Analysis of Tolfenamic Acid using a Simple, Rapid, and Stabilityindicating Validated HPLC Method.

BACKGROUND: Tolfenamic acid (TA) belongs to the fenamates class of non-steroidal anti-inflammatory drugs. Insufficient information is available regarding the availa-bility of a reliable and validated stability-indicating method for the assay of TA. OBJECTIVE: A relatively simple, rapid, accurate, precise, economical, robust, and stability-indicating RP-HPLC method has been developed to determine TA in pure and tablet dosage forms. METHODS: The method was validated according to the ICH guideline, and parameters like linearity, range, selectivity, accuracy, precision, robustness, specificity, and solution stability were determined. TLC and FTIR spectrometry were used to ascertain the purity of TA. The specificity was determined with known impurities and after performing forced degradation, while the robustness was established by Plackett-Burman's experimental design. The mobile phase used for the analysis was acetonitrile and water (90:10, v/v) at pH 2.5. The detection of the active drug was made at 280 nm using a C18 column (tR = 4.3 min.). The method's ap-plicability was also checked for the yellow polymorphic form of TA. RESULTS: The results indicated that the method is highly accurate (99.39-100.80%), precise (<1.5% RSD), robust (<2% RSD), and statistically comparable to the British Pharmacopoeia method with better sensitivity and specificity. CONCLUSION: It was observed that the stress degradation studies do not affect the method's accuracy and specificity. Hence the proposed method can be used to assay TA and its tablet dosage form.

Pharmaceutical based cosmetic serums.

The growth and demand for cosmeceuticals (cosmetic products that have medicinal or drug-like benefits) have been enhanced for the last few decades. Lately, the newly invented dosage form, i.e., the pharmaceutical-based cosmetic serum has been developed and widely employed in various non-invasive cosmetic procedures. Many pharmaceutical-based cosmetic serums contain natural active components that claim to have a medical or drug-like effect on the skin, hair, and nails, including anti-aging, anti-wrinkle, anti-acne, hydrating, moisturizing, repairing, brightening and lightening skin, anti-hair fall, anti-fungal, and nail growth effect, etc. In comparison with other pharmaceutical-related cosmetic products (creams, gels, foams, and lotions, etc.), pharmaceutical-based cosmetic serums produce more rapid and incredible effects on the skin. This chapter provides detailed knowledge about the different marketed pharmaceutical-based cosmetic serums and their several types such as facial serums, hair serums, nail serums, under the eye serum, lip serum, hand, and foot serum, respectively. Moreover, some valuable procedures have also been discussed which provide prolong effects with desired results in the minimum duration of time after the few sessions of the serum treatment.

Nanosponges-based Drug Delivery System for the Cosmeceutical Applications of Stabilized Ascorbic Acid.

BACKGROUND: L-Ascorbic acid (AA) is a highly unstable compound, thus, limiting its use in pharmaceutical and cosmetic products, particularly at higher concentrations. OBJECTIVE: This study aimed to stabilize the highly sensitive molecule (AA) by encapsulating it in ß- cyclodextrin nanosponges (ß-CD NS) that can be used further in preparing cosmeceuticals products with higher AA concentrations and enhanced stability. METHODS: The NS has been synthesized by the melting method. The AA was encapsulated in ß-CD NS by the freeze-drying process. The prepared NS were characterized by FTIR spectrometry, SEM, Atomic Force Microscopy (AFM), zeta sizer, Differential Scanning Calorimetry (DSC), and the physical flow characteristics were also studied. The in vitro drug release was carried out on the Franz apparatus using a combination of two methods: sample & separate and dialysis membrane. The assay was performed using a validated spectrometric method. RESULTS: The entrapment efficiency of AA in ß-CD NS indicated a good loading capacity (83.57±6.35%). The FTIR, SEM, AFM, and DSC results confirmed the encapsulation of AA in ß-CD NS. The particle size, polydispersity index, and zeta potential results ascertained the formation of stabilized monodisperse nanoparticles. The physical flow characteristics showed good flow properties. Around 84% AA has been released from the NS in 4 h following the Korsmeyer-Peppas model. The AA-loaded NS remained stable for nine months when stored at 30±2°C/65±5% RH. CONCLUSION: It is concluded that the prepared NS can protect the highly sensitive AA from degradation and provide an extended-release of the vitamin. The prepared AA-loaded ß-CD NS can be used to formulate other cosmeceutical dosage forms with better stability and effect.

Development and validation of a spectrofluorimetric method for the analysis of tolfenamic acid in pure and tablet dosage form.

Tolfenamic acid (TA) is commonly used in humans and animals because of its anti-inflammatory, antipyretic, and analgesic effects. So far, no study has been carried out to develop a validated spectrofluorimetric method for determination of TA. Therefore, the present study aimed to develop and validate a simple, accurate, rapid, economical, and precise spectrofluorimetric method to assay TA in its pure and dosage forms, and also in degraded solutions. The fluorimetric method had higher sensitivity compared with the spectrophotometric and high-performance liquid chromatography methods and could determine the drug at the microgram level. Optimum pH of TA for maximum fluorescence intensity was 3, and its two pKa values were calculated as 1.95 and 4.05. The proposed method was validated according to the guidelines of the International Council for Harmonisation, and parameters such as linearity, range, accuracy, precision, sensitivity, robustness, specificity, and solution stability were tested. Stress-induced degradation studies on TA did not affect the accuracy and precision of the proposed method. The results obtained indicated that the method was linear over the concentration range 0.2-0.9 × 10-3 M with good accuracy, precision, and robustness for assay of TA in its pure and its tablet dosage forms and was comparable statistically with the British Pharmacopoeia method.

Photolysis of thiochrome in aqueous solution: A kinetic study.

The photolysis of thiochrome (THC), an oxidation product of thiamine (vitamin B1) (THE), used for its fluorimetric assay, has been studied in the pH range 7.0-12.0. THC undergoes photooxidation to oxodihydrothiochrome (ODTHC) which is oxidized to a non-fluorescent compound (OP1) on UV irradiation. The kinetics of the consecutive first-order reactions: THC→k1ODTHC→k2OP1, has been evaluated and the values of first-order rate constants, k1 (0.58-4.20 × 10-5, s-1) and k2 (0.05-2.03 × 10-5, s-1), at pH 7.0-12.0 have been determined. The rates of degradation of THC and ODTHC are enhanced with pH and the second-order rate constants k1' and k2' for the OH- ion-catalyzed reaction are in the range of 0.002-58.3 M-1 s-1. The quantum yields of the photolysis of THC and ODTHC in the pH range 7.0-12.0 have been determined. THC, ODTHC and OP1 have been identified by chromatographic, spectrometric and fluorimetric methods. THC and ODTHC have similar fluorescence characteristics and emit at 450 and 445 nm, respectively. THC, ODTHC and OP1 with distinct absorption maxima (370, 344 and 290 nm, respectively) have been determined by a newly developed and validated multicomponent spectrometric method during the photolysis reactions. The on-line formation of THC by the photooxidation of THE may lead to the degradation of THC and give erroneous results in the fluorimetric assay of THE. A scheme for the photolysis reactions of THC in aqueous solution is presented.

Multicomponent spectrometric analysis of drugs and their preparations.

Pharmaceutical preparations may contain a single ingredient or multi-ingredients as well as excipients. In multicomponent systems, specific analytical methods are required to determine the concentrations of individual components in the presence of interfering substances. Ultraviolet and visible spectrometric methods have widely been developed for the analysis of drugs in mixtures and pharmaceutical preparations. These methods are based on ultraviolet and visible multicomponent analysis and chemometrics (multivariate data analysis). The commonly used chemometric methods include principal component analysis (PCA); regression involving classical least squares (CLS), partial least squares (PLS), inverse least squares (ILS), principal component regression (PCR), multiple linear regression (MLR), artificial neural networks (ANNs); soft independent modeling of class anthology (SIMCA), PLS-discriminant analysis (DA); and functional data analysis (FDA). In this chapter, the applications of multicomponent ultraviolet and visible, derivative, infrared and mass spectrometric and spectrofluorimetric methods to the analysis of multi-ingredient pharmaceutical preparations, biological samples and the kinetics of drug degradation have been reviewed. Chemometric methods provide an efficient solution to calibration problems in the analysis of spectral data for the simultaneous determination of drugs in multicomponent systems. These methods facilitate the assessment of product quality and enhance the efficiency of quality control systems.

Photolysis of carboxymethylflavin in aqueous and organic solvent: a kinetic study.

This is the first study on the photolysis of carboxymethylflavin (CMF), an intermediate in the photolysis of riboflavin (RF). CMF is photodegraded by removal of side-chain to lumichrome (LC) in acid solution and to LC and lumiflavin (LF) in alkaline solution. It also undergoes alkaline hydrolysis to 1,2-dihydro-1-methyl-2-keto-3-quinoxaline carboxylic acid (KA) and 1,2,3,4-tetrahydro-1-methyl-2,3-dioxoquinoxaline (DQ) by cleavage of isoalloxazine ring. CMF degrades to LC in organic solvents. The formation of LC in acid solution and organic solvents takes place by second-order reaction and those of LC, LF, KA and DQ in alkaline solution by first-order reactions. The values of second-order rate constants for the photolysis of CMF at pH 2.0 to 7.0 are in the range of 1.13 to 2.45 M-1 s-1 and those of first-order rate constants (k obs) at pH 8.0-12.0 from 1.53 to 4.18 × 10-4 s-1 and for the formation of photoproducts from 0.37 to 16.6 × 10-5 s-1. The photolysis of CMF is enhanced, with pH, in the alkaline region since the excited state is sensitive to alkaline hydrolysis. The photolysis and fluorescence quantum yields of CMF in aqueous and organic solvents have been reported. CMF and photoproducts have been assayed spectrofluorimetrically. The mode of CMF photolysis is discussed.

Multicomponent spectrofluorimetric method for the assay of carboxymethylflavin and its hydrolytic products: kinetic applications.

The simultaneous assay of carboxymethylflavin (CMF), an intermediate in the photolysis of riboflavin, and its hydrolytic side-chain cleavage products, lumichrome (LC) (acid solution) and LC and lumiflavin (LF) as well as isoalloxazine ring cleavage products, 1,2-dihydro-1-methyl-2-keto-3-quinoxaline carboxylic acid (KA) and 1,2,3,4-tetrahydro-1-methyl-2,3-dioxo-quinoxaline (DQ) (alkaline solution) has been carried out by a multicomponent spectrofluorimetric method. The method is based on the adjustment of pH of the degraded solutions to 2.0 and extraction of LC and LF with chloroform. The chloroform extract is evaporated to dryness under reduced pressure, the residue dissolved in pH 6.5 citro-phosphate buffer and LC and LF determined at their fluorescence maxima at 478 and 530 nm, respectively. The pH of the aqueous phase is re-adjusted to 6.5 and the solution used for the determination of CMF, KA and DQ at the wavelengths of 530, 443 and 420 nm, respectively. The proposed method has been validated according to ICH guidelines. The calibration curves for CMF and its hydrolytic products are linear in the concentration range of 0.5-5.0 × 10-6  M. The mean recovery ranges from 99.0-102.0% with relative standard deviation (RSD) of 0.19-0.99%. The limit of detection (LOD) and the limit of quantification (LOQ) are in the range of 1.17-1.78 × 10-7  M and 3.55-5.40 × 10-7  M, respectively. The uniformity of molar balance of CMF and degradation products during hydrolytic reactions indicates the accuracy of the proposed method for the spectrofluorimetric assay of the compounds. It has been applied to study the kinetics of hydrolytic reactions of CMF.

Multicomponent spectrofluorimetric method for the assay of formylmethylflavin and its hydrolytic products: Kinetic applications.

A multicomponent spectrofluorimetric method has been developed for the simultaneous assay of formylmethylflavin (FMF), an intermediate product in the photolysis of riboflavin (vitamin B2), and its side-chain hydrolytic products, lumichrome (LC) in acidic solution and LC and lumiflavin (LF) in the alkaline solution as well as its ring cleavage products, 1,2-dihydro-1-methyl-2-keto-3-quinoxaline carboxylic acid (KA) and 1,2,3,4-tetrahydro-1-methyl-2,3-dioxo-quinoxaline (DQ) in alkaline solution. The assay method also takes into account an oxidation product of FMF, i.e. carboxymethylflavin (CMF), in both acid and alkaline solutions. The method involves adjustment of the pH of hydrolysed solution to 2.0 to convert FMF to its protonated form, extraction of LC (acid solution) or LC and LF (alkaline solution) with chloroform and their simultaneous assay by fluorescence measurement at 478 and 530 nm, respectively. The aqueous phase is readjusted to pH 6.5, extracted with chloroform to remove undegraded FMF and used for the assay of CMF, KA and DQ at 530, 443 and 420 nm, respectively. The chloroform extract is used for the assay of FMF at 530 nm. The proposed method has been validated and applied to the study of the kinetics of a hydrolysis reaction of FMF at pH 11.0. The calibration curves for FMF and degradation products are linear in the range of 0.1-1.0 × 10-6 M. The limit of detection (LOD) and limit of quantification (LOQ) range from 2.54-5.75 × 10-8 M and 0.78-1.74 × 10-7 M, respectively, for these compounds. The mean recovery ranges from 99.3-102.1% with a RSD of 0.14-0.35%. Judging from the molar balance of FMF and the hydrolytic products, uniformity of analytical data during the reactions and linearity of kinetic plot, the method gives accurate results for the assay of FMF and all of its degradation products. It can be conveniently used for the assay of these compounds and for the kinetics and stability studies of FMF.

Stability-indicating spectrofluorimetric method for the assay of riboflavin and photoproducts: Kinetic applications.

A stability-indicating spectrofluorimetric method has been developed for the simultaneous assay of riboflavin (RF) and photoproducts, formylmethylflavin (FMF), lumichrome (LC) and lumiflavin (LF) in aqueous solution. The method is based on the extraction of LC formed in acid solution and LC and LF formed in alkaline solution with chloroform at pH 2.0 and their assay by fluorescence measurements at 478 and 530 nm, respectively. The aqueous phase, on readjustment of the pH to 6.5, is used to extract FMF with chloroform and its assay is carried out at 530 nm. The aqueous phase is then used for the assay of RF at 530 nm. The proposed method gives more accurate results for the assay of RF compared to those of the United States Pharmacopeia (USP) spectrofluorimetric method which does not take into account the presence of RF photoproducts having similar fluorescence characteristics. The proposed method along with the USP method has been applied to the study of the kinetics of photolysis of RF, assay of stored commercial vitamin preparations and their radiated samples. The results show that the USP method does not distinguish between the fluorescence of RF and its photoproducts, and, therefore, gives erroneous results with about 11% excess in the quantity of the vitamin compared to that of the proposed method. This is due to the interference of the fluorescence of photoproducts in the assay of RF. The method has been validated for various analytical parameters according to the guideline of the International Council for Harmonization (ICH).

Tolfenamic Acid.

Tolfenamic acid (TA) is a nonsteroidal antiinflammatory drug and belongs to the group of fenamates. It is used as a potent pain reliever in the treatment of acute migraine attacks, and disorders like dysmenorrhea, rheumatoid, and osteoarthritis. TA has shown excellent in vitro antibacterial activity against certain ATCC strains of bacteria when complexed with bismuth(III). It has also been reported to block pathological processes associated with Alzheimer's disease. In the recent past, TA has also been used as a novel anticancer agent for the treatment of various cancers. In view of the clinical importance of TA, a comprehensive review of the physical and pharmaceutical properties and details of the various analytical methods used for the assay of the drug in pharmaceutical and biological systems has been made. The methods reviewed include identification tests and titrimetric, spectrophotometric, chromatographic, electrochemical, thermal, microscopic, enzymatic, and solid-state techniques. Along with the analytical profile, the stability and degradation of TA, its pharmacology and pharmacokinetics, dosage forms and dose, adverse effects and toxicity, and interactions have been discussed.

Photochemical interaction of ascorbic acid and nicotinamide in aqueous solution: A kinetic study.

The photodegradation of ascorbic acid (AH2) in the presence of nicotinamide (NA) at pH 2.0-12.0 has been studied using a 30 W UV radiation source. The reaction follows first-order kinetics and the values of apparent first-order rate constants (kobs) at 1 × 10-3 M NA concentration range from 1.17 (pH 2.0) to 3.61 × 10-3 min-1 (pH 12.0). The values of these rate constants (k0) in the absence of NA range from 0.50 (pH 2.0) to 1.75 × 10-3 min-1 (pH 12.0), indicating that the values of kobs for the photodegradation of AH2 in the presence of NA are about 2 fold compared to those of the AH2 alone. The second-order rate constants (k') for the photochemical interaction of AH2 and NA are in the range of 0.67 (pH 2.0) and 1.86 × 10-3 M-1 min-1 (pH 12.0). The k'-pH profile shows a gradual increase in the rate as a function of pH. This is due to the ionization of AH2 to give ascorbyl anions (AH-) which are more susceptible to photodegradation compared to the neutral molecule (AH2). NA appears to undergo photochemical interaction with AH2 during the reaction by acting as an electron acceptor to enhance its rate of photodegradation. The concentrations of AH2 and NA in degraded solutions have been determined by a two-component spectrometric method at 243 and 261 nm (pH 2.0) with a precision of ±2%. The method has been validated and the results are comparable to the HPLC method.

Validation of a Stability-Indicating Spectrometric Method for the Determination of Sulfacetamide Sodium in Pure Form and Ophthalmic Preparations.

INTRODUCTION: Sulfacetamide sodium is a widely used sulfonamide for ophthalmic infections. OBJECTIVE: A number of analytical methods have been reported for the analysis of sulfacetamide but they lack the ability to determine both the active drug and its major degradation product, sulfanilamide, simultaneously in a sample. MATERIALS AND METHODS: In the present study a simple, rapid and economical stability-indicating UV spectrometric method has been validated for the simultaneous assay of sulfacetamide sodium and sulfanilamide in pure form and in ophthalmic preparations. RESULTS: The method has been found to be accurate (recovery 100.03 ±0.589%) and precise (RSD 0.587%) with detectable and quantifiable limits of 1.67×10-6 M (0.04 mg%) and 5.07×10-6 M (0.13 mg%), respectively for the assay of pure sulfacetamide sodium. The method is also found to be accurate and precise to small changes in wavelength, pH and buffer concentration as well as to forced degradation. The study further includes the validation of the method for the assay of pure sulfanilamide in solution, which has been found to be accurate, precise and robust. CONCLUSION: The results indicate that the proposed two-component spectrometric method is stability-indicating and can be used for the simultaneous assay of both sulfacetamide sodium and sulfanilamide in synthetic mixtures and degraded solutions.

Metal ion mediated photolysis reactions of riboflavin: A kinetic study.

The effect of metal ion complexation on the photolysis of riboflavin (RF) using various metal ions (Ag+, Ni2+, Co2+, Fe2+, Ca2+, Cd2+, Cu2+, Mn2+, Pb2+, Mg2+, Zn2+, Fe3+) has been studied. Ultraviolet and visible spectral and fluorimetric evidence has been obtained to confirm the formation of metal-RF complexes. The kinetics of photolysis of RF in metal-RF complexes at pH7.0 has been evaluated. The apparent first-order rate constant (kobs) for the photolysis of RF and the formation of lumichrome (LC) and lumiflavin (LF) (0.001M phosphate buffer) and LC, LF and cyclodehydroriboflavin (CDRF) (0.2-0.4M phosphate buffer) have been determined. The values of kobs indicate that the rate of photolysis of RF is promoted by divalent and trivalent metal ions. The second-order rate constants (k' ) for the interaction of metal ions with RF are in the order: Zn2+>Mg2+>Pb2+>Mn2+>Cu2+>Cd2+>Fe2+>Ca2+>Fe3+>Co2+>Ni2+>Ag+. In phosphate buffer (0.2-0.4M), an increase in the metal ion concentration leads to a decrease in the formation of LC compared to that of CDRF by different pathways. The photoproducts of RF have been identified and RF and the photoproducts have simultaneously been assayed by a multicomponent spectrometric method. The mode of photolysis of RF in metal-RF complexes has been discussed.

Formulations of Amlodipine: A Review.

Amlodipine (AD) is a calcium channel blocker that is mainly used in the treatment of hypertension and angina. However, latest findings have revealed that its efficacy is not only limited to the treatment of cardiovascular diseases as it has shown to possess antioxidant activity and plays an important role in apoptosis. Therefore, it is also employed in the treatment of cerebrovascular stroke, neurodegenerative diseases, leukemia, breast cancer, and so forth either alone or in combination with other drugs. AD is a photosensitive drug and requires protection from light. A number of workers have tried to formulate various conventional and nonconventional dosage forms of AD. This review highlights all the formulations that have been developed to achieve maximum stability with the desired therapeutic action for the delivery of AD such as fast dissolving tablets, floating tablets, layered tablets, single-pill combinations, capsules, oral and transdermal films, suspensions, emulsions, mucoadhesive microspheres, gels, transdermal patches, and liposomal formulations.

Effect of Nicotinamide on the Photolysis of Riboflavin in Aqueous Solution.

The photolysis of riboflavin (RF) in aqueous solution in the presence of nicotinamide (NA) by visible light has been studied in the pH range 1.0-12.0 and the various photoproducts have been identified as known compounds. RF has been determined in degraded solutions by a specific multicomponent spectrometric method in the presence of its photoproducts and NA. The second-order rate constants (k 2) for the bimolecular interaction of RF and NA range from 0.54 (pH 1.0) to 9.66 M(-1) min(-1) (pH 12.0). The log k 2-pH profile for the photolysis reaction follows a sigmoid curve showing a gradual increase in the rate of pH due to a change in the ionization behavior of the molecule. The lower rate in the acid region is probably due to protonation of the molecule since the cationic form of RF is less susceptible to photolysis than the neutral form. Similarly, a slowing of the rate in the alkaline region is due to anion formation of the molecule. NA is involved as an electron acceptor during the sequence of reactions and thus enhances the rate of photolysis of RF. Absorption and fluorescence measurements did not provide evidence for the complex formation between the two compounds under the present conditions.

Ionic strength effects on the photodegradation reactions of riboflavin in aqueous solution.

A study of the effect of ionic strength on the photodegradation reactions (photoreduction and photoaddition) of riboflavin (RF) in phosphate buffer (pH7.0) has been carried out using a specific multicomponent spectrometric method. It has been found that the rates of photodegradation reactions of RF are dependent upon the ionic strength of the solutions at different buffer concentrations. The apparent first-order rate constants (kobs) for the photodegradation of riboflavin at ionic strengths of 0.1-0.5 (0.5M phosphate) lie in the range of 7.35-30.32 × 10(-3) min(-1). Under these conditions, the rate constants for the formation of the major products, lumichrome (LC) by photoreduction pathway, and cyclodehydroriboflavin (CDRF) by photoaddition pathway, are in the range of 3.80-16.03 and 1.70-6.07 × 10(-3) min(-1), respectively. A linear relationship has been observed between log kobs and √µ/1+√µ. A similar plot of log k/ko against √µ yields a straight line with a value of ~+1 for ZAZB showing the involvement of a charged species in the rate determining step. NaCl appears to promote the photodegradation reactions of RF probably by an excited state interaction. The implications of ionic strength on RF photodegradation by different pathways and flavin-protein interactions have been discussed.

Formulation and stabilization of riboflavin in liposomal preparations.

A study of the formulation of liposomal preparations of riboflavin (RF) with compositional variations in the content of phosphatidylcholine (PC) and their entrapment efficiency (26-42%) have been conducted. Light transmission characteristics of the liposomal preparations have been determined to evaluate their effect on the amount of light passing through the system to initiate a photochemical reaction. Dynamic light scattering (DLS) and atomic force microscopy (AFM) have been used to study the physical characteristics of liposomes. The liposomal preparations of RF have been subjected to photolysis using visible light and the apparent first- order rate constant, kobs, for the degradation of RF have been determined. The values of kobs (1.73-2.29×10(-3)min(-1)) have been found to decrease linearly with an increase in PC concentration in the range of 12.15 to 14.85 mM. Thus, an increase in PC concentration of liposomes leads to an increase in the stability of RF. RF and its main photoproduct, lumichrome (LC), formed in liposomes have been assayed by a two-component spectrometric method at 356 and 445 nm using an irrelevant absorption correction to compensate for the interference of liposomal components. The fluorescence measurements of RF in liposomes indicate excited singlet state quenching and the formation of a charge-transfer complex between RF and PC. It results in electron transfer from PC to RF to cause photoreduction and stabilization of RF.

Solvent Effect on the Photolysis of Riboflavin.

The kinetics of photolysis of riboflavin (RF) in water (pH 7.0) and in organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol, ethyl acetate) has been studied using a multicomponent spectrometric method for the assay of RF and its major photoproducts, formylmethylflavin and lumichrome. The apparent first-order rate constants (k obs) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10(-3) min(-1) (water). The values of k obs have been found to be a linear function of solvent dielectric constant implying the participation of a dipolar intermediate along the reaction pathway. The degradation of this intermediate is promoted by the polarity of the medium. This indicates a greater stabilization of the excited-triplet states of RF with an increase in solvent polarity to facilitate its reduction. The rate constants for the reaction show a linear relation with the solvent acceptor number indicating the degree of solute-solvent interaction in different solvents. It would depend on the electron-donating capacity of RF molecule in organic solvents. The values of k obs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.