Simultaneous analysis of 14 non-steroidal anti-inflammatory drugs in human serum by electrospray ionization-tandem mass spectrometry without chromatography

An overview of the recent developments in analytical methodologies for determination of COX-2 inhibitors in bulk drugs, pharmaceuticals and biological matrices

An extensive survey of the literature published in various analytical and pharmaceutical chemistry related journals has been conducted and the instrumental analytical methods which were developed and used for determination of COX-2 inhibitors in bulk drugs, formulations and biological fluids have been reviewed. This review covers the time period from 1995 to 2004 during which 138 analytical methods including all types of spectrophotometric and chromatographic techniques were reported. HPLC with UV detection was found to be the technique of choice for many workers and more than 100 methods were based on LC and UV. A critical analysis of the reported data has been carried out and the present state-of-art of the analytical techniques for determination of celecoxib, rofecoxib, etoricoxib, etodolac, nimesulide and meloxicam has been discussed.

Simultaneous quantitation of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib in plasma by high-performance liquid chromatography with UV detection

A specific, accurate, precise and reproducible high performance liquid chromatography (HPLC) method was developed and validated for the simultaneous quantitation of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib in human plasma. The method employed a simple liquid-liquid extraction of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide and celecoxib and internal standard (IS, DRF-4367) from human plasma (500 microL) into acetonitirile. The organic layer was separated and evaporated under a gentle stream of nitrogen at 40 degrees C. The residue was reconstituted in the mobile phase and injected onto a Kromasil KR 100-5C18 column (4.6 x 250 mm, 5 microm). The chromatographic separation was achieved by gradient elution consisting of 0.05 M formic acid (pH 3)-acetonitrile-methanol-water at a flow rate of 1.0 mL/min. The eluate was monitored using an ultraviolet (UV) detector set at 235 nm. The ratio of peak area of each analyte to IS was used for quantification of plasma samples. Nominal retention times of etoricoxib, salicylic acid, valdecoxib, ketoprofen, nimesulide, IS and celecoxib were 15.63, 17.20, 21.66, 24.95, 26.27, 30.24 and 32.22 min, respectively. The standard curve for etoricoxib, salicylic acid, valdecoxib, ketoprofen and celecoxib was linear (r2 > 0.999) in the concentration range 0.1-50 microg/mL and for nimesulide (r2 > 0.999) in the concentration range 0.5-50 microg/mL. Absolute recovery was >83% from human plasma for all the analytes and IS. The lower limit of quantification (LLOQ) of nimesulide was 0.5 microg/mL and for etoricoxib, salicylic acid, valdecoxib, ketoprofen and celecoxib the LLOQ was 0.1 microg/mL. The inter- and intra-day precisions in the measurement of QC samples, 0.1, 0.3, 15.0 and 40.0 microg/mL (for all analytes except nimesulide), were in the range 2.29-9.37% relative standard deviation (RSD) and 0.69-10.28% RSD, respectively. For nimesulide the inter- and intra-day precisions in the measurement of quality control (QC) samples, 0.5, 1.5, 15.0 and 40.0 microg/mL, were in the range 3.21-7.37% RSD and 0.97-7.06% RSD, respectively. Accuracy in the measurement of QC samples for all analytes was in the range 91.03-106.38% of the nominal values. All analytes including IS were stable in the battery of stability studies, viz. bench top, autosampler and freeze-thaw cycles. Stability of all analytes was established for 21 days at -20 degrees C. The application of the assay in an oral pharmacokinetic study in rats co-administered with celecoxib and valdecoxib is described.

Development and validation of a reversed-phase liquid chromatographic method for separation and simultaneous determination of COX-2 inhibitors in pharmaceuticals and its application to biological fluids

An isocratic reversed-phase high-performance liquid chromatographic method has been developed for separation and simultaneous determination of COX-2 inhibitors, viz., celecoxib, rofecoxib, valdecoxib, nimesulide and nabumetone, using 4-chloro-2-nitroaniline as internal standard. Good chromatographic separation was achieved using a reversed-phase Inertsil C(18) column with mobile phase consisting of methanol and 0.05% aqueous glacial acetic acid (68:32 v/v) using photodiode array (PDA) detector at 230 nm. It was validated with respect to accuracy, precision, linearity, limit of detection and quantification. The linearity range was found to be 1.0--20 microg/mL and the percentage recoveries were between 97.55 and 100.14. The method is suitable not only for the estimation of active ingredients in pharmaceutical dosage forms but also in vitro estimations in human plasma. It is simple, rapid, selective and capable of detecting and determining COX-2 inhibitors with a detection limit of 0.127--1.040 microg/mL simultaneously.

Analysis of ketorolac and its related impurities by capillary electrochromatography

Capillary electrochromatography (CEC) was employed for the assay of ketorolac (KT) and its known related impurities [1-hydroxy analog of ketorolac (HK), 1-keto analog of ketorolac (KK), ketorolac decarboxylated (DK)] in both drug substance and coated tablets. Detection was made at 323 nm and flufenamic acid was selected as internal standard. The experiments were performed in a 100 microm i.d. capillary packed with RP-18 silica particles (33.0, 24.5, 23.0 cm total, effective and packed lengths, respectively). The composition of the mobile phase was optimised by changing pH of the buffer and acetonitrile (ACN) content and by addition of other organic modifiers (methanol, ethanol, isopropanol, n-propanol) in order to evaluate the effect of these factors on the method performance (efficiency, retention and resolution). The optimum mobile phase consisted of a mixture of 50 mM ammonium formate buffer pH 3.5-water-acetonitrile (10:20:70, v/v/v), while voltage and temperature were set at 30 kV and 20 degrees C, respectively. Applying these conditions, all peaks were baseline resolved and the analysis was performed in less than 9 min. Selectivity, repeatability of retention time and peak area, detection and quantitation limits, linearity and range, precision and accuracy were also investigated. R.S.D. and bias values obtained for all the analytes were below 5% and sensitivity was satisfactory, thus the method was deemed suitable for pharmaceutical quality control. Applying the method to coated tablets, a recovery of 98.5+/-0.8% and an R.S.D. of 0.5% were found.

Micellar electrokinetic chromatography for the simultaneous determination of ketorolac tromethamine and its impurities

A simple, fast and selective micellar electrokinetic chromatographic (MEKC) method for the simultaneous assay of ketorolac tromethamine and its known related impurities (1-hydroxy analog of ketorolac, 1-keto analog of ketorolac and decarboxylated ketorolac), in both drug substance and coated tablets, is described. The compounds were detected at 323 nm, and flufenamic acid (FL) and tolmetin (TL) were chosen as internal standards to quantify ketorolac tromethamine and impurities, respectively. The multivariate optimization of the experimental conditions was carried out by means of the response surface study, considering as responses the resolution values and analysis time. The optimized background electrolyte (BGE) consisted of a mixture of 13 mM boric acid and phosphoric acid, adjusted to pH 9.1 with 1 M sodium hydroxide, containing 73 mM sodium dodecyl sulfate (SDS). Optimal temperature and voltage were 30 degrees C and 27 kV. Applying these conditions, all compounds were resolved in about 6 min. The related substances could be quantified up to the 0.1% (w/w) level. Validation was performed, either for drug substances and drug product, evaluating selectivity, robustness, linearity and range, precision, accuracy, detection and quantitation limits and system suitability.

The use of particle beam mass spectrometry for the measurement of impurities in a nabumetone drug substance, not easily amenable to atmospheric pressure ionisation techniques

Liquid chromatography/particle beam mass spectrometry (LC/PB-MS) was used for the structural elucidation of some impurities in nabumetone as this compound poorly ionises by atmospheric pressure ionisation (API) techniques. PB-MS was optimised for nabumetone and a sensitivity study was carried out. To obtain full scan electron ionisation spectra a minimum of 100 ng of compound on column was needed. By using 20 mg/mL solutions of nabumetone, impurities at levels of about 250 ppm mass fraction relative to nabumetone could be detected. Results were compared with LC/API-MS and previous GC/MS.

Screening for drugs in serum by electrospray ionization/collision-induced dissociation and library searching

Factors influencing in-source collision-induced dissociation (ESI/CID) of organic molecules in a Perkin-Elmer/SCIEX ionspray source have been investigated. Breakdown curves of four drugs and organic compounds were acquired by monitoring the intensities of MH+ and specific fragment ions while ramping the orifice voltage. Haloperidol, diazepam, 1,4-acetamido-acetoxybenzene and diacetamido-1,2-benzene were found to be substances with characteristic breakdown curves, with maximums and points of intersection at orifice voltages between 20 and 70 V. The breakdown curves of haloperidol were used for comparison of ESI/CID with ionspray and turboionspray sources on three PE/SCIEX-API instruments. Using standardized source parameters and mass resolution, very similar fragmentation graphs were obtained for haloperidol with all instruments. Infusion of varying concentrations of haloperidol (0.1 to 10 micrograms/mL with ionspray, and 0.01 to 1 microgram/mL with turboionspray) yielded comparable breakdown curves. With turboionspray, a preconcentration of the aerosol occurred, yielding higher ion abundances. Solvent pH and the ratio of aqueous ammonium formate/acetonitrile had minor effects on the degree of fragmentation of haloperidol in a wide range. With these preconditions, a currently expanding mass spectral library of 400 drugs was set up by liquid chromatography/mass spectrometry with alternating orifice voltages (20, 50, and 80 V, respectively) in a looped experiment. An example of drug identification in a patient's serum with library search is shown.

Characterization of a technique for rapid pharmacokinetic studies of multiple co-eluting compounds by LC/MS/MS

A method for rapid pharmacokinetic screening of multiple potential drug candidates has been developed. This technique, based on the ability of liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) to independently monitor multiple components, enables the quantification of substances which may or may not be chromatographically resolved. Our results indicate that the limit of quantitation and accuracy of this multiple-compound LC/MS/MRM quantitation method are comparable to a single-compound LC/MS/MRM quantitation method. No apparent ion suppression due to the existence of extraneous compounds in the analytical solution and biological matrix effect are observed in the range of the calibration curve. The issue of potential residual molecule cross-talk interference existing in the multiple-reaction monitoring mode has been discussed. This multiple-compound LC/MS/MRM quantitation method can be used for high throughput pharmacokinetic screening and to assay mixtures that have co-eluting analytes or similar m/z of precursor/product ion pairs.