Voltammetry determination of trace manganese with pretreatment glassy carbon electrode by linear sweep voltammetry

This paper described the determination of trace manganese using linear sweep voltammetry at a pretreatment glassy carbon electrode. The glassy carbon electrode pretreated by electrochemical method in the 0.1 mol l⁻¹ NaOH solution greatly improved the electrode responsibility in the determination of manganese(II). The barrier to the detection of low manganese concentration was overcome by means of autocatalytic effect of manganese oxide deposited on the electrode in advance. Under the optimum experiments condition (0.04 mol l⁻¹ NH₃-NH₄Cl buffer solution, pH 9.0), the linear range was 4×10⁻⁸ to 1×l0⁻⁶ mol l⁻¹ Mn(II) for linear sweep voltammetry and 1×10⁻⁹ to 4×10⁻⁸ mol l⁻¹ Mn(II) for convolution voltammetry. The relative standard deviation for 2×10⁻⁸ mol l⁻¹ Mn(II) is 3.4%. The proposed method is simple, rapid, sensitive and selective. It had been applied to the determination of trace manganese in samples with satisfactory results.     

Determination of benorilate in pharmaceutical formulations and its metabolite in urine at carbon paste electrode modified by silver nanoparticles

Benorilate was determined by the differential pulse voltammetry (DPV) using a carbon paste electrode modified by silver nanoparticles in 1.25 × 10⁻³ mol l⁻¹ KH₂PO₄ and Na₂HPO₄ buffer solution (pH = 6.88, 25 °C) .The anodic peak potential was +0.970 V (versus SCE). A good linear relationship was realized between the anodic peak currents and benorilate concentrations in the range of 1.0 × 10⁻⁷ to 2.5 × 10⁻⁴ mol l⁻¹ with the detection limit of 1.0 × 10⁻⁸ mol l⁻¹. The recovery was 95.2-103.6% with the relative standard deviation of 3.6% (n = 9). The pharmaceutical preparations, benorilate tablets samples and its metabolite (salicylic acid) in urine were determined with the desirable results.     

Voltammetric determination of pyridoxine (Vitamin B6) at a carbon paste electrode modified with vanadyl(IV)-Salen complex

The preparation and electrochemical characterization of a carbon paste electrode modified with the N,N-ethylene-bis(salicylideneiminato)oxovanadium(IV) complex [VO(Salen)] as well as its behavior in relation to the oxidation of pyridoxine (Vitamin B₆) are described. The electrochemical behavior of the modified electrode and the electrooxidation of pyridoxine were investigated using cyclic voltammetry. The best voltammetric response was obtained for an electrode composition of 15% (m/m) [VO(Salen)] in the paste, KCl solution of pH 5.5-8.0 and scan rate of 25 mV s⁻¹. A sensitive linear voltammetric response for pyridoxine was obtained in the concentration range of 4.5×10⁻⁴ to 3.3×10⁻³ mol l⁻¹ with a slope of 42.5 μA mmol⁻¹ l, and a detection limit (3σ/slope) of 3.7×10⁻⁵ mol l⁻¹ using linear sweep voltammetry. Among several compounds tested only Vitamin B₁ seems to interfere in the analyte signal. The concentrations of pyridoxine in pharmaceutical formulations using the proposed electrode and an official spectrophotometric method based in the reaction with N,N-diethyl-p-phenylenediamine are in agreement at the 95% confidence level and within an acceptable range of error.     

Lithium ions determination by selective pre-concentration and differential pulse anodic stripping voltammetry using a carbon paste electrode modified with a spinel-type manganese oxide

The use of selective pre-concentration and differential pulse anodic stripping voltammetry (DPASV) using a carbon paste electrode modified (CPEM) with spinel-type manganese oxide has been proposed for the determination of lithium ions content in natural waters. The new procedure is based on the effective pre-concentration of lithium ions on the electrode surface containing spinel-type Mn(IV) oxide with the reduction of Mn(IV) to Mn(III) and consequently the lithium ions intercalation (insertion) into the spinel structure. The best DPASV response was reached for an electrode composition of 25% (m/m) spinel-type MnO₂ in the paste, 0.1 mol l⁻¹ tris(hydroxymethyl)aminomethane (TRIS) buffer solution of pH 8.3, scan rate of 5 mV s⁻¹, accumulation potential of 0.3 V versus saturated calomel reference electrode (SCE), pre-concentration time of 30 s and potential pulse amplitude of 50 mV. In these experimental conditions, the proposed methodology responds to lithium ions in the concentration range of 2.8×10⁻⁶ to 2.0×10⁻³ mol l⁻¹ with a detection limit of 5.6×10⁻⁷ mol l⁻¹. The determination of the lithium ions content in different samples of natural waters samples using the proposed methodology and atomic absorption spectrophotometry are in agreement at the 95% confidence level and within an acceptable range of error.     

Inhibition biosensor for determination of nicotine

An amperometric nicotine inhibition biosensor has been substantially simplified and used for determination of nicotine in tobacco sample. Besides the use of single enzyme choline oxidase to replace bienzyme, the use of 1,4-benzoquinone as an electron mediator makes it possible to avoid the use of oxygen or hydrogen peroxide sensor as the internal transducer. Choline oxidase was immobilized on the carbon paste electrode through cross-linking with bovine serum albumin (BSA) by glutaraldehyde. In the presence of choline oxidase and its endogenous cofactor flavin-ademine dinneleotide (FAD), choline was oxidized into betaine while FAD was reduced to FADH₂ which subsequently reduced 1,4-benzoquinone into hydroquinone. The later was finally oxidized at a relatively low potential of +450 mV versus saturated calomel electrode (SCE). Nicotine inhibits the activity of enzyme with an effect of decreasing of oxidation current. The experimental conditions were optimized. The electrode has a linear response to choline within 1.25×10⁻⁴ to 1.25×10⁻³ mol l⁻¹. The nicotine measurements were carried out in 0.067 mol l⁻¹phosphate buffer of pH 7.4 at an applied potential of 450 mV versus SCE. The electrode provided a linear response to nicotine over a concentration range of 2.0×10⁻⁵ to 9.2×10⁻⁴ mol l⁻¹ with a detection limit of 1.0×10⁻⁵ mol l⁻¹. The system was applied to the determination of nicotine in tobacco samples.     

Determination of trace amount of bismuth(III) by adsorptive anodic stripping voltammetry at carbon paste electrode

A sensitive method is described for the determination of trace bismuth based on the bismuth-bromopyrogallol red (BPR) adsorption at a carbon paste electrode (CPE). The overall analysis involved a three-step procedure: accumulation, reduction, and anodic stripping. Optimal conditions were found to be an electrode containing 25% paraffin oil and 75% high purity graphite powder, a 0.30 mol l⁻¹ HCl solution containing 2.0×10⁻⁵ mol l⁻¹ BPR as supporting medium; accumulation potential and time, −0.10 V, 3 min; reduction potential and time, −0.35 V, 60 s; scan rate 100 mV s⁻¹; scan range from −0.35 to 0.15 V. It was found that the Bi(III)-BPR complex could be accumulated on the electrode surface during the accumulation period. Then the Bi(III) in the Bi(III)-BPR complex on the CPE surface was reduced to Bi(0) during reduction interval and finally reoxidized during the anodic stripping step for voltammetric quantification. Factors affecting the accumulation, reduction, and stripping steps were investigated. Interferences by other ions were studied as well. The detection limit was found to be 5×10⁻¹⁰ mol l⁻¹ with a 3 min accumulation time. The linear range was from 1.0×10⁻⁹ to 5.0×10⁻⁷ mol l⁻¹. Application of the procedure to the determination of bismuth in water and human hair samples gave good results.     

p-Aminobenzoate ion determination in pharmaceutical formulations by using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely, Pt|Hg|Hg₂(PABzt)₂| graphite, where PABzt stands for p-aminobenzoate ion, are described. This electrode responds to PABzt with sensivity of (58.1±1.0) mV per decade over the range 1.0×10⁻⁴ to 1.0×10⁻¹ mol l⁻¹ at pH 6.5-8.0 and a detection limit of 3.2×10⁻⁵ mol l⁻¹. The electrode shows easy construction, fast response time (within 10-30 s), low-cost, and excellent response stability (lifetime greater than 6 months, in continuous use). The proposed sensor displayed good selectivity for p-aminobenzoate in the presence of several substances, especially, concerning carboxylate and inorganic anions. It was used to determine p-aminobenzoate in pharmaceutical formulations by means of the standard additions method. The results obtained by using this electrode compared very favorably with those given by an HPLC procedure.     

Biomimetic sensor based on MnMn complex as manganese peroxidase mimetic for determination of rutin

A novel biomimetic sensor for rutin determination based on a dinuclear complex [Mn^IIIMn^II(Ldtb)(μ-OAc)₂]BPh₄ containing an unsymmetrical dinucleating ligand, 2-[N,N-bis(2-pyridylmethyl)-aminomethyl]-6-[N-(3,5-di-tert-butyl-2-oxidoben-zyl)-N-(2-pyridylamino)aminomethyl]-4-methylphenol (H₂Ldtb), as a manganese peroxidase mimetic was developed. Several parameters were investigated to evaluate the performance of the biomimetic sensor obtained after the incorporation of the dinuclear complex in a carbon paste. The best performance was obtained in 75:15:10% (w/w/w) of the graphite powder:Nujol:Mn^IIIMn^II complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0) and 4.0 × 10⁻⁵ mol L⁻¹ hydrogen peroxide. The response of the sensor towards rutin concentration was linear using square wave voltammetry in the range of 9.99 × 10⁻⁷ to 6.54 × 10⁻⁵ mol L⁻¹ (r = 0.9998) with a detection limit of 1.75 × 10⁻⁷ mol L⁻¹. The recovery study performed with pharmaceuticals ranged from 96.6% to 103.2% and the relative standard deviation was 1.85% for a solution containing 1.0 × 10⁻³ mol L⁻¹ rutin (n = 6). The lifetime of this biomimetic sensor was 200 days (at least 750 determinations). The results obtained for rutin in pharmaceuticals using the biomimetic sensor and those obtained with the official method are in agreement at the 95% confidence level.     

Sensitive voltammetric determination of rutin at an ionic liquid modified carbon paste electrode

An ionic liquid modified carbon paste electrode (IL/CPE) had been fabricated by using hydrophilic ionic liquid 1-amyl-3-methylimidazolium bromide ([AMIM]Br) as a modifier. The IL/CPE was characterized by scanning electron microscope and voltammetry. Electrochemical behavior of rutin at the IL/CPE had been investigated in pH 3.29 Britton-Robinson (B-R) buffer solution by cyclic voltammetry (CV) and square wave voltammetry (SWV). The experimental results suggested that the modified electrode exhibited an electrocatalytic activity toward the redox of rutin. The electron transfer coefficient (α) and the standard rate constant (k_s) of rutin at the modified electrode were calculated. Under the selected conditions, the reduction peak current was linearly dependent on the concentration of rutin in the range of 4.0 × 10⁻⁸ to 1.0 × 10⁻⁵ mol L⁻¹ (r = 0.9998), with a detection limit of 1.0 × 10⁻⁸ mol L⁻¹ (S/N = 3). The relative standard deviation (R.S.D.) for six times successful determination of 8.0 × 10⁻⁷ mol L⁻¹ rutin was 1.2%. The proposed method was applied to determine rutin in tablet and urine sample. In addition, the IL/CPE exhibited a distinct advantage of simple preparation, surface renewal, good reproducibility and good stability.     

Electrochemical determination of maltol in beverages with glassy carbon electrode and its silica sol-gel modified electrode

The electrochemical behavior of maltol on a glassy carbon (GC) electrode was investigated. The results were applied to differential pulse voltammetric determination of maltol in beverages pretreated by ultrafiltration. Under the optimum experimental conditions, the linear range is 1×10⁻⁵ to 6×10⁻⁴ mol l⁻¹ maltol and the relative standard deviation for 0.4 mmol l⁻¹ maltol is 0.6% (n=9). The detection limit was 5 μmol l⁻¹. Furthermore, silica sol-gel film on GC electrode could be used as suitable selective membrane, which integrated selective membrane on the electrode and substituted for the pretreatment of ultrafiltration. Under the above conditions, maltol was determined by semi-differential linear sweep voltammetry at a silica sol-gel modified GC electrode in the concentration range of 5×10⁻⁶ to 5×10⁻⁴ mol l⁻¹. The detection limit was 2 μmol l⁻¹ and the relative standard deviation for 0.1 mmol l⁻¹ maltol was 0.7% (n=7). The proposed method is of sensitivity, simplicity, rapidness and no contamination. It had been applied to the direct determination of maltol in beverages such as grape wines, drinks and beers without any pretreatment. The results obtained with the present method were satisfactory with those obtained by spectrophotometry. It could be used as a simple and practical method for the determination of the flavor enhancer maltol in beverages.     

Accumulation and trace measurement of chloroquine drug at DNA-modified carbon paste electrode

The voltammetric behaviour of chloroquine was investigated at carbon paste and dsDNA-modified carbon paste electrodes in different buffer systems over a wide pH range using cyclic and differential pulse voltammetry. Chloroquine was oxidized in the pH range 2.0-11.0 yielding one irreversible main oxidation peak. A second peak was also observed only in the pH range 5.0-7.0. The modification of the carbon paste surface with dsDNA allowed a preconcentration process to take place for chloroquine such that higher sensitivity was achieved as compared with the bare surface. The response was characterized with respect to solution pH, ionic strength, accumulation time and potential, chloroquine concentration, and other variables. Stripping voltammetric response showed a linear calibration curve in the range 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol l⁻¹ with a detection limit of 3.0 × 10⁻⁸ mol l⁻¹ at the dsDNA-modified electrode. Application of the modified electrode to serum, without sample pretreatment, resulted in good recovery higher than 95% and the higher standard deviation was 3.0%.     

Post-column terbium complexation and sensitized fluorescence detection for the determination of norepinephrine, epinephrine and dopamine using high-performance liquid chromatography

Terbium sensitized fluorescence was used as a post-column detection system to develop a simple, sensitive and rapid high-performance liquid chromatographic method for the simultaneous determination of catecholamines norepinephrine (NE), epinephrine (E) and dopamine (DA).Catecholamines were separated by an ion-pair reversed-phase chromatography on a BDS-Hypersil analytical column with a mobile phase of methanol and 50 mmol l⁻¹ acetate buffer (pH 4.7) containing 1.1 mmol l⁻¹ SOS and 0.11 mmol l⁻¹ EDTA (15+85 v/v).Catecholamines and the internal standard (3,4-dihydroxybenzylamine, DHBA) were post-column derivatized by the addition to the eluent of an alkaline solution containing a stoichiometric mixture of terbium(III) chloride and EDTA. Fluorescence detection (λ_ex=300 nm, λ_em=545 nm) is based on the sensitization of terbium ion fluorescence after complexation with catecholamines.The chemical compatibility between the eluent and the post-column reagent was studied and the analytical characteristics of the method were established. Detection limits found were 1.0×10⁻⁸, 4.0×10⁻⁸ and 7.0×10⁻⁸ mol l⁻¹ for NE, E and DA, respectively. The method has been successfully applied to the determination of catecholamines in urine samples after solid-phase extraction (SPE) pre-treatment. Recoveries from urine spiked with NE (4.0×10⁻⁷, 2.0×10⁻⁶ and 4.0×10⁻⁶ mol l⁻¹), E (8.2×10⁻⁸, 4.1×10⁻⁷ and 8.2×10⁻⁷ mol l⁻¹) and DA (1.0×10⁻⁶, 5.0×10⁻⁶ and 1.0×10⁻⁵ mol l⁻¹) varied from 98 to 100% (mean=99.3%), from 106 to 107% (mean=106.3%) and from 98 to 101% (mean=99.3%), respectively. The between-run precision (relative standard deviation, R.S.D.) for the method for three urine samples at different concentration levels of each catecholamine varied from 3.6 to 7.0%.     

Determination of adrenaline by using inhibited Ru(bpy)3 electrochemiluminescence

Adrenaline was found to inhibit strongly the electrochemiluminescence (ECL) from the Ru(bpy)₃²⁺/tripropylamine system when a working Pt electrode was maintained at 1.05 V (versus Ag/AgCl) in pH 8.0 phosphate buffer. On this basis, a flow injection (FI) procedure with inhibited electrochemiluminescence detection has been developed for determination of adrenaline. The method exhibited a good reproducibility, sensitivity, and stability with a detection limit (signal-to-noise ratio = 3) of 7.0×10⁻⁹ mol l⁻¹ and dynamic concentration range of 2×10⁻⁸ to 1×10⁻⁴ mol l⁻¹. The relative standard deviation was 2.2% for 1.0×10⁻⁶ mol l⁻¹ adrenaline (n=11). The method was successfully applied to the determination of adrenaline in pharmaceutical samples. Moreover, ECL emission spectra, UV-Vis absorption spectra and cyclic voltammograms of Ru(bpy)₃²⁺/tripropylamine/adrenaline were studied. The inhibition mechanism has been proposed as the interaction of electrogenerated Ru(bpy)₃^2+* and the o-benzoquinone derivatives, adrenochrome and adrenalinequinone, at the electrode surface.     

Extraction of arsenic compounds from lichens

Different extraction procedures were applied to improve the extraction efficiency of arsenic compounds from lichens. Two lichen species were chosen from an arsenic-contaminated environment: epiphytic Hypogymnia physodes (L.) Nyl. and terricolous Cladonia rei Schaer. Samples were extracted with water at temperatures of 20, 60 and 90 °C, using mixtures of methanol/water (9:1, 1:1 and 1:9), Tris buffer and acetone and the extracts speciated. Water and Tris buffer showed the best extraction efficiency of all extractants used; however, the extraction efficiency was still less than 23%. Since a major fraction of arsenic appeared to be associated with trapped soil particles, a sequential extraction procedure originally designed for soils (extraction steps: (1) 0.05 mol l⁻¹ (NH₄)₂SO₄; (2) 0.05 mol l⁻¹ (NH)₄H₂PO₄; (3) 0.2 mol l⁻¹ NH₄-oxalate buffer, pH 3.25; (4) mixture of 0.2 mol l⁻¹ NH₄-oxalate buffer and 0.1 mol l⁻¹ ascorbic acid, pH 3.25; (5) 0.5 mol l⁻¹ KOH) was applied and found to remove 45% of the total arsenic from H. physodes and 83% from C. rei. The lipid-soluble fraction of arsenic was estimated by k₀-INAA analysis of diethylether extracts and was found to be negligible. An HPLC-UV-HGAFS system was used to determine the arsenic compounds extracted. In both lichen species, arsenous acid, arsenic acid, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, trimethylarsine oxide and glycerol-ribose were detected. In addition, phosphate-ribose was found in H. physodes.     

Voltammetric determination of food colorants using a polyallylamine modified tubular electrode in a multicommutated flow system

This work describes the construction of a polyallylamine modified tubular glassy carbon electrode and its application in the electroreduction of food azo colorants (tartrazine, sunset yellow and allura red) by square wave voltammetry. The electrode modification prevented the surface fouling and, simultaneously, enhanced the analytical signal intensity. The developed unit was coupled to a multicommutated flow system which, given the complexity of samples, was designed to allow the implementation of the standard additions method in an automatic way, using only one standard solution.The described method presented a linear range up to about 2.0 × 10⁻⁴ mol l⁻¹ for the referred colorants, with a detection limit of 1.8 × 10⁻⁶ mol l⁻¹ for tartrazine, 3.5 × 10⁻⁶ mol l⁻¹ for sunset yellow and 1.4 × 10⁻⁶ mol l⁻¹ for allura red. The method was applied in the analysis of these colorants in several food samples, and no statistically significant difference between the results obtained by the proposed and the comparative method (HPLC) was found, at a 95% confidence level. Repeatability in the analysis of samples (expressed in R.S.D.) was about 3% (n = 10).     

Bia-amperometric quantification of salbutamol in pharmaceutical products

This paper presents a simple, rapid and reproducible method of analysis of salbutamol in pharmaceutical products, utilizing batch injection analysis (BIA) associated with amperometric detection. A study of salbutamol oxidation demonstrated a strong dependence between electrode fouling and pH. All determinations were done utilizing a glassy carbon electrode in presence of 3.0 mol l⁻¹ NaOH. A large linear dynamic range from 8×10⁻⁷ to 2×10⁻⁴ mol l⁻¹ was obtained by using an injected volume of 100 μl with a detection limit of 2.5×10⁻⁷ mol l⁻¹. R.S.D. of 0.92% for 50 successive injections of 4×10⁻⁶ mol l⁻¹ of salbutamol and a sample throughput of 60 samples per hour were achieved. The method was applied for salbutamol quantification in syrups.     

New potentiometric sensors for creatinine

Three main types of creatinine potentiometric membrane sensors are described. They are based on the use of dibenzo-30-crown-10 (DB30C10) with potassium tetrakis(p-chlorophenyl)borate type (I), dibenzo-30-crown-10 alone type (II), and potassium tetrakis(p-chlorophenyl)borate alone type (III), incorporating in poly(vinyl chloride) matrix membrane plasticized with either o-nitrophenyl octyl ether or dioctylphthalate. The sensors are used for quantification of creatinine after soaking the membranes in 0.1 M creatinine solution for 2 days. The sensors show almost the same potentiometric response characteristics. Sensor type (I) exhibits Nernstian responses over a concentration range of 5.0 × 10⁻⁵ mol l⁻¹-1.0 × 10⁻² mol l⁻¹ creatinine with cationic slopes of 59.5 ± 0.1 and 60 ± 0.2 mV decade⁻¹ and detection limits of 1.1 × 10⁻⁵ mol l⁻¹ and 8 × 10⁻⁶ mol l⁻¹ creatinine, over the pH range of 3.5-6.5 and 3.5-7.0, for o-NPOE and DOP solvent mediators, respectively. Sensor type (II) displays Nernstian responses over a concentration range of 6.0 × 10⁻⁵ mol l⁻¹-1.0 × 10⁻² mol l⁻¹ creatinine with cationic slopes of 60.0 ± 0.1 and 65.0 ± 0.2 mV decade⁻¹ and detection limits of 1.5 × 10⁻⁵ mol l⁻¹ and 1.4 × 10⁻⁵ mol l⁻¹ creatinine over the pH range of 2.6-6.2 and 2.5-6.0, for o-NPOE and DOP solvent mediators, respectively. Sensor type (III) shows Nernstian responses over a concentration range of 7.0 × 10⁻⁵ mol l⁻¹-1.0 × 10⁻² mol l⁻¹ creatinine with cationic slopes of 60 ± 0.1 and 62.0 ± 0.2 mV decade⁻¹ and detection limits of 2.7 × 10⁻⁵ mol l⁻¹ and 2.0 × 10⁻⁵ mol l⁻¹ creatinine over the pH range of 2.5-6.0, for o-NPOE and DOP solvent mediators, respectively. The response times of the sensors for 10⁻³ mol l⁻¹ creatinine solution are instantaneous (4-10 s). The sensors show long-term stability with life span of ∼6 months. The sensors are used for determination of serum creatinine of rats (Rattus Norvigicus) with mean R.S.D. of 2.62%, and the results agreed well with the Jaffe kinetic method.     

Voltammetric performance and application of a sensor for sodium ions constructed with layered birnessite-type manganese oxide

The preparation and electrochemical characterization of a carbon paste electrode modified with layered birnessite-type manganese oxide for use as a sodium sensor is described. The effects of powder synthesis process (sol-gel and redox precipitation) for birnessite on the electrochemical activity of the sensor was investigated by cyclic voltammetry. The carbon paste electrode modified with birnessite-type manganese oxide that was synthesized by the sol-gel method showed a best electrochemical for sodium ions. The detection is based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the sodium ions extraction into the birnessite structure. The best voltammetric response was obtained for an electrode composition of 15% (w/w) birnessite oxide in the paste, a TRIS buffer solution of pH 8.0 and a scan rate of 50 mV s⁻¹. A sensitive linear voltammetric response for sodium ions was obtained in the concentration range of 7.89 × 10⁻⁵ to 3.49 × 10⁻⁴ mol L⁻¹ with a slope of 37.5 μA L mmol⁻¹ and a detection limit (3σ/slope) of 3.43 × 10⁻⁵ mol L⁻¹ using cyclic voltammetry. Under the working conditions, the proposed method was successfully applied to determination of sodium ions in urine samples.     

Flow-injection chemiluminescence determination of fluoroquinolones by enhancement of weak chemiluminescence from peroxynitrous acid

A flow-injection chemiluminescence (CL) method is described for the determination of fluoroquinolones including ciprofloxacin, norfloxacin and ofloxacin. The method is based on the enhancement by these compounds of the weak CL from peroxynitrous acid. The linear ranges are 1.0×10⁻⁷ to 1.0×10⁻⁵ mol l⁻¹ for ciprofloxacin and norfloxacin, and 3.0×10⁻⁷ to 3.0×10⁻⁵ mol l⁻¹ for ofloxacin, respectively. The detection limits (S/N=3) are 4.5×10⁻⁸ mol l⁻¹ ciprofloxacin, 5.9×10⁻⁸ mol l⁻¹ norfloxacin and 1.1×10⁻⁷ mol l⁻¹ ofloxacin, respectively. The proposed method was applied to the determination of fluoroquinolones in pharmaceutical preparations.     

Determination of diclofenac in pharmaceutical preparations using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely Pt|Hg|Hg₂(DCF)₂|graphite, where DCF stands for diclofenac ion, are described. This electrode responds to diclofenac with sensitivity of (58.1 ± 0.8) mV/decade over the range 5.0 × 10⁻⁵ to 1.0 × 10⁻² mol l⁻¹ at pH 6.5-9.0 and a detection limit of 3.2 × 10⁻⁵ mol l⁻¹. The electrode is easily constructed at a relatively low cost with fast response time (within 10-30 s) and can be used for a period of 5 months without any considerable divergence in potentials. The proposed sensor displayed good selectivity for diclofenac in the presence of several substances, especially concerning carboxylate and inorganic anions. It was used to determine diclofenac in pharmaceutical preparations by means of the standard additions method. The analytical results obtained by using this electrode are in good agreement with those given by the United States Pharmacopeia procedures.