Pharmaceutical grade applications: trihydrate (CAS 7220-79-3) is more commonly used in preparations that meet Pharmacopoeia standards, such as microbial culture media in the United States Pharmacopoeia (USP) or the European Pharmacopoeia (EP)

APPLICATIONS

• Staining biological specimens in microscopy
• Determining cell viability and counting cells
• Assessing microbial growth and vitality
• Detecting bacteria and fungi in laboratory cultures
• Marking tissues and surgical margins in medical procedures
• Testing for leaks in medical devices and plumbing systems
• Visualizing DNA and RNA in gel electrophoresis
• Dyeing fabrics and textiles in industrial applications
• Tracing water and air flow in environmental studies
• Demonstrating chemical reactions and diffusion in educational experiments

Key Differences Between CAS 7220-79-3 and CAS 61-73-4

Structural Differences

• CAS 7220-79-3: Contains 3 water molecules in its crystal lattice, altering its physical properties (e.g., lower density, higher hygroscopicity).

• CAS 61-73-4: Anhydrous form with no bound water, often preferred for precise industrial or analytical applications.

Functional Differences

1. Pharmaceutical Use:

• Trihydrate (7220-79-3): Commonly used in USP/EP-compliant formulations (e.g., injectables, microbiological media).

• Anhydrous (61-73-4): Rarely used in drug manufacturing due to stricter hydration control requirements.

2. Industrial Use:

• Anhydrous (61-73-4): Preferred for dyeing textiles, ink production, and water treatment due to stability and cost-effectiveness.

• Trihydrate (7220-79-3): Less common in industrial settings.

3. Laboratory Use:

• Trihydrate: Used in standardized protocols (e.g., Gram staining, redox experiments like the "Blue Bottle" reaction).

• Anhydrous: Applied in spectrophotometry (e.g., absorbance at 665 nm) or cell biology (nuclear staining).

Safety and Regulatory Notes

• Toxicity: Both forms share similar toxicity profiles (e.g., rat oral LD₅₀ ≈ 1180 mg/kg).

• Labeling:

• Trihydrate (7220-79-3): Often labeled with hydration state and compliance with pharmacopeias (e.g., USP-NF).

• Anhydrous (61-73-4): Typically marked for industrial or reagent-grade use.

References

1. USP-NF Monographs: Search "Methylene Blue" on usp.org for pharmaceutical-grade specifications.

2. PubChem Data:

• CAS 7220-79-3

• CAS 61-73-4

3. Supplier Documentation: Sigma-Aldrich or TCI Chemicals provide COA (Certificate of Analysis) for purity and application details.

Summary

• Trihydrate (7220-79-3): Used in medicine/labs for controlled hydration and compliance with pharmacopeias.

• Anhydrous (61-73-4): Favored in industry and general research for cost and stability.

• Key Distinction: Hydration state drives differences in solubility, stability, and regulatory compliance.