Three simple spectrophotometric methods for the determination of sulphinpyrazone

Three simple and sensitive spectrophotometric methods for the determination of sulphinpyrazone (SP) in bulk samples and pharmaceutical formulations are described. They are based on the oxidation of sulphinpyrazone with excess N-bromosuccinimide (NBS) and determination of the unconsumed NBS with metol-isonicotinic acid hydrazide (method A, lambda(max): 620 nm); by the reduction of Folin-Ciocalteu reagent (method B, lambda(max) 770 nm); or by the formation of a chloroform-soluble, coloured ion-association complex between the drug and Methylene Violet (MV) at pH 7.0 (method C, lambda(max) 545 nm).     

Spectrophotometric determination of astemizole

Four simple and sensitive spectrophotometric methods for the determination of astemizole (AZ) in pure samples and pharmaceutical formulations are described. They are based on the oxidation of astemizole with excess N-bormosuccinimide (NBS) and determination of the unconsumed NBS with, metol-sulphanilamide (method A, lambda(max): 520 nm) or celestine blue (method B, lambda(max): 540 nm); or by the reduction of Folin-ciocalteu reagent (method C, lambda(max): 720 nm); or by the formation of a chloroform-soluble, coloured ion-association complex between the drug and azocarmine G (AG) at pH 1.5 (method D, lambda(max); 540 nm). The results obtained are reproducible with a coefficient of variation of less than 1.0%.     

Determination of doxorubicin hydrochloride by visible spectrophotometry

Four simple and sensitive visible spectrophotometric methods (A-D) have been described for the assay of doxorubicin hydrochloride either in pure form or in pharmaceutical formulations. Method A was developed based on oxidation of the drug with Fe(III) to produce Fe(II), which subsequently reacts with 1.10-ortho-phenanthroline to form a red colored complex (lambda(max): 510 nm) at pH 4.6. Method B involves the reduction of Folin-Ciocalteu (F-C) reagent by the drug and the reduced species formed possesses a characteristic intense blue color (lambda(max): 770 nm). In methods C and D. oxidation of the drug with periodate at specified experimental conditions yields formaldehyde and dialdehyde, which in turn react either with 3-methyl-2-benzothiazolinone hydrazone hydrochloride to form an intensely brilliant blue cationic dye (lambda(max): 620-670 nm. method C) or by condensation with phenylhydrazine hydrochloride (PHH) to form orange-red colored product (lambda(max): 510 nm, method D) in the presence of potassium ferricyanide. All of the variables have been optimized and the reaction mechanisms presented. The concentration measurements are reproducible within a relative standard deviation of 1.0%.     

Spectrophotometric methods for the determination of prazosin hydrochloride in tablets

Four simple and sensitive methods for the assay of prazosin hydrochloride (PRH) are developed. These methods are based on the formation of coloured species by treating it either with excess N-bromosuccinimide (NBS) and determining the unconsumed NBS with p-N-methyl aminophenol sulphate (metol)-sulphanilamide (SA) reagent (method A, lambda(max) 520 nm): with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in the presence of eerie ammonium sulphate (CAS) (method B, lambda(max) 620 nm) or with acidic dyes such as orange-II (O-II) (method C, lambda(max) 490 nm) and alizarin violet 3B (AV-3B) (method D, lambda(max) 570 nm) under the specified experimental conditions. Regression analysis of Beer's law plot showed good correlation in the concentration range of 1.0-10.0, 2.5-25.0, 1.0-17.5 and 2.5-30.0 mug ml for methods A, B, C and D respectively.     

Utility of oxidation-reduction reaction for the determination of ranitidine hydrochloride in pure form,in dosage forms and in the presence of its oxidative degradates

Three simple, accurate and sensitive colorimetric methods (A, B and C) for the determination of ranitidine HCl (RHCl) in bulk sample, in dosage forms and in the presence of its oxidative degradates are described. The first method A is based on the oxidation of the drug by N-bromosuccinimide (NBS) and determination of the unreacted NBS by measurement of the decrease in absorbance of amaranth dye (AM) at a suitable lambda(max)=520 nm. The methods B and C involve the addition of excess Ce(4+) and determination of the unreacted oxidant by decrease the red color of chromotrope 2R (C2R) at a suitable lambda(max)=528 nm for method B or decrease the orange pink color of rhodamine 6G (Rh6G) at a suitable lambda(max)=526 nm for method C. Regression analysis of Beer-Lambert plots showed good correlation in the concentration ranges 0.2-3.6, 0.1-2.8 and 0.1-2.6 microg ml(-1) for methods A, B and C, respectively. The apparent molar absorptivity. Sandell sensitivity, detection and quantitation limits were calculated. For more accurate results, Ringbom optimum concentration ranges were 0.3-3.4, 0.2-2.6 and 0.2-2.4 microg ml(-1) for methods A, B and C, respectively. Analyzing pure and dosage forms containing RHCl tested the validity of the proposed methods. The relative standard deviations were 相似文献   

Spectrophotometric estimation of ketotifen fumarate in pharmaceutical formulations

Four simple and sensitive spectrophotometric methods (A–D) for the determination of Ketotifen fumarate in bulk samples and pharmaceutical formulations are described. They are based on the formation of coloured species by the coupling of the diazotised sulphanilamide with the drug (method A, _max 520 nm) or by oxidizing it with excessN-bromo-succinimide and determining the consumed NBS with decrease in colour intensity of celestine blue (method B: _max 540 nm) or by the reduction of Folin-Ciocalteau reagent (method C: _max 720 nm) or by the formation of a chloroform-soluble, coloured ionassociation complex between the drug and Azocarmine G at pH 1.5 (method D: _max 540 nm). Regression analysis of Beer-Lambert plots showed good correlations in the concentration ranges 1–10, 2–12, 4–28 and 2.5–25 g/ml for methods A–D, respectively. The validity of the proposed methods was tested by analysing pharmaceutical formulations containing KTF: the relative standard deviations were within ±1.0%. Recoveries were 98.9–100.2%.     

Organogermanium reactive intermediates. The direct detection and characterization of transient germylenes and digermenes in solution

Diphenylgermylene (Ph2Ge) and its Ge=Ge doubly bonded dimer, tetraphenyldigermene (6a), have been characterized directly in solution for the first time by laser flash photolysis methods. The germylene is formed via (formal) cheletropic photocycloreversion of 3,4-dimethyl-1,1-diphenylgermacyclopent-3-ene (4a), which is shown to proceed in high chemical (>95%) and quantum yield (phi = 0.62) by steady-state trapping experiments with methanol, acetic acid, isoprene, and triethylsilane. Flash photolysis of 4a in dry deoxygenated hexane at 23 degrees C leads to the prompt formation of a transient assigned to Ph2Ge (lambda(max) = 500 nm; epsilon(max) = 1650 M(-1) cm(-1)), which decays with second-order kinetics (tau approximately 3 micros), with the concomitant growth of a second transient species that is assigned to digermene 6a (tau approximately 40 micros; lambda(max) = 440 nm). Analogous results are obtained from 1,1-dimesityl- and 1,1-dimethyl-3,4-dimethylgermacyclopent-3-ene (4b and 4c, respectively), which afford Mes2Ge (tau approximately 20 micros; lambda(max) = 560 nm) and Me2Ge (tau approximately 2 micros; lambda(max) = 480 nm), respectively, as well as the corresponding digermenes, tetramesityl- (6b; lambda(max) = 410 nm) and tetramethyldigermene (6c; lambda(max) = 370 nm). The results for the mesityl compound are compared to the analogous ones from laser flash photolysis of the known Mes2Ge/6b precursor, hexamesitylcyclotrigermane. The spectra of the three germylenes and two of the digermenes are in excellent agreement with calculated spectra, derived from time-dependent DFT calculations. Absolute rate constants for dimerization of Ph2Ge and Mes2Ge and for their reaction with n-butylamine and acetic acid in hexane at 23 degrees C are also reported.     

Spectrophotometric determination of mebeverine hydrochloride

Three simple, sensitive and reproducible visible spectrophotometric methods (A-C) for the determination of mebeverine hydrochloride (MVH) in bulk samples and pharmaceutical formulations are described. Methods A and B are based on the formation of ion-association complexes between the drug and fast green FCF (FGFCF, _max 625 nm) or bromothymol blue (BTB, _max 405 nm). Method C is based on the formation of a molecular complex between the drug and cobalt thiocyanate (CTC, _max 625 nm). Regression analysis of Beer's plots showed good correlation in the concentration ranges 2–40, 2–25 and 100–600 g/ml for methods A, B and C respectively. No interference was observed from the usually existing additives in pharmaceutical formulations and the applicability of the methods was examined by analysing tablets containing MVH. Standard deviations were typically 0.75 mg per dose (RSD: 0.25–0.5%). Recoveries were 99.0–100.2%.     

TD-DFT investigation of the UV spectra of pyranone derivatives

The UV absorption spectra of more than 80 substituted coumarins and chromones have been investigated with the PCM-TD-DFT theoretical scheme using three hybrid functionals (O3LYP, B3LYP, and PBE0) and taking into account methanol or ethanol solvation effects. For most of the studied derivatives, there are at least two allowed excited states presenting a strong oscillator strength in the UV region. The first allowed excitation is associated to a HOMO-LUMO transition whereas the second corresponds to a transition from the HOMO-1 to the LUMO. Both involve a charge transfer from the benzenic cycle to the pyranone moiety. Statistically treating the PBE0 results allows a prediction of the lambda(max) with small standard deviations: in methanol, 6 nm (0.07 eV) for the first excitation (lambda(max)(1)) and 5 nm (0.08 eV) for the second one (lambda(max)(2)), whereas in ethanol 6 nm (0.08 eV) for (lambda(max)(1)) and 6 nm (0.13 eV) for (lambda(max)(2)).     

Determination of iron(II) with bipyridylglyoxal dithiosemicarbazone

Bipyridylglyoxal dithiosemicarbazone reacts with iron(II) or (III). The Fe(III) complex is yellow (lambda(max) 400 nm). Fe(II) forms a red-violet 1:2 complex at pH 2.5 (lambda(max) 550 nm) and a green-blue 1:1 complex at pH 5-10 (lambda(max) 590-610 nm). Both ferrous complexes can be oxidized to the ferric complex; this reaction is reversible. The quantitative application of the ferrous complex has been studied.     

Spectrophotometric determination of some histamine H1-antagonists drugs in their pharmaceutical preparations

Two rapid, simple and sensitive extractive specrophotometric methods has been developed for the determination of three histamine H1-antagonists drugs, e.g., chlorphenoxamine hydrochloride (CPX), diphenhydramine hydrochloride (DPH) and clemastine (CMT) in bulk and in their pharmaceutical formulations. The first method depend upon the reaction of molybdenum(V) thiocyanate ions (Method A) with the cited drugs to form stable ion-pair complexes which extractable with methylene chloride, the orange red color complex was determined colorimetrically at lambda(max) 470nm. The second method is based on the formation of an ion-association complex with alizarin red S as chromogenic reagents in acidic medium (Method B), which is extracted into chloroform. The complexes have a maximum absorbance at 425 and 426nm for (DPH or CMT) and CPX, respectively. Regression analysis of Beer-Lambert plots showed a good correlation in the concentration ranges of 5.0-40 and 5-70microgmL(-1) for molybdenum(V) thiocyanate (Method A) and alizarin red S (Method B), respectively. For more accurate analysis, Ringbom optimum concentration ranges were calculated. The molar absorptivity, Sandell sensitivity, detection and quantification limits were calculated. Applications of the procedure to the analysis of various pharmaceutical preparations gave reproducible and accurate results. Further, the validity of the procedure was confirmed by applying the standard addition technique and the results obtained in good agreement well with those obtained by the official method.     

High-performance liquid chromatographic assay of pirlimycin in human serum and urine using 9-fluorenylmethylchloroformate

A reversed-phase high-performance liquid chromatographic (HPLC) assay method has been developed for determining pirlimycin in human serum and urine. The method involves chloroform extraction of pirlimycin free base followed by derivatization with 9-fluorenylmethylchloroformate to form a carbamate ester. The reaction is rapid, reproducible, and quantitative. 9-Fluorenylmethylchloroformate reacts with amines to form derivatives sensitive to both ultraviolet and fluorescence detection. Human serum and urine samples following 50-mg and 500-mg single oral doses of pirlimycin were analyzed. The samples were chromatographed on an RP-18 Spherisorb 5-micron, 250 X 4.6 mm I.D. reversed-phase HPLC column. The eluent for the serum assay was acetonitrile-water (58:42) containing 0.02% acetic acid, and for the urine assay was acetonitrile-methanol-tetrahydrofuran-water (48:2:1:49). Fluoranthene was used as an internal standard. The assay sensitivity by ultraviolet detection (lambda max = 264) was about 5 ng/ml and by fluorescence detection (lambda excitation = 270 nm, lambda emission = 300 nm) was 0.1 ng/ml. Statistical analysis indicates an average drug recovery of 101 +/- 4.2% from serum and 102.0 +/- 2.62% from urine.     

Sensitive spectrofluorimetric determination of ruthenium at nanotrace levels using 2-(alpha-pyridyl) thioquinaldinamide [PTQA

A new spectrofluorimetric method for the determination of ruthenium with nonfluorescent 2-(alpha-pyridyl) thioquinaldinamide (PTQA) is described. The oxidative reaction of Ru(III) upon PTQA gives oxidised fluorescent product (lambda(ex(max))=347 nm; lambda(em(max))=486 nm). The sensitivity of the fluorescence reaction between ruthenium and PTQA is greatly increased in the presence of Fe (III). The reaction is carried out in the acidity range 0.01-0.075 M H(2)SO(4). The influence of reaction variables is discussed. The range of linearity is 1-400 microg l(-1) Ru(III). The standard deviation and relative standard deviation of the developed method are +/-1.210 microg l(-1) Ru (III) and 2.4%, respectively (for 11 replicate determinations of 50 microg l(-1) Ru (III)). The effect of interferences from other metal ions, anions and complexing agents was studied; the masking action is discussed. The developed method has been successfully tested over synthetic mixtures of various base metals and platinum group metals, synthetic mixtures corresponding to osmiridium, certified reference materials in spiked conditions and rock samples.     

Comparison of three spectrophotometric methods for the determination of gamma-oryzanol in rice bran oil

A comparison of the results obtained by applying three spectrophotometric methods (at fixed wavelength, second-derivative and multicomponent analysis) to the determination of gamma-oryzanol in rice bran oil is reported.At fixed wavelength the results are more accurate when using isopropyl alcohol, rather than n-heptane, to dilute the oil samples, because the absorption bands of gamma-oryzanol are red-shifted and the absorbance, measured at lambda(max)=327 nm, is less affected by the interference of the oil "matrix" (lambda(max)=314 nm in n-heptane).However, to obtain accurate results also in oils with a low content of gamma-oryzanol, it is necessary to perform the analysis using second-derivative ((2)D330.365) or multicomponent (lambda=310-360 nm) methods. The first one fully removes the interference of oil matrix whilst the second, which needs a specific computational program to process the spectrophotometric data, furnishes evidence the presence of some unexpected interference in the analysis and/or standards which are not representative of the analysed samples, from the square root of the sum of the squared differences at each point between the linear combination of the standards and the unknown spectra (RMS error).Finally, some aspects of the chemical, spectroscopic (UV, IR) and thermoanalytical (TG, DSC) behaviour of gamma-oryzanol and the values of the parameters which enable "computation" of its UV spectra are reported.     

Bioluminescence color determinants of Phrixothrix railroad-worm luciferases: chimeric luciferases, site-directed mutagenesis of Arg 215 and guanidine effect

Chimeric proteins were produced using the green light-emitting luciferase of Phrixothrix vivianii (PxGr: lambda max = 548 nm) and the red light-emitting luciferase of Phrixothrix hirtus (PxRe: lambda max = 623 nm). Constructs containing residues 1-344 of the red light-emitting luciferase with residues 345-545 of the green light emitting one emitted red light (PxReGr; lambda max = 613 nm), while the reverse emitted green light (PxGrRe; lambda max = 552 nm). From these results we conclude that the region 1-344 determines the color of bioluminescence (BL) in railroad-worm luciferases, and that residues above 344 are not involved. The substitution R215S in the green light-emitting luciferase (PxGr) resulted in a approximately 40 nm redshift on the BL spectrum (lambda max = 585 nm) and an associated decrease of activity, whereas the same mutation in PxRe luciferase had little effect. Guanidine was shown to cause blueshifts in the BL spectra and stimulate the activity of the red-emitting luciferases (from lambda max = 623 to lambda max = 600 nm) and in PxGr R215S (from lambda max = 585 to lambda max = 560 nm) mutant luciferase, but not in the green-emitting luciferases, suggesting that guanidine can simulate positively charged residues involved in BL color determination.     

ABSORPTION AND PHOTOCHEMISTRY OF SENSORY RHODOPSIN—I: pH EFFECTS

Pyranine (8-hydroxyl-1,3,6-pyrene-trisulfonate) was used as a pH-probe to test whether there is a light-induced proton release to the bulk phase during the photochemical reaction cycle of sensory rhodopsin-I (SR-I). We conclude that the retinylidene Schiff-base proton is retained by SR-I-containing envelope vesicles during the SR-I photocycle under the conditions described here. Bacteriorhodopsin containing vesicles were used as a control to show that light-induced proton release can be observed under identical data acquisition parameters as those used for SR-I-containing vesicles. In addition, the effects of extravesicular pH on the absorption maximum (lambda max) and the SR-I photocycle were studied. SR-I properties are insensitive to pH in the range approximately 3 to approximately 8 with lambda max remaining at 587 nm. The lambda max shifts to 565 nm below pH 3.0 and to 552 nm at pH 10.8 with an apparent pKa of 8.5. Flash-induced absorbance changes of SR-I are described under neutral, alkaline and acidic conditions. The neutral, alkaline and acid SR-I forms each undergo similar photoreactions producing long-lived (> 500 ms decay half-time) blue-shifted intermediates. The UV/near-UV absorption of the photoproducts from neutral and alkaline SR-I indicate a deprotonated Schiff base, whereas acid SR-I produces a species with lambda max > 460 nm indicative of a protonated Schiff base.     

The facile generation of a tetramethyleneethane type radical cation and biradical utilizing a 3,4-di(alpha-styryl)furan and a photoinduced ET and back ET sequence

Product analyses and nanosecond time-resolved spectroscopy on laser flash photolysis were studied for the photoinduced electron-transfer reaction of 3,4-di(alpha-styryl)furan (6a). A combination of these results, kinetic, density functional theoretical (DFT), and time-dependent DFT analyses enabled assignment of the absorption to the tetramethyleneethane (TME)-type radical cation (7a*+, lambda(max) = 392 nm) and the corresponding singlet biradical ((1)7a**, lambda(max) = 661 nm). These two intermediates were mechanistically linked to each other with a facile back electron-transfer reaction. The present studies provide a new method for the generation of aryl-substituted TME-type intermediates.     

Coloured complexes of all-trans-retinal with benzocaine and other local anaesthetics

Coloured Schiff base complexes with lambda max values of 500 nm or above were formed between the visual pigment all-trans-retinal and the local anesthetics procaine (lambda max = 533 nm), benzocaine (4-amino-benzoic acid ethyl ester, lambda max = 535 nm), 3-amino-benzoic acid ethyl ester (lambda max = 500 nm) and 2-amino-benzoic acid ethyl ester (lambda max = 509 nm) in methanol acidified with HCl. The anaesthetics lidocaine and urethane failed to form coloured compounds with lambda max values greater than 500 nm under the same conditions. The relevance of these observations to the effect of anaesthetics on the visual pigments is discussed.     

FIA-spectrophotometric determination of N-substituted phenothiazine derivatives by oxidation with a solid-phase reactor of manganese dioxide incorporated in polyester resin beads

The determination of several N-substituted phenothiazine derivatives was carried out by the reaction of the drug with managanese dioxide entrapped in a polymeric material in a packed-bed reactor; the oxidized drug was monitored at lambda(max). The calibration graph is linear over the range 5-50 mug/ml of phenothiazine derivatives with a relative standard deviation of 0.5-1% (at 10 mug/ml) and sample throughput of 40-48 h(-1). The influence of foreign compounds was studied and the method was applied to the determination of six different phenothiazine derivatives in pharmaceutical formulations.     

Characterization of reactive intermediates generated during photolysis of 4-acetoxy-4-aryl-2,5-cyclohexadienones: oxenium ions and aryloxy radicals

Aryloxenium ions 1 are reactive intermediates that are isoelectronic with the better known arylcarbenium and arylnitrenium ions. They are proposed to be involved in synthetically and industrially useful oxidation reactions of phenols. However, mechanistic studies of these intermediates are limited. Until recently, the lifetimes of these intermediates in solution and their reactivity patterns were unknown. Previously, the quinol esters 2 have been used to generate 1, which were indirectly detected by azide ion trapping to generate azide adducts 4 at the expense of quinols 3, during hydrolysis reactions in the dark. Laser flash photolysis (LFP) of 2b in the presence of O(2) in aqueous solution leads to two reactive intermediates with lambda(max) 360 and 460 nm, respectively, while in pure CH(3)CN only one species with lambda(max) 350 nm is produced. The intermediate with lambda(max) 460 nm was previously identified as 1b based on direct observation of its decomposition kinetics in the presence of N(3)(-), comparison to azide ion trapping results from the hydrolysis reactions, and photolysis reaction products (3b). The agreement between the calculated (B3LYP/6-31G(d)) and observed time-resolved resonance Raman (TR(3)) spectra of 1b further confirms its identity. The second intermediate with lambda(max) 360 nm (350 nm in CH(3)CN) has been characterized as the radical 5b, based on its photolytic generation in the less polar CH(3)CN and on isolated photolysis reaction products (6b and 7b). Only the radical intermediate 5b is generated by photolysis in CH(3)CN, so its UV-vis spectrum, reaction products, and decay kinetics can be investigated in this solvent without interference from 1b. In addition, the radical 5a was generated by LFP of 2a and was identified by comparison to a published UV-vis spectrum of authentic 5a obtained under similar conditions. The similarity of the UV-vis spectra of 5a and 5b, their reaction products, and the kinetics of their decay confirm the assigned structures. The lifetime of 1b in aqueous solution at room temperature is 170 ns. This intermediate decays with first-order kinetics. The radical intermediate 5b decomposes in a biphasic manner, with lifetimes of 12 and 75 mus. The decay processes of 5a and 5b were successfully modeled with a kinetic scheme that included reversible formation of a dimer. The scheme is similar to the kinetic models applied to describe the decay of other aryloxy radicals.