Potentiometric membrane sensors for the selective determination of pyridoxine hydrochloride (vitamin B6) in some pharmaceutical formulations

The construction and general performance characteristics of two novel potentiometric PVC membrane sensors responsive to the pyridoxine hydrochloride known as vitamin B6 (VB6) are described. These sensors are based on the use of the ion-association complexes of the pyridoxine cation with phosphomolybdate, and phosphotungstate counter anions as ion pair in a plasticized PVC matrix. The electrodes show a stable, near-Nernstian response for 6x10(-5)-1x10(-2) M VB6 at 25 degrees C over the pH range 2-4 with a cationic slope of 54.0+/-0.5 and 54.5+/-0.4 per concentration decade for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate respectively. The two electrodes have the same lower detection limit (4x10(-5) M) and the response times are 45-60 and 30-45 s in the same order for both. Selectivity coefficients for VB6 relative to a number of interfering substances were investigated. There is negligible interference from many cations, some vitamins and pharmaceutical excipients. Direct potentiometric determination of 15-2000 microg/ml pyridoxine shows an average recovery of 98.0% and 99.0% with relative standard deviation 1.5% and 1.2% at 100.0 microg/ml for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate electrodes, respectively. The determination of VB6 in some pharmaceutical preparations using the proposed electrodes gave an average recovery of 98.0 and 99.0% of the nominal value and a mean standard deviation of 1.1% and 0.9% (n=10) for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate electrodes, respectively. The results compare favorably with data obtained by the British Pharmacopoeia method.     

Atropinium scopolaminum integrated microconduits in a potentiometric analytical system

The preparation of the flow-through tubular atropinium and scopolaminum electrodes and assemblage of the integrated microconduit potentiometric analytical system with tubular ISEs, microvalve, chemfold, electrostatic and pulse inhibitors are described. Electrochemical characteristics of new atropinium scopolaminum integrated microconduit FIA-ISEs were studied. The contents of atropine and scopolamine in drugs could be determined at almost equilibrium state at sampling rates of 120/hr. The standard deviation over the linear range was about 0.1 mV (N = 11).     

Liquid and poly (vinyl chloride) matrix membrane electrodes for the selective determination of cocaine in illicit powders

The construction of liquid membrane and PVC matrix-type cocainium ion selective electrodes and their use for direct potentiometry and potentiometric titration of cocaine are described. The ion-pair complexes of cocaine cation with reineckate and tetraphenylborate anions are either dissolved in nitrobenzene solvent or dispersed in a PVC matrix, with DOP or DBS plasticizer, and used as the ion-exchange membranes. The electrochemical response characteristics of electrodes incorporating these types of membranes are evaluated with regard to the effect of pH, foreign basic compounds, temperature and gamma-radiation. The electrodes display a stable fast Nernstian response for 10(-2)-10(-5)M cocainium cation over the pH range 3-7, the lower limit of detection being 1 mug/ml. Determination of as low as 20 mug/ml cocaine hydrochloride shows an average recovery of 98% and a mean standard deviation of +/-0.6%. The electrodes exhibit useful analytical characteristics for determining cocaine in some illicit powders. The results agree fairly well with those obtained by gas-liquid chromatography.     

Construction and analytical applications of liquid-membrane electrodes for atropine and novatropine

Liquid-membrane electrodes sensitive to atropinium and novatropinium cations are described. The atropinium electrode exhibits rapid and near-Nernstian response in the 10^-2–3 × 10^-5 M range over the pH range 2–8.5; the novatropinium electrode shows near-Nernstian response in the 10^-2–3 × 10^-6 M range at pH 2–10. Other alkaloids interfere. Direct potentiometry and potentiometric titrations are used to determine atropine and novatropine in pharmaceutical preparations with satisfactory results.     

Nitron tetrachloroaurate(III) electrodes with poly(vinyl chloride) and liquid membranes for the selective determination of gold

PVC matrix and liquid membrane electrodes have been developed for direct potentiometric determination of gold(III). The membranes incorporate nitron tetrachloroaurate(III) as electroactive material. Fast response for gold(III) over the concentration range 10(-5)-0.1M, with response slopes of 52.8-55.2 mV/decade is obtained. The electrodes show good selectivity for gold(III) at pH 2-5 in the presence of many anions and cations. The PVC membrane electrode offers the advantages of greater selectivity (except for Cr(3+), Mn(2+) and ClO(-)(4)) and higher thermal stability. The liquid membrane electrode gives a higher response slope and faster time of response than the PVC membrane electrode. Determination of AuCl(-)(4) over the range 2 mug/ml-2 mg/ml shows an average recovery of 98.5% and a mean standard deviation of 1.0%. Determination of gold in some gold alloys (58.3-99.9% Au) and pharmaceutical preparations gave an average recovery of 99.4% and a mean standard deviation of 0.7%, which are comparable with the performance obtained with the spectrophotometric Malachite Green and gravimetric U.S. Pharmacopeia methods.     

Papaverine PVC membrane ion-selective electrodes based on its ion-exchangers with tetraphenylborate and tetrathiocyanate anions

The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1 x 10(-2) to 6 x 10(-5) M and 1 x 10(-2) to 1 x 10(-5) M for PA-TPB and PA-TTC respectively at 25 degrees C over the pH range of 3-5.0 with a cationic slope of approximately 56.5 +/- 0.5 mV/decade for both sensors respectively. The lower detection limit is 4 x 10(-5) and 8 x 10(-6) M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0- 3000.0 microg/ml of PA in aqueous solutions shows an average recovery of 99.1% and a mean relative standard deviation of 1.4 at 100microg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out.     

Liquid membrane electrodes for the selective determination of nicotine in cigarette smoke

Five liquid membrane electrode systems responsive to the nicotinium cation are described. These electrodes are based on the use of the ion-association complexes of the nicotinium cation with tetraphenylborate, 5-nitrobarbiturate, flavianate, reineckate and picrolonate counter anions in nitrobenzene solvent as ion-exchange sites. The performance characteristics of these electrodes, evaluated according to IUPAC recommendations, reveal fast, stable and near-Nernstian responses for 10(-2)-10(-5) M nicotine over the pH range 3.5-7. Many inorganic and organic cations do not interfere. The direct potentiometric determination of 3 micrograms ml-1-1.6 mg ml-1 of nicotine in aqueous solutions showed an an average recovery of 99.5% and a mean standard deviation of 1.2%. The electrodes were also used for monitoring the titration of nicotine with sodium tetraphenylborate, measuring the pK of nicotine and determining nicotine in the smoke from different cigarettes. The results compare favourably with those obtained by the standard gas chromatographic method.     

Potentiometric batch and flow injection analysis of betaine hydrochloride

Novel PVC membrane electrodes for the determination of betaine ion based on the formation of betaine-tetraphenylborate (Be-TPB) and betaine-phosphotungstate (Be-PT) ion-exchangers as electroactive materials are described. The sensors show a fast, stable, near Nernstian response for 6.92 x 10(-6) to 7.94 x 10(-3) M and 1.0 x 10(-4) to 1.0 x 10(-2) M betaine hydrochloride (Be.Cl) in case of Be-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 2.95 x 10(-5) to 2.26 x 10(-3) M and 3.16 x 10(-5) to 1.0 x 10(-2) M in case of Be-PT electrode for batch and FIA electrodes, respectively, at 25 degrees C over the pH range of 3.5-10 with a cationic slope of 60.2 and 59.1 mV decade(-1) and a fast potential response of < or =15 s. The lower detection limits are 7.94 x 10(-6) and 3.18 x 10(-5) M Be.Cl for Be-TPB and Be-PT electrodes, respectively. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components other than betaine, of the mixed drug investigated show negligible interference. The electrodes have been applied to the direct potentiometric determination of betaine hydrochloride in water and in a pharmaceutical preparation under batch and FIA conditions. Potentiometric titrations of Be.Cl with NaTPB and PTA as titrants were monitored with the developed betaine electrodes as an end point indicator electrode. The determination of Be.Cl shows an average recovery of 100.8% with mean relative standard deviation of 0.61%. The effect of temperature on the electrodes was also studied.     

PVC Membrane electrodes for manual and flow-injection determination of tetraphenylborate: Applications to separate and sequential titrations of some metal ions

Three novel poly (vinyl chloride) matrix membrane electrodes, highly sensitive and selective for tetraphenylborate anion (TPB), are developed and electrochemically evaluated. They are based on the use of iron(II) bathophenanthroline, nickel(II) bathophenanthroline-and nitron-TPB ion-pair complexes as electroactive materials with dioctylphthalate (DOP) and 2-nitrophenyl phenyl ether (NPPE) as plasticizing solvent mediators. The electrodes exhibit stable and rapid near-Nernstian response for 10(-2)-10(-6)M TPB over the pH range 4-10. Use of these electrodes for direct potentiometric determination and potentiometric titration of as low as 1 mug of TPB/ml and 0.6 mg of TPB/ml give results with average recoveries of 99.3% (mean standard deviation 0.5%) and 99.4% (mean standard deviation 0.2%), respectively. Incorporation of nitron-TPB PVC sensor in a flow-through sandwich cell provides an efficient flow-injection detector for determining TPB with an input rate of at least 60 samples/hr. The limit of detection is 1.6 mug TPB/ml in a 20-mul sample. The electrodes are also used to monitor separate and sequential titrations of some metal ions with TPB. Alkaline earth and transition-metal ions upon reaction with polyethylene glycol and ethylenediamine, respectively, form cationic complexes readily titrated with TPB. Optimum conditions are outlined for sequential titrations of various combinations of metallic species.     

Phosphorated calix[6]arene derivatives as an ionophore for atropine-selective membrane electrodes

37,40-bis-[(diethoxy-thiophosphoryl)oxy]-5,11,17, 23,29,35-hexakis(1,1 -dimethyl-ethyl)-calix[6]arene-8,39,41,42-tetrol; 37,38,39,40,41-pentakis-(di-ethoxythiophosphoryl)-oxy]-5,11,17,23,29,35-hexakis (1,1-dimethylethyl)-calix[6]-arene-42-ol; and 37-[(diethoxythiophosphoryl)oxy]-5,11,17,23,29,35-hexakis-(1,1dimethylethyl)-calix[6]arene-38,39,40, 41,42-pentol were introduced as neutral ionophores for atropine-selective electrodes. Practical Nernstian responses were found (54.3, 49.1, and 50.8 mV/decade) for polyvinyl chloride membrane electrodes incorporating these compounds. They exhibited practical linear ranges of 1.9 x 10(-6)-7.9 x 10(-3), 7.9 x 10(-6)-7.9 x 10(-3), and 6.3 x 10(-6)-7.9 x 10(-3) M, respectively. The optimum pH range was 2.5-8.5. The selectivity coefficient values were estimated and interpreted. The electrode performance was correlated to the calixarene structure. Then, the electrode was applied to an actual analysis of pharmaceutical atropine preparations. The recovery values of 18.7 microg/mL-5.5193 mg/mL atropine sulfate were 97.5-99.1%. The corresponding relative standard deviation values ranged between 0.39-0.72% for 5 determinations. The first electrode was applied successfully for analyzing atropine sulfate in injection solution and eye drops.     

Ion-selective electrodes for potentiometric determination of ranitidine hydrochloride, applying batch and flow injection analysis techniques.

New ranitidine hydrochloride (RaCl)-selective electrodes of the conventional polymer membrane type are described. They are based on incorporation of ranitidine-tetraphenylborate (Ra-TPB) ion-pair or ranitidine-phosphotungstate (RaPT) ion-associate in a poly(vinyl chloride) (PVC) membrane plasticized with dioctylphthalate (DOP) or dibutylphthalate (DBP). The electrodes are fully characterized in terms of the membrane composition, solution temperature, and pH. The sensors showed fast and stable responses. Nernstian response was found over the concentration range of 2.0 x 10(-5) M to 1.0 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-TPB electrode and over the range of 1.03 x 10(-5) M to 1.00 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-PT electrode for batch and FIA systems, respectively. The electrodes exhibit good selectivity for RaCl with respect to a large number of common ions, sugars, amino acids, and components other than ranitidine hydrochloride of the investigated mixed drugs. The electrodes have been applied to the potentiometric determination of RaCl in pure solutions and in pharmaceutical preparations under batch and flow injection conditions with a lower detection limit of 1.26 x 10(-5) M and 5.62 x 10(-6) M at 25 +/- 1 degrees C. An average recovery of 100.91% and 100.42% with a relative standard deviation of 0.72% and 0.53% has been achieved.     

Microdetermination of mercury using silver and copper ion selective electrodes with silver-dithiooxamide and copper-diethyldithiocarbamate loaded polyurethane foams

Summary Microdetermination of Mercury Using Silver and Copper Ion Selective Electrodes with Silver-Dithiooxamide and Copper-Diethyldithiocarbamate Loaded Polyurethane Foams Low levels of mercury(II) are determined by passing their aqueous solutions at pH 1–3 through a column containing silver-dithiooxamide or copper-diethyldithiocarbamate loaded polyurethane foam, followed by monitoring the silver(I) and copper(II) ions released in the effluent with the solid state silver and copper ion selective electrodes, respectively. The rate of the exchange reactions is fast (<3 min) and the efficiency of displacing silver(I) and copper(II) ions is high (>98%). The calibration plots show slopes of 59 and 29 mV/concentration decade of mercury on using the silver and copper sensors, respectively. Determination of 20 ng/ml to 200/ml of mercury(II) in aqueous solutions shows an average recovery of 98.4% and a mean standard deviation of 2%. Many cations and anions do not interfere. Some organomercury compounds are similarly determined after a prior decomposition in an oxygen-filled flask. Results with an average recovery of 98.4% (mean standard deviation 1.9%) are obtained with 10 structurally different mercury compounds.     

A new liquid membrane electrode for the selective determination of perrhenate

A new perrhenate ion-selective electrode has been developed, incorporating a nitrobenzene solution of nitron perrhenate as a liquid membrane. The electrode gives near-Nernstian response to 3 x 10(-5)-10(-2)M perrhenate over the pH range 3-8. Most common anions (except for periodate and perchlorate) give little interference. The electrode has been satisfactory for direct potentiometric determination of as little as 10 mu/ml rhenium. The average recovery and standard deviation were 99% and 2.1%, respectively. Measurements of the solubility products of some sparingly soluble perrhenates gave results that agreed closely with those recorded in the literature and obtained by other procedures.     

An improved voltammetric method for the determination of trace amounts of uric acid with electrochemically pretreated carbon paste electrodes

Carbon paste electrodes, preanodized in alkaline medium at 1.4 V vs SCE for a short period of time, exhibit a great shift of the oxidation potential of uric acid in cathodic direction and a marked enhancement of its current response, compared to unpretreated electrodes. These effects are dependent on the preanodization potential and the time imposed on the electrodes as well as on the alkalinity of the supporting electrolyte. The enhanced voltammetric response can be used to determine uric acid in the concentration range of 5.0-4.0 x 10(4) mug/1 (3.0 x 10(-8)-2.4 x 10(-4)M) with a detection limit (3sigma) of 2.0 mug/1 (1.2 x 10(-8)M). Ascorbic acid in less than 30-fold excess does not interfere. For multiple determinations (5 runs), the relative standard deviation is 2.1% at a concentration of 1 mg/1 uric acid. The proposed procedure can be used to determine uric acid in human urine and serum without any preliminary treatment of the samples in an accurate, rapid and simple way.     

Chemically modified carbon paste electrode for iodide determination on the basis of cetyltrimethylammonium iodide ion-pair.

A new carbon paste electrode (CPE) for the determination of iodide ion based on a cetyltrimethylammonium iodide (CTMAI) ion pair as an electroactive material is described. The electrode shows a linear response for iodide ion over the concentration range of 4 x 10(-5) M to 1 x 10(-1) M with a lower detection limit of 4 x 10(-5) M at 25 degrees C. The electrode has a Nemstian slope of -55.0 +/- 0.4 mV/decade and a fast potential response of 45 s, which is almost constant over a pH range of 5.0 - 9.0. Selectivity coefficient data of the CTMAI-CPE for some common ions show negligible interference, and the electrode has high selectivity towards the iodide ion. An average recovery of 101.83% with a relative standard deviation of 1.53% has been achieved for the determination of iodide in Flaxedil (gallamine triethiodide) ampoules, a muscle relaxant drug. The electrode has been examined for the determination of iodide in saline water; the results were found to compare favorably with those obtained using Metrohm iodide ISE. The electrode has been utilized as an end-point indicator electrode for the determination of Hg(II) and phenylmercury(I) in their aqueous solutions using potentiometric titration with a potassium iodide standard solution.     

Preconcentration and voltammetric measurement of mercury with a crown-ether modified carbon-paste electrode

Carbon-paste electrodes modified with crown-ethers were constructed by mixing the crown-ethers into a graphite powder/Nujol oil matrix. The electrodes so formed were able to bind mercuric ions chemically, and gave greater voltammetric response to mercury than that of ordinary carbon-paste electrodes. The response was characterized with respect to paste composition, crown-ether, preconcentration period, mercury concentration, reproducibility, possible interferences, and other variables. Best results were obtained with 18-crown-6 and an acetate buffer (pH 4.0). The electrode gave good linearity for 1 x 10(-5)-6 x 10(-6)M mercury, a detection limit of 2 x 10(-6)M, and a relative standard deviation of 11%. The investigation may lead to a new class of modified (complexing) electrodes, with different patterns of reactivity.     

高效液相色谱法测定烟叶提取物中茄尼醇的含量

 采用硅胶色谱柱 ,以正己烷 异丙醇 (体积比为 98∶2 )混合液为流动相 ,在紫外检测波长设定为 2 15nm的高效液相色谱仪上测定了烟叶提取物中茄尼醇的含量。实验结果表明 :方法在茄尼醇进样量为 1μg～ 10 μg时有良好线性关系 (Y =16 6 2 0 4X - 32 5 3,r=0 9997) ;加标回收实验 (n =6 )的平均回收率为 98 1% ,RSD为 1 9% ;方法简便 ,有良好的精密度和准确性。     

Plastic membrane electrodes for the potentiometric determination of codeine in pharmaceutical preparations

Four PVC membrane electrode systems responsive to codeinium cation are described. These electrodes are based on the use of the ion-association complexes of the codeinium cation with tetraphenylborate and reineckate counter-anions as ion-exchange sites in a PVC matrix plasticized with dioctylphthalate and dibutylsebacate. The performance characteristics of these electrodes reveal fast, stable and near-Nernstian responses for codeine down to concentrations of 3.5–7.0 × 10^–5 M. Over the pH range 2.5–7, the electrodes are satisfactory for manual and flow injection determination of codeine in various pharmaceutical preparations. There is negligible interference from a number of inorganic and organic cations and some common drug excipients. In the direct determination of 30 g/ml -1.0 mg/ml codeine, the average recovery is 100.6% and the mean standard deviation is ± 0.8%. The results compare favorably with those obtained by the British Pharmacopoeia method.     

A new lead(II)-selective PVC-coated graphite rod electrode based on a Schiff base complex.

A new lead(II)-selective electrode has been developed based on bis(acetylacetone)-p-phenylenediamine-lead(II) [LPb(NO3)2]H2O complex ionophore as a sensing material, dioctylphthalate (DOP) as a solvent mediator and PVC as a matrix. This electrode exhibits a linear Nernstian response over the concentration range of 1 x 10(-5)-1 x 10(-1) mol l(-1) of Pb(II) cation, with a cationic calibration slope of 30.0 +/- 0.2 mV/concentration decade and a detection limit of 2 x 10(-6) mol l(-1) (0.40 ppm). It has a fast response time and can be used for a period of 2 months without any divergence in potentials. The proposed electrode reveals a good selectivity for Pb(II) over a wide variety of other tested cations and could be used in the pH range of 4-8. It was successfully used for direct determination of Pb(II) concentration in some samples. The obtained results show a good agreement with those obtained by an atomic absorption spectrometric method. The average recovery obtained is 96.5 +/- 0.5% with standard deviation of 1.2% (n = 8).     

Determination of EDTA species in water by second-derivative square-wave voltammetry using a chitosan-coated glassy carbon electrode.

Based on the adsorption of Fe(EDTA)- on a chitosan-coated glassy carbon electrode, a second-derivative square-wave voltammetry for the determination of the EDTA species in water samples was investigated. The measuring range of EDTA was from 6.0 x 10(-7) to 5.0 x 10(-5) mol/L with a correlation coefficient of 0.998 and a detection limit of 2.8 x 10(-7) mol/L. The relative standard deviation was less than 6.2% (n = 5) and the recovery was in the range of 98-105% for the determination of practical samples. The result was consistent with that from the HPLC method.