Flow injection spectrophotometric analysis of lead in human saliva for monitoring environmental pollution

A new highly sensitive, simple and low-cost methodology for the direct determination of Pb (II) with 2-(5-bromo-2-pyridylazo)-5-dimethylaminophenol in ethanolic medium has been developed. The absorption spectroscopy of the complex has been examined in detail, and the chemical variables affecting the sensitivity of procedure studied, optimized and applied to the determination of trace amounts of lead in human saliva. Under the optimal experimental conditions, a precision of 1.61x10(-4) mug cm(-2) was achieved, the molar absorptivity being (epsilon) 5.6x10(4) l mol(-1) cm(-1). An FI technique is proposed, and it is possible to determine trace levels of lead by injection into a steam buffered at pH 7.15, containing 70% ethanol: 30% Tris buffer 3.5x10(-3) mol l(-1) (pH=7.2), 1x10(-4) mol l(-1) 5-BrDMPAP. The FIA configuration allows the analysis of 45 samples per hour. The lower limit of detection (LOD) was 1x10(-7) mol l(-1). The calibration plot was linear at least within two orders of magnitude of lead concentration. The use of an HPLC pump for the FI analysis led to a substantial improvement in the analytical performance of the method, which clearly satisfies the typical requirements for control processes.     

Synthesis of a novel chemiluminescent reagent for the determination of hydrogen peroxide in snow waters

7-(4,6-Dichloro-1,3,5-triazinylamino)-4-methylcoumarin (DTMC) was synthesized as a completely new chemiluminescent reagent, and with it a novel chemiluminescence method was developed for the determination of hydrogen peroxide in the absence of any added catalyst or co-oxidant. The chemiluminescence intensity of the DTMC-H(2)O(2) system could be enhanced by the addition of cation surfactants. The chemiluminescence intensity was directly proportional to the concentration of H(2)O(2) in the range 1.0 x 10(-7)-4.0x10(-4) mol l(-1), and the detection limit was 4.0 x 10(-8) mol l(-1). The relative S.D. was 4.9% for 1.0 x 10(-6) mol l(-1) of H(2)O(2) (n=10). The selectivity of this method was high, and most of the transition metal ions have no effect on the determination. The proposed method has been applied to the determination of trace amounts of hydrogen peroxide in snow water. A possible mechanism of the chemiluminescence reaction is also discussed.     

Determination of acetylsalicylic acid by FIA-potentiometric system in drugs after on-line hydrolysis

A potentiometric flow injection (FI) system was developed for the acetylsalicylic acid (ASA) determination in drugs, without previous treatment. The tubular potentiometric electrode for salicylate (SA) was based on tricaprylyl-trimethyl-ammonium-salicylate (aliquat-salicylate) as the ion-exchanger, supported on poly(ethylene-co-vinyl-acetate) (EVA) matrix and applied directly onto a conducting support. The standards and samples were freshly prepared in ethanol solution (0.10 mol l(-1) Tris-SO(4) buffer, pH 8.0, containing 0.25 mol l(-1) Na(2)SO(4) and 8.0% v/v ethanol) to facilitate the dissolution of ASA and were injected directly into the system. The SA formed due to the on-line alkaline hydrolysis of alcoholic ASA solution, with 0.50 mol l(-1) NaOH (coil, 50 cm length), was monitored by the tubular electrode after neutralization with 0.25 mol l(-1) H(2)SO(4). A solution of 0.10 mol l(-1) Tris-SO(4) buffer (pH 8.0), containing 0.25 mol l(-1) Na(2)SO(4) was employed as carrier. In optimized conditions (flow rate of 2.1 ml min(-1) and volume of injection of 150 mul), the tubular electrode showed a linear response to ASA in the concentration range between 4.0x10(-3) and 4.0x10(-2) mol l(-1). A conversion factor of ASA to SA of 85% occurs in these conditions with an increase of about 130% in the signal to the system with on-line hydrolysis (three-channel) in comparison to the system without (one-channel). The response time of the electrode was about 5 s with an analytical frequency of 28 samples per h and a relative standard deviation (R.S.D.) of 2.1% for 30 successive injections. Determinations of ASA in tablet samples by the proposed method exhibited relative differences of 1.0-3.5%, compared to the official method of the British Pharmacopoeia. The useful lifetime of the sensor was greater than 1 month, in continuous use.     

Determination of ascorbic acid in pharmaceuticals and urine by reverse flow injection.

Two reverse flow injection (FI) methods, using spectrophotometric detection, are proposed for the determination of ascorbic acid. Both methods are based on its reaction with the ethylenediaminetetraacetic acid-CoIII complex in a medium of 5% diethylamine. In the first method, using the peak-height FI technique, ascorbic acid is determined over the range from 2 x 10(-4) to 5 x 10(-3) mol dm-3 and in the second, using the peak-width FI method, the working range is extended (2 x 10(-3)-5 x 10(-2) mol dm-3). Both FI methods were applied to the determination of ascorbic acid in pharmaceuticals while the peak-height FI technique was also used to determine ascorbic acid in urine.     

Flow-injection spectrophotometric determination of novalgin in pharmaceuticals using micellar medium.

A sensitive flow-injection (FI) procedure with spectrophotometric detection in a micellar medium is proposed for the determination of novalgin. The method is based on the instantaneous formation of a red-orange product (lambda(max) = 510 nm) after the reaction between novalgin and p-dimethylaminocinnamaldehyde (p-DAC) in a dilute acid medium. The sensitivity of this reaction was increased by a factor of 5.6 in the presence of sodium dodecyl sulfate (SDS). Experimental design methodologies were used to optimize the chemical and FI variables. The calibration curve was linear in the range of 1.45 x 10(-6) to 2.90 x 10(-5) mol L(-1) with an excellent correlation coefficient (r = 0.9999). The detection limit was 1.31 x 10(-7) mol L(-1) (n = 20, RSD = 2.0%). No interferences were observed from the common excipients. The results obtained by the proposed method were favorably compared with those given by the iodometric reference method at 95% confidence level.     

Determination of total phenols in environmental wastewater by flow-injection analysis with a biamperometric detector

A flow injection (FI) method with a biamperometric detector, based on the biamperometry for an irreversible redox couple, is described for the determination of phenols in environmental wastewater. The method relies on coupling of the oxidation of phenols at one platinum-wire electrode with the reduction of MnO4- at another platinum wire electrode to enable biamperometric detection with an applied potential difference of 0 V. The linear dynamic range for the dependence of current on phenol concentration was from 1.0 x 10(-6) to 1.0 x 10(-4) mol L(-1), with a detection limit of 4.0 x 10(-7) mol L(-1) (signal-to-noise ratio, S/N=3). In comparison with the 4-aminoantipyrine (4-AAP) standard method and the 3-methyl-2-benzothiazoline hydrazone (MBTH) method the proposed method can be used to detect many para-substituted phenols that do not react with 4-AAP and MBTH, and response factors are higher for most of the phenols tested. The method, which is simple, economic, and rapid (180 samples h(-1)), has been applied to the analysis of four wastewater samples. The results obtained were compared with those from 4-AAP method. The recoveries obtained by adding phenol standards to samples ranged from 94.3 to 105.2% with a standard deviation of 3.6%.     

Flow-injection spectrophotometric determination of paraoxon by its inhibitory effect on the enzyme acetylcholinesterase.

A spectrophotometric enzymatic flow injection (FI) system for the determination of diethyl-p-nitrophenylphosphate (paraoxon) is proposed. The method was based on the determination of the acetic acid formed by the enzymatic reaction of the acetylcholinesterase, immobilized on glass beads, with the substrate acetylcholine. The acetic acid formed permeates through a PTFE membrane and is received by a solution (pH 7.0) containing the acid-base indicator Bromocresol Purple (B.C.P.), leading to a pH change and therefore to a color change. The variation of the absorbance of the solution is detected spectrophotometrically at 400 nm. The determination of paraoxon is related to its inhibitory action on the enzyme. Therefore the analytical signal is the difference between the signal that corresponds to the free and the one that corresponds to the inhibited enzyme, considering a fixed acetylcholine concentration. The correlation between the peak height and paraoxon concentration at a given acetylcholine concentration is linear in the range from 5.0 x 10(-7) mol L-1 to 5.0 x 10(-5) mol L-1 (r = 0.998) of paraoxon, with a relative estimated standard deviation (R.S.D.) of +/- 1.7% (n = 10) considering a solution containing 5.0 x 10(-6) mol L-1 of paraoxon and a solution containing 5.0 x 10(-3) mol L-1 of acetylcholine. Therefore, the quantitative limit detection is about 2.5 x 10(-7) of paraoxon (3 sigma). A 1,1'-trimethylene-bis(4-formylpyridinium bromide)dioxime (TMB-4) solution was used to reactivate the enzyme.     

Flow injection turbidimetric determination of thiamine in pharmaceutical formulations using silicotungstic acid as precipitant reagent

A simple flow injection system is proposed for the determination of thiamine in pharmaceutical formulations. The determination is based on the precipitation reaction of thiamine with silicotungstic acid in acidic medium to form a thiamine silicotungstate suspension that is measured at 420 nm. Adding 0.05% (w/v) poly(ethyleneglycol) in the carrier solution (0.5 mol l(-1) hydrochloric acid), an improvement in the sensitivity, repeatability and baseline stability of the flow injection system was obtained. The calibration graph was linear in the thiamine concentration range from 5.0x10(-5) to 3.0x10(-4) mol l(-1) with a detection limit of 1.0x10(-5) mol l(-1). The relative standard deviations for ten successive measurements of 1.0x10(-4) mol l(-1) and 2.5x10(-4) mol l(-1) thiamine were less than 1% and an analytical frequency of 90 h(-1) was obtained.     

Kinetic flow-injection determination of hydrogen peroxide by use of iron(III)-catalyzed coloration and its application to the determination of biological substances.

A kinetic flow-injection (FI) method is described for the determination of hydrogen peroxide. This method is based on an iron(III)-catalyzed oxidative coupling of 4-aminoantipyrine with N,N-dimethylaniline by hydrogen peroxide. By measuring the change in the absorbance of the dye formed at 560 nm, 1 x 10(-6) - 6 x 10(-4) M hydrogen peroxide could be determined with a sampling rate of 15 h(-1). The relative standard deviation (n = 30) was 0.8% for 5 x 10(-5) M hydrogen peroxide. There was little interference of the co-existing ions and compounds. After introducing some immobilized enzyme reactors to the FI system, the proposed method allowed the determination of glucose and uric acid ranging from 1 x 10(-6) to 6 x 10(-4) M with relative standard deviations of below 2%. The applicability of the method was demonstrated by determining these substances in serum samples.     

Capillary electrophoretic determination of sulfite using the zone-passing technique of in-capillary derivatization.

A new capillary electrophoretic (CE) method was developed for the simple and selective determination of sulfite. The proposed method is based on the in-capillary derivatization of sulfite with iodine using the zone-passing technique and direct UV detection of iodide formed. The optimal conditions for the separation and derivatization reaction were established by varying concentration of iodine, electrolyte pH and applied voltage. The optimised separations were carried out in 20 mmol l(-1) Tris-HCl electrolyte (pH 8.5) using direct UV detection at 214 nm. Experimental results showed that the injection of the iodine zone from anodic end of the capillary gives significantly better precision. Common UV absorbing anions such as Br-, l-, S2O3(2-), NO3-, NO2-, SCN- did not give any interferences. Valid calibration (r2=0.998) is demonstrated in the range 1 x 10(-5) - 8 x 10(-4) mol l(-1) of sulfite. The detection limit (SIN=3) was 2 x 10(-6) mol l(-1). The proposed system was applied to the determination of free sulfite in wines. The recovery tests established for wine samples were within the range 92-103%. The CE results were compared with those obtained by iodometric titration technique.     

Flotation-spectrophotometric determination of mercury in water samples using iodide and ferroin.

This paper describes a simple and highly selective method for separation, preconcentration and spectrophotometric determination of trace amounts of mercury. The method is based on the flotation of an ion-associate of HgI4(2-) and ferroin between aqueous and n-heptane interface at pH 5. The ion-associate was then separated and dissolved in acetonitrile to measure its absorbance. Quantitative flotation of the ion-associate was achieved when the volume of the water sample containing Hg(II) was varied over 50 - 800 ml. Beer's law was obeyed over the concentration range of 3.2 x 10(-8) - 9.5 x 10(-7) mol l(-1) with an apparent molar absorptivity of 1 x 10(6) l mol(-1) cm(-1) for a 500 ml aliquot of the water sample. The detection limit (n = 25) was 6.2 x 10(-9) mol l(-1), and the RSD (n = 5) for 3.19 x 10(-7) mol l(-1) of Hg(II) was 1.9%. A notable advantage of the method is that the determination of Hg(II) is free from the interference of the almost all cations and anions found in the environmental and waste water samples. The determination of Hg(II) in tap, synthetic waste, and seawater samples was carried out by the present method and a well-established method of extraction with dithizone. The results were satisfactorily comparable so that the applicability of the proposed method was confirmed in encountering with real samples.     

Determination of the herbicide desmetryne in organised media by adsorptive stripping voltammetry

An electroanalytical method for the determination of the herbicide desmetryne at nanomolar levels in dispersed media, based on adsorptive stripping voltammetry, is reported. The adsorption of desmetryne at the hanging mercury drop electrode was checked both in micellar solutions, where the anionic surfactant sodium pentanesulphonate was chosen as the most suitable surfactant agent, and in oil-in-water emulsions prepared with ethyl acetate as the organic solvent. In a micellar medium formed with 0.02% sodium pentanesulphonate and with 0.1 mol l(-1) Britton-Robinson buffer (pH 1.5), the herbicide could be determined over the 1.0 x 10(-8)-4.0 x 10(-7) mol l(-1) concentration range, when an accumulation potential of -0.70 V was applied for 50 s. On the other hand, in an oil-in-water emulsion formed with 2% ethyl acetate and 0.04% sodium pentanesulphonate as emulsifying agent in 0.1 mol l(-1) HClO(4), desmetryne could be determined over the 2.0 x 10(-9)-1.0 x 10(-7) mol l(-1) concentration range. The limits of detection were 2.4 x 10(-9) and 4.2 x 10(-10) mol l(-1) in micellar and emulsified media, respectively, with R.S.D.s (n=10) 3.6 and 3.7%. The degree of interference from some other s-triazines on the desmetryne differential pulse response was also evaluated. Finally, the method developed in emulsified medium was applied to the determination of desmetryne in spiked apple juice.     

Determination of diclofenac sodium by capillary zone electrophoresis with electrochemical detection

Capillary zone electrophoresis was employed for the determination of diclofenac sodium using an end-column amperometric detection with a carbon fiber microelectrode, at a constant potential of 0.83 V vs. saturated calomel electrode. The optimum conditions of separation and detection are 4.90 x 10(-3) mol/l Na2HPO4-3.10 x 10(-3) mol/l NaH2PO4 (pH 7.0) for the buffer solution, 10 kV for the separation voltage, 5 kV and 10 s for the injection voltage and the injection time, respectively. The limit of detection is 2.5 x 10(-6) mol/l or 5.2 fmol (S/N=2). The relative standard deviation is 0.8% for the migration time and 4.7% for the electrophoretic peak current. The method was applied to the determination of diclofenac sodium in human urine.     

Evaluation of luminol-H(2)O(2)-KIO(4) chemiluminescence system and its application to hydrogen peroxide, glucose and ascorbic acid assays

A novel chemiluminescence (CL) system was evaluated for the determination of hydrogen peroxide, glucose and ascorbic acid based on hydrogen peroxide, which has a catalytic-cooxidative effect on the oxidation of luminol by KIO(4). Hydrogen peroxide can be directly determined by luminol-KIO(4)-H(2)O(2) CL system. The detection limit was 3.0x10(-8) mol l(-1) and the calibration graph was linear over the range of 2.0x10(-7)-6.0x10(-4) mol l(-1). The relative standard deviation of H(2)O(2) was 1.1% for 2.0x10(-6) mol l(-1) (N=11). Glucose was indirectly determined through measuring the H(2)O(2) generated by the oxidation of glucose in the presence of glucose oxidase at pH 7.6. The present method provides a source for H(2)O(2), which, in turn, coupled with the luminol-KIO(4)-H(2)O(2) CL reaction system. The CL was linearly correlated with glucose concentration of 0.6-110 mug ml(-1). The relative standard deviation was 2.1% for 10 mug ml(-1) (N=11). Detection limit of glucose was 0.08 mug ml(-1). Ascorbic acid was also indirectly determined by the suppression of luminol-KIO(4)-H(2)O(2) CL system. The calibration curve was linear over the range of 1.0x10(-7)-1.0x10(-5) mol l(-1) of ascorbic acid. The relative standard deviation was 1.0% for 8.0x10(-7) mol l(-1) (N=11). Detection limit of ascorbic acid was 6.0x10(-8) mol l(-1). These proposed methods have been applied to determine glucose, ascorbic acid in tablets and injection.     

Spectrophotometric determination of fluoxetine by batch and flow injection methods

A rapid, simple, and accurate spectrophotometric method is presented for the determination of fluoxetine by batch and flow injection analysis methods. The method is based on fluoxetine competitive complexation reaction with phenolphthalein-beta-cyclodextrin (PHP-beta-CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addition of fluoxetine was measured. The formation constant for fluoxetin-beta-CD was calculated by non-linear least squares fitting. Fluoxetine can be determined in the range 7.0 x 10(-6)-2.4 x 10(-4) mol l(-1) and 5.0 x 10(-5)-1.0 x 10(-2) mol l(-1) by batch and flow methods, respectively. The limit of detection and limit of quantification were respectively 4.13 x 10(-6) mol l(-1) and 1.38 x 10(-5) mol l(-1) for batch and 2.46 x 10(-5) mol l(-1) and 8.22 x 10(-5) mol l(-1) for flow method. The sampling rate in flow injection analysis method was 80+/-5 samples h(-1). The method was applied to the determination of fluoxetine in pharmaceutical formulations and after addition to human urine samples.     

Electroregenerable anion-exchange resin with triiodide carbon paste electrode for the voltammetric determination of adrenaline

An electroregenerable carbon paste electrode modified with triiodide ions immobilized in an anion-exchange resin (Lewatit M500) is proposed for the determination of adrenaline in pharmaceutical products by differential-pulse voltammetry (DPV). Adrenaline was chemically converted into adrenochrome by the I3- ions at the electrode surface. The electrochemical reduction back to adrenaline was obtained at a potential of -0.16 V vs. Ag/AgCl (3 mol l(-1) KCl). A 20% decrease of the initial analytical signal was observed after 350-400 determinations; the carbon paste electrode was 100% electroregenerated at a fixed potential of +0.65 V vs. Ag/AgCl (3 mol l(-1) KCl) in 0.1 mol l(-1) KI solution for 20 min. The differential-pulse voltammograms were obtained by applying a sweep potential between 0.0 and -0.34 V, following the adrenochrome reduction at -0.16 V. Under the optimum conditions established, such as pH 6.0; scan rate 20 mV s(-1) and pulse amplitude 50 mV, the calibration curve was linear from 2.0 x 10(-5) to 3.1 x 10(-4) mol l(-1) adrenaline with a detection limit of 3.9 x 10(-6) mol l(-1). The recovery of adrenaline ranged from 99.8 to 103.1% and the RSD was 2.6% for the solution containing 1.0 x 10(-4) mol l(-1) adrenaline (n = 10). The results obtained for adrenaline in pharmaceutical samples using the proposed carbon paste electrode are in agreement with those obtained using a pharmacopoeial procedure at the 95% confidence level.     

Determination of thallium(I) by flotation-spectrophotometric method using iodide and rhodamine B.

A method for the trace amount determination of Tl(I), via its preconcentration, is proposed. The method is based on the reaction of iodide, Tl(I) and Rhodamine B in a weakly acidic medium. In this process an ion-associated complex is formed, which is floated at the interface of aqueous-cyclohexane layers. Various amounts of Tl(I) by a subsequent separation and dissolution of the floated complex in methanol could be determined, spectrophotometrically. Beer's law was obeyed for the Tl(I) content in the range of (0.8-8.0) x 10(-7) mol l(-1) with a correlation coefficient of 0.9974. The conditional molar absorptivity was found to be 1.0 x 10(6) l mol(-1) cm(-1) at 560 nm, which indicated the considerable sensitivity of the procedure. The detection limit (DL) was 4.7 x 10(-8) mol l(-1) and the RSD (n = 5) for 4 x 10(-7) mol l(-1) of Tl(I) was 3.34%. None of the alkaline cations was interfered, and the interference of many other metal ions was eliminated via ion-exchange separation using a cation-exchanger resin, Amberlite IR-120, before the flotation step. The reliability of the procedure was confirmed by determining the Tl(I) contents of synthetic laboratory waste water by both flotation spectrophotometry and graphite furnace atomic absorption spectrometry (GFAAS). The recovery was 92.3-95.4% for 1 x 10(-7) and 4 x 10(-7) mol l(-1), respectively. The precision and accuracy of the results were comparable via F and t tests at the 95% confidence level.     

Use of ion-selective electrodes in kinetic flow injection: determination of phenolic and hydrazino drugs with 1-fluoro-2,4-dinitrobenzene using a fluoride-selective electrode.

A flow injection (FI) kinetic potentiometric method for the determination of phenolic (acetaminophen and isoxsuprine) and hydrazino (isoniazid) drugs is described. This work shows the usefulness of ion-selective electrodes as detectors in FI systems, not only for direct ion determination but also in routine kinetic analysis. The method is based on the reaction of 1-fluoro-2,4-dinitrobenzene (FDNB) with the analytes in a weakly alkaline medium, which proceeds through the liberation of fluoride from the reagent. The slow reactions with phenols are catalysed by micelles of cetyltrimethylammonium bromide. The reaction rate is monitored with a fluoride-selective electrode in a wall-jet configuration and is used to construct a calibration graph of antilog(delta E/S)-1 versus c (where E = potential, s = slope of the electrode and c = concentration), using the fixed-time approach. The response time and the long-term stability of the electrode were found to be adequate for such kinetic determinations. The proposed method overcomes problems associated with end-point spectrophotometric methods using FDNB and allows measurements in highly coloured or turbid solutions. The optimized method has a linear concentration range of 1 x 10(-4)-50 x 10(-4) mol dm-3, a measurement throughput of 20 or 40 per hour and the precision ranges from 1.8 to 3.6% relative standard deviation (n = 3). Results obtained for commercial pharmaceutical formulations compare favourably with those given by reference methods.     

Chemiluminescence flow injection analysis of 1,3-dichloro-5,5-dimethylhydantoin in swimming pool water

A new chemiluminescence (CL) flow-injection method is proposed for the determination of 1,3-dichloro-5,5-dimethylhydantoin (DDH). The method is based on the chemiluminescent reaction of DDH and luminol-H(2)O(2) in an alkaline medium (pH 12.0-12.5). The concentration of the analyte shows a good linear relationship with the produced luminescence intensity in the range of 3.0x10(-8) to 8.0x10(-6) mol l(-1). The detection limit of the proposed method is 1.0x10(-8) mol l(-1) and the relative standard deviation (R.S.D.) is 4.7% (n=5) at 5.0x10(-7) mol l(-1). This method was successfully applied to the determination of trace amounts of this disinfectant in water samples obtained from five different swimming pools. Satisfying recovery values were also obtained.     

Lead as own luminescent sensor for determination

In our experiments, it was observed that adding bromide to Pb2+ solution of N,N'-dimethylformamide (DMF), the highly emissive cluster Pb4Br11(3-) can be formed and the fluorescence intensity of the formed cluster is proportional to the concentration of Pb2+, based on which, a novel, simple approach that uses the emission from itself as the sensor for determination of Pb2+ is proposed. Under the optimum conditions, the linear range and detection limit is 1.0 x 10(-7) to 1.0 x 10(-5) mol l(-1) (correlation coefficient r = 0.9997) and 7.6 x 10(-9) mol l(-1), respectively. Foreign substrates effects were also investigated. The proposed method has been successfully applied to the determination of lead in the synthetic samples. The mechanism of the reaction is also studied.