Guidelines for Selecting the Appropriate Grade and Specification of Citric Acid (CAS#77-92-9)
Citric acid is a widely used organic acid in industries such as food, pharmaceuticals, chemicals, and detergents. Choosing the correct grade and specification depends on aligning product characteristics with the requirements of the intended application. Different industries have distinct demands regarding purity, particle size, hydration state, and impurity limits. The following sections explain how to select suitable citric acid products from three aspects: basic classification parameters, application-based selection principles, and key points for consideration.
I. Fundamental Classification Parameters of Citric Acid
Before making a selection, it is important to understand the main specification indicators of citric acid, as they determine whether the product will meet application needs.
Form and Water Content
Citric acid is available in two main forms: monohydrate (C₆H₈O₇·H₂O) and anhydrous (C₆H₈O₇). Monohydrate citric acid contains one molecule of crystal water, has a lower melting point (around 100 °C), dissolves readily, and exhibits low hygroscopicity. Anhydrous citric acid contains no crystal water, melts at a higher temperature (about 153 °C), and absorbs moisture more easily, making it suitable for processes where water content must be strictly controlled.
Purity Grade
Based on usage, citric acid is classified into food grade, pharmaceutical grade, industrial grade, and reagent grade (such as AR or CP). In general, the strictness of purity and impurity limits decreases in the following order: reagent grade > pharmaceutical grade > food grade > industrial grade. Correspondingly, allowable levels of impurities such as heavy metals, sulfates, and chlorides become less stringent.
Particle Size and Physical Form
Citric acid is commonly supplied as powder or crystals, with crystal products further divided into fine, medium, and coarse grades. Particle size influences dissolution rate and mixing uniformity. Powders dissolve quickly and are suitable for applications requiring rapid dispersion, while crystalline forms offer better flowability and more accurate dosing.
Applicable Standards
Each industry follows its own standards. For example, food-grade citric acid must meet GB 1886.235-2016, pharmaceutical grade must comply with pharmacopeial standards (such as ChP), and industrial grade follows chemical industry specifications. Conformance to the relevant standard is a basic requirement when selecting citric acid products.
II. Industry-Based Guidelines for Selecting Citric Acid
(1) Food Industry
As the most common application area, the food industry requires high safety, qualified purity, and good process compatibility. Food-grade citric acid that meets GB 1886.235-2016 is essential, and the main selection considerations are form and particle size.
Beverage Applications (carbonated drinks, fruit juices, tea beverages, etc.)
Food-grade monohydrate citric acid in fine crystal or powder form is generally preferred. Its fast solubility allows quick pH adjustment, helping inhibit microbial growth and stabilize flavor. Its low hygroscopicity also supports precise dosing during storage and formulation. For concentrated beverages or products requiring long-term or high-temperature storage, food-grade anhydrous citric acid may be chosen to reduce the influence of moisture on product stability.
