WHO/Food Add./24.65 FAO Nutrition Meetings Report Series No. 38A SPECIFICATIONS FOR IDENTITY AND PURITY AND TOXICOLOGICAL EVALUATION OF SOME ANTIMICROBIALS AND ANTIOXIDANTS The content of this document is the result of the deliberations of the Joint FAO/WHO Expert Committee on Food Additives which met 8-17 December 1964a a Eighth Report of the Joint FAO/WHO Expert Committee on Food Additives, Wld Hlth Org. techn. Rep. Ser., 1965, 309; FAO Nutrition Meetings Report Series 1965, 38. SODIUM NITRATE CHEMICAL NAME Sodium nitrate SYNONYMS Chile saltpetre; cubic or soda nitre EMPIRICAL FORMULA NaNO3 MOLECULAR WEIGHT 85.00 DEFINITION Sodium nitrate after drying contains not less than 99.0% of NaNO3 and conforms to the following specifications. DESCRIPTION Clear, colourless, odourless, transparent crystals, or white granules or powder. Deliquescent in moist air. USE As an antimicrobial preservative and colour fixative in meat, fish and cheese products. Often need In combination with nitrites. IDENTIFICATION TESTS A. Solubility: Water: 1 g is soluble in 1.1 ml Ethanol: 1 g is soluble in 125 ml Glycerol: Slightly soluble B. Sodium nitrate yields with uranyl zinc acetate TS a golden-yellow precipitate, which forms after several minutes' agitation. C. Brownish red fumes are evolved when sodium nitrate is heated with sulfuric acid and metallic copper. PURITY TESTS Loss on drying: Not more than 2% after drying at 105°C for 4 hours. pH of a 5% solution: Dissolve 10 g in 200 ml of carbon dioxide- and ammonia-water, the pH of this solution is between 5.5 and 8.3. Arsenic: Not more than 3 mg/kg. Lead: Not more than 10 mg/kg. Nitrite: Not more than 1000 mg/kg. Dissolve 1 g in 50 ml of carbon dioxide- and ammonia-free water, add 2 drops of dilute ammonia TS, and filter if necessary through paper into a 100-ml volumetric fleck. Add 10 ml of dilute acetic acid TS, shake the mixture, and allow to stand for 5 minutes. Any colour produced is not darker than that of a complete blank to which 1 ml of nitrite standard TS is added. Heavy metals: Not more than 20 mg/kg. Dissolve 3 g in water and dilute to 30 ml. Adjust 20 ml of this solution to a pH between 3.0 and 4.0 and dilute with water to 40 ml. To the remaining 10 ml of sample solution add water to make 35 ml, add a volume of standard lead TS equivalent to 0.02 mg of lead and adjust to a pH between 3.0 and 4.0 and dilute to 40 ml. To each solution add 10 ml of hydrogen sulfide TS, mix, transfer to 50-ml Nessler tubes and observe after 10 minutes. The colour of the test solution should be no darker than that of the solution containing the standard lead solution. ASSAY Weigh 1.000 g of sodium nitrate previously dried at 105°C for 4 hours into the flask of an ammonia distillation apparatus. Add 10 g of Devarda's Alloya and 25 ml of N sulfuric acid and allow the flask to stand, protected from ammonia in the atmosphere, for 1 hour. Add 100 ml of a solution of sodium hydroxide (15 in 100), connect the flask to the remainder of the apparatus and distil 100 ml, collecting the distillate under the surface of 25.0 ml of N hydrochloric acid. Rinse the condenser into the receiving flask, add methyl red-methylene blue TS and titrate the excess acid with N sodium hydroxide. (25-x) %NaNO3 = × 8.5 w POTASSIUM NITRATE CHEMICAL NAME Potassium nitrate SYNONYMS Saltpetre, nitre EMPIRICAL FORMULA KNO3 MOLECULAR WEIGHT 101.11 DEFINITION Potassium nitrate after drying contains not less than 99% of KNO3 and conforms to the following specifications. DESCRIPTION Colourless, odourless, transparent prisms, or white granular or crystalline powder, having a cooling, saline, pungent taste. a Devarda's Alloy (Devarda's Metal) is a grey powder composed of 50 parts of copper, 45 parts of aluminium and 5 parts of zinc. USE As an antimicrobial preservative and colour fixative in meat, fish and cheese products; often used in combination with nitrites. IDENTIFICATION TESTS A. Solubility: Water: 1 g is soluble in 3 ml Ethanol: 1 g is soluble In 620 ml Glycerol: Soluble B. In neutral, concentrated or moderately concentrated solutions of potassium salts, sodium bitartrate TS slowly produces a white, crystalline precipitate which is soluble in ammonia TS and in solutions of alkali hydroxides or carbonates. C. Brownish red fumes are evolved when potassium nitrate is heated with sulfuric acid and metallic copper. PURITY TESTS Loss on drying: Dry at 105°C for 4 hours: it loses not more than 1% of its weight. pH of a 5% solution: Dissolve 10 g in 200 ml of carbon dioxide- and ammonia-free water: the pH of this solution is between 4.5 and 8.5. Arsenic: Not more than 3 mg/kg. Lead: Not more than 5 mg/kg. Heavy metals: Not more than 20 mg/kg. Dissolve 3 g in water and dilute to 30 ml. Adjust 20 ml of this solution to a pH between 3.0 and 4.0 and dilute with water to 40 ml. To the remaining 10 ml of sample solution add water to make 35 ml, add a volume of standard lead TS equivalent to 0.02 mg of lead, and adjust to a pH between 3.0 and 4.0, and dilute to 40 ml. To each solution add 10 ml of hydrogen sulfide TS, mix, transfer to 50-ml Nessler tubes and observe after 10 minutes. The colour of the test solution should be no darker than that of the solution containing the standard lead solution. Nitrite: Not more than 1000 mg/kg. Dissolve 1 g in 50 ml of carbon dioxide- and ammonia-free water, add 2 drops of diluted ammonia TS, and filter if necessary through paper into a 100-ml volumetric flask. Add 10 ml of potassium iodide TS, 2 ml of starch TS, and 10 ml of diluted acetic acid TS, shake the mixture and allow to stand for 5 minutes. Any colour produced is not darker than that of a complete blank to which 1 ml of nitrite standard TS is added. ASSAY Weigh 1.000 g of potassium nitrate previously dried at 105°C for 4 hours into the flask of an ammonia distillation apparatus. Add 10 g of Devarda's Alloy and 25 ml of 1 N sulfuric acid and allow the flask to stand, protected from ammonia in the atmosphere, for 1 hour. Add 100 ml of a solution of sodium hydroxide (15 in 100), connect the flask to the reminder of the apparatus and distil 100 ml, collecting the distillate under the surface of 25.0 ml of 1 N hydrochloric acid. Rinse the condenser into the receiving flask, add methyl red-methylene blue TS and titrate the excess acid with 1 N sodium hydroxide. (25-x) %KNO3 = × 10.11 w Biological Data Biochemical aspects In certain circumstances reduction of nitrate to nitrite can take place in the digestive tract by the activity of the intestinal flora. If appreciable reduction occurs before the normal rapid elimination of the nitrate, poisoning can result. This appears to have occurred in cattle,1 and in babies less than 6 months old, especially in dyspeptic infants.2 In experiments with rabbits about one-half of the ingested amount of nitrate was excreted in the urine, and only 0.5% was recovered as nitrite in the urine.3 Acute toxicity Animal Route Minimum lethal dose LD50 Reference (mg/kg body-weight) (mg/kg body-weight) Rat-male oral 190-2000 - 4 Rat-female oral 460-1200 - 4 Rat oral - 3236 5 Poisoning in man may result from a total oral daily dose in excess of 4 g or from a single dose of more than 1 g. 8 g may be fatal and 13-15 g are generally fatal.6 Short-term studies Cattle. Most data have been obtained from livestock fed various forage crops with a high nitrate content. Poisoning depends upon the conversion of the nitrate to nitrite by the intestinal flora. The lowest level that may result in fatal poisoning in cattle has been reported to be 1.5% of potassium nitrate in the forage.1 Dog. Two dogs were fed 2% of sodium nitrate in their diets for 105 days and for 125 days without any adverse effects.7 Man. Numerous cases have been reported of poisoning in small children and infants from the use of well-water containing nitrates. Among these, them were 26 cases in which the nitrate nitrogen content of the well-water was 21-50 ppm (93-221 ppm as NO3), 54 cases in which it was 51-100 ppm (221-443 ppm as NO3), and 52 cases in which it was over 100 ppm (443 ppm as NO3). In one instance, a level as low as 50 ppm (as NO3) in tap water produced 72% methaemoglobinaemia in a dyspeptic child.2 Healthy babies, however, have tolerated quantities up to 21 mg/kg body-weight (as NO3) for one week without any disturbance.9 Long-term studies Rat. Sodium nitrate was fed to 4 groups of 20 rats each at dosages of 0.1%, 1%, 5% and 10% of the diet for 2 years. Slight growth depression occurred at the 5% level, and additional morphological changes due to inanition occurred at the 10% level.7 Evaluation Levels causing no significant toxicological effect in animals From consideration of the long-term study in rats, the level of sodium nitrate causing no demonstrable effect over a period approximating to the life span is assessed at 1% of the diet, or 500 mg/kg body-weight daily. In the short-term study with dogs fed 2% sodium nitrate in the diet for 105 days, the level producing no demonstrable effect likewise corresponds to 500 mg/kg body-weight per day. Estimate of acceptable daily intakes for man mg/kg body-weight (as sodium nitrate) Unconditional acceptance 0-5 Conditional acceptance 5-10 Comment In establishing tolerances for added nitrate it is important to take into account the amount of nitrate already present in other foods. The sensitivity of normal babies and the apparent sensitivity of dyspeptic babies makes it impossible to make an estimate of an acceptable dose for babies of 6 months of age or less on the basis of animal experimentation or clinical experience. Nitrate should on no account be added to baby-foods. Water with high nitrate content is unsuitable for the preparation of baby-foods. It is recommended that, if possible, sodium nitrate should be used as a 2.5% mixture with common salt. References 1. Bradley, W. B., Eppson, H. F. & Beath, O. A. (1940) Wyom. Univ. agr. exp. Stat. Bull., 24l, 20 2. Thal, W., Lachhein, L. & Martinek, M. (1961) Arch. Toxikol., 19, 25 3. Kilgore, L., Almon, L. & Geiger, M. (1959) J. Nutr., 69, 39 4. Spector, W. S. ed. (1956) Handbook of toxicology, Saunders, Philadelphia & London, vol. 1 5. United States Food and Drug Administration (Unpublished data) 6. Sollmann, T. (1957) A manual of pharmacology, Saunders, Philadelphia & London 7. Lehman, A. J. (1958) Quart. Bull. Ass. Food Drug Off., 22, 136 8. Rosenfield, A. B. & Huston, R. (1950) Minn. Med., 33, 787 9. Kübler, W. (1958) Z. Kinderheilk., 81, 405
See Also: Toxicological Abbreviations Sodium nitrate (ICSC) SODIUM NITRATE (JECFA Evaluation)