enabled this leap forward in productivity are discussed.
A rapid and simple high-performance liquid chromatography (HPLC) method incorporating automated solid-phase extraction (SPE) is described for the determination of bropirimine, 2-amino-5-bromo-6-phenyl-4(3H)-pyrimidinone, in plasma samples from various species. Using an automated sample processor, plasma samples were loaded onto C18 SPE columns and the drug eluted with ethanol-methylene chloride (10:90, v/v). The extracts were analyzed by reversed-phase HPLC using a C8 column with a mobile phase consisting of acetonitrile-water-trifluoroacetic acid (20:80:0.1, v/v/v). The UV absorbance of the column effluent was monitored at a wavelength of 292 nm. Linear calibration curves were obtained in the range of 0.01 to 22 micrograms/ml. Precision (< or = 4% relative standard deviation) and accuracy (< or = 5% error) were acceptable at the concentrations evaluated. Application of this method to the quantitation of bropirimine in rat plasma for a toxicokinetic/bioavailability study is reported.
The potential of immunoaffinity-based solid-phase extraction (IASPE) coupled on-line to gas chromatography (GC) for the determination of micropollutants was studied with emphasis on the interfacing of the immunoaffinity-based SPE and GC parts of the system. The cartridge containing the immobilized antibodies was coupled to the gas chromatograph via a reversed-phase cartridge (copolymer sorbent). After trace enrichment of the analytes on the immunoaffinity cartridge, they were desorbed and recollected on the reversed-phase cartridge by means of an acidic buffer. After clean-up and drying with nitrogen, desorption and transfer to the GC was done with ethyl acetate via an on-column interface in the partially concurrent solvent evaporation mode. The antibodies used in the immunoaffinity cartridge were raised against atrazine; several s-triazines were used as test compounds. Triazines that were structurally similar to atrazine, showed quantitative recovery. As an application, immunoaffinity SPE-GC was used for the analysis of river and waste water and orange juice. The selectivity of the system was such that non-selective flame ionization detection (FID) could be used to detect the analytes of interest in these complex matrices. The detection limits for 10-ml water samples were 15-25 ng/l for FID and about 1.5 ng/l for the nitrogen-phosphorus detection.
An isocratic high-performance liquid chromatographic method with automated solid-phase extraction has been developed to determine foscarnet in calf and human serums. Extraction was performed with an anion exchanger, SAX, from which the analyte was eluted with a 50 mM potassium pyrophosphate buffer, pH 8.4. The mobile phase consisted of methanol-40 mM disodium hydrogenphosphate, pH 7.6 containing 0.25 mM tetrahexylammonium hydrogensulphate (25:75, v/v). The analyte was separated on a polyether ether ketone (PEEK) column 150x4.6 mm I.D. packed with Kromasil 100 C18, 5 microm. Amperometric detection allowed a quantification limit of 15 microM. The assay was linear from 15 to 240 microM. The recovery of foscarnet from calf serum ranged from 60.65+/-1.89% for 15 microM to 67.45+/-1.24% for 200 microM. The coefficient of variation was < or = 3.73% for intra-assay precision and < or =7.24% for inter-assay precision for calf serum concentrations ranged from 15 to 800 microM. For the same samples, the deviation from the nominal value ranged from -8.97% to +5.40% for same day accuracy and from -4.50% to +2.77% for day-to-day accuracy. Selectivity was satisfactory towards potential co-medications. Replacement of human serum by calf serum for calibration standards and quality control samples was validated. Automation brought more protection against biohazards and increase in productivity for routine monitoring and pharmacokinetic studies.
A method using high-performance liquid chromatography (HPLC) and solid-phase extraction (SPE) is described for the determination of ginsenoside Rg3 in human plasma. A 2.5-ml volume of plasma was mixed with 2.5 ml 60% methanol aqueous solution, and centrifuged at 1100 g for 10 min, the supernatant fluid was further purified by SPE with 200 mg/5 ml 40 microns octadecyl silica and separation was obtained using a reversed-phase column under isocratic conditions with ultraviolet absorbance detection. The intra- and inter-day precision, determined as relative standard deviations, were less than 5.0%, and method recovery was more than 97%. The lower limit of quantitation, based on standards with acceptable RSDs, was 2.5 ng/ml. No endogenous compounds were found to interfere with analyte. A good linear relationship with a regression coefficient of 0.9999 in the range of 2.5 to 200 ng/ml was observed. This method has been demonstrated to be suitable for pharmacokinetic studies in humans. Method development for determination of drug with low UV absorption by SPE and HPLC is also discussed.
A method for the isolation of polychlorinated biphenyls (PCBs) from human blood using solid-phase extraction (SPE) has been developed. The procedure incorporates decomposition of lipids by concentrated sulphuric acid directly on the SPE column. Conditions for transferring PCBs onto the SPE column and washing the decomposed blood components from the SPE column were optimised. After clean-up the extracts were analysed using gas chromatography with electron capture detection. An average recovery of PCBs from spiked blood samples was about 78+/-8% and an average precision was about 109+/-7%. Quantitation has been done using four internal standards and calibration curves based on five concentration levels. Low procedural blanks made it possible to determine PCBs in blood quantitatively at a level down to 2-10 pg g(-1). The integrated method for blood is fast, less laborious than methods using liquid-liquid extraction and has a low consumption of organic solvents.
A selective solid-phase extraction technique has been applied to the analysis of cocaine and selected cocaine metabolites in meconium, whole blood, and plasma. This technique uses a mixed-mode Bond Elut Certify column that utilizes the characteristics of hydrophobic and polar interactions and ion exchange chromatography. Following extraction, cocaine, ecgonine methyl ester, benzoylecgonine, and cocaethylene were identified and quantitated using GC/MS. Linear quantitative response curves have been generated for the metabolites over a concentration range of 0-1000 ng/g for meconium and 0-1000 ng/mL for whole blood and plasma. The overall extraction efficiencies, depending on the metabolite, were between 58.1 and 99.7% for meconium, 95.6 and 124.0% for blood, and 86.9 and 128.9% for plasma. Linear regression analyses of the standard curve for the four analytes exhibited correlation coefficients ranging from 0.850 to 0.946 for meconium, 0.939 to 0.993 for whole blood, and 0.981 to 0.996 for plasma. Because of its capability to detect cocaethylene in meconium, blood, and plasma, the procedure can be used to determine if drug exposure occurred during the latter stages of gestation and if it involved only cocaine or a combination of cocaine and ethanol.
We report an expedient analysis of azathioprine (AZN) in plasma by use of a radial compression liquid chromatography and silica solid phase extraction. The separation of the drug and internal standard (antipyrine) was achieved on a C18 cartridge using a mixture of 0.01 M aqueous solution of sodium phosphate (pH = 4.5) and methanol (87:13; vol/vol) as the mobile phase. The assay is highly specific with no interference from any endogenous substance or concomitantly used drug. The peak height ratio of drug to internal standard was linearly (r greater than 0.09976) related to concentration in the range 0.005-2 micrograms/ml, and the within-run and between-day coefficient of variation did not exceed 6.9% at any concentration. This study measured the steady-state concentration of azathioprine in plasma of renal transplants patients. Also, the applicability of this method to study the pharmacokinetics of AZN following a single intravenous administration was examined, using the rabbit as an in vivo model.
Diatomaceous earth columns used with reversed and normal solid phase extraction (SPE) cartridges were evaluated for the quantitative determination of a number of organophosphorus (OP) and organochlorine (OC) pesticide residues in edible vegetable oils and butterfat. An oil or fat sample (about 2 g) in hexane was passed through a diatomaceous earth (Extrelut QE) column and a C18 bonded silica (ODS) SPE cartridge, resulting in the separation of the pesticides from about 98% of the lipids. The eluate was split in half, with the first portion concentrated into acetone for the determination of OP pesticides by gas chromatography with flame photometric detection (GC-FPD). The other half was passed through an Alumina-N SPE cartridge for additional cleanup of lipid matrix to determine OC pesticides by GC with electron-capture detection (GC-ECD). Average recoveries from fortified samples were greater than 89% for the pesticides studied.
A method for the determination of the basic penicillins, amoxicillin and ampicillin, in animal tissue is described. The method used aqueous extraction with tungstate to remove proteins followed by cation exchange solid phase extraction (SPE) clean-up. This extract was further purified using porous graphitic carbon (PGC) SPE. Extracted residues were derivatized with acetic anhydride followed by triazole/mercuric chloride prior to reversed phase HPLC with UV determination at 325 nm. At the Maximum Residue Limit of 50 micrograms/kg in fortified cattle muscle validation gave mean recoveries for amoxicillin of 57% and 50% on two different days with relative standard deviations of 19% and 15% respectively. For ampicillin the recoveries were 72% and 59% with relative standard deviations of 15% and 19% respectively.
Glycopyrrolate (Robinul) is a quaternary ammonium salt which serves as a respiratory enhancing drug. It is reportedly used in horse racing to improve breathing. Extraction of glycopyrrolate from equine urine employing unique solid-phase extraction techniques gave a residue suitable for liquid chromatography-tandem mass spectrometry (LC-MS-MS) and gas chromatography-mass spectrometry (GC-MS). LC-MS-MS analysis employed an extract derived from 5 ml of urine subjected to cation-exchange chromatography. The daughter ion of m/z 318 monitored in the positive-ion mode was m/z 116. Recovery of glycopyrrolate was 99.5% and the within-run coefficient of variation of two quality control samples (1.0 and 10 ng/ml) was less than 5%. The between-run coefficient of variation for the same two quality control samples was less than 6.5%. The minimal detectable concentration for the assay was 250 pg/ml. Due to the extremely low concentration of glycopyrrolate in urine, qualitative detection via full-scan GC-MS required XAD-2 extraction of 50 ml of urine, cation-exchange chromatography clean-up and a tandem hydrolysis-derivatization procedure. The target analyte for GC-MS qualitative analysis was the methyl ester of hydrolyzed glycopyrrolate. Glycopyrrolate could be detected in post-administration (1 mg intravenously) urine samples for up to 9 h by both LC-MS-MS and GC-MS. The success of the method was due to a combination of the extreme sensitivity of the LC-MS-MS method and the very selective extraction process for quaternary ammonium salts.
A highly selective imprinted amino-functionalized silica gel sorbent was prepared by combining a surface molecular imprinting technique with a sol-gel process for on-line solid-phase extraction-HPLC determination of trace pentachlorophenol (PCP) in water samples. The PCP-imprinted amino-functionalized silica sorbent was characterized by FT-IR, SEM, nitrogen adsorption and the static adsorption experiments. The imprinted functionalized silica gel sorbent exhibited high selectivity and offered a fast kinetics for the adsorption and desorption of PCP. The prepared sorbent was shown to be promising for on-line solid-phase extraction for HPLC determination of trace levels of PCP in environmental samples. With a sample loading flow rate of 5 ml min(-1) for 2 min, an enhancement factor of 670 and a detection limit (S/N = 3) of 6 ng l(-1) were achieved at a sample throughput of five samples h(-1). The precision (RSD) for nine replicate on-line sorbent extractions of 10 microgl(-1) PCP was 3.8%. The sorbent also offered good linearity (r = 0.9997) for on-line solid-phase extraction of trace levels of PCP. The method was applied to the determination of PCP in local lake water, river water and wastewater samples.
A simple, fast, sensitive, and economical field method was developed and evaluated for the determination of hexavalent chromium (CrVI) in environmental and workplace air samples. By means of ultrasonic extraction in combination with a strong anion-exchange solid-phase extraction (SAE-SPE) technique, the filtration, isolation, and determination of CrVI in the presence of trivalent chromium (CrIII) and potential interferents was achieved. The method entails (1) ultrasonication in basic ammonium buffer solution to extract CrVI from environmental matrixes; (2) SAE-SPE to separate CrVI from CrIII and interferences; (3) elution/acidification of the eluate; (4) complexation of chromium with 1,5-diphenylcarbazide; and (5) spectrophotometric determination of the colored chromium-diphenylcarbazone complex. Several critical parameters were optimized in order to effect the extraction of both soluble (K2CrO4) and insoluble (PbCrO4) forms of CrVI without inducing CrIII oxidation or CrVI reduction. The method allowed for the dissolution and purification of CrVI from environmental and workplace air sample matrixes for up to 24 samples simultaneously in less than 90 min (including ultrasonication). The results demonstrated that the method was simple, fast, quantitative, and sufficiently sensitive for the determination of occupational exposures of CrVI. The method is applicable for on-site monitoring of CrVI in environmental and industrial hygiene samples.
A fast stepwise systematic approach for the conversion of conventional reversed-phase high-performance liquid chromatographic (HPLC) assays involving liquid-liquid extraction of biological fluids into fully automated HPLC assays using solid-phase extraction and cartridge exchange is described. The suitability of this procedure is demonstrated for the determination of cebaracetam in human urine.
A sensitive high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (MS/MS) method was developed and validated for the simultaneous quantification of trandolapril and its metabolite trandolaprilat in human plasma using ramipril as an internal standard. Following solid-phase extraction, the analytes were separated using an isocratic mobile phase on a reversed-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M-H]- ions, m/z 429/168 for trandolapril, m/z 401/168 for trandolaprilat and m/z 415/166 for the internal standard. The method exhibited a linear dynamic range of 20-10,000 pg/mL for both trandolapril and trandolaprilat in human plasma. The lower limit of quantification was 20 pg/mL for both trandolapril and its metabolite. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.
Accurate monitoring of tea catechins in biological samples might provide a means of better evaluation of their benefits. The aim of the present study was to develop a rapid method for extracting tea catechins from human plasma samples with a solid-phase extraction technique and to subsequently measure their concentrations using an HPLC system. A human plasma sample spiked with known concentrations of the analyte standards was passed through a Waters Oasis HLB cartridge. After repeated washing, tea catechins were eluted with 70% dimethylformamide containing 0.1% phosphoric acid, and the resulting eluate was injected into an HPLC system. Analytes were separated on a reverse-phase C18 column using an isocratic mobile phase and detected electrochemically. The coefficient of variation for inter- and intraday reproducibility was less than 5.0% and 6.4%, respectively. Linearity was established for the concentration range of 0.01-1.0 microM. The method was successfully applied to measure tea catechin concentrations in the plasma of two healthy subjects who received a single ingestion of a green tea beverage. The proposed method enables the rapid and accurate quantitation of plasma tea catechins and might prove useful for the evaluation of beneficial health effects of tea consumption.