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PubMed2005

Determination of the novel non-peptidic HIV-protease inhibitor tipranavir by HPLC-UV after solid-phase extraction.

An HPLC method previously described for the assay of amprenavir (APV), ritonavir (RTV), indinavir (IDV), saquinavir (SQV), nelfinavir (NFV), lopinavir (LPV), atazanavir (ATV), nevirapine (NVP) and efavirenz (EFV) can be also conveniently applied, with minor gradient program adjustment, for the determination of the novel non-peptidic HIV protease inhibitor tipranavir (TPV) in human plasma, by off-line solid-phase extraction (SPE) followed by HPLC coupled with UV-diode array detection (DAD). After viral inactivation by heat, the plasma is diluted with phosphate buffer (pH 7), and subjected to a SPE on a C18 cartridge. Matrix components are eliminated with a solution of 0.1% H3PO4 solution neutralised to pH 7, and TPV is eluted with MeOH. The resulting eluate is evaporated and reconstituted in 100 microl MeOH/H2O 50/50. A 40 microl volume is injected onto a Nucleosil C18 AB column and TPV is analysed by UV detection at 201 nm using a gradient elution program constituted of MeCN and phosphate buffer adjusted to pH 5.12 and containing 0.02% sodium heptanesulfonate. The calibration curves are linear up to 75 microg/ml, with a lower limit of quantification of 0.125 microg/ml. The mean absolute recovery of TPV is 77.1+/-4.0%. The method is precise with mean inter-day coefficient of variations (CVs) within 2.2-3.4%, and accurate (range of inter-day deviations from 0.7 to 1.2%). The method has been validated and is currently applied to the monitoring of TPV plasma levels in HIV patients.

Calibration↗
PubMed2006

Determination of meperidine, tramadol and oxycodone in human oral fluid using solid phase extraction and gas chromatography-mass spectrometry.

Analytical procedures for the determination of meperidine, tramadol and oxycodone in oral fluid have been developed and validated using gas chromatography-mass spectrometry (GC/MS) following initial screening with enzyme linked immunosorbent assay (ELISA). The oral fluid samples were collected using the Quantisal device, and any drugs present were quantified using mixed mode solid-phase extraction and electron impact GC/MS. For confirmation, three ions were monitored and two ion ratios determined, which were within 20% of those of the known calibration standards. The limits of quantitation were 10 ng/mL; the intra-day precision of the assays (n=5) was 2.33%, 1.00% and 7.61%; inter-day precision 2.48%, 2.44% and 5.8% (n=10) for meperidine, tramadol and oxycodone, respectively. The percentage recovery of the drugs from the collection pads was 86.7%, 87.7% and 96.6%, respectively (n=6). The methods were applied to specimens obtained during research studies in the USA.

Analgesics↗
PubMed1994

Quantitation of morphine, morphine-3-glucuronide, and morphine-6-glucuronide in plasma and cerebrospinal fluid using solid-phase extraction and high-performance liquid chromatography with electrochemical detection.

An original, sensitive, and specific high-performance liquid chromatographic (HPLC) assay was developed for the quantitation of morphine and its two major metabolites, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), in human plasma and cerebrospinal fluid (CSF) and in rat plasma, using hydromorphone as the internal standard. Solid-phase extraction was used to separate morphine and its glucuronide metabolites from plasma constituents. Extraction efficiencies of morphine, M3G, and M6G from human plasma samples (0.5 ml) were 84, 87, and 88%, respectively. Extraction efficiencies of morphine, M3G, and M6G did not differ significantly (p > 0.05) between human plasma and CSF or rat plasma. Morphine, M3G, M6G, and hydromorphone were separated on a 10 mu C8 Resolve radially compressed cartridge using a mobile phase comprising methanol:acetonitrile:phosphate buffer, (0.0125M pH 7.5; 10:10:80), in which 11 mg/L of cetyltrimethylammonium bromide (cetrimide) was dissolved. Quantitation was achieved using a single electrochemical detector at ambient temperature (23 degrees C). Standard curves were linear over the ranges 0.020-2.190, 0.027-2.709, and 0.027-0.542 microM for morphine, M3G, and M6G, respectively. Lower limits of detection for morphine, M3G, and M6G in human plasma and CSF samples (0.5 ml) were 0.020, 0.027, and 0.027 microM, respectively. Corresponding lower limits of detection in rat plasma (0.1 ml) were 0.102, 0.135, and 0.135 microM, respectively. Intraassay precision for low and high concentrations of morphine, M3G, and M6G were < 23 and < 8% respectively. Similarly, interassay accuracy for low and medium concentrations of morphine, M3G, and M6G were < 17% and were < 9% for high concentrations.

Animals↗
PubMedDate not supplied

Method development for the analysis of N-nitrosodimethylamine and other N-nitrosamines in drinking water at low nanogram/liter concentrations using solid-phase extraction and gas chromatography with chemical ionization tandem mass spectrometry.

N-nitrosodimethylamine (NDMA) is a probable human carcinogen of concern that has been identified as a drinking water contaminant. U.S. Environmental Protection Agency Method 521 has been developed for the analysis of NDMA and 6 additional N-nitrosamines in drinking water at low ng/L concentrations. The method uses solid-phase extraction with coconut charcoal as the sorbent and dichloromethane as the eluent to concentrate 0.50 L water samples to 1 mL. The extracts are analyzed by gas chromatography-chemical ionization tandem mass spectrometry using large-volume injection. Method performance was evaluated in 2 laboratories. Typical analyte recoveries of 87-104% were demonstrated for fortified reagent water samples, and recoveries of 77-106% were demonstrated for fortified drinking water samples. All relative standard deviations on replicate analyses were < 11%.

Charcoal↗
PubMed1985

Determination of ibuprofen in human plasma by solid phase extraction and reversed-phase high-performance liquid chromatography.

A new, sensitive and simple method for the rapid quantitative determination of ibuprofen in human plasma has been developed. This method involves the use of a solid phase extraction on "Baker" C-18 disposable extraction columns for sample clean-up and uses mefenamic acid as an internal standard. Separation and quantitation are performed by reversed-phase liquid chromatography using a Nucleosil C18 column and methanol-0.04 M phosphoric acid (80:20, v/v), as the mobile phase. Detection was achieved by UV-absorbance measurements at 229 nm.

Journal Article↗
PubMed1995

New solid-phase extraction for an improved high-performance liquid chromatographic procedure for the quantitation of halofantrine and monodesbutylhalofantrine in blood or plasma.

A rapid, accurate, and sensitive high-performance liquid chromatographic (HPLC) method, with fluorimetric detection, for the simultaneous measurement of halofantrine and desbutylhalofantrine in human plasma or whole blood is described. Sample preparation involved protein precipitation, followed by an efficient solid-phase extraction on a C8 cartridge. Analytes were isolated from 1 ml of the biological fluids and recovered by a 2% acetic acid in ethyl acetate solution. Chromatographic separation was carried out on a LiChrospher 60 RP select B, C8 bonded phase (5 microns particle size, 25 cm x 4 mm I.D.) using a mobile phase of water-acetonitrile (35:65, v/v) containing triethylamine (1%) and adjusted to pH 4 with orthophosphoric acid. The total run time was 14 min. Relative standard deviations of the intra-and inter-assay precisions were less than 5.9%. Assumption of linearity was investigated by studying the y-residuals and by ANOVA (analysis of variance). Because of the wide range of calibration (0.1 to 2.0 microgram/ml) variances were non-homogeneous (Hartley's test) and the weighted regression line was computed in order to allow pharmacokinetic studies. Accuracy was tested using a t-statistic. Limits of decision, detection and quantification were realized from an analysis of the blanks. Application of the method to clinical specimens was demonstrated.

Antimalarials↗
PubMed1992

Solid-phase extraction and HPLC determination of 4-vinyl guaiacol and its precursor, ferulic acid, in orange juice.

This study is undertaken to develop a simplified, rapid method to determine both immediate and potential off odors due to 4-vinyl guaiacol and its odorless precursor, ferulic acid, from a single sample preparation and chromatographic analysis. Orange juice sample preparation consists of a simple, C18 solid phase extraction. Utilizing a 5-microns, 25-cm, C18 column, both compounds can be separated within 40 min using a one-step, linear gradient beginning with an aqueous 12% tetrahydrofuran (THF)-5% acetonitrile mixture and ending with 35% aqueous THF. Hesperidin and nariutin have been identified as the compounds that interfered with the ultraviolet (UV) determination of sinapic and caffeic acids. Fluorescence detection with wavelength programming offers optimal sensitivity and selectivity. Recoveries of 4-vinyl guaiacol and ferulic acid range from 90 to 103%. Detection limits are 1 ppm and 5 ppm for ferulic acid and 4-vinyl guaiacol, respectively. Other hydroxycinnamic acids such as coumaric, sinapic, and caffeic acids may also be determined from the same chromatogram.

Beverages↗
PubMed2006

Nonretentive solid-phase extraction of phosphorylated peptides from complex peptide mixtures for detection by matrix-assisted laser desorption/ionization mass spectrometry.

Widespread interest in protein phosphorylation has led to the development of a variety of methods for the analysis of phosphoproteomes of different types of organisms. Many applications involve pretreatment of the sample before mass spectrometric measurement and can crucially improve the detection efficiency of individual phosphopeptides. Despite intense research efforts, separation and extraction of phosphorylated peptides, especially multiphosphorylated ones, remain challenging tasks and need to be further explored and expanded with unconventional approaches. In this study, we describe the application of nonretentive solid-phase extraction (SPE) to the analysis of phosphopeptides using the highly cross-linked polystyrene-divinylbenzene material Strata-X. This study indicates that the procedure allows for the preferential extraction of phosphopeptides regardless of their extent of phosphorylation. The Strata-X material primarily retains nonphosphorylated peptides by hydrophobic interaction, whereas the inherent hydrophilicity of phosphorylated peptides leads to their partitioning into the aqueous phase. Phosphopeptides that were rapidly segregated out of tryptic digest mixtures and collected in the early aqueous fractions generated intense signals in mass spectra. The method was developed using SPE Strata-X columns, then suited for detection and sequencing of phosphopeptides by miniaturizing the system to the scale of custom-made microcolumns. This provided fast isolation of phosphopeptides from protein digests along with direct MALDI on-target deposition. The possibility of on-target washing during sample preparation is also presented.

Amino Acid Sequence↗
PubMed2000

Liquid chromatography/electrospray tandem mass spectrometry method for the quantitation of fosinoprilat in human serum using automated 96-well solid-phase extraction for sample preparation.

A sensitive, specific, accurate and reproducible liquid chromatography/electrospray tandem mass spectrometry method was developed and validated for the quantitation of fosinoprilat in 0.2 mL of human serum. The method employed acidification (with pH 4.0 sodium acetate buffer) of the serum samples to minimize the hydrolysis of the prodrug fosinopril to fosinoprilat prior to purification by automated 96-well solid-phase extraction. The required chromatographic separation of fosinoprilat and fosinopril was achieved isocratically on a Luna C8 analytical column (2 x 50 mm, 3 microm). The total run time was 2 min. The mobile phase contained methanol and water with 10 mM ammonium acetate. Detection was by positive ion electrospray tandem mass spectrometry. The standard curve, which ranged from 2.00 to 500 ng/mL, was fitted to a 1/x(2) weighted linear regression model. Fosinoprilat quality control (QC) samples used to determine the accuracy and precision of the method were prepared in human serum at concentrations of 5.00, 200, 400 and 1000 ng/mL. The assay accuracy was within 8% (dev). The intra- and inter-assay precisions were within 6 and 3% (RSD), respectively. Fosinopril QC samples used to gauge the rate of hydrolysis of fosinopril to fosinoprilat during the assay procedure were prepared in human serum at 500 ng/mL. The hydrolysis of fosinopril to fosinoprilat was </=1%. This degree of conversion would cause little error in the analysis of post-dose serum samples since such samples are known to contain low levels of the prodrug compared with the drug.

Analysis of Variance↗
PubMed1995

Solid-phase extraction of isosorbide dinitrate and two of its metabolites from plasma for gas chromatographic analysis.

A rapid, accurate and selective method for the determination of isosorbide dinitrate and its 2- and 5-isosorbide mononitrate metabolites in 1.0 ml of human plasma has been developed. Before chromatographic quantitation by gas-liquid chromatography with electron-capture detection, the compounds are subjected to solid-phase extraction, using ENVI 18 cartridges (Supelco). The intra-day and inter-day coefficients of variation are less than 10%, except the inter-day coefficient of variation for the assay of 5-isosorbide dinitrate which is less than 15%. Limits of quantitation are 10, 10 and 20 ng/ml for isosorbide dinitrate, 2-isosorbide mononitrate and 5-isosorbide mononitrate, respectively. Recoveries are in excess of 90% for isosorbide dinitrate and 70% for its two metabolites.

Chromatography, Gas↗
PubMed2004

Liquid chromatographic determination including simultaneous "on-cartridge" separation of ranitidine cisapride drug combinations from paediatric plasma samples using an automated solid-phase extraction procedure.

HPLC methodology was investigated for the simultaneous determination of cisapride and ranitidine in small volume paediatric plasma samples. Such a simultaneous determination proved difficult due to the small sample volumes, the low concentrations of the drugs and the different log P values of the two compounds. The two drugs and their respective internal standards were separated "on-cartridge" using HLB Solid Phase Extraction cartridges and the samples quantified by individual HPLC methodologies. The technique has been applied successfully to 60 paediatric plasma samples containing both cisapride and ranitidine.

Automation↗
PubMed1998

Packed-column supercritical fluid chromatography coupled with solid-phase extraction for the determination of organic microcontaminants in water.

A multiresidue method for the analysis of 35 common contaminants (including pesticides, polycyclic aromatic hydrocarbons and phenols) in lough and river waters from Castilla y León Spanish region, by using supercritical fluid chromatography (SFC) with five silica packed columns, is described. In order to decrease the detection limits, a preconcentration step by coupling solid-phase extraction to the SFC system was used. The different variables affecting the extraction procedure were studied and optimized, selecting the Isolute Env+ as the best sorbent. The detection limits achieved ranged from 0.4 to 2.6 micrograms l-1.

Chromatography↗
PubMed2001

Gas chromatographic determination of catecholestrogens following isolation by solid-phase extraction.

A sensitive and specific assay for the determination of the catecholestrogens 2-hydroxyestradiol (2-OHE2) and 4-hydroxyestradiol (4-OHE2) using gas chromatography with electron-capture detection (GC-ECD) is described. The formation of 2- and 4-OHE2 was assessed following activation of 17beta-estradiol in the microsomal fraction of female rat livers. The analytes were isolated by solid-phase extraction, derivatized to their heptafluorobutyryl esters with heptafluorobutyric acid anhydride, and subjected to solvent exchange prior to analysis; this resulted in minimal chromatographic interference, long column life, and stable derivatized analytes. Derivatized catechols were separated and confirmed with dual column chromatography (DB-5 and DB-608) and quantitated using GC-ECD. The DB-608 column was preferred for quantitation as it provided better 4-OHE2 resolution from interference. Key validation parameters for the assay include sensitivity, intra- and inter-assay precision, and accuracy. Instrument sensitivity and limits of detection (LOD) and quantitation (LOQ) were determined statistically from fortification data approaching expected limits. For 2-OHE2 and 4-OHE2, respective values for these parameters were; instrument sensitivities of 0.4 and 0.7 pg, LODs of 0.8 and 1.3 ng/mg, and LOQs of 2.6 and 4.3 ng/mg.

Animals↗
PubMed2003

Validation of a sensitive and automated 96-well solid-phase extraction liquid chromatography-tandem mass spectrometry method for the determination of desloratadine and 3-hydroxydesloratadine in human plasma.

To support clinical development, a liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method was developed and validated for the determination of desloratadine (descarboethoxyloratadine) and 3-OH desloratadine (3-hydroxydescarboethoxyloratadine) concentrations in human plasma. The method consisted of automated 96-well solid-phase extraction for sample preparation and liquid chromatography/turbo ionspray tandem mass spectrometry for analysis. [2H(4)]Desloratadine and [2H(4)]3-OH desloratadine were used as internal standards (I.S.). A quadratic regression (weighted 1/concentration(2)) gave the best fit for calibration curves over the concentration range of 25-10000 pg/ml for both desloratadine and 3-OH desloratadine. There was no interference from endogenous components in the blank plasma tested. The accuracy (%bias) at the lower limit of quantitation (LLOQ) was -12.8 and +3.4% for desloratadine and 3-OH desloratadine, respectively. The precision (%CV) for samples at the LLOQ was 15.1 and 10.9% for desloratadine and 3-OH desloratadine, respectively. For quality control samples at 75, 1000 and 7500 pg/ml, the between run %CV was </=7.5% for desloratadine and </=6.3% for 3-OH desloratadine. Between run %bias ranged from 4.1 to 8.0% for desloratadine and -11.5 to -4.8% for 3-OH desloratadine. Desloratadine and 3-OH desloratadine were stable in human plasma for 401 days at -22 degrees C, after five freeze/thaw cycles, up to 24 h at room temperature, and in reconstituted sample extracts (up to 185 h at 5 degrees C). This LC-MS-MS method for the determination of desloratadine and 3-OH desloratadine in human plasma met regulatory requirements for selectivity, sensitivity, goodness of fit, precision, accuracy and stability.

Automation↗
PubMed2005

Rapid analysis of trace levels of antibiotic polyether ionophores in surface water by solid-phase extraction and liquid chromatography with ion trap tandem mass spectrometric detection.

The occurrence of antibiotics in surface and ground water is an emerging area of interest due to the potential impacts of these compounds on the environment. This paper details a rapid, sensitive and reliable analytical method for the determination of monensin A and B, salinomycin and narasin A in surface water using solid-phase extraction (SPE) and liquid chromatography-ion trap tandem mass spectrometry (LC-MS-MS) with selected reaction monitoring (SRM). Several product ions as sodiated sodium salts for MS-MS detection have been identified and documented with their proposed fragmentation pathways. Statistical analysis for determination of the method detection limit (MDL), accuracy and precision of the method is described. The average recovery of ionophore antibiotics in pristine and wastewater-influenced water was 96.0+/-8.3% and 93.8+/-9.1%, respectively. No matrix effect was seen with the surface water. MDL was between 0.03 and 0.05 microg/L for these antibiotic compounds in the surface water. The accuracy and day-to-day variation of method fell within acceptable ranges. The method is applied to evaluate to the occurrence of these compounds in a small watershed in Northern Colorado. The method verified the presence of trace levels of these antibiotics in urban and agricultural land use dominated sections of the river.

Anti-Bacterial Agents↗
PubMed1999

Sensitive determination of RDX, nitroso-RDX metabolites, and other munitions in ground water by solid-phase extraction and isotope dilution liquid chromatography-atmospheric pressure electro-spray [correction of chemical] ionization mass spectrometry.

Recent improvements in the LC-MS interface have increased the sensitivity and selectivity of this instrument in the analysis of polar and thermally-labile aqueous constituents. Determination of RDX, nitroso-RDX metabolites, and other munitions was enhanced using LC-MS with solid-phase extraction, 15N3-RDX internal standard, and electrospray ionization (ESI) in negative ion mode. ESI produced a five-fold increase in detector response over atmospheric pressure chemical ionization (APCI) for the nitramine compounds, while the more energetic APCI produced more than twenty times the ESI response for nitroaromatics. Method detection limits in ESI for nitramines varied from 0.03 microgram l-1 for MNX to 0.05 microgram l-1 for RDX.

Chromatography, Liquid↗
PubMed2000

Determination of retigabine and its acetyl metabolite in biological matrices by on-line solid-phase extraction (column switching) liquid chromatography with tandem mass spectrometry.

A HPLC assay with tandem mass spectrometric detection in the positive-ion atmospheric pressure chemical ionisation (APCI) mode for the sensitive determination of retigabine [(I), D-23129] and its acetyl metabolite [(II), ADW 21-360] in plasma was developed, utilising the structural analogue (D-10328), (III), as internal standard. Automated on-line solid-phase extraction of diluted plasma samples, based on 200-microl plasma aliquots, at pH 6.5, allowed a reliable quantification of retigabine and the acetyl metabolite down to 1 ng/ml. Injection of 500 microl of diluted plasma onto a C2 stationary phase-based column switching system in combination with a 75 mm x 4 mm reversed-phase analytical column at a flow-rate of 0.5 ml/min provided cycle times of 4 min per sample. The standard curves were linear from 1 to 1000 ng/ml using weighted linear regression analysis (1/x2). The method is accurate (mean accuracy < or = +/- 10%), precise (RSD < +/- 15%) and sensitive, providing lower limits of quantification in plasma of 1 ng/ml for retigabine (I), and 2.5 ng/ml for the metabolite (II) with limits of detection of 0.5 ng/ml for both analytes. Up to 200 unknowns may be analysed each 24 h per analyst.

Anticonvulsants↗
PubMed1996

Use of solid-phase extraction to determine ergosterol concentrations in plant tissue colonized by fungi.

At present, the ergosterol and acetate-to-ergosterol techniques are generally considered to be the methods of choice to quantify fungal biomass, growth rate, and productivity under natural conditions. Both methods rely on the accurate isolation and quantification of ergosterol, a major membrane component of eumycotic fungi. Taking advantage of the solid-phase extraction (SPE) technique, we present a novel method to determine the ergosterol concentration in lipid extracts derived from plant tissues and dead organic matter colonized by fungi. In this method, a primary alkaline extract is acidified and passed through a reversed-phase (C(inf18)) SPE column. The column is then washed with an alkaline methanol-water solution to eliminate interfering substances and increase pH and is thoroughly dried in air. Ergosterol is eluted with alkaline isopropanol. This eluting solvent was chosen to produce a strongly basic pH of the final extract and thus confer stability on the ergosterol molecule before high-performance liquid chromatography analysis. The recovery of ergosterol from plant tissues and the O(infhf) horizon of a woodland soil ranged from 85 to 98%, and the overall extraction efficiency was similar to that obtained by a conventional procedure involving liquid-liquid extraction. Potential pitfalls of ergosterol analysis by SPE include (i) insufficient acidification before sample loading on the extraction column, resulting in a poor affinity of ergosterol for the sorbent; (ii) incomplete drying of the sorbent bed before the elution step; and (iii) chemical breakdown of ergosterol after elution, which was found to be related to a low pH of the final extract and a high concentration of matrix compounds. When these pitfalls are avoided, SPE is an attractive alternative to existing methods of ergosterol analysis of environmental samples.

Journal Article↗