Analysis of ketorolac and its related impurities by capillary electrochromatography

Development of a capillary electrophoretic method for determination of ketorolac enantiomers in human plasma using cationic β-cyclodextrin derivative as a chiral selector

A novel approach for the separation of ketorolac enantiomers by capillary electrophoresis is presented. A cationic β-cyclodextrin derivative based on imidazole was synthesized and used as a chiral selector in the background electrolyte. The influence of pH and ionic strength of background electrolyte, as well as cationic β-cyclodextrin derivative concentration on the resolution of ketorolac enantiomers, was investigated. The highest value of the resolution for ketorolac enantiomers was 1.46 when the background electrolyte consisted of 25 mM NaH₂ PO₄ (pH 6.4) with 1 mM 1-butyl-3-β-cyclodextrinimidazolium tosylate. Additionally, the possibilities of cationic derivatives for the separation of ketoprofen enantiomers were shown (peak resolution 1.06). The two-step preconcentration mode was developed to reduce the limit of detection of individual enantiomers. The proposed approach was successfully applied to determine ketorolac enantiomers in tablet "Ketorol express" and human plasma. The calibration range of ketorolac enantiomers for plasma samples was 0.25-2.50 μg/ml with coefficients of determination ≥ 0.99. The relative standard deviation both of the peak area and migration time was less than 15%, as well as the accuracy ranged from 90.1% to 110.2% for both analytes. The limits of detection were 44 and 55 ng/ml for R- and S-ketorolac. The quantity of ketorolac in plasma was verified with high-performance liquid chromatography.

FeCl3-catalyzed oxidative decarboxylation of aryl/heteroaryl acetic acids: preparation of selected API impurities

There is an ever-increasing demand for impurity compounds for use in impurity profiling as regulatory agencies seek information during registration. Herein, we report the FeCl₃-catalyzed oxidative decarboxylation of aryl- and heteroaryl acetic acids to the corresponding carbonyl compounds. A variety of useful aldehydes and ketones were prepared in a simple one-pot transformation by employing an environmentally benign, low-cost, and readily available iron salt. The utility of this method has been demonstrated by preparing five valuable API impurities including a multi-gram-scale synthesis of ketorolac impurity B for the first time.

Development and Validation of a High-Performance Thin-Layer Chromatographic Method for the Simultaneous Determination of Two Binary Mixtures Containing Ketorolac Tromethamine with Phenylephrine Hydrochloride and with Febuxostat

A validated and highly selective high-performance thin-layer chromatography (HPTLC) method was developed for the determination of ketorolac tromethamine (KTC) with phenylephrine hydrochloride (PHE) (Mixture 1) and with febuxostat (FBX) (Mixture 2) in bulk drug and in combined dosage forms. The proposed method was based on HPTLC separation of the drugs followed by densitometric measurements of their spots at 273 and 320 nm for Mixtures 1 and 2, respectively. The separation was carried out on Merck HPTLC aluminum sheets of silica gel 60 F254 using chloroform-methanol-ammonia (7:3:0.1, v/v) and (7.5:2.5:0.1, v/v) as mobile phase for KTC/PHE and KTC/FBX mixtures, respectively. Linear regression lines were obtained over the concentration ranges 0.20-0.60 and 0.60-1.95 µg band(-1)for KTC and PHE (Mixture 1), respectively, and 0.10-1.00 and 0.25-2.50 µg band(-1) for KTC and FBX (Mixture 2), respectively, with correlation coefficients higher than 0.999. The method was successfully applied to the analysis of the two drugs in their synthetic mixtures and in their dosage forms. The mean percentage recoveries were in the range of 98-102%, and the RSD did not exceed 2%. The method was validated according to ICH guidelines and showed good performances in terms of linearity, sensitivity, precision, accuracy and stability.

Characterization of forced degradation products of ketorolac tromethamine using LC/ESI/Q/TOF/MS/MS and in silico toxicity prediction

Ketorolac, a nonsteroidal anti-inflammatory drug, was subjected to forced degradation studies as per International Conference on Harmonization guidelines. A simple, rapid, precise, and accurate high-performance liquid chromatography combined with electrospray ionization quadrupole time-of-flight tandem mass spectrometry (LC/ESI/Q/TOF/MS/MS) method has been developed for the identification and structural characterization of stressed degradation products of ketorolac. The drug was found to degrade in hydrolytic (acidic, basic, and neutral), photolytic (acidic, basic, and neutral solution), and thermal conditions, whereas the solid form of the drug was found to be stable under photolytic conditions. The method has shown adequate separation of ketorolac tromethamine and its degradation products on a Grace Smart C-18 (250 mm × 4.6 mm i.d., 5 µm) column using 20 mM ammonium formate (pH = 3.2): acetonitrile as a mobile phase in gradient elution mode at a flow rate of 1.0 ml/min. A total of nine degradation products were identified and characterized by LC/ESI/MS/MS. The most probable mechanisms for the formation of degradation products have been proposed on the basis of a comparison of the fragmentation of the [M + H](+) ions of ketorolac and its degradation products. In silico toxicity of the drug and degradation products was investigated by using topkat and derek softwares. The method was validated in terms of specificity, linearity, accuracy, precision, and robustness as per International Conference on Harmonization guidelines.

Enantioselective separation of the novel antidepressant mirtazapine and its main metabolites by CEC

In this work, the simultaneous enantioseparation of the second-generation antidepressant drug mirtazapine and its main metabolites 8-hydroxymirtazapine and N-desmethylmirtazapine by chiral CEC is reported. The separation of all enantiomers under study was achieved employing a capillary column packed with a vancomycin-modified diol stationary phase. With the aim to optimize the separation of the three pairs of enantiomers in the same run, different experimental parameters were studied including the mobile phase composition (buffer concentration and pH, organic modifier type and ratio, and water content), stationary phase composition, and capillary temperature. A capillary column packed with vancomycin mixed with silica particles in the ratio (3:1) and a mobile phase composed of 100 mM ammonium acetate buffer (pH 6)/H(2)O/MeOH/ACN (5:15:30:50, by vol.) allowed the complete enantioresolution of each pair of enantiomers but not the simultaneous separation of all the studied compounds. For this purpose, a packing bed composed of vancomycin-CSP only was tested and the baseline resolution of the three couples of enantiomers was achieved in a single run in less than 30 min, setting the applied voltage and temperature at 25 kV and 20 degrees C, respectively. In order to show the potential applicability of the developed CEC method to biomedical analysis, a study concerning precision, sensitivity, and linearity was performed. The method was then applied to the separation of the enantiomers in a human urine sample spiked with the studied compounds after suitable SPE procedure with strong cation-exchange (SCX) cartridges.

Enhanced Electrochemical Detection of Ketorolac Tromethamine at Polypyrrole Modified Glassy Carbon Electrode

A glassy carbon electrode modified with a coating of polypyrrole (Ppy) exhibited an attractive performance for the detection and determination of a non-steroidal and non-narcotic analgesic compound, ketorolac tromethamine (KT). Cyclic voltammetry, differential pulse and square wave voltammetry were used in a combined way to identify the electrochemical characteristics and to optimize the conditions for detection. For calibrating and estimating KT, square-wave voltammetry was mainly used. The drug shows a well-defined peak at -1.40 V vs. Ag/AgCl in the acetate buffer (pH 5.5). The existence of Ppy on the surface of the electrode gives higher electrochemical active sites at the electrode for the detection of KT and preconcentrate KT by adsorption. The square-wave stripping voltammetric response depends on the excitation signal and the accumulation time. The calibration curve is linear in the range 1 x 10(-11) to 1 x 10(-7) M with a detection limit of 1.0 x 10(-12) M. Applicability to serum samples was also demonstrated. A detection limit of 1.0 ng ml for serum was observed. Square-wave voltammetry shows superior performance over UV spectroscopy and other techniques.

Recent applications in capillary electrochromatography

In this review research papers on the application of CEC are summarized that have been published between May 2003 and May 2005. First, a short overview is given of trends and developments in CEC that may increase the applicability of the separation technique. Next, application-oriented research using CEC is described in biochemical studies, including proteomics and genomics, in the analysis of food and natural products, and in pharmaceutical, industrial, and environmental analysis.

Mixture design in the optimization of a microemulsion system for the electrokinetic chromatographic determination of ketorolac and its impurities: Method development and validation

Microemulsion EKC (MEEKC) was used for the determination of ketorolac and its three impurities. The microemulsion system was optimized, for the first time in the literature, using a multivariate strategy involving a mixture design. A 13-run experimental plan covering an experimental domain defined by the components aqueous phase (10 mM borate buffer pH 9.2), oil phase (n-heptane) and surfactant/cosurfactant (SDS/n-butanol) was carried out. Good results were obtained with all microemulsions tested considering as responses analysis time and resolution, and according to the desirability function the best microemulsion system was constituted by 90.0% 10 mM borate buffer, 2.0% n-heptane, 8.0% of SDS/n-butanol in 1:2 ratio. Finally, with the aim of reducing analysis time, a response surface study was carried out in the experimental domain defined by the process variables temperature and voltage and the best values were 17 degrees C and -17 kV, respectively. Applying the optimised conditions, a complete resolution among the analytes was obtained in about 3 min using the short-end injection method. The method was validated for both drug substances and drug product and was applied to the quality control of ketorolac in coated tablets. A comparison of MEEKC, MEKC and CEC for assaying ketorolac and its related substances has been made.

Selection of two reliable parameters to evaluate the impact of the mobile-phase composition on capillary electrochromatography performance with monolithic and particle-packed capillary columns

Different models have been described in the literature to evaluate the total porosity of CEC columns: gravimetric, flow as well as conductivity-based methods. In this study, these models have been compared for two kinds of CEC columns: two mixed-mode silica particle stationary phases and different monolithic columns (acrylate or polystyrene divinylbenzene-based). The total porosities measured from the conductivity-based methods were lower than the total column porosities obtained by gravimetric or flow methods for all the investigated columns while the wide distribution of observed values shows that conductivity-based methods discriminate columns more efficiently with very different properties. We propose a conductivity-based method taking into account the actual length proposed by Horvath, to evaluate what we call an "actual electrokinetic" porosity (AEP). This parameter, based on electrokinetic theory only, affords the most consistent evaluation of porosity under experimental CEC conditions for the packed- and acrylate-based monolithic columns. To illustrate the potential of AEP and actual EOF for the estimation of the performances of a CEC system (stationary and mobile phases) we studied the influence of the mobile-phase composition on these parameters for CEC separations with an ammonium embedded packed stationary phase. The AEP and the actual electroosmotic mobility should allow a better understanding of the perfusive EOF and stationary-phase wettability. For neutral compounds (substituted phenols), AEP evaluation allowed us to predict the mobile-phase conditions able to enhance the efficiency while both AEP and actual EOF had to be considered in the case of peptide analysis.

Separation of structurally related estrogens using isocratic elution pressurized capillary electrochromatography

In this paper, the pressurized capillary electrochromatography (pCEC) with UV detection was utilized for the separation and determination of three structurally related estrogens, such as diethylstilbestrol (DES), hexestrol (HEX) and dienestrol (DE), which were difficult to be separated by capillary electrophoresis (CE) and HPLC due to their similarity in the structure and charge-to-mass ratios. Experiments were carried out in a commercially available pCEC instrument using a capillary column packed with 3 microm octadecyl silica (ODS). Surfactant sodium dodecyl sulfate (SDS) was introduced in the mobile phase to enhance the speed of analysis. The effective factors on the retention time and separation resolution, such as the applied voltage, supplementary pressure, the pH and the concentration of the buffer solution, the concentration of SDS, and the content of acetonitrile in the mobile phase, were evaluated. Based on the investigation, 31% (v/v) acetonitrile and 69% (v/v) of 10 mmol/L phosphate buffer (pH 6.5) containing 1.0 mmol/L SDS at an applied voltage of -12 kV and a supplementary pressure of 1000 psi were found to be the optimal conditions for pCEC to separate the three estrogens. The method also had been applied to the analysis of fish muscle samples spiked with estrogens.