The purity of a chemical refers to the proportion of the target substance in the chemical, i.e., the ratio of the amount of the target substance to impurities in the chemical. It is a key indicator describing the quality of chemicals, and different application scenarios have varying requirements for chemical purity. The following is a detailed analysis of chemical purity:
- Classification of Purity Grades
Chemical purity grades are usually classified based on their applications and preparation processes. Common purity grades include:
- Electronic Grade
- Purity: Typically 99.999% (5N) to 99.9999% (6N) or even higher.
- Applications: Used in the production of semiconductors, microelectronics, and high-tech materials.
- Impurity Control: Strict control over metals, oxides, and other trace elements that affect electronic performance.
- Pharmaceutical Grade
- Purity: Specific purity is specified in pharmacopoeias (e.g., USP, EP, JP) and usually requires extremely high purity.
- Applications: Used in pharmaceutical preparation and medical applications, such as pharmaceutical raw materials, drug production, and disinfectants for medical equipment.
- Impurity Control: Strict control over harmful impurities to ensure product safety and efficacy. Testing standards are rigorous, covering indicators such as organic impurities, heavy metals, and microorganisms.
- Food Grade
- Purity: Usually relatively high, with specific purity specified in food safety regulations.
- Applications: Used in food additives, food processing, beverage production, and packaging materials.
- Impurity Control: Strict control over harmful impurities (e.g., heavy metals, pesticide residues) to comply with requirements in food regulations.
- Reagent Grade
- Purity: Between industrial grade and analytical grade, with specific purity varying by application.
- Applications: Used in routine laboratory operations, such as solvents, extractants, and intermediates for chemical synthesis.
- Impurity Control: Relatively lenient control, suitable for daily experimental operations that do not require high purity.
- Analytical Reagent (AR): Also known as secondary reagent, with high purity (99.7%), slightly lower than Guaranteed Reagent. Suitable for important analytical work and general research.
- Guaranteed Reagent (GR): Also known as primary reagent or guaranteed reagent, with the highest purity (99.8%) and low impurity content. Suitable for important precision analytical work and scientific research.
- Chemical Pure (CP): Also known as tertiary reagent, with significantly lower purity than Analytical Reagent. Suitable for general analytical work in industrial and mining enterprises and schools.
- Laboratory Reagent (LR): Also known as quaternary reagent, with poor purity and no selective control over impurity content. Only suitable for general chemical experiments and synthetic preparation.
- High-Purity Reagents
Including ultra-pure, extra-pure, and high-pure grades, used for preparing standard solutions.
- Spectrum Pure (SP): Used in spectral analysis, suitable for standard samples of spectrophotometers, atomic absorption spectroscopy, and atomic emission spectroscopy, respectively.
- Primary Reagent (JZ): Used as a primary standard substance for calibrating standard solutions.
- Biochemical Reagent (BR): Used for preparing test solutions for biochemical analysis and biochemical synthesis.
- Biological Stain (BS): Used for preparing staining solutions for microbial specimens.
- Impact of Purity on Chemical Performance
The purity of chemicals has a significant impact on their performance, specifically reflected in the following aspects:
- Physical Properties: Chemicals with high purity tend to have more stable physical properties, such as melting point, boiling point, and density.
- Chemical Properties: High-purity chemicals exhibit higher reactivity and selectivity in chemical reactions, with faster reaction rates and higher yields.
- Safety: High-purity chemicals usually have lower toxicity and less irritation, resulting in less impact on the human body and the environment.
III. Recommendations for Purity Selection
When selecting chemical purity, careful consideration should be given based on actual needs. The following are some recommendations:
- High-Precision Analysis: For experiments requiring high-precision analysis, high-purity chemicals should be selected to avoid interference from impurities on analysis results.
- Pharmaceutical Manufacturing: In the pharmaceutical manufacturing process, pharmaceutical-grade chemicals that meet pharmacopoeia requirements should be selected to ensure the safety and efficacy of drugs.
- Semiconductor Production: In the semiconductor production process, electronic-grade chemicals with extremely high purity should be selected to ensure the performance and reliability of semiconductor devices.
- General Experiments: For general chemical experiments and synthetic preparation, reagent-grade chemicals can be selected to meet daily experimental needs.
The purity of chemicals is a key indicator describing their quality, and different application scenarios have varying requirements for chemical purity. When selecting chemical purity, careful consideration should be given based on actual needs to ensure the reliability of experimental results and the high quality of products.