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.     

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.     

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.     

The effect of trimethyltin on acetylcholine release in the guinea-pig trachea

The purpose of the present work was to characterise the effects of trimethyltin on the release of acetylcholine from parasympathetic nerves and its effect on the postjunctional cholinergic stimulation of a smooth muscle. The guinea-pig trachea has been used as a model. Prejunctionally, trimethyltin (3.0 × 10⁻³ M) significantly enhanced in a reversible manner the high K⁺ (75 mM) evoked release of endogenous acetylcholine and [³H]acetylcholine. The evoked release of endogenous acetylcholine and [³H]acetylcholine was released from a pool of acetylcholine being independent of extraneuronal Ca²⁺ in the presence, but not in the absence of trimethyltin. The effect of trimethyltin on the release was not inhibited by low Ca²⁺ (0 mM and 1.0 × 10⁻⁴ M) or by Ca²⁺ channel blockers (verapamil, 1.0 × 10⁻⁴ M, flunarizine, 1.0 × 10⁻⁴ M, ω-conotoxin GVIA, 2.0 × 10⁻⁷ M and ω-agatoxin, 2.0 × 10⁻⁷ M). The present results also demonstrate that trimethyltin induce emptying of a non-vesicular, probably a cytoplasmic storage pool of acetylcholine, since AH5183 (2.0 × 10⁻⁵ M), an inhibitor of the translocation of acetylcholine into synaptic vesicles, and -latrotoxin (1.0 × 10⁻⁸ M), a toxin from black widow spider venom inducing vesicle depletion, had no inhibitory effects on the release of [³H]acetylcholine evoked by trimethyltin (3.0 × 10⁻³ M). The release of [³H]acetylcholine was moreover enhanced by trimethyltin when the vesicular uptake of [³H]acetylcholine was inhibited by AH5183, probably as a result of a higher cytoplasmic concentration of [³H]acetylcholine. Trimethyltin also reduced the neuronal uptake of [³H]choline and this was probably due to a depolarising effect of trimethyltin on the cholinergic nerve terminals. A similar depolarisation induced by trimethyltin was observed during patch clamping of GH₄ C₁ neuronal cells. Postjunctionally, trimethyltin had no effect by itself or on the carbachol-induced smooth muscle contraction, indicating that trimethyltin did not have a general depolarising effect on smooth muscle cells or an effect on muscarinic receptors. Furthermore, the reduced electrical field-induced contraction and the subsequent increase in the basal smooth muscle tension that was observed by addition of trimethyltin was activity-dependent, and was most probably due to emptying of a nervous non-vesicular storage pool of acetylcholine, followed by rapid hydrolysis of acetylcholine by acetyl- and pseudocholinesterases.     

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.     

Use of palladium(II) chloride as colour-forming reagent in determination of pralidoxime chloride in water and tablets

Pralidoxime chloride (PAM-2Cl) has been determined spectrophotometrically in Britton—Robinson buffer solution at pH = 6.45; the method is based on measurement of the absorbance of the Pd(II)-pralidoxime complex at 327 nm. Studies of the composition of the complex by Job's continuous variation method, the molar ratio method and Bent—French's method yielded a Pd(II):pralidoxime ratio of 1:1. The conditional stability constant (K′) of the complex at the optimum pH of 6.45 and an ionic strength (μ) of 0.3 M was found to be 10^5.2. The molar absorptivity was 1.05 × 10⁴ 1 mol⁻¹ cm⁻¹. Beer's law was obeyed at concentrations up to 60 μM. The detection limit was 0.55 μg ml⁻¹. The relative standard deviation (N = 10) was 0.28–1.03%. The method was accurate and sensitive for the analysis of PAM-2Cl in water and tablets.     

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.     

KATP channels do not mediate vasodilation by 3-morpholinosydnonimine in goat coronary artery

The present study investigated the role of ATP-sensitive potassium (K_ATP) channels in mediating relaxation to the nitric oxide (NO) donor, 3-morpholinosydnonimine (SIN-1) in goat coronary arteries. SIN-1 (10⁻⁸–10⁻⁵ M) caused concentration-dependent relaxations of the coronary artery ring segments contracted with K⁺ (30 mM) with an EC₅₀ of 6.61×10⁻⁷ M. Methylene blue (3×10⁻⁶ M) caused a rightward shift in the concentration–response curve of SIN-1 (10⁻⁸–3×10⁻⁵ M) with a corresponding increase in the EC₅₀ (3.62×10⁻⁶ M) of the nitrovasodilator. While the K_ATP channel blocker, glibenclamide (1 and 3×10⁻⁶ M) caused dose-dependent inhibition of vasorelaxations produced by pinacidil (10⁻⁸–10⁻⁴ M), it had no effect on the vasodilations elicited by SIN-1 (10⁻⁸–10⁻⁵ M) in the coronary arterial smooth muscle. Increasing the extracellular K⁺ concentration from 30 mM to 80 mM to reduce the K⁺ gradient across the cell membrane, inhibited the relaxations elicited by pinacidil (10⁻⁸–10⁻⁴ M). On the other hand, SIN-1 (10⁻⁸–10⁻⁵ M)-induced relaxations were potentiated in high K⁺ (80 mM) compared to those observed at K⁺ (30 mM). These results suggest that goat coronary artery vasodilations caused by the NO donor, SIN-1, do not involve K_ATP channels.     

Poly(ethylene-co-methyl acrylate) membranes as rate-controlling barriers for drug delivery systems: characterization, mechanical properties and permeability

Poly(ethylene-co-methyl acrylate) (EMA) membranes with different amounts of methyl acrylate (MA) content were studied in terms of the thermal and mechanical properties, swelling and drug permeation. The increase in MA content in the copolymer significantly increased the percentage of elongation and decreased the tensile strength and modulus of elasticity of the membranes. The degree of swelling of the EMA membranes increased with the ethanol composition and MA content. The contact angle of a sessile drop (10 μL of ethanol/water solution) decreased with an increase in the ethanol fraction suggesting that the membrane wettibility increased with the ethanol content. The flux of diltiazem hydrochloride increased from 0.012 to 0.018 mg cm⁻² h⁻¹ with an increase in the MA content from 16.5 to 29.0%. By increasing the ethanol fraction from 0.4 to 1.0, the flux of diltiazem hydrochloride into the membranes with 29.0% MA, increased from 2.56 (±0.09)×10⁻³ to 18.38 (±0.62)×10⁻³ mg cm⁻² h⁻¹. The permeability coefficient increased from 5.85×10⁻⁶ to 3.53×10⁻⁴ cm h⁻¹ with an increase in the ethanol fraction. The flux can also be correlated with the drug solubility in the membrane and ethanol. For example, the solubilities of diltiazem hydrochloride, paracetamol and ibuprofen were 0.64, 6.68 and 504.48 mg cm⁻³ in the membrane, respectively. Under the same conditions, the flux for the above mentioned drugs was 0.08 (±0.01), 0.53 (±0.01) and 45.11 (±2.00) mg cm⁻² h⁻¹.     

A surface plasmon resonance method for detecting multiple modes of DNA-ligand interactions

A simple and general surface plasmon resonance (SPR) based method has been developed to detect and quantitate binding of low molecular weight compounds (200–1200 Da) to double stranded DNA. Several compounds were chosen to probe three different modes of binding interactions, intercalation, minor groove binding and electrostatic interactions. Ethidium bromide (MW 390 Da), a probe of intercalative binding, was tested by plotting the steady state SPR responses measured on a DNA modified surface versus ethidium bromide concentration. The best fit of the binding isotherm gave a K_eq of 1.8×10⁵ M⁻¹. Co-solvents such as DMSO are often used in activity assays to increase the solubility of poorly water-soluble drugs. The effect of DMSO on the ethidium bromide/DNA interaction was also tested by measuring binding in the presence of 0, 1 and 5% DMSO. No effect on the measured K_eq was observed at these DMSO concentrations. The binding of actinomycin (MW 1255 Da), an antibiotic known to bind DNA through intercalation and minor groove binding, was also tested. The K_eq estimated from the steady state responses on a DNA surface was 1.9×10⁶ M⁻¹. DAPI (MW 350 Da) (4′,6-diamidino-2-phenylindole) a fluorescent probe which binds the minor groove of DNA was also tested and gave a K_eq of 1.8×10⁶ M⁻¹ measured by SPR. Finally, spermine (MW 202) a compound known to bind DNA through ionic interactions gave the weakest K_eq of 1.7×10⁴ M⁻¹. All the K_eq values measured by SPR and reported for these compounds were in good agreement with literature values measured by other techniques.     

Definition of the alpha-KTx15 subfamily

Three novel scorpion toxins, Aa1 from Androctonus australis, BmTX3 from Buthus martensi and AmmTX3 from Androctonus mauretanicus were shown able to selectively block A-type K⁺ currents in cerebellum granular cells or cultured striatum neurons from rat brain. In electrophysiology experiments, the transient A-current completely disappeared when 1 μM of the toxins was applied to the external solution whereas the sustained K⁺ current was unaffected.

The three toxins shared high sequence homologies (more than 94%) and constituted a new ‘short-chain’ scorpion toxin subfamily: -KTx₁₅. Monoiododerivative of ¹²⁵I-sBmTX3 specifically bound to rat brain synaptosomes. Under equilibrium binding conditions, maximum binding was 14 fmol/mg of protein and the dissociation constant (K_d) was 0.21 nM. This K_d value was confirmed by kinetic experiments (k_on=6.0×10⁶ M⁻¹ s⁻¹ and k_off=6.0×10⁻⁴ s⁻¹). Competitions with AmmTX3 and Aa1 with ¹²⁵I-sBmTX3 bound to its receptor on rat brain synaptosomes showed that they fully inhibited the ¹²⁵I-sBmTX3 binding (K_i values of 20 and 44 pM, respectively), demonstrating unambiguously that the three molecules shared the same target in rat brain. A panel of toxins described as specific ligands for different K⁺, Na⁺ and Ca²⁺ channels were not able to displace ¹²⁵I-sBmTX3 from its binding site. Thus, ¹²⁵I-sBmTX3 is a new ligand for a still unidentified target in rat brain. In autoradiography, the distribution of ¹²⁵I-sBmTX3 binding sites in the adult rat brain indicated a high density of ¹²⁵I-sBmTX3 receptors in the striatum, hippocampus, superior colliculus, and cerebellum.     

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 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.     

Growth promoting and metabolic activity of the human insulin analogue [Gly,Arg,Arg]insulin (HOE 901) in muscle cells

[Gly^A21,Arg^B31,Arg^B32]insulin (HOE 901) represents a biosynthetic human insulin analogue that, due to its isoelectric point, precipitates at neutral tissue pH leading to a retarded absorption rate and a corresponding longer duration of action. In the present investigation we have evaluated the growth promoting and metabolic activity of this analogue in muscle tissue using exponentially growing H9c2 cardiac myoblasts and adult rat ventricular cardiomyocytes. Equilibrium binding studies of ¹²⁵I-labelled IGF-I (insulin-like growth factor I) to differentiating myoblasts revealed the presence of 7×10³ IGF-I receptors per cell. In contrast, no specific binding of insulin could be detected. Competition binding experiments showed a slightly higher affinity of HOE 901 for the IGF-I receptor when compared to regular human insulin with IC₅₀ (half-inhibitory concentration) values of 70 and 101 nM, respectively. However, the supermitogenic insulin analogue [Asp^B10]insulin competed significantly more efficiently for IGF-I binding (IC₅₀: 44 nM). Maximum growth promoting activity of the peptides was then determined in serum-starved myoblasts by an incubation with the peptides (5×10⁻⁷ M) for 16 h in the presence of [³H]thymidine. [Asp^B10]Insulin produced a stimulation of DNA synthesis (about 3-fold) which was comparable to the effect of IGF-I and significantly (P<0.005) higher than the effect of HOE 901 with the latter being essentially equipotent to native insulin. Comparable results were obtained at lower concentrations of the peptides (10⁻⁹ to 10⁻⁸ M). Metabolic activity of HOE 901 was determined by measuring the dose-dependent stimulation of 3-O-methylglucose transport in adult cardiomyocytes. Maximum transport stimulation was identical for insulin and HOE 901 with EC₅₀ (half-effective concentration) values of 0.7×10⁻¹⁰ and 1.9×10⁻⁹ M, respectively. We concluded that the IGF-I receptor-mediated growth promoting activity of HOE 901 in muscle cells and the maximal metabolic activity of this analogue are not different from those of native human insulin. It is suggested that differential interaction with IGF-I receptors significantly contributes to the action profile of insulin analogues.     

Simultaneous LC determination of paracetamol and related compounds in pharmaceutical formulations using a carbon-based column

A simple, rapid and convenient high performance liquid chromatographic method, which permits the simultaneous determination of paracetamol, 4-aminophenol and 4-chloracetanilide in pharmaceutical preparation has been developed. The chromatographic separation was achieved on porous graphitized carbon (PGC) column using an isocratic mixture of 80/20 (v/v) acetonitrile/0.05 M potassium phosphate buffer (pH 5.5) and ultraviolet detection at 244 nm. Correlation coefficient for calibration curves in the ranges 1–50 μg ml⁻¹ for paracetamol and 5–40 μg ml⁻¹ for 4-aminophenol and 4-chloroacetanilide were >0.99. The sensitivity of detection is 0.1 μg ml⁻¹ for paracetamol and 0.5 μg ml⁻¹ for 4-aminophenol and 4-chloroacetanilide. The proposed liquid chromatographic method was successfully applied to the analysis of commercially available paracetamol dosage forms with recoveries of 98–103%. It is suggested that the proposed method should be used for routine quality control and dosage form assay of paracetamol in pharmaceutical preparations. The chromatographic behaviour of the three compounds was examined under variable mobile phase compositions and pH, the results revealed that selectivity was dependent on the organic solvent and pH used. The retention selectivity of these compounds on PGC was compared with those of octadecylsilica (ODS) packing materials in reversed phase liquid chromatography. The ODS column gave little separation for the degradation product (4-aminophenol) from paracetamol, whereas PGC column provides better separation in much shorter time.     

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.     

Carbon film resistor electrode for amperometric determination of acetaminophen in pharmaceutical formulations

Flow injection analysis (FIA) with amperometric detection was employed for acetaminophen quantification in pharmaceutical formulations using a carbon film resistor electrode. This sensor exhibited sharp and reproducible current peaks for acetaminophen without chemical modification of its surface. A wide linear working range (8.0 × 10⁻⁷ to 5.0 × 10⁻⁴ mol L⁻¹) in phosphate buffer solution as well as high sensitivity (0.143 A mol⁻¹ L cm⁻²) and low submicromolar detection limit (1.36 × 10⁻⁷ mol L⁻¹) were achieved. The repeatability (R.S.D. for 10 successive injections of 5.0 × 10⁻⁶ and 5.0 × 10⁻⁵ mol L⁻¹ acetaminophen solutions) was 3.1 and 1.3%, respectively, without any memory effect between injections. The new procedure was applied to the analyses of commercial pharmaceutical products and the results were in good agreement with those obtained utilizing a spectrophotometric method. Consequently, this amperometric method has been shown to be very suitable for quality control analyses and other applications with similar requirements.     

LC determination of dinitrosopiperazine in simulated gastric juice

A simple and specific reversed phase HPLC method for the determination of dinitrosopiperazine in simulated gastric juice using UV detection was reported. The chromatographic resolution of the analyte and the internal standard isosorbide dinitrate was performed without extraction from the gastric juice on a reversed phase ODS column. Isocratic elution was carried out with methanol–0.02 M sodium dihydrogen phosphate (60:40 v/v, pH 3.0) at a flow rate of 1.0 ml min⁻¹ with UV detection at 238 nm. The calibration graph was linear over the concentration range 0.072–2.88 μg ml⁻¹ of dinitrosopiperazine with minimum detectability (S/N=2) of 0.01 μg ml⁻¹ (8×10⁻⁸ M). Inter-day and intra-day precisions calculated as% RSD were in the range 0.32–0.38% and 0.19–0.25% respectively. Inter-day and intra-day accuracies calculated as% error were in the range 0.18–0.21 and 0.08–0.11% respectively. The proposed method was successfully applied to the study of the possible in–vivo production of DNPZ under the standard nitrosation conditions recommended by WHO.     

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.