Molar Absorptivity Values Research Articles

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.

Study of Spectrophotometric Characteristics of the Charge Transfer Reaction of Aminomethylbenzoic Acid with 7,7,8,8-Tetracyanoquinodimethane

A new spectrophotometric method was developed for the determination of aminomethylbenzoic acid (PAMBA) using 7,7,8,8-tetracyanoquinodimethane (TCNQ). The method was based on the formation of charge transfer (CT) complex of this drug as n-electron donor with the π-acceptor TCNQ. TCNQ was found to react with PAMBA to produce a kind of yellow complex. The CT reaction proceeded quantitatively in pH 8.5 buffer solution. Different variables affecting the reaction were carefully studied and optimized. Under optimal reaction conditions, the stoichiometric ratio of the reaction, maximum absorption wavelength and the value of molar absorptivity were measured to be 1:1, 425 nm, and 1.9×104 L·mol−1·cm−1, respectively. Beer′s law was obeyed in the range of 1–9 µg·mL?1 of PAMBA. The data have been filled to a linear regression equation A=−0.2612+0.1123c (µg·mL−1), with a correlation coefficient of 0.9996. The detection limit was 0.4 µg·mL−1, R.S.D. was less than 1.9%, and average recovery was over 97.6%. The formation of the CT complex was also confirmed by both infrared and 1H NMR measurements. The thermodynamic property, kinetic property and reaction mechanism have also been discussed. The method developed was applied successfully to the determination of the subject drug in its pharmaceutical dosage forms with good precision and accuracy compared to official method revealed by t- and F-tests.

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.

SENSITIVE AND SELECTIVE EXTRACTION FREE ION-PAIR COMPLEXOMETRIC DETERMINATION OF DOMPERIDONE IN PHARMACEUTICALS AND IN SPIKED HUMAN URINE

Domperidone (DOM) is a drug used as an antiemetic and to control gastrointestinal effects of dopaminergic drugs in the management of perkinsonism. Two simple, rapid, sensitive and selective extraction free spectrophotometric methods have been developed for the assay of DOM in pure drug, in pharmaceuticals and in spiked human urine sample. The methods are based on the formation of yellow ion-pair complexes between DOM and two sulphonphthalein dyes viz., thymol blue (method A) and bromothymol blue (method B) in acetone and dichloromethane medium. The complexes showed absorption maxima at 390 nm and 410 nm in method A and method B, respectively. Reaction conditions were optimized to obtain the maximum color intensity. The absorbance was found to increase linearly with increase in concentration of DOM, which was corroborated by the calculated correlation values of 0.9991 in method A and 0.9986 in method B. The systems obeyed Beer’s law over the concentration range of 1.25 - 20 µg mL-1 in both the methods. The molar absorptivity values are calculated to be 1.53 × 104 and 2.06 × 104 L mol-1 cm-1 for method A and method B, respectively and the corresponding Sandell sensitivity values are 0.028 and 0.021 μg cm-2. The composition of the ion-pairs was found to be 1 : 1 by Job’s method and the conditional stability constant (K f ) of the complexes have been calculated. The proposed methods were applied successfully to the determination of DOM in tablets as well as in spiked urine sample with good accuracy and precision.

Optimized and validated spectrophotometric methods for the determination of hydroxyzine hydrochloride in pharmaceuticals and urine using iodine and picric acid

Two simple, rapid, cost-effective and sensitive spectrophotometric procedures are proposed for the determination of hydroxyzine dihydrochloride (HDH) in pharmaceuticals and in spiked human urine. The methods are based on the charge transfer complexation reaction of the drug with either iodine (I2) as a ?-acceptor (method A) in dichloromethane or picric acid (PA) as a ?-acceptor (method B) in chloroform. The coloured products exhibit absorption maxima at 380 and 400 nm for I2 and PA, respectively. The Beer Law was obeyed over the concentration ranges of 1.25-15 and 3.75-45 ?g mL-1 for method A and method B, respectively. The molar absorptivity values, Sandell sensitivities, limits of detection (LOD) and quantification (LOQ) are reported. The accuracy and precision of the methods were evaluated on intra-day and inter-day basis. The proposed methods were successfully applied for the determination of HDH in tablets and spiked human urine.

Extractive spectrophotometric determination of Quetiapine fumarate in pharmaceuticals and human urine using calmagite as an ion-pair reagent

Quetiapine fumarate (QTF) is an antipsychotic drug belonging to the benzisoxazole derivatives indicated for the treatment of schizophrenia. A sensitive and selective method based on dichloromethane-extractable ion-pair of QTF with calmagite (CGT), which exhibited an absorption maximum at 490 nm, is described. At this wavelength, Beer?s law is obeyed over the concentration range of 3.0 - 30.0 ?g ml-1. The apparent molar absorptivity, limit of detection (LOD) and quantitation (LOQ) values are 1.32 ? 104 l mol-1 cm-1, 0.27 and 0.81 ?g ml-1 respectively. The reaction is extremely rapid at room temperature and the absorbance values remain unchanged upto 19 h. The precision results, expressed as intra-day and inter-day relative standard deviation values, are satisfactory (RSD ? 2.2%). The accuracy is satisfactory as well (RE ? 2.44%). The method was successfully applied to the determination of QTF in pharmaceuticals and spiked human urine with satisfactory results. No interference was observed from common pharmaceutical adjuvants in tablets. Statistical comparison of the results with official method showed an excellent agreement and indicated no significant difference in precision.

Spectrophotometric determination of repaglinide in tablets based on charge-transfer complexation reaction with chloranilic acid and dichloro-dicyano benzoquinone

Two simple, accurate, precise, inexpensive, selective and sensitive spectrophotometric methods are described for the determination of repaglinide (RPG) in bulk drug and its tablets. The methods were based on the charge- transfer complex reaction between RPG in acetonitrile with p-chloranilic acid (CAA) or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in dioxane and subsequent formation of intensely colored radical anions of the reagents which were measured at 520 nm (CAA) or 590 nm (DDQ). Several experimental variables affecting the complex formation, stability of the colored species and sensitivity of the reaction were optimized. Under the optimized conditions, Beer?s law was obeyed over the concentration ranges of 20-400 and 5-80 ?g ml-1 RPG for CAA and DDQ methods, respectively, and the corresponding correlation coefficients were 0.9995 and 0.9998. The apparent molar absorptivity values were 1.02x103 and 4.60x103 for CAA and DDQ methods respectively, with corresponding Sandell sensitivity values of 0.4438 and 0.0984 ?g cm-2. Limits of detection (LOD) were calculated to be 7.07 and 2.42 ?g ml-1 and the limits of quantification (LOQ) were 21.43 and 7.33 ?g ml-1 RPG, for CAA method and DDQ method, respectively. Validation results demonstrated that the inter day and intra day accuracy were up to 97.56%. The precision determined did not exceed 2.5% of RSD. The methods were successfully used for the determination of RPG in tablet form and the results were in good agreement with the label claims as shown by the recoveries which were in the range of 99.22- 102.8% with standard deviation values < 2%. The accuracy of the method was confirmed by recovery studies via standardaddition procedure with excellent recovery 98.24-104.0 ? 1.08-3.35.

Solvent Extraction Studies on Copper(II) and Silver(I) Complexes of Bis(4‐hydroxypent‐2‐ylidene)diaminoethane: Composition of Extracted Copper(II) Species

Copper(II) complexes of bis(4‐hydroxypent‐2‐ylidene)diaminoethane (BHPDE) were prepared by extractive method. Job’s continuous variation and equilibrium constant methods, as well as spectral and elemental analyses were applied in the determination of the nature of extracted species. The results indicate the formation of mixed ionic complexes of the types Cu(H2L)X2, Cu(H2L)2X2 and CuL (where H2L = BHPDE and X = NO3-, CIO4-, Cl- or ½SO42-). Cu(H2L)X2 and Cu(H2L)2X2 predominate at low pH extractions while CuL chelate predominates at high pH extraction. The complexes exist in two isomeric forms, the blue readily‐water‐soluble and the violet less water‐soluble forms. Both complexes show maximum absorption at 540 nm and molar absorptivity values of about 2.0 x 102 dm3 mole-1 cm-1.

Development and validation of spectrophotometric method for the determination of DPP-4 inhibitor, sitagliptin, in its pharmaceutical preparations

A simple, sensitive and reproducible spectrophotometric method was developed for the determination of sitagliptin phosphate in bulk and in pharmaceutical formulations. The proposed method is based on condensation of the primary amino group of sitagliptin phosphate with acetyl acetone and formaldehyde producing a yellow colored product, which is measured spectrophotometrically at 430nm. The color was stable for about 1 hour. Beer’s law is obeyed over a concentration range of 5-25 μg/ml. The apparent molar absorptivity and Sandell sensitivity values are 1.067 x 104 Lmol-1cm-1 and 0.0471 μgcm-2 respectively. All the variables were studied to optimize the reaction conditions. No interference was observed in the presence of common pharmaceutical excipients. The validity of the method was tested by analyzing sitagliptin phosphate in its pharmaceutical preparations. Good recoveries were obtained. The developed method was successfully employed for the determination of sitagliptin phosphate in various pharmaceutical preparations.

Development and validation of spectrophotometric method for the determination of DPP-4 inhibitor, sitagliptin, in its pharmaceutical preparations

A simple, sensitive and reproducible spectrophotometric method was developed for the determination of sitagliptin phosphate in bulk and in pharmaceutical formulations. The proposed method is based on condensation of the primary amino group of sitagliptin phosphate with acetyl acetone and formaldehyde producing a yellow colored product, which is measured spectrophotometrically at 430nm. The color was stable for about 1 hour. Beer’s law is obeyed over a concentration range of 5-25 μg/ml. The apparent molar absorptivity and Sandell sensitivity values are 1.067 x 104 Lmol-1cm-1 and 0.0471 μgcm-2 respectively. All the variables were studied to optimize the reaction conditions. No interference was observed in the presence of common pharmaceutical excipients. The validity of the method was tested by analyzing sitagliptin phosphate in its pharmaceutical preparations. Good recoveries were obtained. The developed method was successfully employed for the determination of sitagliptin phosphate in various pharmaceutical preparations.

Sensitive Bromatometric Methods for the Determination of Sumatriptan Succinate in Pharmaceutical Formulations

Two simple and sensitive spectrophotometric methods are described for the determination of sumatriptan succinate (STS) in pure and tablets using bromate‐bromide as the bromination reagent in acid medium and two dyes as subsidiary reagents. The two methods are based on the bromination of STS by a known excess of in situ generated bromine followed by determination of unreacted bromine by reacting with a fixed amount of methyl orange (Method A) or indigo carmine (Method B) and measuring the absorbance at 508 or 610 nm. In both methods, the amount of bromine reacted corresponds to the amount of STS. The experimental conditions for the assay have been optimized. In two methods, the absorbance was found to increase linearly with the concentration of STS at the respective wavelengths. Beer’s law was obeyed over the ranges 0.2‐1.6 and 2.0‐12.0 μg mL-1 for method A and method B respectively and the respective molar absorptivity values were 1.898×105 and 2.71×104 L mol-1 cm-1. The statistical analysis of the methods was validated according to the present ICH guidelines. The proposed methods were applied to the analysis of tablet form of STS and the results tallied well with the label claim.

Spectrophotometric Determination of Reboxetine through Condensation and Diazo‐Coupling Reactions

In the present study, two simple, sensitive and reproducible visible spectrophotometric methods were developed for the determination of reboxetine in pure form and in pharmaceutical formulations. The methods involve acid hydrolysis of reboxetine methane sulphonate (Reboxetine as methane sulphonate) and the product obtained was used for the estimation. Out of the two methods developed in the laboratory, the first method involves the condensation reaction of hydrolysed reboxetine methane sulphonate with ethyl acetoacetate in sulphuric acid medium and the second method involves the diazocoupling reaction of hydrolysed reboxetine methane sulphonate with diazotized p‐sulphanilic acid in alkaline medium. They have absorption maxima at 400 nm and 430 nm respectively and obey Beer’s law in the concentration ranges of 0.5 ‐ 0.3 μgmL-1 and 1.0 ‐ 7.5 μgmL-1 respectively. Results of analysis were validated statistically and by recovery studies. The apparent molar absorptivity values (∈max) obtained are 7.549 x 104 L mol-1 cm-11 and 2.656x104 Lmol-1cm-1 respectively. Both these have correlation coefficient value of 0.9999. The proposed methods have good precision and accuracy.

Spectrophotometric determination of diphenhydramine hydrochloride in pharmaceutical preparations and biological fluids via ion-pair formation

A simple, sensitive and accurate spectrophotometric method has been described for the assay of diphenhydramine hydrochloride (DPH) in raw material and in biological samples. The method is based on extraction of DPH into dichloromethane as ion-pair complexes with patent blue (PB), eriochrome black T (EBT), methyl orange (MO) and bromocresol purple (BCP) in acidic medium. The coloured species exhibited absorption maxima at 632, 514, 428 and 414nm for PB, EBT, MO and BCP, with molar absorptivity values of 1.32×105, 2.36×104, 3.68×104 and 3.07×104lmol−1cm−1, respectively. The reaction conditions were optimized to obtain the maximum colour intensity. Beer’s law was obeyed with a good correlation coefficient (0.9982–0.9993) in the concentration ranges 0.5–3, 2.0–16, 2.0–10 and 1.0–10μgml−1 for PB, EBT, MO and BCP methods, respectively. The composition ratio of the ion-association complexes was found to be 1:1 in all cases as established by Job’s method. The conditional stability constant (Kf) and the free energy changes (ΔG°) were determined for all complexes formed. The proposed method was successfully applied for the determination of DPH in tablets and human urine with good accuracy and precision. Statistical comparison of the results with those obtained by the official method showed good agreement and indicated no significant difference in accuracy and precision.

Highly sensitive spectrophotometric determination of olanzapine using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl

Two highly sensitive spectrophotometric methods have been developed for the determination of olanzapine (OLP) in pharmaceuticals using cerium(IV) and iron(II) complexes of 1,10-phenanthroline and 2,2′-bipyridyl as reagents. The methods are based on the oxidation of OLP in acidic medium by a known excess of cerium(IV) followed by the determination of the unreacted oxidant by reacting with either ferroin and measuring the absorbance at 510 nm (method A) or iron(II)-2,2′-bipyridyl complex and measuring the absorbance at 525 nm (method B). The amount of cerium(IV) reacted corresponds to the amount of OLP. In both the methods, the absorbance is found to increase linearly with OLP concentration as shown by the correlation coefficient (r) of 0.9980 and 0.9958 for method A and method B, respectively. The calibration graphs are linear over the concentration range of 0.2–2.0 μg/mL in both the methods. The calculated molar absorptivity values are 1.00 × 106 and 7.03 × 105 L/mol cm, for method A and method B. The LOD and LOQ values for method A are calculated to be 0.04 and 0.13 μg/mL and the values are 0.07 and 0.22 μg/mL for method B, respectively. The methods were validated as per the current ICH guidelines. Both the methods gave similar results in terms of accuracy and precision. The RSD was less than 3% and the accuracy, obtained from recovery experiments, was 98.76–101.4%. The methods developed were applied to the determination of OLP in tablets and results agreed well with the label claim.

Colorimetric determination of simvastatin and lovastatin in pure form and in pharmaceutical formulations

Simple, accurate and precise colorimetric method for the determination of simvastatin and lovastatin in tablets is described. The method is based on the reaction of simvastatin or lovastatin with hydroxylamine in alkaline medium to form the corresponding hydroxamic acid derivatives which, on treatment with ferric ion in acid medium, yield highly colored ferric-chelate complex with maximum absorption at 513nm. Beer's law is obeyed in the concentration ranges 0.04-0.4mgml(-1) for both simvastatin and lovastatin, respectively. Molar absorptivity values, as calculated from Beer's law data, were found to be 1.15x10(3) and 1.09x10(3)lmol(-1)cm(-1) for simvastatin and lovastatin, respectively. Optimal experimental parameters for the reaction have been studied. The validity of the described procedures was assessed. Statistical analysis of the results reflects that the proposed procedures are precise, accurate and easily applicable for the determination of simvastatin and lovastatin in pure form and in pharmaceutical preparation.

Coupling reaction and complex formation for the spectrophotometric determination of physiologically active catecholamines in bulk, pharmaceutical preparations and urine samples of schizophrenic patients

A simple and sensitive spectrophotometric method for the determination of three catecholamines namely dopamine hydrochloride (DO.HCl), dobutamine hydrochloride (DOB.HCl) and vanillymandelic acid (VMA), in both pure form or in their commercially available pharmaceutical formulations or urine samples of schizopherinic patients is described. The method is based on the reaction of diazotized 4-aminoantipyrine (4-AAP) with catecholamines in a basic medium (pH = 10-11) to yield pink-coloured products having absorption maxima at 500, 505 and 480 nm for DO.HCl, VMA and DOB.HCl, respectively. Before carrying out Beer's Law, different experimental conditions, such as time, temperature, sequence of addition, and pH are optimized. The coloured species obeyed Beer's Law in the range of 47.4-417.2, 59.45-445.9 and 67.57-405.4 mg/L for DO.HCl, VMA and DOB.HCl, respectively. The molar absorptivity values as obtained from Beer's Law data were found to be 2.979 x 10(4), 4.39 x 10(4) and 1.036 x 10(4) L mol(-1) cm(-1), while Sandell's sensitivity values were observed to be 3 x 10(-3), 4.4 x 10(-3) and 1.3 x 10(-3) microg cm(2-) for DO.HCl, VMA and DOB.HCl, respectively. Common excipients did not interfere with the proposed method. The results of the proposed method compare favourably with those of official methods. The proposed method offers simplicity, reliability, rapidity, and accuracy compared to the existing methods.

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. Beer’s 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 Job’s 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.

Synergistic liquid–liquid extractive spectrophotometric determination of gold(III) using 1-(2′,4′-dinitro aminophenyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-thiol

Synergistic liquid-liquid extractive spectrophotometric determination of gold(III) using 1-(2',4'-dinitro aminophenyl)-4,4,6-trimethyl-1,4-dihydro pyrimidine-2-thiol [2',4'-dinitro APTPT] has been described. Equal volumes (5cm(3)) of the 2',4'-dinitro APTPT (0.02molL(-1)) in the presence of pyridine (0.5molL(-1)) form an orange-red coloured ternary complex with gold(III) of molar ratio 1:1:1 at pH 1.8-2.4 with 5min of shaking. The absorbance of coloured organic layer in 1,2-dichloroethane is measured spectrophotometrically at 445nm against reagent blank. A pronounced synergism has been observed by the binary mixture of 2',4'-dinitro APTPT and pyridine, which shows that the enhancement in the absorbance is observed in the presence of pyridine by the adduct formation in the organic phase. Beer's law was obeyed in the concentration range 2.5-20.0microgmL(-1), with molar absorptivity and Sandell's sensitivity values of 8.7x10(3)dm(3)mol(-1)cm(-1) and 0.023microgcm(-2) respectively. A repetition of the method was checked by finding relative standard deviation (R.S.D.) (n=10) which was 0.17%. The composition of the gold(III)-2',4'-dinitro APTPT-pyridine adduct was established by slope analysis, molar ratio and Job's method. The ternary complex was stable for more than 48h. The influence of various factors such as pH, 2',4'-dinitro APTPT concentration, solvent and pyridine on the degree of complexation has been established. A number of foreign ions tested for their interferences and use of suitable masking agents wherever necessary are tabulated, which show that selectivity of the method has been enhanced. The method is successfully employed for the determination of gold(III) in binary, synthetic mixtures and ayurvedic samples. The reliability of the method is assured by inter-comparison of experimental values, using an atomic absorption spectrometer.

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. Beer’s 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 104L 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 Job’s 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.

Titrimetric and spectrophotometric determination of doxycycline hyclate using bromate-bromide, methyl orange and indigo carmine

One titrimetric and two indirect spectrophotometric methods are described for the determination of doxycycline hyclate (DCH) in bulk drug and in its formulations. The methods use bromate-bromide, methyl orange and indigo carmine as reagents. In titrimetry (method A), DCH is treated with a known excess of bromate-bromide mixture in acid medium and the residual bromine is back titrated iodometrically after the reaction between DCH and in situ bromine is ensured to be complete. In spectrophotometric methods, the excess of bromine is estimated by treating with a fixed amount of either methyl orange (method B) or indigo carmine (method C) and measuring the change in absorbance either at 520 or 610 nm. Titrimetric method is applicable over 1-8 mg range and the calculations are based on a 1:2 (DCH:bromate) stoichiometric ratio. In spectrophotometry, the calibration graphs were found to be linear over 0.25-1.25 and 1-5 ?g mL-1 for method B and method C, respectively, with corresponding molar absorptivity values of 2.62 ?105 and 6.97 ? 104 L mol-1 cm-1. Accuracy and precision of the assays were determined by computing the intra-day and inter-day variations at three different levels of DCH.