Pure Chlorite Standard Developed

The difference in the chloride level before and after purification of the NaClO2 is illustrated below in chromatograms I and II.

This method measures the ClO₂^- and Cl^- content together. As is visible on Chromatogram II (~20 µg/g ClO₂^- made from NaClO₂ after purification), there is still a small amount of Cl^- left in the material.

B. Chlorite Determination: Iodometric titration in the presence of starch indicator, versus a standard thiosulfate (S₂O₃^2-) solution (standardized vs. NIST SRM 136e potassium dichromate).

Chemistry:

ClO₂^- + 4I^- + 4H⁺ ⇀ Cl^- + 2H₂O + 2I₂

2I₂ + 4S₂O₃^2- ⇀ 4I^- + 2S₄O₆^2-

Note that this method measures only the ClO₂^- content.

C. Chloride Level: (using collected data)

• The ClO₂^- level obtained from method B (iodometric titration) is 983 µg/mL. This is equivalent to 983 × 0.5256 = 516.66 µg/mL Cl^-.

The total Cl^- level obtained from method A is 525.33 µg/mL Cl^-. The difference of the total Cl^- level (525.33) and the ClO₂^- as Cl^- (516.66) gives the Cl^- level in the purified ClO₂^- lot, which in this case is 8.67 ≈ 9 µg/mL.

• Another way of determining the Cl^- level in the ClO₂^- solution is to dilute the sample with deionized water and compare to a known concentration (Cl^- NIST SRM 3182). See Chromatogram IV and conditions below.

If 1.0 mM NaHCO₃ is used as eluent, the separation of ClO₂^- and Cl^- is better.

Results obtained from C-1 and C-2 (two different methods) above agree with one another, and no other peaks are detected in Chromatogram IV. Thus, it is safe to assume that there are no other species containing Cl (ClO₃^-, ClO₄^-, ClO₂, ClO^-, Cl₂) in our ClO₂^- CRM solution, and our methodology is accurate.

In addition to chlorite (EPA methods 300.1, 317.1, 325.0), our facility also manufactures bromate (EPA methods 300.1, 317.1, 321.8, 325.0) and bromide (EPA methods 300.1, 317.1, 325.0), both of which are included in the group of Disinfectants and Disinfection Byproducts Anions.