Quantitative determination of p-aminosalicylic acid and its degradation product m-aminophenol in pellets by ion-pair high-performance liquid chromatography applying the monolithic Chromolith Speedrod RP-18e column

An ion-pair high performance liquid chromatographic method was developed for the simultaneous determination of p-aminosalicylic acid (PAS) and its degradation product m-aminophenol (MAP) in a newly developed multiparticular drug delivery system. Owing to the concentration differences of PAS and MAP, acetanilide and sulfanilic acid were used as internal standards, respectively. The separation was performed on a Chromolith SpeedROD RP-18e column, a new packing material consisting of monolithic rods of highly porous silica. The mobile phase composition was of 20 mm phosphate buffer, 20 mm tetrabutylammonium hydrogen sulphate and 16% (v/v) methanol adjusted to pH 6.8, at a flow-rate of 1.0 mL/min, resulting in a run-time of about 6 min. Detection was by UV at 233 nm. The method was validated and proved to be useful for stability testing of the new dosage form. Separation efficiency was compared between the new packing material Chromolith SpeedROD RP-18e and the conventional reversed-phase cartridge LiChroCART 125-4 (5 microm). A robustness test was carried out on both columns and different separation parameters (retention, resolution, run time, temperature) were determined.

Review: HPLC Determination of Fumonisin Mycotoxins

An overview of liquid chromatographic methods, mainly employing fluorescence detection together with sample pre-treatment methods, is presented for the determination of the toxic group of fumonisin mycotoxins in various matrices.

Application of an alkyl-diol silica precolumn in a column-switching system for the determination of meloxicam in plasma

The group of LiChrospher alkyl-diol silica (ADS) phases that make part of the unique family of restricted-access materials, have been developed as special packings used in the liquid chromatographic integrated sample processing of biofluids. The advantage of these phases lies in the possibility of direct injection of untreated plasma. An on-line elimination of the protein matrix is achieved with a quantitative recovery together with an on-column enrichment. The present method describes a hand-operated on-line switching high-performance liquid chromatographic system for the determination of meloxicam. Spiked plasma samples were introduced on the ADS precolumn using a 0.05 M phosphate buffer, pH 6.0. After washing with the buffer the ADS column was backflushed with the mobile phase 0.05 M phosphate buffer-30% (v/v) acetonitrile (ACN)-25 mM t-butylamine (TBA) at a pH of 7.0, thus transferring the analyte to the analytical column LiChrocart 125-4 LiChrospher RP-8. The eluent was monitored by a UV-detector set at 364 nm. The developed column-switching method is fully applicable to plasma injections.

Comparison of morphine and hydromorphone analysis on reversed phase columns with different diameters

A comparison of a reversed phase high-performance liquid chromatographic (HPLC) method performed on columns with different internal diameters is reported for the quantitative routine determination of morphine.HCl and hydromorphone.HCl in solutions used for intramuscular injection. The method is based on the ion-pairing properties of sodium dodecyl sulphate (SDS) with alkaloids on a reversed phase LiChrospher RP-18 packing material and UV-detection at 230 nm. The mobile phase consisted of an acetonitrile: water mixture 35:65 (v/v) containing 0.5% (w/v) SDS and 0.4% (v/v) acetic acid. Precision, linearity and limit of detection were compared on the 2, 3 and 4 mm i.d. x 125 mm columns. A robustness test for the determination of hydromorphone.HCl was also evaluated.

A validated HPLC method for the determination of thiazinamium methylsulphate in pharmaceutical preparations

The phenothiazine derivative thiazinamium methylsulphate is a drug with antihistaminic and anticholinergic properties, often used in some types of obstructive lung diseases. Because there is a lack of chromatographic data available for its determination, the objective of the present investigation was to develop a sensitive and rapid HPLC method for the quantitative estimation of thiazinamium methylsulphate in a pharmaceutical dosage form, applicable to routine analysis. The drug was chromatographed on a C18-reversed phase system applying a Licrocart column (LiChrospher 100 RP 18, 125 x 4 mm) with a mobile phase consisting of acetonitrile-water (3:7, v/v), employing as ion-pairing agent octanesulphonic acid sodium salt (20 mM) together with N,N-dimethyloctylamine (20 mM), adjusted to pH 3. Detection occurred at 254 nm. Propylparaben was used as an internal standard. The method was applied to solutions for intramuscular injection containing thiazinamium methylsulphate (65 mg/2 ml). Since little sample preparation is required, most analyses can be carried out within 15 min. The optimized method was validated and provided acceptable results with respect to linearity (r = 0.9999), precision and accuracy in the concentration range of 26-78 microg/ml. The proposed method is presently employed to investigate the stability of thiazinamium methylsulphate in solutions for intramuscular injection in the presence of anti-oxidizing agents.

Application of the restricted-access precolumn packing material alkyl-diol silica in a column-switching system for the determination of ketoprofen enantiomers in horse plasma

The group of LiChrospher ADS (alkyl-diol silica) sorbents that make part of a unique family of restricted-access materials, have been developed as special packings for precolumns used in the LC-integrated sample processing of biofluids. The advantage of these sorbents lies in the direct injection of untreated biological fluids, that is without sample clean-up, the elimination of the protein matrix with a quantitative recovery together with an on-column enrichment. The present method is based on previous work applying UV detection at 260 nm for ketoprofen determinations. Plasma samples introduced to the ADS precolumn using a 0.1 M phosphate buffer, pH 7.0. After washing with the buffer the ADS column was backflushed with the mobile phase 0.01 M phosphate buffer-6% (v/v) 2-propanol-5 mM octanoic acid at a pH of 5.5, thus transporting the analytes to the chiral-HSA (human serum albumin) (100x4.0 mm) column where the separation of the ketoprofen enantiomers was achieved with a resolution factor of 1.4. The developed column-switching method was fully applicable to plasma injections.

Direct HPLC analysis of ketoprofen in horse plasma applying an ADS-restricted access-phase

Making up part of the unique family of restricted access materials (RAM) the Lichrospher ADS (alkyl-diol silica) sorbents have been developed as special packing materials for precolumns used for LC-integrated sample processing of biofluids. The advantage of such phases consists of direct injection of untreated biological fluids without sample clean-up and elimination of the protein matrix together with an on-column enrichment. The plasma samples, with internal standard phenacetin added (not essential), were brought onto the precolumn (C-18 ADS, 25 micron, 25 x 4 mm i.d.) using a phosphate buffer, 0.1 M, pH 7.0. After washing with the buffer, the ADS column was backflushed with the mobile phase phosphate buffer 0. 05 M pH 7.0: acetonitrile (80:20), thus transporting the analytes onto a reversed-phase column Ecocart 125-3 HPLC cartridge with a LiChrocart 4-4 guard column, both packed with LiChrospher 5 micron 100 RP-18; after separation detection was performed in UV at 260 nm. Essential features of the method include the novel precolumn packing, the absence of sample pretreatment, a quantitave recovery, good precision and accuracy, as well as a considerable reduction of analysis time compared to conventional manual methods applied in bioavailability studies.

A first and straightforward approach to detection limits for narrow-bore HPLC and CE

Two methodologies have been proposed for a simple statistical estimation of the detection limits in microbore-HPLC and CE techniques. Due to the impossibility to measure the blank, by using the extrapolated or approximated expressions it is possible to obtain a straightforward approach of the detection limits from the study of the residuals of the calibration data set, avoiding tedious treatment of the signals. The utility of these expressions has been checked on the data from an experimental microbore HPLC system.

Chemiluminescence determination of tiopronin by flow injection analysis based on cerium(IV) oxidation sensitized by quinine

A flow injection analysis method is proposed for the determination of tiopronin based upon the oxidation by cerium(IV) in dilute sulfuric acid medium and sensitized by quinine. With the peak height as a quantitative parameter applying optimum working conditions, tiopronin is determined over the 1-400 microM range (150 microliters per injection, n = 10, r = 0.9994) with a detection limit of 0.34 microM and an RSD (n = 10) less than 2% at 20 and 50 microM. The proposed method, combining the advantages of speed and sensitivity, was applied to the routine determination of tiopronin in a pharmaceutical preparation.

Bioavailability of ketoprofen in horses after rectal administration

Six healthy mares ranging in age from 6 to 12 years and weighing from 415 to 540 kg were used to determine the rectal bioavailability of ketoprofen. For the rectal administration, three different formulations, each containing 1 g of ketoprofen, were administered in a fatty and a hydrophilic suppository base and as a liquid suspension. An average elimination half-life of 1.3 h (+/-1.2) was found. The average value for the total plasma clearance (ClT) was 131.9mL/ min.kg (range 95-183.5). The volume of distribution Vd(area) was 255 mL/kg and the mean residence time (MRT) value was 0.47 h. After rectal administration, the mean maximal plasma ketoprofen concentrations were 1.6(+/-0.8), 1.1(+/-0.7) and 1.6(+/-0.2) micrograms/mL for the fatty suppository, the hydrophilic suppository and the liquid suspension respectively. The absolute bioavailability of ketoprofen in horses after rectal administration of the three formulations was relatively low, with a large interindividual variability (24.5 +/- 9.5%, 28.7 +/- 18% and 31.3 +/- 6.8% for the fatty suppository, the hydrophilic suppository and the liquid suspension respectively). These values were not significantly different (P = 0.05; Friedman test). Despite the low rectal bioavailability obtained in this study, there was some evidence for the clinical effectiveness of the rectal formulations.

Chemiluminescence flow-injection analysis of captopril applying a sensitized rhodamine 6G method

A flow-injection analysis with chemiluminescence detection is described for the determination of captopril based on the photochemical reaction with cerium(IV) in sulphuric acid medium yielding a strong chemiluminescent signal which can be sensitized by some fluorescers. The proposed procedure has a linear application range of 1 x 10(-6) - 2 x 10(-4) M (r = 0.997) with a detection limit of 2 x 10(-7) M, an RSD of 2.8% at 1 x 10(-6) M captopril, and a sample measurement frequency of 500 h-1. The method was used for the simple and rapid determination of captopril in a pharmaceutical preparation.

Chemiluminescence analysis of captopril: comparison between luminol and rhodamine B-sensitized cerium(IV) methods

Two chemiluminescence methods for the determination of captopril are compared in the present paper. The first method is based on the reaction of captopril with the luminol-hydrogen peroxide-copper(II) system, the copper(II) ion acting as a key species in the light-emitting process. The catalytic activity of copper(II) decreases due to complex formation with the sulphhydrylic captopril analyte. Application of this indirect method allows captopril determinations in the 8.0-1.0 microM range as starting concentrations. Similarly, captopril was capable of generating chemiluminescence from acid cerium(IV) solutions, a reaction that could be analytically exploited by the inclusion of the rhodamine B fluorophore yielding a sensitized-type of chemiluminescence emission that allowed quantitation of captopril concentrations in the 0.1-6.0 microM range with a detection limit of 0.037 microM (original concentration). For both types of reaction the experimental conditions were optimized and a direct application was carried out on a commercial drug formulation.

Determination of S-carboxymethylcysteine in serum by reversed-phase ion-pair liquid chromatography with column switching following pre-column derivatization with o-phthalaldehyde

A method is described for the determination of S-(carboxymethyl)-L-cysteine in serum. After addition of S-(carboxyethyl)-L-cysteine as internal standard, both compounds are extracted into methanol, converted into fluorescent derivatives with o-phthalaldehyde and quantitatively determined by reversed-phase high-performance liquid chromatography. Chromatography of unwanted amino acid derivatives is avoided by column switching, thereby shortening analysis time and increasing column lifetime. The technique was applied in a study of the bioavailability of S-(carboxymethyl)-L-cysteine after oral administration to humans. The concentration-response curve was linear from 2 to 16 micrograms/ml; mean serum concentrations are reported.

Quantitative liquid chromatographic determination of cefatrizine in serum and urine by fluorescence detection after post-column derivatization

A fast, specific and sensitive high-performance liquid chromatographic procedure for the determination of cefatrizine, an orally active cephalosporin, in serum and urine is proposed. The drug is determined by the internal standard method, using cephradine as the internal standard. The separation is carried out on a reversed-phase column, filled with octadecylsilane chemically bonded microparticles. The eluent is a mixture of acetonitrile with 0.025 M sodium phosphate buffer (pH 7). Quantitation is effected by fluorescence detection of the fluorophores formed after post-column derivatization with fluorescamine in a packed-bed reactor. The chromatographic conditions and the conditions for the post-column derivatization are discussed. The method has been applied to serum and urine samples, which were analysed after deproteinization with trichloroacetic acid and injection of the clear supernatant. The accuracy and reproducibility of the procedure were investigated by the determination of the cefatrizine content in spiked serum and urine samples.

Determination of cefatrizine in serum and urine by reversed-phase high-performance liquid chromatography

A fast and simple high-performance liquid chromatographic procedure for the determination of cefatrizine, an orally active cephalosporin, in serum and urine is proposed. Reversed-phase liquid chromatography on the octoadecylsilane chemically bonded microparticulate packing, using methanol in 0.03 M sodium phosphate buffer (pH 5) as eluent, was used to separate and quantitate the antibiotic. The samples were analysed after deproteinization with trichloroacetic acid and injection of the clear supernatant. The accuracy and reproducibility of the procedure were investigated by determination of the cefatrizine content in spiked serum and urine samples, using cephradine as the internal standard.