Description
Citric acid anhydrous is a form of citric acid that has had all of its water molecules removed. It is a white, crystalline powder with a strong acidic taste. The chemical formula for citric acid anhydrous is C₆H₈O₇.
Properties and Key Differences
Citric acid exists in two main forms: anhydrous and monohydrate. The key distinction between them is the presence of a water molecule.
| Property | Citric Acid Anhydrous | Citric Acid Monohydrate |
| Chemical Formula | C₆H₈O₇ | C₆H₈O₇·H₂O |
| Molecular Weight | 192.12 g/mol | 210.14 g/mol |
| Water Content | None (water-free) | One water molecule per molecule of citric acid |
| Appearance | Fine, white powder or crystals | Larger, more transparent crystals |
| Melting Point | Approximately 153°C (307°F) | Approximately 135°C (275°F) |
| Production | Crystallization from a hot, concentrated solution | Crystallization from a cold aqueous solution |
Common Grades of Citric Acid
The various grades are defined by quality standards and are regulated by different organizations.
- Food Grade / Preservative Grade (FCC):
- This is the most common grade of citric acid, used extensively in the food and beverage industry.
- It serves as an acidulant to provide a tart flavor, a preservative to prevent microbial growth, and a chelating agent.
- It is used in soft drinks, candies, processed foods, and canned goods.
- The purity is typically very high, often 99.5% to 100.5%. The Food Chemicals Codex (FCC) sets the quality standards for this grade.
- Pharmaceutical Grade (USP/BP/Ph. Eur.):
- This grade has a higher level of purity and is produced according to strict regulations set by pharmacopeias like the United States Pharmacopeia (USP), British Pharmacopoeia (BP), and European Pharmacopoeia (Ph. Eur.).
- It is used in medicines and dietary supplements as a stabilizer, preservative, and to enhance the absorption of minerals.
- It is also used to adjust the pH of pharmaceutical formulations.
- Reagent / Laboratory Grade (ACS):
- This is a very high-purity grade used for analytical and research purposes in laboratories.
- It meets the specifications of organizations such as the American Chemical Society (ACS) and is used for reliable and consistent results in chemical investigations.
- Industrial / Technical Grade:
- This grade has a lower assay of citric acid (around 96-97%) compared to the other grades.
- It is used in non-food and non-pharmaceutical applications where a high level of purity is not required.
- Common uses include detergents, cleaning agents, water softeners.
Uses and Applications
Citric acid anhydrous is a versatile compound used across various industries. Its properties as an acidulant, preservative, and chelating agent make it highly valuable.
- Food and Beverage: It’s a common additive used as a natural preservative and to provide a tart or sour flavor. It’s found in soft drinks, candies, jams, and other processed foods. It also acts as a chelating agent, preventing unwanted flavor or color changes.
- Pharmaceuticals: In the pharmaceutical industry, it’s used as a pH adjuster and stabilizer in a variety of medications, including effervescent tablets and oral solutions.
- Cosmetics and Personal Care: It helps to balance the pH of products like creams and lotions. As a type of alpha hydroxy acid (AHA), it’s also used in some skin care products for its exfoliating properties.
- Cleaning Products: Due to its acidic nature, it is an effective and environmentally friendly cleaning agent. It’s used in descalers, bathroom cleaners, and detergents to remove mineral deposits, limescale, and rust. It can also act as a water softener.
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