Spectrophotometric Determination of Nitrites

Since practically all nitrates are soluble, no gravimetric method is suitable with the exception of precipitation with an organic basernitron. The usual volumetric method is to reduce nitrate to ammonia, which is distilled into a known excess of standard acid, back titrating the excess with standard alkali (compare Sec. 14.6.1). 

However, the easiest instrumental mediod which is suitable in presence of nitrite is by ion chromatography (Sec.2.8.3). The ion chromatogram has separate peaks for the two ions. The concentration in an unknown is found by comparing the peak area with a calibration curve. 

Prepare a stock solution which is 0.01 M in potassium nitrate and 0.01 M in potassium nitrite as well as separate solutions with the same concentration in eitfier anion. By appropriate dilution prepare a series of solutions with a range of nitrite concentrations from 5 to 100 mg dm. Prepare a similar range of concentrations of die nitrate and of the mbcture of the two anions. Follow the instructions of the Manufacturer of the ion chromatograph and determine the peak area of each solution (or the peak height counts) and plot against anion concentration. Use the calibration plots to determine concentrations of unknown solutions. Determine the concentration of die two anions in a sample of acid rain (Dionex Application Note 31). 

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Besides potential pharmacological applications, a number of other uses have been described for phenoxazine derivatives. The semi-quinone radical obtained on oxidation of phenoxazine with various oxidants, which has been shown to give a characteristic absorption at about 530 mp., was used by Sawicki et al.110 in a new method for the spectrophotometric determination of nitrite the aqueous nitrite sample is treated with a 0.1% solution of phenoxazine in glacial acetic acid and the absorbance is read at 530 mp. 

Ensafi, A. A., Rezaei, B. and Nouroozi, S. (2004) Simultaneous spectrophotometric determination of nitrite and nitrate by flow injection analysis. Anal Sci, 20 (12), 1749-1753. 

L. Andersson, Simultaneous Spectrophotometric Determination of Nitrite and Nitrate by Flow Injection Analysis. AnaL Chim. Acta, 110 (1979) 123. 

A. Kazemzadeh, A.A. Ensafi, Sequential flow injection spectrophotometric determination of nitrite and nitrate in various samples. Anal. Chim. Acta 442 (2001) 319-326. 

Oliveira, S. M., T. I. M. S. Lopes, and A. O. S. S. Rangel. 2004. Spectrophotometric determination of nitrite and nitrate in cured meat by sequential injection analysis. J. Food Set. 69 C690-C695. 

Ahmed, M. J., C. D. Stalikas, S. M. Tzouwara-Karayanni, and M. I. Karayannis. 1996. Simultaneous spectrophotometric determination of nitrite nitrate by flow-injection... 

Ameida, F. L., S. G. dos Santos Filho, and M. B. A. Fontes. 2013. FIA-automated system used to electrochemically measure nitrite and interfering chemicals through a 1-2 DAB/Au electrode Gain of sensitivity at upper potentials./. Phys. Conf Ser. 421 1-8. Anderson, L. 1979. Simultaneous spectrophotometric determination of nitrite and nitrate by flow injection analysis. Anal. Chim Acta 110 123-128. 

Liang, B., M. Iwatsuki, and T. Fukasawa. 1994. Catalytic spectrophotometric determination of nitrite using the chlorpromazine hydrogen-peroxide redox reaction in acetic-acid medium. Analyst 119 2113-2117. 

Spencer and Brewer [144] have reviewed methods for the determination of nitrite in seawater. Workers at WRc, UK [ 145] have described an automated procedure for the determination of oxidised nitrogen and nitrite in estuarine waters. The procedure determines nitrite by reaction with N-1 naphthyl-ethylene diamine hydrochloride under acidic conditions to form an azo dye which is measured spectrophotometrically. The reliability and precision of the procedure were tested and found to be satisfactory for routine analyses, provided that standards are prepared using water of an appropriate salinity. Samples taken at the mouth of an estuary require standards prepared in synthetic seawater, while samples taken at the tidal limit of the estuary require standards prepared using deionised water. At sampling points between these two extremes there will be an error of up to 10% unless the salinity of the standards is adjusted accordingly. In a modification of the method, nitrate is reduced to nitrite in a micro cadmium/copper reduction column and total nitrite estimated. The nitrate content is then obtained by difference. 

Le Corre and Treguer [49] developed an automated procedure based on oxidation of the ammonium ion by hypochlorite in the presence of sodium bromide followed by spectrophotometric determination of the nitrite. The standard deviation on a set of samples containing 1 p,g NH -N per litre was 0.02. This method was compared with an automated method for the determination of ammonia as indophenol blue. The results from the two methods are in good agreement. 

Wetters JH, Uglum KL. Direct spectrophotometric simultaneous determination of nitrite and nitrate in the ultraviolet. Anal. Chem. 1970 42 335-340. 

Nitrite ion, N02, is a preservative for bacon and other foods, but it is potentially carcinogenic. A spectrophotometric determination of N02 makes use of the following reactions ... 

Garcia Gutierrez [19] has described an azo coupling spectrophotometric method for the determination of nitrite and nitrate in soils. Nitrite is determined spectrophotometrically at 550 nm after treatment with sulfuric acid and N-1 -naphlhylclhylcnediamine to form an azo dye. In another portion of the sample, nitrate is reduced to nitrite by passing a pH 9.6 buffered solution through a cadmium reductor and proceeding as above. Soils were boiled with water and calcium carbonate, treated with freshly precipitated aluminium hydroxide and active carbon, and filtered prior to analysis by the above procedure. 

Garcia-Gutierrez [15] has described an azo-coupling spectrophotometric method for the determination of nitrite and nitrate in vegetables. 

Kim and Kim [6] have described an extremely sensitive determination of nitrite in drinking water (tap water and underground water) and environmental samples (rain, lake water, and soil) by ion exclusion chromatography with electrochemical detection. Potential interferences in the determination of nitrite by the standard spectrophotometric method or by the ion exchange chromatographic method with either conductivity or ultraviolet detection were eliminated. The detection limit was 0.1 pg L 1 without preconcentration. 

Bendschneider, K., Robinson, R. J., 1952. A new spectrophotometric method forthe determination of nitrite in seawater. Journal of Marine Research, 11, 87-93. 

The spectrophotometric determination of bromate can be based on the reactions of Br03 ions with o-arsanilic acid [26], antipyrine (in the presence of nitrite) [27], 1,3,4-trihydroxyanthraquinone-2-carboxylic acid [28], Pyrogallol Red [29], or 2-oxyminedimedonodithiosemicarbazone [30]. 

Nitrogen dioxide in air and nitrate and/or nitrite in water, soil, analytical-grade KBr, potassium sulfate, ammonium sulfate, potassium nitrate and ammonium nitrate and toothpaste were determined by means of the decrease in absorbance of Neutral Red caused by diazotization with nitrite from the sample [4]. A mixture of oxalic acid, p-aminoacetophenone and Al-1-naphthyl ethylenediamine has been proposed as an efficient absorbing system for in situ spectrophotometric determination of nitrogen dioxide in environmental samples [5]. 

G.M. Greenway, S.J. Haswell, P.H. Petsul, Characterisation of a micro-total analytical system for the determination of nitrite with spectrophotometric detection, Anal. Chim. Acta 387 (1999) 1. 

Sandwich techniques can also be implemented in a sequential injection analyser, as demonstrated by the spectrophotometric determination of nitrate and nitrite in natural waters [12]. The sample plug was set between two reagent plugs and the assembly was aspirated towards the holding coil of an ordinary sequential injection analyser. Two Griess reaction zones were established at both ends of the sample zone, and only one was... 

Nitrite. This chemical species, formed in-line by passing a potassium nitrate stream through a copperised cadmium solid-phase reactor, was used in the spectrophotometric determination of sulfadiazine in pharmaceutical formulations [99]. A nitrite solution that would normally be stored in a refrigerator, standardised and frequently replaced was therefore not required. 

The spectrophotometric determination of Fe(II), Fe(III), nitrate and nitrite ions in natural and wastewaters in a sequential injection system [298] is an interesting example of this innovation. In-line tangential filtration was performed prior to the sample insertion port as part of the sampling step. Particulate material was not aspirated towards the holding coil and several samples could be analysed without the need for frequent cleaning of the filtration unit. Analytical figures of merit were similar to those for the corresponding flow-based analytical procedure with manual sample filtration prior to flow analysis. 

A. Mellado-Romero, C. Gomez-Benito, J. Martinez-Calatayud, Continuous-flow spectrophotometric determination of sulfadiazine by diazotisation with in situ preparation of nitrite, Anal. Chim. Acta 308 (1995) 451. 

S. Xu and Z. Fang, Sinultaneous Spectrophotometric Determination of Nitrate and Nitrite in Water and Soil Extracts by Flow Injection Analysis [in Chinese]. Fenxi Huaxue, 11 (1983) 93. 

The standard-addition method can take several forms." The one most often chosen for photometric or spectrophotometric analyses, and the one that was discussed in some detail in Section ID-.1, involves adding one or more increments of a standard solution to sample aliquots. Each solution is then diluted to a fixed volume before measuring its absorbance, lix-ample 14-1 illustrates a spreadsheet approach to the multiple-additions method for the photometric determination of nitrite. 

The major limitation on the use of visible spectrophotometric or colorimetric methods is the fact that the analyte must absorb within the visible domain of the electromagnetic spectrum. Many analytes of environmental interest are colorless. Many can be chemically converted to a colored product by direct chemical change of the analyte, formation of a metal chelate, or formation of an ion pair. An example of a chemical conversion of the analyte of interest is the colorimetric determination of nitrite-nitrogen via reaction of the nitrite ion with sulfanilic acid in acidic media to form the diazonium salt with subsequent reaction with chromotropic acid to form a highly colored azo dye. 

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