Molar Absorptivity Values Research Articles

Rapid and Sensitive Extraction-Free Spectrophotometric Methods for the Determination of Pheniramine Maleate Using Three Sulphonthalein Dyes

Three extraction- free spectrophotometric methods which are simple, selective and sensitive are described for the quantitation of pheniramine maleate (PAM), an anti allergic drug, in pure form and in its formulations. The methods are based on formation of yellow colored ion-pair complexes between PAM and three sulphonthalein dyes viz., bromothymol blue (method A), and bromocresol purple (method B) in dichloromethane, and bromocresol green (method C) in chloroform medium. The experimental variables such as reagent concentration, solvent medium and reaction time have been carefully optimized to achieve the highest sensitivity. Beer’s law is obeyed over the concentration ranges 1.0–16.0 for method A and method B, and 0.6–12 μg ml−1 PAM for method C with correlation coefficient of 0.999 for method A and method B, and 0.997 for method C. The molar absorptivity values are calculated to be 2.3 × 104, 2.5 × 104 and 3.0 × 104 l mol−1 cm−1 for the methods in the same order. The composition of the ion-pairs was found to be 1:1 by Job’s method of continuous variations and the conditional stability constant (Kf) of the complexes have been calculated. The proposed methods were applied successfully to the determination of PAM in tablets and injection with good accuracy and precision and without interferences from common additives. The results obtained by the proposed methods were compared favourably with those of the reference method.

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

Titrimetric and spectrophotometric assay of ganciclovir (GNC) is described using cerium(IV) sulphate as the oxidimetric reagent. The methods are based on the oxidation of GNC with a measured excess of cerium(IV) sulphate in acid medium followed by determination of the unreacted oxidant by two different reaction schemes. In titrimetry, the unreacted oxidant was determined by back titration with ferrous ammonium sulphate (FAS) in sulphuric acid medium, and spectrophotometry involves the reaction of residual cerium(IV) with p-DMAB to form brownish-coloured p-dimethylamino quinoneimine whose absorbance was measured at 460 nm. In both methods, the amount of cerium(IV) sulphate reacted corresponds to GNC concentration. Titrimetry is applicable over 3–10 mg range where as, in spcetrophotometry, the calibration graph is linear over the range of 2–10 μg mL−1 and the calculated molar absorptivity value is L mol−1 cm−1. The validity of the proposed methods was tested by analyzing pure and dosage forms containing GNC. Statistical treatment of the results reflects that the proposed procedures are precise, accurate, and easily applicable for the determination of GNC pure form and in pharmaceutical formulations.

Optimized and validated spectrophotometric methods for the determination of levocetirizine in pharmaceuticals based on charge transfer reaction

Three rapid, selective and sensitive spectrophotometric methods have been proposed for the quantitative determination of levocetirizine dihydrochloride (LCT) in pure form as well as in its pharmaceutical formulation. The methods are based on the charge transfer complexation reaction of LCT as n-electron donor with 2,4-dinitrophenol (DNP), picric acid (PA) as π-acceptors and iodine (I2) as σ-acceptor to give highly colored radical anion species. The colored products were quantified spectrophotometrically at 420nm with both DNP (method A) and PA (method B) and at 375nm with I2 (method C). Under the optimized experimental conditions, Beer’s law is obeyed over the concentration ranges of 1.2–24, 1.6–32 and 2.4–48μgmL−1 LCZ for method A, method B and method C, respectively. The values of molar absorptivity, Sandell sensitivity, limits of detection and quantification are also reported. The effect of reaction medium, reaction time and reagent concentration on the sensitivity and stability of the complexes formed has been examined. The proposed methods were successfully applied to the determination of LCT in pure form and commercial tablets and in syrup with good accuracy and precision. Statistical comparison of the results was performed using Student’s t-test and F-ratio at 95% confidence level and the results showed no significant difference between the reference and proposed methods with regard to accuracy and precision. Further to the accuracy and reliability the methods were confirmed by recovery studies via the standard addition technique.

Application of potassium permanganate to spectrophotometric assay of metoclopramide hydrochloride in pharmaceuticals

Two simple, sensitive, and cost-effective spectrophotometric methods are described for the determination of metoclopramide hydrochloride (MCP) in pharmaceutical dosage forms. The methods are based on a redox reaction between MCP and KMnO4 in alkaline and acid media. Direct spectrophotometry (method A) involves treating MCP with permanganate in an NaOH medium and measuring a bluish green product at 610 nm. In indirect spectrophotometry (method B), MCP is treated with a fixed concentration of KMnO4 in an H2SO4 medium, and after a specified time, the unreacted KMnO4 is measured at 545 nm. Under optimum assay conditions, Beer’s law is obeyed over the ranges of 0.75–12.0 and 2.5–30.0 g/ml for methods A and B, respectively. Molar absorptivity values are calculated to be 2.33∙104 and 2.66∙104 l/mol cm for methods A and B, respectively, and corresponding Sandell’s sensitivity values are 0.015 and 0.013 g/cm2. Limits of detection (LOD) and quantification (LOQ) are also reported. The applicability of the developed methods was demonstrated by the determination of MCP in tablet and injection forms. The accuracy and reliability of the proposed methods were further ascertained by recovery studies via standard addition technique.

Spectrophotometric determination of dothiepin hydrochloride in pharmaceuticals through ion-pair complexation reaction

Two simple, sensitive and extraction-free spectrophotometric methods are described for the determination of dothiepin hydrochloride (DOTH) both in pure form and in pharmaceutical tablets. The methods are based on ion-pair complex formation between dothiepin base (DOT) and two acidic dyes, namely, bromophenol blue (BPB) or bromocresol green (BCG) with absorption maximum at 425 nm for BPB method or 430 nm for BCG method. Beer?s law is obeyed over the concentration ranges of 1.0-15.0 and 1.0-17.5 ?g mL-1 DOT for BPB and BCG methods, respectively. The molar absorptivity values and Sandell?s sensitivity values are reported for both methods. The limits of detection (LOD) and quantification (LOQ) were calculated to be 0.18 and 0.53 ?g mL-1 for BPB method, and 0.17 and 0.50 ?g mL-1 for BCG method, respectively. The stoichiometry of the complex in either case was found to be 1: 1 and the conditional stability constant (KF) of the complexes has also been calculated. The proposed methods were applied successfully to the determination of DOTH in pure form and in its tablet form with good accuracy and precision. Statistical comparison of the results was performed using Student's t-test and variance ratio F-test at 95% confidence level and there was no significant difference between the official and proposed methods with regard to accuracy and precision. Further, the validity of the proposed methods was confirmed by recovery studies via standard addition technique.

New Approach for the Determination of Tricyclic Antidepressant Amitriptyline Using <i>β</i>-Cyclodextrin-PEG System via Spectrophotomerty

A new and simple procedure for the spectrophotometric determination of the tricyclic antidepressant drug amitriptyline is proposed. The method is based on enhancement of sensitivity of the [AMIYTP]+ β-cyclodextrin and PEG molecules involved in formation of molecules inclusion complex, in presence of polyethylene glycol (PEG) medium. The mole ratio of [AMIYTP]+ β-cyclodextrin and PEG molecules in inclusion complex were determined by the curve fitting method. The value of molar absorptivity of {[AMIYTP: (β CD)] PEG} complex in term of the drug lies in rage of (2.20 - 2.23) × 104 L·mole–1·cm–1 at absorption maximum 242 nm. The slope, intercept and correlation co-efficient were found to be 14.21, 0.0046, and 0.998, respectively. The effect of analytical variables on the determination of the drug and composition of the ion associated complex are discussed in the paper. This method is applicable in the determina-tion of amitriptyline in the pharmaceutical preparations.

Extractive Spectrophotometric Determination of Quetiapine Fumarate in Pharmaceuticals and Spiked Human Urine

A simple, sensitive and selective extractive spectrophotometric method for the determination of quetiapine fumarate (QTF) in bulk drug, tablets and spiked human urine sample is described. The method is based on the formation of a chloroform extractable yellow ion-pair complex between basic nitrogen of the drug (QTF) and the dye quinoline yellow (QY) in acetate-hydrochloride buffer (pH 2.56) medium. The formed ion-pair complex exhibited an absorption maximum at 420 nm. Beer's law is obeyed over the concentration range 2.5-25 mu g mL(-1) with an apparent molar absorptivity value of 2.02 x 10(4) L mol(-1) cm(-1). The Sandell sensitivity, limits of detection (LOD) and quantification values are also reported. The composition of the ion-pair was established by Job's continuous variations method and it was found to be 1:1 (QTF:QY). The proposed method was successfully applied for the determination of QTF in bulk drug, tablets and spiked human urine without any interference. (doi: 10.5562/cca1770)

Simple and Sensitive Spectrophotmetric Determination of Lamotrigine in Pure Form and in Dosage Forms

Two new simple, sensitive and cost-effective spectrophotometric methods for the determination of lamotrigine (LMT) in bulk drug and in tablets are described. The methods are based on the measurement of absorbance of LMT either in 0.1 M H2SO4 (method A) or in methanol (method B) at 225 nm. Linearity was found to be in the ranges, 0.5- 5.0 and 1.25-12.5 μgmL-1 LMT, for method A and method B, respectively with apparent molar absorptivity values of 8.65×104 and 2.11×104 l mol-1cm-1. The Sandell sensitivity values, limits of detection (LOD) and quantification (LOQ) values have also been reported for both the methods. The accuracy and precision of the methods were evaluated on intra-day and inter-day basis; the relative error (%RE) and the relative standard deviation (RSD) were <2.0%. The proposed methods were applied to the determination of the examined drug in coated tablet and no interference from any common pharmaceutical additives and diluents was observed. Results of assay were validated statistically by parallel analysis and by recovery studies.

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). Beer's 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 Sandell's 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.

Spectrophotometric determination of quetiapine fumarate in pharmaceuticals and human urine by two charge-transfer complexation reactions

Two simple, rapid and accurate spectrophotometric procedures are proposed for the determination of quetiapine fumarate (QTF) in pharmaceuticals and in spiked human urine. The methods are based on charge transfer complexation reactions of free base form of the drug (quetiapine, QTP), as n-electron donor (D), with either p-chloranilic acid (p-CAA) (method A) or 2,3-dichloro-5,6-dicyanoquinone (DDQ) (method B) as ?-acceptors (A). The coloured charge transfer complexes produced exhibit absorption maxima at 520 and 540 nm, in method A and method B, respectively. The experimental conditions such as reagent concentration, reaction solvent and time have been carefully optimized to achieve the maximum sensitivity. Beer?s law is obeyed over the concentration ranges of 8.0 - 160 and 4.0 - 80.0 ?g ml-1, for method A and method B, respectively. The calculated molar absorptivity values are 1.77 ? 103 and 4.59 ? 103 l mol-1cm-1, respectively, for method A and method B. The Sandell sensitivity values, limits of detection (LOD) and quantification (LOQ) have also been reported. The stoichiometry of the reaction in both cases was accomplished adopting the limiting logarithmic method and was found to be 1: 2 (D: A). 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 QTF in pharmaceutical formulations and spiked human urine.

Simple and Rapid Spectrophotometric Determination of Propranolol Hydrochloride as Base Form in Pharmaceutical Formulation through Charge Transfer Complexation

Two simple and selective spectrophotometric methods are described for the determination of propranolol hydrochloride (PPH) as base form (PPL) in bulk drug, and in tablets and capsules. The methods are based on the molecular charge-transfer complexation of propranolol base (PPL) with either 2,4,6-trinitrophenol (picric acid; PA) or 2,4-dinitrophenol (DNP). The yellow colored radical anions formed on dissociation, are quantitated at 425 nm (PA method) or 415 nm (DNP method). The assay conditions were optimized. Beer\\\'s law is obeyed in the concentration ranges 2.4-42.0 μg ml-1 in PA method and 9.0-126.0 μg ml- 1in DNP method, with respective molar absorptivity values of 4.97 × 103 and 1.66 × 103 l mol-1 cm-1. The reaction stoichiometry in both methods was evaluated by Job’s method of continuous variations and was found to be 1:1 (PPL:PA, PPL:DNP). The developed methods were successfully applied to the determination of PPL in pure form and commercial tablets/capsules with good accuracy and precision. Statistical comparison of the results was performed using Student\\\'s t-test and F-ratio at 95% confidence level and the results showed no significant difference between the reference and proposed methods with regard to accuracy and precision. Further, the accuracy and reliability of the methods were confirmed by recovery studies via standard addition technique

Assay of lercanidipine hydrochloride in dosage forms using nucleophilic substitution reaction

A simple and sensitive spectrophotometric method has been developed for the assay of lercanidipine hydrochloride (LER) in bulk and in formulations. The method is based on the formation of coloured species between the drug and 1,2-naphthaquinone-4-sulphonic acid sodium salt (NQS) by means of nucleophilic substitution reaction. Absorbance was measured at λ(max) = 460 nm. The method was analyzed statistically. The system obeyed the Beer's law in the range 20-100 μg mL⁻¹. Molar absorptivity value was found to be 4.79 × 10³ L mol⁻¹ cm⁻¹. Limits of detection and quantification were found to be as low as 0.04 and 0.13 μg mL⁻¹. Precision (RSD, 0.4%) and accuracy (recovery 99.2 ± 0.6 to 101.1 ± 0.8%) of the developed method were evaluated.

CERIMETRIC DETERMINATION OF FOUR ANTIHYPERTENSIVE DRUGS IN PHARMACEUTICAL PREPARATIONS

A sensitive spectrophotometric method is described for the determination of atenolol (ATE), timolol maleate (TIM), captopril (CPL) and diltiazem hydrochloride (DIL.HCl) in bulk drugs and in pharmaceutical preparations. The method is based on the oxidation of the studied drugs by a known excess of cerric (IV) in acid medium followed by determination of unreacted oxidant by adding a fixed amount of methyl orange dye (MO) and the increasing in absorbance is measured at 510 nm. In this method the amount of cerium (IV) reacted corresponds to drugs concentration. The experimental conditions were optimized. Regression analysis of a Beer’s plot showed good correlation in the concentration ranges of 3.2-6.4, 8.0-18, 3.4-5.2 and 3.6-5.2 µg/ml for ATE, TIM, CPL and DIL.HCl, respectively. The calculated molar absorptivity values are 5.28×104, 3.27×104, 6.43×104 and 1.12×105 L /mol cm, respectively and the corresponding Sandell’s sensitivity values are 5.043, 13.2, 3.381 and 4.024 ng/cm2, respectively. The limit of detection (LOD) and quantification (LOQ) are reported. No interference was observed from the additives and the applicability of the method was tested by analyzing the pharmaceutical preparations containing the investigated drugs. Statistical comparison of the results with those of official methods shows excellent agreement and indicates no significant difference in precision.

Iron(III) oxidized nucleophilic coupling of catechol with o-tolidine/p-toluidine followed by 1,10-phenanthroline as new and sensitivity improved spectrophotometric methods for iron present in chemicals, pharmaceutical, edible green leaves, nuts and lake water samples

A nucleophile formed from iron(III) oxidized catechol in 0.1 M hydrochloric acid couple with o-tolidine, system 1/p-toluidine, system 2 to produce dye product, λ max 520 nm. The system 1/2 obeys Beer's law in the range 0.08–8.0 μg ml −1 with molar absorptivity, Sandell sensitivity and regression coefficient values, 4.225 × 10 3/3.140 × 10 3 l mol −1 cm −1, 0.0132/0.0178 μg cm −2 and 0.9987/0.9981. Iron(II) formed from iron(III) in system 1/2 reacts with 1,10-phenanthroline, λ max 510 nm, will constitute sensitivity improved iron determinations with values 0.08–1.6 μg ml −1, 2.4136 × 10 4/2.2511 × 10 4 l mol −1 cm −1, 0.0023/0.0025 μg cm −2 and 0.9980/0.9997 corresponding to range, molar absorptivity, Sandell sensitivity and regression coefficient. The results of the systems for iron present in chemicals, pharmaceutical, edible green leaves, nuts and lake water samples are satisfactory since they are comparable with the results of iron determined separately from 1,10-phenanthroline method.

Sensitive and selective spectrophotometric assay of rizatriptan benzoate in pharmaceuticals using three sulphonphthalein dyes

Three simple, rapid, selective and sensitive spectrophotometric methods are described for the determination of rizatriptan benzoate (RTB) in bulk drug and in tablets. The methods are based on the formation of intense yellow colored ion–pair complexes between RTB and sulphonphthalein acid dyes, namely, bromophenol blue (BPB), bromocresol purple (BCP), bromothymol blue (BTB) in chloroform medium. The colored products are measured at 425nm (RTB–BPB complex, RTB–BCP complex) and 420nm (RTB–BTB complex). The reactions were extremely rapid at room temperature and the absorbance values remained constant for 90min (methods A and B) and over 12h (method C). Beer’s law was obeyed in the concentration ranges of 0.8–16.0, 1.0–20.0 and 1.2–24μgml−1 with molar absorptivity values of 1.76×104, 1.96×104 and 1.63×104lmol−1cm−1 for BPB, BCP and BTB methods, respectively. The limits of quantification (LOQ) were 0.39, 0.34 and 0.27μgml−1 for BPB, BCP and BTB methods, respectively. Other method validation parameters, such as precision, accuracy, robustness, ruggedness and selectivity, were satisfactory. The composition of the ion–pair was found to be 1:1 by Job’s method. The proposed methods were successfully applied to the determination of RTB in commercial tablets. No interference was observed from common tablet adjuvants. Statistical comparison of the results with the reference method showed excellent agreement and indicated no significant difference in accuracy and precision.

Preparation of Distinct Ubiquitin Chain Reagents of High Purity and Yield

The complexity of protein ubiquitination signals derives largely from the variety of polyubiquitin linkage types that can modify a target protein, each imparting distinct functional consequences. Free ubiquitin chains of uniform linkages and length are important tools in understanding how ubiquitin-binding proteins specifically recognize these different polyubiquitin modifications. While some free ubiquitin chain species are commercially available, mutational analyses and labeling schemes are limited to select, marketed stocks. Furthermore, the multimilligram quantities of material required for detailed biophysical and/or structural studies often makes these reagents cost prohibitive. To address these limitations, we have optimized known methods for the synthesis and purification of linear, K11-, K48-, and K63-linked ubiquitin dimers, trimers, and tetramers on a preparative scale. The high purity and relatively high yield of these proteins readily enables material-intensive experiments and provides flexibility for engineering specialized ubiquitin chain reagents, such as fluorescently labeled chains of discrete lengths.

Development and validation of indirect visible spectrophotometric methods for oxcarbazepine in pure and the tablet dosage form

Three simple, accurate and highly sensitive indirect spectrophotometric methods have been developed for the determination of oxcarbazepine (OXC) in both pure and in pharmaceutical preparations. The methods are based on the oxidation of oxcarbazepine by a known excess of cerium(IV) in acid medium. This was followed by the determination of unreacted cerium(IV), which oxidizes leuco dyes to colored dyes in the same acid medium. In method A, an unreacted cerium(IV) oxidizes leuco crystal violet to crystal violet dye which is measured at 580nm. A bluish-colored malachite green with a maximum absorption at 610nm is developed in method B. In method C, cerium(IV) oxidizes leuco xylene cyanol FF to blue colored xylene cyanol FF having absorption maximum at 610nm. In all these methods, the amount of cerium(IV) reacted corresponds to the amount of OXC and the absorbance is found to decrease linearly with OXC concentration. Beer’s law was obeyed in the concentration range of 0–2.5, 0–2.0 and 0–2.5μgml−1 for methods A, B and C, respectively, and the corresponding molar absorptivity values are 3.86×104, 4.41×104 and 2.16×104lmol−1cm−1. All variables have been optimized and the results were statistically compared with those of a literature method by employing the student’s t-test and F-test. No interference was observed from excipients normally added to the tablets.

Simple and sensitive spectrophotometric method for determination of tricyclic antidepressant imipramine using Fe(III)-SCN− complex

A new simple procedure for the spectrophotometric determination of tricyclic antidepressant drug imipramine is proposed. The method is based on the enhancement of the colour intensity of the Fe(III)-SCN− complex due to the addition of the drug imipramine. The value of molar absorptivity of the Fe(III)-SCN− imipramine complex in terms of the drug lies in the range of (2.77–3.16) × 103 L/mol cm at the absorption maximum 460 nm. The detection limit of the method was 250 μg/L. The slope, intercept, and correlation co-efficient for the present method were found to be 0.008, 0.005, and 0.998, respectively. The effect of analytical variables on the determination of the drug and the composition of the complex are discussed. The method is applicable to the determination of imipramine in the drug samples.

Quantitative determination of lansoprozole in capsules and spiked human urine by spectrophotometry through ion-pair complex formation reaction

Two simple, rapid and sensitive extraction-free spectrophotometric methods are proposed for the determination of lansoprazole (LAN) in bulk drug and in its capsule formulation. The methods are based on the interaction of LAN in dichloromethane (DCM) with acidic sulfonphthalein dyes, namely, bromocresol purple (BCP) in method A and bromothylmol blue (BTB) in method B to form stable, yellow-colored, ion-pair complexes peaking at 400 and 430 nm, respectively. The parameters that affect the reaction were carefully optimized, and under the optimized conditions, linear relationships were obtained in the ranges of 0.5–15.0 and 1.25–20.0 μg mL−1 LAN for method A and method B, respectively. The molar absorptivity values are calculated to be 2.10 × 104 and 1.50 × 104 L mol−1 cm−1 for method A and method B, respectively. The composition of the ion-pairs was found to be 1:1 by Job’s method of continuous variations and the conditional stability constant (logKf) of the complexes has been calculated. The proposed methods were applied successfully to the determination of LAN in capsules as well as in spiked urine sample with good accuracy and precision. The results obtained by the proposed methods were compared favorably with those of the reference method.

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.