Cathode ray polarography and differential pulse polarography of the catalytic molybdenum(VI) wave

The optimum conditions of electrolyte composition and pH were studied for the cathode ray polarography (c.r.p.) of the catalytic molybdenum(VI) wave; 1–2 M potassium nitrate at pH 1.6–2.2 is optimum, the detection limit is 3 × 10^-9 M (0.3 ppb) molybdenum(VI). Equal molar concentrations of foreign electroactive substances do not interfere at the potential of the molybdenum wave and 500-fold amounts of these can be tolerated if their c.r.p. peaks are separated from the molybdenum wave by 0.1 or 0.2 V. Similar conditions were used for the differential pulse polarography of the catalytic wave. The detection limit is 2 × 10^-8 M (2 ppb). being limited in part by lead impurities which contribute to the background.     

An electroanalytical study of the anticancer drug dacarbazine

The electrochemical behaviour of dacarbazine [5-(3,3-dimethyl-1-triazenyl) imidazole-4-carboxamide; DTIC] was investigated by Tast and differential pulse polarography (d.p.p.) at the dropping mercury electrode, by cyclic and differential pulse voltammetry at the hanging mercury drop electrode and by anodic voltammetry at the glassy carbon electrode. Calibration graphs were obtained for 2×10^?8?2×10^?5 M DTIC by d.p.p., for 5×10^?9?1×10^?5 M by adsorptive stripping voltammetry ar a hanging mercury drop electrode, and for 1?10×10^?5 M by high-performance liquid chromatography with oxidative amperometric detection at a glassy carbon electrode. The methods are compared and applied to determine DTIC added to blood serum after a simple clean-up procedure.     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.     

Adsorptive stripping voltammetry of chlordiazepoxide at the hanging mercury drop electrode

Controlled adsorptive accumulation at the hanging mercury drop electrode enables 0.8–11 × 10^?5 M chlordiazepoxide to be quantified by differential-pulse stripping voltammetry with accumulation times of 1–3 min. With 3-min accumulation, the peak current is enhanced 12-fold for 1.0 × 10^?7 M chlordiazepoxide compared to the current from differential pulse polarography. The detection limit is 0.9 × 10^?9 M for 4-min accumulation. The procedure is applied to spiked human serum after preseparation of the drug on a Sep-Pak C₁₈ cartridge.     

Contamination of water and organic solvents stored in plastic bottles with phthalate ester plasticizers

Migration of phthalic acid esters into water, n-hexane, and methanol kept in polyethy-lene bottles or PVC tubes was investigated by high-performance liquid chromatography with a variable wavelength u.v. detector. The content of esters in water kept in contact with PVC for one day was 0.44 ppm and the migration rate of dibutyl phthalate was 4.8 × 10^-5 mg h^-1 cm^-2 of PVC tube. n-Hexane stored in a polyethylene bottle for 7 days contained 6 ppm esters; the migration rate of dibutyl phthalate was 6.4 × 10^-5 mg h^-1 cm^-2 of polyethylene. PVC tubing connected to ion-exchange resin columns contaminates deionized water with the esters.     

Determination of Methimazole and Carbimazole Using Polarography and Voltammetry

Abstract

Anodic waves of methimazole (I) (1-methylimidazole-2-thiol) and carbimazole (II) (1-ethoxycarbonyl-3-methyl-2-thio-4-imidazoline) on mercury electrodes correspond to mercury salt formation. Both compounds form in the thiono form a soluble complex at pH < 6, compound (I) at higher pH-values a slightly soluble salt of the thiol form. Electrode processes involving the thiol form are complicated by adsorption. Oxidation at solid electrodes occurs only at potentials more than 0.5 V more positive. For compound (I) spectrophotometry indicated pK_a=12.0 ± 0.2. By d.c. polarography in 0.1 M H₂SO₄ containing 10% ethanol the determination of both compounds is possible between 4 × 10^? and 1 × 10^?3 M, by differential pulse polarography between 1 × 10^? and 1 × 10^?4 M, by differential pulse voltammetry at HMDE between 5 × l0^?7 and 6 × 10^? M.     

Determination of chlorite at very low levels by using differential pulse polarography

A method is reported for the determination of μgl^?1 levels of chlorite by using differential pulse polarography. The electrochemical reduction of chlorite was studied between pH 3.7 and 14 and in an ionic strength range of 0.05–3.0 M. The optimum conditions are pH 4.1–4.4 and an ionic strength of 0.45 M. The current under these conditions is diffusion-controlled and is a linear function of chlorite concentration ranging from 2.77×10^?7 to 2.80×10^?4 M (19 μgl^?1 to 19 mg l^?1). The imprecision is better than ±1.0% and ±3.4% at concentrations of 2.87×10^?5 M and 1.74×10^?6M, respectively, with a detection limit of 1×10^?7 M (7μgl^?1). An interference study and the application of this method for determining chlorite in drinking water are reported.     

Polarographic study of 1-methyl-5-o-chloropheyl-7- ethyl-1,2-dihydro-3H-thieno[2,3-e],[1,4]-diazepin-2-one (clotiazepam)

The electroeducation of 1-methyl-5-o-chlorphenyl-7-ethyl-1,2-dihydro-3H-thieno[2,3-e],[1,4]-diazepin-2-one (Clotiazepam) is investigated by different polarographic techniques. The electrochemical reactioninvolves a 2-electron exchange in both acidic and alkaline media. The reduction process is irreversible and the current is diffusion-controlled. With differential pulse polarography, the linear response range is 6.5 × 10^-7— 1.10 × 10^?5 M, with a relative standard deviationof 1.2% at the 2.6 × 10^?6 M level. The method is applied to the determinationof Clotiazepam in tablets after simple dissolution in 0.1 M sulphuric acid.     

Flow-injection determination of sodium and potassium by separationon a silica column and extraction-spectrophotometry with benzo-18-crown-6 and tetrabromophenolphthalein ethyl ester

Sodium and potassium ions in waters are determined by flow-injection extraction-spectrophotometry. The ion-association complexes formed between the metal/crown ether cations and the tetrabromophenolphthalein ethyl ester anion (TBPE^-) are extracted into chlorobenzene/benzene (1:3) and the absorbance of the organic phase is measured after phase separation with a porous membrane. Sodium and potassium are separated on-line with a column (1 mm i.d.×30 cm) packed with silica gel (100-200 mesh). The manifold comprises four streams, each at 0.8 ml min^?1. The sample is injected into a water stream and mixed with a reagent stream containing lithium acetate and benzo-18-crown-6 before entering the silica gel column; after the separation, the stream is mixed with EDTA (trilithium salt) and lithium hydroxide, and then with the extraction solution containing TBPE.H. Extraction proceeds in a 2-m coil; the absorbance of the organic phase is measured at 620 nm. CAlibration graphs are linear inthe ranges 0–×10^?3 M sodium and 0–2×10^?4 M potassium. The sample throughput is 15 h^?1. The procedure is applicable to river and tap waters.     

Novel Potentiometric Sensors for Determination of Melatonin and Oxomemazine in Biological Samples and in Pharmaceutical Formulations

Simple, selective and accurate sensors were developed for the determination of melatonin and oxomemazine in biological samples (urine) and in pharmaceutical preparations. Potentiometric measurements were based on bismus tetraiodate‐drug ion‐pair as novel electroactive materials incorporating a plasticized PVC membrane with o‐nitrophenyl octyl ether or dioctyl phthalate. Each sensor was conditioned for at least two days in 0.1 M drug solution before use. It exhibited fast and stable Nernstian response for melatonin and oxomemazine over the concentration range of 1.0×10^?6–1.0×10^?2 M and 1.0×10^?5–1.0×10^?2 M, pH range of 3.0–6.5 and 3.5–6.0 for melatonin and oxomemazine sensors, respectively. Results with an average recovery not more than 101 % and a mean standard deviation less than 1.0 % of the nominal were obtained for the four sensors. The sensors showed reasonable selectivity towards investigated drugs in presence of many cations.     

Extraction-spectrophotometric determination of mercury with 1,2,4,6-tetraphenylpyridinium perchlorate

The characteristics of 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) as a reagent for the formation of ion-pair complexes with metal-bromide anions, and its application to the spectrophotometric determination of mercury are described. This reagent forms a 1:1 complex with bromomercurate(II) ions that is slightly soluble in water and can be extracted with isopentyl acetate. The optimum conditions are about 0.5 M sulphuric acid and 0.03 M potassium bromide. Mercury can be determined at 310 nm in the range 0.04–0.5 μg ml^?1; the apparent molar absorptivity is 2.63 × 10⁴ l mol^?1 cm^?1, and the conditional stability constant is log K - 4.7 ± 0.1 at 20°C. The main interferences are easily removed. Mercury can be determined in sphalerites and zinc amalgams.     

Spectrophotometric and spectrofluorimetric determination of iodide by extraction of ICl−2 with rhodamine B

Iodide is determined after oxidation with nitrous acid in 5 M hydrochloric acid to ICl^?₂. The ion-pair formed with rhodamine B is extracted into toluene and measured spectrophotometrically (0.5–5 × 10^?5 M) or spectrofluorimetrically (1–10 × 10^?6 M). The relative standard deviations were 1.8% for the determination of 5 × 10^?6 M iodide (n = 5) by spectrofluorimetry and 2.3% (n = 50) for 1 × 10^?5 M iodide by spectrophotometry. Periodate, iodate and iodine responded exactly as iodide.     

Study of iron and titanium complexes with propylenediaminetetraacetic acid by differential pulse polarography : Determination of iron and titanium in Portland cements

Differential pulse polarography is used to study the iron(III) and titanium(IV) complexes with propylenediaminetetraacetic acid (PDTA). The complexes produce reduction peaks at –0.09 V and –0.32 V (vs. Ag/AgCl/3 M KCl), respectively, at pH 4.5. This is used for a simultaneous, precise determination of iron and titanium. The detection limits in aqueous solutions were 5.0 × 10^?7 M for iron and 3.0 × 10^?7 M for titanium and linear calibrations were obtained in the range 4.0 × 10^?4–6.0 × 10^?4 M in both cases. Correct results were obtained for iron trioxide (ca. 2%) and titanium dioxide (ca. 0.3%) in Portland cements, with relative standard deviations of about 3% and 6%, respectively.     

Chromium(III) Potentiometric Sensor Based on Para‐Tertiary‐Butyl Calix[4]arene

A new chromium(III) PVC membrane sensor incorporating p‐tertiary‐butyl calix[4]arene as ionophore, potassium tetrakis as additive and dibutyl phthalate (DBP) as plasticizer was constructed. The electrode exhibited an excellent potentiometric response over a wide concentration range of 1.0×10^?7–1.0×10^?1 M with a Nernstian slope of 20±0.5 mV per decade. The detection limit was 5.0×10^?8 M. The electrode showed a better performance over a pH range of 3.0–8.0, and had a short response time of about <15 s.The electrode was successfully applied to potentiometric titration of Cr (III) with EDTA and for direct determination of chromium(III) in waste water.     

Electrochemical study and polarographic determination of ranitidine

In the polarographic reduction of ranitidine, an H₂-antagonist of histamine, three waves are observed; their half-wave potentials and limiting currents depend strongly on the pH of the solution. The first and second waves are due to reduction of teh protonated, CHNO₂H⁺, and unprotonated, CHNO₂, nitroethene group of ranitidine, respectively; the origin of the third wave is unknown. The characteristics of the second and third waves are studied in acetic acid/acetate buffer at pH 5.5; the first wave does not appear at this pH. The second wave (E_{$\text{1}\text{2}$} = ?0.90 V, vs. Ag/AgCl) is useful for determining ranitidine in the range 2.4–4.9 × 10^?4 M by direct current polarography and in the range 2.5 × 10^?7?2.05 × 10^?5 M by differential pulse polarography.     

Liquid-liquid extraction of zirconium from hafnium and other elements with dicyclohexyl-18-crown-6

Zirconium was quantitatively extracted with 2.5 × 10^?2 M dicyclohexyl-18-crown-6 in dichloromethane from 8.5 M hydrochloric acid. It was stripped with 0.5 M hydrochloric acid and was determined spectrophotometrically as its complex with Arsenazo III. Hafnium was not extracted under these conditions, but from the residual aqueous phase it was extracted with 7.0 × 10^?2 M dicyclohexyl-18-crown-6 in dichloromethane from 9.0 M hydrochloric acid. It was stripped with 0.1 M perchloric acid and determined spectrophotometrically at 540 nm as its complex with xylenol orange. The separation of zirconium and hafnium from other metals is also described.     

The application of 2,4,6-trinitrobenzene-1-sulphonic acid in the differential pulse polarographic determination of amines

The differential pulse polarographic behaviour of 2,4,6-trinitrophenyl (TNP) derivatives of several primary amines and amino acids was investigated in the presence of sulphite ion. All the derivatives produced a polarographic peak for their complexes with sulphite (1 × 10^?2 M) in pH 8.0 phosphate buffer (0.05 M)/0.1 M potassium chloride. The derivatives of proteins and peptides did not give such a peak. A 5-min reaction time at room temperature (or 50°C for lysine) and pH 10.5 using 1 × 10^?4 M 2,4,6-trinitrobenzene-1-sulphonic acid provides the optimal conditions for the determination of 5 × 10^?6?2.5 × 10^?5 M amines. The relative standard deviation for determining 1 × 10^?5 M glycine (n = 5) was 1%.     

Simultaneous Determination of Epinephrine, Noradrenaline and Dopamine in Human Serum Samples by High Performance Liquid Chromatography with Chemiluminescence Detection

A simple, rapid and accurate high performance liquid chromatographic （HPLC） technique coupled with chemiluminescence （CL） detection was developed for the simultaneous determination of epinephrine （E）, noradrenaline （NA） and dopamine （DA）. It was based on the analyte enhancement effect on the CL reaction between luminol and potassium ferricyanide. The effects of various parameters, such as potassium ferricyanide concentration, luminol concentration, pH value and component of the mobile phase on chromatographic behaviors of the analytes （E, NA and DA） were investigated. The separation was carded out on C18 column using the mobile phase of 0.01 mol/L potassium hydrogen phthalate solution and methanol （92 ： 8, V/V）. Under the optimum condi- tions, E, NA and DA showed good linear relationships in the range of 1 × 10^-8 -5 × 10^-6, 5.0× 10^-9 -1.0× 10^-6 and 5.0×10^-9-1.0× 10^-6 g]mL respectively. The detection limits for E, NA and DA were 4.0×10^-9, 1.0× 10^-9 and 8.0 × 10^-10 g/mL. The proposed method has been applied successfully to the analysis of E, NA and DA in human serum samples.     

Precise polarographic determination of the stability constants of cadmium and lead with oxalate and sulphate

Precise polarographic determinations of the stability constants of some complexes of lead and cadmium with oxalate and sulphate were made using differential-pulse polarography, normal- pulse polarography and direct-current polarography at three different concentrations of the metal ions in the range 1 × 10^?4 to 9 × 10^?8 M. The stability constants, evaluated with the DeFord-Hume procedure, at the different metal ion concentrations and using the different techniques are in good agreement with each other and with literature values. In the calculations corrections were made for changes in liquid-junction potentials and the effect of alterations in the diffusion coefficient of the reactant was also considered for diffusion towards a spherical electrode. For metal ion concentrations above approximately 10^?6 M the precision of the determinations of the half-wave potentials and of the calculations of the stability constants approaches that commonly obtained in potentiometric measurements on similar systems.     

A nafion/crown ether film electrode and its application in the anodic stripping voltammetric determination of traces of silver

Glassy carbon electrodes are modified by coating with dicyclohexyl-18-crown-6 in Nafion-117. The electrode is used for a very sensitive anodic stripping voltammetric determination of silver. High sensitivity is obtained owing to the release of crown molecules from the silver-crown complex during the deposition. The detection limit is 2×10^?12 M after electrodeposition for 30 min. The recommended supporting electrolyte is 4×10^?3–7×10^?3 M potassium chloride in 0.01 M nitric acid with a deposition potential of ?0.30 V vs. SCE and a linear potential scan. Three typical calibration graphs were linear over the range 2×10^?11–1×10^?8 M for deposition times of 30, 20 and 8 min, respectively. The silver content of reagent-grade ammonium nitrate was found to be 0.48×10^?4% with a relative standard deviation of 3.7% (n=7) for parallel determinations.