Statistical optimisation applied to the spectrophotometric study of the tolmetin-Fe(III) complex.

Tolmetin sodium has been examined and determined from dosage forms as its Fe(III) complex and the method has been optimized by statistical optimization.

Spectrophotometric study of polythiazide-palladium (II) complex.

A quantitative spectrophotometric method using Pd(II) chloride as analytical reagent for the determination of polythiazide in pharmaceutical preparations is described in this study. It has been found that polythiazide reacts with Pd(II) chloride in the pH range 3.6-5.8, forming a red, water-soluble (1:1) complex with maximum absorbance at 527 nm. At the optimum pH of 4.8 and an ionic strength mu = 0.1 M, the conditional stability constant of the complex is found to be log K' = 4.77. The molar absorptivity at 527 nm is 3.2 x 10(3) l mol-1 cm-1. Good agreement with Beer's law was found for polythiazide concentrations up to 2.2 mmol l-1. The nominal percent recovery of polythiazide was 99.5% (n = 20). The simplicity, selectivity and sensitivity of the method described is suitable for rapid and accurate determinations of polythiazide in tablets.

Determination of lidocaine in pharmaceutical preparations using thin-layer chromatographic densitometry.

A thin-layer chromatographic (TLC)-UV-densitometric method has been developed for the analysis of lidocaine in ointments, suppositories and gels. The method is quantitative, rapid and able to separate lidocaine from other components in the pharmaceutical dosage forms investigated without preliminary extraction. The method gave precise and reproducible results.

Use of ANN modelling in structure--retention relationships of diuretics in RP-HPLC.

Structure retention relationship study, conducted by RP HPLC, was used to investigate physical chemical parameters related to the RP retention times of amiloride, hydrochlorothiazide and methyldopa in order to predict the separation of amiloride and methylclothiazide from Lometazid tablets. Retention data were obtained with an ODS column using a mobile phase methanol water (pH adjusted with phosphoric acid). Physical chemical properties were calculated directly from the molecular structure. Artificial neural networks (ANNs) were used to correlate chromatograms retention times with mobile phase composition and pH, and with physical chemical properties of amiloride, hydrochlorothiazide and methyldopa and to predict separation of amiloride and methylclothiazide from Lometazid tablets. Sensitivity analysis was performed to interpret the meaning of the descriptors included in the models. Results confirmed the dominant role of the polar modifier in such chromatographic systems. Within a series of solutes chromatographed under identical conditions, the retention parameters could be approximated by a non-linear combination of logP, logD, pKa, surface tension, parachor, molar volume and to minor extend by polarisability, reetractivity index and density. This study has demonstrated that the use ANNs techniques can result in much more efficient use of experimental information. As HPLC is the most popular analytical technique, improvements in HPLC methods development can yield significant gains in the overall analytical effort. The ANNs extension presented could be the method of choice in some advanced research settings and serves as an indication of the broad potential of neural networks in chromatography analysis.

Spectrophotometric study of diclofenac-Fe(III) complex.

A multifactor optimisation technique is successfully applied to develop a new spectrophotometric method in which diclofenac sodium is analysed and determined as it's Fe(III) complex. The effect of simultaneously varying the pH, ionic strength and concentration of colour reagents in the reaction mixture were studied. A four-variable two-level factorial design was used to investigate the significance of each variable and interactions between them. A response surface design was used to optimise complex formation and extraction. It was established that diclofenac reacts with Fe(III) chloride, in the presence of ammonium thiocyanate, in the pH range 4.2-6.5, forming a red chloroform extractable (2:1) complex with maximum absorbance at 481 nm. By applying the methods of Sommer and Job involving non-equimolar solutions the conditional stability constant of the complex, at the optimum pH of 6.0 and an ionic strength mu = 0.19M, was found to be 10(6.4). Good agreement with Beer's law was found for diclofenac concentrations up to mmol 1(-1). The nominal percent recovery of diclofenac was 98.8% (n = 10). The lower limit of sensitivity of the method was found to be 14.7 micrograms ml(-1).

Application of artificial neural networks in HPLC method development.

The use of artificial neural networks (ANNs) for response surface modelling in HPLC method development for amiloride and methychlothiazide separation is reported. The independent input variables were pH and methanol percentage in mobile phase. The outputs were capacity factors. The results were compared with a statistical method (multiple nonlinear regression analysis). Networks were able to predict the experimental responses more accurately than the regression analysis.

Investigation of the pindolol-Fe(III) complex and its use in the spectrophotometric determination of pindolol in bulk drug and tablets.

It was found that pindolol reacts with Fe(III) chloride producing a green water soluble complex (1:1, v/v) with maximum absorbance at 635 nm. By applying the methods of Sommer and Job [Sommer et al., Folia, tomus XI, Chemia 7, 25, 1970] the conditional stability constant of the complex at pH = 1.70 +/- 0.02 was found to be log K' = 4.95 and the molar absorptivity of the complex to be 206 l mol-1 cm-1. Beer's law was obeyed up to a concentration of 220 mumol l-1 of pindolol. The recoveries were 98-101% (n = 7) and the detection limit was 5 micrograms ml-1. The described method was sufficiently simple, selective and sensitive to be suitable for the rapid and accurate determination of pindolol in tablets.

Statistical optimization applied to the spectrophotometric study of a tolmetin-copper(II) complex.

Tolmetin sodium has been investigated and determined from dosage forms as its Cu(II) complex and method optimized by statistical optimization. The assay was developed using two mathematical statistical models: factorial design and response-surface mapping. The decision to apply experimental design techniques to the development of the method was made after a series of screening experiments revealed that the complex formation and extraction are maximized as a function of supporting electrolyte concentration, concentration of Cu(II) acetate and pH of the reaction mixture. One set of two-level three variable factorial experiments was carried out in order to evaluate the main effect, as well as the interaction among factors. The final step was to optimize the values of variables using response surface design. The best set of conditions was selected for further investigation.

Comparison of high-performance and thin-layer chromatographic methods for the assay of lidocaine.

Reversed-phase high-performance liquid chromatographic (HPLC) and thin-layer chromatographic (TLC)-UV densitometric methods were developed for the quality control of lidocaine hydrochloride bulk drug and its injection solutions. The HPLC method used an RP-18 reversed-phase column with methanol-water-1% phosphoric acid-hexylamine (30:70:100:1.4, v/v/v/v) as the mobile phase and detection at 254 nm, with a capacity factor k' = 0.8. The TLC-UV densitometric method was performed on silica gel plates using diisopropyl ether-acetone-diethylamine (85:10:5, v/v/v) as the developing solvent and UV detection at 254 nm. The response was linear up to 10 micrograms ml-1 (HPLC) and 8 mg ml-1 (TLC). The RSD of the peak areas was 1.71% for HPLC and 0.55% for TLC, with recoveries in the range 99.6-100.2% for HPLC and 99.2-100.7% for TLC.

Statistical optimization of a reversed-phase liquid chromatographic method for the determination of amiloride and methyclothiazide in tablets.

A quantitative high-performance liquid chromatographic method in which amiloride is separated from methyclothiazide on a C18 column with detection at 286 mm was developed with the aid of the 'window diagram' technique of Laub and Purnell. The effect of simultaneously varying the pH and methanol to water ratio in the mobile phase were studied to optimize the separation. The method was applied to the quantitative analysis of Lometazid tablets. The powdered tablets were extracted with methanol, containing phenacetin as the internal standard, and assayed by comparison of peak heights after liquid chromatography.

The use of a response surface methodology on HPLC analysis of methyldopa, amiloride and hydrochlorothiazide in tablets.

A multifactor optimisation technique is successfully applied to develop a new HPLC method in which methyldopa, hydrochlorothiazide and amiloride were analysed and determined on a C18 column with detection at 286 nm. The optimal conditions of HPLC separation were determined with the aid of the response surface diagram -- 'window diagram'. The effect of simultaneously varying the pH, proportion aqueous acetic acidum and methanol in the mobile phase were studied to optimise the separation. The mobile phase composition that provides an acceptable resolution methyldopa, hydrochlorothiazide and amiloride in a short elution time is water--methanol (75:25) and pH 3.60. The k' values for methyldopa, hydrochlorothiazide and amiloride after optimisation were 1.40, 2.50 and 5.33, respectively. Relative retention (alpha) for ratio hydrochlorothiazide/methyldopa and amiloride/hydrochlorothiazide were 1.767 and 2.159, respectively. Correlation coefficients of the calibration curves for all analytes were greater than 0.995 and the R.S.D. values for the slope and the intercept with respect to the linearity were less than 2%. A method is applied for the quantitative analysis of Alatan tablets (Lek-Ljubljana). The powdered tablets are extracted with methanol, containing caffeine as the internal standard and assayed by comparison of peak areas after liquid chromatography. The high recovery (for all analytes about 100%) and the low R.S.D. (<2%) confirm good precision and reproducibility of the chromatographic method.

Investigation of penbutolol-iron (III) complex and its spectrophotometric determination in tablets.

It has been established that penbutolol reacts with iron(III) chloride in the presence of ammonium thiocyanate to form a pink complex (2:1) that is soluble in chloroform with a maximum absorbance at 478 nm. By application of the methods of Sommer and Job involving non-equimolar solutions, the conditional stability constant (log k') of the complex at the optimum pH of 1.5 +/- 0.02 and an ionic strength of (mu) 0.14 M, was found to be 5.769. The molar absorptivity at 478 nm was 136 1 mol-1 cm-1 at pH 1.5 +/- 0.02. The validity of Beer's law has been tested in the concentration range 3-18 x 10(-4) M; the relative standard deviation (n = 8) was 1.52-3.21%. The proposed method was found to be suitable for the accurate, simple and rapid analysis of penbutolol in the bulk drug and in tablets.

Statistical optimization of a reversed-phase liquid chromatographic method for the analysis of amiloride and hydrochlorothiazide in tablets.

A method has been developed for the separation of hydrochlorothiazide and amiloride by high-performance liquid chromatographic (HPLC) method on a C18 column with detection at 280 nm. The optimal conditions of separation were determined with the aid of 'window diagram' technique of Laub and Purnell. The effect of simultaneously varying the pH, proportion aqueous acetic acid and methanol in the mobile phase were studied to optimize the separation. A response surface diagram was used to optimize the experimental conditions for the separation. The mobile phase composition that provides an acceptable resolution hydrochlorothiazide and amiloride in a short elution time is water:methanol (60:40) and pH 3.2 (pH adjusted to 3.2 with CH3COOH). A method is applied for the quantitative analysis of Moduretic tablets (Merck Sharp & Dokme International). The powdered tablets are extracted with methanol, containing caffeine as the internal standard, and assayed by comparison of peak areas after liquid chromatography.

Spectrophotometric investigation of metoprolol-benzyl orange reaction and its application to the assay in pharmaceutical dosage forms.

A sensitive spectrophotometric method for the determination of metoprolol tartrate in tablets and ampoules is presented. Using spectrophotometric measurements, it was found that metoprolol tartrate and benzyl orange form a chloroform soluble ion-pair complex with an absorption maximum at 401 nm. The composition of the ion-pair complex was determined by applying Job's method to equimolar solutions of metoprolol tartrate: benzyl orange (1:2); molar absorptivity 7.39 x 10(3) mol-1 cm-1. Extraction of the ion-pair complex in chloroform was accomplished easily at a Britton-Robinson's buffered optimum pH = 5.2, mu = 0.1 mol/dm3. The relative stability constant, calculated according to the method of Sommer and Job's non-equimolar solutions, was log K = 9.72 (avg. value). Beer's law was obeyed up to 3.42 micrograms/ml of metoprolol tartrate (the detection limit was also 3.42 micrograms/ml). The precision of the method was checked at three different concentrations. The RSD (n = 7) varied from 0.51 to 2.03%. Reproducibility was examined by analysing Lopresor tablets and ampoules. Recoveries varied from 99-101%. The reported method, applied to the assay of metoprolol tartrate in tablets and ampoules, gives precise and reproducible results.

High-performance liquid chromatographic determination of tilidine in pharmaceutical dosage forms.

A reversed-phase high performance liquid chromatographic method for the determination of tilidine in bulk drug and its liquid and solid dosage forms is described. The method uses reversed-phase column RP-8 with methanol -0.2% water solution of ammonium carbonate (75:25,v/v) as the mobile phase and UV detector. The time taken for separation is 6.17 min. The response is linear up to 3.6 mmol/l, with recovery levels ranging from 98.2 to 101.2%. The present method is rapid, simple and reproducible.

HPLC determination of sodium cromoglycate in pharmaceutical dosage forms.

A reversed-phase high-performance liquid chromatography (HPLC) method is described for the determination of sodium chromoglycate (SCG) in bulk drug and pharmaceutical dosage forms (capsules, solutions, gels). Aliquots were chromatographed on C18 columns using methanol: phosphate buffer (50:50 v/v) at pH 2.3 as the mobile phase. Detection was performed at 326 nm with a linear range of 0.05-0.5 microgram/ml (r = 0.9999). Recovery values ranged from 99.21 to 106.31% (N = 9). The proposed method is rapid and simple, free from interference by excipient and degradation products, and can be recommended for routine control analysis of sodium chromoglycate commercial products and magistral formulations.

Spectrophotometric determination of oxprenolol hydrochloride as its Fe (III) complex.

A spectrophotometric determination of oxprenolol hydrochloride in pharmaceutical preparations is described. The method is based on the reaction of oxprenolol hydrochloride with Fe (III) ion in the presence of ammonium thiocyanate, in acid media. The complex formed between oxprenolol hydrochloride and Fe (III) ion was extracted with chloroform and assayed spectrophometrically at 477 nm. The results obtained are reproducible and hence the method is suitable for the determination of oxprenolol hydrochloride in pharmaceutical dosage forms.

Determination of sodium cromoglycate in pharmaceutical dosage forms using TLC-densitometry.

A TLC-UV densitometric method for the determination of sodium cromoglycate (SCG) in ophthalmic solutions, gels and capsules has been developed. After TLC separation of active substance on silica gel GF254 using methanol-water-ethylacetate (15:45:40 v/v/v) as the mobile phase, densitometric measurements were performed with HPTLC scanner at 254 nm. The proposed method is rapid and simple, free from interference by adjuvants and can be suggested for the routine analysis of sodium cromoglycate.

Investigation of Fe(III) chloride as a colour reagent for the spectrophotometric determination of bumetanide in the pure form and in preparations.

The formation and stability of the complex between bumetanide (3-butylamino-4-phenoxy-5-sulphamoylbenzoic acid) and Fe(III) ion was studied. It has been found that bumetanide reacts with Fe(III) chloride in the presence of ammonium thiocyanate at the pH 1.83-1.92 to form a violet complex soluble in chlorophorm, with the maximum absorbance at 514.5 nm. At the optimum experimental conditions the conditional stability constant of the complex was found to be log K' = 7.34. The Beer's law was obeyed up to the 160 microg x cm(-3) and the relative standard deviation varied from 0.406% to 0.475% (n = 10). The proposed method was found to be suitable for the accurate and sensitive analysis of bumetanide as a pure compound and from tables and ampoules.

Colorimetric assay of methyldopa bulk drug and tablets as its Fe(III) complex.

A new colorimetric method for the determination of methyldopa is described. The method is based on the reaction of methyldopa with ferric chloride in the pH range of 3.0-3.5 and producing a water soluble (1:2) brown complex with maximum absorbance at 423 nm. The conditional stability constant of the complex at the optimum pH 3.0 and ionic strength 0.4 M, is found to be 10(7.5). Beer's low is obeyed up to 6 mmol/l methyldopa concentration. The RSD of the method is 0.708-1.226%. The proposed method was found to be suitable for the accurate and reproducible analysis of methyldopa bulk drug and tablets which is pointed by high recovery values 99.20-99.79%.