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Biomedical subjects

L Zivanović

Publications and source records attributed to L Zivanović.

At least 19 recordsLinked to original sources
PubMed2001

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.

Amiloride↗
PubMed1997

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).

Chlorides↗
PubMed1994

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.

Chromatography, High Pressure Liquid↗
PubMed1992

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.

Capsules↗
PubMed1991

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.

Ferric Compounds↗
PubMed1991

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.

Copper↗
PubMed1990

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.

Hydrogen-Ion Concentration↗
PubMed1990

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.

Drug Stability↗
PubMed1981

[Monotypic IgM euglobulin precipitating upon exposure to air at room temperature].

A monoclonal lambda IgM euglobulin with peculiar precipitable characteristics in vitro was found in the serum of a patient with Waldenström macroglobulinaemia. The precipitation was observed at room temperature only when serum was exposed to air. Covalent disulphide bonds probably contribute to the mechanism involved in the formation of precipitate in this case.

Chemical Precipitation↗