ASC is a broad spectrum antimicrobial solution that has FDA
approved uses in the veterinary, food processing and medical
device fields.
Some ASC formulations are approved for use on food contact
surfaces while others are approved as secondary food additives
when used as antimicrobials on poultry, red meat, fruits,
vegetables and seafood.
The chlorite ion (ClO2-) in sodium chlorite (NaClO2) is stable in
aqueous solutions. Under acidic conditions, chlorite forms a semistable intermediate, chlorous acid (HClO2).
ASC solutions are mixed and immediately applied on site.
ASC solutions have a mild chlorine-like odor when operated in the
pH range 2.5 – 2.9. (21 CFR 173.325)
NaClO2 + HX
HClO2 + NaX
(salt)
Chlorous Acid (HClO2)
5HClO2
Chlorine Dioxide (ClO2)
4ClO2 + Cl- + HCl + 2H2O
Chlorite (ClO2-)
Chloride (Cl-)
NaClO2 + HX
HClO2 + ClO2 + ClO2- + Cl-
Ka
Ka Value for Acids: Relative Acid Strengths
HCl (Hydrochloric)
Ka = 1.3 x 106
109
H3PO4 (Phosphoric) Ka1 = 7.11 x 10-3
Very Complex
Chemistry!
C6H8O7 (Citric)
Ka1 = 7.45 x 10-4
C4H6O5 (Malic)
Ka1 = 3.98 x 10-4
pH
Active Oxychlorine Species
ClO2 + ClO2- + Cl-
NaClO2 + HX
HClO2
pH
HClO2(1)
Other (2)
2.3
31%
69%
2.9
10%
90%
3.2
6%
94%
Notes:
1. Rao 2007 measured HClO2 in 50 ppm ASC solution – values are time
dependent related to Ka and pH!
2. Other species including unreacted chlorite