UV-absorption and fluorimetric methods for the determination of alprazolam in pharmaceutical formulation

The development of UV and fluorescence spectrophotometric methods for the quantitative determination of alprazolam in dosage forms using As(III)?SDS system. The two simple and sensitive, spectrophotometric and spectrofluorimetric methods were developed for the determination of alprazolam (ALP) in tablets. These methods are based on formation of ALP?As(III) complex in the presence of SDS. The UV-spectrum of 30% methanolic solution of ALP (5 × 10^?5 M) at pH 6.5 (Mclivaine buffer) was run between 200 and 380 nm. The absorption spectrum of ALP exhibits two peaks with a λ_max. at 255 nm and a weak band at 325 nm. When the spectra of the drug were run at varying pH in the region 200–380 nm, one isosbestic point at 290 nm was observed, which indicated the presence of two ionic conditions in solution. The complex exhibited an absorption maximum at 265 nm and emission peak at 520 nm with respect to the excitation wavelength of 325 nm. The spectrophotometric method was found to be linear in 8.0–17.0 μg ml^?1 range with detection limit of 13.520 μg ml^?1, while 0.05–9.5 μg ml^?1 range was with detection limit of 1.048 × 10^?2 μg ml^?1 by spectrofluorimetric method. The mean percentage recovery of the added quantity was found to be 99.54 (spectrophotometric method) and 100.22 (spectrofluorimetric method) and the %RSD are lower than 0.478 and 0.296 determined spectrophotomerically and spectrofluorimtrically, respectively. This indicates that the proposed method is accurate. The apparent ionization constant of ALP was found to be 9.29. The spectra, experimental conditions were set followed by determination stoichiometry, stability constant and thermodynamic parameters of the As(III), Co(II), Ni(II), and Zn(II) complexes with ALP at pH 6.5. The proposed methods have been successfully applied to the assay of ALP in tablets and the results were statistically evaluated.     

Copper(II)–neocuproine reagent for spectrophotometric determination of captopril in pure form and pharmaceutical formulations

A simple, rapid, sensitive and accurate spectrophotometric method for the determination of captopril in pure form and pharmaceutical formulations is developed. The procedure is based on the reaction of copper(II) with captopril in the presence of neocuproine (NC) (2,9-dimethyl-1,10-phenanthroline) reagent in acetate buffer at pH 5.0. Copper(II) is reduced easily by captopril to Cu(I)–neocuproine complex, which shows an absorption maximum at 448 nm. Beer’s law was obeyed in the concentration range 0.3–3.0 μg mL^?1 with a minimum detection limit (LOD) of 0.039 μg mL^?1 and a quantification limit (LOQ) of 0.129 μg mL^?1. For more accurate results, Ringbom optimum concentration ranges was 0.5–2.7 μg mL^?1. The apparent molar absorbtivity and Sandell sensitivity were calculated. The validity of the proposed method was tested by analyzing the pure and pharmaceutical formulations and compared well with those obtained by the official method and demonstrated good accuracy and precision.     

Spectrophotometric determination of sildenafil citrate in pure form and in pharmaceutical formulation using some chromotropic acid azo dyes

Two simple and highly sensitive spectrophotometric methods were developed for the quantitative determination of the drug sildenafil citrate (SC), Viagra, in pure form and in pharmaceutical formulations, through ion-associate formation reactions (method A) with mono-chromotropic acid azo dyes, chromotrope 2B (I) and chromotrope 2R (II) and ion-pair reactions (method B) with bi-chromotropic acid azo dyes, 3-phenylazo-6-o-carboxyphenylazo-chromotropic acid (III), bis-3,6-(o-hydroxyphenylazo)-chromotropic acid (IV), bis-3,6-(p-N,N-dimethylphenylazo)-chromotropic acid (V) and 3-phenylazo-6-o-hydroxyphenylazo-chromotorpic acid (VI). The reaction products, extractable in methylene chloride, were quantitatively measured at 540, 520, 540, 570, 600 and 575 nm using reagents, I–VI, respectively. The reaction conditions were studied and optimized. Beer's plots were linear in the concentration ranges 3.3–87.0, 3.3–96.0, 5.0–115.0, 2.5–125.0, 8.3–166.7 and 0.8–15.0 μg mL^?1 with corresponding molar absorptivities 1.02 × 10⁴, 8.34 × 10³, 6.86 × 10³, 5.42 × 10³, 3.35 × 10³ and 2.32 × 10⁴ L mol^?1 cm^?1 using reagents I–VI, respectively. The limits of detection and Sandell's sensitivities were calculated. The methods were successfully applied to the analysis of commercial tablets (Vigoran) and the recovery study reveals that there is no interference from the common excipients that are present in tablets. Statistical comparison of the results was performed with regard to accuracy and precision using Student's t- and F-tests at 95% confidence level. There is no significant difference between the reported and proposed methods with regard to accuracy and precision.     

Ion-pairing and reversed phase liquid chromatography for the determination of three different quinolones: Enrofloxacin,lomefloxacin and ofloxacin

Two simple and sensitive high performance liquid chromatographic (HPLC) methods have been developed for the simultaneous determination of three different quinolones: enrofloxacin, lomefloxacin and ofloxacin in their pure and dosage forms, one with reversed phase HPLC and the other with ion-pair HPLC. In reversed phase HPLC, method (A), the mobile phase consists of 2.18% aqueous solution of KH₂PO₄ with pH adjusted to 2.4 ± 0.2 with acetonitrile (80:20; v/v), the mobile phase pumped at flow rate of 1.2 ml min^?1. A Neucleosil C₁₈ column (10 μm, 100 Å), 250 mm length × 4.6 mm diameter was utilized as stationary phase. Detection was affected spectrophotometrically at 294 nm. While in ion-pair HPLC, method (B), the mobile phase was aqueous solution of 0.65% sodium perchlorate and 0.31% ammonium acetate adjusted to pH 2.2 ± 0.2 with orthophosphoric acid: acetonitrile (81:19; v/v), the mobile phase pumped at flow rate of 1.5 ml min^?1. A μ bondapack C₁₈ column (10 μm, 100 Å), 250 mm length × 4.6 mm diameter was utilized as stationary phase. Detection was affected spectrophotometrically at 294 nm. Linearity ranges for enrofloxacin, lomefloxacin and ofloxacin were 4.0–108, 7.0–112 and 8.0–113 μg ml^?1, respectively using method A and 8.0–112, 7.0–112 and 5.0–105 μg ml^?1, respectively applying method B. Minimum detection limits obtained were 0.013, 0.023 and 0.035 μg ml^?1 for enrofloxacin, lomefloxacin and ofloxacin, respectively using method A, and 0.028, 0.023 and 0.011 μg ml^?1 using method B. The proposed methods were further applied to the analysis of enrofloxacin in injection and tablets containing the ofloxacin and lomefloxacin drugs, and the results were satisfied.     

Ultrasensitive determination of serum albumin using resonance light scattering based on ZnS-polyacrylic acid nanoparticles

ZnS-polyacrylic acid (ZnS-PAA) was prepared by an in situ polymerization method using nano-ZnS as core in the presence of acrylic acid (AA), and ZnS-PAA nanoparticles was characterized by ultraviolet spectrometry (UV) and transmission electron microscopy (TEM). Based on the significant increase of the resonance light scattering (RLS) intensity with the interaction between nanoparticles and serum albumin, RLS method was developed for the sensitive determination of serum albumin (BSA and HSA). Under optimum conditions, the change of the intensity (ΔI) of the RLS spectra at λ = 392 nm was linearly proportional to the concentration of BSA and HSA. The linear range was 1–100 ng mL^?1 for HSA and 1–120 ng mL^?1 for BSA, and the limit of detection (LOD) was 0.4 ng mL^?1 for HSA and 0.5 ng mL^?1 for BSA. This method proved to be very sensitive, rapid, simple and tolerant of most interfering substances.     

Spectrophotometric and titrimetric methods for the determination of nordiazepam in pure and pharmaceutical dosage form

A spectrophotometric method and two titrimetric methods for the determination of nordiazepam via its iodobismuthate complex are described. These methods depend on the reaction of nordiazepam with potassium bismuth iodide which give an orange precipitate. Determination of nordiazepam in the precipitated complex is done iodometrically using standard potassium iodate solution or complexometrically using standard EDTA solution and xylenol orange indicator. Alternatively, the complex is dissolved in ethanol and its absorbance is measured at 323 nm. The three methods were applied for the determination of reference samples of nordiazepam in the concentration range of 1–30 mg ml^?1 (for the iodometric method) and of 5–30 mg ml^?1(for the complexometric method) and of 0.04–3.2 mg ml^?1 (for the spectrophotometric method). The proposed methods were applied for the determination of nordiazepam in madar tablets and the validity of the proposed methods was assessed by applying the standard addition technique.     

An application of second-order UV-derivative spectrophotometry for study of solvolysis of a novel fluocinolone acetonide ester

A novel topical corticosteroid FA-21-PhP, 2-phenoxypropionate ester of fluocinolone acetonide, has been synthesized in order to investigate the possibility of decreasing systemic side effects. In this study model system for in vitro solvolytic reaction of FA-21-PhP has been analyzed in ethanol/water (90:10, v/v) with excess of sodium hydrogen carbonate. The selected conditions have been used as in vitro model for activation of corticosteroid C-21 ester prodrug. The second-order derivative spectrophotometric method (DS) using zero-crossing technique was developed for monitoring ternary mixture of solvolysis. Fluocinolone acetonide (FA) as a solvolyte was determined in the mixture in the concentration range 0.062–0.312 mM using amplitude ²D_274.96. Experimentally determined LOD value was 0.0295 mM. The accuracy of proposed DS method was confirmed with HPLC referent method. Peak area of parent ester FA-21-PhP was used for solvolysis monitoring to ensure the initial stage of changes. Linear relationship in HPLC assay for parent ester was obtained in the concentration range 0.054–0.54 mM, with experimentally determined LOD value of 0.0041 mM. Investigated solvolytic reaction in the presence of excess of NaHCO₃ proceeded via a pseudo-first-order kinetic with significant correlation coefficients 0.9891 and 0.9997 for DS and HPLC, respectively. The values of solvolysis rate constant calculated according to DS and HPLC methods are in good accordance 0.038 and 0.043 h^?1, respectively.     

Stability-indicating liquid chromatography for determination of clopidogrel bisulfate in tablets: Application to content uniformity testing

The present study describes a simple stability-indicating reversed-phase HPLC assay for antiplatelet drug, clopidogrel bisulfate. Separation of the drug and the degradation products, under stress conditions was successfully achieved on a C-18 column utilizing 0.01 M Na₂HPO₄ (pH 4): acetonitrile in the ratio 80:20 v/v, pumped at a flow rate of 0.5 ml min^?1 with UV detection at 235 nm. The retention time of clopidogrel was 6.84 min. The method was satisfactorily validated with respect to linearity, precision, accuracy, selectivity, sensitivity and ruggedness. The response was linear in the range of 0.2–3.5 μg ml^?1 with detection limit 0.079 μg ml^?1. The suggested method was successfully applied for the analysis of clopidogrel in bulk and in commercial tablets. The results were favorably compared to those obtained by a reference method. The proposed method was successfully applied to the content uniformity testing of tablets and for determination of clopidogrel in presence of its co-administered drug, acetyl salicylic acid.     

Determination of gallium at trace levels using a spectrofluorimetric method in synthetic U–Ga and Ga–As solutions

A simple, easy to use and selective spectrofluorimetric method for the determination of trace levels of gallium has been developed. A new Schiff base, N-o-vanillidine-2-amino-p-cresol (OVAC) was synthesized and its fluorescence activity with gallium investigated. Based on this chelation reaction, a spectrofluorimetric method has been developed for the determination of gallium in synthetically prepared Ga–U and Ga–As samples buffered at pH 4.0 using acetic acid–sodium acetate. The chelation reaction between Ga(III) and N-o-vanillidine-2-amino-p-cresol was very fast, requiring only 30 min at room temperature to complex completely. The limit of detection (LOD) (3σ) for Ga(III) was 7.17 nM (0.50 μg L^?1), determined from the analysis of 11 different solutions of 20 μg L^?1 Ga(III).     

Spectrophotometric determination of diphenhydramine hydrochloride in pharmaceutical preparations and biological fluids via ion-pair formation

A simple, sensitive and accurate spectrophotometric method has been described for the assay of diphenhydramine hydrochloride (DPH) in raw material and in biological samples. The method is based on extraction of DPH into dichloromethane as ion-pair complexes with patent blue (PB), eriochrome black T (EBT), methyl orange (MO) and bromocresol purple (BCP) in acidic medium. The coloured species exhibited absorption maxima at 632, 514, 428 and 414 nm for PB, EBT, MO and BCP, with molar absorptivity values of 1.32 × 10⁵, 2.36 × 10⁴, 3.68 × 10⁴ and 3.07 × 10⁴ l mol^?1 cm^?1, respectively. The reaction conditions were optimized to obtain the maximum colour intensity. Beer’s law was obeyed with a good correlation coefficient (0.9982–0.9993) in the concentration ranges 0.5–3, 2.0–16, 2.0–10 and 1.0–10 μg ml^?1 for PB, EBT, MO and BCP methods, respectively. The composition ratio of the ion-association complexes was found to be 1:1 in all cases as established by Job’s method. The conditional stability constant (K_f) and the free energy changes (ΔG°) were determined for all complexes formed. The proposed method was successfully applied for the determination of DPH in tablets and human urine with good accuracy and precision. Statistical comparison of the results with those obtained by the official method showed good agreement and indicated no significant difference in accuracy and precision.     

Development of a headspace–SPME–GC/MS method to determine volatile organic compounds released from textiles

A method for determining the volatile organic compounds (VOCs) in textiles was developed, by the use of high capacity headspace, solid phase micro extraction (SPME) and gas chromatography–mass spectrometry (GC/MS). The detection targets contained total organic compounds (TVOCs) and six specific substances (toluene, vinylcyclohexene, styrene, 4-phenylcyclohexene, vinylchloride and butadiene), according to Oeko-Tex Standard 100. A designed experiment was used to optimize the headspace–SPME–GC/MS operation, and the method was validated in terms of linearity, limit of detection (LOD) and method precision. It was found that at a loading ratio of 10 m²/m³, the LODs for toluene, vinylcyclohexene, styrene and 4-phenylcyclohexene were 0.0002 mg/m², 0.01 mg/m², 0.01 mg/m² and 0.0001 mg/m² respectively, while for vinylchloride and butadiene they were both 0.08 mg/m². SPME exhibited better adsorption performance for toluene, vinylcyclohexene, styrene and 4-phenylcyclohexene, for which the extraction fractions were 10 times of those for vinylchloride and butadiene. The method developed was successfully applied to analyze several commercial textiles, and would be a simple, efficient and promising technique for the analysis of volatile compounds from textiles or other samples (such as polymer materials).     

Dual-signal anodic stripping voltammetric determination of trace arsenic(III) at a glassy carbon electrode modified with internal-electrolysis deposited gold nanoparticles

A glassy carbon electrode (GCE) modified with internal-electrolysis deposited gold nanoparticles (AuNPs_ied) was applied to sensitively and selectively detect As(III) by anodic stripping linear sweep voltammetry (ASLSV). The AuNPs_ied/GCE was prepared based on the redox replacement reaction between a supporting-electrolyte-free aqueous HAuCl₄ and a copper sheet in saturated KCl separated by a salt bridge. Under optimum conditions (0.5 M aqueous H₂SO₄, 300-s preconcentration at − 0.4 V), the ASLSV peak current for the As(0)–As(III) oxidation responded linearly to As(III) concentration from 0.02 to 3 μM with a limit of detection (LOD) of 0.9 nM (0.07 μg L^− 1) (S/N = 3), while that for the As(III)–As(V) oxidation was linear with As(III) concentration from 0.02 to 1 μM with a LOD of 4 nM (0.3 μg L^− 1) (S/N = 3). An appropriate high-scan-rate for ASLSV can enhance both the sensitivity and signal-to-noise ratio. This method was applied for analyses of As(III) in real water samples.     

Validated voltammetric method for the determination of some antiprotozoa drugs based on the reduction at an activated glassy carbon electrode

A sensitive electrochemical procedure based on reduction of secnidazole (I), tinidazole (II) and ornidazole (III) at a glassy carbon electrode (GCE) was introduced. A study of the variation of the peak current with solution variables such as pH, ionic strength, concentration of drugs, possible interference, and instrumental variables such as scan rate, pulse amplitude, preconcentration time, accumulation potential, has resulted in the optimization of the reduction signal for analytical purposes. Linear calibration plots were obtained over the concentration ranges of 50–800, 50–750 μg mL^?1 for I, and both (II, III) respectively, in Britton–Robinson buffer of pH 7. The relative standard deviations of five replicate measurements of 1.0 and 10.0 μg mL^?1 of I, II and III concentrations were 4.7%, 4.9% and 5.3%, and 2.2%, 2.6% and 2.8%, respectively. The limits of detection (LOD) for I, II and III were found to be 2 × 10^?10, 3 × 10^?10 and 2.5 × 10^?10 mol L^?1 and limits of quantification (LOQ) for I, II and III were found to be 4.0 × 10^?8, 1.2 × 10^?8 and 4.4 × 10^?8 mol L^?1, respectively. The optimal conditions were: E_acc = ?0.9 V, t_acc = 30 s, scan rate = 20 mV s^?1, pulse-height = 90 mV and Britton–Robinson buffer of pH 7. The method was applied for the determination of the cited drugs both in raw materials and in pharmaceutical preparations with satisfactory results and compared with the official reference method. Complete validation of the proposed method was also done.     

Anodic stripping voltammetric analysis of trace arsenic(III) enhanced by mild hydrogen-evolution at a bimetallic Au–Pt nanoparticle modified glassy carbon electrode

A glassy carbon electrode (GCE) modified with electrodeposited bimetallic Au–Pt nanoparticles (Au–PtNPs) was applied to sensitively detect As(III) by linear sweep anodic stripping voltammetry (LSASV). In 0.5 M aqueous H₂SO₄, atomic hydrogen and molecular hydrogen were easily electrogenerated at the Pt sites on Au–PtNPs/GCE, which can chemically reduce As(III) to As(0) and enhance the cathodic preconcentration of As(0) at both the Pt sites and the neighboring Au sites. Since the As(0)–Au affinity is weaker than the As(0)–Pt affinity, the preconcentrated As(0) can be rapidly oxidized on/near the surface Au sites of Au–PtNPs/GCE, yielding sharper and higher LSASV current peaks. Under optimum conditions (700 s preconcentration at − 0.1 V, 5 V s^− 1), the LSASV peak current for the As(0)–As(III) oxidation responded linearly to As(III) concentration from 0.005 to 3.0 μM with a limit of detection (LOD) of 3.7 nM (0.28 ppb) (S/N = 3), while that for the As(III)–As(V) oxidation was linear with As(III) concentration from 0.01 to 3.0 μM with a LOD of 6.0 nM (0.45 ppb) (S/N = 3). This method was applied for analysis of As(III) in real water samples.     

Vacuum ultraviolet spectroscopic properties of rare earth (RE) (RE = Eu,Tb, Dy,Sm, Tm)-doped K2GdZr(PO4)3 phosphate

The luminescent characteristics of RE (RE³⁺ = Eu, Tb, Dy, Sm and Tm)-doped K₂GdZr(PO₄)₃ have been investigated. The band in the range of 130–157 nm in the VUV excitation spectra of these compounds is attributed to the host lattice or PO₄^3? group absorption and the band from 157 nm to 215 nm with the maximum at 188 nm is due to the O–Zr charge transfer transition. For Eu³⁺-doped sample, the relatively weak band of O^2?–Eu³⁺ charge transfer (CTB) at 222 nm is observed and for Tb³⁺-doped sample, the band at 223 nm is related to the 4f–5d spin-allowed transition of Tb³⁺. For Dy³⁺- and Sm³⁺-doped samples, the O^2?–Dy³⁺ and O^2?–Sm³⁺ CTBs have not been observed, probably due to the 2p electrons of oxygen tightly bound to the zirconium ion in the host lattice. In Tm³⁺-doped sample, the weak O^2?–Tm³⁺ CTB is located at 170 nm. It is observed that there is energy transfer between the host and the luminescent activators (e.g. Eu³⁺, Tb³⁺ and Sm³⁺) except for Tm³⁺.     

Simultaneous determination of ascorbic acid,epinephrine, and uric acid by differential pulse voltammetry using poly(p-xylenolsulfonephthalein) modified glassy carbon electrode

A novel poly(p-xylenolsulfonephthalein) modified glassy carbon electrode was prepared for the simultaneous determination of ascorbic acid (AA), epinephrine (EP) and uric acid (UA). Cyclic voltammetric, chronoamperometric, and differential pulse voltammetric methods were used to investigate the modified electrode for the electrocatalytic oxidation of EP, AA, and UA in aqueous solutions. The separation of the oxidation peak potentials for AA–EP and EP–UA was about 200 and 130 mV, respectively. The calibration curves obtained for AA, EP, and UA were in the ranges of 10–1343, 2–390, and 0.1–560 μmol L⁻¹, respectively. The detection limits (S/N = 3) were 4, 0.1, and 0.08 μmol L⁻¹ for AA, EP and UA, respectively. The diffusion coefficient and the catalytic rate constant for the oxidation of EP at the modified electrode were calculated as 1.40(±0.10) × 10⁻⁴ cm² s⁻¹ and 1.06 × 10³ mol⁻¹ L s⁻¹, respectively. The present method was applied to the determination of EP in pharmaceutical and urine samples, AA in commercially available vitamin C tablet, and EP plus UA in urine samples.     

Kinetic spectrophotometric determination of pravastatin in drug formulations via derivatization with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl)

A simple and sensitive kinetic spectrophotometric method for the quantitative analysis of pravastatin sodium (PVS) in pure and pharmaceutical formulations has been described. The method is based on the formation of colored product between PVS and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in acetone medium at 55 ± 2 °C. The reaction is followed spectrophotometrically by measuring the increase in absorbance at 462 nm as a function of time. The initial rate and fixed time methods were adopted for constructing the calibration curves. The linearity ranges were found to be 15.0–50.0 and 10.0–70.0 μg mL^?1 for initial rate and fixed time methods, respectively. The limits of detection for initial rate and fixed time methods are 0.029 and 0.086 μg mL^?1, respectively. Both methods have been applied successfully for the estimation of PVS in commercial dosage forms with no interference from the excipients. The results are compared with the HPLC pharmacopoeial method.     

Optical and dielectric properties of isothermally crystallized nano-KNbO3 in Er3+-doped K2O–Nb2O5–SiO2 glasses

Precursor glass of composition 25K₂O–25Nb₂O₅–50SiO₂ (mol%) doped with Er₂O₃ (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO₃ nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO₃ estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO₃ phase. The measured visible photoluminescence spectra have exhibited green emission transitions of ²H_11/2, ⁴S_3/2 → ⁴I_15/2 upon excitation at 377 nm (⁴I_15/2 → ⁴G_11/2) absorption band of Er³⁺ ions. The near infrared (NIR) emission transition ⁴I_13/2 → ⁴I_15/2 is detected around 1550 nm on excitation at 980 nm (⁴I_15/2 → ⁴I_11/2) of absorption bands of Er³⁺ ions. It is observed that photoluminescent intensity at 526 nm (²H_11/2 → ⁴I_15/2), 550 nm (⁴S_3/2 → ⁴I_15/2) and 1550 nm (⁴I_13/2 → ⁴I_15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime (τ_f) of the ⁴I_13/2 → ⁴I_15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er³⁺ ions gradually enter into the KNbO₃ nanocrystals.     

Spectrophotometric study of stability constants of cimetidine–Ni(II) complex at different temperatures

Cimetidine, a histamine H₂-receptor, has a structure which enables it to act as a chelating agent. The formation of nickel(II) complex with cimetidine has been studied spectrophotometrically at an absorption maximum of 622 nm at different temperatures. The data show that nickel(II) and cimetidine combine in the molar ratio of 1:2. The stability constants of the complex were calculated to be 1.40–2.4 × 10⁸ by continuous variation method and 1.24–2.4 × 10⁸ by mole ratio method at 25 and 40 °C, respectively. The immediately formed complex shows stability with respect to time and temperature.     

Spectrophotometric determination of carbamazepine and mosapride citrate in pure and pharmaceutical preparations

Simple, rapid and sensitive spectrophotometric methods were developed for the determination of carbamazepine and mosapride citrate drugs in pure and pharmaceutical dosage forms. These methods are based on ion pair and charge transfer complexation reactions. The first method is based on the reaction of the carbamazepine drug with Mo(V)–thiocyanate in hydrochloric acid medium followed by an extraction of the coloured ion-pair with 1,2-dichloroethane and the absorbance of the ion pair was measured at 470 nm. The second method is based on the formation of ion-pairs between mosapride citrate and two dyestuff reagents namely bromothymol blue (BTB) and bromocresol green (BCG) in a universal buffer of pH 4 and 3, respectively. The formed ion-pairs are extracted with chloroform and methylene chloride and measured at 412 and 416 nm for BTB and BCG reagents, respectively. The third method is based on charge transfer complex formation between mosapride citrate (electron donor) and DDQ (π-acceptor reagent) and the absorbance of the CT complexes was measured at 450 nm. All the optimum conditions are established. The calibration graphs are rectilinear in the concentration ranges 10–350 for carbamazepine using Mo(V)–thiocyanate and 4–100, 4–60 and 10–150 μg mL^?1 for mosapride citrate using BTB, BCG and DDQ reagents, respectively. The Sandell sensitivity (S), molar absorptivity, correlation coefficient, regression equations and limits of detection (LOD) and quantification (LOQ) are calculated. The law values of standard deviation (0.04–0.09 for carbamazepine using Mo(V)–thiocyanate and 0.022–0.024, 0.013–0.018 and 0.013–0.020 for mosapride citrate using BTB, BCG and DDQ, respectively) and relative standard deviation (0.630–2.170 for carbamazepine using Mo(V)–thiocyanate and 0.123–1.43, 0.102–0.530 and 0.226–1.280 for mosapride citrate using BTB, BCG and DDQ, respectively) reflect the accuracy and precision of the proposed methods. The methods are applied for the assay of the two investigated drugs in pharmaceutical dosage forms. The results are in good agreement with those obtained by the official method.