Fluorimetric determination of nitrate in natural waters with 3-amino-1,5-naphthalenedisulphonic acid in a flow-injection system

A rapid, sensitive and precise flow-injection method for the determination of nitrate in natural waters is presented. Nitrate is first reduced in a copperized cadmium column to nitrite, which reacts with 3-amino-1,5-naphthalenedisulphonic acid to form the azoic acid. This acid forms a fluorescent salt in alkaline medium. The injecton rate is about 30 h^?1, the relative standard deviation for 10 injections of 2 × 10^?5 M nitrate is 0.8%, and the detection limit (S/N = 3)_is 1 × 10^?8 M nitrate.     

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.     

Determination of nitrate in natural waters by flow-injection analysis

Summary Nitrate was determined in natural water samples by flow-injection spectrophotometry. It was reduced to nitrite with copperized cadmium and the nitrite thus produced reacted with p-aminoacetophenone and m-phenylenediamine. The limit of detection was about 1.5 g l^–1 for sample injections of 650 l. The sampling rate was about 40 samples h^–1 and the relative standard deviation was above 1% for 0.1–0.3 mg l^–1 nitratenitrogen. Nitrite present in the sample was determined separately and subtracted.

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Nitratbestimmung in natürlichen Wässern mit Hilfe der Fließinjektions-Analyse

Zusammenfassung Nitrat wird bei dieser Methode mit Hilfe einer Cu/Cd-Reduktionssäule zu Nitrit reduziert, das mit p-Aminoacetophenon und m-Phenylendiamin zur Reaktion gebracht wird. Die gebildete Verbindung wird spektral-photometrisch gemessen. Die Nachweisgrenze beträgt etwa 1,5 g/l bei injizierten Probevolumina von 650 l. Der Probendurchsatz beträgt 40/h. Die relative Standardabweichung liegt über 1% bei 0,1–0,3 mg/l Nitrat-Stickstoff. Vorhandenes Nitrit wird gesondert bestimmt und abgezogen.

     

Fluorometric determination of nitrite with acetaminophen

A simple, sensitive and selective fluorometric method for the determination of nitrite is described. The fluorometric determination is based on the reaction of acetaminophen with nitrite in an acidic medium followed by alkalinization of the reaction which yields a highly fluorescent product, exhibit (λ_ex/λ_em=325/430 nm). The optimum experimental conditions were studied. The fluorescene intensity is linear over a nitrite concentration of 0.08–1.3 μg/ml with a detection limit of 2.7 ng/ml (S/N=3). The effect of interferences from various metals/ions were studied. The proposed method is accurate, reproducible, shows satisfactory results and compares successfully with the reference method.     

Fluorometric determination of nitrite

A sensitive, simple and rapid fluorometric procedure for the determination of nitrite is described. It is based on the reaction of nitrite with 2,3-diaminonaphthalene in acidic solution to form 1-[H]-naphthotriazole, a highly fluorescent compound in alkaline medium. The detection limit is approximately 0.5 ng ml in the test sample (1% relative fluorescence intensity). Application of the method to analysis of a milk sample was tested with aliquots spiked with known amounts of nitrite.     

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%.     

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。     

Determination of sulfate in natural and residual waters by turbidimetric flow-injection analysis

A turbidimetric flow-injection system was developed for the determination of sulfate in natural and residual water samples, with no previous treatment, using spectrophotometric detection. The precipitating agent, 7.0% (w/v) barium chloride solution prepared in 0.10% (w/v) polyvinyl alcohol, was added by using the merging-zones approach. A 100 mg/L sulfate solution in 0.07M nitric acid was mixed with the sample before it entered the injection loop to improve the detection limit, provide in-line pH adjustment, and prevent the interference of some anionic species. The relative standard deviations of the results were between 1.4 and 3.0% and were in agreement with results obtained by the reference method. Samples within a linear concentration range of 10-120 mg SO4(2-)/L can be analyzed at a rate of 40/h. The detection limit is 5 mg SO4(2-)/L.     

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 .     

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.     

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.     

On-line determination of residual aluminium in potable and treated waters by flow-injection analysis

A portable, automated, flow-injection-based solid-state spectrophotometric field monitor for the determination of residual dissolved aluminium in potable and treated waters is described. Aluminium is determined by complexation with pyrocatechol violet to form a colloidal lake with a maximum absorbance at 580 nm. Interference from iron(III) is masked by reduction to iron(II) and complexation with 1,10-phenanthroline. The monitor operates on a 30-min analytical cycle, i.e., with 48 results per day, and each cycle includes an autocalibration step. Over the course of a 3-month field trial the reliability was greater than 90%. The performance conforms to industry specifications for both overall accuracy (bias < ± 10%) and repeatability (relative standard deviation < ± 10%), the linear range is 0–1000 μg l^?1 and the practical limit of detection is 45 μg l^?1.     

Chemiluminescence determination of carbofuran at trace levels in lettuce and waters by flow-injection analysis

A simple, fast chemiluminescence (CL) flow-injection (FI) method based on the reaction of luminol with KMnO₄ in alkaline medium has been described for the direct determination of carbofuran. The method is based on the enhancing effect in the emission light from the oxidation of luminol produced in presence of carbofuran. The optimisation of instrumental and chemical variables influencing the CL response of the method has been carried out by applying experimental design, using the proposed flow-injection manifold. Under the optimal conditions, the CL intensity was linear for a carbofuran concentration over the range of 0.06-0.5 μg ml⁻¹, with a detection limit of 0.02 μg ml⁻¹. The method has been successfully applied to the determination of carbofuran residues in spiked water and lettuce samples.     

Spectrophotometric determination of nitrite in polluted waters using 3-nitroaniline

Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid to form a diazonium cation, which is subsequently coupled with N-(1-naphtyl)ethylenediammonium chloride to form a stable purple azo dye. The method is suitable for the determination of 0.01–0.80 μg ml^?1 nitrite. The reactions are very fast and require no control of temperature. The observed molar absorptivity and Sandell's sensitivity of the azo dye are 4.9 × 10⁴ l mol^?1 cm^?1 and 9.4 × 10^?4 μg cm^?2, respectively. The method is free from most interferences. The method has been applied successfully to polluted river water.     

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.     

A gas chromatographic method for the determination of nitrite ions in natural waters

Following the treatment of the sample with zinc hydroxide, nitrite reacts with potassium iodide in the presence of acetone and sulphuric acid. The released iodine and the propanone derivative resulting from the acetone are extracted in n-hexane. The extract is subjected to gas chromatographic separation and detection using an electron capture detector. The calibration curve was found to be linear up to a concentration of 2.5 mg 1(-1) NO(-)(2). The detection limit calculated from the threefold noise level and the slope of the calibration curve is 0.008 mg 1(-1). The relative standard deviation (including that of the blank) was less than 8%. The reliability of the method is adequate for practical uses. Amongst the advantages is that the method does not require the use of exceedingly toxic reagents. On the other hand, the method is applicable for samples that even after being subjected to clarification procedures still do not become fully transparent.     

Configuration with internally coupled valves to overcome shortcomings in the simultaneous determination of nitrite and nitrate by flow-injection analysis

A configuration with internally coupled valves and a reductant column located in the loop of the secondary valve is proposed for the simultaneous determination of nitrite and nitrate. Depending on the column characteristics, a washing stream flowing in the opposite direction to the sample may or may not be required. The washing step may conveniently be performed by use of the proposed configuration.     

Trace determination of α-keto acid in natural waters

Numerous chromatographic methods have been developed to detect α-keto acids in physiological or sea-water samples. These methods generally involve derivatization in a strongly acidic medium with elevated temperatures, desalting, preconcentration, and liquid-liquid extraction procedures prior to chromatographic analysis. These procedures may introduce significant errors because of adsorption losses, contamination, or decomposition of the α-keto acids. To avoid these potential problems, a chemically mild method to detect α-keto acids in sea water was developed. The method is based on the reaction of α-keto acids with 2,4-dinitrophenylhydrazine in sea water to form stable hydrazone derivatives. Desalting of the reaction mixture and preconcentration of the hydrazone derivatives is accomplished by a column-switching technique. The derivatives are separated by reversed-phase, high-performance liquid chromatography and detected by absorption spectrometry. Quantification of α-keto acids in the nM to μM concentration range shows complete recovery in sea water, excellent precision at 10–20 pmol (<5% relative standard deviation), and absorbances that are linearly related to α-keto acid concentrations. The detection limit of this method is 1–5 pmol for a 2-ml injection. Applications of this method to the detection of α-keto acids in marine sediment and sea-water samples are illustrated, and the first shipboard results are presented.