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PubMed1999

Characterization of a solid-phase extraction device for discontinuous on-line preconcentration in capillary electrophoresis-based peptide mapping.

Peptide mapping by capillary electrophoresis (CE) with UV detection is problematic for the characterization of proteins that can only be obtained at low micromolar concentrations. Dilution of peptide fragments during digestion of the protein can further reduce the detection sensitivity in peptide mapping to the point where analysis at sub-micromolar concentrations is not possible. A remedy to this problem is preconcentration (sample enrichment) of the proteolytic digest by solid-phase extraction (SPE). To minimize non-specific adsorptive losses during sample handling, on-line SPE-CE is preferred. However, packed-inlet SPE-CE is not always feasible due to either instrument or sample limitations. We describe here a simple method of preconcentration by discontinuous on-line SPE-CE, specifically applied to peptide mapping in low-pH separation buffer after protein digestion in a solid-phase enzyme microreactor. The SPE-CE system does not require application of a low pressure during electrophoretic separation to overcome reversed electroosmotic flow because the preconcentrator device is disconnected from the separation capillary before the electric field is applied. Up to a 500-fold preconcentration factor can be achieved with this device, which can be reused for many samples. Parameters such as the volume of desorption solution, the adsorption/desorption (chromatographic) process, reproducibility of packing the SPE preconcentrator and effects of sample concentration on the peptide map are investigated.

Adsorption↗
PubMed1985

Solid phase extraction system for vitamin D and its major metabolites in human plasma.

A new procedure using C18 and silica cartridges for the extraction and subsequent separation of vitamin D and its major metabolites from plasma has been developed and compared to a conventional extraction procedure with respect to lipophilic material extracted as evaluated by high-performance liquid chromatographic profiles. The C18 cartridges were efficient in extracting all compounds tested while subsequent chromatography of the extract on silica cartridges was effective in resolving vitamin D and its metabolites based on increasing polarity. High-performance liquid chromatographic profiles of each silica cartridge fraction clearly demonstrated that the newly conceived solid phase extraction was superior to conventional extraction methods with respect to cleanliness of sample fractions. This difference in lipophilic load between the new and conventional extraction systems was most apparent in the vitamin D and 25-hydroxyvitamin D containing fractions. The new extraction system can be used when total extraction and subsequent analysis of vitamin D and its major metabolites is desired.

Chromatography, Gel↗
PubMed2005

Simultaneous determination of a novel KDR kinase inhibitor and its N-oxide metabolite in human plasma using 96-well solid-phase extraction and liquid chromatography/tandem mass spectrometry.

To support pharmacokinetic studies, a selective and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the simultaneous determination of a novel KDR kinase inhibitor (1) and its active metabolite (2) in human plasma. The method is fully automated using a Packard MultiPROBE II system and a TomTec Quadra 96 liquid handling workstation to perform sample preparation and solid-phase extraction (SPE). Following the extraction on a mixed-mode SPE using Oasis MCX 96-well plate, the analytes were separated on a Aquasil C18 column (50 mm x 2.1 mm, i.d., 3 microm) with a mobile phase consisting of acetonitrile/ammonium acetate buffer (5 mM, pH 5.0) (60/40, v/v). The run time for each injection was 4.5 min with the retention times of approximately 2.0 and 2.7 min for 1 and 2 respectively, at a flow rate of 0.25 mL/min. A tandem mass spectrometric detection was conducted using multiple reaction monitoring (MRM) under the positive ion mode with a turbo ion-spray interface. The linear ranges of the calibration curves were 0.05-400 ng/mL for 1 and 0.1-400 ng/mL for 2 on a PE Sciex API 4000 LC-MS/MS system. The lower limits of quantitation (LLOQ) of the assay were 0.05 and 0.1 ng/mL for 1 and 2 respectively, when 0.4 mL of plasma was processed. Intra-day assay precision (using five standard curves prepared by spiking compounds to five lots of plasma) was less than 4.9% for 1 and less than 9.6% for 2 on each concentration. Assay accuracy was found to be 95.1-104.6% of nominal for 1 standards and 93.5-105.6% for 2 standards. QC samples were stable when kept at room temperature for 4 h, at -70 degrees C for 10 days, and after three freeze-thaw cycles. The extraction recoveries were 80%, 83% and 84% for 1 and 2 and I.S. respectively, and no significant matrix effects were observed. The method was successfully applied to plasma samples from clinical studies after oral administration of compound 1.

Chromatography, High Pressure Liquid↗
PubMed1989

Determination of baclofen and alpha-baclofen in rat liver homogenate and human urine using solid-phase extraction, o-phthalaldehyde-tert.-butyl thiol derivatization and high-performance liquid chromatography with amperometric detection.

Methods were developed for the determination of the zwitterionic compounds baclofen and alpha-baclofen in complex biological samples (rat liver homogenates and human urine) in concentration ranges that would be suitable for pharmacokinetic studies of these compounds. In the procedure, the biological samples along with an internal standard were selectively concentrated using C18 solid-phase extraction cartridges, evaporated, derivatized with o-phthalaldehyde and tert.-butyl thiol at room temperature for 2 min, then subjected to high-performance liquid chromatographic analysis. The reversed-phase (C18) chromatographic analysis with amperometric detection (glassy carbon electrode in oxidative mode, +0.6 V vs. Ag/AgCl) was found to be useful for the measurement of both baclofen and alpha-baclofen from 10 ng/ml to 10 micrograms/ml in these complex biological samples. The primary advantage of the method was that the derivatives formed using tert.-butyl thiol were markedly more stable than the previously reported derivatives prepared using mercaptoethanol.

Animals↗
PubMed2007

Simultaneous determination of N7-alkylguanines in DNA by isotope-dilution LC-tandem MS coupled with automated solid-phase extraction and its application to a small fish model.

In the present study, we report the development of a sensitive and selective assay based on LC (liquid chromatography)-MS/MS (tandem MS) to simultaneously measure N7-MeG (N7-methylguanine) and N7-EtG (N7-ethylguanine) in DNA hydrolysates. With the use of isotope internal standards (15N5-N7-MeG and 15N5-N7-EtG) and on-line SPE (solid-phase extraction), the detection limit of this method was estimated as 0.42 fmol and 0.17 fmol for N7-MeG and N7-EtG respectively. The high sensitivity achieved here makes this method applicable to small experimental animals. This method was applied to measure N7-alkylguanines in liver DNA from mosquito fish (Gambusia affinis) that were exposed to NDMA (N-nitrosodimethylamine) and NDEA (N-nitrosodiethylamine) alone or their combination over a wide range of concentrations (1-100 mg/l). Results showed that the background level of N7-MeG in liver of control fish was 7.89+/-1.38 mmol/mol of guanine, while N7-EtG was detectable in most of the control fish with a range of 0.05-0.19 mmol/mol of guanine. N7-MeG and N7-EtG were significantly induced by NDMA and NDEA respectively, at a concentration as low as 1 mg/l and increased in a dose-dependent manner. Taken together, this LC-MS/MS assay provides the sensitivity and high throughput required to evaluate the extent of alkylated DNA lesions in small animal models of cancer induced by alkylating agents.

Alkylation↗
PubMed2005

Purification and determination of plant hormones auxin and abscisic acid using solid phase extraction and two-dimensional high performance liquid chromatography.

A method for separation and purification of plant hormones auxin and abscisic acid based on mixed mode reversed-phase anion-exchange solid phase extraction and two-dimensional HPLC was developed. Two-dimensional HPLC in "heart cutting" mode was very efficient in the purification of these two hormones. Its purification power is high enough to allow reliable on-line quantification of both hormones even with non-selective detectors.

Abscisic Acid↗
PubMed2004

Determination of celecoxib in human plasma using solid-phase extraction and high-performance liquid chromatography.

A simple reversed phase high-performance liquid chromatography (HPLC) method was developed for determination of celecoxib levels in human plasma. The procedure involves solid-phase extraction of celecoxib and the internal standard (SC-236) from plasma using C(18) extraction cartridges. The chromatographic separation of celecoxib and SC-236 was achieved with a Nova Pak C(8) column (3.8 mm x 150 mm) eluted with a mobile phase consisting of acetonitrile-tetrahydrofuran-sodium acetate buffer (pH 5.0) in the ratio of 30:8:62. An ultraviolet light detector with the wavelength set at 215 nm was employed for detection. Celecoxib was well resolved from the plasma constituents and the internal standard. The extraction recovery of celecoxib and SC-236 from human plasma was greater than 88%. Linear calibration curves were established over a concentration range of 40-4000 ng/ml when 0.25 ml aliquots of plasma were used. The inter- and intra-day R.S.D. for the assay was less than 12 and 5%, respectively. This assay has been applied to the analysis of celecoxib levels in plasma samples collected from healthy participants entered into a Phase II clinical study.

Celecoxib↗
PubMed1997

Solid-phase extraction method for the quantitative analysis of organochlorine pesticides in wildlife urine.

A gas chromatographic method for the analysis of nine organochlorine pesticides in wildlife urine is described. Reversed-phase solid-phase extraction is utilized to extract the organochlorine pesticides from urine. The pesticides are recovered by elution with hexane-ethyl ether (1:1) and quantified by gas chromatography with electron-capture detection. Method detection limits range from 1.4 to 2.7 micrograms/L. Mean recoveries for all pesticides are 90.6%.

Animals↗
PubMed2003

Determination of atrazine, deethylatrazine and simazine in water at parts-per-trillion levels using solid-phase extraction and gas chromatography/ion trap mass spectrometry.

Methods for trace analysis of atrazine and simazine in water have been developed by using stable-isotope dilution with detection by gas chromatography/mass spectrometry. D(5)-Atrazine was used as the internal standard for the determination of atrazine and deethylatrazine, while (13)C(3)-simazine was used for simazine analysis. Water samples were fortified with known amounts of the internal standards and submitted to solid-phase extraction with a C(18) bonded-silica cartridge. A gas chromatograph coupled with an ion-trap mass spectrometer was used to analyze the water sample extracts. Method detection limits were 38 parts-per-trillion (ppt) for atrazine and deethylatrazine and 75 ppt for simazine. The accuracy of the method, represented by relative analytical errors, was less than 15%, and the method precision was less than 5% (relative standard deviation, n = 9). The method was successfully applied to analyze surface water samples collected from a reservoir and a river at ppt levels.

Atrazine↗
PubMed1996

Solid-phase extraction of polar pesticides from environmental water samples on graphitized carbon and Empore-activated carbon disks and on-line coupling to octadecyl-bonded silica analytical columns.

The suitability of Empore-activated carbon disks (EACD), Envi-Carb graphitized carbon black (GCB) and CPP-50 graphitized carbon for the trace enrichment of polar pesticides from water samples was studied by means of off-line and on-line solid-phase extraction (SPE). In the off-line procedure, 0.5-2 l samples spiked with a test mixture of oxamyl, methomyl and aldicarb sulfoxide were enriched on EnviCarb SPE cartridges or 47 mm diameter EACD and eluted with dichloromethane-methanol. After evaporation, a sample was injected onto a C18-bonded silica column and analysed by liquid chromatography with ultraviolet (LC-UV) detection. EACD performed better than EnviCarb cartridges in terms of breakthrough volumes (> 2 l for all test analytes), reproducibility (R.S.D. of recoveries, 4-8%, n = 3) and sampling speed (100 ml/min); detection limits in drinking water were 0.05-0.16 microgram/l. In the on-line experiments, 4.6 mm diameter pieces cut from original EACD and stacked onto each other in a 9 mm long precolumn, and EnviCarb and CPP-50 packed in 10 x 2.0 mm I.D. precolumn, were tested, and 50-200 ml spiked water samples were preconcentrated. Because of the peak broadening caused by the strong sorption of the analytes on carbon, the carbon-packed precolumns were eluted by a separate stream of 0.1 ml/min acetonitrile which was mixed with the gradient LC eluent in front of the C18 analytical column. The final on-line procedure was also applied for the less polar propoxur, carbaryl and methiocarb. EnviCarb could not be used due to its poor pressure resistance. CPP-50 provided less peak broadening than EACD: peak widths were 0.1-0.3 min and R.S.D. of peak heights 4-14% (n = 3). In terms of analyte trapping efficiency on-line SPE-LC-UV with a CPP-50 precolumn also showed better performance than when Bondesil C18/OH or polymeric PLRP-S was used, but chromatographic resolution was similar. With the CPP-50-based system, detection limits of the test compounds were 0.05-1 microgram/l in surface water.

Adsorption↗
PubMed2004

Automated solid phase extraction and quantitative analysis of human milk for 13 phthalate metabolites.

While the demonstrated benefits associated with breastfeeding are well recognized, breast milk is one possible route of exposure to environmental chemicals, including phthalates, by breastfeeding infants. Because of the potential health impact of phthalates to nursing children, determining whether phthalates are present in breast milk is important. We developed a sensitive method for measuring 13 phthalate metabolites in breast milk using automated solid phase extraction (SPE) coupled to isotope dilution-high-performance liquid chromatography (HPLC)-negative ion electrospray ionization-tandem mass spectrometry. We used D(4)-phthalate diesters to unequivocally establish the presence in human breast milk of enzymes capable of hydrolyzing the ubiquitous phthalate diesters to their respective monoesters. The analytical method involves acid-denaturation of the enzymes after collection of the milk to avoid hydrolysis of contaminant phthalate diesters introduced during sampling, storage, and analysis. The method shows good reproducibility (average coefficient of variations range between 4 and 27%) and accuracy (spiked recoveries are approximately 100%). The detection limits are in the low ng/ml range in 1ml of breast milk. We detected several phthalate metabolites in pooled human breast milk samples, suggesting that phthalates can be incorporated into breast milk and transferred to the nursing child.

Chromatography, High Pressure Liquid↗
PubMed2001

Automated solid-phase extraction for sample preparation followed by high-performance liquid chromatography with diode array and mass spectrometric detection for the analysis of resveratrol derivatives in wine.

A method has been developed for the simultaneous determination of resveratrol in all its forms (free isomers and glycosylates) in wines by high-performance liquid chromatography with diode array and mass spectrometric detection. Prior to injection into the column, preconcentration of the sample by automated solid-phase extraction is carried out. In the detection by UV absorption, quantitation was carried out at 280 and 305 nm, and in detection by mass spectrometry, quantitation was performed in the selected ion monitoring mode at m/z 228 and at m/z 238. A comparative study between both detection systems was carried out.

Automation↗
PubMed2005

Development of a sensitive and specific solid phase extraction--gas chromatography-tandem mass spectrometry method for the determination of elenolic acid, hydroxytyrosol, and tyrosol in rat urine.

A novel gas chromatography-tandem mass spectrometry (GC-MS/MS) method was developed, using an ion trap mass spectrometer, for the simultaneous determination of olive oil bioactive components, elenolic acid, hydroxytyrosol, and tyrosol, in rat urine. Samples were analyzed by GC-MS/MS prior to and after enzymatic treatment. A solid phase extraction sample pretreatment step with greater than 80% analytical recoveries for all compounds was performed followed by a derivatization reaction prior to GC-MS/MS analysis. The calibration curves were linear for all compounds studied for a dynamic range between 1 and 500 ng. The limit of detection was in the mid picogram level for tyrosol and elenolic acid (300 pg) and in the low picogram level for hydroxytyrosol (2.5 pg). The method was applied to the analysis of rat urine samples after sustained oral intake of oleuropein or extra virgin olive oil as a diet supplement.

Animals↗
PubMed2002

A new method for determination of halogenated flame retardants in human milk using solid-phase extraction.

A method has been developed for quantitation of a selection of halogenated flame retardants in human milk. The method has been validated for seven polybrominated diphenyl ethers (PBDEs), BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, and BDE-183, and the halogenated phenols 2,4,6-tribromophenol (TriBP), pentabromophenol (PeBP), tetrachlorobisphenol-A (TCBP-A), and tetrabromobisphenol-A (TBBP-A). The sample preparation includes solid-phase extraction using an N-vinylpyrrolidone-divinylbenzene copolymer with on-column lipid decomposition followed by additional cleanup on sulfuric acid-silica columns and methylation of the phenolic compounds. Separation and detection were performed by gas chromatography-electron capture mass spectrometry, using a 5% phenyl 95% dimethylpolysiloxane column. The method has been validated in the range of 1.8-180 pg/g milk for most of the halogenated flame retardants. The average absolute recoveries were from 49 to 83%, and the average recoveries with respect to internal standards were in the range of 53 to 121%. Estimated limits of detection were in the range of 0.3 to 1.0 pg/g milk using a sample size of 5 g for all compounds, except TCBP-A, for which the limit of detection was estimated to 6.7 pg/g milk.

Female↗
PubMed2005

On-line solid phase extraction using the Prospekt-2 coupled with a liquid chromatography/tandem mass spectrometer for the determination of dextromethorphan, dextrorphan and guaifenesin in human plasma.

An on-line liquid chromatography/tandem mass spectrometry (LC-MS/MS) procedure, using the Prospekt- 2 system, was developed and used for the determination of the levels of the active ingredients of cough/cold medications in human plasma matrix. The experimental configuration allows direct plasma injection by performing on- line solid phase extraction (SPE) on small cartridge columns prior to elution of the analyte(s) onto the analytical column and subsequent MS/MS detection. The quantitative analysis of three analytes with differing polarities, dextromethorphan (DEX), dextrorphan (DET) and guaifenesin (GG) in human plasma presented a significant challenge. Using stable-isotope-labeled internal standards for each analyte, the Prospekt-2 on-line methodology was evaluated for sensitivity, suppression, accuracy, precision, linearity, analyst time, analysis time, cost, carryover and ease of use. The lower limit of quantitation for the on-line SPE procedure for DEX, DET and GG was 0.05, 0.05 and 5.0 ng mL(-1), respectively, using a 0.1 mL sample volume. The linear range for DEX and DET was 0.05-50 ng mL(-1) and was 5-5,000 ng mL(-1) for GG. Accuracy and precision data for five different levels of QC samples were collected over three separate days. Accuracy ranged from 90% to 112% for all three analytes, while the precision, as measured by the %RSD, ranged from 1.5% to 16.0%

Antitussive Agents↗
PubMed1994

Solid-phase extraction combined with radioimmunoassay for measurement of zalcitabine (2',3'-dideoxycytidine) in plasma and serum.

Of the antiviral agents that are currently in clinical use in the US for therapy for human immunodeficiency virus infections, zalcitabine (ddC) is the most potent and is effective at the lowest plasma concentrations. The two reported procedures for measuring these low concentrations involve a chromatographic technique coupled with mass spectrometry. We have developed a procedure combining solid-phase extraction with a strong cation-exchange resin and commercially available RIA reagents for the quantification of ddC in plasma or serum. The method demonstrates good linearity, specificity, and precision, with overall CVs of < 10% from 2-20 micrograms/L and 17% at 0.8 microgram/L (the lower limit of quantitation). No significant cross-reactivity with nucleoside analogs other than ddC analogs was noted. The major advantages of this assay are its efficiency and relative simplicity, which should facilitate its performance in many laboratories.

Antiviral Agents↗
PubMed1992

Automated analysis of the pyridinium crosslinks of collagen in tissue and urine using solid-phase extraction and reversed-phase high-performance liquid chromatography.

A fully automated method for assaying the collagen crosslinking amino acids, pyridinoline and deoxypyridinoline, in human urine samples or tissue hydrolysates is described. Samples were processed using a Gilson ASPEC system with solid-phase extraction of the crosslinks on columns containing 100 mg of microgranular cellulose. Introduction of an additional solvent step during sample preparation allowed direct analysis by reversed-phase HPLC and elimination of the drying step used previously in a manual method. Use of a synthetic pyridinoline derivative as internal standard enabled accurate quantification of the crosslinks by correcting for recoveries through the whole assay. Samples were analyzed in sequential mode with a total assay time of 30 min. The automated assay showed close correlation with the manual method for both free and total crosslink determinations in human urine (r > 0.97). Reproducibility was improved, as seen from replicate analyses of human urine (CV < 3% for automated pyridinoline measurement compared with 8-12% previously observed for the manual method). Crosslink excretion is the most useful marker of collagen degradation in metabolic bone diseases and arthritic disorders. The automated assay which has been developed is rapid, convenient, and reliable and will greatly facilitate the monitoring of urinary collagen crosslinks and their tissue levels in clinical investigations.

Amino Acids↗
PubMed2004

Continuous solid-phase extraction and preconcentration of bisphenol A in aqueous samples using molecularly imprinted columns.

A bisphenol A (BPA) molecularly imprinted polymer, the composition of which was optimised using a chemometric approach, has been applied to the selective preconcentration of the template from aqueous samples. The selectivity of the polymer toward BPA and related compounds was evaluated chromatographically. The BPA-imprinted polymer was packed in a column and used for continuous on-column solid-phase extraction (MISPE) of aqueous samples followed by subsequent analysis by HPLC with fluorescence detection of the eluted fractions. The composition of the washing solvent applied in the MISPE procedure was optimised to favour the specific interactions of the MIP with BPA and to remove the non-selectively bound matrix components. The MISPE method has proven to be effective for selective preconcentration of BPA in aqueous samples (recoveries >84% obtained in the eluate for 10-100 mL sample volumes) enabling detection and quantification limits of 1.0 and 3.3 ng mL(-1), respectively (based on 25 mL sample size). Analytical recoveries were between 92 and 101% for river water samples spiked with known amounts of BPA (30, 60, and 80 ng mL(-1)); relative standard deviations (RSD) were lower than 5.0%.

Benzhydryl Compounds↗