Fluorimetric determination of arsanilic acid by flow-injection analysis using on-line photo-oxidation

A flow-injection-fluorimetric method for the determination of arsanilic acid is proposed. The assay is based on the on-line decomposition of arsanilic acid in the presence of peroxydisulfate on irradiation with UV light. The arsenate generated in the photochemical reaction was reacted with molybdate in dilute nitric acid to form arsenomolybdic acid, which oxidised thiamine to thiochrome. The thiochrome was monitored fluorimetrically at 440 nm with excitation at 375 nm. The calibration graph was linear in the range 0.10-10.8 microg mL(-1) with a correlation coefficient of 0.999. The detection limit was 0.01 microg mL(-1) and the sample throughput was 55 samples h(-1). The applicability of the method was demonstrated by determining arsanilic acid in animal foodstuffs and water.     

Fluorimetric differential-kinetic determination of silicate and phosphate in waters by flow-injection analysis

A flow-injection analysis (FIA) method for simultaneous determination of silicate and phosphate, based on the different rates of formation of their molybdate heteropoly acids is suggested. The fluorimetrically monitored product is thiochrome, formed by oxidation of thiamine by the heteropoly acid. The FIA configurations designed allow performance of two measurements at different times on each sample injected. The method permits the determination of these anions in the range 30-600 ng ml in ratios from 1:10 to 10:1 and can be applied to samples of running and bottled water with good results. The sampling frequency achievable is 60 hr .     

Fluorimetric determination of phenothiazine derivatives by photooxidation in a flow-injection system

Flow-injection analysis (FIA) was combined with photochemically induced fluorescence (PF) detection for the determination of four phenothiazine derivatives, including unsubstituted phenothiazine, thionine, Azure A and Methylene Blue. The working analytical parameters (flow-rate, injected volume, photoreactor length) were optimized. Linear calibration graphs were obtained over about two orders of magnitude, with relative standard deviation within the range 1-2.3%. Limits of detection were between 13 and 35 ng/ml, according to the compound. The FIA-PF method was applied to the determination of phenothiazines in urine samples. Mean recoveries ranged from 94 to 117%.     

Fluorimetric enzymatic flow-injection determination of bile acids in human serum

Summary A fast, simple and convenient method for the individual and total determination of bile acids based on the enzymatic oxidation of the analytes and the fluorimetric measurement of a reaction product (the reduced form of the coenzyme, NADH) is proposed. The method allows the determination of the analytes (taurocholic, chenocholic, glycocholic and chenodesoxycholic acid) over the range of 0.3–10.0 g ml^–1, with an r.s.d. smaller than 3.0% in each case. It was applied to the determination of total bile acids in human serum. The simplicity of the method makes it useful for screening clinical samples in order to avoid implementing chromatographic processes on samples with analyte overall contents clearly below pathological limits.     

Fluorometric determination of diphenhydramine by flow-injection analysis

A sensitive, rapid and simple flow injection procedure for the determination of diphenhydramine has been designed based on a fluorometric approach. An aqueous solution of diphenhydramine is injected into a carrierreagent stream containing Ce(IV) in dilute sulphuric acid and the fluorescence intensity of the Ce(III) produced is monitored. Chemical, FIA and instrumental variables were optimized. Analytical features of the method are: linear range 0.2–2 ppm, precision 0.7%, sample throughput 80/h. The influence of some foreign substances which can be found in typical pharmaceutical samples containing diphenhydramine was also investigated. The diphenhydramine content of a pharmaceutical preparation was determined.     

Fluorimetric determination of uranium(VI) in waters by flow-injection analysis after preconcentration on a silica gel microcolumn

A method was developed for the selective determination of trace concentrations of uranium(VI) by flow-injection analysis (FIA) with fluorimetric detection. Uranium(VI) is selectively separated and/or pre-concentrated from a volume up to 20 ml on an activated silica gel microcolumn (2 x 40 mm) from a medium of 0.03M EDTA, 0.06M tartrate, and/or 0.05M NaF at pH = 9.3. After washing the column the uranium is eluted with a mixture of 1.33M sulphuric and phosphoric acids and determined with a relative standard deviation not exceeding 6% for concentrations in the range 10-250 mug/l. The detection limit was estimated to be 0.1-0.2 mug of uranium. The method has been verified on artificial water samples with high content of the interfering elements and applied to analysis of waste and natural waters.     

流动注射结合化学发光法测定没食子酸

基于没食子酸与铬 (Ⅵ )的氧化还原反应 ,产生的铬 (Ⅲ )催化鲁米诺 H2 O2 化学发光体系的研究 ,结合流动注射技术 ,优化反应条件 ,建立了一种高灵敏度的快速测定没食子酸的新方法。方法的线性范围为 2 .0× 1 0 - 9～ 5 .0× 1 0 - 6g/mL ,检出限为 1 .2× 1 0 - 9g/mL ,对 1 .0× 1 0 - 7g/mL的没食子酸进行了 1 1次平行测定 ,相对标准偏差为 2 .1 %。方法成功地用于健民咽喉片中没食子酸的测定。     

Sequential determination of iron and titanium by flow-injection analysis

A flow-injection method has been developed for the sequential spectrophotometric determination of iron and titanium using 3,4 dihydroxybenzoic acid as chromogenic reagent. The system involves the sequential measurement of the absorbances of the complexes at 380 and 570 nm. The system is designed using a simultaneous injection of sample and reagent into separate carrier streams. The proposed method is characterized by a precision of about 2%, a sampling rate of about 50 samples per hour, and a reagent consumption of 200 mul (0.50% solution) per sample. It is relatively free of interferences and was used for the sequential determination of titanium and iron in rocks.     

Spectrophotometric determination of iron with ferrozine by flow-injection analysis

Two methods for the determination of iron by normal FIA and reversed FIA were developed using sodium 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4'-disulphonate (ferrozine). The reagent formed a chelate with Fe(II) in hexamethylentetramine buffered medium at pH 5.5. In one previous reaction coil Fe(III) was reduced to Fe(II) by ascorbic acid and in the other reaction coil the complexation reaction was developed. The linear range of the determination was 0.5-6 and 0.1-5 mug ml(-1) of iron for normal FIA and reversed FIA respectively. The proposed method was sensitive (detection limit 0.012 and 0.010 mug ml(-1)), rapid and reproducible (RSD 0.3 and 0.28%). The method was satisfactorily applied to the determination of iron in waste water, toadstool tissue, potato leaves, human hair and bauxites at a sampling rate of 90 and 50 samples h(-1) for normal FIA and reversed FIA respectively.     

On-line determination of sulphite in brine by flow-injection analysis

A spectrophotometric flow-injection procedure for the determination of sulphite in aqueous media over the range 0.5–20 mg 1^?1 is described. The reagent used was the organic disulphide 5,5′-dithiobis(2-nitrobenzoic acid). Results are presented for a laboratory-based method for sulphite in water and a potential on-line method for sulphite in high ionic strength potassium chloride brine. The general attractions of flow-injection-based monitors for the on-line analysis of liquid process streams are also discussed.     

Spectrophotometric determination of silicon in silicates by flow-injection analysis

A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values.     

Spectrophotometric determination of catecholamines with metaperiodate by flow-injection analysis

A flow-injection Spectrophotometric method for the determination of adrenaline and isoprenaline, based on the reaction with metaperiodate, is described. The calibration graphs are linear up to 2 × 10⁻⁴ M. Flow injection allows the measurement of 120 samples per hour. The method was successfully applied to the determination of both catecholamines in pharmaceuticals.     

Simultaneous catalytic-fluorimetric determination of copper and mercury by flow-injection analysis

Summary A catalytic-fluorimetric method is presented for the simultaneous determination of copper(II) and mercury(II) based on their catalytic effects on the oxidation of dipyridyldiketone phenylhydrazone and 2,2-dipyridylketone hydrazone, respectively, using the FIA/ stopped-flow mode. The errors in the determination of these cations are less than 10%, with a sampling rate of 45 samples per hour and the r.s.d. is 0.91% and 1.6% for Cu(II) and for Hg(II), respectively.

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Simultane katalytisch-fluorimetrische Bestimmung von Kupfer und Quecksilber durch Flow-Injection-Analyse

Zusammenfassung Mit Hilfe der FIA/stopped-flow-Technik wurde eine Simultanbestimmung von Cu(II) und Hg(II) durchgeführt, die auf der katalytischen Wirkung dieser Elemente auf die Oxidation von Dipyridyldiketon-phenylhydrazon bzw. 2,2-Dipyridylketon-hydrazon beruht. Die Fehler sind geringer als 10% mit einem Probendurchsatz von 45 Proben je Stunde. Die relative Standardabweichung beträgt 0,91% für Cu und 1,6% für Hg.

     

Spectrophotometric determination of silicate with Rhodamine B by flow-injection analysis

A spectrophotometric flow-injection method for the determination of silicate based on the formation of an ion pair between molybdosilicic acid and Rhodamine B is proposed. It allows silicate to be determined over the concentration range 0.17–2.0 mg 1^?1 at a sampling rate of 40 h^?1, is reasonably precise and is highly tolerant to ions that commonly occur in waters. It has been applied with satisfactory results to the determination of silicate in various types of water.     

Simultaneous spectrophotometric determination of nitrite and nitrate by flow-injection analysis

An automatic direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid (0.96-1.8 M HCl or pH 0.5-0.7) to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a stable purple azo dye, the absorbance of which is measured at 535 nm. Nitrate is reduced on-line to nitrite in a copper-coated cadmium column which is then treated with azo dye reagent and the absorbance due to the sum of nitrite and nitrate is measured; nitrate is determined from the difference in absorbance values. A copper column incorporated into the reaction manifold before the copperised cadmium column not only improves the long-term accuracy, but also extends the life time of the copperised cadmium column. Various analytical parameters, such as effect of acidity (pH), flow rate, sample size, dispersion coefficient, time, temperature, reagent concentration and interfering species, were studied. The calibration graphs were rectilinear for 0.1-3.5 mug ml(-1) of NO(3) and 10 ng ml(-1)-2.2mug ml(-1) of NO(2). The method is successfully applied to some food samples (meat, flour and cheese), environmental waters (inland and surface), beer and soil samples. Up to 30 samples can be analysed per hour with a relative precision of approximately 0.1-2%.     

Chemiluminometric -lysine determination with immobilized lysine oxidase by flow-injection analysis

An enzymatic flow-injection procedure for the determination of -lysine was developed. A lysine oxidase reactor is combined with a fibre-optic hydrogen peroxide detector. Hydrogen peroxide detection is based on the peroxidase-catalysed luminol reaction. The chemiluminescent light is detected by a photomultiplier. -Lysine can be determined in the range 10–1000 μM. A sampling rate of up to 90 h⁻ can be achieved. The whole sensing assay works for more than 1 month. The double logarithmic graph of the peak signal height vs. the lysine concentration is linear, the slope being larger than unity (r² = 0.991, n = 4).     

Ultraviolet spectrophotometric determination of copper in copper ores by flow-injection analysis

A flow-injection analysis (FIA) method for the ultraviolet spectrophotometric determination of copper in copper ores is described. The ore samples are dissolved in concentrated perchloric acid, the excess acid is neutralized with ammonia solution, and the resulting solution is used for the determination of copper. The UV-FIA system is based on the reaction of copper (II) ions with pyrophosphate and subsequent measurement of the absorbance of the dipyrophosphatocuprate (II) complex at 240 nm. The main factors which control the formation of this complex and the FIA variables influencing the system are discussed. The calibration graph is linear from 2-50 ppm copper. At a sampling rate of about 70 samples h(-1) with 50 mul sample injections, precision was about 1% relative standard deviation. Results obtained compare well with those obtained by atomic absorption spectrometry.     

Spectrophotometric determination of sulphate in sodium hydroxide solutions by flow-injection analysis

A spectrophotometric flow-injection procedure is described for the determination of sulphate in sodium hydroxide solutions. Sulphate catalyses the reaction between zirconium and methylthymol blue to form a complex measured at 586 nm. Optimal reaction conditions are discussed. The calibration graph is linear over the range 0.05–0.5 g l^?1 sulphate with a relative standard deviation of 0.02. The sample throughput is 20 h^?1. Sulphate is easily determined in 1 M sodium hydroxide; the results agree with those obtained by the conventional gravimetric method and by ion chromatography.     

Indirect spectrophotometric determination of ascorbic acid with ferrozine by flow-injection analysis

A FIA indirect spectrophotometric determination of ascorbic acid was developed using its reducing action on Fe(III) in acidic medium and following the spectrophotometric determination of the reduced iron by using sodium 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4'-disulphonate (ferrozine) as chromogenic reagent in buffered medium (pH 5.5) and monitoring the absorbance signal at 562 nm. A three-line manifold with two reaction coils was used: in the first reaction coil, ascorbic acid reduces Fe(III) to Fe(II); and in the second one, the complexation reaction is developed. The linear range of the method was 0.5-10 mug ml(-1) of ascorbic acid, the detection limit being 0.028 mug ml(-1). The proposed method was sensitive, rapid (sampling rate of 90 samples h(-1)) and reproducible (RSD 0.19%, n=10). Satisfactory results were obtained in the determination of ascorbic acid in pharmaceutical preparations, fruit juices and urine testifying the applicability of the method to real samples.