Flow-through chloroquine sensor and its applications in pharmaceutical analysis.

Poly (vinyl chloride) membrane electrodes that responded selectively towards the antimalarial drug chloroquine are described. The electrodes were based on the use of the lipophilic potassium tetrakis(4-chlorophenyl)borate as ion-exchanger and bis(2-ethylhexyl)adipate (BEHA), or trioctylphosphate (TOP) or dioctylphenylphosphonate (DOPP) as plasticizing solvent mediator. All electrodes produced good quality characteristics such as Nernstian- and rapid responses, and are minimally interfered with by the alkali and alkaline earth metal ions tested. The membranes were next applied to a flow-through device, enabling it to function as flow-injection analysis (FIA) detector. The performance of the sensor after undergoing the FIA optimization was further evaluated for its selectivity characteristics and lifetime. Results for the determination of chloroquine in synthetic samples that contained common tablet excipients such as glucose, starch, and cellulose, and other foreign species such as cations, citric acid or lactic acid were generally satisfactory. The sensor was also successfully used for the determination of the active ingredients in mock tablets, synthetic fluids and biological fluids. The sensor was applied for the determination of active ingredients and the dissolution profile of commercial tablets was also established.     

Flow‐Through Assay of Quinine Using Solid Contact Potentiometric Sensors Based on Molecularly Imprinted Polymers

Miniaturized potentiometric membrane sensors for quinine incorporated with molecular imprinted polymer (MIP) were synthesized and implemented. Planar PVC based polymeric membrane sensors containing quinine‐methacrylic and/or acrylic acid‐ethylene glycol methacrylate were dispensed into anisotropically etched wells on polyimide wafers. The determination of quinine was carried out in acidic solution at pH 6, where positively charged species predominated prevalently. The suggested miniaturized planner sensors exhibited marked selectivity, sensitivity, long‐term stability and reproducibility. At their optimum conditions, the sensors displayed wide concentration ranges of 4.0×10^?6–1.0×10^?2mol L^?1 and 1.0×10^?5–1.0×10^?2 mol L^?1 with slopes of about 61.3–55.7 mV decade^?1; respectively. Sensors exhibit detection limits of 1.2×10^?6 and 8.2×10^?6 mol L^?1 upon the use of methacrylic and acrylic acid monomers in the imprinted polymer, respectively. Validation of the assay method according to the quality assurance standards (range, within‐day repeatability, between‐day variability, standard deviation, accuracy, and good performance characteristics) which could assure good reliable novel sensors for quinine estimation was justified. Application of the proposed flow‐through assay method for routine determination of quinine in soft drinks was assayed and the results compared favorably with data obtained by the standard fluorimetric method.     

Enhanced flow injection analysis for measurements of S-nitrosothiols species in biological samples using highly selective amperometric nitric oxide sensor

A highly selective nitric oxide(NO) sensor is fabricated and applied to devise an enhanced flow injection analysis(FIA) system for S-nitrosothiols(RSNOs) measurement in biological samples.The NO sensor is prepared using a polytetrafluoroethylene(PTFE) gas-permeable membrane loaded with Teflon AF? solution,a copolymer of tetrafluoroethylene and 2,2-bis(trifluoroethylene)-4,5-difluoro -l,3-dioxole,to improve selectivity.This method is much simpler and possesses good performance over a wide range of RSNOs concentrations.Standard deviation for three parallel measurements of blood plasma is 4.0%.The use of the gas sensing configuration as the detector enhances selectivity of the FIA measurement vs.using less selective electrochemical detectors that do not use PTFE/Teflon type outer membranes.     

On-line coupling of gas diffusion to capillary electrophoresis

On-line gas diffusion has been coupled to a capillary electrophoresis system (CE) via a specially designed interface. The sample is merged with a modifying solution, e.g., a strong acid, in a flow system to transform the analytes of interest into their respective gaseous forms. These transformed, gaseous analytes permeate through a PTFE membrane into an acceptor stream comprising of a tris-buffer. The continuously flowing acceptor stream is led into an injector forming an integrated part of a flow injection analysis (FIA) system. The sample receiving carrier stream in the FIA system, a chromate buffer, brings the sample, 50 mul, to the FIA-CE interface into which one end of a separation capillary has been inserted. A small portion of the injected sample enters the capillary (electrokinetic injection) and separation takes place. A UV detector is placed at the other capillary end and a run potential of 25 kV is applied to two platinum electrodes positioned in the flow system. Multiple sample injections can be performed in one uninterrupted electrophoretic run. A typical sampling frequency is 15 h(-1); each run may result in quantitation of at least five anions. The overall repeatability is in the range 1.8-3.6% (RSD). The technique has been applied to the analysis of real samples such as soft drinks, vinegar and wine. Selective discrimination of anions which are unable to form volatile species is accomplished. No off-line sample pre-treatment is needed.     

Exploiting green analytical procedures for acidity and iron assays employing flow analysis with simple natural reagent extracts

Green analytical methods employing flow analysis with simple natural reagent extracts have been exploited. Various formats of flow based analysis systems including a single line FIA, a simple lab on chip with webcam camera detector, and a newly developed simple lab on chip system with reflective absorption detection and the simple extracts from some available local plants including butterfly pea flower, orchid flower, and beet root were investigated and shown to be useful as alternative self indicator reagents for acidity assay. Various tea drinks were explored to be used for chromogenic reagents in iron determination. The benefit of a flow based system, which allows standards and samples to go through the analysis process in exactly the same conditions, makes it possible to employ simple natural extracts with minimal or no pretreatment or purification. The combinations of non-synthetic natural reagents with minimal processed extracts and the low volume requirement flow based systems create some unique green chemical analyses.     

Flow-injection analysis for hypoxanthine in meat with dissolved oxygen detector and enzyme reactor

A low cost flow-injection analysis (FIA) with a dissolved oxygen (DO) detector and a xanthine oxidase immobilized column for the analysis of hypoxanthine as an index to determine degree of aging in meat was developed for quality control in the food industry. In this system, hypoxanthine is oxidized by an enzyme reaction with xanthine oxidase immobilized on the column to produce xanthine. Then the catalytic reaction between hypoxanthine and DO with xanthine oxidase proceeds with the DO concentration decreasing in the stream of the flow system. Decrease in the DO concentration was monitored by a DO detector located downstream of the flow system. This decrease in DO concentration was proportional to the hypoxanthine concentration. For detecting the decreased DO concentration efficiently a flow-through cell with a polarographic-type DO sensor was specially designed. As a result, a linear working curve was obtained from 3.68 × 10⁻⁵ to 1.84 × 10⁻³ M hypoxanthine concentrations with this FIA system. We applied the present system with a DO detector for the determination of hypoxanthine in meat samples and compared the results with those obtained by the conventional HPLC method. The data obtained with the present FIA method were in fairly good agreement with those obtained by the conventional HPLC method for the meat samples. Correlation factor and regression line between the two methods were 0.998 and Y= 1.51X-32.64 respectively. We concluded that the present FIA system with a DO detector was suitable as a simple, easy to handle and reliable instrument for quality control in the food industry.     

Flow injection analysis of high chloride levels in electroplating baths using on-line dialysis and potentiometric detection

A method for the flow injection analysis (FIA) of high concentrations of chloride in electroplating baths using potentiometric detection is proposed. The system includes a unit of dialysis to promote dilution of samples and a tubular electrode with an homogeneous crystalline membrane as detector. The system was optimized in order to analyse samples within a broad range of concentrations and at high levels of chloride, thereby making pretreatment of the samples unnecessary. It results in a simple manifold applicable over the 4.0×10^–2 and 3.0 mol L^–1 range with a throughput of about 30 samples/h. Seven different plating bath samples were analysed by the proposed method and the quality of the results compared with those obtained by the conventional procedure. Satisfactory agreement was observed.     

Adaptation of a commercial ion selective fluoride electrode to a tubular configuration for analysis by flow methodologies

The determination of fluoride ions in water samples is accomplished by using a tubular flow through detector constructed by drilling a channel through a commercially available LaF(3) crystal electrode in such a way that the original contacts of the non-modified unit are maintained. Its performance when incorporated in both FIA and SIA systems was evaluated and the results show that the tubular unit retains the characteristics of the non-modified electrode. In SIA conditions an extended linear range of response and lower detection limit were achieved when compared with the electrode performance in FIA conditions. These aspects together with the additional advantage of low sample and reagent consumptions in SIA when compared to FIA, makes the incorporation of the proposed tubular ISE in a SIA system the preferred approach for on line determination and monitoring of fluoride content in natural water samples.     

Flow injection analysis of Zn and Co in beverages, biological, environmental and pharmaceutical samples

A new, simple, rapid and selective flow injection analysis (FIA) method for the spectrophotometric quantification (speciation of inorganic and organic form) of Zn and Co with ammonium thiocyanate and malachite green (MG) in the presence of surfactants (CPC and TX-100) is described. The value of apparent molar absorptivity of the Zn- and Co- complexes are (1.23) × 10⁴ and (8.67) × 10³ L mol^–1cm^–1 at absorption maximum, 635 nm, respectively. The detection limit (amount causing a peak height > 3 s) is 15 ppb Zn and 20 ppb Co, whereas their optimum working ranges for the quantitative determinations are 0.05–2.0 ppm Zn and 0.07–2.5 ppm Co in the real samples. The sample thoughput of the method is 120 samples/h at the flow rate of 5.0 mL/min with rel. std. dev. of < ± 1%. The method is free from interferences of almost all ions which are commonly associated with these metals in the complex materials. The composition of the complexes and their reaction mechanism involved are discussed. The effect of FIA and analytical variables for the determination of the metals are optimized. The method has been applied to the quantification of Zn and Co in beverages, biological, environmental, and pharmaceutical samples.     

Flow-injection systems for determination of trace manganese in various salts by catalytic photometric detection

Two flow-injection analysis (FIA) systems for the determination of trace manganese in salts are presented using highly sensitive catalytic detection based on the oxidation of 3,4-dihydroxybenzoic acid by hydrogen peroxide. Two different approaches, the use of a large sample volume injection in a usual FIA mode (system A) and on-line coupling of a cation-exchange separation column with detection in a continuous flow system (system B), have proved very effective for eliminating the blank peak problem and thus affording direct injection of a sample solution containing a large concentration of salt. The limits of determinations are 0.04 ppm and 0.01 ppm for systems A and B respectively, when a 5 g sample is used for preparing the 100 ml sample solution. The proposed FIA systems were satisfactorily applied to the determination of manganese at 0.03-1.59 ppm in solar salts (salts made by exposing brine to the sun) with good precision.     

Flow injection determination of anisidine value in palm oil samples using a triiodide potentiometric detector

A flow injection analysis (FIA) procedure for the determination of anisidine value (AV) in palm olein using a triiodide detector is described. Undiluted oil sample and chloramine-T reagent were added to a reaction chamber, and reaction was accelerated by applying a short vortex action (typically for 30 s). After allowing the emulsified oil phase to be separated from the aqueous phase (bottom layer), an aliquot of the aqueous phase (containing unreacted chloramine-T) was aspirated into a carrier stream that contained I⁻ where the chloramine-T oxidized the I⁻ to form I₃⁻ which was finally detected by a flow-through triiodide potentiometric detector. Variables that affect the FIA signals such as size of the reaction chamber, oil and reagent flow rates, chloramine-T concentration, vortex time, time for phase separation, carrier stream pH and injected volume were studied. The optimized FIA procedure is linear over 1.0-23.0 AV. The method exhibits good repeatabililty (R.S.D. of ±3.16% (n = 4) for the determination of 5.0 AV) and a sampling rate of 40 samples per hour was achieved. Good correlation (r² = 0.996 (n = 4)) between the proposed method and the manual American Oil Chemists’ Society procedure was found when applied to the determination of twenty different types of palm olein samples.     

Citrate selective electrodes for the flow injection analysis of soft drinks, beers and pharmaceutical products

Aiming the establishment of simple and accurate readings of citric acid (CA) in complex samples, citrate (CIT) selective electrodes with tubular configuration and polymeric membranes plus a quaternary ammonium ion exchanger were constructed. Several selective membranes were prepared for this purpose, having distinct mediator solvents (with quite different polarities) and, in some cases, p-tert-octylphenol (TOP) as additive. The latter was used regarding a possible increase in selectivity. The general working characteristics of all prepared electrodes were evaluated in a low dispersion flow injection analysis (FIA) manifold by injecting 500 μl of citrate standard solutions into an ionic strength (IS) adjuster carrier (10⁻² mol l⁻¹) flowing at 3 ml min⁻¹. Good potentiometric response, with an average slope and a repeatability of 61.9 mV per decade and ±0.8%, respectively, resulted from selective membranes comprising additive and bis(2-ethylhexyl)sebacate (bEHS) as mediator solvent. The same membranes conducted as well to the best selectivity characteristics, assessed by the separated solutions method and for several chemical species, such as chloride, nitrate, ascorbate, glucose, fructose and sucrose. Pharmaceutical preparations, soft drinks and beers were analyzed under conditions that enabled simultaneous pH and ionic strength adjustment (pH=3.2; ionic strength=10⁻² mol l⁻¹), and the attained results agreed well with the used reference method (relative error<4%). The above experimental conditions promoted a significant increase in sensitivity of the potentiometric response, with a supra-Nernstian slope of 80.2 mV per decade, and allowed the analysis of about 90 samples per hour, with a relative standard deviation <1.0%.     

Ruthenium Oxide Hexacyanoferrate Modified Electrode for Hydrogen Peroxide Detection

A sensor for H₂O₂ amperometric detection based on a Prussian blue (PB) analogue was developed. The electrocatalytic process allows the determination of hydrogen peroxide at 0.0 V with a limit of detection of 1.3 μmol L^?1 in a flow injection analysis (FIA) configuration. Studies on the optimization of the FIA parameters were performed and under optimal FIA operational conditions the linear response of the method was extended up to 500 μmol L^?1 hydrogen peroxide with good stability. The possibility of using the developed sensor in medium containing sodium ions and the increased operational stability constitute advantages in comparison with PB‐based amperometric sensors. The usefulness of the methodology was demonstrated by addition‐recovery experiments with rainwater samples and values were in the 98.8 to 103% range.     

Fluorometric Determination of Fructose, Glucose, and Sucrose Using Zirconyl Chloride

Zirconyl chloride upon hydrolysis in water to form Zr(OH)⁺ has been found to react to form a fluorescent derivative with not only a ketose such as fructose but also a hexose such as glucose and the disaccharide sucrose. When reaction conditions such as a temperature of 99°C and a time of 60 min are used, detection limits below 1 μg/mL are possible. All three zirconyl–sugar derivatives show very similar absorbance and fluorescence spectra, indicating a common mechanism involving formation of an enediol which can be complexed with ZrOH⁺ is likely. Because the reactivity order is glucose < sucrose < fructose, the reaction can be made selective for fructose at a lower reaction temperature and time such as 60°C at 5 min. Because interference from ascorbic acid and caffeine is also avoided, the fluorescent determination of fructose in soft drink samples after simply a dilution step is possible. We have also employed this reaction for flow injection analysis (FIA) using a polystyrene–divinylbenzene-packed HPLC column as a mixing device. Using a 0.01 M HClO₄ with 1% zirconyl chloride carrier, we obtained a linear calibration curve from 2 to 30 μg/mL with a correlation coefficient of 0.994. A detection limit less than 2 μg/mL was possible. A comparison of results for the FIA of soft drinks with the enzymatic method involving fructose-5-dehydrogenase confirmed the FIA method was quite specific for fructose.     

Electroanalytical Study of the Pesticide Asulam

The electrochemical behaviour of the herbicide Asulam was studied by cyclic and square wave voltammetry. Asulam may be irreversibly oxidised at a glassy carbon electrode. Maximum currents were obtained at pH = 1.9 in aqueous electrolyte solution. Based on the electrochemical behaviour of Asulam, two analytical methodologies were developed for its determination in water samples, using square wave voltammetry (SWV) and flow injection analysis (FIA) coupled with an amperometric detector. Limits of detection of 7.1 2 10 m 6 mol L m 1 and 1.2 2 10 m 8 mol L m 1 for SWV and FIA respectively, were achieved. Repeatability was calculated by assessing the relative standard deviation (%) for 10 consecutive determinations of one sample. The found values were 2.1% for SWV and 5.0% for FIA. Validation of the results provided by SWV and FIA methodologies was performed by comparison with results from an HPLC-DAD technique. Good relative deviations were found (< 5%). Recovery trials were performed to assess the accuracy of the results and the obtained values were between 84% and 107% for both methods.     

A new screening procedure for the estimation of oxidizable organic compounds in water samples

Summary Immobilized lead dioxide (supported on SiO₂) has been used as the packing material in a solid phase reactor for the oxidation of organic compounds in water samples by flow injection analysis (FIA). On-line oxidation takes place in a FIA-system; this allows the detection of mobilized Pb²⁺ either photometrically, after complex formation with 4-(2-pyridylazo)-recorcinol (PAR), or directly with flame-AAS. The oxidation yield is quite different (0–100%) for a variety of organic compounds; however, calibration was possible in all cases investigated. Thus the systems can be used for the screening of polluted waters and as a post-column chemical-reaction detector (e.g. after HPLC-separation of organic compounds). After modification the FIA determination of COD equivalent values should be possible.     

New approaches to molecular spectroscopic detection in flow-injection analysis

A state-of-the-art overview of molecular spectroscopy as applied in flow injection analysis (FIA) is presented. It deals chiefly with the most interesting FIA approaches aimed at improving detector performance, innovations in the detection system itself and the coupling of FIA with unusual detectors for this technique. The most salient trends in relation to this association are also commented upon.     

Enzymatic detection of glucose using fluoride-selective electrodes with polymeric membranes

The feasibility of using polymeric membrane fluoride-selective electrodes based on zirconium(IV) 5,10,15,20-tetraphenylporphyrin as a detector in a flow-injection analysis (FIA) system for glucose determination was examined. The optimization of enzymatic reactions, FIA system configuration and enzyme-immobilization process was performed. It was shown that the resulting flow-injection system exhibits good working parameters, such as reproducibility, linear range of glucose concentration (3 × 10⁻³–10⁻¹ M), sampling rate (60 samples per minute) and lifetime (over 1 month). The performance of the polymeric membrane electrode was similar to that of a crystalline LaF₃ electrode. The results of glucose determination in synthetic samples with the proposed system show good agreement with real glucose concentrations.     

Application of A Multichannel Potentiostat to Metal Ion Determinations in Flow Injection Analysis

Abstract

A 4-channel potentiostat has been developed for use with an amperometric array and applied to the determination of a mixture of metal ions in flow injection analysis (FIA). The use of an array facilitates the acquisition of three dimensional electrochemical information in real-time (current vs. potential vs. time). The data acquired can be saved in ASCII format which facilitates post-run plotting of the 2-and 3-D voltammograms in Microsoft Excel. The results demonstrate the increased information content available with an amperometric array over fixed potential electrodes. The ability to identify the individual species in mixed component injections, which is normally not possible with FIA without a prior separation step has been demonstrated. Linear responses to injections of copper(II) ions in the concentration range 500 ppm to 100 ppb were obtained.     

Flow injection spectrophotometric determination of cyanide by the phenolphthalin method

The phenolphthalin method for the determination of cyanide has been modified and adapted to a continuous flow system based on the flow injection principle. Aqueous cyanide samples are injected into a carrier stream (0.001 M NaOH), which is then merged with the combined reagent stream of phenolphthalin and carbonate buffer (pH 10.3), and the mixture is passed through an on-line cupric sulfide packed column. The resulting phenolphthalein (the oxidized form of phenolphthalin) is measured in a flow-through spectrophotometer at 552 nm, to determine the cyanide content. The chemical factors and flow injection analysis (FIA) variables influencing the system are discussed. The calibration graph is linear from 0.6 to 4.3 ppm cyanide. At a sampling rate of about 70 samples h(-1) with 50 mul sample injections, precision was about 1% relative S.D.