Indirect kinetic spectrophotometric determination of hydroxylamine based on its reaction with iodate.

A simple, precise and accurate method is proposed for rapid determination of trace amounts of hydroxylamine based on the reaction of hydroxylamine with iodate in acidic media. The reaction of neutral red by the produced nitrite ion was used to monitor the reaction spectrophotometrically at 525 nm by a fixed time method. Hydroxylamine in the range of 0.0400-1.200 microg mL(-1) could be determined. The relative standard deviation for 10 determinations of 0.500 microg mL(-1) hydroxylamine was 1.81% and the limit of detection was 0.010 microg mL(-1). The proposed method was applied to the determination of hydroxylamine in water samples with satisfactory results.     

A sensitive spectrophotometric method for the determination of hydroxylamine by use of p-nitroaniline and N-(1-naphthyl)-ethylenediamine

A sensitive method for the spectrophotometric determination of hydroxylamine is described, based on known diazotization and coupling reactions. Hydroxylamine is oxidized by iodine in acetic acid medium to nitrite which then diazotizes p-nitroaniline to form a diazonium salt which is later coupled with N-(1-naphthyl)ethylenediamine to give a purple dye which has an absorption maximum at 545 nm, with a molar absorptivity of 6.6 x 10(4) l.mole(-1).cm(-1). Beer's law is obeyed over the hydroxylamine concentration range 0-8(microg/25 ml) (0.0-0.32 ppm) in the final solution.     

Kinetic spectrophotometric determination of low levels of nitrite by catalytic reaction between pyrogallol red and bromate

A kinetic spectrophotometric method for the determination of trace nitrite (0.003-1.000 microg/ml) based on its catalytic effect on the reaction between potassium bromate and pyrogallol red in acidic media is described. The reaction is monitored spectrophotometrically by measuring the decreasing colour of pyrogallol red at 467 nm by the fixed-time method. At a given time of 3.0 min at 30 degrees, the detection limit is 0.001 microg/ml and the relative standard deviation for 0.010 microg/ml nitrite is 1.8% (n = 8). The method is free from most interferences, especially from large amounts of nitrate and ammonium. The procedure was successfully applied to the determination of trace nitrite in natural water without preconcentration.     

Indirect voltammetric determination of trace hydroxylamine using magnetic microspheres

A new indirect voltammetric method for the determination of hydroxylamine is described. It is based on the reduction of an electroactive derivative of hydroxylamine on the surface of a magnetic electrode. The electroactive derivative produced by hydroxylamine reacted with magnetic polymer microspheres containing carbonyl groups on the surface. The experimental conditions are discussed. It was found that the peak potential (Ep) of the derivative was -0.46 V (vs. Ag/AgCl) under optimum conditions. Hydroxylamine could be determined in the range of 5-2,000 microg l(-1) with the detection limit of 2 microg l(-1) and relative standard deviation for the determination of 100 microg l(-1) hydroxylamine was 2.35%. Satisfactory results were obtained for the determination of hydroxylamine in aqueous medium.     

Dapsone and iminodibenzyl as novel reagents for the spectrophotometric determination of trace amounts of nitrite in water samples.

A rapid, simple, sensitive and selective spectrophotometric determination of nitrite using new diazotizing and coupling reagents is described. The method is based on a diazotization-coupling reaction between dapsone and iminodibenzyl in a hydrochloric acid medium. The molar absorptivity and Sandell's sensitivity were found to be 7.5 x 10(4) l mol(-1) cm(-1) and 0.000613 microg ml(-1), respectively. The interference effects of various cations and anions were also studied and reported. This method has been found to be applicable for the determination of nitrite in various water samples.     

An Extractive Spectrophotometric Method for the Determination of Nitrite Using Fluorescein Amine Isomer I

ABSTRACT

A sensitive spectrophotometric method for the determination of nitrite using fluorescein amine isomer I is described. The method is based on the formation of azido derivative of fluorescein amine isomer I, which is selectively extracted into 20% iso amyl alcohol in toluene and is stripped to aqueous phase using NaOH. Formation of the azido derivative depends on nitrite concentration and the system obeys Beer's law in the range 0-0.4 ppm of nitrite at 495 nm. The molar absorptivity of the colour system is 6.67 × 10⁴ L mol^-1 cm^-1 with a relative standard deviation of 3% for 10 determinations at 1 μg of nitrite. The proposed method is successfully applied for the determination of nitrite and nitrate in soil, water and radiator coolant sample, NO₂ gas in a laboratory fume cupboard is determined after fixing it as nitrite in sodium arsenite absorber solution.     

Sensitive spectrophotometric determination of nitrite in human saliva and rain water and of nitrogen dioxide in the atmosphere

A new simple, sensitive, and selective spectrophotometric method was developed for the determination of nitrite. The method is based on the reaction of nitrite with sulfathiazole in acidic medium to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)ethylenediamine dihydrochloride to form a highly stable, violet azo dye. The reaction product has an absorption maximum at 546 nm and obeys Beer's law over a nitrite range of 0.054-0.816 microg/mL. The molar absorptivity of the colored compound is 4.61 x 10(4) L/mol x cm). The detection limit is 12.1 microg/L. The relative standard deviation is 0.85% for 5 determinations of nitrite at 0.27 microg/mL. The reproducibility and validity of the proposed method are discussed in the present paper. The simplicity of the method is demonstrated by the high stability of the azo-dye product as well as the short time required for its complete formation in a reaction at room temperature without pH control or extra extraction. The sensitivity of the method is shown by the successful determination of nitrite in human saliva and rain water, and of nitrogen dioxide in the atmosphere. The results compare favorably with those obtained by the reference method. The selectivity of the method is indicated by its freedom from most interferences, even at high concentrations of nitrate (500 microg/mL).     

Flow-injection spectrophotometric determination of sulfadiazine and sulfamethoxazole in pharmaceuticals and urine.

A rapid and sensitive flow-injection spectrophotometric method is proposed for the determination of sulfadiazine and sulfamethoxazole. This method is based on the diazotization of sulfonamide with sodium nitrite, and a coupling reaction of the diazo-compound with alpha-naphthylamine. The optimum experimental conditions are obtained by using the controlled and weighted centroid simplex method. The linear ranges for the determination of sulfadiazine and sulfamethoxazole are 0.2-20 microg ml(-1) and 0.1-20 microg ml(-1), and their detection limits are 0.06 microg ml(-1) and 0.05 microg ml(-1), respectively, and the sampling frequency is 130 samples per hour. The method has been used to determine sulfadiazine and sulfamethoxazole in pharmaceuticals and urine without separation. The results are in agreement with those obtained by a high-performance liquid chromatograph technique at the 95% confidence level.     

The application of strongly reducing agents in flow injection analysis : Part 3. Vanadium(II)

The application of vanadium(II) as a powerful reducing reagent in flow injection analysis is described. Results are presented for the determination of various organic and inorganic substances. With spectrophotometric detection, based on the absorption by vanadium(II)-EDTA at 350 nm, limits of determination were about 5 X 10^?5 mol 1^?1. Nitrate, nitrite and hydroxylamine were measured with amperometric detection. The limit of determination was about the same as with spectrophotometric detection. In a slightly acidic medium, hydrazine could be determined with the amperometric detector, with a limit of determination of about 10^?4 mol l^?1. By coupling an ammonia detection device to the reduction system, the percentage conversions of nitrate, nitrite and hydroxylamine to ammonia were shown to be 26%, 54% and 47%, respectively.     

Kinetic spectrofluorimetric determination of trace ascorbic acid based on its inhibition on the oxidation of pyronine Y by nitrite

A highly sensitive spectrofluorimetric method is proposed for the determination of trace amount of ascorbic acid using a new indication. The method is based on the inhibition of ascorbic acid on the oxidation of pyronine Y (PRY) by nitrite. The detection limit for ascorbic acid is 0.012 microg ml(-1), the linear range of the determination is 0.02-0.36 microg ml(-1). Analytical parameters, such as reagent concentration, pH, reaction temperature and time, were optimized. The relative standard deviations of eleven replication determinations of 0.12 and 0.24 microg ml(-1) ascorbic acid were 1.4 and 0.72%, respectively. This method has been used to determine ascorbic acid in pharmaceuticals, vegetables, fruits and soft drink with satisfactory results.     

Flow injection spectrophotometric determination of nitrite

4-Nitroaniline, which gives intensely yellow solution on dissolution in dilute hydrochloric acid, has been found to react with nitrite almost instantaneously in acidic medium yielding a colourless product that has been identified as 4-nitrophenyl diazo cation. The measurement of decrease in colour intensity suggested a new, simple and one-step reaction procedure that has been used for the reversed flow injection determination of 5microg-5 mg/l. NO(2)-N. The limit of detection has been found to be 2 microg/l. NO(2)-N. A number of species such as copper(II) and lead(II), which interfere in other spectrophotometric procedures, do not affect the results. The method has been applied to determine nitrite in natural waters when the %RSD was in the range 1.8-3.5%.     

A kinetic method for the determination of nitrite by its catalytic effect on the oxidation of chlorpromazine with nitric acid.

A catalytic spectrophotometric method for the determination of trace amounts of nitrite is proposed. In acidic solution, chlorpromazine (CP) is oxidized by nitric acid to form a red compound, which is further oxidized to a colorless compound. The reaction is accelerated by trace amounts of nitrite and can be followed by measuring the absorbance at 525 nm: nitrite ion is regenerated and multiplied by nitric acid. The absorbance of the reaction increased with an increase in the reaction time, reached a maximum and decreased rapidly. Since the time required for the absorbance to reach the maximum decreased with increasing nitrite concentration, this value was used as the measured parameter for the nitrite determination. Under the optimum experimental conditions (2.3 M nitric acid, 1.2 x 10(-5) M CP, 40 degrees C), nitrite can be determined in the range 0-100 microg l(-1). The relative standard deviations (n = 6) are 4.7 and 1.8% for 40 and 100 microg l(-1) nitrite, respectively. The detection limit of this method (3sigma) is 1.2 microg l(-1). This method was successfully applied to a determination of nitrite in natural water samples.     

A simple and rapid spectrophotometric method for the determination of nitrite by its decolorizing effect on peroxovanadate complex

A rapid, simple, and most economical spectrophotometric method was proposed for the determination of nitrite in various water samples, soil samples, and roots of leguminous plants. The method is based on decolorizing effect of nitrite on complex formed between hydrogen peroxide and vanadate in acidic medium. The decolorization of that complex by nitrite was exploited to monitor the reaction spectrophotometrically at 470 nm.The method was optimized for effect of concentrations of ammonium metavanadate, hydrogen peroxide, various acids, concentrations of sulphuric acid, order of reagents addition and color stability. The color of the complex was found to be stable for about 2 days, and the stability constant of the complex was also calculated by modified Job's method. The linearity range of the calibration graph was over 6.67-66.7 microg ml(-1) of nitrite with molar absorptivity, 0.276 x 10(3) mol(-1) l cm(-1) and Sandell's sensitivity, 0.1667 microg cm(-2). The method was applied successfully for the determination of nitrite in soil samples, various wastewater samples and roots of leguminous plants.     

Spectrophotometric determination of hydrazine

Hydrazine is determined spectrophotometrically by forming the derivative 2,4-dinitrophenylhydrazine from 2,4-dinitrochlorobenzene. The formed dinitro derivative undergoes condensation reaction to form the hydrazone with p-dimethylaminobenzaldehyde (p-DAB). The resulting yellow colored product is stable in acidic medium and has a maximum absorption at 458 nm. The colour system obeys Beer's law in the range 0-7 microg of hydrazine in an overall volume of 25 mL. The molar absorptivity is calculated to be 8.1 x 10(4) L mol(-1)cm(-1) with a correlation coefficient of 0.998. The relative standard deviation is 1.7% (n=10) at 6 microg of hydrazine. Interferences due to foreign ions have been studied and the method has been applied for the determination of hydrazine in boiler feed water.     

Test strip for determination of nitrite in water

A disposable test strip is proposed for the determination of nitrite in waters. The strip is an inert rectangular strip of polyester with a 6 mm o.d. circular, transparent and colorless film attached to its surface. This film contains the chemicals required for reaction and fixation of the dye formed, sulfanilamide, N-(1-naphthyl)ethylenediamine on Nafion. When the test strip is placed in an acidified (pH 2.0) sample solution containing nitrite a red-violet color develops; the absorbance of this is measured at 536 nm. The linear range of the method depends on the time of equilibration of the test strip with the sample solution. When the equilibration time was 45 min, the linear range was 8.9-500 microg L(-1) whereas for an equilibration time of 60 min it was 4.7-200 microg L(-1). The detection limit was 1.4 microg L(-1) for an equilibration time of 60 min. The precision of the method, expressed as RSD, was 8.8 % at 100.0 microg L(-1). The method was applied, and validated chemometrically, for the determination of nitrite in different types of water (spring, mineral, tap, well, and sea).     

Colour reaction of free chlorine with p-amino-N,N-diethylaniline in the presence of alcohol and its analytical application

A simple, precise, rapid-colour-forming and stable spectrometric method has been developed for determining free chlorine in water. p-Amino-N,N-diethylaniline reacts with free chlorine almost instantaneously in the presence of alcohol to form a red oxidized product with absorption maximum at 513 nm. Beer's law is obeyed in the free chlorine concentration range of 0-2 microg ml(-1). The molar absorptivity is 1.79 x 10(4) l mol(-1) cm(-1), limit of detection 0.0036 microg ml(-1), relative standard deviation 1.51%, and amount of free chlorine 7 microg. The colour reaction rate and absorbance are independent of temperature in the range 3-45 degrees C and the stable absorptivity lasts for at least 1 h. The method is satisfactory for the determination of free chlorine in aqueous solution.     

Dapsone a new diazotizing reagent for the spectrophotometric determination of nitrite in waste and natural water samples

A new diazotizing reagent for the spectrophotometric determination of nitrite is described. The method is based on diazotization-coupling reaction between dapsone and phloroglucinol in hydrochloric acid medium. The reactions were conducted at room temperature, the molor absorptivity at 425 nm is 4.28 x 10(4) l mol-1cm-1 and was stable for 50 h. Beer's law was obeyed in the nitrite range of 0.008-1.0 microgram ml-1. Tolerance limits were tested for 33 species. The method has been found to be applicable for the determination of nitrite in natural and wastewater.     

Extractive spectrophotometric determination of trace amounts of nitrogen dioxide,nitrite, and nitrate

A sensitive extractive spectrophotometric method for the determination of nitrogen dioxide in air and nitrite and nitrate in water, soil and blood serum is described. Nitrogen dioxide in air is fixed as nitrite in a suitable trapping solution. The method is based on the diazo coupling reaction betweenp-nitroaniline andN-(1-naphthyl)ethylenediamme dihydrochloride [NEDA]. The azo dye formed under aqueous conditions is extracted with isobutyl methyl ketone [IBMK]. The system obeys Beer's law over the range 0–3 g of nitrite at 545 nm and the colour is stable for 3h. The molar absorptivity of the colour system is 5.7 × 10⁴ L mol^–1 cm^–1. The relative standard deviation is 1.3% for ten determinations at 2 ug of nitrite. Nitrate is determined as nitrite after reduction on a cadmium column. Negative interferences from SO₂, H₂S, Cu²⁺ and Cr³⁺ and positive interference from Fe²⁺ and Fe³⁺ can be simply masked.     

Determination of nitrite by flow injection spectrophotometry using a home-made flow cell detector.

A simple, rapid, low cost and accurate determination using flow injection spectrophotometry with a home made flow cell detector, in combination with green LED and photodiode, had been developed for nitrite based on the Griess-Saltzman reaction, measuring the absorbance at 525 nm. The proposed system is able to monitor nitrite in freshwater samples at a throughput of 60 samples per hour with a relative standard deviation (%RSD) of less than 2.4% and a detection limit of <7 microg dm(-3). The calibration graph was linear between 0.010 - 1.0 mg dm(-3).     

An improved colorimetric determination of micro amounts of chromium(VI) and chromium(III) using <Emphasis Type="Italic">p</Emphasis>-aminoacetophenone and phloroglucinol in different samples

The reaction of Cr(VI) with hydroxylamine resulting in its oxidation to nitrite has been utilized for the determination of chromium. The nitrite thus liberated diazotizes p-aminoacetophenone to form diazonium salt which is further coupled with phloroglucinol in an alkaline medium, to form an azo dye. The dye gave maximum absorbance at 420 nm and when extracted in an amino cartridge obeyed Beer’s law in the range from 0.04 to 0.36 μg/mL of Cr(VI) and has a molar absorptivity of 1.04 × 10⁵ L/mol cm. Optimum reaction conditions for diazotization, full colour development and the effect of variables such as temperature, time, and pH have been studied. The proposed method was applied to the determination of chromium in certified samples, air particulates, industrial effluents, and pharmaceutical preparations. The results are in agreement with those obtained by atomic absorption spectrometry.