Kinetic spectrophotometric determination of the macrolide antibiotic josamycin in formulations

A simple kinetic spectrophotometric method was developed for the determination of josamycin in its dosage forms. The method is based on oxidation of the drug with alkaline potassium permanganate at room temperature for a fixed time of 20 min and measuring the produced green color at 611 nm. The absorbance-concentration plot is rectilinear over the range of 2-10 microg/mL (2.4 x 10(6)-1.2 x 10(-5)M) with minimum detectability of 1.0 microg/mL (1.2 x 10(-6)M). The determination of josamycin by fixed concentration and the rate-constant methods is also feasible with the calibration equations obtained, but the fixed-time method proved to be more applicable. The procedure was applied successfully to commercial tablets, and statistical analysis showed that the results compared favorably with those obtained by reference methods. The effect of sensitizers and surfactants on the performance of the proposed method was also studied. A proposal of the reaction pathway was presented.     

A simple and rapid spectrophotometric method for determination of ultra trace amounts of thallium(III) with 4-(4'-N,N-dimethylaminophenyl) urazole as a new reagent

A simple and selective spectrophotometric method is proposed for the determination of ultra trace amounts of Tl(III). The reported method is based on the oxidation of 4-(4'-N,N-dimethylaminophenyl)urazole (DAPU) to the corresponding triazolinedione (TAD) by Tl(III) at pH 4.0. The reaction was monitored spectrophotometrically by measuring the increasing color of TAD compound at 514 nm by the fixed-time method. At a given time of 2.0 min at 30 degrees C, the working range of calibration was 5.0 x 10(-8) - 2.0 x 10(-5) M Tl(III) and detection limit of 5.0 x 10(-8) M was obtained. The influences of pH, reagent concentration, ionic strength and temperature were studied. The effect of diverse ions on the determination of Tl(III) by the proposed method was also investigated. Thallium in real samples was determined by this method, with satisfactory results.     

Flow-injection stopped-flow kinetic spectrophotometric determination of drugs, based on micellar-catalysed reaction with 1-fluoro-2,4-dinitrobenzene

A flow-injection stopped-flow kinetic spectrophotometric method for the determination of hydrazines, hydrazides, amines and amino-acids, based on the cetyltrimethylammonium bromide catalysed reaction with 1-fluoro-2,4-dinitrobenzene is described. With the proposed method dihydralazine, isoniazid, levodopa and aspartame can be determined at concentrations of 0.1-6 x 10(-4)M. The calibration ranges can be varied by adjusting the pH and surfactant concentration. The determination of amphetamine, cysteine, s-carboxymethylcysteine, cephalexin, tobramycin and gentamicin is also feasible. The method has been applied to the determination of levodopa, isoniazid and aspartame in commercial pharmaceutical formulations. The determination of isoniazid in formulations containing the highly coloured antibiotic rifamycin, and of aspartame in coloured beverages was also accomplished. The results were in good agreement with those obtained by reference methods and the throughput was 40 measurements per hour with 0.4-3.9% RSD.     

Kinetic study of the determination of hydrazines, isoniazid and sodium azide by monitoring their reactions with 1-fluoro-2,4-dinitrobenzene, by means of a fluoride-selective electrode

A kinetic potentiometric method is described for the determination of hydrazines (hydrazine, phenylhydrazine, hydralazine and procarbazine), isoniazid and sodium azide, based on monitoring their reactions at 25 degrees and pH 9.0 with 1-fluoro-2,4-dinitrobenzene by means of a fluoride-selective electrode. Initial-rate and fixed-time methods were used to construct calibration graphs, generally over the range 1 x 10(-4)-1 x 10(-2)M. Hydralazine, procarbazine and isoniazid were determined in commercial formulations with a precision and error of 2-3% and the results were comparable with those of the official methods. The presence of common excipients and concomitant drugs in combination products do not interfere and the method can be used for coloured and cloudy sample solutions. A kinetic study of the reactions was made and the overall second-order rate constants are given. Base catalysis was observed. The fluoride-selective electrode is shown to be a valuable tool for monitoring fluoride-liberating organic reactions in kinetic studies and kinetic analysis.     

Kinetic spectrophotometric determination of josamycin in formulations and spiked human plasma using 3-methylbenzothiazolin-2-one hydrazone/Fe+3 system

A simple kinetic spectrophotometric method was developed for the determination of josamycin in its dosage forms and spiked human plasma. The method is based on reaction of the drug with 3-methylbenzothiazolin-2-one hydrazone/ferric chloride system for a fixed time of 20 min at 70 degrees C and measuring the produced color at 665 nm. The absorbance-concentration plot is rectilinear over the range of 5.0-30.0 microg/mL with detection limit of 1.0 microg/mL (1.2 x 10(-6) M). The determination of josamycin by the fixed concentration and the rate-constant methods is also feasible with the calibration equations obtained, but the fixed-time method proved to be more applicable. The procedure was successfully applied to commercial tablets. The results obtained were favorably compared with those given by reference methods. The method was further extended to the in vitro determination of josamycin in spiked human plasma. The recovery (n = 8) was 100.76 +/- 3.43%. The stoichiometry of the reaction between the drug and the reagent was studied by adopting the limiting logarithmic method, and a proposal of the reaction pathway was presented.     

Development of a spectrophotometric determination of siderophores using flow-injection analysis

A method has been developed for the spectrophotometric determination of siderophores using flow-injection analysis (FIA) based on the reaction of siderophores with the ternary complex Eriochrome Cyanine R-Fe(III)-cetyltrimethylammonium bromide. 2,3-Dihydroxybenzoic acid, 2,3-dihydroxynaphthalene, and tolypocine were used as the model iron-binding ligands. The calibration curve for one of the siderophores (tolypocine) is linear in the concentration range 2.6 x 10(-6)-1.5 x 10(-4)M. The determination limit (10sigma) for tolypocine was 2.6 x 10(-6)M. The applicability of the method was demonstrated on the determination of the complexation ability of siderophores produced by some entomopathogenic fungi. Samples can be analysed at a rate of 30 samples per hour.     

Fluorimetric determination of hydrogen peroxide in water using acetaminophen

A fluorimetric procedure for the determination of hydrogen peroxide, based on the oxidation of acetaminophen with hydrogen peroxide in acidic medium, is described. The calibration graph was linear in the range 5.0 x 10(-8) - 2.4 x 10(-5) M hydrogen peroxide at an emission wavelength of 333 nm with excitation at 298 nm. The method has been applied to the determination of hydrogen peroxide in rain water, and the recoveries in milk samples were good.     

Chemiluminescent determination of EDTA and related compounds using tris(2,2′-bipyridyl)ruthenium(III) photogenerated on-line

A rapid and sensitive chemiluminescence method using flow-injection has been developed for the determination of EDTA. The method is based on the chemiluminescent reaction of EDTA with tris(2,2'-bipyridyl)ruthenium(III), which is generated on-line through the photooxidation of tris(2,2'-bipyridyl)ruthenium(II) with peroxydisulfate. After optimizing the different experimental parameters, a calibration graph was obtained over the concentration range of 7 x 10(-8) M to 3 x 10(-6) M, with a minimum detectability of 7.2 x 10(-9) M (S/N = 3) observed. The correlation coefficient was 0.9992 (n = 8). The repeatability was 0.88 % (for a level of 4 x 10(-7) M) expressed as the relative standard deviation (n = 10), and the reproducibility (studied on five consecutive days) was 1.5%. The method was successfully applied to the determination of EDTA in ophthalmic collyrium and sauce samples. The method is also useful for determining other aminopolycarboxylic acids, such as NTA, EGTA, DTPA, DCTA and EDDS.     

A simple and rapid flow injection chemiluminescence determination of cysteine with Ru(phen)3(2+)-Ce(IV) system

A new chemiluminescence system was developed for the determination of cysteine by flow injection system. This method is based on the reaction of L-cysteine with Ru(phen)3(2+) and Ce(IV) to produce chemiluminescence. The calibration curve was linear over the range 8.0x10(-7) to 4.0x10(-5) and 4.0x10(-5) to 1.0x10(-3) M with a detection limit of 7.0x10(-7) M (S/N=3). The relative standard deviation of 4.0x10(-6) M cysteine was found 3.5% (n=10). The influence of potential interfering substances was studied. The proposed method was successfully applied for the flow injection determination of cysteine in the real samples with minimum sampling rate of 90 sample/h.     

Kinetic-spectrophotometric determination of ascorbic acid by inhibition of the hydrochloric acid-bromate reaction

A new analytical method was developed for the determination of ascorbic acid in fruit juice and pharmaceuticals. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolourisation of Methyl Orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The linearity range of the calibration graph depends on bromate concentration. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.6 x 10(-6) M and calibration rang is 8 x 10(-6)-1.2 x 10(-3) M ascorbic acid. The relative standard deviation of seven replication determinations of 8 x 10(-6) and 2 x 10(-5) M ascorbic acid was 2.8 and 1.7%, respectively. The influence of potential interfering substance was studied. The method was successfully applied for the determination of ascorbic acid in pharmaceuticals.     

Kinetic spectrophotometric determination of famotidine in commercial dosage forms.

A simple kinetic spectrophotometric method is described for the determination of famotidine. The method is based on the oxidation of the drug with alkaline potassium permanganate. The reaction is followed spectrometrically by measuring the rate of change of the absorbance at 610 nm. The initial-rate and fixed-time (at 12 min) methods are adopted for determining the drug concentration. The calibration graphs are linear in the ranges of 2-10 microg mL(-1) and 1-8 microg mL(-1) using the initial-rate and fixed-time methods, respectively. The method has been applied to the determination of famotidine in tablet formulations. The obtained results are compared statistically with those given by a reference spectrophotometric method.     

Quantitative analysis of irbesartan in commercial dosage forms by kinetic spectrophotometry

The objective of this work is to develop a new kinetic spectrophotometric method for the determination of irbesartan in pharmaceutical formulations. The method is based on the reaction of carboxylic acid group of the oxidized irbesartan with a mixture of potassium iodate (KIO(3)) and iodide (KI) to form yellow colored triiodide ions in aqueous medium at 30+/-1 degrees C. The reaction is followed spectrophotometrically by measuring the rate of change of absorbance at 352 nm. The initial-rate and fixed-time (DeltaA) methods are adopted for constructing the calibration curves, which were found to be linear over the concentration ranges of 10.0-60.0 and 7.5-60.0 microg ml(-1) respectively. The regression analysis of calibration data yielded the linear equations: rate=-2.138 x 10(-6)+1.058 x 10(-4)C and DeltaA=-3.75 x 10(-3)+3.25 x 10(-3)C for initial rate and fixed time (DeltaA) methods, respectively. The limit of detection for initial rate and fixed time methods are 0.21 and 2.40 mug ml(-1), respectively. The various activation parameters such as E(a), DeltaH++, DeltaS++ and DeltaG++ are also calculated for the reaction and found to be 70.95+/-0.43 kJ mol(-1), 68.48+/-0.21 kJ mol(-1), 16.54+/-0.24 J K(-1) mol(-1) and -4.94+/-0.07 kJ mol(-1), respectively. The proposed methods are optimized and validated as per the guidelines of International Conference on Harmonisation (U.S.A.). The point and interval hypothesis tests have been performed which indicate that there is no significant difference between the proposed methods and the reference method. The methods have been successfully applied to the determination of irbesartan in commercial dosage forms.     

Kinetic fluorimetric determination of Cu(II) and Zn(II) by their incorporation reactions into a water-soluble porphyrin

Kinetics of incorporation of Cu, Zn, Fe, Co, Ni and Mn divalent ions into coproporphyrin-I in imidazole buffer solution, pH 7.0, has been studied by monitoring the decrease in fluorescence intensity of the free base porphyrin. All reactions followed simple second-order rate law, the rate constants being decreased in the order Zn > Cu > Co > Fe > Mn, Ni. the kinetic fluorimetric method for the determination of Cu(II) and Zn(II) using their incorporation reactions into the porphyrin was developed. Initial rate and fixed-time methods were used to construct calibration graphs over the range 0-1.0 x 10(-5)M of both metals. The analytical characteristics of the method and effect of foreign ions were determined. In the presence of sodium thiosulphate as the masking reagent the determination of micromolar concentrations of Zn in the presence of a 10-fold excess of Cu is possible.     

Flow-injection analysis method for the determination of nitrite and nitrate in natural water samples using a chemiluminescence NOx monitor.

A flow-injection analysis method for the determination of nitrite and nitrate in natural water samples has been developed that consists of two systems based on their reduction to NO with hydrazine and/or ascorbic acid, followed by chemiluminescence detection. The procedure of sweeping the generated NO into an NOx monitor, by means of a gas-liquid separating coil consisting of microporous polytetrafluoroethylene (PTFE) tubing, offers practical advantages. The adjustment of the carrier gas-flow rates could yield the same calibration graphs for the two measurement systems, and the accumulation sweeping mode provides a higher sensitivity. Chemiluminescence detection allows a wide linear calibration range of 5 x 10(-8) to 5 x 10(-5) M. The detection limits for nitrate and nitrite, defined as three-times the standard deviation of measurement blanks, are 2 x 10(-8) M and 1 x 10(-8) M, respectively, and the average precision was 3.2% at ambient natural concentration levels. Recovery tests were between 94% and 106% for a variety of natural water samples. The method is relatively free from interferences from the substances normally found in natural water, and only ferric ion has an effect for the nitrite determination.     

Kinetic spectrophotometric determination of atenolol in dosage forms

A simple kinetic procedure is described for the determination of atenolol in its dosage forms. The procedure is based on coupling the drug with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole in pH 8 borate buffer at the boiling temperature for a fixed time of 30 min, and then measuring the absorbance of the reaction product at 460 nm. The absorbance-concentration plot is rectilinear over the range 5-50 microg/mL with a minimum detection limit of 1.3 microg (4.9 x 10(-6) M). The determination of atenolol by the fixed-concentration and rate-constant methods is also feasible with the calibration equations obtained, but the fixed-time method proved to be more applicable. The procedure was applied successfully to commercial tablets, and statistical analysis showed that the results compared favorably with those obtained by the official methods. The interference likely to be introduced from some coformulated drugs and the effect of sensitizers and surfactants on the performance of the proposed method were also studied. A proposed reaction pathway is presented.     

Validated kinetic spectrophotometric method for the determination of metoprolol tartrate in pharmaceutical formulations

A kinetic spectrophotometric method has been described for the determination of metoprolol tartrate in pharmaceutical formulations. The method is based on reaction of the drug with alkaline potassium permanganate at 25+/-1 degrees C. The reaction is followed spectrophotometrically by measuring the change in absorbance at 610 nm as a function of time. The initial rate and fixed time (at 15.0 min) methods are utilized for constructing the calibration graphs to determine the concentration of the drug. Both the calibration graphs are linear in the concentration range of 1.46 x 10(-6)-8.76 x 10(-6) M (10.0-60.0 microg per 10 ml). The calibration data resulted in the linear regression equations of log (rate)=3.634+0.999 log C and A=6.300 x 10(-4)+6.491 x 10(-2) C for initial-rate and fixed time methods, respectively. The limits of quantitation for initial rate and fixed time methods are 0.04 and 0.10 microg ml(-1), respectively. The activation parameters such as E(a), DeltaH(double dagger), DeltaS(double dagger) and DeltaG(double dagger) are also evaluated for the reaction and found to be 90.73 kJ mol(-1), 88.20 kJ mol(-1), 84.54 J K(-1) mol(-1) and 63.01 kJ mol(-1), respectively. The results are validated statistically and through recovery studies. The method has been successfully applied to the determination of metoprolol tartrate in pharmaceutical formulations. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.     

Spectrophotometric reaction rate method for determination of barbituric acid by inhibition of the hydrochloric acid-bromate reaction

A new kinetic-spectrophotometric method was developed for the determination of barbituric acid. The method is based on its inhibition effect on the reaction between hydrochloric acid and bromate. The decolorization of methyl orange by the reaction products was used to monitor the reaction spectrophotometrically at 510 nm. The variable affecting the rate of the reaction was investigated. The method is simple, rapid, relatively sensitive and precise. The limit of detection is 7.9x10(-7) M and calibration rang is 1x10(-6)-6.0x10(-4) M barbituric acid. The linearity range of the calibration graph is depends on bromate concentration. The relative standard deviation of seven replication determination of 5.6x10(-6) M barbituric acid was 1.8%. The influence of potential interfering substance was studied.     

Determination of gallium by square-wave voltammetry anodic stripping, based on the electrocatalytic action of 2,2'-bipyridine in dimethylsulphoxide: comparison with an aqueous NaSCN/NaClO(4) electrolyte

Deposition potential, deposition time, square-wave frequency, 2,2'-bipyridine concentration, and gallium concentration have been studied in detail, for the determination of trace concentration levels of the metal by square-wave voltammetry anodic stripping analysis, in dimethylsulphoxide. Optimum conditions have been found for gallium(III) determination and results compared to those obtained in 0.5M NaSCN + 4.2M NaClO(4) aqueous electrolyte by obtaining calibration graphs for the range 1 x 10(-8)M-1 x 10(-5)M gallium. Accuracy (+/- 3%) and precision (4-6% SD) of this method were assessed with both 4 x 10(-8)M and 4 x 10(-7)M gallium solutions used as synthetic samples. The efficiency of solvent extraction of gallium with di-isopropyl ether was found to be 99.98% at a 4 x 10(-7)M gallium concentration. The proposed method was applied to the determination of the gallium content in rock mineral samples (using the above mentioned solvent extraction procedure), are compared to those obtained with the NaSCNNaClO(4) based electrolyte. No statistically significant difference was observed. Analytical procedures followed are given in detail.     

Differential pulse polarographic determination of dicrotophos, crotoxyphos and chlorfenvinphos in grains and soils

A simple, sensitive and rapid differential pulse polarographic method has been developed for the quantitative determination of organophosphorus pesticides such as dicrotophos, crotoxyphos and chlorfenvinphos in agricultural formulations in universal buffers of a pH range 2.0-12.0. The sample is treated with ethanol to facilitate the dissolution of these pesticides. Both standard addition and calibration methods can be used for the analyses. The lower detection limits are 1.25x10(-9), 1.05x10(-9) and 1.0x10(-9) M, respectively. The method can be applied successfully to determination of these pesticides in grains and soil.     

Differential pulse anodic stripping voltammetric determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone modified carbon paste electrode

A sensitive and selective method for the determination of lead(II) with a 1,4-bis(prop-2'-enyloxy)-9,10-anthraquinone (AQ) modified carbon paste electrode has been developed. The method is based on non-electrolytic preconcentration via complex formation with modifier, followed by an accumulation period with a negative potential (-1.5 V), and then by a proper anodic stripping. The analytical performance was evaluated with respect to the quantity of modifier in the paste, concentration of electrolyte solution, preconcentration time, lead(II) concentration, and other variables. A linear calibration graph was obtained in the concentration range 2.00x10(-9)-1.06x10(-5) M Pb(II) (n=21, r=0.9999) with 30 s preconcentration time. The detection limit was found to be 1x10(-9) M. For eight preconcentration/determination cycles, the differential pulse voltammetric response was reproduced with 5.0 and 3.7% relative standard deviations at 2.00x10(-8) and 2.00x10(-6) M Pb(II), respectively. Rapid and convenient renewal of electrode surface allows the use of a single modified electrode surface in multiple analytical determinations over several weeks. Many coexisting metal ions had little or no effect on the determination of lead(II). The developed method was applied to lead determination in waste waters.