Spectrophotometric study of polythiazide—palladium(II) complex

A quantitative spectrophotometric method using Pd(II) chloride as analytical reagent for the determination of polythiazide in pharmaceutical preparations is described in this study. It has been found that polythiazide reacts with Pd(II) chloride in the pH range 3.6–5.8, forming a red, water-soluble (1:1) complex with maximum absorbance at 527 nm. At the optimum pH of 4.8 and an ionic strength μ = 0.1 M, the conditional stability constant of the complex is found to be log K′ = 4.77. The molar absorptivity at 527 nm is 3.2 × 10³ 1 mol⁻¹ cm⁻¹. Good agreement with Beer's law was found for polythiazide concentrations up to 2.2 mmol l⁻¹. The nominal percent recovery of polythiazide was 99.5% (n = 20). The simplicity, selectivity and sensitivity of the method described is suitable for rapid and accurate determinations of polythiazide in tablets.     

Spectrophotometric determination of oxytetracycline in pharmaceutical preparations using sodium molybdate as analytical reagent

A spectrophotometric method is proposed for the determination of oxytetracycline in pharmaceutical preparations. The method is based on the measurement of the absorbance of the molybdate—oxytetracycline complex at 404 nm (pH 5.50; μ = 0.1 M; 20°C). The composition of the complex (1:1) was determined by the application of the spectrophotometric methods of Job and Bent—French (pH 5.50; λ = 390 nm; μ = 0.1 M). The relative stability constant (K′ = 10^4.6) of the complex was obtained by the methods of Sommer and Nash (pH 5.50; λ = 390 nm; μ = 0.1 M; 20°C). The molar absorptivity of the complex was 9.5 × 10³ l mol⁻¹ cm⁻¹. Beer's law was obeyed over the concentration range 2.48–34.78 μg ml⁻¹. The relative standard deviation RSD (n = 10) was 0.27–0.39%. The method proposed can be applied to the assay of oxytetracycline in capsules. The detection limit of oxytetracycline is 2.5 μg ml⁻¹.     

Spectrophotometric determination of pefloxacin in pharmaceutical preparations

It has been established that the antibiotic pefloxacin (Abaktal) methane-sulphonate reacts with Fe(III) at pH 1.00–8.00 to form a water-soluble complex with maximum absorbance at 360 nm. The composition of the complex, determined spectrophotometrically by the application of Job's, molar-ratio and Bent—French's methods, was pefloxacin: Fe(III) = 1:1 (pH = 2.50; λ = 360 nm; μ = 0.1 M). The relative stability constant, obtained by the methods of Sommer and Asmus was 10^5.02 (pH = 2.50; λ = 360 nm; μ = 0.1 M). The molar absorptivity of the complex at 360 nm was found to be 4.8 × 10³ l mol⁻¹ cm⁻¹, Beer's law was followed for pefloxacin concentrations of 2.15–85.88 μg ml⁻¹. The lower sensitivity limit of the method was 2.15 μg ml⁻¹. The relative standard deviation (n = 10) was 0.57–1.07%. The method can be applied to the rapid and simple determination of pefloxacin in aqueous solutions and tablets.     

Use of xylenol orange and cetylpyridinium chloride in rapid spectrophotometric determination of zinc in pharmaceutical products

A simple, rapid, and sensitive spectrophotometric method for the determination of zinc(II) is performed, based on colour reaction between the metal ion and xylenol orange in the presence of surfactant cationic cetylpyridinium chloride. The important analytical parameters and their effects on the reported system are investigated. Zinc(II) reacts with the reagent and surfactant in the ratio 1:2:4 (metal:ligand:surfactant) in the pH range 5.0–6.0 to form a ternary complex with an absorption maximum at 580 nm. The reaction was extremely rapid at room temperature, and the absorbance value remains unchanged for at least 168 h. The apparent stability constant of the complex was found to be K=1.05×10¹⁰, and the method adheres to Beer's law for 1–20 μg zinc(II) per 25 ml with apparent molar absorptivity of 1.1×10⁴ l mol cm⁻¹. The effect of foreign ions was tested by taking a constant concentration of metal ion and determining its concentration in the presence of large number of foreign ions. The method was applied for determination of zinc(II) in dermal ointments where excellent agreement between reported and obtained results were achieved. The relative standard deviation was better than 2%.     

Determination of benzalkonium chloride in contact lens solutions by positive-ion fast atom bombardment mass spectrometry

Under positive-ion fast atom bombardment (FAB) mass spectrometric conditions, benzalkonium chloride (BAK) afforded intense peaks at m/z 304 and 332, corresponding to the intact cations [M---Cl]⁺ of C₁₂ and C₁₄ homologues, respectively. The use of benzethonium chloride as an internal standard and thioglycerol as a FAB matrix allowed the direct and specific determination of the BAK content (0.004–0.020%) in commercial hard contact lens solutions through the individual assay of the two alkyl homologues. A linear relationship between the homologue concentration and the peak—area ratio was observed over the concentration range 3–180 μg ml⁻¹.     

A rapid colorimetric method for the determination of Losartan potassium in bulk and in synthetic mixture for solid dosage form

Two new rapid reproducible and economical spectrophotometric methods are described for the determination of Losartan potassium in bulk and in synthetic mixture for solid dosage forms. Both methods are based on the formation of an orange-red and orange ion-pair complex due to the action of Calmagite (CT) and Orange-II (O-II) on Losartan potassium in acidic medium (pH 1.2). Under optimised conditions, they show an absorption maxima at 491 nm (CT) and 486 nm (O-II), with molar absorptivities of 1.74×10³ and 1.75×10³ l mol⁻¹ cm⁻¹ and Sandell's sensitivities of 0.2649 and 0.2637 per 0.001 absorbance unit for CT and O-II, respectively. The colour is stable for 5 min after extraction. In both cases Beer's law is obeyed between 10 and 100 μg ml⁻¹. The proposed method was successfully extended to synthetic mixture for solid dosage forms.     

Spectrophotometric and atomic absorption spectrometric determination of ramipril and perindopril through ternary complex formation with eosin and Cu(II)

Two sensitive, spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of ramipril and perindopril. Both methods are based on the formation of a ternary complex, extractable with chloroform, between copper(II), eosin and the two cited drugs. Spectrophotometrically under the optimum condition, the ternary complexes showed an absorption maximum at 535 nm, with apparent molar absorptivities of 6.55 and 4.00×10³ mol⁻¹cm⁻¹ and Sandell’s sensitivities of 5.80×10⁻² and 1.04×10⁻¹μg cm⁻² for perindopril and ramipril, respectively. The solution of ternary complex obeyed Beer’s law in concentration ranges 10–60 and 20–100 μg ml⁻¹ for perindopril and ramipril, respectively. The proposed method was applied to the determination of the two cited drugs in pharmaceutical tablets. The atomic absorption spectrometric method, directly through the quantitative determination of copper content of the organic extract of the complex, was also investigated for the purpose of enhancing the sensitivity of the determination. The spectrophotometric and atomic absorption spectrometric procedures hold their accuracy and precision well when applied to the determination of ramipril and perindopril dosage forms.     

Investigation of penbutolol—iron(III) complex and its spectrophotometric determination in tablets

It has been established that penbutolol reacts with iron(III) chloride in the presence of ammonium thiocyanate to form a pink complex (2:1) that is soluble in chloroform with a maximum absorbance at 478 nm. By application of the methods of Sommer and Job involving non-equimolar solutions, the conditional stability constant (log k′) of the complex at the optimum pH of 1.5±0.02 and an ionic strength of (μ) 0.14 M, was found to be 5.769. The molar absorptivity at 478 nm was 136 l mol⁻¹ cm⁻¹ at pH 1.5±0.02. The validity of Beer's law has been tested in the concentration range 3–18 × 10⁻⁴ M; the relative standard deviation (n = 8) was 1.52–3.21%. The proposed method was found to be suitable for the accurate, simple and rapid analysis of penbutolol in the bulk drug and in tablets.     

Lobeline inhibits nicotine-evoked [H]dopamine overflow from rat striatal slices and nicotine-evoked Rb efflux from thalamic synaptosomes

The present study evaluated the interaction of lobeline with neuronal nicotinic acetylcholine receptors using two in vitro assays, [³H] overflow from [³H]dopamine ([³H]DA)-preloaded rat striatal slices and ⁸⁶Rb⁺ efflux from rat thalamic synaptosomes. To assess agonist interactions, the effect of lobeline was determined and compared to S(−)-nicotine. To assess antagonist interactions, the ability of lobeline to inhibit the effect of S(−)-nicotine was determined. Both S(−)-nicotine (0.1–1 μM) and lobeline (>1.0 μM) evoked [³H] overflow from superfused [³H]DA-preloaded striatal slices. However, lobeline-evoked [³H] overflow is mecamylamine-insensitive, indicating that this response is not mediated by nicotinic receptors. Moreover, at concentrations (<1.0 μM) which did not evoke [³H] overflow, lobeline inhibited S(−)-nicotine (0.1–10 μM)-evoked [³H] overflow, shifting the S(−)-nicotine concentration–response curve to the right. S(−)-Nicotine (30 nM–300 μM) increased (EC₅₀ VALUE=0.2 μM) ⁸⁶Rb⁺ efflux from thalamic synaptosomes. In contrast, lobeline (1 nM–10 μM) did not evoke ⁸⁶Rb⁺ efflux, and the lack of intrinsic activity indicates that lobeline is not an agonist at this nicotinic receptor subtype. Lobeline completely inhibited (IC₅₀ VALUE=0.7 μM) ⁸⁶Rb⁺ efflux evoked by 1 μM S(−)-nicotine, a concentration which maximally stimulated ⁸⁶Rb⁺ efflux. Thus, the results of these in vitro experiments demonstrate that lobeline inhibits the effects of S(−)-nicotine, and suggest that lobeline acts as a nicotinic receptor antagonist.     

Biphasic effects of mianserin and desipramine on serotonin-evoked current and Cl- efflux in Xenopus oocytes.

Serotonin (5-HT, 1 μM) elicited two phases of Cl⁻ inward current in Xenopus oocytes injected with rat brain mRNA: a transient current (T-current), which was generated rapidly (within 1 min), and a sustained current (S-current), which persisted for 10 min. Each type of 5-HT-evoked response was time-dependent after mRNA injection. The T-current was generated at 20-30 h and the S-current at 30–40 h. Although mianserin at 0.1 μ M completely inhibited the T-current, 10 μ M mianserin was required to suppress the S-current. 5-HT also caused Cl⁻ efflux from oocytes preloaded with ³⁶Cl⁻, Cl⁻ efflux during 1 min, corresponding to the T-current, was inhibited by 0.1 μ M mianserin. A higher concentration of mianserin (10 μ M) was required to block the efflux for 10 min, corresponding to the S-current, as well as the current response. Desipramine selectively inhibited the T-current and Cl⁻ efflux for 1 min. The mechanisms underlying the different sensitivity to mianserin of oocytes injected with rat brain mRNA are discussed.     

Simultaneous separation and determination of active components in Cordyceps sinensis and Cordyceps militarris by LC/ESI-MS

A simple and rapid isocratic LC/MS coupled with electrospray ionization (ESI) method for simultaneous separation and determination of adenine, hypoxanthine, adenosine and cordycepin in Cordyceps sinensis (Cs) and its substitutes was developed. 2-Chloroadenosine was used as internal standard for this assay. The optimum separation for these analytes was achieved using the mixture of water, methanol and formic acid (85:14:1, v/v/v) as a mobile phase and a 2.0×150 mm Shimadzu VP-ODS column. Selective ion monitoring (SIM) mode ([M+H]⁺ at m/z 136, 137, 268, 252 and 302) was used for quantitative analysis of above four active components. The regression equations were liner in the range of 1.4–140.0 μg ml⁻¹ for adenine, 0.6–117.5 μg ml⁻¹ for hypoxanthine, 0.5–128.5 μg ml⁻¹ for adenosine and 0.5–131.5 μg ml⁻¹ for cordycepin. The limits of quantitation (LOQ) and detection (LOD) were, respectively 1.4 and 0.5 μg ml⁻¹ for adenine, 0.6 and 0.2 μg ml⁻¹ for hypoxanthine, 0.5 and 0.1 μg ml⁻¹ for adenosine and cordycepin. The recoveries of four constituents were from 93.5 to 107.0%. The nucleoside contents of various types of natural Cs and its substitutes were determined and compared with this developed method.     

Flow injection spectrophotometric determination of Al in hemodialysis solutions

A flow analysis (FA) system with spectrophotometric detection for Al determination in hemodialysis solutions was developed. The method was based on the reaction of Al with eriochrome cyanine R (ECR). The complex formed associated with cetyltrimethylammonium bromide (CTAB) — a cationic surfactant, which showed enough sensitivity to execute the direct analyte determination. All interferences were eliminated with the matrix matching calibration. The system presented the following analytic parameters: sensitivity (m) of 8.10 × 10⁻⁴ L μg⁻¹, limit of detection (LOD) of 3.24 μg L⁻¹ (3σ), linear correlation coefficient of 0.9966 and linear range response from 10.8 to 650 μg L⁻¹. The accuracy of the proposed method was checked by comparison with electrothermal atomic absorption spectrometry (ET-AAS) method. There were no differences among the results obtained from both methods, at a confidence level of 95% (paired t-test). Recovery tests were also made, values obtained were from 90.4 to 109 of recovery for Al-spiked samples.     

A capillary GC-MS method for analysis of phenytoin and [C3]-phenytoin from plasma obtained from pulse dose pharmacokinetic studies

Stable isotope analogues of phenytoin are useful for pulse dose pharmacokinetic studies in epilepsy patients. A simultaneous assay was developed to quantitate phenytoin (5,5-diphenylhydantoin) and its stable isotope analogue [¹³C₃]-phenytoin (5,5-diphenyl-2,4,5-¹³C₃-hydantoin) from plasma. Quantitation was achieved by GC-MS analysis of liquid/liquid extracted plasma samples, with [²H₁₀]-phenytoin (5,5-di(pentadeuterophenyl)-hydantoin) as an internal standard. The total coefficients of variance (C.V._t) were <7% for phenytoin (2.5–40 μg ml⁻¹) and <10.3% for [¹³C₃]-phenytoin (0.1–6.0 μg ml⁻¹). The accuracy of the assay varied from 87.8–100.1% (phenytoin, 2.5–40 μg ml⁻¹) and 89.6–116.3% ([¹³C₃]-phenytoin, 0.02–6.0 μg ml⁻¹). The assay was tested under in vivo conditions by administration of a pulse dose of the stable isotope analogue to a single rat dosed to steady-state with fosphenytoin, a phenytoin prodrug. The results of the in vivo experiment demonstrate the usefulness of this assay for future pharmacokinetic studies in special population epilepsy patients.     

Spectrophotometric determination of alendronate in pharmaceutical formulations via complex formation with Fe(III) ions

The formation of the complex between alendronate, non-chromophoric bisphosphonate drug important for the treatment of a variety of bone diseases, and iron(III) chloride in perchloric acid solution was studied. The stoichiometric ratio of alendronate to Fe(III) ions in the chromophoric complex was determined to be 1:1. The conditional stability constant was log K′_ave=4.50 (SD=0.15), indicating that the Fe(III)–alendronate complex is a complex of medium stability. The optimum conditions for this reaction were ascertained and a spectrophotometric method was developed for the determination of alendronate in the concentration range 8.1–162.5 μg ml⁻¹, the detection limit being 2 μg ml⁻¹. The method was validated for the direct determination of alendronate in tablet dosage formulations.     

Method development and validation for isoflavones in soy germ pharmaceutical capsules using micellar electrokinetic chromatography

The separation of six soy isoflavones (Glycitein, Daidzein, Genistein, Daidzin, Glycitin and Genistin) was approached by a 3² factorial design studying MEKC electrolyte components at the following levels: methanol (MeOH; 0–10%) and sodium dodecylsulfate (SDS; 20–70 mmol L⁻¹); sodium tetraborate buffer (STB) concentration was kept constant at 10 mmol L⁻¹. Nine experiments were performed and the apparent mobility of each isoflavone was computed as a function of the electrolyte composition. A novel response function (RF) was formulated based on the productory of the mobility differences, mobility of the first and last eluting peaks and the electrolyte conductance. The inspection of the response surface indicated an optimum electrolyte composition as 10 mmol L⁻¹ STB (pH 9.3) containing 40 mmol L⁻¹ SDS and 1% MeOH promoting baseline separation of all isoflavones in less than 7.5 min.

The proposed method was applied to the determination of total isoflavones in soy germ capsules from four different pharmaceutical laboratories. A 2 h extraction procedure with 80% (v/v) MeOH under vortexing at room temperature was employed. Peak assignment of unknown isoflavones in certain samples was assisted by hydrolysis procedures, migration behavior and UV spectra comparison. Three malonyl isoflavone derivatives were tentatively assigned. A few figures of merit for the proposed method include: repeatability (n = 6) better than 0.30% CV (migration time) and 1.7% CV (peak area); intermediate precision (n = 18) better than 6.2% CV (concentration); recoveries at two concentration levels, 20 and 50 μg mL⁻¹, varied from 99.1 to 103.6%. Furthermore, the proposed method exhibited linearity in the concentration range of 1.6–50 μg mL⁻¹ (r² > 0.9999) with LOQ varying from 0.67 to 1.2 μg mL⁻¹. The capsules purity varied from 93.3 to 97.6%.     

Bead injection spectroscopy-flow injection analysis (BIS-FIA): an interesting tool applicable to pharmaceutical analysis. Determination of promethazine and trifluoperazine

A bead injection spectroscopy-flow injection analysis (BIS-FIA) system for the spectrophotometric detection of promethazine and trifluoperazine is developed. The sensor is based in the oxidation of the phenothiazines by Fe(III) which is later determined by formation of the complex between Fe(II) and Ferrozine, [FeFz₃]⁴⁻. Immediately, this complex is retained on a homogeneous bead suspension of Sephadex QAE A-25 resin (500 μl) which has been injected previously in the system to fill a commercial flow-cell (Hellma 138-OS). The use of BI with respect to the use of a reusable flow-through sensor is justified because the complex is so strongly retained on the beads that the regeneration of the solid support becomes extraordinarily difficult in the proposed method. At the end of the analysis, beads are automatically discarded from the flow-cell, by reversing the flow, and transported out of the system. The analytical signals are measured at a wavelength of 567 nm, corresponding to the absorbance of the complex. Using a sample volume of 600 μl, the analytical signal showed a very good linearity in the range 0.5–8.0 μg ml⁻¹ and 0.5–10.0 μg ml⁻¹, with detection limits of 0.09 and 0.14 μg ml⁻¹ for promethazine and trifluoperazine, respectively. R.S.D.s (%) lower than 2% were obtained for both analytes. The proposed method is highly selective in the presence of other species that are normally encountered with these analytes. The sensor was satisfactorily applied to pharmaceutical preparations.     

Extraction spectrophotometric determination of aluminum in dialysis concentrates with 3,5-ditertbutylsalicylfluorone and ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate

The paper describes a highly sensitive and selective extraction spectrophotometric method for determination of aluminum in dialysis concentrates with new reagent 3,5-ditertbutylsalicylfluorone abbreviated as DTBSF, in which the ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate abbreviated as [C₄tmsim][PF₆] was used as novel medium for liquid/liquid extraction of aluminum(III). Under optimal condition, DTBSF reacted with aluminum(III) to form a neutral Al–DTBSF complex rapidly, the complex was then extracted into the [C₄tmsim][PF₆] phase, the absorbance of the complex in ionic liquid at 542 nm was recorded and used to determine aluminum(III). The apparent molar absorptivity of the complex and detection limit were found to be 3.52 × 10⁶ l mol⁻¹ cm⁻¹ and 0.06 μg/l, respectively. The absorbance of the complex at 542 nm increases linearly with the concentration of aluminum(III) up to 3 μg of aluminum(III) in 250 ml of aqueous solution. The interference study show the determination of aluminum is free from interferences of almost all positive and negative ions found in dialysis concentrate samples. The determination of aluminum in dialysis concentrates were carried out by the present method and electrothermal atomic absorption spectrometry (GTAAS). The results were satisfactorily comparable so that the applicability of the proposed method with the ionic liquid system was also investigated. Moreover, the synthesis of and conditions for the formation and extraction of Al–DTBSF complex were investigated as well.     

Determination of trace elements in a large series of spent peritoneal dialysis fluids by atomic absorption spectrometry

An analytical procedure is reported for the determination of six elements in a large series of spent dialysis fluid samples. Determinations of aluminium, chromium, copper, manganese and iron were made by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman background correction, while zinc was analysed by flame atomic absorption spectrometry (FAAS). Because of the complex matrix with high salt content and a high content of proteins, the measurement parameters were optimised for each particular element determined by ETAAS. The samples were collected in polyethylene eppendorf cups and stored in a freezer at −20°C. When the elements were determined by ETAAS the standard addition method was applied in the calibration procedure. The sample (10 μl) was injected into a cuvette and careful drying and long ashing of samples at temperatures between 850 and 1000°C performed. Triton X-100 was added before each determination to reduce the matrix effects of the proteins. Zinc was determined by FAAS in an air–acetylene flame under the usual recommended procedure, calibrating with aqueous standards. The limits of detection (3σ basis) were 1.0 μg l⁻¹ for aluminium, 0.20 μg l⁻¹ for chromium, 0.40 μg l⁻¹ for copper, 0.20 μg l⁻¹ for manganese, 0.50 μg l⁻¹ for iron and 5.0 μg l⁻¹ for zinc. The reproducibility of the measurements for aluminium, copper, iron and zinc was better than ±3.0%. It was worse for manganese and chromium (±6.0 and ±12.0%, respectively), since these two elements were present in very low concentrations in all the samples analysed.     

Differential Mechanisms Involved in the Effect of Nicotinic Agonists DMPP and Lobeline to Release [H]5-HT from Rat Hippocampal Slices

In the present study we investigated the effect of different nicotinic agonists (dimethylphenylpiperazinium-iodide (DMPP), (−)nicotine, cytisine, (−)-lobeline, and (−)epibatidine) and antagonists (mecamylamine and dihydro-β-erythroidine) on the release of [³H]5-HT from hippocampal slices. The nicotinic agonists DMPP and lobeline and electrical field stimulation, released [³H]5-HT from the hippocampus; other nicotinic agonists, such as (−)-nicotine, cytisine, and (−)-epibatidine had no effect. Unlike lobeline-induced release of [³H]5-HT, the effect of DMPP (10 and 40 μM) was antagonized by mecamylamine (20 and 10 μM). The effect of DMPP was [Ca²⁺]_o-independent. In experiments carried out at 7°C, i.e. the membrane carrier proteins are inhibited and the release by lobeline was abolished while the DMPP-induced release of 5-HT was rather potentiated. It is proposed that the effect of DMPP and lobeline, to enhance the release of [³H]5-HT from the hippocampus, was mediated by two different mechanisms. While DMPP-induced 5-HT release can be linked to a non-classical nAChR activation ([Ca²⁺]_o-independence), the effect of lobeline was likely mediated by uptake carriers. © 1997 Elsevier Science Ltd. All rights reserved.     

Similarities of the in vivo and in vitro effects of mercuric chloride on H]ouabain binding and potassium activation of Na/K-ATPase in isolated rat cerebral microvessels

A previous study revealed that a single i.p. administration of 6 mg/kg body wt. of mercuric chloride (MC) durably inhibits the rat cerebral microvascular Na⁺/K⁺-ATPase activity [1]. In this study, cerebral microvessels isolated 18 h after MC treatment were compared to those obtained from control rats and subsequently treated or not treated with MC in vitro, with regard to: (a) ³H]ouabain binding to, and (b) K⁺-activation kinetics of, the Na⁺/K⁺-ATPase. Microvessels from MC-treated rats showed a decrease of ³H]ouabain binding down to 62% of the control binding, and the same degree of inhibition was attained in microvessels treated in vitro with 5 μM MC. Analysis of the K⁺-activation kinetics of Na⁺/K⁺-ATPase revealed a decrease of V_max from the control value of 13.1 to 7.67 μmol/mg/h in microvessels from MC-treated rats and 6.07 μmol/mg/h in microvessels treated in vitro with 5 μM MC, with no change in K_m in either case. The similarity of the effects of in vivo and in vitro treatments suggests that the inhibition of the cerebromicrovascular Na⁺/K⁺ATPase following in vivo administration of MC results from a direct interaction of Hg⁺ with the enzyme.