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PubMed1991

Solid-phase extraction of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid from human urine with gas chromatographic-mass spectrometric confirmation.

A selective and sensitive technique has been developed for detecting and identifying 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) in human urine. Using a new, "mixed-mode", bonded silica gel, solid-phase extraction column cartridge, THC-COOH was selectively isolated from urine components. Following extraction, the presence of THC-COOH was confirmed and quantitated using gas chromatography-mass spectrometry (GC-MS) or gas chromatography-flame ionization detection. A linear quantitative response curve for THC-COOH was generated over a concentration range of 10 to 300 ng/ml. Overall extraction efficiency averaged greater than 85% and the quantitative response curve exhibited a correlation coefficient of 0.999. The limit of detection and identification using GC-MS for the drug metabolite was found to be six times below the present NIDA guidelines cut-off concentration of 15 ng/ml.

Chromatography, Gas↗
PubMed2000

Solid-phase extraction for multiresidue analysis of organic contaminants in water.

To overcome the limitations of the detection systems associated with gas or liquid chromatography, a sample pretreatment is required with the objective to provide a sample fraction enriched with all the target analytes and as free as possible from other matrix components. There is now no doubt that solid-phase extraction (SPE) has now become the method of choice for carrying out simultaneously the extraction and concentration of many compounds in aqueous samples. Many recent applications of SPE to multiresidue analysis are reviewed with an emphasis on the importance of the choice of the sorbent and of the sample volume. SPE is particularly well adapted to multiresidue analysis including compounds from a wide range of polarity or characterized by various physico-chemical properties. However, SPE is not completely free from practical problems inherent to the nature of the compounds or to the coupling to the chromatographic systems. Many examples are reported to illustrate these problems which can in most cases be circumvented. New developments in SPE are also reviewed.

Chromatography, Liquid↗
PubMed2000

Mass spectrometric analysis of platelet-activating factor after isolation by solid-phase extraction and direct derivatization with pentafluorobenzoic anhydride.

Platelet-activating factor is the term used to denote a class of extremely potent lipid mediators that consist predominantly of 1-O-alkyl- and 1-O-acyl-2-acetyl-sn-glycero-3-phosphocholines. A method has been devised for rapid isolation of these acetylated phospholipids by solid-phase extraction prior to direct derivatization with pentafluorobenzoic anhydride and analysis by gas chromatography (GC)/electron-capture mass spectrometry. Recovery through the entire method (lipid isolation, derivatization, and purification) typically ranged from 70% to 85%. Using the direct derivatization procedure described here, the practical limit of detection for each of the standard alkyl- and acyl-platelet-activating factor homologs was 1 fmol injected into the GC. Results from the application of the method to the analysis of alkyl and acyl homologs of platelet-activating factor isolated from stimulated human umbilical vein endothelial cells are presented, exhibiting excellent accuracy and precision for a wide range of tissue levels of this class of potent autacoids.

Anhydrides↗
PubMed1988

Measurement of antidepressants using solid-phase extraction and wide-bore capillary gas chromatography with nitrogen-selective detection.

A comprehensive method is presented for the determination of nine antidepressant drugs and metabolites in serum: (1) amitriptyline, (2) nortriptyline, (3) imipramine, (4) desipramine, (5) maprotiline, (6) doxepin, (7) desmethyldoxepin, (8) protriptyline, and (9) trimipramine. Chlorimipramine is used as the internal standard. A simple solid-phase extraction procedure utilizing disposable reversed-phase C18 columns is described. Samples are analyzed by gas chromatography with nitrogen-selective detection using a wide-bore capillary column with a permanently bonded, non-polar stationary phase. The assay possesses linearity to 800 ng/mL for maprotiline and 500 ng/mL for the other antidepressants, sensitivity to at least 25 ng/mL, recovery ranging from 96 to 107%, and between-run precision reflected by CVs of 4.4 to 8.1%. Lack of interference is documented for over 27 commonly prescribed drugs. We conclude that the method reported here is ideally suited for monitoring therapeutic and toxic levels of antidepressant drugs.

Antidepressive Agents↗
PubMed1999

Determination of indinavir in plasma by solid-phase extraction and column liquid chromatography.

Indinavir is a specific and potent HIV protease inhibitor. A new column liquid chromatographic method for the determination of this drug is described. This assay was developed for the clinical monitoring of trough concentrations in AIDS patients, using a 1-mL plasma sample volume. Determination of indinavir was made by a rapid solid-phase extraction procedure with the new polymeric Oasis HLB sorbent followed by a reversed-phase liquid chromatography and a UV detection at 210 nm. A weighted least squares linear regression (weighting factor = 1/y where y = peak height ratio) was used to calculate the equation relating the peak-height ratio of the drug and the internal standard to the concentration of indinavir in the range 10-800 ng/mL (0.014-1.124 microM). At the lower limit of quantification (10 ng/mL), the mean accuracy was 102 +/- 7% and 104 +/- 11% for within- and between-day analysis, respectively. The limit of detection, based on a signal-to-noise ratio of 2:1, was 4 ng/mL (0.006 microM). Compounds of interest were eluted from the extraction cartridges with 300 microL of mobile phase, and mean absolute recoveries of indinavir and internal standard were 66.4% and 80.3%, respectively. No metabolite of indinavir was found to co-elute with the drug or its internal standard. Among the tested drugs, especially nucleoside analogues and the other protease inhibitors used in clinical care, none was found to interfere with the assay at this time. This simple and selective method is suitable for therapeutic indinavir monitoring.

Anti-HIV Agents↗
PubMed2000

Simultaneous determination of the five HIV-protease inhibitors: amprenavir, indinavir, nelfinavir, ritonavir, and saquinavir in human plasma by solid-phase extraction and column liquid chromatography.

A sensitive and selective liquid chromatographic assay has been developed for the determination of the five protease inhibitors currently approved by the Food and Drug Administration (FDA) (amprenavir, indinavir, nelfinavir, ritonavir, and saquinavir) in a single run. Pretreatment of a 1-mL plasma sample spiked with internal standard was made by a solid-phase extraction procedure using a polymeric reversed-phase sorbent. Liquid chromatography was performed using a narrowbore C18 reversed-phase column and gradient elution. A double ultraviolet detection at 265 nm (amprenavir) and at 210 nm (indinavir, nelfinavir, ritonavir, saquinavir and internal standard) was used. Calibration curves were linear in the range 25-10000 ng/mL and the assay has been validated over the range 25-5000 ng/mL. Average accuracy at four concentrations was in the range of 100.5-104.2% and 96.9-100.5% for within-day and between-day, respectively. The coefficients of variation were less than 10%. Mean absolute recoveries varied from 85.4% (ritonavir) to 98.8% (saquinavir). No metabolite of the protease inhibitors was found to coelute with the drugs of interest or with the internal standard. At this time, among the tested drugs, especially all the presently licensed nucleoside and nonnucleoside reverse transcriptase inhibitors that can be used in combination with the protease inhibitors, none was found to interfere with the assay. This method is now in use in the authors' laboratory for the therapeutic monitoring of the HIV-protease inhibitors.

Carbamates↗
PubMed2001

Bioanalysis of racemic reboxetine and its desethylated metabolite in a therapeutic drug monitoring setting using solid phase extraction and HPLC.

Reboxetine is a new antidepressant drug acting as a potent and selective noradrenaline reuptake inhibitor on the noradrenergic neuronal system. Because of an expected interindividual variability in drug metabolism in the clinical practice the need for therapeutic drug monitoring routines in psychiatry is always a prominent feature. In this application, the preferred bioanalytic methodology was solid phase extraction combined with reversed-phase high-performance liquid chromatography and ultraviolet detection at 210 nm. The technique proved reliable, with interday and intraday variation of less than 5% and a quantification limit for reboxetine and one of its main metabolites O-desethylreboxetine (O-reboxetine) at 5 and 30 nmol/L, respectively. The method was applied on serum samples from 38 patients treated chronically with reboxetine. These samples were drawn as trough levels in steady state with a dosage range of 2-16 mg/day. They evidenced a mean reboxetine concentration that was fairly linear and dose proportional, although the variance in concentration was large between patients, even those taking the same dosage. O-reboxetine was detected in quantifiable amounts in only 1 of the 38 patients (<3%). In conclusion, these results suggest that a routine reboxetine therapeutic drug monitoring service that is robust enough to produce reliable and reproducible results may be introduced into everyday clinical practice.

Adrenergic Uptake Inhibitors↗
PubMedDate not supplied

Urinary 5 alpha-androstanediol and 5 beta-androstanediol measurement by gas chromatography after solid-phase extraction and high-performance liquid chromatography.

Urinary androstanediol measurement, often in association with other androgens, is commonly used to support the clinical diagnosis of idiopathic hirsutism. In addition, androgen excess has been shown to be the endocrine abnormality which characterizes patients with breast cancer. We recently developed a method for the measurement of urinary testosterone employing solid-phase extraction and HPLC purification before quantitative measurement by gas chromatography. In the present report we verify the feasibility of the method for the simultaneous measurement of 5 alpha-androstane-3 alpha,17 beta-diol and 5 beta-androstane-3 alpha,17 beta-diol in addition to testosterone in the same urine sample. The mean recovery for the whole procedure was 89.8% for 5 alpha-androstane-3 alpha,17 beta-diol and 87.8% for 5 beta-androstane-3 alpha, 17 beta-diol. The estimates of the coefficients of variation were 4.9% (95% confidence limits: 3.9-6.5%) and 3.9% (95% confidence limits: 3.1-5.2%), respectively. Accuracy was evaluated by standard addition and dilution assays and a linear relationship was found between expected and observed values (r2 = 0.997 for 5 alpha-androstane-3 alpha,17 beta-diol and r2 = 0.999 for 5 beta-androstane-3 alpha,17 beta-diol). The method is rapid, effective and suitable for the measurement of testosterone, 5 alpha-androstanediol and 5 beta-androstanediol in the same urine sample.

Androstane-3,17-diol↗
PubMedDate not supplied

Solid phase extraction and simultaneous high performance liquid chromatographic determination of antipyrine and its major metabolites in urine.

A reversed phase gradient high performance liquid chromatographic method utilizing solid phase extraction has been described for the simultaneous determination of antipyrine (AP), 4-hydroxyantipyrine (4-OHAP), norantipyrine (NorAP) and 3-hydroxymethylantipyrine (3-OHMAP) in human urine after hydrolysis with beta-glucuronidase. The C-18 sorbent cartridges were conditioned and urine samples were applied, washed with 1 x 4 mL of phosphate buffer and eluted with 3 x 100 microL of 20% v/v of acetonitrile in methylene chloride. The eluent was evaporated to dryness, reconstituted in 100 microL phosphate buffer and injected. The calibration ranges were 2.0-250 micrograms/mL (AP), 2.5-250 micrograms/mL (NorAP), 2.0-250 micrograms/mL (3-OHMAP) and 5.0-500 micrograms/mL (4-OHAP) with regression coefficients of 0.998 or greater. Specificity was indicated by the absence of interferences in chromatogram of blank urine from normal as well as cirrhotic patients. The average recovery was 86.7% for AP, 90.5% for NorAP, 85.2% for 4-OHAP and 74.2% for 3-OHMAP. The within-assay precision as indicated by the reproducibility of the assayed spiked urine was less than 9% in all cases and the between-assay precision was less than 12%. The method was applied to studies on antipyrine metabolism in stable cirrhotic patients. Following administration of a single oral dose of about 1000 mg to nine stable cirrhotic patients and eight age-matched healthy volunteers, the cumulative account excreted in the urine up to 48 h for AP and the three metabolites was comparable to other literature reports.

Antipyrine↗
PubMed1996

Solid-phase extraction of the chromium(III)-diphenylcarbazone complex prior to ion-pair chromatography and application to geological samples.

A method for the pre-treatment of acid samples prior to ion chromatography is described. In a strong acid medium, Cr(VI) oxidizes diphenylcarbazide, the resulting products forming a stable complex which can be transferred in a methanolic medium by solid-phase extraction using polyethylene as sorbent. This methanolic sample solution can be injected directly into a chromatographic system with a silica-based column. The separation and determination of the chromium complex can be performed by HPLC-using a mobile phase of 15% (v/v) acetonitrile containing 1 mmol/L tetrabutyl ammonium hydroxide (TBAH). The detection limit is estimated to be 2 microg/L chromate and the linear range is at least 0.05-2 mg/L chromate.

Journal Article↗
PubMed1993

Simultaneous screening and quantitation of alpidem, zolpidem, buspirone and benzodiazepines by dual-channel gas chromatography using electron-capture and nitrogen-phosphorus detection after solid-phase extraction.

A rapid twin-column gas chromatographic (GC) method for simultaneous screening and determination of commonly prescribed benzodiazepines and other new anxiolytics from plasma is described. Identical fused-silica Ultra 2 (5% phenyl methyl silicone) columns were connected to nitrogen-phosphorus and electron-capture detectors. The drugs were isolated from 1 ml of plasma by solid-phase extraction (SPE) onto a C8 reversed-phase sorbent and recovered with 0.5% acetic acid in methanol. The eluate was reconstituted with isopropanol which was found suitable for on-column injection. Prazepam was used as internal standard. The method was found appropriate for the quantification in a single run of alpidem, alprazolam, buspirone, chlordiazepoxide, clobazam, clotiazepam, diazepam, estazolam, flunitrazepam, lorazepam, midazolam, oxazepam, tofisopam, triazolam, and zolpidem within 30 min. Limits of quantification allow toxicological or pharmacological determinations, except for buspirone: only toxic blood levels can be quantified by this method. This first SPE of imidazopyridines (alpidem and zolpidem) provides faster, more efficient and cheaper sample preparation than the traditional liquid-liquid procedure. This GC analysis of alpidem and zolpidem is also the first described procedure for simultaneous quantification of all different classes of anxiolytics.

Anti-Anxiety Agents↗
PubMed1987

Determination of ethylenediaminetetra-acetic acid in aqueous rinses of detergent-washed rubber stoppers of pharmaceutical vials using solid-phase extraction and capillary gas chromatography.

A fused silica capillary gas chromatographic method is presented for the determination of traces of ethylenediaminetetra-acetic acid (EDTA) in aqueous rinses of rubber stoppers of pharmaceutical vials after treatment with detergents containing EDTA. Isolation and enrichment of EDTA from the aqueous medium is achieved using a commercially available strong anion-exchange solid-phase extraction cartridge, transformed to the formate form. A 2.0-ml volume of methanolic HCl is used for both elution of EDTA from the extraction column and formation of the tetramethyl ester derivative. With the incorporation of a methanolic wash to eliminate interfering components prior to elution with methanolic HCl, a limit of detection of 25 ng EDTA per ml water with a non-selective flame ionization detector is possible.

Journal Article↗
PubMed2004

Determination of alkylbenzene metabolites in groundwater by solid-phase extraction and liquid chromatography-tandem mass spectrometry.

Benzylsuccinate (BSA), methylbenzylsuccinate (methylBSA), and ethylbenzylsuccinate (ethylBSA) are unambiguous anaerobic biotransformation products from toluene, xylenes, and ethylbenzene decay, respectively, and may be used to indicate intrinsic bioremediation is occurring at hydrocarbon-contaminated sites. In order to improve upon current methods that detect and quantify anaerobic hydrocarbon metabolites in field samples, solid-phase extraction (SPE) and direct sample injection methods coupled with liquid chromatography-tandem mass spectrometry (LC-MS-MS) were evaluated. In laboratory studies, recoveries of authentic standards of non-deuterated or deuterated benzylsuccinates and toluates ranged from 80 to 106% with relative standard errors ranging from 2 to 4%. The method detection limits for these analytes using SPE-LC-MS-MS ranged from 0.006 to 0.029 microg/L whereas those for direct injection-LC-MS-MS ranged from 0.61 to 1.5 microg/L. Given the increased sensitivity of using SPE coupled with LC-MS-MS, this technique was then used to analyze for the presence of putative anaerobic alkylbenzene metabolites in groundwater from a hydrocarbon-contaminated site where single-well push-pull tests were conducted using deuterated aromatic hydrocarbons. Both deuterated and non-deuterated benzylsuccinates and toluates were successfully detected and quantified in field samples using this method.

Benzene Derivatives↗
PubMed1998

Comparative study of a solid-phase extraction system coupled to capillary electrophoresis in the determination of haloacetic compounds in tap water.

This study compares four different commercial sorbents, LC-SAX (a quaternary ammonium anion exchanger), LiChrolut EN (a highly crosslinked styrene-divinylbenzene), Envi-Carb (a graphitized carbon black) and Oasis HLB [a macroporous poly(divinylbenzene-co-N-vinylpyrrolidone) copolymer], for the solid-phase extraction (SPE) of various haloacetic compounds from aqueous samples. The recoveries with the different sorbents were studied by coupling an off-line SPE system to capillary electrophoresis with indirect photometric detection. The recoveries were highest when LiChrolut EN was used. The limits of detection for the compounds are in the low microgram per litre range and the recovery values are over 80% for dichloroacetic acid and trichloroacetic acid, two of the most habitual haloacetic acids in chlorinated water, when 500 ml of standard solution was preconcentrated using this sorbent. Finally, the performance of the method with different water samples, the effect of chlorination in a treatment plant and the evolution of the haloacetic acids in the water distribution system were tested and the results were compared with those obtained using liquid-liquid extraction and gas chromatography-mass spectrometry.

Dichloroacetic Acid↗
PubMed2005

Automated on-line solid-phase extraction coupled with HPLC for measurement of 5-hydroxyindole-3-acetic acid in urine.

BACKGROUND: Quantification of 5-hydroxyindole-3-acetic acid (5-HIAA) in urine is useful in diagnosing and monitoring of patients with carcinoid tumors and in the study of serotonin (5-hydroxytryptamine) metabolism in various disorders. We describe an automated method that incorporates on-line solid-phase extraction (SPE) and HPLC to measure urinary 5-HIAA. METHODS: Automated prepurification of urine was accomplished with HySphere-resin GP SPE cartridges containing strong hydrophobic polystyrene resin. The analyte (5-HIAA) and internal standard [5-hydroxyindole-3-carboxylic acid (5-HICA)] were eluted from the SPE cartridge, separated by reversed-phase HPLC, and detected fluorometrically with a total cycle time of 20 min. Urinary excretion of 5-HIAA was measured in a group of patients with known and suspected carcinoid tumors (n=63) and in 20 patients with autism. RESULTS: The internal standard (5-HICA) and 5-HIAA were recovered in high yields (87.2%-114%). Within- and between-series CVs for the measurement of 5-HIAA in urine ranged from 1.2% to 3.9% and 3.2% to 7.6%, respectively. For urine samples from patients with known or suspected carcinoid tumors, results obtained by the automated method were highly correlated (r=0.988) with those from an established manual extraction method. For samples from autistic patients, urinary excretion of 5-HIAA was similar to that reported for healthy individuals. CONCLUSION: This SPE-HPLC method demonstrated lower imprecision and time per analysis than the manual solvent extraction method.

Autistic Disorder↗
PubMed2002

Stability study and determination of benzene- and naphthalenesulfonates following an on-line solid-phase extraction method using the new programmable field extraction system.

Seven benzene- and naphthalenesulfonates (3-nitrobenzenesulfonate, 4-methylbenzenesulfonate, 1-hydroxy-4-naphthalenesulfonate, 1-amino-7-naphthalenesulfonate, 4-chlorobenzenesulfonate, 1-naphthalenesulfonate and 2-naphthalenesulfonate) were studied. A rapid method for quantifying aromatic sulfonated compounds from waste water samples was developed. This method consists in on-line in-field sampling and monitoring based on ion-pair solid-phase extraction with PLRP-S sorbent, using the new programmable field extraction system and ion-pair liquid chromatography with UV diode-array and electrospray mass spectrometry. Limits of detection for the studied compounds, using the SIM acquisition mode, ranged from 0.01 to 0.33 ng ml(-1). The influence of the aqueous matrix on the on-line SPE was checked by spiking ground and waste waters. Recoveries varied from 70 to 99% when 10 ml of water sample were enriched. The method was applied to the analysis of some environmental sewage samples. This study confirmed that high concentration levels of aromatic sulfonated compounds can be found in sewage samples. In addition, the stability of the seven studied sulfonated benzene and naphthalene compounds was investigated using on-line polymeric SPE pre-columns, based on the styrene-divinylbenzene polymer PLRP-S. Different storage conditions were tested to carry out the stability survey, which included storage at room temperature, at 4 degrees C and at -20 degrees C, during a period of up to 2 weeks. This study showed that the stability of aromatic sulfonic acids on disposable on-line SPE polymeric pre-columns is related to temperature and that the target compounds are more stable at lower temperatures.

Benzenesulfonates↗
PubMed2006

Solid-phase extraction of 4(5)-methylimidazole (4MeI) and 2-acetyl-4(5)-(1,2,3,4-tetrahydroxybutyl)-imidazole (THI) from foods and beverages with subsequent liquid chromatographic-electrospray mass spectrometric quantification.

A method for the simultaneous determination of 4(5)-methylimidazole (4MeI) and 2-acetyl-4(5)-(1,2,3,4-tetrahydroxybutyl)-imidazole (THI) was developed using SPE and HPLC/MS. Solid-phase extraction using SCX Disc cartridges was used for isolation of the analytes from liquid samples. The lower LOQwas 0.1 ng/mL for 4MeI and 0.2 ng/ mL for THI. The linearity of the calibration curves was satisfactory as indicated by correlation coefficients >0.999. The CV for the intra- and inter-day precision was <5% (n = 6); the accuracy was in the range 98-103%. The recovery was > or = 97 and > or = 98% for THI and 4MeI, respectively. The method was used to determine THI and 4MeI in beverages, coffee, caramel colours and other samples.

Beverages↗
PubMed1994

Isolation and quantitation of long-chain acyl-coenzyme A esters in brain tissue by solid-phase extraction.

Long-chain acyl-CoA's are important intermediates in fatty acid oxidation and phospholipid metabolism. For quantitative analysis of brain acyl-CoA's, and to avoid decomposition due to high brain acyl-CoA hydrolase activity, a fast and efficient analytical method was developed for isolation and determination of acyl-CoA's. The analysis includes solid-phase extraction by an oligonucleotide purification cartridge and HPLC measurements using a synthetic internal standard. Estimates of concentration in rat brain are oleoyl-CoA (11.0 nmol/g), palmitoyl-CoA (6.0 nmol/g), stearoyl-CoA (4.0 nmol/g), and linoleoyl- and arachidonoyl-CoA (2.0 nmol/g) for a total concentration of 23 nmol/g brain.

Acyl Coenzyme A↗