りん酸二水素ナトリウム

外観

無色若しくは白色の結晶又は粉末

定義

本品は、リン酸(*)のナトリウム塩であり、次の化学式で表される。
参照表示名称：リン酸

溶解性

水に溶けやすく、エタノールに極めて溶けにくい。

解説

リン酸二水素ナトリウム(monosodium dihydrogenphosphate)：NaH2PO4(119.98)．略称MSP．第一リン酸ナトリウム(primary sodium phosphate)，第一リン酸ソーダともいう．リン酸に1：1のモル比で水酸化ナトリウムまたは1：2のモル比でリン酸水素二ナトリウムを加え，溶液の pH を4.4～4.6にし，加熱濃縮すると得られる．水溶液41 ℃ 以下では二水和物，41～58 ℃ では一水和物，58 ℃ 以上では無水和物が得られる．無水和物は，無色の単斜晶系結晶．密度2.37 g cm－3．潮解性で，200 ℃ に加熱すると水を放出し，二リン酸二水素二ナトリウムNa2H2P2O7[CAS 7758-16-9]を生成する．250 ℃ でメタリン酸ナトリウムとなる．水溶液は酸性を呈する．一水和物は，無色の斜方晶系結晶．密度2.04 g cm－3．溶解度71 g/100 g 水(0 ℃)．加熱すると100 ℃ で無水和物になる．二水和物は，無色の斜方晶系結晶．密度1.91 g cm－3．融点60 ℃．溶解度91.1 g/100 g 水(0 ℃)．エタノールに不溶．

用途

研究用等(二りん酸塩不含オルトりん酸塩)。

用途

清缶剤、染色助剤

用途

りん酸二水素ナトリウム，洗剤，緩衝剤，清缶剤，細菌培養基，染色助剤，食品安定剤(指定添加物)，食肉結着剤，金属表面処理剤などとして使用される．

化粧品の成分用途

緩衝剤、消臭剤

効能

緩衝剤

使用上の注意

吸湿性あり

化学的特性

White, slightly deliquescent crystals or granules.

物理的性質

Anhydrous salt: white crystalline powder; slightly hygroscopic; forms sodium acid pyrophosphate, Na2H2P2O7 on heating above 225°C and sodium metaphosphate (NaPO₃)_n at about 350 to 400°C; very soluble in water, aqueous solution acidic.
Monohydrate: white orthorhombic crystals or granules; density 2.04 g/cm³; loses its water of crystallization at 100°C; very soluble in water, pH of 1% solution 4.5; insoluble in alcohol.
Dihydrate: large transparent crystals; orthorhombic bisphenoidal structure; density 1.915 g/cm3; decomposes at 60°C; very soluble in water; insoluble in alcohol.

使用

Sodium phosphate monobasic monohydrate is used as sequestrant, emulsifier, mordant in dyeing, reagent and buffer in foods and analytical chemistry. It was applied as a fireproofing agent and for weighting silk in tanning. It is employed in manufacturing of enamels, ceramics, detergents, boiler compounds, in soldering and brazing instead of borax.

製造方法

Monobasic sodium phosphate can be prepared by partial neutralization of phosphoric acid with sodium hydroxide in equimolar amounts: H₃PO₄ + NaOH → NaH₂PO₄ + H₂O
It also can be made by treating disodium hydrogen phosphate with phosphoric acid in proper stoichiometric amount: Na₂HPO₄ + HPO₄ → 2NaH₂PO₄.

調製方法

Monobasic sodium phosphate is prepared by adding phosphoric acid to a hot, concentrated solution of disodium phosphate until the liquid ceases to form a precipitate with barium chloride. This solution is then concentrated and the monobasic sodium phosphate is crystallized.

一般的な説明

Sodium phosphate monobasic is an effective oral osmotic laxative at minimal concentration. It is used for colonic cleansing before endoscopic examination of colon.

応用例（製薬）

Monobasic sodium phosphate is used in a wide variety of pharmaceutical formulations as a buffering agent and as a sequestering agent. Therapeutically, monobasic sodium phosphate is used as a mild saline laxative and in the treatment of hypophosphatemia.
Monobasic sodium phosphate is also used in food products, for example, in baking powders, and as a dry acidulant and sequestrant.

安全性プロファイル

Poison by intramuscular route. Mdly toxic by ingestion. A human and experimental eye irritant. When heated to decomposition it emits toxic fumes of POx and Na2O. See also PHOSPHATES.

安全性

Monobasic sodium phosphate is widely used as an excipient in parenteral, oral, and topical pharmaceutical formulations.
Phosphate occurs extensively in the body and is involved in many physiological processes since it is the principal anion of intracellular fluid. Most foods contain adequate amounts of phosphate, making hypophosphatemia virtually unknown except in certain disease states or in patients receiving total parenteral nutrition. Treatment is usually by the oral administration of up to 100 mmol of phosphate daily.
Approximately two-thirds of ingested phosphate is absorbed from the gastrointestinal tract, virtually all of it being excreted in the urine, and the remainder is excreted in the feces. Excessive administration of phosphate, particularly intravenously, rectally, or in patients with renal failure, can cause hyperphosphatemia that may lead to hypocalcemia or other severe electrolyte imbalances. Adverse effects occur less frequently following oral consumption, although phosphates act as mild saline laxatives when administered orally or rectally (2–4 g of monobasic sodium phosphate in an aqueous solution is used as a laxative). Consequently, gastrointestinal disturbances including diarrhea, nausea, and vomiting may occur following the use of monobasic sodium phosphate as an excipient in oral formulations. However, the level of monobasic sodium phosphate used as an excipient in a pharmaceutical formulation is not usually associated with adverse effects.
LD50 (rat, IM): 0.25 g/kg(10)
LD50 (rat, oral): 8.29 g/kg

貯蔵

Monobasic sodium phosphate is chemically stable, although it is slightly deliquescent. On heating at 100°C, the dihydrate loses all of its water of crystallization. On further heating, it melts with decomposition at 205℃, forming sodium hydrogen pyrophosphate, Na2H2P2O7. At 250℃ it leaves a final residue of sodium metaphosphate, NaPO3.
Aqueous solutions are stable and may be sterilized by autoclaving.
Monobasic sodium phosphate should be stored in an airtight container in a cool, dry place.

不和合性

Monobasic sodium phosphate is an acid salt and is therefore generally incompatible with alkaline materials and carbonates; aqueous solutions of monobasic sodium phosphate are acidic and will cause carbonates to effervesce.
Monobasic sodium phosphate should not be administered concomitantly with aluminum, calcium, or magnesium salts since they bind phosphate and could impair its absorption from the gastrointestinal tract. Interaction between calcium and phosphate, leading to the formation of insoluble calcium phosphate precipitates, is possible in parenteral admixtures.

規制状況(Regulatory Status)

GRAS listed. Accepted for use as a food additive in Europe. Included in the FDA Inactive Ingredients Database (injections; infusions; ophthalmic, oral, topical, and vaginal preparations). Included in nonparenteral and parenteral medicines licensed in the UK. Included in the Canadian List of Acceptable Non-medicinal Ingredients.