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At least 1,513 records · Page 84Linked to original sources
PubMed1987

Liquid chromatographic determination of diltiazem and its metabolites using trans isomers as internal standards, with dynamic modification of the solid phase by addition of an amine to the mobile phase.

A selective and sensitive reversed-phase high-performance liquid chromatographic method for simultaneous analysis of diltiazem and its five metabolites known to occur in man is presented. Different C18 columns are compared. The influences of organic co-solvent, pH, ionic strength and the addition of various amines are studied. The use of trans-diltiazem as internal standard is advocated. UV detection at 237 nm is used for plasma analyses. The possibilities of electrochemical detection are also discussed. Before solvent extraction, plasma samples are saturated with sodium chloride and made alkaline. Triethylamine is also added. The use of the method in pharmacokinetic applications is exemplified.

Amines↗
PubMed1987

Comparative study of solid-phase and liquid-phase extraction techniques for isolation of phospholipids from plasma.

A liquid-liquid extraction technique and six solid absorbents, silica gel, octadecyl silica (C18), XAD-2, XAD-4, XAD-7 and XAD-8, were compared as effective tools for extraction of phosphatidylcholine (Ptd C), phosphatidylethanolamine (Ptd E), phosphatidylinositol (Ptd I) and phosphatidylserine (Ptd S) from plasma. Using liquid-liquid extraction the recovery of the four phospholipids was in the order of 60% in organic phase and 20% in the liquid interface. Neither silica gel nor C18 materials significantly adsorbed phospholipids from plasma. Amberlite resins were more selective for removal of phospholipids. A recovery of greater than 85% was obtained for Ptd C, Ptd I and Ptd S when XAD-7 or XAD-8 were used as adsorbents. A recovery of approximately 90% for Ptd E was obtained when XAD-2 or XAD-4 were used as adsorbents. A solvent mixture of isopropanol-acetonitrile (1:1) was found to be the most effective eluent for removal of phospholipids from amberlite polymeric resins. These results suggest that resins could be used as an extracting tool for removal of phospholipids from body fluids.

Chromatography, High Pressure Liquid↗
PubMed1995

Amphetamine and methamphetamine determination in urine by reversed-phase high-performance liquid chromatography with sodium 1,2-naphthoquinone 4-sulfonate as derivatizing agent and solid-phase extraction for sample clean-up.

A rapid method is described for the identification and determination of amphetamine and methamphetamine in human urine samples by liquid chromatography with UV-Vis detection. The samples were transferred onto a C18 solid-phase extraction column and chromatographed on a Hypersil ODS RP C18, 5 microns (250 x 4 mm I.D.) with an acetonitrile-water elution gradient containing propylamine. Under these conditions, the amines are eluted with a short retention time. The procedure has been applied to the determination of amphetamine and methamphetamine in the range 0.3-4.0 micrograms/ml in spiked urine samples. The detection limits at 280 nm were 4 and 2 ng/ml for amphetamine and methamphetamine, respectively. The intra-day and inter-day precision and accuracy of the method were studied.

Amphetamine↗
PubMed1995

Determination of the angiotensin-converting enzyme inhibitor lisinopril in urine using solid-phase extraction and reversed-phase high-performance liquid chromatography.

A simple, accurate and precise high-performance liquid chromatographic method is described for assaying lisinopril in human urine. Urine (1 ml) containing lisinopril and enalaprilat (internal standard) was acidified with 10 microliters of 6 M nitric acid, passed through a Sep-Pak C18 cartridge and eluted with 3 ml of 10% acetonitrile, followed by 6 ml of distilled water. the separations were carried out using a mu Bondapak c18 column with a mobile phase comprising acetonitrile (60 ml), methanol (10 ml) and tetrahydrofuran (10 ml) in 15 mM phosphate buffer (920 ml) at pH 2.90. Separations were performed at 40 degrees C and detection was at 206 nm. Standard calibration plots of lisinopril in urine were linear (r > 0.998) and recovery was greater than 64%. The lowest quantifiable concentration was 0.5 micrograms/ml. Within-day and between-day imprecision (coefficient of variation) ranged from 2.51% to 9.26%, and inaccuracy was less than 8.3%.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

Solid-phase extraction of arginine vasotocin and isotocin in fish samples and subsequent gradient reversed-phase high-performance liquid chromatographic separation.

Gradient high-performance liquid chromatography (HPLC) preceded by a solid-phase extraction (SPE) step is described for determining arginine vasotocin and isotocin, the neurohypophysial nonapeptides, in fish plasma samples. The combination of these two methods significantly improves the separation and increases the sensitivity of the assay. The proposed assay may be a useful alternative for analysis of similar nonapeptides in plasma without the use of radioisotopes, while taking into consideration a difference in detection sensitivity.

Amino Acid Sequence↗
PubMed1996

Sensitive fluorimetric determination of gentamicin sulfate in biological matrices using solid-phase extraction, pre-column derivatization with 9-fluorenylmethyl chloroformate and reversed-phase high-performance liquid chromatography.

A high-performance liquid chromatographic method is described for the determination of gentamicin in bacterial culture medium or plasma with increased sensitivity and improved separation of the C1 component. Gentamicin was extracted from the biological matrix with high efficiency using carboxypropyl (CBA)-bonded silica. Derivatization with 9-fluorenylmethyl chloroformate (FMOC-Cl) followed by C18 reversed-phase chromatography allowed the fluorimetric detection of gentamicins C1, C1a and C2. A fourth component, considered to be gentamicin C2a, was partially resolved from the C2 peak. Optimal conditions for the extraction and derivatization of gentamicin are described. The detection limit was below 50 micrograms/l, the assay was linear to 5 mg/l and showed good reproducibility. It is concluded that pre-column derivatization with FMOC-Cl substantially improves the analysis of gentamicin compared with present methods based on reaction with o-phthaldialdehyde.

Chromatography, High Pressure Liquid↗
PubMed1996

Determination of fenbufen and its metabolites in serum by reversed-phase high-performance liquid chromatography using solid-phase extraction and on-line post-column ultraviolet irradiation and fluorescence detection.

An improved analytical method for the detection and quantification of fenbufen and its two major metabolites is described. The assay consists of reversed-phase high-performance liquid chromatography and post-column irradiation with ultraviolet light and fluorescence detection. A highly selective chromatography separation was established on a cyanopropyl column at ambient temperature with a flow-rate of 0.5 ml/min. The analytes of interest were isolated from serum using a Bond-Elut CIN column with high recovery and selectivity. The fluorescence response of all three analytes upon UV irradiation was investigated. The post-column UV irradiation was optimized and the effect of irradiation time on the fluorescence response was determined for all three analytes. The detection limits were 10 ng/ml for each analyte using 1 ml of serum. Linear calibration curves from 50 to 375 ng/ml for all three analytes show coefficients of determination of 0.99. Precision and accuracy of the method were within 3.9-6.5 and 5.1-7.4% for fenbufen, 3.5-6.4 and 4.9-6.3% for metabolite II (expressed as lactone III) and 5.4-7.4 and 2.6-7.4% for metabolite IV, respectively.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1990

On-line recovery of trimeprazine enantiomers following chiral separation by reversed-phase high-performance liquid chromatography using a beta-cyclodextrin-containing mobile phase.

A procedure is described which allows the on-line recovery of enantiomers following semi-preparative chiral separation by RP-HPLC using beta-cyclodextrin in the mobile phase. By this method, the phenothiazine antihistamine trimeprazine (I) was resolved into its antipodes at greater than 95% optical purity at a throughput of more than 1 mg of each enantiomer per hour, using 4 mm i.d. columns. The recovered trimeprazine was found to be free from cyclodextrin.

Chromatography, High Pressure Liquid↗
PubMed1991

NMR-monitored solid-phase extraction of phenolphthalein glucuronide on phenylboronic acid and C18 bonded phases.

Preliminary studies have been undertaken to evaluate the potential of immobilized phenylboronic acid (PBA) for the solid-phase extraction (SPE) of glucuronide metabolites from urine. These studies have demonstrated that immobilized PBA can be used to specifically extract phenolphthalein glucuronide (5 mM) from urine. Urine samples were loaded onto the PBA SPE column in glycine buffer (pH 8.5) and were eluted using methanol-1% HCl (90:10, v/v). The overall recoveries of the phenolphthalein glucuronide for this procedure were high (99%), which compared well with similar studies carried out concomitantly on C18 bonded columns (93%).

Boronic Acids↗
PubMedDate not supplied

Antibodies to Campylobacter flagellin recognize epitopes common to phase 1 and phase 2 flagella.

We used a simple method to obtain purified flagellin from Campylobacter, suitable for an immunization procedure in mice. Western blot analysis of cross-reacting antibodies showed that there were epitopes common to phase 1 and 2 flagellins. Analysis by ELISA suggested that certain common flagellar epitopes are conformational, and antibody immobilization tests confirmed that common surface-exposed epitopes exist in a region of flagella necessary for conferring motility to the bacteria.

Animals↗
PubMed2006

Solid-phase classical complement activation by C-reactive protein (CRP) is inhibited by fluid-phase CRP-C1q interaction.

C-reactive protein (CRP) interacts with phosphorylcholine (PC), Fcgamma receptors, complement factor C1q and cell nuclear constituents, yet its biological roles are insufficiently understood. The aim was to characterize CRP-induced complement activation by ellipsometry. PC conjugated with keyhole limpet hemocyanin (PC-KLH) was immobilized to cross-linked fibrinogen. A low-CRP serum with different amounts of added CRP was exposed to the PC-surfaces. The total serum protein deposition was quantified and deposition of IgG, C1q, C3c, C4, factor H, and CRP detected with polyclonal antibodies. The binding of serum CRP to PC-KLH dose-dependently triggered activation of the classical pathway. Unexpectedly, the activation was efficiently down-regulated at CRP levels > 150 mg/L. Using radial immunodiffusion, CRP-C1q interaction was observed in serum samples with high CRP concentrations. We propose that the underlying mechanism depends on fluid-phase interaction between C1q and CRP. This might constitute another level of complement regulation, which has implications for systemic lupus erythematosus where CRP is often low despite flare-ups.

C-Reactive Protein↗
PubMed2004

Microwave-immobilized polybutadiene stationary phase for reversed-phase high-performance liquid chromatography.

Polybutadiene (PBD) has been immobilized on high-performance liquid chromatography (HPLC) silica by microwave radiation at various power levels (52-663 W) and actuation times (3-60 min). Columns prepared from these reversed-phase HPLC materials, as well as from similar non-irradiated materials, were tested with standard sample mixtures and characterized by elemental analysis (%C) and infrared spectroscopy. A microwave irradiation of 20 min at 663 W gives a layer of immobilized PBD that presented good performance. Longer irradiation times give thicker immobilized layers having less favorable chromatographic properties.

Butadienes↗
PubMed2005

Vapor-phase analysis of isobutyl acetate, isopropyl acetate, n-propyl acetate and their respective alcohols using solid-phase microextraction-gas chromatography with a mass selective detector.

A solid-phase microextraction (SPME)-GC-MS method for three esters and the corresponding alcohols was tested for responses in accuracy, within-run precision (repeatability), and between-run precision (reproducibility) due to individual operators, individual analysis days, and differing analyte concentrations. At 5 ppm (v/v) [ppmv], three of the six analytes showed significant (p < 0.05) operator effects, while five of six analytes gave a significant effect due to the days of analysis. At 20 ppmv, five of the six analytes gave significant operator and daily effects. At 100 ppmv, all the analytes showed significant daily effects but no operator effects were observed. The repeatability was concentration dependent, with all six analytes combining for an average RSD of 12.1 +/- 6.1% at 1 ppmv, becoming most precise at 50 ppmv at 1.01 +/- 0.45%, then increasing at 100 ppmv to 4.12 +/- 1.88%. The contributors to error trended as: concentration > daily effects > operator.

2-Propanol↗
PubMed2005

Determination of triptolide in root extracts of Tripterygium wilfordii by solid-phase extraction and reverse-phase high-performance liquid chromatography.

Extracts of Tripterygium wilfordii roots have a long history of use in traditional Chinese medicine and have shown great promise in recent clinical trials as a treatment for rheumatoid arthritis. The major active component of Tripterygium root extracts is the diterpenoid triptolide. This paper describes a method for the determination of triptolide in root extracts that is suitable for the analysis of many small samples simultaneously. Extracts are applied to aminopropyl solid-phase extraction (SPE) tubes that are then eluted with dichloromethane-methanol (49:1, v/v). The eluate is chromatographed on a pentafluorophenyl HPLC column using an acetonitrile:water gradient. Triptolide is quantified by ultraviolet detection at 219 nm. Using this method, it was shown that smaller diameter roots with secondary growth contained higher triptolide concentrations than larger roots. This suggests that roots to be used for production of the drug extract could be harvested while still small, which would reduce the growing time necessary and thus be economically beneficial for the growers.

Celastraceae↗
PubMed2005

Development and validation of a microsomal online cytochrome P450 bioreactor coupled to solid-phase extraction and reversed-phase liquid chromatography.

The development and validation of an online cytochrome P450 (CYP)-based bioreactor coupled to automated solid-phase extraction (SPE) and gradient HPLC separation is described. The analytical method was checked on intra- and inter-day repeatability of the ethoxyresorufin-O-demethylation (EROD) reaction with CYP 1Al/1A2 containing beta-NF induced rat liver microsomes as an enzyme source. These experiments showed that CYP activity was linearly decreased with 16% over an 11 h period. Inter-day measurements had a CV of 9.1%. Furthermore, Km and Vmax values of the EROD reaction, measured with the bioreactor, were 2.72 +/- 0.46 microM and 7.9 +/- 0.5 nmol/min/mg protein, respectively. These were in good correspondence with Km and Vmax values, measured with standard batch assay, which amounted 0.66 +/- 0.08 microM and 6.4 +/- 0.2 nmol/min/mg protein respectively. In conclusion the newly developed analytical method can be used effectively and at a microliter scale for online generation, extraction and separation of metabolites.

Animals↗
PubMed2006

Solid-phase extraction-gas chromatography and solid-phase extraction-gas chromatography-mass spectrometry determination of corrosion inhibiting long-chain primary alkyl amines in chemical treatment of boiler water in water-steam systems of power plants.

Gas chromatography with simultaneous flame-ionization detection (FID) and a nitrogen-phosphorus detection (NPD) as well as gas chromatography-mass spectrometry (GC/MS) has been used to characterize long-chain primary alkyl amines after derivatization with trifluoroacetic anhydride (TFAA). Electron impact ionization- (EI) and negative chemical ionization (NCI) mass spectra of trifluoroacetylated derivatives of the identified tert-octadecylamines are presented for the first time. The corrosion inhibiting alkyl amines were applied in a water-steam circuit of energy systems in the power industry. Solid-phase extraction (SPE) with octadecyl bonded silica (C18) sorbents followed by gas chromatography were used for quantification of the investigated tert-octadecylamines in boiler water, superheated steam and condensate samples from the power plant. The estimated values were: 89 microg l(-1)(n = 5, RSD = 7.8%), 45 microg l(-1) (n = 5, RSD = 5.4%) and 37 microg l(-1)(n = 5, RSD = 2.3%), respectively.

Amines↗
PubMed2006

On-fibre solid-phase microextraction coupled to conventional liquid chromatography versus in-tube solid-phase microextraction coupled to capillary liquid chromatography for the screening analysis of triazines in water samples.

This paper compares the advantages and disadvantages of two different configurations for the extraction of triazines from water samples: (1) on-fibre solid-phase microextraction (SPME) coupled to conventional liquid chromatography (LC); and (2) in-tube SPME coupled to capillary LC. In-tube SPME has been effected either with a packed column or with an open capillary column. A critical evaluation of the main parameters affecting the performance of each method has been carried out in order to select the most suitable approach according to the requirements of the analysis. In the on-fibre SPME configuration the fibre coating was polydimethylsiloxane (PDMS)-divinylbenzene (DVB). The limits of detection (LODs) obtained with this approach under the optimized extraction and desorption conditions were between 25 and 125 microg/L. The in-tube SPME approach with a C18 packed column (35 mm x 0.5 mm I.D., 5 microm particle size) connected to a switching micro-valve provided the best sensitivity; under such configuration the LODs were between 0.025 and 0.5 microg/L. The in-tube SPME approach with an open capillary column coated with PDMS (30 cm x 0.25 mm I.D., 0.25 microm of thickness coating) connected to the injection valve provided LODs between 0.1 and 0.5 microg/L. In all configurations UV detection at 230 nm was used. Atrazine, simazine, propazine, ametryn, prometryn and terbutryn were selected as model compounds.

Chromatography, Liquid↗
PubMed2006

Determination of triphenylphosphine oxide in active pharmaceutical ingredients by hollow-fiber liquid-phase microextraction followed by reversed-phase liquid chromatography.

A versatile procedure has been developed and validated for the determination of triphenylphosphine oxide (TPPO) at low levels in various active pharmaceutical ingredients (APIs). This procedure incorporates the use of the novel hollow-fiber liquid-phase microextraction (LPME) for the measurement of this potential process-related impurity in aqueous solutions of APIs. A small volume (40 microL) of 1-octanol contained within a hollow polypropylene fiber is used for the extraction of TPPO from low pH aqueous API solutions. More than a 100-fold increase in the TPPO concentration is obtained without additional evaporation of the extract. Experimental parameters of the extraction procedure were investigated to optimize extraction efficiency and minimize sample matrix interference. Using HPLC/UV as the end analysis technique, the procedure was validated for TPPO in the concentration range of 3-16 microg/L with an API present at 1500 mg/L. The versatility of the method was demonstrated by applying the procedure to the analysis of APIs with different molecular structures. This simple LPME procedure is inexpensive and offers appropriate sensitivity for the intended use while providing several advantages over other analysis methods for pharmaceutical samples.

Chemical Fractionation↗