Working Principle of Sodium Dichloroisocyanurate (SDIC)

Sodium dichloroisocyanurate (SDIC) works primarily by releasing free available chlorine (FAC) upon contact with water, which then oxidizes and destroys microbial cell components to achieve rapid disinfection.

Core Mechanism: Hydrolysis and Chlorine Release

When SDIC dissolves in water, it undergoes hydrolysis. This process generates hypochlorous acid (HClO) and hypochlorite ions (ClO⁻), establishing an equilibrium mixture. These chlorine species constitute the "free available chlorine" that delivers the antimicrobial effect.

A key distinction from liquid sodium hypochlorite (bleach) is the release profile. While sodium hypochlorite releases its chlorine immediately, SDIC acts as a stabilized chlorine source. The parent compound retains chlorine and releases it more gradually. Research shows that a standard NaDCC solution can completely release its free chlorine in roughly 0.91 hours in water. This sustained release maintains an effective residual chlorine concentration, contributing to its stability profile.

Antimicrobial Action

The hypochlorous acid generated is a potent oxidizer. It attacks a broad spectrum of microorganisms—including bacteria, viruses, fungi, and spores—by oxidizing their cellular components, leading to rapid inactivation. Studies confirm that SDIC solutions demonstrate bactericidal effects against organisms such as S. mutans, S. aureus, and E. coli within a short contact time (e.g., 1 minute at 1,000 ppm).

Key Performance Considerations

Two factors significantly influence SDIC's working principle in practice:

Organic Matter Tolerance: SDIC is more resistant to inactivation by organic material than sodium hypochlorite. It can maintain an appropriate available chlorine level and is effective even in the presence of blood or other organic matter.

Stability and Concentration: SDIC solutions maintain stable available chlorine levels over time (e.g., over 1,000 ppm for 7 days) and are less affected by temperature and pH compared to bleach. However, in the presence of high organic loads (e.g., 30% human serum), both SDIC and bleach decompose, though SDIC retains a higher residual chlorine concentration (6,600 ppm vs. 2,600 ppm) immediately after preparation.