Development of a multivariate model with desirability-based optimization for determination of atenolol and hydrochlorothiazide by eco-friendly HPLC method with fluorescence detection.

Determination of a widely used antihypertensive combination of atenolol and hydrochlorothiazide was achieved by rapid and eco-friendly high-performance liquid chromatography method combined with fluorescence detection. The response surface methodology is conducive to the complete separation of the two drugs in a shorter analysis time. The separation of the mixture was achieved using an Inertsil C18 analytical column (150 × 4.6 mm, 5 µ). The mobile phase used was ethanol: potassium dihydrogen phosphate at pH 3 (65:35 v/v) and the flow rate was 0.7 mL/min. The fluorescence detector operated at excitation and emission wavelengths of 230 and 310 nm (atenolol) and 270 and 375 nm (hydrochlorothiazide). The linearity of the developed method covered a concentration of atenolol of 0.05-5 µg/mL and a concentration of hydrochlorothiazide of 0.02-1 µg/mL. The greenness of the developed method was evaluated by analytical eco-scale and the recently reported evaluation method, that is, green analytical procedure index, and it was found to be an excellent, sensitive, and green alternative to the reported methods. The developed method was validated according to the ICH guidelines and compared with the reference method. No significant difference was found in terms of accuracy.

Diuretic and Antiurolithic Effect of Garcinia humilis (Vahl) C.D. Adams Leaves, a Medicinal Plant Native to South American Countries.

This study evaluated the diuretic and antiurolithic effect of methanolic extract (MEGHL), dichloromethane (DCM), and ethyl acetate (EtA) fractions obtained from the leaves of Garcinia humilis, a medicinal plant known as achachairu and native to South American countries such as Bolivia, Peru, and Brazil. For the analysis of diuretic effect, the female rats received the treatment with MEGHL (3, 10, and 30 mg/kg), DCM (1, 3 and 10 mg/kg), EtA (1, 3, and 10 mg/kg), hydrochlorothiazide (HCTZ; 10 mg/kg), or vehicle (VEH) after an overload of saline solution. At the end 8 h of the experiment, the urinary parameters were measured. Additionally, the antiurolithic effect was analyzed, in which sodium oxalate was added in synthetic urine in the presence or absence of MEGHL, DCM, and EtA in different concentrations (0.1, 0.3, and 1 mg/mL). MEGHL, DCM, and EtA were able to promote 8-h diuresis in rats. MEGHL treatment at dose 30 mg/kg was accompanied by increased urinary Na+ , K+ and Cl- excretion. Moreover, the DCM and EtA fractions treatment increased K+ and Cl- excretion in the urine, although it does not cause any change in Na+ elimination. All the preparations were able to exert an antiurolithic effect in vitro, decreasing the number of calcium oxalate crystals of the monohydrate and dihydrate types. Taking together, the results presented herein showed that the preparations of G. humilis leaves are promising strategies to induce diuresis and antiurolithic effects.

Development and validation of a stability-indicating UPLC method for the determination of olmesartan medoxomil, amlodipine and hydrochlorothiazide degradation impurities in their triple-combination dosage form using factorial design of experiments.

The current work describes the development and validation of a stability-indicating UPLC method for the determination of olmesaratan medoxomil (OLM), amlodipine besylate (AMB), hydrochlorothiazide (HCT) and their degradation products in the triple-combination tablet dosage form. The separation was achieved using a Zorbax Eclipse plus C8 RRHD (100 mm × 3.0 mm), 1.8 µm column with gradient elution of mobile phase A containing 0.02 m of sodium phosphate buffer (pH 3.35) and mobile phase B as acetonitrile and water (90:10, v/v). The detector signal was monitored at UV 250 nm. Analytical performance of the optimized UPLC method was validated as per International Conference on Harmonization guidelines. The linearity ranges for OLM, AMB and HCT were 0.59-240, 0.30-60 and 0.37-150 µg/ml, respectively, with correlation coefficients >0.999. The dosage form was subjected to forced-degradation conditions of neutral, acidic and alkaline hydrolysis, oxidation and thermal and photodegradation. The method was proved to be stability indicating by demonstrating the specificity of the drugs from degradation products. The robustness of the method was evaluated through a two-level, three-factorial design with a multivariate approach. Statistical data analysis with best model fit P-value < 0.05 from an ANOVA test indicated that the influence of individual factors is relatively higher than the interaction effects. The method is useful for the analysis of drug products.

HPLC method transfer study for simultaneous determination of seven angiotensin II receptor blockers.

In this study, a sensitive high-performance liquid chromatography method was developed and validated for the simultaneous determination of seven angiotensin II receptor blockers, namely, hydrochlorothiazide, chlorthalidone, eprosartan mesylate, valsartan, losartan potassium, irbesartan, and candesartan cilexetil. Different chromatographic parameters were tested and fully optimized. Best chromatographic separation was accomplished on a reversed-phase octadecylsilyl column (250 × 4.6 mm id; 5 µm) under gradient elution using methanol/sodium phosphate monobasic buffer (0.01 M, pH 6.5) as mobile phase. The detection of target analytes was obtained at 254 nm. The pH of the buffer has been selected according to Marvin® sketch software. The proposed method was validated according to ICH guidelines and showed good precision (relative standard deviation < 1), good linearity (square of correlation coefficient ≥ 0.999), and high accuracy (between 98 and 102%) with detection limit and quantitation limit (40 and 160 ng/mL, respectively) for all the detected analytes.

Analysis of the Overlapped Electrochemical Signals of Hydrochlorothiazide and Pyridoxine on the Ethylenediamine-Modified Glassy Carbon Electrode by Use of Chemometrics Methods.

In this work, the electrochemical behavior of hydrochlorothiazide and pyridoxine on the ethylenediamine-modified glassy carbon electrode were investigated by differential pulse voltammetry. In pH 3.4 Britton-Robinson (B-R) buffer solution, both hydrochlorothiazide and pyridoxine had a pair of sensitive irreversible oxidation peaks, that overlapped in the 1.10 V to 1.20 V potential range. Under the optimum experimental conditions, the peak current was linearly related to hydrochlorothiazide and pyridoxine in the concentration range of 0.10-2.0 µg/mL and 0.02-0.40 µg/mL, respectively. Chemometrics methods, including classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS), were introduced to resolve the overlapped signals and determine the two components in mixtures, which avoided the troublesome steps of separation and purification. Finally, the simultaneous determination of the two components in commercial pharmaceuticals was performed with satisfactory results.

Green micellar HPLC analysis of three angiotensin-converting enzyme inhibitors in their mixtures with hydrochlorothiazide and modeling of their retention behavior by fitting to Foley's model.

We present an environmentally friendly method for the analysis of three angiotensin-converting enzyme inhibitors and hydrochlorothiazide simultaneously using a green micellar eluent for the first time. The chromatographic separation of enalapril maleate, lisinopril dihydrate, benazepril hydrochloride, and hydrochlorothiazide was implemented on an octadecyl silica column with a solution containing sodium dodecyl sulfate (0.12 M), 1-propyl alcohol (10% v/v), triethylamine (0.3% v/v), and H3 PO4 (0.02 M) at pH 3.6 as the mobile phase and UV detection at 210 nm. Validity of the method was confirmed and it exhibited good linearity within the ranges of 5.0-50.0 µg/mL for hydrochlorothiazide and 10.0-60.0 µg/mL for the three angiotensin-converting enzyme inhibitors with a limit of detection of 0.39 to 1.15 µg/mL for all the studied drugs. The developed micellar high-performance liquid chromatography method enables the quantification of the targeted angiotensin-converting enzyme inhibitors in combined tablets with hydrochlorothiazide by isocratic elution. There is no need for special precautions to prevent broadening and splitting of their chromatographic peaks. The method fulfills the society rights for safe and green analytical methods. The retention behavior of the four studied drugs was fitted to Foley's model and their association equilibria to the micelles (KAM ) and to the surface-modified stationary phase (KAS ) were calculated.

Development and validation of a reversed-phase high-performance liquid chromatographic method with solid-phase extraction for the quantification of hydrochlorothiazide in ex vivo permeation studies.

Hydrochlorothiazide (HCT) is a diuretic used to treat hypertension. In order to study its intestinal permeation behavior applying an ex vivo methodology, a rapid, sensitive and selective reversed-phase liquid chromatography (RP-HPLC) method coupled with UV detection (RP-HPLC UV) was developed for the analysis of HCT in TC199 culture medium used as mucosal and serosal solutions in the everted rat intestinal sac model. Also, analytical procedures for the quantification of HCT by RP-HPLC with UV detection required a sample preparation step by solid-phase extraction. The method was validated in the concentration range of 8.05 × 10-7 to 3.22 × 10-5 m for HCT. Chromatographic parameters, namely carry-over, lower limit of quantification (1.4491 × 10-7 m), limit of detection (3.8325 × 10-8 m), selectivity, inter- and intraday precision and extraction recovery, were determined and found to be adequate for the intended purposes. The validated method was successfully used for permeability assays across rat intestinal epithelium applying the ex vivo everted rat gut sac methodology to study the permeation behavior of HCT.

Chemiluminescence selectivity enhancement in the on-chip Ru(bpy)32+ system: The potential role of buffer type and pH in the determination of hydrochlorothiazide in combined formulations and human plasma.

A simple and highly selective on-chip Ru(bpy)32+ -oxidant chemiluminescence (CL) approach for estimation of a diuretic drug, hydrochlorothiazide (HCZ), in biological fluids was realized in the presence of other fixed-dose combination drugs by manipulating simultaneously the method of active species (Ru(bpy)33+ ) production and type of carrier buffer with pH used for the CL reaction. Chemical oxidation processes involved in the Ru(bpy)32+ -Ce(IV) CL system have been successfully miniaturised in this study using a microfabricated device to generate Ru(bpy)33+ instantaneously. The proposed system was then screened using HCZ and other drugs in the presence of various buffers and pH to explore the difference in CL emission. Ammonium formate buffer (0.15 M) at pH 4.5 exhibited excellent selectivity towards HCZ when Ru(bpy)33+ was produced by chemical oxidation using Ce(IV). The newly developed conditions do not involve any kind of prior separation or isolation procedure to remove other combination therapy drugs in formulation and biological samples. The method under fully optimised conditions exhibited wide linearity over the concentration range 0.5-1000 ng ml-1 and low detection and quantification limits of 0.13 and 0.47 ng ml-1 respectively for HCZ. Acceptable levels of recoveries were obtained for HCZ from human plasma using the proposed method (98.9-100.8%) in the presence of other antihypertensive combination therapy drugs. This study postulates that such miniaturised devices may find applications especially for on-site analysis, such as doping control examinations.

New conformational polymorph of hydrochlorothiazide with improved solubility.

CONTEXT: To characterize a new conformation of hydrochlorothiazide (HCT) with better solubility and establishing its relationship with previously reported form I, obtained during attempted crystallization experiments. OBJECTIVE: The aim of present investigation is to unveil a new conformational polymorph (form IA) having a higher solubility compared to commercially available form I. MATERIALS AND METHODS: New form (IA) was obtained from slow evaporation as well as by solvent-antisolvent method and was then characterized by DSC, FTIR, PXRD and SCXRD. Equilibrium solubility profile shows that it is more soluble than form I. RESULTS: Appearance of phase transition endotherm at 215.87 °C in DSC spectra indicated the existence of new polymorph which was further confirmed by FTIR and PXRD. Single crystal study showed significant difference in various bond angles and torsion angles of the two forms. The solubility exhibited by form IA was (938 µg/mL) compared to form I (791 µg/mL) in water. DISCUSSION: Complete structural analysis and molecular arrangements in the unit cell along with the DSC and FTIR data confirm the existence of new conformer of HCT. CONCLUSION: This study reveals the existence of a new conformational polymorph of HCT molecule having higher solubility could prove to be promising in pre-formulation.

Simultaneous determination of valsartan, amlodipine besylate and hydrochlorothiazide using capillary zone electrophoresis (CZE).

A capillary zone electrophoresis method was developed for the simultaneous determination of valsartan (VAL), amlodipine besylate (AML) and hydrochlorothiazide (HCZ) in their combined tablets. Separation was achieved on a fused silica capillary by applying a potential of 15 kV (positive polarity) and a running background electrolyte containing 40 mM phosphate buffer at pH 7.5 with UV detection at 230 nm. The samples were injected hydrodynamically for 3s at 0.5 psi and the temperature of the capillary cartridge was kept at 25 degrees C. Pyrazinoic acid was used as an internal standard. The method was validated according to ICH guidelines regarding specificity, linearity, limits of detection and quantitation, accuracy and precision, (Supplementary materials, Table S2). The method showed satisfactory linearity in the ranges of 10-200, 2-20 and 2-20 µg mL(-1) with LODs of 1.82, 0.39, 0.65 µg mL(-1) and LOQs of 5.51, 1.17, 1.96 µg mL(-1) for VAL, AML and HCZ, respectively. The proposed method was successfully applied for the analysis of the studied drugs in their laboratory prepared mixtures and co-formulated tablets. The results were compared with reported methods and no significant differences were found. The proposed method can be used for quality control of the cited drugs in ordinary laboratories.

Preliminary study of an offline simultaneous determination of metoprolol tartrate and hydrochlorothiazide in powders and tablets by reflectance near-infrared spectroscopy.

A preliminary study of the feasibility of using near-infrared spectroscopy (NIRS) for the offline simultaneous determination of metoprolol tartrate (MTP) and hydrochlorothiazide (HTZ) in powders and tablets has been carried out. An industrial tableting process was simulated using an instrumented tablet press replicator - Presster™. Conventional reference analytics were replaced with gravimetric analysis. The NIRS models for powder and tablet analysis were developed using 55 samples, and tested on 80 independent samples. Powder mixture components were weighed in glass vials to collect reference values, mixed and manually transferred to a tablet press replicator and compacted to form tablets. NIRS calibration models were developed using spectral and gravimetric reference data. The two model drugs were simultaneously quantified exhibiting root mean-squared error of prediction (RMSEP) of 1.69 and 1.31 mg for HTZ powder and tablet samples, respectively, and RMSEP of 3.15 and 3.00 mg for MTP powder and tablet samples, respectively. NIRS analysis of MTP and HTZ in powder and tablet form has not been reported elsewhere.

Simultaneous determination of aliskiren hemifumarate, amlodipine besylate, and hydrochlorothiazide in their triple mixture dosage form by capillary zone electrophoresis.

A novel, specific, reliable, and accurate capillary zone electrophoretic method was developed and validated for the simultaneous determination of aliskiren hemifumarate, amlodipine besylate, and hydrochlorothiazide in their triple mixture dosage form. Separation was carried out in a fused-silica capillary (57.0 cm total length and 50.0 cm effective length, 75.6 µm internal diameter) by applying a potential of 17 kV and a running buffer consisting of 40 mM phosphate buffer at pH 6.0 with UV detection at 245 nm. The method was suitably validated with respect to specificity, linearity, LOD, and LOQ, accuracy, precision, and robustness. The method showed good linearity in the ranges 1-10, 2.5-25, and 30-300 µg/mL with LODs of 0.11, 0.33, and 5.83 µg/mL for amlodipine besylate, hydrochlorothiazide, and aliskiren hemifumarate, respectively. The proposed method was successfully applied for the analysis of the studied drugs in their coformulated tablets. The results of the proposed method were statistically compared with those obtained by the RP-HPLC reference method revealing no significant differences in the performance of the methods regarding accuracy and precision.

A stability-indicating HPLC method for the quantification of aliskiren and hydrochlorothiazide in a pharmaceutical formulation.

A novel, fast, and sensitive stability-indicating HPLC method was developed, fully validated, and applied to the simultaneous determination of aliskiren and hydrochlorothiazide in a combined formulation. Effective chromatographic separation was achieved using a phenyl analytical column with isocratic elution using the mobile phase 0.030 M ammonium acetate-acetonitrile (60 + 40, v/v) at a flow rate of 0.40 mL/min. The UV spectrophotometric detector was set at 280 nm. The method was linear over the concentration ranges of 1.5-4.5 and 0.125-0.375 µg/mL for aliskiren and hydrochlorothiazide, respectively. The intraday and interday RSD values were less than 6.1%, while the relative percentage error, Er, was less than 5% for both analytes. Both drugs were subjected to stress conditions of acidic and alkaline hydrolysis, oxidation, and thermal degradation. The proposed method proved to be stability indicating by resolution of the drugs from their forced degradation products. The method was applied successfully to the QC and content uniformity tests in combined commercial tablets.

[Process monitoring of dissolution of valsartan and hydrochlorothiazide tablets by fiber-chemical sensor assisted by mathematical separation model of linear equations].

A method for on-line monitoring the dissolution of Valsartan and hydrochlorothiazide tablets assisted by mathematical separation model of linear equations was established. UV spectrums of valsartan and hydrochlorothiazide were overlapping completely at the maximum absorption wavelength respectively. According to the Beer-Lambert principle of absorbance additivity, the absorptivity of Valsartan and hydrochlorothiazide was determined at the maximum absorption wavelength, and the dissolubility of Valsartan and hydrochlorothiazide tablets was detected by fiber-optic dissolution test (FODT) assisted by the mathematical separation model of linear equations and compared with the HPLC method. Results show that two ingredients were real-time determined simultaneously in given medium. There was no significant difference for FODT compared with HPLC (p > 0.05). Due to the dissolution behavior consistency, the preparation process of different batches was stable and with good uniformity. The dissolution curves of valsartan were faster and higher than hydrochlorothiazide. The dissolutions at 30 min of Valsartan and hydrochlorothiazide were concordant with US Pharmacopoeia. It was concluded that fiber-optic dissolution test system assisted by the mathematical separation model of linear equations that can detect the dissolubility of Valsartan and hydrochlorothiazide simultaneously, and get dissolution profiles and overall data, which can directly reflect the dissolution speed at each time. It can provide the basis for establishing standards of the drug. Compared to HPLC method with one-point data, there are obvious advantages to evaluate and analyze quality of sampling drug by FODT.

Resolution of overlapping spectra using chemometric manipulations of UV-spectrophotometric data for the determination of Atenolol, Losartan, and Hydrochlorothiazide in pharmaceutical dosage form.

Simultaneous determination of atenolol (ATN), losartan potassium (LOS), and hydrochlorothiazide (HCZ) in presence of HCZ impurity B was conducted by chemometric approaches and radial basis function network (RBFN) using UV-spectrophotometry without preliminary separation. Three chemometric models namely, classical least-squares (CLS), principal component regression (PCR), and partial least-squares (PLS) along with RBFN were utilized using the ternary mixtures of the three drugs. The multivariate calibrations were obtained by measuring the zero-order absorbance of the mixtures from 250 to 270 nm at the interval of 0.2 nm. The models were built covering the concentration range of (4.0 to 20.0), (3.8 to 20.2), and (0.9 to 50.1) µg mL-1 for ATN, LOS, and HCZ, respectively. The regression coefficient was calculated between the actual and predicted concentrations of the 3 drugs using CLS, PCR, PLS and RBFN. The accuracy of the developed models was evaluated using the root mean square error of prediction (RMSEP) giving satisfactory results. The proposed methods were simple, accurate, precise and were applied efficiently for the quantitation of the three components in laboratory-prepared mixtures, and in dosage form showing good recovery values. In addition, the obtained results were compared statistically with each other using ANOVA test showing non-significant difference between them.

Analytical QbD for the optimization of a multimode HPLC method for the investigation of hydrochlorothiazide, diltiazem and propranolol release from 3D printed formulation.

Since 3D printing technology is an emerging field in pharmaceutical technology, the present study aimed at the development of a mixed-mode liquid chromatographic method for the separation and determination of hydrochlorothiazide, diltiazem, and propranolol to investigate their in-vitro release performance from 3D printed tablets. Due to the unique properties of the mixed-mode stationary phase, the three drugs were separated in less than 8 min under isocratic elution. Method development was accomplished following the Analytical Quality by Design principles and was evaluated using risk assessment and multivariate analysis. The influences of critical method parameters on critical method attributes (were screened using a 2-level fractional factorial design and subsequently optimized through a central composite design. The method operable design region was approved by the establishment of a robust zone using Monte Carlo simulation and capability analysis. The validation of the HPLC method was performed based on the total error concept. The relative bias was varied between ─ 11.6 % and 10.5 % and the RSD values for repeatability and intermediate precision were below 4.4 % in all cases. The limits of detection (LOD) ranged between 0.17 - 0.90 µg/mL and were adequate for the specific application. The developed method was successfully applied to the analysis of the studied drugs in in-vitro drug release samples obtained from 3D-printed tablets combining the above-mentioned active pharmaceutical ingredients (APIs).

Fully validated simultaneous determination of bisoprolol fumarate and hydrochlorothiazide in their dosage forms using different voltammetric, chromatographic, and spectrophotometric analytical methods.

Voltammetric, chromatographic, and spectrophotometric methods were developed for the simultaneous determination of bisoprolol fumarate (BIS) and hydrochlorothiazide (HCZ). Differential pulse and square wave voltammetry techniques were used to analyze BIS and HCZ simultaneously by measuring at about 1400 and 1100 mV, respectively. RP-HPLC was the second method for simultaneous analysis of the compounds. The mixture of BIS, HCZ, and moxifloxacin as an internal standard was separated on an RP Zorbax Eclipse XDB-C18 column (150 x 4.6 mm, id, 5 microm particle size) using acetonitrile-15 mM phosphate (25+75, v/v) mobile phase at a 1.0 mL/min flow rate. The third method was based on first derivative of the ratio-spectra method obtained from the measurements of the amplitudes at 246 and 257 nm for BIS and HCZ, respectively. All the proposed methods were effectively applied for the simultaneous determination of BIS and HCZ in tablet dosage forms without any time-consuming extraction, sample preparation, or derivatization procedures.

Validated stability-indicating capillary electrophoresis method for the separation and determination of a fixed-dose combination of carvedilol and hydrochlorothiazide in tablets.

A novel, fast, sensitive, and specific capillary electrophoresis (CE) technique coupled to a diode array detector has been developed for the separation and simultaneous determination of carvedilol (CRV) and hydrochlorothiazide (HCT) in two combination formulations. The proposed method utilized a fused silica capillary (55 cm x75 microm id) and the background electrolyte solution phosphate buffer (12.5 mM, pH 7.4)-methanol (95+5, v/v). The separation was achieved at 30 kV applied voltage and 24 degree C. Atorvastatin (80 microg/mL) was chosen as the internal standard. The described method was linear over the range of 1-200 and 0.2-150 microg/mL for CRV and HCT, respectively. Intraday and interday RSD (n = 6) was < or =1.4%. The LOD values of CRV and HCT were 0.26 and 0.07 microg/mL, respectively. The validated CE method was successfully applied to the analysis of two commercial tablet dosage forms. Forced degradation studies were performed on bulk samples of the two drugs using thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were analyzed by the proposed method. Degradation products produced as a result of stress studies did not interfere with the determination of CRV and HCT; the assay could, therefore, be considered stability-indicating.

Mechanism considerations for photocatalytic oxidation, ozonation and photocatalytic ozonation of some pharmaceutical compounds in water.

Aqueous solutions of four pharmaceutical compounds, belonging to the group of emergent contaminants of water: atenolol (ATL), hydrochlorothiazide (HCT), ofloxacin (OFX) and trimethoprim (TMP), have been treated with different oxidation systems, mainly, photocatalytic oxidation, ozonation and photocatalytic ozonation. TiO2 has been used as semiconductor for photocatalytic reactions both in the presence of air, oxygen or ozone-oxygen gas mixtures. Black light lamps mainly emitting at 365 nm were the source of radiation. In all cases, the influence of some variables (concentrations of semiconductor, ozone gas and pharmaceuticals and pH) on the removal of pharmaceuticals, total polyphenol content (TPC) and total organic carbon (TOC) was investigated. A discussion on the possible routes of pharmaceutical and intermediates (as TPC and TOC) elimination has been developed. Thus, OFX TiO2/UVA degradation mechanism seems to develop through the participation of non-hydroxyl free radical species. Furthermore, the presence of OFX inhibits the formation of hydroxyl radicals in the photocatalytic process. The most effective processes were those involving ozone that lead to complete disappearance of parent compounds in less than 30 min for initial pharmaceutical concentrations lower than 2.5 mg L(-1). In the ozonation systems, regardless of the pH and the presence of TiO2, pharmaceuticals are degraded through their direct reaction with ozone. Photocatalytic ozonation was the most efficient process for TPC and TOC removals (≥ 80% and ≥60% elimination after 2 h of treatment, respectively) as well as in terms of the ozone consumption efficiency (1, 5.5 and 4 mol of ozone consumed per mol of TOC mineralized, at pH 4, 7 and 9, respectively). Weakly acid conditions (pH 4) resulted to be the most convenient ones for TPC and TOC removal by photocatalytic ozonation. This was likely due to formation of hydroxyl radicals through the ozonide generated at these conditions.

Simultaneous determination of aliskiren and hydrochlorothiazide in tablets and spiked human urine by ion-pair liquid chromatography.

An alternative method for analysis of aliskiren (ALI) and hydrochlorothiazde (HCT) in combined dosage forms by ion-pair reversed phase high performance liquid chromatography was developed and validated. The pharmaceutical preparations were analyzed using a C18 column (250 mm x 4.6 mm, 3 microm) with a mobile phase consisting of 25% methanol, 50% sodium monobasic phosphate aqueous solution containing 6 mM tetrabutylammonium bromide and 25% water at pH 7.2. Isocratic analysis was performed at a flow rate of 1 mL/min and a column temperature of 30 degrees C under direct UV detection at 210 nm. Paracetamol was used as internal standard. The validation was performed according to the ICH guidelines. The proposed method was linear over the concentration range of 0.250 to 60 and 0.1 to 10 microg/mL for ALI and HCT, respectively. The limits of detection and quantitation (LOD and LOQ) were 0.075 and 0.198 microg/mL, respectively, for ALI and 0.04 and 0.062 microg/mL, respectively, for HCT. The method proved to be specific, sensitive, precise and accurate with mean recovery values of 101.1 +/- 0.32% and 100.9 +/- 0.41% for ALI and HCT, respectively. The method robustness was evaluated by means of an experimental design. The proposed method was applied successfully to spiked human urine samples with mean recoveries of 98.8 +/- 0.36% and 98.1 +/- 0.21% for ALI and HCT, respectively.