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PubMed2007

Control of matrix effects in the analysis of urinary F2-isoprostanes using novel multidimensional solid-phase extraction and LC-MS/MS.

F(2)-isoprostanes (F(2)-iPs), established markers of oxidative stress, exist as four sets of regioisomers. Simultaneous and specific determination of F(2)-iPs can be achieved by liquid chromatography-tandem mass spectrometry (LC-MS/MS). We developed novel methods for urine sample preparation and HPLC to control matrix-related ion suppression effects in the LC-MS/MS analysis of F(2)-iPs. A selective solid-phase extraction (SPE) wash protocol was developed with an Oasis HLB (hydrophilic-lipophilic balance) SPE cartridge using an elution profile of [(3)H]8-iso-prostaglandin (PG)F(2alpha) (iPF(2alpha)-III) when the methanol concentration was increased under acidic, neutral, and base wash conditions. A multidimensional (MD)-SPE method that incorporated size exclusion chromatography [corrected] reverse-phase chromatography, and normal-phase chromatography was developed using an Oasis HLB SPE cartridge and an HLB microElution SPE plate. Average extraction recoveries of the deuterated internal standards of iPF(2alpha)-III and iPF(2alpha)-VI were 62 +/- 8% and 60 +/- 10%. A buffer-free HPLC method for the separation of F(2)-iP isomers was developed on base-deactivated C8 columns. Average matrix effects for iPF(2alpha)-III and iPF(2alpha)-VI were 95 +/- 6% and 103 +/- 5%. The clean extraction of urine F(2)-iPs using MD-SPE and the separation of F(2)-iP isomers using a novel HPLC method did not cause apparent ion suppression in the analysis of iPF(2alpha)-III and iPF(2alpha)-VI using LC-MS/MS. These findings should be useful for establishing a routine LC-MS/MS method for the analysis of F(2)-iPs.

Chromatography, High Pressure Liquid↗
PubMed1999

Determination of zearalenone in grains by high-performance liquid chromatography-tandem mass spectrometry after solid-phase extraction with RP-18 columns or immunoaffinity columns.

In this paper a robust, sensitive and selective LC-MS-MS method for the determination of zearalenone (ZON) in several cereals is described. Sample preparation was performed by extraction of the commodities with a mixture of acetonitrile and water followed by solid-phase extraction with RP-18 columns or immunoaffinity columns. The selective determination of ZON was achieved with an atmospheric pressure chemical ionization interface. Using the negative ion mode a detection limit of 0.5 microg/kg and a determination limit of 1 microg/kg grain was achieved, which is by a factor of 100 more sensitive than the positive ion mode. Zearalanone (ZAN), which does not occur in nature, was used as internal standard for quantification. A linear working range from 1.0 microg/kg to 1000 microg/kg could be achieved in grains with a standard deviation of 4% and recovery rates around 100%. All these results were independent from the grain matrices (maize, barley, oats, wheat) when ZAN was used as internal standard. Sample preparation with RP-18 and immunoaffinity materials gave comparable results. In addition, the method was successfully used for the investigation of naturally contaminated maize samples in the course of an interlaboratory comparison test.

Chromatography, Affinity↗
PubMed2006

Simple, rapid solid-phase extraction procedure for the determination of ultra-trace levels of pyrethroids in ground and sea water by liquid chromatography/electrospray ionization mass spectroscopy.

A method based on liquid chromatography/mass spectroscopy with electrospray ionization in positive mode (LC/ESI-MS) to determine trace levels of pyrethroids in environmental water samples has been developed. The chromatographic and the MS parameters were optimized to obtain the best sensitivity and selectivity for all pesticides. Solid-phase extraction (SPE) using C18 cartridges was applied for preconcentration of pesticide trace levels (ng/L) in both ground and sea water samples. The preconcentration step was carried out with 800 mL of water sample modified with 200 mL of MeOH to improve the recovery percentages in the SPE procedure. The SPE-LC/ESI-MS methodology was applied to determine pyrethroids in ground and sea water samples spiked at ng/L concentration levels. Recoveries obtained in ground water were satisfactory (between 72 and 110%). However, an enhancement of the signals of all pesticides in the sea water was found due to the negative effect of the salt in the ionization source. To eliminate this effect a simple cleanup step of the SPE cartridge using 200 mL of Milli-Q water was performed. The cleanup removed the matrix effect completely from the marine samples. Thus, the recovery percentages ranged from 80 to 115%. The method was applied to determine ng/L of pyrethroids in both ground and marine water samples with precision values lower than 10%.

Chromatography, Liquid↗
PubMed2000

Determination of rotenone residues in raw honey by solid-phase extraction and high-performance liquid chromatography.

A method for determining residues of the insecticide rotenone in raw-honey by high-performance liquid chromatography (HPLC) is described. To extract the residues, organic solvents such as ethyl acetate, n-hexane/dichloromethane and solid-phase extraction with octadecylsilane cartridges or Florisil packed columns were tested. Determination was carried out by reversed-phase HPLC using acetonitrile-buffer phosphate (pH 7) (60:40, v/v) as mobile phase and detection at 210 nm. Although the data showed that the two extraction methods were able to isolate the pesticide residues, the extraction on octadecylsilane cartridges was preferred due to its simplicity and higher recovery. Recoveries depended strongly on the fortification level for the two extraction procedures. Practical determination limits of 0.015 mg/kg were obtained. In the analysis of honeys, from beehives treated with rotenone at therapeutical doses for 1 month, residual amounts below 0.2 mg/kg were found.

Chromatography, High Pressure Liquid↗
PubMed2001

[Determination of polyphenols in tobacco by solid phase extraction and high performance liquid chromatography].

A high performance liquid chromatographic (HPLC) method for the determination of polyphenols in tobacco was studied. Polyphenols can be extracted from tobacco sample by refluxing with 80% (volume fraction) methanol, then subjected to degrease by solid phase extraction with Sep-Pak-C18 column. Chlorogenic acid, rutin, scopoletin, caffeic acid, scopolin and other polyphenols can be separated on a Nova-Pak-C18 column (3.9 mm i.d. x 150 mm) gradiently eluted with methanol and 0.05 mol.L-1 potassium dihydrogen phosphate buffer solution as mobile phase at a flow-rate of 0.5 mL.min-1. Polyphenols were determined at the maximum wavelength of each polyphenol, for chlorogenic acid 326.1 nm, rutin 354.8 nm, scopoletin 344.0 nm, caffeic acid 323.7 nm and scopolin 365.2 nm by photodiode array detector. The main polyphenols in tobacco can be identified with UV spectroscopy. The recoveries of tobacco polyphenols were 94%-105%, and the relative standard deviations were 1.28%-1.49%. This method can be applied to the determination of polyphenols in tobacco with satisfactory results.

Chromatography, High Pressure Liquid↗
PubMed2001

Miniaturized fiber-in-tube solid-phase extraction as the sample preconcentration method for microcolumn liquid-phase separations.

Miniaturized fiber-in-tube solid-phase extraction (fiber-in-tube SPE) has been developed as a solventless sample preconcentration technique for microcolumn liquid-phase separation methods. Short capillaries packed with polymer filaments were employed as the extraction tube and the preconcentration power for phthalates in aqueous solutions was studied. On the basis of the successful on-line coupling of this preconcentration method with liquid chromatography (LC), a more miniaturized extraction cartridge, which is installed in the rotor of the micro-injector, has been developed. With a modified commercially available valve, on-line coupling of this sample preconcentration method to capillary electrochromatography (CEC) was also investigated.

Journal Article↗
PubMedDate not supplied

Plate-to-plate fluorous solid-phase extraction for solution-phase parallel synthesis.

A commercially available Argonaut VacMaster-96 plate-to-plate solid-phase extraction (SPE) station equipped with 24 FluoroFlash cartridges is employed for parallel purification of fluorous reaction mixtures. Each cartridge charged with 3 g of fluorous silica gel has the capability to produce up to 100 mg of purified small molecules. The 24-well receiving plate has a standard footprint that can be directly concentrated in a Genevac vacuum centrifuge. Important issues such as sample loading, product cross-contamination, cartridge reuse, and reproducibility are investigated. The SPE system has been demonstrated in the purification of three small libraries that were produced involving amine scavenging reactions with fluorous isatoic anhydride, amide coupling reactions with 2-chloro-4,6-bis[(perfluorohexyl)propyloxy]-1,3,5-triazine (fluorous CDMT), and amide coupling reactions with a newly developed fluorous Mukaiyama condensation reagent.

Chromatography↗
PubMed1992

Determination of methadone and its metabolites by high performance liquid chromatography following solid-phase extraction in rat plasma.

This paper describes a rapid, quantitative liquid chromatographic analysis and extraction of methadone and its two major metabolites from rat plasma, using difenoxin as the internal standard. Using a C18 column, resolution of all sample components and the internal standard is achieved with a mobile phase of 25:75 acetonitrile-0.08% diethylamine in 1000 mL water, pH 2.3, at a flow rate of 1.5 mL/min. The injection volume is 100 microL. Standards are linear over the range 25-100 ng, with a lower limit of detection for methadone of 0.25 ng. Within- and between-run coefficients of variation (CV) are 1.24% and 2.94%, respectively. Extraction of methadone and its metabolites from rat plasma uses a solid-phase extraction technique that is highly efficient. Extraction efficiencies of 90.3%, 99.6%, 85.9% and 93.8% were achieved for methadone, its primary and secondary metabolites, and difenoxin, respectively.

Animals↗
PubMed2000

On-line coupling of solid-phase extraction with mass spectrometry for the analysis of biological samples. II. Determination of clenbuterol in urine using multiple-stage mass spectrometry in an ion-trap mass spectrometer.

Solid-phase extraction (SPE) was coupled to ion-trap mass spectrometry to determine clenbuterol in urine. For SPE a cartridge exchanger was used and, after extraction, the eluate was directly introduced into the mass spectrometer. For two types of cartridges, i.e. C18 and polydivinylbenzene (PDVB), the total SPE procedure (including injection of 1 mL urine, washing, and desorption) has been optimised. The total analysis, including SPE, elution, and detection, took 8.5 min with PDVB cartridges, while an analysis time of 11.5 min was obtained with C18 cartridges. A considerable amount of matrix was present after extraction of urine over C18 cartridges, resulting in significant ion suppression. With PDVB cartridges, the matrix was less prominent, and less ion suppression was observed. For single MS, a detection limit (LOD) of about 25 ng/mL was found with PDVB cartridges. With C18 cartridges an LOD of only about 50 ng/mL could be obtained. Applying tandem mass spectrometry (MS/MS) did not lead to an improved LOD due to an interfering compound. However, a considerable improvement in the LOD was obtained with MS3. The selectivity and sensitivity were increased by the combination of efficient fragmentation of clenbuterol and reduction of the noise. Detection limits of 2 and 0.5 ng/mL were obtained with C18 and PDVB cartridges, respectively. The ion suppression was 4 to 45% (concentration range: 250 to 1.0 ng/mL) after extraction of urine using PDVB cartridges, and up to 70% ion suppression was observed using C18 cartridges. With MS4, no further improvement in selectivity and sensitivity was achieved, due to inefficient fragmentation of clenbuterol and no further reduction of noise.

Amino Acid Sequence↗
PubMed1995

Development and validation of a sensitive solid-phase-extraction and high-performance liquid chromatography assay for the bioreductive agent tirapazamine and its major metabolites in mouse and human plasma for pharmacokinetically guided dose escalation.

A sensitive solid-phase-extraction and high-performance liquid chromatography (HPLC) method has been developed to investigate the pharmacokinetics and metabolism of the hypoxic-cell cytotoxic agent tirapazamine (1,2,4-benzotriazine-3-amine 1,4-di-N-oxide; WIN 59075, SR 4233), currently in phase I/II studies in the United Kingdom and United States. A sample extraction and concentration process was devised using strong cation-exchange Bond Elut cartridges. Tirapazamine, the mono and zero-N-oxide metabolites (WIN 64012, WIN 60109) were isocratically resolved using a microBondapak phenyl HPLC column and measured using photodiode-array detection. The minimal quantifiable level (MQL) of tirapazamine was 40 ng/ml in mouse plasma and 20 ng/ml in human plasma. Recovery was consistently greater than 80% for all compounds over the concentration range of 20 ng/ml to 20 micrograms/ml. No significant decomposition was observed following up to three freeze/thaw cycles and storage at -70 degrees C for 52 days. The assay was accurate and reproducible, with measured values lying within the limits of defined acceptance criteria. Additional studies to investigate the degree of plasma protein binding showed that tirapazamine did not bind extensively to plasma proteins (binding, 9.7% +/- 0.1% and 18.7% +/- 1.3% in mouse and human plasma, respectively). These small species differences in protein binding are unlikely to have any major impact on the extrapolation of pharmacokinetic data from mice to humans. The assay has now been successfully applied to investigate the pharmacokinetics and metabolism of tirapazamine in mice and patients as part of a pharmacokinetically guided dose-escalation strategy for phase I clinical trials.

Animals↗
PubMed2006

Rapid and simultaneous determination of nonsteroidal anti-inflammatory drugs in human plasma by LC-MS with solid-phase extraction.

A rapid, selective and sensitive analytical method for the simultaneous determination of 16 nonsteroidal anti-inflammatory drugs (NSAIDs) in human plasma was carried out using Oasis HLB solid-phase extraction (SPE), followed by reversed-phase high-performance liquid chromatography and quadrupole mass spectrometry with electrospray ionization operated in the negative ion mode. The recoveries of NSAIDs from human plasma by SPE were greater than 76.7%. The use of a short column packed with small particles enabled rapid and simultaneous determination within 7 min. The detection limits for the NSAIDs were 0.01-0.9 mug/ml using the selected ion monitoring mode.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2006

Sensitive determination of thiamethoxam, imidacloprid and acetamiprid in environmental water samples with solid-phase extraction packed with multiwalled carbon nanotubes prior to high-performance liquid chromatography.

This paper describes a novel method for sensitive determination of thiamethoxam, imidacloprid and acetamiprid based on solid-phase extraction with multiwalled carbon nanotubes as the packed materials. Factors that maybe influence the enrichment efficiency, such as sample flow rate, sample pH, and sample volume, were investigated in detail. Under the optimized conditions, the detection limits of thiamethoxam, imidacloprid and acetamiprid were 6.1, 5.4 and 6.7 ng L(-1), respectively. The experimental results indicated that there was good linearity (R2>0.9993) over the range of 0.08 approximately 100 ng mL(-1) and good reproducibility with the relative standard deviations over the range of 0.7 approximately 1.1% (n=6). The proposed method has been applied to the analysis of real-world water samples, and satisfactory achievements were obtained. The average spiked recoveries were in the range of 87.5 approximately 109.8%. All the results indicated that the proposed method could be used for the simultaneous determination of the three pesticides in environmental water samples at trace levels.

Chromatography, High Pressure Liquid↗
PubMed1993

High-performance liquid chromatographic determination of cardenolides in Digitalis leaves after solid-phase extraction.

For HPLC analysis of cardenolide glycosides of Digitalis lanata the separation of the main compounds from other constituents is useful. An improved method for doing this, based on solid-phase extraction on a C18 modified poly(styrene-divinylbenzene) polymer, is described. The presented assay permits quantitative estimation of more than 50 cardenolides in about 2 mg of dried leaf powder of Digitalis lanata with high speed and accuracy.

Carbohydrate Sequence↗
PubMed1994

Determination of organophosphorus and triazine pesticides in ground- and drinking water by solid-phase extraction and gas chromatography with nitrogen-phosphorus or mass spectrometric detection.

Trace enrichment and determination of ethoprophos, fenamiphos, fenthion, isophenphos, mevinphos, monocrotophos, atrazine and simazine were performed by solid-phase extraction on XAD-2 columns and Sep-Pak C18 cartridges, subsequent elution with an organic solvent and determination by GC with nitrogen-phosphorus detection (NPD) and mass spectrometry in the selected-ion monitoring mode (MS-SIM). Ground- and drinking water volumes of 1-2.5 l at concentrations levels of 0.1-5 micrograms/l were used for application of the method. Both adsorbents provided recoveries of 75-95%. The limits of detection were 0.08-0.60 micrograms/l with NPD and 0.03-0.13 micrograms/l with MS-SIM.

Gas Chromatography-Mass Spectrometry↗
PubMed1992

Determination of pentoxifylline and its metabolites in human plasma by high-performance liquid chromatography with solid-phase extraction.

A simple and reliable method for the determination of pentoxifylline and its main metabolites in human plasma has been developed using high-performance liquid chromatography. After selective solid-phase extraction, pentoxifylline, its metabolites and an internal standard, 7-(2'-chloroethyl)theophylline, were separated on a 5-micron LiChrospher 100 RP-18 column using water-dioxan-acetonitrile (87:6.5:6.5, v/v/v) acidified with acetic acid (0.5%, v/v) as the mobile phase. The analytes were detected at 275 nm. The lowest detectable concentration for all analytes was 25 ng/ml; the recovery was 85%. The assay has been successfully applied to analysis of these compounds in human plasma after administration of an oral dose of 400 mg of pentoxifylline to healthy volunteers.

Administration, Oral↗
PubMed1994

High-performance liquid chromatographic assay for ibuprofen in whole blood using solid-phase extraction.

A precise, accurate, reproducible one-step method for the high-performance chromatographic determination of ibuprofen in whole blood is described. Samples were, after haemolysis, prepared by solid-phase extraction. Analyses were performed using reversed-phase chromatography on a Separon SGX C18 column with a mobile phase of methanol-water (pH 3) and ultraviolet detection at 222 nm. The method was used for pharmacokinetic studies in rabbits.

Animals↗
PubMed1994

Sensitive assay for cocaine and benzoylecgonine using solid-phase extraction and gas chromatography.

An improved method for the simultaneous determination of cocaine and benzoylecgonine by means of gas chromatography with nitrogen-phosphorus detection is described. Following a solid-phase extraction and derivatization of benzoylecgonine to its butyl ester, chromatography was performed using a capillary column. The n-propylester of benzoylecgonine served as the internal standard. The assay was linear from 4 to 2000 ng/ml for both cocaine and benzoylecgonine, with a good precision over this concentration range. This method may be particularly useful for small volume samples since it requires only 250 microliters of plasma for analysis of both cocaine and benzoylecgonine.

Chromatography, Gas↗
PubMed1994

Liquid chromatographic determination of the adenosine receptor agonist CGS 21680 in blood using on-line solid-phase extraction on a phenylboronic acid support and fluorescence detection.

An analytical method is described for the selective determination of A1 or A2 adenosine receptor agonists in blood. By implementing solid-phase extraction using immobilized-phenylboronic acid (PBA) in sample pretreatment, all adenosine derivatives are retained via their intact cis-diol group. On-line desorption of the analytes from the PBA support to the C18 analytical column is performed by injection of a small plug of perchloric acid. Fluorescence and UV detection are employed for the different adenosine derivatives. The method is applied to the determination of 2-[p-(2-carboxyethyl)phenylethylamino]-5'-N- ethylcarboxyamidoadenosine (CGS 21680, I) in blood using fluorescence detection. The only off-line sample handling step is the extraction of blood with ethyl acetate and subsequent evaporation of the extraction solvent. The detection limit of the method was 0.25 ng (signal-to-noise ratio 3:1) and the determination limit for I in blood (pretreatment of 100 microliters) was 5 ng/ml. The method was validated and used to study the pharmacokinetics of I in rats.

Acetates↗