Potentiometric sensor for the high throughput determination of tetramisole hydrochloride

The electrochemical response characteristics of poly(vinyl)chloride (PVC) based membrane sensors for determination of tetramisole hydrochloride (TmCl) is described. The membranes of these electrodes consist of tetramisole-tetraphenyl borate (Tm-TPB), chlorophenyl borate (Tm-ClPB), and phosphotungstate (Tm(3)-PT) ion associations dispersed in a PVC matrix with dibutylpthalate as a plasticizer. The electrodes were fully characterized in terms of composition, life span, usable pH range, and working concentration range and ionic strength. The electrodes showed Nernstian response over the concentration ranges of 7.4 x 10(-7) to 1.0 x 10(-2) M, 1.7 x 10(-6) to 1.0 x 10(-2) M, and 5.6 x 10(-6) to 1.0 x 10(-2) M TmCl, respectively, and were applied to the potentiometric determination of tetramisole ion in pure solutions and pharmaceutical preparations. The potentiometric determination was also used in the determination of tetramisole in pharmaceutical preparations in four batches of different expiration dates. The electrodes exhibited good selectivity for TmCl with respect to a large number of excipients such as inorganic cations, organic cations, amino acids, and sugars. The solubility product of the ion-pair and the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductometrically. The new potentiometric method offers the advantages of high-throughput determination, simplicity, accuracy, automation feasibility, and applicability to turbid and colored sample solutions.     

An extractive spectrophotometric method for the determination of tetramisole hydrochloride in pharmaceutical preparations

A simple extractive photometric method for the determination of tetramisole hydrochloride in pharmaceutical preparations is described. The method uses the formation of coloured complexes of the drug with reagents such as Solochrome Dark Blue, Solochrome Black T, Bromocresol Purple, Bromothymol Blue, Bromophenol Blue and Bromocresol Green in an acidic buffer. The ion-pair complexes formed are quantitatively extracted into chloroform under the experimental conditions.     

New colorimetric and fluorimetric methods for the determination of 1,4-cyclohexanedione

1,4-Cyclohexanedione has been determined by reaction with o-phthalaldehyde in sulfuric acid. The determinations depend on the formation of a dicationic salt of pentacenequinone. A sensitive and highly selective fluorimetric method is recommended, but the reaction can also be used spectrophotometrically. Many organic compounds, as well as the isomers of 1,4-cyclohexanedione, give negative results. A spot test is described which can be used for quick preliminary investigations of complex mixtures for I,4-cyclohexanedione.     

Comparison of three colorimetric methods for the determination of manganese in freshwaters

Three calorimetric methods for the determination of manganese in freshwaters have been investigated and compared with the atomic-absorption spectrometry (AAS) method. Two of the methods, viz. the formaldoxime (FAD) and pyridylazonaphthol (PAN) methods were found to yield poor calibration curves upon standardization, and to have high average errors for the estimation of manganese concentrations in standard solutions. The FAD method, when applied to freshwater samples, was found to be subject to an interfering UV absorbance which could not be negated successfully by a reagent blank; the method thus tended to give high estimations at low concentrations of manganese, but the results obtained also appear to be very sensitive to the nature of the freshwater matrix. On the other hand the PAN method was found to give very high estimations for the concentration of manganese, in both standard solutions and in freshwater samples, owing to the nature of the absorbance of the ligand used for manganese determination. This method also appears to be affected by the freshwater matrix, leading to gross overestimation of manganese levels. A third method, based on a porphyrin ligand [T-(4-CP)P], was found to give results comparable with those of the AAS method in estimating the soluble manganese content in freshwaters.     

Spectrophotometric methods for the determination of prazosin hydrochloride in tablets

Four simple and sensitive methods for the assay of prazosin hydrochloride (PRH) are developed. These methods are based on the formation of coloured species by treating it either with excess N-bromosuccinimide (NBS) and determining the unconsumed NBS with p-N-methyl aminophenol sulphate (metol)-sulphanilamide (SA) reagent (method A, lambda(max) 520 nm): with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in the presence of eerie ammonium sulphate (CAS) (method B, lambda(max) 620 nm) or with acidic dyes such as orange-II (O-II) (method C, lambda(max) 490 nm) and alizarin violet 3B (AV-3B) (method D, lambda(max) 570 nm) under the specified experimental conditions. Regression analysis of Beer's law plot showed good correlation in the concentration range of 1.0-10.0, 2.5-25.0, 1.0-17.5 and 2.5-30.0 mug ml for methods A, B, C and D respectively.     

A critical evaluation of colorimetric methods for the determination of platinum metals. ii

This paper is the second review of quantitative colorimetric methods for the six platinum metals and covers the period from May, 1953 to March, 1957. Each method is evaluated from the point of view of the optimum concentration range, specified and practical applications to thr assay for platinum metals.     

Extractive colorimetric method for the determination of dothiepin hydrochloride and risperidone in pure and in dosage forms

Three rapid, simple, reproducible and sensitive extractive colorimetric methods (A--C) for assaying dothiepin hydrochloride (I) and risperidone (II) in bulk sample and in dosage forms were investigated. Methods A and B are based on the formation of an ion pair complexes with methyl orange (A) and orange G (B), whereas method C depends on ternary complex formation between cobalt thiocyanate and the studied drug I or II. The optimum reaction conditions were investigated and it was observed the calibration curves resulting from the measurements of absorbance concentration relations of the extracted complexes were linear over the concentration range 0.1--12 microg ml(-1) for method A, 0.5--11 mug ml(-1) for method B, and 3.2--80 microg ml(-1) for method C with a relative standard deviation (RSD) of 1.17 and 1.28 for drug I and II, respectively. The molar absorptivity, Sandell sensitivity, Ringbom optimum concentration ranges, and detection and quantification limits for all complexes were calculated and evaluated at maximum wavelengths of 423, 498, and 625 nm, using methods A, B, and C, respectively. The interference from excipients commonly present in dosage forms and common degradation products was studied. The proposed methods are highly specific for the determination of drugs I and II, in their dosage forms applying the standard additions technique without any interference from common excipients. The proposed methods have been compared statistically to the reference methods and found to be simple, accurate (t-test) and reproducible (F-value).     

Spectrophotometric methods for the determination of the antidepressant drug paroxetine hydrochloride in tablets

Simple, sensitive, and accurate visible spectrophotometric methods are described for the determination of paroxetine hydrochloride (PA) in tablets. Among them, the first 3 methods are based on the ion-pair complexes of PA formed with bromothymol blue (BTB), bromophenol blue (BPB), and bromocresol green (BCG) in aqueous acidic buffers. The complex species extracted into chloroform were quantitatively measured at 414 nm with BTB and BCG and at 412 nm with BPB. Beer's law was obeyed over the concentration ranges of 2-20, 2-16, and 2-16 microg/mL, respectively. The fourth method described is based on a coupling reaction between PA and 7-chloro-4-nitrobenzofurazon (NBD-Cl) in borate buffer, pH 8.5, in which a yellow reaction product that was measured at 478 nm was formed. The Beer's law range for this method was 2-10 microg/mL. The last method developed describes the interaction of PA base, as an n-electron donor, with 7,7,8,8-tetracyanoquinodimethane (TCNQ), as a pi-acceptor, in acetonitrile to give blue-colored TCNQ- radical anion with absorption maxima at 750 and 845 nm. Measured at 845 nm, the absorbance-concentration plot was rectilinear over the range of 1.5-15 microg/mL. The new methods developed were successfully applied to the determination of PA in tablets without any interference from common tablet excipients. The results of the methods were in good agreement with those obtained with an official liquid chromatographic method. This report describes first colorimetric methods for the determination of PA.     

Oxidants for the colorimetric determination of pindolol

A simple, sensitive and accurate colorimetric method is described for the quantitative determination of pindolol either in the pure form or in its tablets. The method is based on the oxidation of the indole moiety in pindolol with potassium persulphate or hydrogen peroxide-in acid medium-to give a highly coloured product that exhibits maximum absorption at 535 nm and 570 nm, respectively. Beer's law is obeyed over concentrations ranging from 0.07-0.35 mg/10 ml for potassium persulphate and 0.1-0.5 mg/10 ml for hydrogen peroxide with mean recoveries of 99.6+/-0.6 and 99.8+/-0.9%, respectively. The method is applied for the assay of pindolol tablets without any interference due to tablet fillers.     

Spectrophotometric methods for the determination of labetalol hydrochloride in pure and dosage forms

Simple and sensitive Spectrophotometric methods for the determination of labetalol hydrochloride are described. The first two are based on the oxidative coupling reaction of labetalol hydrochloride withp-N,N-dimethyl-phenylenediamine dihydrochloride (method A, _max 685 nm) and 3-methyl-2-benzothiazolinone hydrazone hydrochloride (method B, _max 545 nm) in the presence of sodium hypochlorite and eerie ammonium sulphate as oxidants, respectively. The third depends on the formation of an ion-association complex of labetalol hydrochloride with suprachen violet 3B at pH 1.3, which is extracted into chloroform (method C, _max 565 nm). The methods obey Beer's law and the precision and accuracy of the methods were checked against the B.P. reference method and the relative standard deviations were in the range 0.35–0.52%. These methods are applied to the determination of labetalol in dosage forms.     

Sensitive extractive spectrophotometric methods for the determination of nortriptyline hydrochloride in pharmaceutical formulations

Two simple, sensitive and rapid extractive spectrophotometric methods have been developed for the assay of the antidepressant drug nortriptyline (NOR) hydrochloride in pure form and in different dosage forms. The methods involve the formation of colored ion-pairs between the drug and the complex of niobium(V)-thiocyanate (Nb-SCN) or iron(III)-thiocyanate (Fe-SCN) followed by their extraction with butanol or a mixture of butanol and chloroform and quantitative determination at 360 nm and 490 nm, using Nb-SCN and Fe-SCN, respectively. The experimental conditions were optimized to obtain the maximum colour intensity. The methods permit the determination of nortriptyline over a concentration range of 15-100 microg/ml and 5-24 microg/ml with the detection limit of 0.84 microg/ml and 0.32 microg/ml, using Nb-SCN and Fe-SCN, respectively. The proposed methods are applicable for the assay of the investigated drug in different dosage forms and the results are in good agreement with those obtained by the official and HPLC methods. No interference was observed from common excipients present in pharmaceutical formulations. The proposed procedures were applied to determine the amount of nortriptyline hydrochloride as active ingredient in the presence of its degradation product, dibenzosuberone. The extractive spectrophotometric methods can also be used to determine the amount of nortriptyline hydrochloride in tablets after its solid phase extraction (SPE).     

Sensitive extractive spectrophotometric methods for the determination of trazodone hydrochloride in pharmaceutical formulations

Two simple, rapid and sensitive extractive spectrophotometric methods have been developed for the assay of trazodone hydrochloride (TRH) in pure and pharmaceutical formulations. These methods are based on the formation of chloroform soluble ion-association complexes of TRH with bromothymol blue (BTB) and with bromocresol purple (BCP) in KCl-HCl buffer of pH 2.0 (for BTB) and in NaOAc-AcOH buffer of pH of 3.6 (for BCP) with absorption maximum at 423 nm and at 408 nm for BTB and BCP, respectively. Reaction conditions were optimized to obtain the maximum color intensity. The absorbance was found to increase linearly with increase in concentration of TRH, which was corroborated by the calculated correlation coefficient values (0.9996, 0.9945). The systems obeyed Beer's law in the range of 0.2-14.5 and 0.2-14.1 microg/ml for BTB and BCP, respectively. Various analytical parameters have been evaluated and the results have been validated by statistical data. No interference was observed from common excipients present in pharmaceutical formulations. The proposed methods are simple, accurate and suitable for quality control applications.     

Facile synthesis of colorimetric histone deacetylase substrates

Here we report a simple procedure for generating colorimetric histone deacetylase (HDAC) substrates by solid-phase peptide synthesis based on racemization-free couplings of amino acid chlorides. We demonstrate the applicability of these substrates in HDAC assays.     

New colorimetric method for the determination of nystatin

A new colorimetric method for the determination of nystatin is reported, based on the reaction of the alkaline hydrolysis product of nystatin with p-aminoacetophenone in presence of concentrated hydrochloric acid. The proposed method determines 0.2-1.0mg of nystatin with recovery of 100.7 +/- 1.2%. The method is adopted to the determination of nystatin in pharmaceutical preparations, and interference due to the presence of sugar is eliminated.     

Use of alizarin red S as a chromogenic agent for the colorimetric determination of dothiepin hydrochloride in pharmaceutical formulations

The present study describes two simple, rapid, selective and cost-effective spectrophotometric methods for the determination of dothiepin hydrochloride (DOTH), an antidepressant drug, in bulk drug and pharmaceutical formulations. The first method (method A) is based on the formation of yellow colored ion-pair complex between DOTH and alizarin red S (ARS) in acid medium which was extracted into dichloromethane and the absorbance was measured at 445 nm. The second method (method B) is based on the breaking of the yellow DOTH–ARS ion-pair complex in alkaline medium followed by the measurement of the violet color free dye at 570 nm. Under the optimized conditions, Beer’s law is obeyed over the concentration ranges of 2.50–55.0 and 1.00–35.0 μg ml⁻¹ DOTH for method A and method B, respectively. The molar absorptivity, Sandell’s sensitivity, detection and quantification limits are also calculated. The methods were validated for intra-day and inter-day accuracy and precision; selectivity and robustness and ruggedness. The proposed methods were applied successfully to the determination of DOTH in pure drug and commercial formulations. The accuracy and reliability of the proposed methods were further established by parallel determination by the official method and also by recovery studies via standard addition technique.     

A colorimetric method for the determination of nitrazepam

A simple colorimetric method for the determination of nitrazepam is described. Nitrazepam dissolved in ethyl alcohol (95%) produces a yellow anion on addition of aqueous sodium hydroxide, and this is measured spectrophotometrically. The method has been applied to pharmaceutical formulations containing nitrazepam.     

Kinetic spectrophotometric methods for the determination of alfuzosin hydrochloride in bulk and pharmaceutical formulations

Simple and sensitive kinetic spectrophotometric methods were established for the determination of alfuzosin hydrochloride in bulk and in its pharmaceutical preparations using alkaline potassium permanganate as an oxidizing agent. The methods involve determination of alfuzosin HCl by kinetic studies of its oxidation at room temperature for a fixed time of 15 min. The absorbance of the colored manganate ions was measured at 610 nm. Alternatively, the decrease in the absorbance of permanganate upon addition of the studied drug was also measured at 525 nm. The absorbance-concentration plots in both procedures were rectilinear over the range of 2.0–30.0 μg/mL. The different experimental parameters affecting the development were carefully studied and optimized. The determination of alfuzosin HCl by the fixed concentration and initial rate methods is also feasible with the calibration equations obtained but the fixed time method has been found to be more applicable. Both procedures were applied to the determination of alfuzosin HCl in formulations. The results obtained were in good agreement with those obtained using reference methods.     

Validated spectrophotometric methods for the simultaneous determination of ciprofloxacin hydrochloride and metronidazole in tablets

A binary mixture of ciprofloxacin hydrochloride (CIP) and metronidazole (MET) was determined by five simple and accurate methods, without prior separation. In the first method, CIP was determined by second derivative spectrophotometric method ((2)D) by measuring the amplitude at 282 nm (zero ordinate value of MET). On the other hand, the determination of MET was based on isosbestic point technique, where the total content of the mixture was determined at 294.5 nm (isosbestic point), then the content of MET could be calculated by subtraction. The second method was first derivative ratio spectrophotometric method ((1)DD) where the total amplitude at 261 and 285 nm and the amplitude at 295.5 nm were selected to simultaneously determine CIP and MET in binary mixture, respectively. The third method was based on dual wavelength analysis, in which two wavelengths were selected, at which the absorbances of the other component were the same. The fourth method depends on using Q-analysis method (absorbance ratio) which involves the formation of Q-absorbance equation using the respective absorptivity values at 294.5 nm (isosbestic point) and 281.5 nm (λ(max) of CIP). The fifth method is partial least-squares (PLS) chemometric technique for determination of CIP and MET. The developed methods were successfully applied to the analysis of CIP and MET in laboratory prepared mixtures and tablets with good recoveries and their validation was carried out following the International Conference on Harmonization (ICH) guidelines. The results obtained were statistically compared with each other showing no significant difference with respect to accuracy and precision.     

A colorimetric method for the determination of carboxylic acids

A new colorimetric method for the determination of carboxylic acids using bromocresol green reagent is established. The formed color follows Beer's Lambert law and is stable for 24 hr. The method is successfully applied for measuring the disappearance of volatile fatty acids in P. oxalicum culture media. The method is reproducable and is used also for the quantitative determination of carboxylic acids in Dowex 1-X8 eluates. A linear relationship between the pK₁ of different carboxylic acids and the calculated molar extinction coefficients of the color formed at 440 nm is demonstrated.