Spectrofluorometric determination of montelukast in dosage forms and spiked human plasma

The native fluorescence of montelukast has been studied under different experimental conditions. The highest fluorescence intensity was obtained in methanol at 390 nm using 340 nm for excitation. Surfactants and sensitizers had either a negative or a slightly positive effect on its fluorescence intensity. The fluorescence intensity-concentration plot was rectilinear over the range 0.125 to 5 microg/ml with a lower detection limit of 0.02 microg/ml (3.4 x 10(-8) M). Interference likely to be introduced from co-formulated drugs (such as loratadine) or co-administered drugs (such as verapamil, carbazepam, propranolol) or other common drugs, was studied. The method was successfully applied to the determination of the drug in tablets (pediatric tablets, chewable tablets and adult tablets). The mean % recoveries were in agreement with those provided by the manufacturer. The method was further applied to the in vitro determination of montelukast in spiked human plasma, the mean % recovery (n = 5) was 100.08 +/- 1.40.

Spectrofluorometric determination of some beta-blockers in tablets and human plasma using 9,10-dimethoxyanthracene-2-sodium sulfonate

A simple and sensitive spectrofluorometric method was developed for the quantitative determination of some beta-blockers, namely arotinolol, atenolol and labetalol as hydrochloride salts. The method is based on the reaction of these drugs as n-electron donors with the fluorogenic reagent 9,10-dimethoxy-2-anthracene sulfonate (DMAS) as pi-acceptor in acidic medium. The obtained ion-pairs were extracted into chloroform and measured spectrofluorometrically at 452 nm after excitation at 385 nm. The fluorescence intensity-concentration plots are rectilinear over the ranges of 0.5-5 microg x ml(1), 1.0-11.0 microg x ml(1) and 0.6-6.4 microg x ml(1) for labetalol, atenolol and arotinolol, respectively. The different parameters affecting the reaction pathway were thoroughly studied and optimized. No interference was observed from the common pharmaceutical excipients. The proposed method was successfully applied to the analysis of tablets and the results were statistically compared with those obtained by reference methods. The method was further extended to the in vitro determination of the drugs in spiked human plasma, the % recoveries (n = 3) ranged from 96.98 +/- 1.55 to 98.28 +/- 2.19. A proposal of the reaction pathway was postulated.

Voltammetric study of danazol and its determination in capsules and spiked biological fluids

The voltammetric behaviour of danazol DZ (antigonadotropin) was studied using cyclic voltammetry, direct current, differential pulse polarography (DPP) and alternating current polarography. Danazol exhibited irreversible cathodic waves over the pH range of 1-5 in Britton Robinson buffers. At pH 1 (the analytical pH), a well-defined wave with E1/2 of -1.04 V versus Ag/AgCl reference electrode was obtained. The diffusion current constant (Id) was 4.8+/-0.14 microA.L.m mole(-1) and the current-concentration plot was rectilinear over the range from 5 x 10(-6) to 1 x 10(-4) M with correlation coefficient (n = 11) of 0.995. The calculated detection limit was 1 x 10(-6) M using the DPP mode. The wave was characterized as being irreversible, diffusion-controlled although adsorption phenomenon played a limited role in the electrode process. The proposed method was applied to commercial capsules and the average percentage recovery was in agreement with that obtained by the official USP method. The method was extended to the in vitro determination of DZ in spiked human urine and plasma samples, the percentage recoveries were 96+/-4 and 97+/-5, respectively. A proposal of the electrode reaction was postulated.

Stability studies on diloxanide furoate: effect of pH, temperature, gastric and intestinal fluids

The degradation of the amoebicide diloxanide furoate in alkaline medium at different temperatures was investigated using both a spectrophotometric and a developed HPLC method. In solutions, the drug was found to undergo decomposition, i.e., temperature and pH dependent. The pH-rate profile at pH between 7.6 and 9.6 indicated a first-order dependence of Kobs on [-OH]. Arrhenius plot obtained at pH 8 was linear between 40 and 63 degrees C. The estimated activation energy of hydrolysis was found to be 18.25 kcal degree.mol(-1). The effect of simulated gastric and intestinal fluids on the drug was also investigated. A new thin-layer chromatographic (TLC) procedure for the fractionation of the drug and its alkaline hydrolysis products has been developed and was found to compare favorably with that of the British Pharmacopoeia. Three hydrolysis products of a basic methanolic solution of the drug, namely furoic acid, diloxanide and methylfuroate could be identified by the use of TLC, HPLC, infrared and mass spectrometry.

High Performance Liquid Chromatoqraphic Method for the Simultaneous Determination of Labetalol and Hydrochlorothiazide in Tablets and Spiked Human Plasma

A reversed-phase HPLC method with spectrophotometric detection was developed for the simultaneous determination of labetalol (LBT) and hydrochloro-thiazide (HCD). The chromatographic separation was performed using a Microbondapak C18 column (4.6 i.d. x 250 nm) and paracetamol as internal standard. A mobile phase consisting of 0.05 M phosphate buffer/acetonitrile of pH 4 (7:3) at a flow rate of 0.7 ml/min was used. The detection was affected spectrophotornetrically at 302 nm. The working concentration range was 0.3–10 µg/ml with detection limits of 0.05 µg/ml for both drugs. The lower quantitation limit was 0.25 µg/ml in the two cases. The method was successfully applied to tablets, the % recoveries were 99.45 ± 0.68 for LBT and 99.79 ± 0.75 for HCD. The method was extended to the in-vitro determination in spiked human plasma. The % recoveries were 91.12 ± 0.33 for LBT and 91.37 ± 0.40 for HCD. The interday and intraday precision and accuracy were evaluated in plasma by calculating the % RSD (n=5) and the % error and were found to be in the ranges of 1.18–4.1% and 0.38–0.36% for both drugs, respectively.

Anodic Polaroqraphic Determination of lsradipine in Pharmaceutical Formulations

The anodic behaviour of isradipine was studied using cyclic voltammetry (CV), direct current (DCt) and differential-pulse (DPP) polarography. lsradipine exhibited well-defined anodic polarographic waves over the pH range of 4–8 in Britton-Robinson buffer (BRb). At pH 6, the analytical pH, the diffusion-current constant (Id) was 2.12 ± 0.42 (n = 4). The oxidation potential is −0.10 V vs AgIAgCl reference electrode with correlation coefficients of 0.9977 and 0.9948 in the DCt and DPP modes, respectively. The current-concentration plots were rectilinear over the ranges 5–14 µg/ml and 2.4–12 µg/ml using the DCt and DPP modes, respectively. The lower detection limit was 1.12 µg/ml (3.02 x 10−6 M) adopting the DPP mode. The proposed method was applied to commercial tablets and capsules, the % recoveries were 100.52 ± 1.267 and 99.4 ± 0.87 (n = 6) for the tablets and 101.3 ± 1.57 and 100.7 ± 2.10 (n = 6) for the capsules adopting both DCt and DPP modes, respectively. The number of electrons involved in the electrode process was accomplished and a proposal of the electrode reaction was presented.

Spectrofluorometric determination of nimodipine in dosage forms and human urine

A simple sensitive and specific spectrofluorometric method was developed for the determination of nimodipine (NDP) in pharmaceutical preparations and human urine. The method is based on reduction of nimodipine with Zn/HCl and measuring the obtained fluorescence at 425 nm after excitation at 360 nm. The factors affecting the development of the fluorophore and its stability were studied and optimized. The effect of some surfactants such as beta-cyclodextrin (betaCD), carboxymethylcelullose (CMC), sodium dodecyl sulphate (SDS) and Triton X-100, on the fluorescence intensity was studied. The fluorescence intensity-concentration plot is rectilinear over the range 0.1-5.0 microg/ml in presence of Triton X-100 with a minimum detectability limit of 0.06 microg/ml (1.62 x 10(-7) M). The proposed method was successfully applied to commercial tablets containing NDP, the percentage recovery agreed well with those obtained using the official methods. The method was further extended to the in vitro determination of NDP in spiked human urine samples. The % recovery was 102.1 +/- 2.54 (n = 4). A proposal of the reduction reaction pathway was postulated.

Spectrophotometric determination of fenoterol hydrobromide in pure form and dosage forms

A sensitive and rapid spectrophotometric procedure has been investigated for the determination of fenoterol either per se or in pharmaceutical preparations. The proposed procedure is based on the reaction between the drug and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) at pH 7.2, using borate buffer, to produce a yellow adduct. The latter has maximum absorbance at 400 nm and obeys Beer's law within the concentration range 5-30 microg/ml. Regression analysis of the calibration data showed a good correlation coefficient (r=0.9996) with minimum detection limit of 0.24 microg/ml (6.2 x 10(-8) M). The proposed procedure has been successfully applied to the determination of this drug in its tablets and in syrup, the mean percent recoveries were 97.45+/-0.59 and 98.7+/-0.64%, respectively. The results obtained are in good agreement with those given using a reference method. The pharmaceutical additives other than active ingredient did not interfere. A proposal of the reaction pathway has been postulated.

Polarographic determination of flubendazole in spiked human urine and plasma

The voltammetric behavior of flubendazole was studied using direct current (DCt), differential pulse (DPP) and alternating current (ACt) polarography. The drug manifests a cathodic wave in 20% v/v formic acid solution. The wave was characterized as being irreversible, diffusion-controlled with limited adsorption properties. The diffusion current-concentration relationship was found to be rectilinear over the range 3.2-14.4 microg/ml and 0.1 to 12.8 microg/ml, using DCt and DPP modes, respectively, with minimum detectability of 0.161 microg/ml (5.14 x 10(-7) M) and 0.0.057 microg/ml (1.82 x 10(-8) M) using DCt and DPP modes, respectively. Furthermore, the proposed method was applied to the in-vitro determination of flubendazole in spiked human urine and plasma adopting the DPP technique. The percentage recoveries were 100.20+/-0.62 and 97.42+/-0.95, respectively.

Spectrofluorimetric determination of manzamine A in spiked human urine and plasma

The native fluorescence of manzamine A (a biologically active beta-carboline marine-derived alkaloid) has been studied under different conditions. The highest fluorescence intensity was obtained in methanol. Two wavelength settings were found to be suitable for excitation, 280 nm and 340 nm; while lambdamax emission was constant in both cases at 387 nm. The fluorescence intensity at 340/387 nm setting was 1.6 greater than that obtained at 280/387 nm settings. The calibration curves were rectilinear over the range 0.1-2.0 and 0.5-2.5 microg/ml for the two settings, respectively. The detection limits were 0.05 microg/ml (9.1 x 10(-9) M) and 0.1 microg/ml (1.82 x 10(-8) M) at 340/387 nm and 280/387 nm, respectively. The proposed method was applied to the determination of manzamine A in spiked human urine and plasma samples adopting the 340/387 nm wavelength setting, the % recoveries (n = 6) were 99.61 +/- 0.90 and 100.25 +/- 1.63, respectively.

Spectrophotometric determination of labetalol in pharmaceutical preparations and spiked human urine

Two simple and sensitive spectrophotometric methods were developed for the spectrophotometric determination of labetaolol (LBT). Both methods are based on the phenolic nature of the drug. The first method (Method I) is based on coupling LBT with diazotized benzocaine in presence of trimethylamine. A yellow colour peaking at 410 nm was produced and its absorbance is linear with the concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.9993. The molar absorptivity was 2.633 x 10(4) l mol(-1) cm(-1). The second method (Method II) involves coupling LBT with diazotized p-nitroaniline in presence of sodium carbonate. An orange colour peaking at 456 nm was obtained and its absorbance is linear with concentration over the range 1-10 microg ml(-1) with correlation coefficient (n=5) of 0.99935. The stoichiometry of the reaction in both cases was accomplished adopting the limiting logarithmic method and was found to be 1:1. The developed method could be successfully applied to commercial tablets. The results obtained were in good agreement with those obtained using the official methods. No interference was encountered from co-formulated drugs, such as hydrochlorothiazide. The method was further extended to the in-vitro determination of LBT in spiked human urine. The % recovery (n=4) were 97.7+/-5.75 and 103.27+/-5.42 using the Methods I and II, respectively.

Voltammetric determination of isradipine in dosage forms and spiked human plasma and urine

The voltammetric behavior of isradipine was studied using direct current (DC(t)), differential-pulse (DPP) and alternating current (AC(t)) polarography. Isradipine exhibited well-defined cathodic waves over the whole pH range in Britton-Robinson buffer (BRb). At pH 5, the analytical pH, the diffusion-current constant (Id) was 8.27+/-0.52. The current-concentration plots were rectilinear over the range 1-20 and 0.1-18 microg/ml using the DC(t) and DPP modes, respectively, with minimum detectability of 0.01 microg/ml (2.7 x 10(-8) M) using the latter technique. The current has been characterized as being diffusion-controlled, although adsorption phenomenon played a limited role in the electrode process. The proposed method was applied to commercial tablets and capsules. The percentage recoveries were in good agreement with those given by the manufacturer. The method was further extended to the in-vitro determination of the drug in spiked human urine and plasma, the percentage recoveries were (n = 4) 100.12+/-1.42 and 103.88+/-5.13, respectively. The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented.

Spectrofluorometric determination of labetolol in pharmaceutical preparations and spiked human urine through the formation of coumarin derivative

A simple, sensitive and specific spectrofluorimetric method has been developed for the determination of labetalol (LBT). The method is based on the reaction between LBT and ethylacetoacetate in the presence of sulphuric acid to give yellow fluorescent product with excitation wavelength of 312 nm and emission wavelength of 432 nm. The reaction conditions were studied and optimized. The fluorescence intensity-concentration plot is rectilinear over the range 1-15 microgram/ml with minimum detectability limit of 0.8 microgram/ml (2.16 x 10(-6) M). The proposed method was successfully applied to commercial tablets containing LBT, the percentage recoveries agreed well with those obtained using the official methods. Hydrochlorothiazide, which is frequently co-formulated with LBT did not interfere with the assay. The method was further extended to the in-vitro determination of LBT in spiked human urine samples. The percentage recovery was 101.50+/-6.18 (n=6). A proposal of the reaction pathway was postulated.

Voltammetric determination of josamycin (a macrolide antibiotic) in dosage forms and spiked human urine

The voltammetric behaviour of josamycin (a macrolide antibiotic) has been studied using direct current (DC(t)) alternating current (AC(t)) and differential pulse polarography (DPP). In Britton-Robinson buffers, josamycin developed cathodic waves over the pH range 7-12. At pH 10, a well-defined cathodic wave with diffusion current constant of 1.06 +/- 0.19 (n = 5) was obtained. The wave was characterized as being diffusion-controlled; and partially affected by adsorption phenomenon. The current-concentrations plots are rectilinear over the range 10-60 and 6-50 microg/ml using DC(t) mode and DPP mode, respectively. The minimum detectability limit was 1.2 microg/ml (1.9 x 10(-6) M) adopting the DPP mode. A method was proposed for the determination of josamycin in its tablets adopting both DC(t) and DPP modes. The results obtained were in good agreement with those given by the manufacturer. The method was extended to the in-vitro determination of the drug in spiked human urine; the % recovery was 98.06 +/- 1.76% (n = 5). The number of electrons involved in the reduction process was accomplished and a proposal of the electrode reaction was presented.

Voltammetric determination of nitrosocimetidine in simulated gastric juice

OBJECTIVE

To develop a voltammetric method for the determination of nitrosocimetidine in simulated gastric juice (SGJ).

METHOD

Measurement of the polarographic wave of the nitroso derivative at the dropping mercury electrode in 0.1 m HCl.

RESULTS

A well-defined diffusion-controlled cathodic wave was obtained at -0.34 V vs. Ag/AgCl electrode. The current-concentration relationship was found to be rectilinear over the range 10-80 microg/mL and 2-50 microg/mL with percentage recovery of 101.24 +/- 0.79 and 100.79 +/- 0.56 for the direct current (DCt) and differential pulse polarography (DPP) modes, respectively, with a minimum detectability (S/N=2) of 0.16 microg/ml (5.6 x 10-7 m) using DPP mode.

CONCLUSION

The proposed method was successfully applied to study the nitrosation of cimetidine in SGJ.

Voltammetric analysis of trazodone HCl in pharmaceuticals and biological fluids

The voltammetric behavior of trazodone (TRZ) HCl was studied using direct current (DC(t)), differential pulse (DPP) and alternating current (AC(t)) polarography. The drug manifests cathodic waves over the pH range of 10-14. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. At pH 10, the diffusion current-concentration relationship was found to be rectilinear over the range 4-32 and 0.8-24 microg ml(-1) using DC(t) and DPP modes, respectively, with minimum detectability (S/N=2) of 0.104 microg ml(-1) (2.45 x 10(-6) M) and 0.314 microg ml(-1) (7.397 x 10(-6) M) using the DPP and DC(t) modes, respectively. The diffusion-current constant (I(d)) is 4.31+/-0.02 (n=6). The proposed method was successfully applied to the determination of the studied compound either in pure form or in formulations. The results obtained were favorably compared with those given using a reference method. Furthermore, the proposed method was applied to the determination of TRZ in spiked human urine and plasma adopting the DPP technique. No prior extraction step is needed in case of urine. The percentage recoveries were 98.43+/-0.79 and 97.44+/-0.705 (n=4) in spiked human urine and plasma, respectively. A pathway for the electrode reaction was postulated.

A simple kinetic spectrophotometric method for the determination of isoxsuprine in dosage forms

A simple and sensitive kinetic method was developed for the determination of isoxsuprine in pharmaceutical preparations. The method is based upon a kinetic investigation of the oxidation reaction of the drug with alkaline potassium permanganate at room temperature for a fixed time of 30 min. The absorbance of the coloured manganate ion was measured at 610 nm. Alternatively, the decrease in the absorbance of potassium permanganate after addition of the drug was measured at 525 nm. The absorbance-concentration plots in both procedures were rectilinear over the range of 0.5-4 microg ml(-1) (r = 0.9998) with a minimum detectability of 0.05 microg ml (-1) (1.48 x 10(-7) M). The different experimental parameters affecting the development and stability of the colours were carefully studied and optimized. The determination of isoxsuprine by the fixed concentration and rate constant 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 isoxsuprine in formulations. The results obtained were in good agreement with those obtained using a reference method. The proposed method was also adopted to detect isoxsuprine in spiked human plasma at its therapeutic level of concentration (0.4 microg ml(-1)). A proposal of the reaction pathway was postulated.

Simple spectrophotometric determination of cinnarizine in its dosage forms

A direct, extraction-free spectrophotometric method has been developed for the determination of cinnarizine in pharmaceutical preparations. The method is based on ion-pair formation between the drug and three acidic (sulphonphthalein) dyes; namely bromocresol green (BCG), bromocresol purple (BCP) and bromophenol blue (BPB) which induces an instantaneous bathochromic shift of the maximum in the drug spectrum. Conformity to Beer's law enabled the assay of dosage forms of the drug. Compared with a reference method, the results obtained were of equal accuracy and precision. A more detailed investigation of the cinnarizine-BCG ion pair complex was made with respect to its composition, association constant and free energy change. In addition, this method was also found to be specific for the analysis of cinnarizine in the presence of some of the co-formulated drugs, such as pyridoxine hydrochloride and digoxin.

LC of pharmaceutically important halogenated 8-hydroxyquinolines after precolumn derivatization with Pd (II)

An accurate, sensitive, and selective reversed phase high performance liquid chromatographic (HPLC) method was developed for the analysis of two halogenated 8-hydroxyquinoline derivatives; clioquinol (CQN) and iodoquinol (IQN). The proposed method depends on the complexation ability of the studied compounds with Pd(II) ions. Reversed phase chromatography was conducted using a 300 x 3.9 mm i.d. stainless steel column packed with 10 microm Bondclone phenyl at ambient temperature. A solution containing 0.005% w/v of Pd(II)-chloride in a mixture of acetonitrile-methanol-water (3:3:4 v/v/v) of pH 3.7 as a mobile phase pumped at a flow rate of 0.75 ml min(-1). UV-detection was performed at 282 and 285 nm for CQN and IQN, respectively. The method showed excellent linearity in the range 0.05-1.8 and 0.1-3.0 microg ml(-1) with limit of detection (S/N=2) 4.8 ng ml(-1) (1.57 x 10(-8) M) and 6.4 ng ml(-1) (1.61 x 10(-8) M) for CQN and IQN, respectively. The suggested method was successfully applied for the analysis of the studied drugs in bulk with average% recoveries of 99.68+/-0.44 for CQN and 99.65+/-0.53 for IQN. The proposed method was successfully applied for the analysis of the studied drugs in single or combined dosage forms with average% recoveries of 99.41+/-0.51-100.02+/-0.63. The proposed method could be used successfully for the determination of the studied compounds in the presence of their degradation product as they could be eluted with different retention times. The presence of metronidazole (MNZ) or tolnaftate (TFT) with the studied drugs does not affect their accurate determination. The results obtained were favorably compared with those obtained by the reference method. The results were satisfactorily, accurate, and precise.