Spectrophotometric and atomic absorption spectrometric determination of certain cephalosporins

Two sensitive spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of certain cephalosporins (cefotaxime sodium and cefuroxime sodium). The spectrophotometric methods are based on the charge-transfer complex formation between these drugs as n-donors and 7,7,8,8-tetracyano-quinodimethane (TCNQ) or p-chloranilic acid (p-CA) as π-acceptors to give highly coloured complex species. The coloured products are measured spectrophotometrically at 838 and 529 nm for TCNQ and p-CA, respectively. Beer’s law is obeyed in a concentration range of 7.6–15.2 and 7.1–20.0 μg ml⁻¹ with TCNQ, 95.0-427.5 and 89.0-400.5 μg ml⁻¹ with p-CA for cefotaxime sodium and cefuroxime sodium, respectively. The atomic absorption spectrometric methods are based on the reaction of the above cited drugs after their alkali-hydrolysis with silver nitrate or lead acetate in neutral aqueous medium. The formed precipitates are quantitatively determined directly or indirectly through the silver or lead content of the precipitate formed or the residual unreacted metal in the filtrate by atomic absorption spectroscopy. The optimum conditions for hydrolysis and precipitation have been carefully studied. Beer’s law is obeyed in a concentration range of 1.9–11.4 and 1.78–8.90 μg ml⁻¹ with Ag(I), 14.2–57.0 and 13.3–53.4 μg ml⁻¹ with Pb(II) for cefotaxime sodium and cefuroxime sodium, respectively (for both direct and indirect procedures). The spectrophotometric and the atomic absorption spectrometric procedures hold well their accuracy and precision when applied to the analysis of cefotaxime sodium and cefuroxime sodium dosage forms.     

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.     

Flow injection and HPLC determination of furosemide using pulsed amperometric detection at microelectrodes

The flow-injection and HPLC determination of the diuretic drug furosemide using pulsed amperometric detection (PAD) at cylindrical carbon fibre microelectrodes (CFMEs) is reported. Experimental conditions such as pH (6.5) and buffer concentration (0.05 mol l⁻¹ HPO₄²⁻/H₂PO₄⁻) were optimized using square-wave voltammetry (SWV). Repetitive flow-injection amperometric measurements at +1.25 V for furosemide showed a continuous decrease in the peak current, probably as a consequence of the microelectrode surface fouling. However, a suitable amperometric detection of furosemide was achieved using a PAD program consisting of a two-step potential waveform with alternating anodic and cathodic polarization. The anodic (detection) potential was +1.25 V (time of application 0.1 s), and the cathodic (cleaning) potential was −0.20 V (t=0.2 s). A linear calibration graph was obtained for furosemide in the 5.0×10⁻⁷–1.0×10⁻⁴ mol l⁻¹ concentration range, with a limit of detection of 1.7×10⁻⁷ mol l⁻¹. HPLC-PAD at carbon fibre microelectrodes was used for the determination of furosemide in the presence of several thiouracil drugs and oxytetracycline (OTC). The mobile phase selected was a 25:75 acetonitrile:5.0×10⁻³ mol l⁻¹ NaH₂PO₄ (pH 5.0) mixture. A linear calibration graph was obtained for furosemide in the 1–100 μM range, with a limit of detection of 0.55 μM. The usefulness of this method for the determination of furosemide in real samples was evaluated by performing the analysis of commercial milk samples spiked with furosemide at a concentration level of 4.5×10⁻⁷ mol l⁻¹ (150 ng ml⁻¹), as well as with other thiouracil drugs and OTC. A mean recovery of 95±5% furosemide was obtained.     

Spectrophotometric and AAS determination of ramipril and enalapril through ternary complex formation

Two sensitive, spectrophotometric and atomic absorption spectrometric procedures are developed for the determination of two antihypertensive agents (enalapril maleate and ramipril). The spectrophotometric procedures for the two cited drugs are based on ternary complex formation. The first ternary complex (copper(II), eosin, and enalapril) was estimated by two methods; the first depends on its extraction with chloroform measuring at 533.4 nm. Beer's law was obeyed in concentration range from 56 to 112 microg ml(-1). The second method for the same complex depends on its direct measurement after addition of methylcellulose as surfactant at the pH value 5 at 558.8 nm. The concentration range is from 19 to 32 microg ml(-1). The second ternary complex (iron(III), thiocyanate, and ramipril) was extracted with methylene chloride, measuring at 436.6 nm, with a concentration range 60-132 microg ml(-1). The direct atomic absorption spectrometric method through the quantitative determination of copper or iron content 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 enalapril dosage forms.     

Fluorimetric determination of some antibiotics in raw material and dosage forms through ternary complex formation with terbium (Tb(3+))

A highly sensitive and specific fluorimetric method was developed for the determination of cefazolin sodium I, cefoperazone sodium II, ceftriaxone sodium III, and cefixime IV. The proposed method involves the formation of ternary complex with Tb³⁺ in the presence of Tris buffer. The quenching of the terbium fluorescence due to the complex formation was quantitative for the four studied drugs. The effect of pH, concentration of Tris buffer and terbium were studied. The formation of the complex was highly dependent on the pH. The optimum pH was found to be pH 8 for cefazolin sodium I, ceftriaxone sodium III, cefixime IV and pH 10 for cefoperazone sodium II. The optimum concentration for Tb³⁺ was found 1 ml of 10⁻⁴ M solution and for Tris buffer 1 ml of the prepared solution. Under the described conditions, the proposed method was applicable over the concentration range 8.79×10⁻⁶–7.91×10⁻⁵, 9.7×10⁻⁶–4.49×10⁻5, 6.10×10⁻⁶–2.50×10⁻⁵, and 4.92×10⁻⁶–2.95×10⁻⁵ mol with mean percentage accuracy of 99.79±0.24, 98.97±1.25, 100.05±0.79, and 100.15±0.54 for I, II, III, and IV, respectively. The proposed method was applied successfully for the determination of studied drugs in bulk powder and in pharmaceutical formulations. The results obtained by applying the described method were statistically analyzed and compared with those obtained by applying the official method. The proposed method was used as stability indicating method for the determination of the studied drugs in the presence of their degradation products.     

Enzyme-amplified lanthanide luminescence based on complexation reaction--a new technique for the determination of doxycycline

A new spectrofluorimetric method is described for the determination of doxycycline, based on modified enzyme-amplified lanthanide luminescence. Under the optimum conditions, Eu³⁺–doxycycline forms a ternary complex with lysozyme in close proximity and lysozyme can remarkably enhance the characteristic fluorescence intensity of Eu³⁺ at 612 nm in doxycycline–Eu³⁺ binary complex. The enhanced fluorescence intensity is in proportion to the concentration of doxycycline. The limit of detection is 1.28×10⁻⁸ mol l⁻¹, with a linear range from 1.7×10⁻⁷ to 1.7×10⁻⁶ mol l⁻¹. Interferences of other coexisting substances were studied. The developed method was successfully applied to the determination of doxycycline in serum, urine and real samples. The mechanism of fluorescence enhancement was also studied.     

Polarographic determination of diazepam with its parallel catalytic wave in the presence of persulfate

A new method for the determination of diazepam was proposed based on its polarographic catalytic wave in the presence of persulfate. In 0.20 M NaAc–HAc (pH 4.7)–2.0×10⁻² M K₂S₂O₈ supporting electrolyte, the reduction wave of diazepam with peak potential −0.89 V (versus SCE) was catalyzed, producing a parallel catalytic wave. The peak current of the catalytic wave was 15 times higher than that of the corresponding reduction wave for 4.0×10⁻⁶ M diazepam, and was rectilinear to diazepam concentration in the range of 5.6×10⁻⁸ to 8.8×10⁻⁶ and 8.8×10⁻⁶ to 2.0×10⁻⁴ M. The detection limit was 9.6×10⁻⁹ M. The mechanism of the parallel catalytic wave of diazepam was discussed.     

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.     

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.     

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%.     

Preparation of a diclofenac potentiometric sensor and its application to pharmaceutical analysis and to drug recovery from biological fluids

A novel diclofenac ion-selective electrode is prepared, characterized and used in pharmaceutical analysis. The diclofenac complex with hexadecylpyridinium bromide is obtained in situ by soaking the PVC-membranes in a 1 × 10⁻² M diclofenac solution. Among four different solvent mediators tested, dibutyl phthalate (DBP) exhibited a proper behavior including Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of −59 ± 1 mV decade⁻¹ for diclofenac in the concentration range 1.0 × 10⁻⁵ to 1.0 × 10⁻² M with a limit of detection of 4.0 × 10⁻⁶ M. The electrode displays a good selectivity for diclofenac with respect to a number of common inorganic and organic species. It can be used in a pH range of 6.0–9.0. The membrane sensor was successfully applied to the determination of diclofenac in its tablets as well as for its recovery from blood serum and urine samples.     

Preparation of a cimetidine ion-selective electrode and its application to pharmaceutical analysis

A novel cimetidine ion-selective electrode is prepared, characterized and used in pharmaceutical analysis. The electrode incorporates PVC-membrane with cimetidine–phospohotungstate ion pair complex. The electrode exhibits a Nernstian response for cimetidine in the concentration range 1.0×10⁻⁵–1.0×10⁻² M with a slope of 58±1 mV per decade. The limit of detection is 5.0×10⁻⁶ M. The electrode displays a good selectivity for cimetidine with respect to a number of common foreign inorganic and organic species. It can be used in the pH range 3.0–5.5. The membrane sensor was successfully applied to the determination of cimetidine in its tablets as well as its recovery from a urine sample.     

The action of trelibet, a new antidepressive agent on [H]noradrenaline release from rabbit pulmonary artery

Trelibet, a new antidepressant, used at 10⁻⁷–10⁻⁴ M failed to affect the [³H]noradrenaline ([³H]NA) release evoked from the isolated main pulmonary artery of the rabbit low frequency (2 Hz) nerve stimulation whether the neuronal uptake inhibitor cocaine (3 × 10⁻⁵ M) was present or not. Its metabolite (EGYT-2760) however, potentiated the nerve-evoked release of [³H]NA. In the absence of cocaine both the resting and the stimulation-evoked release of ³H increased in response to EGYT-2760. These effect were accompanied by muscle contraction. The EGYT-2760-potentiated transmitter release was inhibited either by exogenously applied 1-noradrenaline (10⁻⁶ M) or clonidine (10⁻⁶ M), preferential agonists of presynaptic ₂-adrenoceptors. The 1-noradrenaline-induced inhibition of transmitter release potentiated by EGYT-2760 was antagonized by 3 × 10⁻⁷ M yohimbine, a preferential ₂-adrenoceptor inhibitor. In the absence of cocaine, Ca²⁺ removal from the external medium failed to affect the ³H outflow-increasing effect of EGYT-2760 but abolished the nerve-evoked release-potentiating action of this compound. It is concluded that the metabolite of trelibet exerts a ‘yohimbine-like’ action, as well as a ‘tyramine-like’ effect in peripheral sympathetic nerve fibres.     

Potentiometric sensor for methylene blue based on methylene blue–silicotungstate ion association and its pharmaceutical applications

A methylene blue (MB) poly(vinyl chloride) membrane sensor based on MB–silicotungstate (SLT) ion association as electroactive material was described. The linear response covered the range 1×10⁻³–1×10⁻⁶ mol dm⁻³ MB solution, with a slope 52.0±0.8 mV decade⁻¹ (pH range 3.0–10.0). The detection limit was 7.65×10⁻⁷ mol dm⁻³. The electrode showed stability, good reproducibility and fast response. Interferences from common inorganic cations, some organic base were negligible. These characteristics of the electrode enabled it to be used successfully for the determination of MB in injection. There was a good agreement for the results of MB content in injection between potentiometric method and USP standard procedure.     

Lung tissue binding of iodobenzyl-propanediamine: Involvement of beta-adrenergic receptors

The basic compound N-N-N′-trimethyl-N′-(2-hydroxy-3-methyl-5-iodobenzyl)-1,3-propanediamine (HIPDM) accumulates in human and rabbit lungs, where it forms a slowly effluxable pool. In isolated perfused rat lung, HIPDM is taken up by a saturable, energy-independent mechanism, which is competitively inhibited by imipramine, chlorpromazine and propranolol. To ascertain whether beta-adrenergic receptors are involved in the binding process of HIPDM to lung tissue, the ability of unlabelled HIPDM to displace the beta-adrenergic receptor ligand [¹²⁵I]iodocyano-pindolol (ICYP) from rabbit lung beta-receptors was examined. Lung microsomal membrane fractions (75 μg ml⁻¹) were incubated at 37°C for 3 h with 68 pM ICYP (with or without 1 μM of (±)-propranolol) in the presence of HIPDM (10⁻¹⁰−10⁻³ M). Bound and free radioactivity were separated through glass-fibre filters and the retained radioactivity was counted in a gamma-spectrometer. HIPDM competed with ICYP for beta-adrenoceptors (13% displacement at 10⁻⁵ M, 50% at 5 × 10⁻⁵ M, and 90% at 2 × 10⁻⁴ M). The inhibition curve of ICYP binding by HIPDM was similar to that observed for (−)-noradrenaline. Although the results of the in vitro studies cannot be extrapolated to in vivo conditions, they suggest that beta-adrenergic receptors may be involved in the observed lung uptake of the basic amine HIPDM.     

Study on the fluorescence system of chlortetracycline-Eu-TOPO-sodium dodecyl sulfonate and the determination of chlortetracycline

The fluorescence system of Eu-chlortetracycline-TOPO-sodium dodecyl sulfonate was studied. It was found that chlortetracycline formed a complex with Eu(III) at pH 8.0–9.0 and then emitted the characteristic fluorescence of Eu(III). TOPO and sodium dodecyl sulfonate greatly enhanced the fluorescence intensity of the system. The experiments indicated that under the optimum determining conditions a linear relationship was obtained between the fluorescence intensity and chlortetracycline concentration in the range of 2.0 × 10⁻⁸−1.0 × 10⁻⁵ M. The detection limit was 6.0 × 10⁻⁹ M. In addition, the luminescence mechanism of the complex system has been discussed.     

Flow-injection amperometric determination of dopamine in pharmaceuticals using a polyphenol oxidase biosensor obtained from soursop pulp

The amperometric determination of dopamine (Do) in pharmaceuticals formulations by flow injection analysis (FIA) is proposed. An enzymatically modified carbon paste electrode constituted by 25% (w/w) of polyphenol oxidase obtained from Annona muricata L. tissue, 30% (w/w) of graphite, 30% (w/w) of silicone and 15% (w/w) of 7,7,8,8 tetracyanoquinodimethane (TCNQ), was used as flow-through detector. The flow amperometric detection was carried out at a potential of 0.10 V (vs. Ag/AgCl) when an injected sample volume of 250 μl was inserted on a 0.3 M phosphate buffer carrier solution (pH 7.8) flowing at 2.5 ml/min. The developed biosensor showed good stability and reproducibility, enabling up to 500 determinations in 60 days, without considerable loss of enzymatic activity. The FIA system presented a linear response to Do concentrations in the interval from 2×10⁻² to 2×10⁻⁴ M, with relative standard deviations lower than 1.5%. The kinetic parameter K_M for the soluble and immobilized enzyme was 1.45×10⁻² and 1.91×10⁻² M, respectively. In the analyses of different commercially pharmaceutical formulations a relative deviation lower than about 3.4% was obtained.     

Effects of papaverine on isolated rabbit papillary muscle

The effect of papaverine on the positive inotropic response to isoprenaline and to calcium was studied on the rabbit isolated papillary muscle; theophylline and the calcium antagonistic D600 were used for comparison. The dose—response curve for isoprenaline was shifted to the left by papaverine (3 × 10⁻⁶ to 3 × 10⁻⁵ M), in a dose-dependent manner, while that for calcium was not affected by the same concentration. In this respect papaverine was about 30 times more potent than theophylline. In the presence of papaverine isoprenaline induced arrhythmic contractions of the papillary muscle: the incidence of arrhythmic contractions correlated to the concentration of papaverine. Papaverine 10⁻⁵ to 10⁻⁴ M caused only a positive inotropic response whereas 3 × ⁻¹⁰ to 10⁻³ M induced a biphasic response, i.e., after a positive inotropic effect followed a negative one. In the presence of 3 × 10⁻⁴ M papaverine isoprenaline failed to cause a positive inotropic response but exclusively induced arrhythmic contractions. Calcium, on the other hand, readily antagonized the negative inotropic effectof papaverine (3 × 10⁻⁴ M) and caused a contracture of the papillary muscle. The results indicate that papaverine (3 × 10⁻⁶ to 10⁻⁵ M) like theophylline (10⁻⁴ to 10⁻³ M) produces its effect by phosphodiesterase inhibition and thereby specifically potentiates the response through β-adrenoceptor stimulation. In higher concentrations (3 × 10⁻⁴ to 10⁻³ M) it act as a calcium antagonistic, like D600, and furthermore may interact with calcium moving through myocardial cell membranes to cause a contracture via a mechanism which it shares with theophylline.     

Polarographic behavior of cephalexin and its determination in pharmaceuticals and human serum

Cephalexin gives a reduction wave in 0.03 mol/l HCl medium at ca. −1.24 V. With cephalexin concentration higher than 2.5×10⁻⁵ mol/l, another reduction wave is observed at ca. −0.90 V. These reduction waves are attributed to the reduction of ethylenic bond of a six-membered dihydrothiazine ring. When H₂O₂ is present, the reduction wave at ca. −0.90 V is catalyzed by H₂O₂ and its reduction intermediate hydroxyl radical √OH, producing a catalytic wave. However, the reduction wave at ca. −1.24 V remains nearly unchanged. A sensitive polarographic method for the determination of cephalexin is proposed based on the reduction wave of cephalexin. The second-order derivative peak current of the wave at ca. −1.24 V is rectilinear to the cephalexin concentration in the range 1.0×10⁻⁷ to 2.5×10⁻⁵ mol/l, and the detection limit is 5.0×10⁻⁸ mol/l. The proposed method is applied to the individual tablet dosage form and human serum.     

Voltammetric investigation of diethylstilbestrol

In this work electrooxidation of diethylstilbestrol (DES) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using a glassy carbon (GC) electrode. It was statistically shown that both methods could be used for the determination of DES in the concentration range of 2×10⁻⁵–6×10⁻⁴ M by CV and 1×10⁻⁵–1×10⁻³ M in methanol (MeOH) and 4×10⁻⁵–6×10⁻⁴ M in acetonitrile (ACN) by DPV and both of the methods could be applied to human serum. A mechanism was proposed about the electrooxidation of this substance.