Spectrophotometric and liquid chromatographic determination of trimebutine maleate in the presence of its degradation products

Three methods are presented for the determination of trimebutine maleate (TM) in the presence of its degradation products. The first method was based on a high performance liquid chromatographic (HPLC) separation of TM from its degradation products using an ODS column at ambient temperature with a mobile phase consisting of acetonitrile-5 mM heptane sulfonic acid disodium salt (45:55, v/v, pH 4) with UV detection at 215 nm. The second method depends on using first derivative spectrophotometry (1D) by measurement of the amplitude at 252.2 nm. The third method depends on using first derivative of the ratio spectrophotometry (1DD) by measurement of the amplitude at 282.4 nm where a normalized spectrum of 3,4,5-trimethoxy benzoic acid is used as divisor. The proposed HPLC and 1D methods were used to investigate the kinetics of acidic and alkaline degradation processes. The pH-rate profile of degradation of TM in Britton-Robinson buffer solutions within the pH range 2-11.9 was studied.     

First derivative spectrophotometric, TLC-densitometric, and HPLC determination of acebutolol HCL in presence of its acid-induced degradation product

Three methods are presented for the determination of acebutolol HCl in presence of its acid-induced degradation product. The first method was based on measurement of the first derivative amplitude of acebutolol HCl at 266.6 nm. The second method was based on separation of acebutolol HCl from its acid-induced degradation product followed by densitometric measurement of the spots at 230 nm. The separation was carried out on silica gel 60 F254, using ethanol-glacial acetic acid (4:1, v/v) as mobile phase. Second order polynomial equation was used for the regression line. The third method was based on high performance liquid chromatographic (HPLC) separation of acebutolol HCl from its acid-induced degradation product on a reversed phase, ODS column using a mobile phase of methanol-water (55:45, v/v) with UV detection at 240 nm. The first derivative spectrophotometric method was utilized to investigate the kinetics of the acid degradation process at different temperatures.     

First derivative spectrophotometric and high-performance liquid chromatographic determination of cinchocaine hydrochloride in presence of its acid degradation product

Two methods are presented for the determination of cinchocaine HCl in presence of its acid-induced degradation product using first (¹D) derivative spectrophotometry and high-performance liquid chromatography. Cinchocaine HCl was determined by measurement of its first derivative amplitude at the zero crossing point of 2-hydroxyquinoline-4-carboxylic acid diethylaminoethylamide as its acid degradation product (at 333.5 nm). The HPLC method depends upon using a μBondapak C₁₈ column at ambient temperature with a mobile phase consisting of acetonitrile—0.01 M sodium acetate trihydrate (45:55, v/v) containing 0.06% (w/v) heptane sulphonic acid sodium salt and adjusted to apparent pH 4.5 with acetic acid at a flow rate 2 ml min⁻¹. Quantitation was achieved with UV detection at 254 nm based on peak area. The HPLC method was applied for simultaneous determination of cinchocaine HCl, methylparaben and propylparaben. The two proposed methods were successfully applied to the determination of the cinchocaine HCl in laboratory-prepared mixtures in the presence of its acid degradation product and in cream. Moreover, the proposed methods were utilized to investigate the kinetics of the acid degradation process at different temperatures and the apparent pseudo first-order rate constant, half-life and activation energy calculated.     

Derivative spectrophotometric, thin layer chromatographic-densitometric and high performance liquid chromatographic determination of trifluoperazine hydrochloride in presence of its hydrogen peroxide induced-degradation product.

Three methods are presented for the determination of trifluoperazine HCl in presence of its hydrogen peroxide induced degradation product. The first method was based on measurement of first (1D) and second (2D) derivative amplitudes of trifluoperazine HCl in 0.1 N hydrochloric acid at the zero crossing point of its sulfoxide derivative, main degradation product, (at 268.4 and 262.5 nm for 1D and 2D, respectively). The second method was based on the separation of trifluoperazine HCl from its sulfoxide derivative followed by densitometric measurement of the intact drug spot at 255 nm. The separation was carried out on Merck aluminum sheet of silica gel 60 F(254), using chloroform-methanol (7:3 v/v) as mobile phase. The third method was based on high performance liquid chromatographic separation of trifluoperazine HCl from its sulfoxide derivative on reversed phase, ODS column, using a mobile phase of acetonitrile-phosphate buffer pH 4.2 (60:40 v/v) at ambient temperature. Quantitation was achieved with UV detection at 255 nm based on peak area. The first derivative spectrophotometric method was utilized to investigate the kinetics of the hydrogen peroxide degradation process at different temperatures. The apparent pseudo first-order rate constant, half life and activation energy were calculated.     

Spectrophotometric and chromatographic determination of rabeprazole in presence of its degradation products

Three methods were presented for the determination of rabeprazole (RA) in presence of its degradation products. The first method was based on high performance liquid chromatographic (HPLC) separation of RA from its degradation products on a reversed phase, ODS column using a mobile phase of methanol-water (70:30, v/v) and UV detection at 284 nm. The second method was based on HPTLC separation followed by densitometric measurement of the spots at 284 nm. The separation was carried out on Merck HPTLC sheets of silica gel 60 F 254, using acetone-toluene-methanol (9:9:0.6 v/v) as mobile phase. The third method depends on first derivative of the ratio spectra (1DD) by measurement of the amplitudes at 310.2 nm. Moreover, the proposed HPLC method was utilized to investigate the kinetics of the oxidative and photo degradation processes. The pH-rate profile of degradation of RA in Britton-Robinson buffer solutions within the pH range 3-11 was studied. In addition, the activation energy of RA degradation was calculated in Britton-Robinson buffer solution pH 7.     

Validated stability-indicating derivative and derivative ratio methods for the determination of some drugs used to alleviate respiratory tract disorders and their degradation products

Derivative and derivative ratio methods are presented for the determination of butamirate citrate, formoterol fumarate, montelukast sodium, and sodium cromoglycate. Using the second derivative ultraviolet (UV) spectrophotometry, butamirate citrate and formoterol fumarate were determined by measuring the peak amplitude at 260.4 and 261.8 nm, respectively, without any interference of their degradation products. Butamirate citrate degradation product, 2-phenyl butyric acid, was determined by the measurement of its second derivative amplitude at 246.7 nm where butamirate citrate displays zero crossing. Formoterol fumarate degradation product, desformyl derivative, could be evaluated through the use of the first derivative at peak amplitude of 264.8 nm where interference of formoterol fumarate is negligible. In the first mode, the zero-crossing technique was applied at 305 nm for the determination of montelukast sodium in the presence of its photodegradation product, cis-isomer. The derivative of ratio spectra of montelukast sodium and its cis- isomer were used to determine both isomers using the first derivative of the ratio spectra by measuring the amplitudes of the trough at 305 nm and the peak at 308 nm, respectively. The later technique was also used for the determination of a ternary mixture of sodium cromoglycate and its two degradation products using zero-crossing method. In the derivative ratio spectra of the ternary mixture, trough depths were measured at 271.6, 302.8 and 302.2 nm, using the second, the first, and the second mode to evaluate sodium cromoglycate, degradation product (1) and degradation product (2), respectively. All the methods were applied successfully to the pharmaceutical preparation and were validated according to ICH guidelines.     

Development and validation of a stability-indicating high performance liquid chromatographic assay for benoxinate

Benoxinate is a local anaesthetic used for ophthalmic applications. The aim of this study was to develop a rapid and simple stability-indicating method for the determination of benoxinate formulated for ophthalmic use, evaluate its long-term stability and identify its major degradation product. Benoxinate was eluted on a 10 microm Spherisorb phenyl column, 250 x 3.2 mm, with a mobile phase consisting of acetonitrile-buffer (pH 3.5) (35:65, v/v), pumped at 0.8 ml min(-1) flow rate. The buffer was composed of sodium dihydrogen phosphate (50 mM), sodium hydrogen sulfate (2.5 mM) and 1-heptanesulfonic acid sodium salt (5 mM). The analyte was quantified spectrophotometrically at 308 nm. The chromatograms of benoxinate formulations obtained by this method showed benoxinate (t = 4.5 min) well resolved from its degradation product (t = 2.3 min), which was separately identified by means of HPLC-MS as 4-amino-3-butoxybenzoic acid. The assay was demonstrated to have high accuracy, precision and linearity. The method was implemented in investigating the long-term stability of benoxinate 0.4% ophthalmic solutions. The method was found to be simple, quick and selective in determining benoxinate concentrations in fresh and aged preparations.     

Rapid and simple methods for quantitative analysis of some antidepressant in pharmaceutical formulations by using first derivative spectrophotometry and HPLC

Two rapid, simple and accurate first derivative spectrophotometry and HPLC method for the determination of nefazodone hydrochloride and sertraline hydrochloride in pharmaceutical formulations are discussed. The first one is a derivative spectrophotometric procedure and the second one is based on a HPLC method with a UV detector. In the first method, first derivative spectrophotometry, nefazodone hydrochloride or sertraline hydrochloride by measurement of their first derivative signals at 241.8-256.7 nm (peak-to-peak amplitude), or 271.6-275.5 nm (peak-to-peak amplitude), respectively. Calibration graphs were established for 10.0-42.0 microg ml(-1) nefazodone hydrochloride, or 8.0-46.0 microg ml(-1) sertraline hydrochloride. In the other method, HPLC, the UV detection was carried out at 265.0 nm (nefazodone hydrochloride) and 270.0 nm (sertraline hydrochloride). The samples were chromatographed on a Supercosil RP-18 column. The mobile phases were methanol:acetonitrile:phosphate buffer at pH 5.5 (10:50:40 v/v/v) (nefazodone hydrochloride) and methanol:phosphate buffer at pH 4.5 (20:80 v/v) (sertraline hydrochloride). The results obtained from first derivative spectrophotometric method were comparable with those obtained by using HPLC. It was concluded that both the developed methods are equally accurate, sensitive, and precision could be applied directly and easily to the pharmaceutical formulations of nefazodone hydrochloride and sertraline hydrochloride, respectively.     

First derivative ratio spectrophotometric,HPTLC-densitometric,and HPLC determination of nicergoline in presence of its hydrolysis-induced degradation product

Three methods are presented for the determination of Nicergoline in presence of its hydrolysis-induced degradation product. The first method was based on measurement of the first derivative of ratio spectra amplitude of Nicergoline at 291 nm. The second method was based on separation of Nicergoline from its degradation product followed by densitometric measurement of the spots at 287 nm. The separation was carried out on HPTLC silica gel F(254) plates, using methanol-ethyl acetate-glacial acetic acid (5:7:3, v/v/v) as mobile phase. The third method was based on high performance liquid chromatographic (HPLC) separation and determination of Nicergoline from its degradation product on a reversed phase, nucloesil C(18) column using a mobile phase of methanol-water-glacial acetic acid (80:20:0.1, v/v/v) with UV detection at 280 nm. Chlorpromazine hydrochloride was used as internal standard. Laboratory prepared mixtures containing different percentages of the degradation product were analysed by the proposed methods and satisfactory results were obtained. These methods have been successfully applied to the analysis of Nicergoline in Sermion tablets. The validities of these methods were ascertained by applying standard addition technique, the mean percentage recovery +/- R.S.D.% was found to be 99.47 +/- 0.752, 100.01 +/- 0.940, 99.75 +/- 0.740 for the first derivative of ratio spectra method, the HPTLC method and the HPLC method, respectively. The proposed methods were statistically compared with the manufacturer's HPLC method of analysis of Nicergoline and no significant difference was found with respect to both precision and accuracy. They have the advantage of being stability indicating. Therefore, they can be used for routine analysis of the drug in quality control laboratories.     

Stability‐indicating methods for the determination of famciclovir in the presence of its alkaline‐induced degradation product

Five sensitive, selective and precise stability‐indicating methods are presented for the determination of famciclovir (FCV) in the presence of its alkaline‐induced degradation product. Method A utilizes the first derivative spectrophotometry at 321 nm. Method B depends on using the first derivative of the ratio spectrophotometry (DD¹) by measurement of the amplitude at 256 nm. Method C is based on the reaction of FCV with hydroxylamine to form hydroxamic acid, causing the hydroxamic acid to react with triferric ion to form ferric hydroxamate that is measured at 503 nm. Method D is based on the separation of FCV from its degradation product followed by densitometric measurement of the bands at 304 nm. The separation was carried out on silica gel 60 F₂₅₄, using chloroform: methanol (70:30, v/v) as a mobile phase. Method E is based on a high performance liquid chromatographic (HPLC) separation of FCV from its degradation product using an ODS column with a mobile phase consisting of methanol–50 mM dipotassium hydrogen phosphate (25:75, v/v, pH 3.0)with UV detection at 304 nm. Regression analysis showed good correlation in the concentration ranges 16–72 µg/ml, 40–240 µg/ml, 40–240 µg/ml, 0.75–5.25 µg/band and 20–240 µg/ml with percentage recoveries of 99.65 ± 0.85, 100.27 ± 0.91, 99.72 ± 0.84, 100.65 ± 1.52 and 99.88 ± 0.50 for methods A, B, C, D and E, respectively. These methods are suitable as stability‐indicating methods for the determination of FCV in the presence of its degradation product either in bulk powder or in pharmaceutical formulation. Statistical analysis of the results has been carried out revealing high accuracy and good precision. Copyright © 2010 John Wiley & Sons, Ltd.     

Spectrophotometric and liquid chromatographic determination of fenofibrate and vinpocetine and their hydrolysis products

Several spectrophotometric and HPLC methods are presented for the determination of fenofibrate, vinpocetine and their hydrolysis products. The resolution of either fenofibrate or vinpocetine and their hydrolysis products has been accomplished by using numerical spectrophotometric methods as partial least squares (PLS-1) and principal component regression (PCR) applied to UV spectra; and graphical spectrophotometric methods as first derivative of ratio spectra (1DD) or first (1D) and second (2D) derivative spectrophotometry for vinpocetine and fenofibrate, respectively. In addition HPLC methods were developed using ODS column with mobile phase consisting of acetonitrile-water (80:20, v/v, pH 4) with UV detection at 287 nm for fenofibrate and a mobile phase consisting of acetonitrile-10 mM KH2PO4, containing 0.1% diethylamine (60:40, v/v, pH 4.6) with UV detection at 270 nm for vinpocetine. The proposed methods were successfully applied for the determination of each drug and its hydrolysis product in laboratory-prepared mixture and pharmaceutical preparation. The proposed HPLC and derivative spectrophotometric methods were used to investigate the kinetics of acidic and alkaline hydrolytic processes of each drug. The pH-rate profile of hydrolysis of each drug in Britton-Robinson buffer solutions was studied.     

Stability-indicating spectrophotometric and spectrofluorimetric methods for determination of alfuzosin hydrochloride in the presence of its degradation products

Validated stability-indicating spectrophotometric and spectrofluorimetric assays (SIAMs) were developed for the determination of alfuzosin hydrochloride (ALF) in the presence of its oxidative, acid, and alkaline degradation products. Three spectrophotometric methods were suggested for the determination of ALF in the presence of its oxidative degradation product; these included the use of zero order (0D), first order (1D), and third order (3D) spectra. The absorbance was measured at 330.8 nm for (0D) method, while the amplitude of first derivative (1D) method and that of third derivative (3D) method were measured at 354.0 and 241.2 nm, respectively. The linearity ranges were 1.0-40.0 microg/ml for (0D) and (1D) methods, and 1.0-10.0 microg/ml for (3D) method. Two spectrofluorimetric methods were developed, one for determination of ALF in the presence of its oxidative degradation product and the other for its determination in the presence of its acid or alkaline degradation products. The first method was based on measuring the native fluorescence of ALF in deionized water using lamda(excitation) 325.0 nm and lamda(emission) 390.0 nm. The linearity range was 50.0-750.0 ng/ml. This method was also used to determine ALF in human plasma with the aid of a suggested solid phase extraction method. The second method was used for determination of ALF via its acid degradation product. The method was based on the reaction of fluorescamine with the primary aliphatic amine group produced on the degradation product moiety. The reaction product was determined spectrofluorimetrically using lamda(excitation) 380.0 nm and lamda(emission) 465.0 nm. The linearity range was 100.0-900.0 ng/ml. All methods were validated according to the International Conference on Harmonization (ICH) guidelines, and applied to bulk powder and pharmaceutical formulations.     

High performance liquid chromatographic determination of oxeladin citrate and oxybutynin hydrochloride and their degradation products

Two high performance liquid chromatographic (HPLC) methods are presented for the determination of oxeladin citrate (OL) and oxybutynin hydrochloride (OB) and their degradation products. The first method was based on HPLC separation of OL from its degradation product using a Nucleosil C(18) column with a mobile phase consisting of acetonitrile -0.1% phosphoric acid (60:40 v/v). The second method was based on HPLC separation of OB from its degradation product using a VP-ODS C(18) column with a mobile phase consisting of acetonitrile/0.01 M potassium dihydrogen phosphate/diethylamine (60:40:0.2). Quantitation was achieved with UV detection at 220 nm based on peak area. The two HPLC methods were applied for the determination of OL or OB, their degradation products, methylparaben and propylparaben in pharmaceutical preparations. The proposed methods were used to investigate the kinetics of acidic and alkaline degradation processes of OL and OB at different temperatures and the apparent pseudofirst-order rate constant, half-life and activation energy were calculated. The pH-rate profiles of degradation of OL and OB in Britton-Robinson buffer solutions within the pH range 2-12 were studied.     

Study of forced degradation behavior of enalapril maleate by LC and LC-MS and development of a validated stability-indicating assay method

In the present study, comprehensive stress testing of enalapril maleate was carried out according to ICH guideline Q1A(R2). The drug was subjected to acid (0.1N HCl), neutral and alkaline (0.1N NaOH) hydrolytic conditions at 80 degrees C, as well as to oxidative decomposition at room temperature. Photolysis was carried out in 0.1N HCl, water and 0.1N NaOH at 40 degrees C. Additionally, the solid drug was subjected to 50 degrees C for 60 days in a dri-bath, and to the combined effect of temperature and humidity, with and without light, at 40 degrees C/75% RH. The products formed under different stress conditions were investigated by LC and LC-MS. The LC method that could separate all degradation products formed under various stress conditions involved a C18 column and a mobile phase comprising of ACN and phosphate buffer (pH 3). The flow rate and detection wavelength were 1 ml min(-1) and 210 nm, respectively. The developed method was found to be precise, accurate, specific and selective. It was suitably modified for LC-MS studies by replacing phosphate buffer with water, where pH was adjusted to 3.0 with formic acid. The drug showed instability in solution state (under acidic, neutral, alkaline and photolytic stress conditions), but was relatively stable in the solid-state, except formation of minor products under accelerated conditions. Primarily, maximum degradation products were formed in acid conditions, though the same were also produced variably under other stress conditions. The LC-MS m/z values and fragmentation patterns of two of the five products matched with enalaprilat and diketopiperazine derivative, previously known degradation products of enalapril. Also, m/z value of another product matched with an impurity listed in the drug monograph in European Pharmacopoeia. Rest two were hitherto unknown degradation products. The products were characterized through LC-MS fragmentation studies. Based on the results, a more complete degradation pathway for the drug could be proposed.     

Stability-indicating methods for the determination of sumatriptan succinate

Four stability-indicating methods were developed for the determination of sumatriptan succinate in the presence of its degradation products. The first method depends on the quantitative densitometric evaluation of thin-layer chromatography of sumatriptan succinate in the presence of its degradation products without any interference. Cyclohexane–dichloromethane–diethylamine (50:40:10 v/v/v) was used as a mobile phase and the chromatogram was scanned at 228 nm. This method determines sumatriptan succinate in the concentration range l–8 μg per spot with mean percentage recovery 100.52±1.23%. The second and third methods depend on the use of first-derivative (D₁) and second-derivative (D₂) spectrophotometry at 234 and 238 nm, respectively. These methods determine the drug in the concentration range 1.25–10 μg ml⁻¹ with mean percentage recovery 99.91±1.01% and 99.96±1.13% for (D₁) and (D₂), respectively. The fourth method depends on the use of ratio derivative spectrophotometric technique. The amplitude in the first derivative of the ratio spectra at 235 nm was selected to determine the cited drug in the presence of its degradation products. Calibration graph is linear in the concentration range 1.25–10 μg ml⁻¹ with mean percentage recovery 100.19±1.19%. The suggested methods were successfully applied for determining sumatriptan succinate in bulk powder, laboratory-prepared mixtures and pharmaceutical dosage forms (Imigran tablet) with good accuracy and precision. The results obtained by applying the proposed methods were statistically analyzed and compared with those obtained by the reported method.     

Development of a Validated Stability Indicating HPLC Method for Ranitidine Hydrochloride Syrup

An isocratic reversed-phase high-performance liquid chromatographic method was developed and validated for the determination of ranitidine HCl in syrup. The samples were analyzed by high-performance liquid chromatography (HPLC). Chromatographic separation was achieved on a C₁₈ column using an acetonitrile–aqueous phosphate buffer (20:80, v/v) elution, buffer being 10 mM disodium hydrogen phosphate brought to pH 7.1 with sodium hydroxide (0.1 N). Validation steps involved measurement of selectivity, accuracy, and precision under conditions of repeatability, reproducibility, sensitivity, and robustness. The lower limit of quantification was 10μg/mL. The validated method has been demonstrated to be reliable for the determination of ranitidine HCl and its related compound C. Stress degradation studies included exposing ranitidine HCl powder and Zantac syrup to acid, alkali, oxidation, and accelerated temperature of 50 °C for 24 hrs and photolysis for 8 hrs. The peaks of degraded products were well resolved from the drug peak. The validation of this method indicated that it could be effectively used to monitor the stability of ranitidine HCl syrup.     

Stability indicating methods for the determination of diloxanide furoate

Five new selective, precise and accurate methods are described for the determination of diloxanide furoate (DI) in presence of its degradation products. Method A utilizes the first and second derivative spectrophotometry at 270 and 280 nm, respectively. Method B is a RSD(1) spectrophotometric method based on the simultaneous use of the first derivative of ratio spectra and measurement at 270 nm. Method C is a pH-induced difference spectrophotometry using UV measurement at 295 nm. Method D is a densitometric one, after separation on silica gel plate using chloroform: methanol as mobile phase and the spots were scanned at 258 nm. Method E is reversed phase high performance liquid chromatography using methanol: water (80:20% v/v) as mobile phase at a flow rate of 1 ml/min and UV detection at 258 nm. Regression analysis showed good correlation in the concentration ranges 5-30, 5-25, 10-40 microg/ml, 100-500 ng/spot, 2-50 microg/ml with percentage recoveries of 99.92+/-0.56 and 99.79+/-0.47, 99.23+/-0.38, 99.96+/-0.06, 99.03+/-0.51, 98.81+/-0.68 for methods A, B, C, D and E, respectively. These methods are suitable as stability indicating methods for the determination of DI in presence of its degradation products either in bulk powder or in pharmaceutical formulations.     

First-derivative spectrophotometric and LC determination of cefuroxime and cefadroxil in urine

Two methods are presented for the determination of cefuroxime and cefadroxil in human urine using first (1D) derivative spectrophotometry and high-performance liquid chromatography. Cefuroxime and cefadroxil were determined by measurement of their first-derivative amplitude in 0.1 N sodium hydroxide at 292.5 and 267.3 nm, respectively in the concentration range of 2-10 microg ml(-1) for each drug. The HPLC method depends upon using a LiChrospher 100 RP-18 (5 microm) column at ambient temperature for cefuroxime and 35 degrees C for cefadroxil with mobile phases consisting of water-acetonitrile-acetic acid (85:15:0.1 v/v) at a flow rate of 1.5 ml min(-1) for cefuroxime; and 0.02 M potassium dihydrogen phosphate-acetonitrile (95:5 v/v) containing 0.003% (w/v) hexanesulphonic acid sodium salt and adjusted to apparent pH 3 with phosphoric acid at a flow rate of 2 ml min(-1) for cefadroxil. Quantitation was achieved with UV detection at 275 and 260 nm for cefuroxime and cefadroxil, respectively, based on peak area with linear calibration curves at the concentration ranges of 2-10 microg ml(-1) for cefuroxime and 5-20 microg ml(-1) for cefadroxil. The proposed methods were applied to the determination of dissolution rate for tablets and capsules containing each drug. The urinary excretion patterns as the cumulative amounts excreted have been calculated for each drug using the proposed methods.     

Comparison of spectrophotometric and an LC method for the determination perindopril and indapamide in pharmaceutical formulations.

A new sensitive, simple, rapid and precise reversed-phase high performance liquid chromatographic (HPLC) and two spectrophotometric methods have been developed for resolving binary mixture of perindopril and indapamide in the pharmaceutical dosage forms. The first method is based on HPLC on a reversed-phase column using a mobile phase of phosphate buffer pH 2.4 and acetonitrile (7:3 v/v) was used. Linearity range for perindopril and indapamide was 5.0-70.0 and 8.0-35.0 microg ml(-1). In the second method, the first derivative spectrophotometry with a zero-crossing technique of measurement is used for the simultaneous quantitative determination of perindopril and indapamide in binary mixtures without previous separation step. Linear calibration graphs of first derivative values at 225.7 and 255.4 nm for perindopril and indapamide, respectively. The third method is based on ratio derivative spectrophotometry, the amplitudes in the first derivative of the ratio spectra at 226.5 and at 255.3 nm were selected to determine perindopril and indapamide in the binary mixture. All the proposed methods showed good linearity, precision and reproducibility. The proposed methods were successfully applied to the pharmaceutical dosage forms containing the above-mentioned drug combination without any interference by the excipients.     

Stability study of the anticonvulsant enaminone (E118) using HPLC and LC-MS.

The stability of the new chemical synthetic enaminone derivative (E118) was investigated using a stability-indicating high-performance liquid chromatography (HPLC) procedure. The examined samples were analyzed using a chiral HSA column and a mobile phase (pH 7.5) containing n-octanoic acid (5 mM), isopropyl alcohol and 100 mM disodium hydrogen phosphate solution (1:9 v/v) at a flow rate of 1 ml min(-1). The developed method was specific, accurate and reproducible. The HPLC chromatograms exhibited well-resolved peaks of E118 and the degradation products at retention times <5 min. The stability of E118 was performed in 0.1 M hydrochloric acid, 0.1 M sodium hydroxide, water/ethanol (1:1) and phosphate buffer (pH approximately 7.5) solutions. E118 was found to undergo fast hydrolysis in 0.1 M hydrochloric acid solution. The decomposition of E118 followed first order kinetics under the experimental conditions. The results confirmed that protonation of the enaminone system in the molecule enhanced the hydrolysis of E118 at degradation rate constant of 0.049 min(-1) and degradation half-life of 14.1 min at 25 degrees C. However, E118 was significantly stable in 0.1 M sodium hydroxide, physiological phosphate buffer (pH 7.5) and ethanol/water (1:1) solutions. The degradation rate constants and degradation half-lives were in the ranges 0.0023-0.0086 h(-1) and 80.6-150.6 h, respectively. Analysis of the acid-induced degraded solution of E118 by liquid chromatography-mass spectrometry (LC-MS) revealed at least two degradation products of E118 at m/z 213.1 and 113.1, respectively.