The use of nitrate and nitrite

The most promising of the nontraditional treatments is the use of nitrate (Larsen, 2002 Thorstenson et al, 2002) and/or nitrite (Sturman et al, 1999) to reduce H2S concentrations. This technology involves the continuous downhole injection of either nitrate or nitrite solutions to reduce the occurrence of souring. Several field evaluations of these chemicals have demonstrated that the continuous injection of nitrate or nitrite reduces the amount of H2S that is produced from the field. The benefits of this technology are that nitrate and nitrite are not considered biocides and therefore do not require any special regulatory approvals and may be easier to handle than traditional biocides. There are however, some environmental concerns about the use of nitrate and nitrite, specifically the disposal of produced water that may contain residuals of each chemical. 

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The use of nitrates and nitrites in cured meat products must comply with the provisions set out in Directive 2006/52/EC, which amends Directive 95/2/EC on additives other than colours and sweeteners. Currently authorised as food additives are sodium and potassium nitrites and sodium and potassium nitrates that may be sold only in a mixture with salt or a salt substitute. The indicative ingoing amount of potassium and sodium nitrites that are authorised for use are 150mg/kg and the residual amount is 50mg/kg (KNOj) in non-heat-treated, dried meat products, 100 mg/kg (NaNOj) in other cured meat products, canned meat products and 175 mg/kg (NaNOj) in cured bacon. The indicative ingoing amount of potassium and sodium nitrates is 300 mg/kg in all cured products and the residual amount in cured and canned meat products is 250 mg/kg, in pickled herring and sprat 200 mg/kg and in hard, semi-hard and semi-soft cheeses and dairy-based cheese analogues 50 mg/kg. 

The use of nitrates and nitrites in food (such as vegetables, meat products, and cheese) is regulated in the European Union (Spanish Royal Decree 1118/2007 approving the positive list of additives other than colorings and sweeteners for use in the manufacture of food products and conditions of use). This statute establishes and differentiates between the maximum amount that may be added during manufacture... 

A very good illustration of the risk/benefit balance is provided by the use of nitrates and nitrites in certain meat products, such as bacon, some sausages, lightly pasteurised canned luncheon meats and hams, pressed cured meat loaves, cold-cuts , canned tongue, corned beef, etc., and in certain cheeses. The nitrite in meats can be added as such or as a mixture of nitrate and nitrite, with the former being reduced to the latter by enzymes. 

Flow injection analysis is another technique that has been applied to the determination of nitrate and nitrite in seawater. Anderson [ 126] used flow injection analysis to automate the determination of nitrate and nitrite in seawater. The detection limit of his method was 0.1 imol/l. However, the sampling rate was only 30 per hour which is low for flow injection analysis. Reactions seldom go to completion in a determination by flow injection analysis [127,128] because of the short residence time of the sample in the reaction manifold. Anderson selected a relatively long residence time so that the extent of formation of the azo dye was adequate to give a detection limit of 0.1 pmol/l. This reduced the sampling rate because only one sample is present at a time in the post-injector column in flow injection analysis. Any increase in reaction time causes a corresponding increase in the time needed to analyse one sample. 

An interesting application of this region of the spectrum is the determination of nitrate and nitrite in soil extracts. Nitrate is very soluble in water and can be extracted using a simple water extraction procedure. Nitrate absorbs at 210 nm and nitrite at 355 nm, and both can be quantified using these absorption maxima ( max). Other materials extracted from soil, as noted previously, however, can obscure this region, and thus caution must be exercised to determine if there are any interfering components in such extracts [6-10],... 

Stathakis and Cassidy, on his part, used a-, y- (0—40mM/L), or -cyclodextrin (0—lOmM/L) to separate a mix containing iodide, nitrate, perchlorate, thiocyanate, bromate, iodate, ethanesulfonate, pentanesulfonate, and octanesulfonate. The separation of nitrate and nitrite can be improved by the addition of 3% a-cyclodextrin in a 30mM PDC buffer at pH 5.4 (Figure 15). 

Samples of natural water should either be analysed immediately or be stored (not for a very long time) at a decreased temperature to suppress microbial processes. For the determination of nitrate and nitrite it is useful to conserve the samples by addition of 1 ml chloroform or 0.1% phenylmercuric acetate per Utre. To prevent oxidation of sulphide and some other substances in water samples, reductants are added [5, 147]. If the distribution of a species between the f ree ionic form and various complexes is to be studied, as is of ten the case, care must be taken not to shift the equiUbrium by adding substances that would enter into side reactions with the studied species. 

This automated procedure for the determination of nitrate and nitrite uses the procedure whereby nitrate is reduced to nitrite by a copper-cadmium reduc-tor column.52 The nitrite ion then reacts with sulphanilamide under acidic conditions to form a diazo compound. This compound then couples with N-1 -naphthylethylenediamine dihydrochloride to form a reddish-purple azo dye. 

This method can be used to determine the nitrate content in precipitation within the range from 0.02 to 0.23 mg NO3-N/L (0.1-1.0 mg N03/L). Nitrate is reduced to nitrite using cadmium treated with copper sulfate as reducing agent in the presence of ammonium chloride. With this method the sum of nitrate and nitrite is determined. Nitrite and sulfanilamide form a diazo compound that couples with N-(l-naphthyl)-ethylenediamine dihydrochloride to form a red azo dye. The concentration in the solution is determined spectrophotometrically at 520 nm. Note that nitrite will interfere with the determination of nitrate. 

This technique has been applied by Iskandami and Petrzyk [316] to the determination of nitrate and nitrite in water. Chemically bonded amine materials have been used to remove interference by humic substances prior to the ion chromatographic determination of nitrate and sulphate in non saline waters. 

The detection of nitrates and nitrites present in FDR using a color reaction with diphenylamine in sulfuric acid was first applied to firearms related examinations about 1911, and in 1914 Doctor Iturrioz used paraffin wax as a lifting medium for propellant residue on clothing prior to treatment with... 

An efficient possible application of diamond electrodes is their use in the reduction of hard-to-reduce compounds. Fujishima, Tenne, Levy-Clement et al. studied the electroreduction of nitrate and nitrite ions to ammonia [132-134], The reaction... 

The NOj ion is reduced only with difficulty, e.g., by A1 in NaOH, which gives NH3. In view of the problem of nitrate (and nitrite) pollution63 through the use of nitrogen fertilizers, many studies of their removal as NH3, NHJ, or N2 have been made, but no very practical method yet exists. A recent example of homogeneous reduction is that using ethanol, ethers, or carboxylic adds in sulfuric add to give ammonium sulfate.64... 

Segmented CFA has been used widely at sea, and it has proven to be an extremely valuable tool. The analyses of all major nutrients in seawater have been automated by segmented CFA, including the determination of nitrate and nitrite 1, 2), silicate 2, 3), phosphate 2, 4), and ammonia (5). The applications of segmented CFA to analyses in seawater were summarized previously (6-8). 

Figure 6. Manifold for the detertnination of nitrate and nitrite. A four-way valve (Rheodyne Model 50, 4V) is used to switch the cadmium column out of line for the determinatioii of nitrite only. (Reproduced with permission from Ref. 12. Copyright 1983, American Society of Limnology and Oceanography.)...

The method for nitrite determination based on the diazotization-coupling reaction by column preconcentration and on the reduction of nitrate to nitrite using the Cd-Cu reductor column has been proposed for the determination of nitrate and nitrite in water and some fruit samples [6]. On-line monitoring of nitrite in fertilizer process streams, natural and waste water effluents based on the diazotization of nitrite in the sequential injection system with N-(l-naphthyl)etylenediammonium dichloride and the formation of a highly coloured dye has been described [7]. 

Similar to conventional CE, HT-CE and HT-ME are applicable to quantitative analyses, as the calibration curve constructed from the transformed data shows good linearity even at concentrations less than the concentration limit of detection obtained using conventional CE (18, 29). HT-CE has been used in the analysis of actual samples. For instance, McReynolds et al. have successfully applied the HT-CE method with UV detection to the analysis of nitrates and nitrites in biological samples (30). We have also shown that the HT... 

Anions have also been determined using conventional IMS with an FSI ion source and included arsenate, phosphate, sulfate, nitrate, nitrite, chloride, formate, and acetate. Distinct peak patterns and reduced mobility constants were observed for respective anions. Application to authentic water samples for the determination of nitrate and nitrite demonstrated the feasibility of using FSI-IMS as a rapid analytical method for monitoring nitrate and nitrite in water systems. The method was used for on-site measurement by exchanging air for nitrogen as the drift gas without complications. The linear dynamic range was 1,000, and detection limits were 10 ppb for nitrate and 40 ppb for nitrite. 

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