Spectrophotometric determination of nitrate using chromotropic acid

A spectrophotometric method is described for the determination of nitrate in the 0.5 to 50μg range using chromotropic acid as the reagent and masking agents for the elimination of possible critical interferences due to chloride, chlorine, iron(III) and oxidants. The method can be applied directly for the determination of 0.2–20 mg of nitrate/l in 2.5-ml samples of water. Over 4000 mg of chloride/l can be tolerated. The method is simple, rapid and reliable. At the 1 mg/l level for nitrate the coefficient of variation at the 95% confidence limit is 4% There are no interferences.     

药物中亚硝酸根的流动注射催化光度法分析

以亚硝酸根催化溴酸钾在磷酸介质中氧化维多利亚天蓝Ｂ褪色为指示反应，建立了反相流动注射催化光度法测定痕量亚硝酸根的新方法。本法操作简单、快速，灵敏度高，测定亚酸根的线性范围为２￣８０μｇ／Ｌ，直接用于含硝酸内服药和针剂中亚硝酸根的测定，与α－萘胺比色法对照结果一致。     

A solid-phase spectrophotometric method for the determination of sulphathiazole

A spectrophotometric method for the determination of sulphathiazole (ST) has been developed, based on solid-phase spectrophotometry. The influence of experimental variables on fixation on Sephadex SP C-25 is discussed. The applicable concentration range is 0.10-10.00 mg/l., with a relative standard deviation of 0.62% and a detection limit of 0.02 mg/l. The accuracy and precision of the method are reported. The proposed method has been satisfactorily applied to the determination of sulphathiazole in pharmaceuticals.     

Determination of small amounts of water with coulometrically generated Karl Fischer reagent

A coulometric method for the determination of small amounts of water described in a previous report has been further developed. Improved electronic circuitry and a redesigned electrolysis cell have extended the range of determination and decreased the time of analysis. By means of a movable oven specially adapted to the cell, water in solids has also been determined. The method presented is applicable with high accuracy in the range 0.005–5 mg of water in a large variety of substances.     

Amperometric determination of organic isothiocyanates

An amperometric titration method is described for the determination of 1-5 mg of organic isothiocyanates, based on their quantitative reaction with n-butylamine in dimethylfonnamide to form N,N-disubstituted thioureas which are then titrated amperometrically in aqueous ammonia-ammonium nitrate buffer with silver nitrate (dropping mercury electrode at -0.56V). The end-point corresponds to a silver:thiourea ratio of 2:1, with precipitation of silver sulphide. The method is simple, accurate, widely applicable, and gives reproducible results.     

Rapid titrimetric determination of microgram amounts of fluoride ion with spadns -thorium lake

A rapid titrimetric method has been developed for the determination of microgram amounts of fluoride ion in the range from Img-Ioomg, in 50 ml final volume. It involves the adjustment of pH, addition of 1 ml of 0.02% SPADNS indicator, dilution to volume and titration with standard 0.004M Th(NO₃)₄ until the colour obtained matches a blank containing the buffered solution of the indicator with a. trace of thorium nitrate solution. Interference by various ions was also studied. The method described for the determination of fluoride ion is very rapid and the colour change at the end point being sharp, the detection of the end point is very easy. The method is applicable to pure solutions of fluondes.     

Serial potentiometric and conductometric detection in fast non-suppressed ion chromatography applied to the analysis of filter collected airborne particulates

Non-suppressed ion chromatography (NSIC) has been optimized to permit the determination of chloride, nitrate and sulfate in the low mg/l concentration range within 3 min. Using conductometric detection the extraneous (positive) injection peak was found to adversely affect the early eluting chloride signal when samples with high amounts of total cations are analyzed. The serial arrangement of a downstream potentiometric detector with a chloride ion selective electrode, which does not respond to other alterations of the composition of the eluent than the change in chloride concentrations, is shown to be suitable for interference-free, sensitive and reliable chloride evaluation. Application of the proposed system to the determination of chloride in extracts of filter collected airborne particulates revealed (for those samples that could be evaluated by both detection methods) high precision and no systematic deviations between conductometric and potentiometric detection.     

Determination of anions in rainwater by capillary electrophoresis with conductivity detection

A routine method for the determination of chloride, nitrate and sulfate anions in rainwater by capillary electrophoresis was developed. The system uses an end-column non-suppressed conductivity detector. Linear calibration plots were generated from 0.050 to 20 mg/l, which is the range generally found in wet depositions. Accuracy and precision were evaluated by analyzing certified standards of simulated rainwater and environmental samples, or by comparing CE results with those obtained by IC, the reference technique for anion analysis in wet deposition. The reproducibility of the method was satisfactory except at the lower and upper limits of the analytical range. Sensitivity lay in the range of few μg/l.     

Determination of carbohydrazide at trace and subtrace levels

We developed three analytical methods for the determination of carbohydrazide at different concentration levels. One involves the volumetric titration of the analyte with bromate ion and dead-stop end-point detection, and is applicable to concentrations above 10 mg/l., so it can be used for standardizing carbohydrazide solutions. A second, spectrophotometric method is based on the reduction of FE(III) and measurement of the absorbance of the Fe(II)-ferrozine complex, and features an applicability range of 25-700,mug/l. carbohydrazide. The third method uses differential pulse polarography and the oxidation of carbohydrazide in a basic medium at a dropping mercury electrode to determine the analyte. This last method is the most sensitive of the three and also that offering the widest determination range: from 4 to 3000 mug/l. carbohydrazide.     

光化学反应在流动注射分析中的应用研究 Ⅲ.甲基橙光化学反应体系测定亚硝酸根、硝酸根和铁(Ⅲ)

基于NO_2~-、NO_3~-和Fe(Ⅲ)对甲基橙光化学褪色反应的催化作用,利用自制流通式光化学反应器,建立了流动注射光化学反应同时测定NO_2~-和NO_3~-以及测定Fe(Ⅲ)的新方法。测定NO_2~-和NO_3~-的线性范围都是0.1～3.2mg/L,每小时可测30～40个样品,测定Fe(Ⅲ)的线性范围为0.06～1.2mg/L,进样频率为60～80次/h。应用于蔬菜中NO_2~-、NO_3~-的测定和茶叶中铁的测定,结果满意。     

Determination of anions with capillary electrophoresis and indirect ultraviolet detection

A method is validated for the determination of anions with capillary electrophoresis (CE) in combination with indirect UV detection. The method described here is used for the analysis of eight of the most common anions (fluoride, chloride, bromide, sulphate, nitrate, nitrite, thiosulphate and phosphate). Next, the method is compared with a another buffer system for the determination of anions with CE and indirect UV detection. Typical limits of detection are obtained between 1 and 3 mg/l for the above-mentioned compounds. The repeatability and reproducibility of the system differs per compound and is, with the exception of fluoride and phosphate, between 4 and 6% and 5–10%, respectively. Linearity was observed between 1 and 10 mg/l. The method is applied for the determination of anions in drinking water, serum and urine.     

Back titration with mercuric ntrate in alkaline medium; potentiometric estimation of aluminium and manganese

Summary Mercuric nitrate has been successfully used for back titrating excess EDTA amounts than required for chelation with Al³⁺ or Mn²⁺ ions. This principle was the basis underlying the potentiometric determination of small amounts of both metals in the range of 10 g to 6 mg. End points are attended within 0.01 to 0.02 ml of titrant with fair accuracy and reasonable jumps ranging from 35 to 88 mv per 0.1 ml of titrant.     

Direct determination of phosphate esters in concentrated nitrate media by capillary zone electrophoresis

The potential of capillary zone electrophoresis (CZE) for the determination of dibutyl phosphate (DBP) and monobutyl phosphate (MBP), two degradation products of the tributyl phosphate extractant used in the nuclear fuel reprocessing industry, was evaluated. Analysis conditions were optimised, taking particularly into account that many determinations had to be performed in concentrated aqueous nitrate or nitric acid solutions. Separations were therefore carried out using the counter-electroosmotic mode with cathodic detection in a pH 8.3 electrolyte containing a suitably selected chromophore, salicylate, to ensure the indirect UV detection of the analytes. Various aspects of the method, including its sensitivity, working range, repeatability, and rapidity, were examined. Quantification of both phosphate esters was achieved in less than 3 min at concentrations ranging from 2 x 10(-6) to 10(-3) mol l(-1) in samples containing no macro-component. The lower end of this range increased to 5 x 10(-6) mol l(-1) for MBP and 1.5 x 10(-5) mol l(-1) for DBP in samples containing 5 x 10(-2) mol l(-1) of sodium nitrate, thus enabling their determination in solutions containing nitrate or nitric acid at concentrations up to, respectively, 10,000 and 3000 times higher than the target analyte concentration. This simple, fast and reliable method is routinely applicable to aqueous samples with no other preliminary treatment than a proper dilution; analysis was also performed in organic matrices after a prior extraction. The method was validated by an excellent correlation with the standard DBP analysis technique, gas chromatography (GC). In order to develop appropriate chemical treatments to destroy these compounds, the method was applied to the monitoring of DBP and MBP degradation by hydrogen peroxide in 1 mol l(-1) nitric acid solutions.     

Ion chromatographic method for the simultaneous determination of nitrite and nitrate by post-column indirect fluorescence detection

This short paper highlights the suitability of ion chromatography with post-column indirect fluorescence detection to determine simultaneously nitrite and nitrate based on the quenching of tryptophan native fluorescence. The method uses an enhanced fluorescence mobile phase containing tryptophan and detects the suppression of fluorescence of the mobile phase due to the elution of the target ions. The phenomenon of fluorescence quenching of tryptophan is highly induced by the presence of phosphate ions. The quenched fluorescence intensity exhibits concentration dependence in the range 1-25 mg/l and 3-65 mg/l for nitrite and nitrate, respectively. The relative standard deviation for five replicates of a standard solution containing a mixture of 5 mg/l of nitrite and 10 mg/l of nitrate lies around 2.8%. This simple coupling technique results in a relatively sensitive, fast, and accurate method, allowing for both qualitative and quantitative analysis of nitrite and nitrate. The method can easily be implemented to real samples such as foodstuffs, fertilizers and soils and is proven to be precise and accurate when compared with reference methods.     

Serial potentiometric and conductometric detection in fast non-suppressed ion chromatography applied to the analysis of filter collected airborne particulates

Non-suppressed ion chromatography (NSIC) has been optimized to permit the determination of chloride, nitrate and sulfate in the low mg/l concentration range within 3 min. Using conductometric detection the extraneous (positive) injection peak was found to adversely affect the early eluting chloride signal when samples with high amounts of total cations are analyzed. The serial arrangement of a downstream potentiometric detector with a chloride ion selective electrode, which does not respond to other alterations of the composition of the eluent than the change in chloride concentrations, is shown to be suitable for interference-free, sensitive and reliable chloride evaluation. Application of the proposed system to the determination of chloride in extracts of filter collected airborne particulates revealed (for those samples that could be evaluated by both detection methods) high precision and no systematic deviations between conductometric and potentiometric detection.Dedicated to Professor Dr. Peter Brätter on the occasion of his 60th birthday     

Simplified column-switching technology for the determination of traces of anions in the presence of high concentrations of other anions

A binary eluent model was proposed to study the retention behavior of trace anions in the presence of high concentrations of co-eluent anions. According to this model, the effect of the matrix on the retention of trace anions can be suppressed by using a high-concentration eluent. Based on the model, a simplified 'heart-cut' column-switching technology was proposed, in which the column-switching time window can be determined directly by standard solution of the analyte. By using this technology, a detection limit of 50 microg/l was obtained for nitrate in the presence of 5,000 mg/l chloride and 250 mg/l sulfate. The effect of the matrix on the concentration efficiency of weak acid anions was studied according to the result of phosphate. The possibility of the determination of weak acid anion by the 'heart-cut' technology was also discussed. The technology has been applied for the determination of nitrate in high salinity sea water, the spike recovery is in the range of 89.2-101.3%.     

Differential pulse polarographic determination of orthophosphate in aqueous media

The determination of orthophosphate in aqueous media by differential pulse polarography is described. It is based on determination of the molybdenum in 12-phosphomolybdic acid. High sensitivity is achieved by measuring the polarographic wave due to the catalytic reduction of perchlorate or nitrate in the presence of molybdenum(VI). The method is suitable for samples as small as 3.5 ml which contain as little as 9 ng of phosphorus per ml. The average relative deviation is 3.0% at the 0.045 mg/l. phosphorus level and 1.6% at the 1.2 mg/l. level. Results for the analysis of EPA quality-control water and real surface-water samples are reported.     

Colorimetric determination of nitrites with p-diaminodiphenylsulphone-diphen-ylamine as reagent

Diaminodiphenylsulphone-diphenylamine is used in a new colorimetric method for the determination of nitrite over a range of 0.1-2.5 mg/l . at pH 1.8 and 0.22-0.4 mg/l . at pH about 0.1. The coloured solutions are stable, follow Beer's law and are suitable for determination of traces by visual comparison. The method is selective and neither chlorine nor nitrogen trichloride gives similar colour reactions.     

Polarographic determination of nitrate in vegetables

A polarographic method for the determination of nitrate in vegetables is presented. The method is based on the reduction of nitrate to nitric oxide which reacts in solution with colbalt (II) and thiocyanate ions forming an electroactive complex that is reduced at the dropping mercury electrode at -0.5 V (vs. SCE). The nitric oxide is generated outside the polarographic cell by addition of ferrous ammonium sulfate and ammonium molybdate in hydrochloric acid to the previously triturated vegetable matrices. The calibration graph was linear in the range of 2-12x10(-6) mol nitrate. The recovery of nitrate in vegetable matrices (broccoli, kale, lettuce, radish, red beet, spinach, turnip and watercress) varied from 85.4 to 107.4 % and the nitrate content, expressed as sodium nitrate, varied from 751 to 10 806 mg kg(-1) of fresh vegetable. The relative standard deviation for the proposed method is lower than 7% and considering a sample of 5.0 g, the determination limit was 39 mg of nitrate per kg fresh vegetable weight. The precision and accuracy of the polarographic method were comparable to those of the reference spectrophotometric method (official AOAC reference method for the determination of nitrate in foodstuffs).     

Flow injection-spectrophotometric determination of metoclopramide hydrochloride

The determination of metoclopramide hydrochloride is spectrophotometrically determined by the Bratton-Marshall method in a flow injection assembly. The required nitrite is prepared on-line in the flow assembly by reducing a nitrate solution with the aid of a copperised cadmium solid-phase reactor. The calibration graph is linear over the range 0.5-85 mg l(-1), with a relative standard deviation (RSD) of 0.89%, and sample throughput of 51 samples h(-1). The method is easy and simple, and it is applied to determination of metoclopramide in some pharmaceutical formulations. The method eliminates the need for frequent preparation of unstable nitrite solutions.