K. B. Vinay

Sensitive spectrophotometric determination of lamotrigine in bulk drug and pharmaceutical formulations using bromocresol green

Two new, simple, rapid and reproducible spectrophotometric methods have been developed for the determination of lamotrigine (LMT) both in pure form and in its tablets. The first method (method A) is based on the formation of a colored ion-pair complex (1:1 drug/dye) of LMT with bromocresol green (BCG) at pH 5.02±0.01 and extraction of the complex into dichloromethane followed by the measurement of the yellow ion-pair complex at 410 nm. In the second (method B), the drug-dye ion-pair complex was dissolved in ethanolic potassium hydroxide and the resulting base form of the dye was measured at 620 nm. Beers law was obeyed in the concentration range of 1.5-15 µg mL-1 and 0.5-5.0 µg mL-1 for method A and method B, respectively, and the corresponding molar absorptivity values are 1.6932 x 104 and 3.748 x 104 L mol-1cm-1. The Sandell sensitivity values are 0.0151 and 0.0068 µg cm-2 for method A and method B, respectively. The stoichiometry of the ion-pair complex formed between the dug and dye (1:1) was determined by Jobs continuous variations method and the stability constant of the complex was also calculated. The proposed methods were applied successfully for the determination of drug in commercial tablets.

A Stability Indicating UPLC Method for the Determination of Tramadol Hydrochloride: Application to Pharmaceutical Analysis

The use of Ultra Performance Liquid Chromatography (UPLC), with a rapid 5-minute reversed phase isocratic separation on a 1.7 μm reversed-phase packing material to provide rapid ‘‘high throughput’’ support for tramadol hydrochloride (TMH) is demonstrated. A simple, precise and accurate stability-indicating isocratic UPLC method was developed for the determination of TMH in bulk drug and in its tablets. The method was developed using Waters Aquity BEH C18 column (100 mm × 2.1 mm, 1.7 μm) with mobile phase consisting of a mixture of potassium dihydrogen phosphate buffer of pH 2.8 and an equal volume of acetonitrile (60 : 40 v/v). The eluted compound was detected at 226 nm with a UV detector. The standard curve of mean peak area versus concentration showed an excellent linearity over a concentration range 0.5–300 μg mL−1 TMH with regression coefficient (r) value of 0.9999. The limit of detection (S/N = 3 ) was 0.08 μg mL−1 and the limit of quantification (S/N = 10 ) was 0.2 μg mL−1. Forced degradation of the bulk sample was conducted an accordance with the ICH guidelines. Acidic, basic, hydrolytic, oxidative, thermal and photolytic degradation were used to assess the stability indicating power of the method. TMH was found to degrade significantly in acidic, basic and oxidative stress conditions and stable in thermal, hydrolytic and photolytic conditions.

VALIDATED SPECTROPHOTOMETRIC METHODS FOR THE DETERMINATION OF RALOXIFENE HYDROCHLORIDE IN PHARMACEUTICALS

Two new simple, precise, rapid and extraction-free spectrophotometric methods are proposed for the determination of raloxifene hydrochloride (RLX) using bromate-bromide mixture and two dyes, methylene blue and rhodamine B, as reagents. The methods entail the addition of a known excess of bromate-bromide mixture to RLX in hydrochloric acid medium followed by determination of residual bromine by reacting with a fixed amount of either methylene blue and measuring the absorbance at 665 nm (Method A) or rhodamine B and measuring the absorbance at 555 nm (Method B). The amount of bromate reacted corresponds to the amount of RLX. In both the methods, the absorbance is found to increase linearly with the concentration of RLX. Under the optimum conditions, RLX could be assayed in the concentration ranges 0.5-5.0 and 0.1-2.0 µg mL-1 from method A and method B, respectively. The apparent molar absorptivities are calculated to be 7.0x104 and l.1x105 L mol-1cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.0073 and 0.0048 µg cm-2. The limits of detection and quantification have also been reported for both the spectrophotometric methods. The overall reproducibility of the methods was excellent and recoveries were 98.3-102.5% and 98.2-103.2% for method A and method B, respectively. The proposed methods can be readily utilized for bulk drug and in pharmaceutical formulations

Optimized and validated spectrophotometric methods for the determination of raloxifene in pharmaceuticals using permanganate.

Two simple and sensitive spectrophotometric methods are described for the determination of raloxifene hydrochloride (RLX) in pure form and in tablets. The first method (method A) is based on the formation of a yellowish-brown chromogen peaking at 430 nm when RLX was reacted with permanganate in acetic acid medium. In the second method (method B), RLX was reacted with a measured excess of permanganate in H2SO4 medium followed by the spectrophotometric measurement of the unreacted KMnO4 at 550 nm. Under the optimized experimental conditions, Beer’s law is obeyed in the concentration range 0.6–6.0 and 1.5–15.0 µg mL−1 with molar absorptivity of 7.01 × 104 and 2.8 × 104 L mol−1 cm−1 for method A and method B, respectively. The limits of detection (LOD) and quantification (LOQ) have also been reported. The intra-day and inter-day RSD and RE values at three different concentrations were assessed. The proposed methods were applied to the commercially available tablets, and the results were statistically compared with those of the reference method. The accuracy and reliability of the methods were further ascertained by recovery studies.

Use of two sulfonthalein dyes in the extraction-free spectrophotometric assay of tramadol in dosage forms and in spiked human urine based on ion-pair reaction

Tramadol is a centrally acting analgesic used in the prevention and treatment of moderate to severe pain. Two sensitive, selective, and rapid spectrophotometric methods are described for the determination of tramadol in its dosage forms and in spiked human urine. The methods are based on formation of yellow ion-pairs between tramadol and two sulfonthalein dyes; bromocresol purple (BCP) and bromocresol green (BCG) in dichloromethane medium followed by absorbance measurement at 400 and 410 nm, respectively. Under the optimum conditions, tramadol could be assayed in the concentration ranges, 1-15 and 1-16 µg ml(-1) with correlation coefficient greater than 0.999 in both cases. The molar absorptivity values are calculated to be 1.84 × 10(4) and 1.97 × 10(4) l mol(-1) cm(-1) for BCP and BCG methods, respectively; and the corresponding Sandell sensitivity values are 0.0143 and 0.0134 µg cm(-2). The limits of detection (LOD) and quantification (LOQ) have also been reported. The stoichiometry of the reaction was found to be 1:1 in both cases and the conditional stability constant (K(f)) values of the ion pairs have been calculated. The within-day and between-day RSD were 0.9-1.96% and 1.56-3.21%, respectively. The methods were successfully applied to the determination of tramadol in tablets and injections and also in spiked human urine with good recoveries. The procedures are simple, accurate, and suitable for quality control application.

Determination of raloxifene hydrochloride in human urine by LC-MS-MS

A sensitive and selective liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method was developed to determine raloxifene hydrochloride (RLX) in human urine. After a solid-phase extraction with SPE cartridge, the urine sample was analyzed on a C18 column (Symmetry 3.5μm; 50 mm×4.6 mm i.d) interfaced with a triple quadruple tandem mass spectrometer. A positive electrospray ionization was employed as the ionization source. The mobile phase consisted of ammonium acetate (pH 4.0)-acetonitrile (60:40, v/v).The method was linear over a concentration range of 20-1000 ng mL-1. The lower limit of quantitation was 20 ng mL-1. The intra-day and inter-day relative standard deviation across three validation runs over the entire concentration range was <10.5%. The accuracy determined at three concentrations (50, 500 and 850 ng mL-1 RLX) was within ±0.84% in terms of relative errors.

Simple UV and visible spectrophotometric methods for the determination of doxycycline hyclate in pharmaceuticals

Doxycycline hyclate (DOX), a broad spectrum antibiotic with activity against a wide range of gram-positive and gram-negative bacteria, is widely used as a pharmacological agent and as an effector molecule in inducible gene expression system. Three simple, selective, rapid, accurate, precise and cost-effective spectrophotometric methods for the determination of DOX in bulk drug and in tablets have been developed and validated. First method (method A) is based on the measurement of absorbance of DOX in 0.1 M HCl at 240 nm. The second method (method B) is based on the measurement of yellow chromogen at 375 nm which is formed in 0.1 M NaOH. The third method is based on the measurement of 2: 1 complex formed between DOX and iron(III) in H2SO4 medium, the complex peaking at 420 nm (method C). The optimum conditions for all the three methods are optimized. Beer’s law was obeyed over the ranges 2.5–50.0, 1.50–30.0 and 10–100 g/mL for method A, method B and method C, respectively. The apparent molar absorptivity values are calculated to be 1.03 × 104, 1.73 × 104, and 5.21 × 103 L mol−1 cm−1 for method A, method B, and method C, respectively. The Sandell sensitivity, limit of detection (LOD) and limit quantification (LOQ) values are also reported. All the methods were validated in accordance with current ICH guidelines. The developed methods were employed with high degree of precision and accuracy for the estimation of total drug content in commercial tablet formulations of DOX.

Spectrophotometric determination of isoxsuprine hydrochloride using 3-methyl-2-benzothiazolinone hydrazone hydrochloride in spiked human urine and pharmaceuticals

Two selective and sensitive spectrophotometric methods are proposed for the determination of isoxsuprine hydrochloride (ISX) in spiked human urine and in pharmaceuticals. The methods are based on the oxidative-coupling reaction between 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) and ISX in the presence of Ce(SO(4))(2). The novelty of the proposed reaction is the formation of two different colored chromogens at two different pHs. The resulting product at pH<1.5 is a red colored chromogen peaking at 500nm (method A) and that formed between the pH 3.85 and 4.15, is violet colored with an absorption maximum at 580nm (method B). In both the methods, absorbance of the chromogen is found to increase linearly with the concentration of ISX as is corroborated by the correlation coefficients of 0.9989 and 0.9970, and the systems obey Beers law over the ranges of 1.4-21.0 and 1.0-15.0microgml(-1), for method A and method B, respectively. The calculated molar absorptivities are 1.08 x 10(4) and 1.78 x 10(4)lmol(-1)cm(-1) for method A and method B, respectively with corresponding Sandell sensitivity values of 0.0311 and 0.0190microgcm(-2). The reaction stoichiometry, in both the methods, was evaluated by the limiting logarithmic method and was found to be 1:1 (ISX:MBTH). The methods were successfully applied to the determination of ISX in spiked human urine and pharmaceutical formulation.

Spectrophotometric Determination of Mycophenolate Mofetil as Its Charge-Transfer Complexes with Two π-Acceptors

Two simple, selective, and rapid spectrophotometric methods are described for the determination of mycophenolate mofetil (MPM) in pure form and in tablets. Both methods are based on charge-transfer complexation reaction of MPM with p-chloranilic acid (p-CA) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dioxane-acetonitrile medium resulting in coloured product measurable at 520 nm (p-CA) or 580 nm (DDQ). Beers law is obeyed over the concentration ranges of 40–400 and 12–120 μg mL−1 MPM for p-CA and DDQ, respectively, with correlation coefficients (r) of 0.9995 and 0.9947. The apparent molar absorptivity values are calculated to be 1.06 × 103 and 3.87 × 103 L mol−1 cm−1, respectively, and the corresponding Sandells sensitivities are 0.4106 and 0.1119 μg cm−1. The limits of detection (LOD) and quantification (LOQ) are also reported for both methods. The described methods were successfully applied to the determination of MPM in tablets. Statistical comparison of the results with those of the reference method showed excellent agreement. No interference was observed from the common excipients present in tablets. Both methods were validated statistically for accuracy and precision. The accuracy and reliability of the methods were further ascertained by recovery studies via standard addition procedure.

Titrimetric and Spectrophotometric Assay of Pantoprazole in Pharmaceuticals Using Cerium(IV) Sulphate as Oxidimetric Agent

Titrimetric and spectrophotometric assay of pantoprazole sodium sesquihydrate (PSS) using cerium(IV) sulphate as the oxidimetric reagent is described. The methods are based on the oxidation of PSS with a measured excess of Ce(IV) sulphate followed by the determination of unreacted oxidant using different reaction schemes. In titrimetry, the unreacted oxidant was determined by back titration with ferrous ammonium sulphate (FAS) in sulphuric acid medium. Spectrophotometry involves the reduction of unreacted Ce(IV) sulphate with a fixed quantity of Fe(II). The resulting Fe(III) is complexed with thiocyanate and the absorbance is measured at 470 nm. In both the methods, the amount of Ce(lV) sulphate reacted corresponds to PSS concentration. Titrimetry is applicable over 1–10 mg range whereas in spectrophotometry, the calibration graph is linear in the range of 0.5–7.0 μg/mL and the calculated molar absorptivity value is 1.58 × 105 L/mol cm. The validity of the proposed methods was tested by analyzing pure and dosage forms containing PSS. Statistical treatment of the results reflects that the proposed procedures are precise, accurate and easily applicable to the determination of PSS in pure form and in pharmaceutical formulations.