A new potentiometric ibuprofenate ion sensor immobilized in a graphite matrix for determination of ibuprofen in tablets

The characteristics, performance, and application of an electrode, namely, Pt vertical bar Hg vertical bar Hg-2(IBP)(2)vertical bar Graphite, where IBP stands for ibuprofenate ion, are described. This electrode responds to IBP with sensitivity of (58.6 +/- 0.9) mV decade 1 over the range 5.0 x 10(-5)-1.0 x 10(-1) mol L-1 at pH 6.0-9.0 and a detection limit of 3.8 x 10(-5) mol L-1. The electrode is easily constructed at a relatively low cost with fast response time (within 1530 s) and can be used for a period of 5 months without any considerable divergence in potentials. The proposed sensor displayed good selectivity for ibuprofen in the presence of several substances, especially concerning carboxylate and inorganic anions. It was used for the direct assay of ibuprofen in commercial tablets 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 procedure. (c) 2006 Elsevier B.V. All rights reserved.

Analytical procedure for total mercury determination in fishes and shrimps by chronopotentiometric stripping analysis at gold film electrodes after microwave digestion

A method for the total mercury determination in fish and shrimps employing chronopotentiometric stripping analysis on gold film electrodes is described. Fish and shrimp tissues were digested using a microwave oven equipped with closed vessels. We developed a microwave heating program which decomposed all the samples employing diluted nitric acid and hydrogen peroxide. The proposed method was validated by analyzing a certified reference material and then applied for different fish species from fresh water and seawater acquired in local markets of São Paulo city, Brazil. The Brazilian legislation establishes 0.5 and 1 mg per kilogram of fish as upper limit of mercury for omnivorous and predator species, respectively. Except for blue shark tissues, the mercury content was situated below 0.5 mu g g(-1) for all the analyzed samples. The detection limit of the proposed method was calculated as 5 ng g(-1) of sample utilizing 5 minutes of electrodeposition (+300 mV vs. Ag/AgCl) on the gold electrode. (c) 2006 Elsevier Ltd. All rights reserved.

Benzoate ion determination in beverages by using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely. Pt\Hg\Hg-2(Bzt)(2)\graphite, where Bzt stands for benzoate ion. are described. This electrode responds to Bzt with sensitivity of 57.7 +/- 1.0 mV/decade over the range 5 x 10(-4)-1 x 10(-1) mol l(-1) at pH 6.0-8.0 with a detection limit of 1.6 x 10(-4) mol l(-1). The electrode shows easy construction, fast response rime (between 10-30 s), low-cost, acid excellent response stability (lifetime > 6 months, in continuous use), the proposed sensor displayed good selectivity for benzoate in the presence of several carboxylate and inorganic anions. It was used to determine benzoate in various beverages by means of the standard additions method. The results obtained by using this electrode compared very favorably with those given by the official AOAC spectrophotometric method and by a HPLC procedure as well. (C) 2001 Elsevier B.V. B.V. All rights reserved.

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\Hg-2(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 x 10(-4) to 1.0 x 10(-1) mol l(-1) at pH 6.5-8.0 and a detection limit of 3.2 x 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. (C) 2004 Elsevier B.V. All rights reserved.

Application of voltammetric technique to the analysis of indanthrene dye in alkaline solution

The Indanthrene Olive Green B (C.I. Vat Green 3; C.I. 69500), VG3 dye, a vat dye bearing an anthraquinonoid group and a ketonic group, can be detected by differential pulse voltammetry in alkaline solution using glassy carbon electrode. on the adsorbed form the dyes are reduced into three cathodic steps at -0.54 V, -0.65 V and -0.93 V vs Ag/AgCl. The leuco form generated after previous electrolysis at controlled potential of -1 V can be detected by voltammetry due to its reoxidation peak at -0.08 V. An analytical method is proposed for determining the vat dye using modified glassy carbon electrode by electrochemical activation in alkaline medium. Linear relationship was observed between l(Pu) vs concentration from I X 10(-5) mol L-1 to 6.0 X 10(-4) mol L-1. The detection limit was calculated to be 9.3 X 10(-6) mol L-1. (c) 2005 Elsevier Ltd. All rights reserved.

Electrochemical reduction and determination of Cibacron Blue F3GA at poly-L-lysine modified glassy carbon electrode

The oxidation of a reactive dye, Cibacron Blue F3GA, CB, (C.I. 61211), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode occurs in two steps at 2.0 < pH < 10 involving one electron transfer each to the amine group leading to the imide derivative. Stable films of poly-L-lysine (PLL) in the presence of glutaraldehyde (GA) 97.5%:2.5% on glassy carbon electrode can be used to detect low levels of dye using its oxidation peak at +0.75V by voltammetry. Linear calibration graphs were obtained for the CB reactive dye, from 1.0 X 10(-6) to 1.0 X 10(-5) mol L-1 in B-R buffer, pH 2.0, using a pre-concentration off-line during 10 min. The detection limit (3 sigma/slope) was calculated to be 4.5 X 10(-8) mol L-1. Films of PLL can readily be applied for the determination of CB dye bearing aminoanthraquinone as chromophore and chlorotriazinyl as reactive group at concentrations at least 100 times lesser than using a glassy carbon electrode without modification. The method described was applied for the determination of CB dye in tap water and raw water collected from the municipal treatment plant with a recovery of 89.2% +/- 5.4 and 88.0% +/- 6.5, respectively. (c) 2005 Elsevier Ltd. All rights reserved.

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 mu L and analytical path of 30 cm it is possible to construct a linear calibration curve from 9.0 x 10(-6) to 1.0 x 10(-4) mol L-1. The relative standard deviation for 5.0 x 10(-5) mol L-1 procaine (15 repetitions using the same electrode) is 3.2% and detection limit calculated is 6.0 x 10(-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. (c) 2006 Elsevier B.V. All rights reserved.

Differential pulse polarographic determination of clotrimazole after derivatization with Procion Red HE-3B

Clotrimazole was shown to react at room temperature in Britton Robinson buffer pH 2 with the reactive dye Procion Red HE-3B. The product exhibited a differential pulse polarographic peak at -0.38 V, which was well separated from the peaks of the reactive dye at -0.08, -0.80 and -0.95 V, and this allowed the indirect determination of clotrimazole in the presence of excess of the reactive dye. The method has been applied satisfactorily to the determination of clotrimazole in pharmaceutical formulations, calibration graphs are rectilinear up to at least 40 mug ml(-1). The detection limit was calculated to be 2.6 mug ml(-1) (3 sigma). (C) 2002 Elsevier B.V. B.V. All rights reserved.

Electrochemical study of hydroxychloroquine and its determination in plaquenil by differential pulse voltammetry

Hydroxychloroquine (HCQ) is a halogenated aminoquinoline that presents wide biological activity, often being used as an antimalarial drug. The electrochemical reduction of HCQ was investigated by cyclic voltammetry and chronoamperometry using glassy carbon electrodes. By cyclic voltammetry, in acid medium, only the cathodic peak was observed. The electrochemical behavior of this peak is dependent on pH and the electrodic process occurs through an ErCi mechanism. The electron number (le) consumed in the reduction of HCQ was obtained by chronoamperometry. A method for the electrochemical determination of HCQ in pharmaceutical tablets was developed using differential pulse voltammetry. The detection limit reached was 11.2 mug ml(-1) of HCQ with a relative standard deviation of 0.46%. A spectrophotometric study of HCQ has been also carried out utilizing a band at 343 nm. The obtained detection limit and the relative standard deviation were 0.1 mug ml(-1) and 0.36%, respectively. The electrochemical methods are sufficiently accurate and precise to be applied for HCQ determination, in laboratorial routine, which can be used to determine the drug at low level. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Development of a potentiometric mefenamate ion sensor for the determination of mefenamic acid in pharmaceuticals and human blood serum

The characteristics, performance, and application of a novel and simple electrode, namely Pt vertical bar Hg vertical bar Hg-2(MF)(2)vertical bar Graphite, where MF stands for mefenamate ion, are described. This electrode responds to MF with sensitivity of (58.9 +/- 0.7) mV decade(-1) over the range 1.0 x 10(-6) to 1.0 x 10(-2) mol L-1 at pH 6.0-9.0 and a detection limit of 6.2 x 10(-7) mol L-1. The electrode is easily constructed at a relatively low cost with fast response time (within 10-25 s) and can be used for a period of 4 months without significant change in its performance characteristics. The proposed sensor displayed good selectivity for mefenamate in the presence of several substances, especially concerning carboxylate and inorganic anions. The potentiometric sensor was successfully applied to the determination of mefenamic acid in pharmaceuticals and human serum samples. (c) 2007 Elsevier B.V. All rights reserved.

Compact disks, a new source for gold electrodes. Application to the quantification of copper by PSA

In this work we describe a versatile and very sensitive way for copper quantification by potentiometric stripping analysis using gold electrodes obtained from recordable compact disks (CDs). This new source of electrodes (CDtrodes) shown similar performance to the commercial gold electrodes with superior versatility and lower cost. Recordable CDs contains a highly pure gold film with thickness between 50 and 100 nm and superficial area of ca. 100 cm(2). The working electrode developed was used successfully in stationary cell and many experimental parameters have been optimized. For copper, the detection limit attained was 30 ng L-1 (600 s deposition time) with remarkable precision (standard deviation of 1.8 % for 20 repetitive measurements using 25 mu gL(-1) of copper with 60 s of deposition time). The gold electrode developed was used for analysis of copper in sugar cane spirits and tap water samples. The results were compared with those obtained by atomic absorption spectroscopy.

Determination of the betaine content of feed ingredients using high-performance liquid chromatography

A series of studies was conducted to establish a methodology for the accurate and efficient determination of betaine in different feed ingredients. The final methodology involves an extraction step in which the feed sample is heated for 3h in a methanolic KOH solution using a Goldfisch apparatus. Impurities are removed by the addition of activated charcoal and concentrated (36%) HCl. After centrifugation the extractant is passed through a strong cation exchange resin (Dowex 50W-X12, H+). The betaine retained in the column is eluted with 1.5 N HCl. A 2 nil aliquot of the elute is air dried and reconstituted with 1 ml of deionised water. HPLC separation with a cation exchange column (Partisil SCX-10) is used for the separation of betaine from other compounds. The mobile phase is kept constant at 50mm KH2PO4 in water, and eluted compounds are detected by UV absorbance (200nm). The flow rate is maintained at 1.5ml min(-1). This assay is very accurate over the range of betaine concentrations from 15 to 650 mug ml(-1), with a lower detection limit in feeds of approximately 500 mug g(-1) when 4g of sample is extracted. Recovery assays done with standard betaine hydrochloride and hard red wheat resulted in a consistent recovery of 80%. Betaine content was quantified in several feed ingredients, including alfalfa (1.77 mg kg(-1)), wheat (3.96 mg kg(-1)), wheat middlings (4.98 mg kg(-1)) and poultry meal (0.77 mg kg(-1)). Betaine in corn and soybean meal was not detectable by this method, even when 16g of sample was used (<125 mg kg(-1)). Betaine present in several feed ingredients should influence choline supplementation to animal feeds and may have implications for human health. (C) 2002 Society of Chemical Industry.

Voltammetric sensor for sodium nitroprusside determination in biological fluids using films of poly-L-lysine

Sodium nitroprusside (NP), a commercial vasodilator, can be pre-concentrated on vitreous carbon electrode modified by films of 97.5%: 2.5% Poly-L-lysine (PLL): glutaraldehyde (GA). This coating gives acceptable anion exchange properties whilst giving the required improvement of adhesion to the glassy carbon electrode surface. Linear response range and detection limit on nitroprusside in B-R buffer pH 4.0, were 1 x 10(-6) to 2 x 10-(5) mol L-1 and 1 x 10(-7) mol L-1, respectively. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was measured as 4.1% for 10 experiments. The voltammetric sensor was directly applied to determination of nitroprusside in human plasma and urine samples and the average recovery for these samples was around 95-97% without any pre treatment.

Colorimetric determination of ammonia in air using a hanging drop

A simple and sensitive method for determining atmospheric ammonia (NH3), using a hanging drop, is described. A colorimetric sensor is composed of two optical fibers and the source of monochromatic light implemented was a red light emitting diode (LED) (635 nm). Preliminary experiments were carried out in order to optimize the geometry of the sensor. These tests showed that the best signal absorbance was obtained using a 22 muL deionized water drop for sampling the gas and as addition of 4 muL of each of the reactants to form the blue dye (indophenol). Some important analytical parameters were also studied, including sampling time and flow rate. The analytical curve was constructed with a concentration range of 3-20 ppbv of gaseous NH3 standard. The detection limit reached was of ca 0.5 ppbv. It was observed that formaldehyde and diethylamine did not interfere. However, studies showed that hydrogen sulfide caused a negative interference of 20%, when present in the atmosphere in a concentration equal to that of NE3. The method considered here was shown to be easy to apply, making it possible to make a determination every 17 min.

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|Hg-2(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 x 10(-5) to 1.0 x 10(-2) Mol l(-1) at pH 6.5-9.0 and a detection limit of 3.2 x 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. (c) 2005 Elsevier B.V. All rights reserved.