- Sodium citrate, also known as trisodium citrate, is the sodium salt of citric acid, with the chemical formula Na₃C₆H₅O₇.
- Structurally, it consists of three sodium ions (Na⁺) bonded to the citrate ion (C₆H₅O₇³⁻), which is derived from citric acid, a weak organic acid naturally found in citrus fruits.
- The citrate ion features a central carbon backbone with three carboxylate groups (-COO⁻) and a hydroxyl group (-OH), forming a stable, negatively charged trivalent ion.
- Sodium citrate typically exists as a dihydrate (Na₃C₆H₅O₇·2H₂O), incorporating two water molecules in its crystalline structure, which influences its solubility and stability. This ionic compound is highly polar, contributing to its excellent solubility in water and its ability to act as a chelating agent by binding to metal ions such as calcium.
- Sodium citrate appears as a white, crystalline powder or granules with a slightly salty, tart taste.
- It is odorless and highly soluble in water (approximately 425 g/L at 25°C), but insoluble in ethanol and most organic solvents. Its aqueous solutions are mildly alkaline, with a pH typically ranging from 7.5 to 9.0, due to the partial hydrolysis of the citrate ion.
- Sodium citrate is thermally stable under normal conditions but may decompose at high temperatures, releasing carbon dioxide and forming sodium carbonate.
- As a chelating agent, it effectively binds divalent cations like calcium and magnesium, forming stable complexes that prevent precipitation or scaling. This property, combined with its non-toxic and biodegradable nature, makes sodium citrate a versatile compound in various applications.
- It is also hygroscopic, meaning it can absorb moisture from the air, which requires careful storage to maintain its integrity.
- In the food industry, sodium citrate is widely used as an additive, primarily as an acidity regulator, emulsifier, and preservative, identified by the E number E331.
- It stabilizes pH in food products like beverages, jams, and dairy products, enhancing shelf life and flavor consistency.
- Its emulsifying properties are critical in processed cheese production, where it prevents fat separation and ensures a smooth, creamy texture by binding calcium ions that would otherwise cause protein coagulation.
- Sodium citrate is also used in gel-based desserts and ice creams to control texture and prevent crystallization.
- Additionally, it serves as an antioxidant synergist, extending the shelf life of foods by reducing oxidative rancidity.
- Its Generally Recognized as Safe (GRAS) status by regulatory authorities like the FDA underscores its safety for consumption in specified amounts.
- Sodium citrate plays a significant role in medical and pharmaceutical applications due to its anticoagulant and buffering properties.
- In medicine, it is commonly used in blood collection tubes to prevent clotting by chelating calcium ions, which are essential for the coagulation cascade. This makes it indispensable in blood transfusions and diagnostic testing.
- In pharmaceuticals, sodium citrate is a key ingredient in effervescent tablets and oral rehydration solutions, where it acts as a buffering agent to neutralize stomach acid or maintain electrolyte balance.
- It is also used in urinary alkalinization therapies to treat conditions like kidney stones or metabolic acidosis, as it increases urine pH, reducing the risk of stone formation. Its biocompatibility and low toxicity make it suitable for these critical applications.
- Beyond food and medicine, sodium citrate finds use in various industrial applications.
- In detergents and cleaning products, it acts as a water softener by binding calcium and magnesium ions, enhancing the effectiveness of surfactants and preventing scale buildup in washing machines and dishwashers.
- In the cosmetic industry, it is used in formulations like shampoos and bath products to adjust pH and stabilize emulsions.
- Sodium citrate is also employed in electroplating processes to control metal deposition and in water treatment to prevent scaling in pipes and boilers.
- Its versatility extends to biotechnology, where it serves as a buffering agent in biochemical assays and cell culture media. The compound’s eco-friendly profile, being biodegradable and non-toxic, aligns with the growing demand for sustainable industrial chemicals.
- Sodium citrate is a multifaceted compound with a well-defined chemical structure and a broad range of properties that make it invaluable across multiple industries. Its ability to chelate metal ions, regulate pH, and act as an emulsifier underpins its utility in food production, medical applications, and industrial processes. As a safe, biodegradable, and effective chemical, sodium citrate continues to be a staple in both consumer and industrial products, with ongoing research exploring new applications in sustainable technologies and advanced medical therapies.
