Cathodic Adsorptive Stripping Voltammetry for Estimation of the Forest Area Pollution with Nickel and Cobalt

 Necessary conditions were established for simultaneous nickel and cobalt determination in environmental samples, such as oak wood and soil, based on cathodic adsorptive stripping voltammetry. Ni(II) and Co(II), complexed with dimethylglyoxime, were determined using a hanging mercury drop electrode. Optimum conditions were found to be: accumulation time 90 s, accumulation potential −0.80 V vs. SCE, supporting electrolyte 0.2 mol dm⁻³ ammonia-ammonium chloride buffer (pH = 9.4) + 0.05 mol dm⁻³ NaNO₂ and dimethylglyoxime 2 × 10⁻⁴ mol dm⁻³. A linear current-concentration relationship was observed up to 7.51×10 ⁻⁷ mol dm⁻³ for Ni(II) and 7.0 × 10⁻⁷ mol dm⁻³ for Co(II). Excess amounts of zinc(II) interfering with cobalt peaks were masked by complexation with EDTA. Wood and soils were mineralized by applying a microwave digestion system, using the mixtures H₂O₂ + HNO₃ or HNO₃ + HF, respectively. The developed procedure was tested by analysing international reference materials (BCR 62 Olive Leaves and GBW 08302 Tibet Soil). The developed procedure was used to determine pollution of oak stand with nickel and cobalt in different regions of Poland. Received August 10, 2000. Revision May 22, 2001.     

Hydrazones Possessing a Phenyl-1,2,3,4-tetrahydroquinoline Moiety as Hole Transporting Materials

Hydrazones containing 1-phenyl-1,2,3,4-tetrahydroquinoline units were synthesized starting from diphenylamine. These compounds were found to constitute novel hole transporting materials and were characterized by the time of flight method. The hole drift mobility in these compounds exceeds 10⁻⁶ cm² V⁻¹ s⁻¹ at an electric field of 10⁶ V cm⁻¹.     

Hydrazones Possessing a Phenyl-1,2,3,4-tetrahydroquinoline Moiety as Hole Transporting Materials

Summary.  Hydrazones containing 1-phenyl-1,2,3,4-tetrahydroquinoline units were synthesized starting from diphenylamine. These compounds were found to constitute novel hole transporting materials and were characterized by the time of flight method. The hole drift mobility in these compounds exceeds 10⁻⁶ cm² V⁻¹ s⁻¹ at an electric field of 10⁶ V cm⁻¹.     

EPMA and Quantitative MCs+-SIMS of Metal-DLC Coating Materials

 Compositional characterization of metal-DLC (metal-containing diamond-like carbon) hard coatings is carried out by (WDS)-EPMA and MCs⁺-SIMS. EPMA enables accurate (± 5% relative) quantitative analysis including minor concentrations (0.1–10 at%) of N, O and Ar. Under conditions of “near-surface” EPMA (E₀ < 10 keV) the influence of surface oxide films on “pure” metal standards may be a limiting factor in respect of accuracy. Depth profiling of sufficiently “thick” layered structures (film thickness ≥ 2 μm) is carried out by EPMA-line scans along mechanically prepared bevels. The depth resolution is about 0.2 μm. SIMS in the MCs⁺-mode enables high resolution (< 20 nm) depth profiling of metal-DLC layered structures including the determination of H (1–20 at%). MCs⁺-SIMS, i.e. employing Cs⁺ primary ions and monitoring MCs⁺ molecular secondary ions (M is the element of interest) is presented as a promising route towards sufficiently accurate (10–20%) SIMS-quantification. Matrix-independent relative sensitivity factors for MCs⁺-SIMS are derived from homogeneous coating materials defined by EPMA. EPMA proves to be also useful to detect problems related to SIMS of Ar in metal-DLC materials. The combination EPMA-SIMS is demonstrated as an effective analytical strategy for quality control in industrial production and to support the development of metal DLC layered structures with optimum tribological properties.     

Comparison of Pyrolysis and Microwave Acid Digestion Techniques for the Determination of Mercury in Biological and Environmental Materials

 Microwave digestion reduction-aeration and pyrolysis combined with cold vapour atomic absorption and cold vapour atomic fluorescence are compared for the determination of total mercury in several biological and environmental matrices. The biological samples were digested in a mixture of HNO₃/H₂O₂, the environmental samples in a mixture of HNO₃/HClO₄. After reduction with SnCl₂, the mercury was collected by two-stage gold amalgamation. After microwave digestion reduction-aeration, detection limits of 1.4 ng g⁻¹ and 0.6 ng g⁻¹ were obtained for cold vapour atomic absorption spectrometry (CVAAS) and cold vapour atomic fluorescence spectrometry (CVAFS), respectively, for 250 mg of environmental samples. For biological samples (500 mg) the detection limits were 0.7 ng g⁻¹ (CVAAS) and 0.4 ng g⁻¹ (CVAFS). After pyrolysis, detection limits of 3.5 ng g⁻¹ and 1.6 ng g⁻¹ for CVAAS and CVAFS, respectively, were obtained for a 10 mg sample. Pyrolysis can only be applied when the organic content of the sample is not too high. Accurate results were obtained for 8 certified reference materials of both environmental and biological origin. In addition, a real sludge sample was analysed. Author for correspondence. E-mail: richard.dams@rug.ac.be Received September 18, 2002; accepted December 3, 2002 Published online May 5, 2003     

Development of membrane electrodes for selective determination of some antiepileptic drugs in pharmaceuticals,plasma and urine

Newly developed, simple, low-cost and sensitive ion-selective electrodes have been proposed for determination of some antiepileptic drugs such as lamotrigine, felbamate, and primidone in their pharmaceutical preparations as well as in biological fluids. The electrodes are based on poly(vinyl chloride) membranes doped with drug–tetraphenyl borate (TPB) or drug–phosphotungstic acid (PT) ion-pair complexes as molecular recognition materials. The novel electrodes displayed rapid Nernstian responses with detection limits of approximately 10⁻⁷ M. Calibration graphs were linear over the ranges 5.2 × 10⁻⁷–1.0 × 10⁻³, 1.5 × 10⁻⁶–1.0 × 10⁻³, and 2.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–TPB and 5.8 × 10⁻⁷–1.0 × 10⁻³, 1.8 × 10⁻⁷–1.0 × 10⁻³, and 6.6 × 10⁻⁷–1.0 × 10⁻³ M for drug–PT electrodes, respectively, with slopes ranging from 52.3 to 62.3 mV/decade. The membranes developed have potential stability for up to 1 month and proved to be highly selective for the drugs investigated over other ions and excipients. The results show that the selectivity of the ion-selective electrodes is influenced significantly by the plasticizer. The proposed electrodes were successfully applied in the determination of these drugs in pharmaceutical preparations in four batches of different expiry dates. Statistical Student’s t test and F test showed insignificant systematic error between the ion-selective electrode methods developed and a standard method. Comparison of the results obtained using the proposed electrodes with those found using a reference method showed that the ion-selective electrode technique is sensitive, reliable, and can be used with very good accuracy and high percentage recovery without pretreatment procedures of the samples to minimize interfering matrix effects. Figure Structure of lamotrigine, felbanate and primidone     

Synthesis and Photophysical Properties of Ferrocene Containing Monomer and Polymer

Summary. Synthesis of a new monomer and polymer containing both ferrocene and hydrazone moieties are reported. The obtained materials were examined by various techniques including differential scanning calorimetry, UV, IR, NMR spectroscopy, and time of flight method. These materials may be of particular interest for the development of future electrophotographic photoreceptors as electron photoemission spectra of the layers showed ionization potentials of 5.35–5.41 eV. The hole drift mobility values in compositions of the designed structures with bisphenol Z polycarbonate exceeded 10⁻⁸ cm²/Vs at strong electric fields.     

FAD-modified SiO2/ZrO2/C ceramic electrode for electrocatalytic reduction of bromate and iodate

SiO₂/ZrO₂/C carbon ceramic material with composition (in wt%) SiO₂ = 50, ZrO₂ = 20, and C = 30 was prepared by the sol–gel-processing method. A high-resolution transmission electron microscopy image showed that ZrO₂ and the graphite particles are well dispersed inside the matrix. The electrical conductivity obtained for the pressed disks of the material was 18 S cm⁻¹, indicating that C particles are also well interconnected inside the solid. An electrode modified with flavin adenine dinucleotide (FAD) prepared by immersing the solid SiO₂/ZrO₂/C, molded as a pressed disk, inside a FAD solution (1.0 × 10⁻³ mol L⁻¹) was used to investigate the electrocatalytic reduction of bromate and iodate. The reduction of both ions occurred at a peak potential of −0.41 V vs. the saturated calomel reference electrode. The linear response range (lrr) and detection limit (dl) were: BrO₃ ⁻, lrr = 4.98 × 10⁻⁵–1.23 × 10⁻³ mol L⁻¹ and dl = 2.33 μmol L⁻¹; IO₃ ⁻, lrr = 4.98 × 10⁻⁵ up to 2.42 × 10⁻³ and dl = 1.46 μmol L⁻¹ for iodate.     

Preconcentration and Voltammetric Determination of the Antihypertensive Doxazosin on a C8 Modified Carbon Paste Electrode

 An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques has been carried out. The process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V in citric acid-citrate buffer (pH 3.0). A mechanism based on the oxidation of the amine group is postulated. Two methods based on adsorptive stripping (AdS) of doxazosin at the C₈-modified carbon paste electrode (C₈-MCPE), before its voltammetric determination, are studied, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. By means of AdS-DPV and C₈-MCPE, doxazosin can be determined over the 1.0 × 10⁻⁹ to 3.0 × 10⁻⁸ mol L⁻¹ range with a variation coefficient of 2.2% (2.0 × 10⁻⁸ mol L⁻¹) and a limit of detection of 7.4 ×10⁻¹⁰ mol L⁻¹. If AdS-SWV is used, a linear range from 1.0 × 10⁻⁹ to 4.0 × 10⁻⁸ mol L⁻¹ is obtained, the variation coefficient being 2.8% (2.0 × 10⁻⁸ mol L⁻¹, and the limit of detection reached 7.7 × 10⁻¹⁰ mol L⁻¹. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations. Received March 13, 1999. Revision December 23, 1999.     

Simultaneous and sensitive determination of procaine and its metabolite for pharmaceutical quality control and pharmacokinetic research by using a graphite paste electrode

A simple, rapid, sensitive, and accurate method for simultaneous electrochemical determination of procaine and its metabolite (p-aminobenzoic acid, PABA) for pharmaceutical quality control and pharmacokinetic research was developed using a graphite paste electrode. The differential pulse voltammetric results revealed that procaine and p-aminobenzoic acid, respectively, showed well-defined anodic oxidation peaks on a carbon paste electrode with a current peak separation of 155 mV at a scan rate of 100 mV s⁻¹. This well separation of the current peaks for these two compounds in voltammetry enables us to simultaneously determine them. Good linearity (r > 0.998) between oxidation peak current and concentration was obtained in the range of 5.0 × 10⁻⁷–5.0 × 10⁻⁵ M for procaine and 5.0 × 10⁻⁷–2.0 × 10⁻⁵ M for PABA in pH 4.50 acetate buffer solution. The detection limit for both analytes is 5 × 10⁻⁸ M (S/N = 3:1). The present voltammetric method has been successfully used to determine trace p-aminobenzoic acid in procaine hydrochloride injection and procaine in plasma with a linear relationship of current to its concentration ranging from 1.0 × 10⁻⁶ to 5.0 × 10⁻⁵ M (correlation coefficient of 0.9981) with a low detection limit of 5.0 × 10⁻⁷ M (S/N = 3:1). This validated method is promising to the study of pharmacokinetics in Sprague–Dawley rat and rabbit plasma after an intravenous administration of procaine hydrochloride injection.     

Ion specificity and viscosity of rutile dispersions

The isoelectric point (IEP) of rutile is shifted to higher pH values in the presence of greater than 10⁻⁴ mol dm⁻³ Ba²⁺, Ca²⁺ and Mg²⁺, and when a critical concentration (5 × 10⁻⁴ mol dm⁻³ for Ba²⁺ and 1 × 10⁻³ mol dm⁻³ for Ca²⁺) is exceeded there is no IEP at all and the ζ potential is always positive. A common intersection point for the ζ-potential curves of the different concentrations of salt is found, but for the various salts the point is shifted from ζ = 0 mV for Mg²⁺ up to ζ = 20 mV for Ba²⁺. Between the IEP and the charge-reversal point a rheologically unstable region is discovered. The shear stress of rutile dispersions (2.5 g rutile + 4 g electrolyte solution) at shear rates of 116 s⁻¹ shows the same pH dependence irrespective of the concentration of alkaline-earth metal cations up to 10⁻² mol dm⁻³. The shear stress is less than 1 Pa below pH 3.8 and in the pH range 5–12 it assumes a value between 50 and 80 Pa at 116 s⁻¹ with some scatter; however, no systematic trend with concentration of alkaline-earth metal cations and a rather insignificant decrease with pH at pristine conditions are observed. The acidic branch of the yield stress (pH) and low shear rate viscosity (pH) curves is insensitive to the presence of alkaline-earth metal cations, and the same behaviour is found for the ζ potential. The alkaline-earth metal cations induce an increase in viscosity in the basic region and a shift in the pH of maximum viscosity to high pH values. It was also discovered that the effect different alkaline-earth metal cations have on the rheological properties at the same concentration is different from the effect induced by indifferent electrolytes. When the ζ potential increases the viscosity at high pH is increased in a series which follows the increase in size of the cation. Received: 9 September 1998 Accepted in revised form: 12 January 1999     

On-line ionic imprinted polymer selective solid-phase extraction of nickel and lead from seawater and their determination by inductively coupled plasma-optical emission spectrometry

Nickel(II) and lead(II) ionic imprinted 8-hydroxyquinoline polymers were synthesized by a precipitation polymerization technique and were used as selective solid phase extraction supports for the determination of nickel and lead in seawater by flow injection solid phase extraction on-line inductively coupled plasma-optical emission spectrometry. An optimum loading flow rate of 2.25 mL min⁻¹ for 2 min and an elution flow rate of 2.25 mL min⁻¹ for 1 min gave an enrichment factor of 15 for nickel. However, a low dynamic capacity and/or rate for adsorption and desorption was found for lead ionic imprinted polymer and a flow rate of 3.00 mL min⁻¹ for 4-min loading and a flow rate of 2.25 mL min⁻¹ for 1-min elution gave a enrichment factor of 5. The limit of detection was 0.33 μg L⁻¹ for nickel and 1.88 μg L⁻¹ for lead, with a precision (n = 11) of 8% (2.37 μg Ni L⁻¹) for nickel and 11% (8.38 μg Pb L⁻¹) for lead. Accuracy was also assessed by analyzing SLEW-3 (estuarine water) and TM-24 (lake water) certified reference materials, and the values determined were in good agreement with the certified concentrations.     

Development of a liquid chromatography-mass spectrometry method for the determination of ursolic acid in rat plasma and tissue: application to the pharmacokinetic and tissue distribution study

A fast and sensitive liquid chromatography–mass spectrometry method was developed for the determination of ursolic acid (UA) in rat plasma and tissues. Glycyrrhetinic acid was used as the internal standard (IS). Chromatographic separation was performed on a 3.5 μm Zorbax SB-C18 column (30 mm × 2.1 mm) with a mobile phase consisting of methanol and aqueous 10 mM ammonium acetate using gradient elution. Quantification was performed by selected ion monitoring with (m/z)⁻ 455 for UA and (m/z)⁻ 469 for the IS. The method was validated in the concentration range of 2.5 − 1470 ng mL⁻¹ for plasma samples and 20 − 11760 ng g⁻¹ for tissue homogenates. The intra- and inter-day assay of precision in plasma and tissues ranged from 1.6% to 7.1% and 3.7% to 9.0%, respectively, and the intra- and inter-day assay accuracy was 84.2 − 106.9% and 82.1 − 108.1%, respectively. Recoveries in plasma and tissues ranged from 83.2% to 106.2%. The limits of detections were 0.5 ng mL⁻¹ or 4.0 ng g⁻¹. The recoveries for all samples were >90%, except for liver, which indicated that ursolic acid may metabolize in liver. The main pharmacokinetic parameters obtained were T _max = 0.42 ± 0.11 h, C _max = 1.10 ± 0.31 μg mL⁻¹, AUC = 1.45 ± 0.21 μg h mL⁻¹ and K _a = 5.64 ± 1.89 h⁻¹. The concentrations of UA in rat lung, spleen, liver, heart, and cerebellum were studied for the first time. This method is validated and could be applicable to the investigation of the pharmacokinetics and tissue distribution of UA in rats.     

Low-concentration aqueous solutions of undecenoic acid and sodium undecenoate

The behaviors of low-concentration aqueous solutions of 10-undecenoic acid and its sodium salt were studied by several techniques. The acid does not have a critical micelle concentration, but gives an emulsion of very small droplets at (0.8–1) ×  10⁻⁴ mol dm⁻³. The emulsion was clearly visible by eye at 0.002 mol dm⁻³. The sodium salt has a stepwise aggregation process, giving premicellar aggregates at 0.023 ± 0.008 mol dm⁻³, which grow to form micelles at 0.117 ± 0.007 mol dm⁻³. The compositions of the solution and the micelles were also studied. Received: 25 February 1999 Accepted in revised form: 21 June 1999     

Polarographic Catalytic Wave of Prednisone in the Presence of Persulfate and its Application

 A polarographic catalytic wave of prednisone in the presence of K₂S₂O₈ was observed. The polarographic catalytic wave of prednisone as catalyst was attributed to such chemical reaction parallel to electrode reaction as oxidized the free radical from one electron reduction of the Δ^1,4-3 keto group of prednisone to regenerate the original keto group. The catalytic wave can be used for the determination of prednisone with the help of conventional polarographic equipment, such as linear-potential scan polarograph. In 0.12 mol l⁻¹ HAc-0.08 mol l⁻¹ NaAc-0.014 mol l⁻¹ K₂S₂O₈ (pH 4.6) supporting electrolyte, the second-order derivative peak current of the catalytic wave was rectilinear to prednisone concentration in the range of 3.2 × 10⁻⁷∼1.6 × 10⁻⁵ mol l⁻¹. The detection limit was 8.0 × 10⁻⁸ mol l⁻¹. Received August 6, 2001; accepted April 17, 2002; published online July 22, 2002     

Potentiometric Determination of Menadione (Vitamin K3)

 The construction and electrochemical response characteristics of poly(vinyl) chloride matrix membrane sensors for menadione (vitamin K₃) are described. Membranes incorporating the ion association complexes of menadione anion with bathophenanthroline nickel(II) and iron(II) as electroactive materials show linear response for menadione over the range 10⁻¹–10⁻⁵ M with anionic slopes of 58.2–51.4 mV per concentration decade. Both sensors exhibit fast response time (20–30 s), low detection limit (2 × 10⁻⁵ M), good stability (4–6 weeks) and selectivity coefficient (10⁻¹–10⁻³). Direct potentiometric determination of menadione under static and hydrodynamic mode of operations shows average accuracies of 98.8 and 98.5% with relative standard deviations of 0.6% and 1.3%, respectively. Application of the method for the determination of menadione in human plasma gives favourable results compared with those obtained by the standard spectrophotometric method. Received February 26, 2001. Revision October 1, 2001.     

Determination of Zirconium (IV) and Aluminium (III) in Waste Water

 Zirconium (IV) was determined spectrophotometrically by reaction with quercetin as primary ligand and oxalate as secondary ligand. Polyvinylpyrrolidone (PVP) was used as protective colloid to solubilize the formed zirconium quercetin oxalate ternary complex. The molar absorptivity of the 1:3:1 (zirconium–quercetin–oxalate) complex is 7.31 × 10⁴ L·mol⁻¹ cm⁻¹ at 430 nm with a stability constant of 8.2 × 10²⁰ and its detection limit is 0.16 mg/L. Beer’s law is rectilinear up to 1.46 mg/L of zirconium (IV). The sensitivity index is 1.25 ng cm⁻². The reaction of aluminium (III) with quercetin in presence of PVP as a surfactant has been studied spectrophotometrically. The molar absorptivity of the 1:3 (aluminium–quercetin) complex is 8.09 × 10⁴ × L·mol⁻¹·cm⁻¹ at 433 nm, its stability constant is 2.6 × 10¹³ with sensitivity index of 0.33 ng·cm⁻² and its detection limit is 0.08 mg/L. The optimal conditions for the quantitative determination of zirconium and aluminium were studied. The proposed methods are examined by statistical analysis of the experimental data. The methods are free from interference of most cations and anions. The proposed methods have been used to determine zirconium and aluminium in industrial waste water. Received May 30, 2001; accepted November 2, 2001; published online July 15, 2002     

Electrochemical behaviors of metol on ionic-liquid-modified carbon paste electrode and its analytical application

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k _s) as 4.02 × 10⁻³ s⁻¹, and the diffusion coefficient (D) as 6.35 × 10⁻⁵ cm²/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10⁻⁶ ∼ 1.0 × 10⁻³ mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10⁻⁶ mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.     

Flavonol Derivatives for Determination of Cr(III) and W(VI)

 Simple, rapid, sensitive and selective methods for the determination of Cr(III) and W(VI) with flavonol derivatives in the presence of surface-active agents are proposed. In the pH ranges 3.4–4.2 and 1.9–2.5, the molar absorptivities of Cr(III)-morin-emulsifier S (EFA) and W(VI)-morin-polyvinylpyrrolidone (PVP) systems are 1.13×10⁵ and 2.13×10⁴ L mol⁻¹ cm⁻¹ at 435 and 415 nm, respectively. The Cr(III)-quercetin-PVP and W(VI)-quercetin-cetylpyridinium bromide (CPB) systems are formed in the pH ranges 4–4.6 and 2.2–2.8 with molar absorptivities 1.02×10⁵ and 9.02×10⁴ L. mol⁻¹ cm⁻¹ at 441 and 419 nm, respectively. The linear dynamic ranges for the determination of Cr(III) and W(VI) with morin in the presence of EFA and PVP are 0.03–0.46 and 0.71–8.1 μg mL⁻¹, respectively. The corresponding ranges with quercetin are 0.04–0.54 and 0.14–2.1 μg mL⁻¹ of Cr(III) and W(VI), respectively. The r.s.d (n = 10) for the determination of 0.25 and 3.7 μg mL⁻¹ of Cr(III) and W(VI) with morin and their detection limits are 0.88 and 0.99% and 0.016 and 0.63 μg mL⁻¹, respectively. Using quercetin, the r.s.d (n = 10) for 0.22 and 1.2 μg mL⁻¹ of Cr(III) and W(VI) and their detection limits are 0.92 and 0.91% and 0.015 and 0.08 μg mL⁻¹, respectively. The critical evaluation of the proposed methods is performed by statistical analysis of the experimental data. The proposed methods are applied to determine Cr in steel, non-ferrous alloys, wastewater and mud filtrate and to the determination of W in steel. Received March 8, 1999. Revision January 21, 2000.     

Electrochemical behavior and determination of epinephrine at a mercaptoacetic acid self-assembled gold electrode

The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry. The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10⁻⁶ cm² s⁻¹. In 0.1 mol L⁻¹ phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the concentration of EP in the range of 1.0 × 10⁻⁵–2.0 × 10⁻⁴ mol L⁻¹ and 1.0 × 10⁻⁷–1.0 × 10⁻⁶ mol L⁻¹. The detection limit is 5 × 10⁻⁸ mol L⁻¹. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The method is simple, quick, sensitive and accurate.