Determination of bromide ions in seawater using flow system with chemiluminescence detection

A simple flow-based procedure with chemiluminescence (CL) detection is proposed for bromide ion determination in seawater. The procedure was based on the oxidation of bromide to bromine by chloramine-T followed by the reaction of bromine with luminol resulting in CL emission. Since no significant reaction within chloramine-T and luminol was observed, the detection was carried out without bromine extraction from the oxidant medium. The proposed flow system had a sampling rate of 40 determinations per hour, reagents consumption of 100 μg luminol and 60 μg chloramine-T per determination, a limit of detection of 0.5 mg l⁻¹ bromide ions, a linear concentration range (r = 0.999 and n = 7) between 0 and 100 mg l⁻¹, and a coefficient of variance better than 2.5% (for 10 measurements of a 10 mg l⁻¹ Br⁻ solution) were achieved. The analytical system was applied for the determination of bromide in seawater and estuarine-water samples, obtaining an analyte recovery ranging from 94 to 102% and comparing the results with a reference spectrophotometric method no significant difference was observed in 95% confidence level.     

Determination of bismuth and zinc in pharmaceuticals by first derivative UV-Visible spectrophotometry

A first order derivative spectrophotometric method has been developed for the simultaneous determination of bismuth and zinc by dithizone without time-consuming extraction step. The reactions of bismuth and zinc with dithizone in a three component solution prepared in water, acetone and n-propanol mixture have been investigated. These cations react with dithizone in this mixture at pH 5.0, forming coloured complex that is stable for at least 2 h. The linear range in D evaluation was between 3.0 × 10⁻⁶ and 1.8 × 10⁻⁵ mol l⁻¹ for Zn and 2.4 × 10⁻⁶ and 1.2 × 10⁻⁵ mol l⁻¹ for Bi. The limits of detection for the analytical procedure were found 0.05 mg l⁻¹ for both cations. The relative standard deviations for the determination of 0.5 mg l⁻¹ bismuth and 0.5 mg l⁻¹ zinc were 1.2 and 1.1%, respectively, for five determinations. The procedure is simple, rapid and reliable. This method was applied to the determination of bismuth and zinc in the pharmaceutical materials successfully. Good agreement was achieved between the results obtained by the proposed and comparative methods.     

Evaluation of a fluorometric-enzymatic method based on 3alpha-hydroxysteroid dehydrogenase for the mycotoxin zearalenone determination in corn

A new method for the fluorometric determination of zearalenone (ZEN) based on its reaction with βNADH in the presence of the enzyme 3α-hydroxysteroid dehydrogenase (3α-HSD) is described. The procedure is based on the change in fluorescence intensity that takes place during the enzymatic reaction (excitation at 340 nm and emission at 454 nm). The optimum reaction conditions and the analytical characteristics were studied; linear response range (1-10 mg l⁻¹) and reproducibility (8 mg l⁻¹, 2.7%, n=7). Moreover, a mathematical model explaining the analytical signal is proposed. The method has been applied to zearalenone determination in a spiked corn sample.     

Sensor film for Vitamin C determination based on absorption properties of polyaniline

An analytical method based on the absorption changes of chemically polymerised polyaniline at 700 nm is proposed for the determination of Vitamin C. Vitamin C produces a polyaniline film reduction, originating changes in its absorbance proportional to the Vitamin C concentration. The optimum reaction conditions and the analytical characteristics have been studied. The linear response of the method ranged from 0.10 to 1.0 mg l⁻¹ for a 6 min reaction time and from 1.0 to 8.0 mg l⁻¹ for a 2 min reaction time. Reproducibility, expressed as the coefficient of variation, was 0.8% (6 min reaction time) and 2.3% (2 min reaction time) (n = 10). The method has been applied to Vitamin C determination in pharmaceutical preparations and commercial fruit juices. The results were compared with those obtained by the 2,6-dichlorophenolindophenol titration method (the AOAC Official Method) and no systematic errors were observed.     

Spectrofluorimetric determination of tannins based on their activative effect on the Cu(II) catalytic oxidation of rhodamine 6G by hydrogen peroxide

A simple and highly sensitive kinetic fluorimetric method is proposed for the determination of trace tannins, based on the activation of tannins on the oxidation of rhodamine 6G (Rh 6G) by hydrogen peroxide catalyzed by Cu(II) ion. The calibration graph was rectilinear in the range 0.08-1.28 mg l⁻¹ for tannin, the 3σ detection limit for tannin is 0.0455 mg l⁻¹. The relative standard deviation for 11 determinations of 0.4 mg l⁻¹ tannin is 0.96%. The proposed method has been successfully used to determine tannins in tea and Chinese gall. The results obtained were compared with those provided by the Folin-Ciocalteu method. This is the first procedure to be reported for the determination of tannins based on fluorimetric measurements.     

Sequential injection spectrophotometric determination of phenylephrine hydrochloride in pharmaceutical preparations

A fully automated sequential injection spectrophotometric method for the determination of phenylephrine hydrochloride in pharmaceutical preparations is reported. The method is based on the condensation reaction of the analyte with 4-aminoantipyrine in the presence of potassium ferricyanide. The absorbance of the condensation product was monitored at 503 nm. A linear relationship between the relative peak height and concentration was obtained in the range 0.5-17.5 mg l⁻¹. The detection limit (as 3σ value) was 0.09 mg l⁻¹ and repeatability was 0.8 and 0.6% at 2.5 and 5 mg l⁻¹, respectively. Results obtained by this method agreed very well with those obtained by the AOAC official method.     

A multicommuted flow system for sequential spectrophotometric determination of hydrosoluble vitamins in pharmaceutical preparations

A multicommuted flow system is proposed for spectrophotometric determination of hydrosoluble vitamins (ascorbic acid, thiamine, riboflavine and pyridoxine) in pharmaceutical preparations. The flow manifold was designed with computer-controlled three-way solenoid valves for independent handling of sample and reagent solutions and a multi-channel spectrophotometer was employed for signal measurements. Periodic re-calibration as well as the standard addition method was implemented by using a single reference solution. Linear responses (r=0.999) were obtained for 0.500-10.0 mg l⁻¹ ascorbic acid, 2.00-50.0 mg l⁻¹ thiamine, 5.00-50.0 mg l⁻¹ riboflavine and 0.500-8.00 mg l⁻¹ pyridoxine. Detection limits were estimated as 0.08 mg l⁻¹ (0.5 μmol l⁻¹) ascorbic acid, 0.8 mg l⁻¹ (2 μmol l⁻¹) thiamine, 0.2 mg l⁻¹ (0.5 μmol l⁻¹) riboflavine and 0.1 mg l⁻¹ (0.9 μmol l⁻¹) pyridoxine at 99.7% confidence level. A mean sampling rate of 60 determinations per hour was achieved and coefficients of variation of 1% (n=20) were estimated for all species. The mean reagent consumption was 25-fold lower in relation to flow-based procedures with continuous reagent addition. Average recoveries between 95.6 and 100% were obtained for commercial pharmaceutical preparations. Results agreed with those obtained by reference methods at 95% confidence level. The flow system is suitable for application in quality control processes and in dissolution studies of vitamin tablets.     

Artificial neural networks study of the catalytic reduction of resazurin: stopped-flow injection kinetic-spectrophotometric determination of Cu(II) and Ni(II)

An artificial neural network (ANN) procedure was used in the development of a catalytic spectrophotometric method for the determination of Cu(II) and Ni(II) employing a stopped-flow injection system. The method is based on the catalytic action of these ions on the reduction of resazurin by sulfide. ANNs trained by back-propagation of errors allowed us to model the systems in a concentration range of 0.5-6 and 1-15 mg l⁻¹ for Cu(II) and Ni(II), respectively, with a low relative error of prediction (REP) for each cation: REP_Cu(II) = 0.85% and REP_Ni(II) = 0.79%. The standard deviations of the repeatability (s_r) and of the within-laboratory reproducibility (s_w) were measured using standard solutions of Cu(II) and Ni(II) equal to 2.75 and 3.5 mg l⁻¹, respectively: s_r[Cu(II)] = 0.039 mg l⁻¹, s_r[Ni(II)] = 0.044 mg l⁻¹, s_w[Ni(II)] = 0.045 mg l⁻¹ and s_w[Ni(II)] = 0.050 mg l⁻¹. The ANNs-kinetic method has been applied to the determination of Cu(II) and Ni(II) in electroplating solutions and provided satisfactory results as compared with flame atomic absorption spectrophotometry method. The effect of resazurin, NaOH and Na₂S concentrations and the reaction temperature on the analytical sensitivity is discussed.     

Chemiluminometric determination of the pesticide 3-indolyl acetic acid by a flow injection analysis assembly

A new method is proposed for the chemiluminescent determination of the pesticide 3-indolyl acetic acid by means of an flow injection analysis system. The chemiluminescence emission is obtained by oxidation of the analyte with Ce (IV) in nitric acid and presence of β-cyclodextrine.The continuous-flow method allows the determination of 159 samples h⁻¹ of 3-indolyl acetic acid in an interval of concentrations over the range 0.5-15.0 mg l⁻¹. The limit of detection was 0.1 μg l⁻¹ and the R.S.D. (n, 17) at 2.0 mg l⁻¹ of the pesticide level was 2.7%. The method was applied to water samples.     

Determination of myo-inositol hexakisphosphate (phytate) in urine by inductively coupled plasma atomic emission spectrometry

Myo-inositol hexakisphosphate (phytate) is a substance present in urine with an important role in preventing calcium renal calculi development. In spite of this, the use of urinary phytate levels on stone-formers’ evaluation and treatment is still notably restricted as a consequence of the enormous difficulty to analyze this substance in urine. In this paper, a simple procedure for routinary urinary phytate determination based on phosphorus determination through inductively coupled plasma atomic emission spectrometry is described.The method only requires a previous separation of phytate from other components by column anion exchange chromatography. The working linear range used was 0-2 mg l⁻¹ phosphorus (0-7 mg l⁻¹ phytate). The limit of detection was 64 μg l⁻¹ of phytate and the limit of quantification was 213 μg l⁻¹. The relative standard deviation (R.S.D.) for 1.35 mg l⁻¹ phytate was 2.4%. Different urine samples were analyzed using an alternative analytical methodology based on gas chromatography (GC)/mass detection used for inositol determination (phytate was previously hydrolyzed), resulting both methods comparable using as criterion to assess statistical significance P<0.05.     

Flow injection-chemiluminescence determination of propranolol in pharmaceutical preparations

A rapid and precise continuous-flow method is described for the determination of propranolol based on the chemiluminescence (CL) produced by its reaction with potassium permanganate in a sulphuric acid medium. The optimum chemical conditions for the chemiluminescence emission were investigated. Two manifolds were tested and their characteristics such as the length of the reactor, injection volume and flow rate were compared. When using the selected manifold, propranolol gives a linear calibration graph over the concentration range 1.0-17.5 mg l⁻¹. The detection limit calculated as proposed by IUPAC was 70 ng ml⁻¹ and the detection limit calculated as proposed by Clayton was 0.87 mg l⁻¹. For analysis of 10 solutions of 10.0 mg l⁻¹ propranolol, if error propagation theory is assumed, the relative error was 0.1%. The standard deviation (S.D.) for 10 replicate samples was 0.07 mg l⁻¹. The method has been validated versus a published fluorimetric method.The present chemiluminescence procedure was applied to the determination of propranolol in simple British and Spanish pharmaceutical formulations, with excellent recoveries, as the determination is free from interference from common excipients. However, some drugs, such as hydralazine and bendroflumethizide which may also be present in the formulation, increase the emission intensity.     

An improved flow system for chloride determination in natural waters exploiting solid-phase reactor and long pathlength spectrophotometry

A single and sensitive spectrophotometric method for chloride ions determination based on a commuted flow system with a 100 cm optical path flow cell and a solid-phase reactor containing immobilized silver chloranilate was proposed. This procedure exploited the AgCl formation in the solid-phase reactor leading the chloranilate ions, monitored spectrophotometrically at 530 nm. The analytical signals were 75-fold higher and the sensitivity was 12-fold than that achieved with a 1 cm flow cell, allowed a chloride determination in the 0.5-100 mg l⁻¹ range. The R.S.D. was 1.1% (n = 20) with a sample throughput of 80 h⁻¹ and a waste generated of ca. 100 ng of chloranilate ions per determination. Four samples of natural waters from São Carlos and Araraquara cities were evaluated using the proposed method. Results agreed with the obtained by a reference method at the 95% confidence level.     

Fluorescence anisotropy: application in quantitative enzymatic determinations

In this work a method is presented for the enzymatic determination of glucose using fluorescence anisotropy. During the enzymatic reaction a change in the fluorescence anisotropy of the glucose oxidase (GOx) is produced; the reaction time at which this change appears (t_m) depends on the glucose concentration. A theoretical study has been developed which enables: (a) the correlation of this change in anisotropy with changes in the intensity and the lifetime of the enzyme fluorescence; from this a model which could be generalized to other flavo-enzymes is proposed; (b) the linking of t_m with glucose concentration.After optimisation, the proposed method allows the determination of glucose over the range 100-1000 mg l⁻¹. The detection limit is 90 mg l⁻¹and the reproducibility is better than 4% (n = 6, [glucose] = 250 mg l⁻¹). Anisotropy is more selective than conventional fluorescence intensity, and this method has therefore been applied to direct glucose determination in fruit juices without the interference caused by the inner filter effect.     

Chemiluminometric photo-induced determination of Strychnine in a Multicommutation flow assembly

This paper deals on the determination of Strychnine, a potent and dangerous pesticide and the analytical procedure is based on the photo-induced chemiluminescence of the pesticide by means of the Multicommutation continuous-flow methodology. Small segments of the pesticide solution were sequentially alternated with segments of the solution for adjusting the suitable medium for the photodegradation. The required time of UV irradiation was obtained by stopped-flow during 150 s; then, the resulting solution formed alternated segments with the oxidizing solution containing 5 × 10⁻³ mol l⁻¹ Ce(IV) in 0.6 mol l⁻¹ nitric acid. The calibration range, from 2 μg l⁻¹ to 50 mg l⁻¹, resulted in a linear behaviour over the range 25 μg l⁻¹ to 20 mg l⁻¹ and fitting the equation: I = 4706x + 624 with a correlation coefficient of 0.9955. The limit of detection was 2 μg l⁻¹ and the sample throughput 15 h⁻¹. After testing the influence of a large series of potential interferents, the method was applied to different kinds of samples.     

Solvent extraction flow-injection manifold for the simultaneous spectrophotometric determination of free cyanide and thiocyanate ions based upon on-line masking of cyanides by formaldehyde

This study reports a sensitive solvent extraction flow-injection (FI) method for the simultaneous spectrophotometric determination of free cyanide and thiocyanate in human saliva and pralidoxime solutions. Cyanide and thiocyanate form colored (λ_max=540 nm) ternary complexes with copper and 2,2′-dipyridyl-2-quinolylhydrazone (DPQH) that are extractable into chloroform. The determination of thiocyanates in the presence of cyanides is accomplished after on-line masking of the latter with formaldehyde through a binary inlet static mixer (BISM). Total thiocyanates and cyanides are determined in a second run, without the use of the masking agent. The proposed method allows the determination of the analytes in the range of 0-4 mg l⁻¹ thiocyanates and 0-3 mg l⁻¹ cyanides, with the 3σ detection limits being 0.007 and 0.004 mg l⁻¹, respectively. The precision of the method (s_r<1.0% at 1 mg l⁻¹ CN⁻ or SCN⁻, n=12 in both cases) and the sampling rates were quite satisfactory (60 injections per hour). The method was applied to the analysis of human saliva and pralidoxime solutions and gave recoveries in the range of 98.0-102.2% for both analytes whereas the mean relative error was e_r=1.7%.     

Flow-injection turbidimetric determination of homatropine methylbromide in pharmaceutical formulations using silicotungstic acid as precipitant reagent

A flow-injection turbidimetric procedure exploiting merging zones is proposed for determining homatropine methylbromide (HMB) in pharmaceutical preparations. The determination is based on the precipitation reaction of homatropine methylbromide with silicotungstic acid in acidic medium to form a precipitate, which was measured at 410 nm. The analytical curve was linear in the HMB concentration range from 8.1 × 10⁻⁵ to 2.2 × 10⁻⁴ mol l⁻¹, with a detection limit of 5.0 × 10⁻⁶ mol l⁻¹. The recoveries ranged from 96 to 103%, the sampling frequency was 70 determinations per hour and relative standard deviations were less than 1.5% (n = 10). The results obtained for commercial formulations using the FIA procedure were in good agreement with those obtained by using a comparative method.     

Sequential injection lab-on-valve simultaneous spectrophotometric determination of trace amounts of copper and iron

A sequential injection (SI) method in a lab-on-valve (LOV) format for simultaneous spectrophotometric determination of copper and iron has been devised. The detection chemistry is based on the complex formation of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) with copper(II) and/or iron(II) at pH 4.6. Copper(II) reacts with 5-Br-PSAA to form the complex which has an absorption maximum at 580 nm but iron(III) does not react. In the presence of a reducing agent only iron(II)-5-Br-PSAA complex is formed and detected at 558 nm. Under the optimum experimental conditions, the determinable ranges are 0.1-2 mg l⁻¹ for copper and 0.1-5 mg l⁻¹ for iron, respectively, with a sampling rate of 18 h⁻¹. The limits of detection are 50 μg l⁻¹ for copper and 25 μg l⁻¹ for iron. The relative standard deviations (n = 15) are 2% for 0.5 mg l⁻¹ copper and 1.8% for 0.5 mg l⁻¹ iron when determined in standard solutions. The recoveries range between 96 and 105% when determining 0.25-2 mg l⁻¹ of copper and 0.2-5 mg l⁻¹ of iron in artificial mixtures at copper/iron ratios of 1:10 to 5:1. The proposed SI-LOV method is successfully applied to the simultaneous determination of copper and iron in multi-element standard solution and in industrial wastewater samples.     

Analytical strategy photodegradation/chemiluminescence/continuous-flow multicommutation methodology for the determination of the herbicide Propanil

The present paper is dealing with an analytical strategy based on coupling photodegradation, chemiluminescence and multicommutation continuous-flow methodology for the determination of the pesticide Propanil, a common herbicide. The pesticide solution is inserted as small segments sequentially alternated with segments of the solution for adjusting the suitable medium for the photodegradation. Both flow-rates (sample and medium) are adjusted to required time for photodegradation, 2.0 min; and then, the resulting solution is also sequentially inserted as segments alternated with segments of the oxidizing solutions system, 1.00 × 10⁻⁴ mol l⁻¹ potassium permanganate in 2.00 mol l⁻¹ sulphuric acid medium. The calibration range, from 10 μg l⁻¹ to 25 mg l⁻¹, resulted in a linear behaviour over the range 10 μg l⁻¹-5 mg l⁻¹ and fitting the linear equation: I = 780.30C + 95.28; correlation coefficient 0.9999. The limit of detection was 8 μg l⁻¹ and the sample throughput 20 h⁻¹. After testing the influence of a large series of potential interferents the method is applied to water samples obtained from different places and to one formulation. The method is valid for the determination of other pesticides from the same chemical family, namely: alachlor, flumetsulam, furalaxyl and ofurace. Calibration graphs, limits of detection, repeatability and determination in water samples are obtained for each reported pesticide.     

A green analytical procedure for flow-injection determination of nitrate in natural waters

Nitrate determination in waters is generally carried out with cadmium filings and carcinogenic reagents or by reaction with phenolic compounds in highly concentrated sulfuric acid medium. In this work, it was developed a green analytical procedure for nitrate determination in natural waters based on direct spectrophotometric measurements in ultraviolet, using a flow-injection system with an anion-exchange column for separation of nitrate from interfering species. The proposed method employs only one reagent (HClO₄) in a minimum amount (equivalent to 18 μL concentrated acid per determination), and allowed nitrate determination within 0.50-25.0 mg L⁻¹, without interference of up to 200.0 mg L⁻¹ humic acid; 1.0 mg L⁻¹ NO₂⁻; 200.0 mg L⁻¹ PO₄³⁻; 75.0 mg L⁻¹ Cl⁻; 50.0 mg L⁻¹ SO₄²⁻ and 15.0 mg L⁻¹ Fe³⁺. The detection limit (99.7% confidence level) and the coefficient of variation (n = 20) were estimated as 0.1 mg L⁻¹ and 0.7%, respectively. The results obtained for natural water samples were in agreement with those achieved by the reference method based on nitrate reduction with copperized cadmium at the 95% confidence level.     

Solid-phase fluorescence spectroscopy for the determination of acetylsalicylic acid in powdered pharmaceutical samples

A rapid, simple and rugged procedure without requiring any prior sample treatment was developed for the determination of acetylsalicylic acid (ASA) in tablets formulations by solid-phase fluorescence spectroscopy. The method was carried out on powdered samples, consisting of an active substance dispersed in lactose, maize starch, talc and magnesium stearate. Previous knowledge of the sample bulk composition is needed for proper application of the method. Wavelengths for maximum excitation and emission were 288 and 318 nm, respectively, and the fluorescence intensity was linear with ASA concentration within the 50-170 mg g⁻¹ range. Detection and quantification limits were 2.2 and 7.3 mg g⁻¹, and the analytical frequency was 200 h⁻¹. For a typical sample, the relative standard deviation of results was estimated as 2.3% (n = 10). Accuracy was assessed by comparing the analytical results obtained with the proposed method with those related to a reference method recommended by British Pharmacopoeia: no differences between the methods were found at the 95% confidence level.