Flow injection amperometric determination of procaine in pharmaceutical formulation using a screen-printed carbon electrode

A rapid and simple method for procaine determination was developed by flow injection analysis (FIA) using a screen-printed carbon electrode (SPCE) as amperometric detector. The present method is based on the amine/hydroxylamine oxidation from procaine monitored at 0.80 V on SPCE in sodium acetate solution pH 6.0. Using the best experimental conditions assigned as: pH 6.0, flow rate of 3.8 mL min(-1), sample volume of 100 microL and analytical path of 30 cm it is possible to construct a linear calibration curve from 9.0x10(-6) to 1.0x10(-4) mol L(-1). The relative standard deviation for 5.0x10(-5) mol L(-1) procaine (15 repetitions using the same electrode) is 3.2% and detection limit calculated is 6.0x10(-6) mol L(-1). Recoveries obtained for procaine gave a mean values from 94.8 to 102.3% and an analytical frequency of 36 injections per hour was achieved. The method was successfully applied for the determination of procaine in pharmaceutical formulation without any pre-treatment, which are in good accordance with the declared values of manufacturer and an official method based on spectrophotometric analysis.     

Chemically modified carbon paste electrode for the potentiometric flow injection analysis of piribedil in pharmaceutical preparation and urine

A new carbon paste electrode selective for piribedil (PD) was prepared and fully characterized in terms of composition, usable pH range, response time and thermal stability. The electrode active recognition is by liquid ion-exchange mechanism via the use of piribedil phosphomolybdate as ion-exchanger dissolved in tricresyl phosphate as a more suitable solvent mediator for the paste. The modified electrode showed a Nernstian slope of 58.4+/-0.6 mV over the concentration range of 7.5 x 10(-7) to 1 x 10(-3)M with an average recovery of 98.3-101.0% and R.S.D. of 0.45-1.31%. The electrode exhibits good selectivity for PD with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The developed electrode was successfully used for the potentiometric determination of PD in its aqueous solutions, pharmaceutical preparation, and urine in batch and flow injection analysis (FIA).     

Determination of baclofen enantiomers in pharmaceutical formulations using maltodextrin-based enantioselective, potentiometric membrane electrodes

Two enantioselective, potentiometric membrane electrodes (EPMEs) based on maltodextrins with different value of dextrose equivalent (DE) (maltodextrin I: DE 4.0-7.0; maltodextrin II: DE 16.5-19.5) were proposed for the assay of baclofen enantiomers in baclofen raw materials and from its pharmaceutical formulation, Norton-Baclofen tablets. The slopes of the electrode function of the proposed electrodes were 55.0 mV/pS-baclofen for maltodextrin I-based electrode and 59.0 mV/pR-baclofen for maltodextrin II-based electrode and the detection limits were 1.34 x 10(-6) mol l(-1) (S-baclofen) and 2.52 x 10(-10) mol l(-1) (R-baclofen), respectively. The surfaces of the electrodes are stable and easily renewable by simply polishing on alumina paper.     

Potentiometric flow-injection determination of vitamin C and glutathione with a chemically prepared tubular silver electrode

This paper describes the preparation and use of a tubular electrode by means of chemical pretreatment of a silver tube with mercuric (II) chloride solution and iodide solution in flow injection analysis (FIA). The electrode was used as a potentiometric sensor for the indirect determination of vitamin C and glutathione in a carrier stream containing iodine. A simple FIA system that consists of a peristaltic pump, an injection T valve, a tubular silver electrode and a saturated calomel reference electrode (SCE) was used. Some typical FIA parameters such as flow rate, tube length, sample volume and composition of the carrier stream were varied. After optimisation of these parameters, the electrode was further characterised by a constant linear response within the concentration range for the vitamin C between 5 x 10(-5) and 5 x 10(-3) M at the slope of 60.5 +/- 1.0 mV/p (vitamin C). Glutathione has a linear concentration range between 5 x 10(-5) and 10(-2) M at a slope of 55.2 +/- 1.0 mV/p (glutathione). The experimental slope was in good agreement with the theoretical values. Some pharmaceutical products containing vitamin C were also tested. These results can be compared to the results obtained by the standard volumetric method for the determination of vitamin C and are also in good agreement with values declared by pharmaceutical manufacturers.     

Improving the detection limits of antispasmodic drugs electrodes by using modified membrane sensors with inner solid contact

Three coated wire electrodes (CWEs) for the antispasmodic drugs; dicyclomine (Dc), mebeverine (Mv) and drotaverine (Dv) hydrochlorides were developed. Each electrode based on ion-associate of a heteropoly anion with the drug cation incorporated in membrane sensor modified with graphite and deposited on silver internal solid contact. The influence of addition of graphite to the membranes and the type of the internal solid contact on the potentiometric responses of the electrodes was investigated. The characteristics of the new electrodes were compared to the characteristics of previously reported traditional liquid inner contact electrodes of the same drugs. The lower detection limits of the proposed electrodes were somewhat better than those observed with the corresponding liquid contact ISEs and reached (1.2-2.0)x10(-7)M. The potentiometric selectivity of the CWEs revealed a significant improvement and much faster response times compared to the liquid contact ISEs. The practical utility of each electrode has been demonstrated by using it successfully in potentiometric determination of its respective drug in pharmaceutical preparations both in batch and flow injection conditions. Each electrode was also used as an indicator electrode in the potentiometric titration of the drug against standard silicotungstic acid and in potentiometric determination of the drug concentration in urine samples.     

Chemically prepared silver electrode for determination of N-acetyl-L-cysteine by flow-injection potentiometry

This paper describes the use of the silver electrode by means of chemical pretreatment of the electrode surface with mercuric(II) chloride solution and potassium iodide solution in flow injection analysis (FIA). The electrode is used as a potentiometric sensor for the indirect determination of NAC in a carrier stream containing iodine. A one-channel flow system that consists of a peristaltic pump, injection valve, a silver wire electrode and a saturated calomel reference electrode (SCE) was used. Some typical FIA parameters such as flow rate, tube length and composition of the carrier stream were varied. The electrode is further characterised by a constant linear response within the concentration range for NAC between 4.0 x 10(-6) and 1.0 x 10(-3) M at the slope of 60.6 +/- 1.0 mV/p(NAC). Some pharmaceutical products containing NAC were also tested. These results can be compared to the results obtained by the direct potentiometric titrations with silver nitrate and are also in good agreement with values declared by pharmaceutical manufacturers.     

Single and mixed chemically modified carbon paste ion‐selective electrodes for determination of ketotifen fumarate

New modified carbon paste electrodes for determination of ketotifen fumarate in its pure and pharmaceutical preparations were constructed. The used modifiers are ketotifen phosphotungestate (Keto₃PT), and ketotifen tetraphenylborate (Keto‐TPB). Single and mixed ion‐associate electrodes were prepared. Both Keto‐TPB and mixed (Keto‐TPB and Keto₃PT) electrodes have a linearity range of 1.00 × 10^?5‐1.00 × 10^?2 mol L^?1. The slopes were 58.30 and 54.20 mV/decade for Keto‐TPB and mixed chemically modified carbon paste electrodes (CMCPE), respectively. The limits of detection were 1.42 × 10^?6 and 1.00 × 10^?5 mol L^?1 for Keto‐TPB and mixed CMCPEs, respectively. The potential variation due to pH change is considered acceptable in the pH ranges 4.44–9.11 and 2.50–9.00 for Keto‐TPB and mixed ion‐exchanger CMCPE, respectively. The response time was ≤10 s for both electrodes. Selectivity coefficients values towards different inorganic cations, sugars, and amino acids reflect high selectivity of the prepared electrodes. Potentiometric titrations and standard addition methods were applied for the determination of ketotifen ion in its pure samples and pharmaceutical formulations (Zaditen tablet and syrup) using proposed electrodes. The electrodes were also tested in flow injection analysis (FIA). The results obtained from both methods were statistically treated by F‐ and t‐tests. The carbon paste electrodes have the advantages of being more easily prepared and longer life span compared to the plastic membrane electrodes previously reported. Copyright © 2011 John Wiley & Sons, Ltd.     

Nafion修饰玻碳电极阳极溶出伏安法测定盐酸异丙嗪

用Nafion膜玻碳电极阳极溶出伏安法测定盐酸异丙嗪。在4.0×10^-8～5.0×10^-5mol/L和8×10^-5～1×10^-3mol/L范围内,盐酸异丙嗪的浓度与氧化电流的峰高呈良好的线性关系。对原料试样和片剂进行了测定,均获得满意结果。     

柔红霉素在钴离子注入修饰电极上的电化学行为及其应用

目的研究柔红霉素在Co/GC离子注入修饰玻碳电极上的电化学行为及其应用。方法柔红霉素在0.05 mol·L^-1 Na₂HPO₄-KH₂PO₄溶液(pH 6.82)中，用Co/GC离子注入修饰电极进行伏安测定。结果得到一个良好的还原峰，峰电位为-0.60 V (vs SCE)。峰电流与柔红霉素的浓度在2.84×10^-8～1.42×10^-6 mol·L^-1和1.42×10^-6～1.28×10^-5 mol·L^-1呈线性关系，r分别为0.999 2和0.999 3，检出限为1.42×10^-8 mol·L^-1。用于注射液中柔红霉素的测定，回收率为95.8%～102.8%。用线性扫描、循环伏安法研究了柔红霉素的电化学行为及其机制。结论电极反应为具有吸附性质的准可逆过程，质子化的柔红霉素在电极表面得到2个电子和1个质子还原。离子注入电极对柔红霉素具有电催化活性。     

匹鲁卡品的电分析化学研究

本文用微分脉冲极谱法和循环伏安法研究了匹鲁卡品的电化学行为,选择了Zn(Ⅱ)—匹鲁卡品法测定的最佳条件,建立了测定方法,俭出限可达8.0×10^-7mol/L;同时还制备了匹鲁卡品—PVC膜离子选择性电极,直接应用于匹鲁卡品注射液的测定,毋需分离,简便快速,结果良好。     

Towards disposable sensors for drug quality control: Dextromethorphan screen‐ printed electrodes

A simple, rapid, reliable, and reproducible method for mass production of disposable sensors using screen‐printing technology is described. Homemade printing has been characterized and optimized on the basis of effects of the modifier and plasticizers. The fabricated bi‐electrode potentiometric strip containing both working and reference electrode was used as dextromethorphan (DXM) sensor. The proposed sensors worked satisfactorily in the concentration range from 10^?5 to 10^?2 mol L^?1 with detection limit reaching 6 × 10^?6 mol L^?1 and adequate shelf life of 8 months. DXM was determined in pharmaceutical formulations under batch and flow injection analysis (FIA) conditions with sampling output 120 h^?1. Copyright © 2010 John Wiley & Sons, Ltd.     

Flow-injection analysis of dopamine in injections with a periodate-selective electrode

Dopamine determination in pharmaceutical preparations based on its oxidation with periodate (IO(4)(-)) using a new IO(4)(-)-selective electrode under flow conditions is presented. An electrode with a tubular configuration, no internal reference solution, and a PVC (31. 2%) membrane, with metaperiodate bis(triphenylphosphoranylidene)ammonium (1.3%) as ion exchanger and 2-nitrophenyloctylether (67.5%) as mediator solvent, was used. Optimization procedures were directed at potentials versus dopamine readings instead of potential versus the remaining IO(4)(-). This approach was achieved by selecting a 50-cm reactor and an overall flow of 7 mL/min, and injecting 70 microL of dopamine standards in a 3.0 x 10(-4) M IO(4)(-) solution. Under these conditions, a linearity range of 8.0 x 10(-3) to 2.7 x 10(-1) g/L, with a slope of 310.1 +/- 7.4 mV L g(-1) and a reproducibility of +/-0.4 mV, were recorded (n = 8). Interference from common excipients was negligible. Under these conditions, analysis of dopamine injections (n = 12) presenting 200 mg/injection gave average and standard deviation values of 201.0 and 3.3 mg/injection, respectively. A simple and inexpensive flow-injection analysis (FIA) manifold, with a good potentiometric detector, enabled the analysis of 200 samples/h without requiring pretreatment procedures. Comparison with the dopamine injection analysis in the United States Pharmacopoeia monograph showed good accuracy, with a relative deviation of -0.2%.     

Determination of codeine and its metabolite in human urine by CE with amperometric detection

The amperometric detection of codeine and its metabolite, morphine following capillary zone electrophoretic separation is described. A carbon-disk electrode used as working electrode for two analytes exhibited a good response at 0.90 V (vs. Ag/AgCl). The optimal conditions of separation and detection were pH 8.4 phosphate buffer solution (0.06 mol x l(-1)), 12 kV for the separation voltage, sample injection at 12 kV for 10 s. The linear ranges were from 3.1 x 10(-7) to 2.5 x 10(-5) mol x l(-1) for codeine and 1.9 x 10(-7) to 1.5 x 10(-5) x mol l(-1) for morphine with a correlation coefficient of 0.9996 and 0.9999, respectively. The detection limits for codeine and morphine were 1.6 x 10(-7) and 6.8 x 10(-8) x mol l(-1). The method developed was successfully applied to the determination of codeine and its metabolite, morphine in the human urine without any other sample pretreatment except filtration, and the results were satisfactory.     

Flow injection analysis of doxazosin mesylate using UV-detection

A flow injection analysis (FIA) of doxazosin mesylate (DOX) using UV detection is described in this study. The best solvent system was found to be consisting of 0.1 mol l(-1) acetate buffer at pH 4 having 10%MeOH. A flow rate of 1 ml min(-1) was pumped and active material was detected at 365 nm. The calibration equation was linear in the range of 1.3 x 10(-5) to 6.4 x 10(-5) mol l(-1). Limit of detection and limit of quantitation were calculated to be 1.6 x 10(-6) and 4 x 10(-6) mol l(-1) with a RSD 1.27 and 1.16% (n=8), respectively. The proposed method was applied to the determination of DOX in the pharmaceutical preparations. The results were compared with those obtained from UV-Spectrophotometry. The results showed that there is a good agreement between FIA method and UV-Spectrophotometry. The validation studies were realised by the related applications and the results were evaluated statistically. According to the results, insignificant difference was observed between the methods.     

The determination of levofloxacin by flow injection analysis using UV detection,potentiometry, and conductometry in pharmaceutical preparations

A flow injection analysis (FIA) using UV detection, potentiometry and conductometry for levofloxacin (LVF) are described in this study. The best solvent system was found to consist of 0.2 M acetate buffer at pH 3 having 10% MeOH. A flow rate of 1 ml min(-1) was pumped and active material was detected at 288 nm. The detection limit (LOD) and limit of quantification (LOQ) for FIA were calculated to be 3 x 10(-7) M (S/N = 3) and 1 x 10(-7) M (S/N = 10), respectively. In the analysis of tablets, the RSD values were found to be 0.83, 0.98 and 0.99 for FIA, potentiometric and conductometric methods, respectively.     

Polymeric membrane ion-selective electrode for determination of bismuth (III) in pharmaceutical substances

A PVC-based membrane of tridecylmethylammonium chloride reveals a Nernstian potentiometric response (with slope of 55 mV/decade and a correlation coefficient of 0.99) for complex of bismuth (III) with ethylenediaminetetraacetate-anion [Bi(EDTA)](-) over a wide concentration range (1 x 10(-1) to 3 x 10(-5) mol/l). The potential of this electrode is independent of pH in the range of 4.0-11.0. It has a fast response time of about 30 s and was used for a period of 3 months with good reproducibility. The detection limit of this membrane electrode was 1 x 10(-5) M. This sensor exhibits a very good selectivity for [Bi(EDTA)] over a wide variety of complex metal ions with ethylenediaminetetraacetic acid. The proposed electrode has been used in the direct potentiometric monitoring of bismuth (III) in stomach anti-acids.     

Tetracycline-selective electrode for content determination and dissolution studies of pharmaceuticals by flow-injection analysis (FIA)

The present work describes the construction and evaluation of different tetracycline (TC)-selective electrodes without inner reference solution and with polymer membranes. The several electrodes were prepared with poly(vinyl chloride) or ethylene(vinyl acetate) membranes comprising o-nitrophenyl octyl ether or bis(2-ethylhexyl)sebacate as mediator solvents and tetracycline tetrakis(4-clorophenyl)borate as ion exchanger. The best performance was recorded for the poly(vinyl chloride) membranes with bis(2-ethylhexyl)sebacate. Using solutions with adjusted ionic strength, this type of electrode presented a slope of 57.4 mV decade(-1) and a reproducibility of +/-0.3 mV day(-1), for an analytical range from 1.2 x 10(-4) to 1.0 x 10(-2) M. The pH working range was 2.0-3.8. Tubular-shaped potentiometric detectors based on the same selective membrane were also constructed. When TC solutions with adjusted ionic strength of concentrations ranging from 1.0 x 10(-4) to 1.0 x 10(-2) M were injected into a single-channel flow manifold, the detectors presented a slope of 56.6 mV decade(-1) and a reproducibility of +/-0.5 mV day(-1). The pH working range was 1.9-3.9. Both batch and flow procedures were applied to the potentiometric analysis of oral dosage forms. Average recoveries were within 98.6 to 100.3% and the t test indicated the accuracy of these results in comparison to an independent methodology. The flow system with the potentiometric detector was employed in dissolution studies as well.     

Ion selective electrodes for penicillin-G based on Mn(III)TPP-Cl and their application in pharmaceutical formulations control by sequential injection analysis

The work describes the construction, evaluation and analytical application of ion selective electrodes sensitive to penicillin-G antibiotics for pharmaceutical products analysis. Different types of polymeric membranes based on PVC (poly(vinyl chloride)) and EVA (ethyl-vinyl-acetate), without internal reference solution, were prepared using 5,10,15,20-tetraphenylporphyrinate (TPP) manganese(III) (Mn(III)TPP-Cl) as electroactive material. Different additives such as tetra-n-octylammoniumbromide (cationic additive) and sodium tetraphenylborate (anionic additive) were incorporated into the membranes to evaluate their influence on electrodes performance. The comparison of the developed detectors was based on general analytical characteristics, selectivity and lifetime. To accomplish the analysis of real samples, two selective membranes composed of 33.0% (w/w) of PVC, 66.0% (w/w) of o-NPOE and 1.0% (w/w) of Mn(III)TPP-Cl (type A) and 33.0% (w/w) of PVC, 66.0% (w/w) of o-NPOE, 1.0% (w/w) of Mn(III)TPP-Cl and 10% mol (relative to the molar concentration of Mn(III)TPP-Cl) of sodium tetraphenylborate (type B) were used. Type A electrode presented a linear response between 2 x 10(-5) and 10(-1) moll(-1) for penicillin-G, a slope of about -59 mVdec(-1) and a reproducibility of about +/-0.5 mVday(-1), while type B exhibited a linear response between 5 x 10(-5) and 10(-1) moll(-1) for penicillin-G, a slope of about -61 mVdec(-1) and a reproducibility of about +/-0.3 mV day(-1). The potentiometric analysis of penicillin-G in pharmaceutical products was carried out by direct potentiometry and the results obtained were compared with those provided by the HPLC reference method. These membranes (type A and type B) were used to prepare tubular electrodes that were coupled to a sequential injection system (SIA) and presented a linear range between 2 x 10(-4) and 1 x 10(-2) moll(-1) and slopes of -59.3 +/- 0.8 and -57.3 +/- 1.2 mVdec(-1), respectively. The tubular electrode constructed using type B membrane (type TB) was used to carry out the potentiometric analysis of penicillin-G in pharmaceutical formulations. The proposed procedure enabled relative errors between 0.1% and 1.2% (n = 4) and a sampling-rate of about 25 samples per h.     

A disposable electrochemical sensor for the rapid determination of levodopa

Levodopa (L-dopa), the biological precursor of catecholamines, is the most widely prescribed drug in the treatment of Parkinson's disease. The present work presents a proposal for the application of a gold screen-printed electrode an electrochemical sensor for monitoring L-dopa in stationary solution and a flow system. Using the electrooxidation of L-dopa at +0.63 V in acetate buffer pH 3.0 on a gold screen-printed electrode it is possible to obtain a linear calibration curve from 9.9 x 10(-5) to 1.2 x 10(-3) mol L(-1) and a detection limit of 6.8 x 10(-5) mol L(-1). Under amperometric conditions (E(app) = 0.8 V; flow rate = 14.1 mL min(-1); pH 3.0), an analytical calibration graph for l-dopa was obtained from 1.0 x 10(-6) mol L(-1) 6.6 x 10(-4) mol L(-1) with a detection limit of 9.9 x 10(-7) mol L(-1). The method was successfully applied to the determination of L-dopa in commercial dosage forms without any pre-treatment.     

谷胱甘肽在10-甲基吩噻嗪修饰碳糊电极上的电催化氧化及电分析方法

研究了谷胱甘肽(还原型, glutathione, GSH)在10-甲基吩噻嗪(10-methylphenothiazine, MPT)修饰碳糊电极(MPT/CPE)上的电催化氧化行为。GSH在裸碳糊电极(carbon paste electrode， CPE)上的直接电化学氧化过程十分迟缓， 但在MPT/CPE上于0.702 V处出现一个不可逆氧化峰， 氧化电流大幅度增大。计时电流(chronoamperometry， CA)实验测得该电催化氧化反应速率常数k为(5.44±0.03)×10² (mol·L^-1)^-1·s^-1。用线性扫描伏安法(linear sweep voltammetry, LSV)测得催化氧化峰电流与GSH在5.0×10^-6～2.0×10^-3 mol·L^-1呈良好的线性关系， 线性回归方程I_pa=3.536c+2.117， r=0.999 0， 检测限为1.0×10^-6 mol·L^-1。同时用本方法对含GSH的市售药品进行了含量测定， 结果可靠。