Hach DR2400 - Page 155

Chlorine Dioxide
Chlorine Dioxide
ChlorineDio_AVPP_Other_DPD_Eng_Ody.fm Page 5 of 6
c. Pipet the volume of standard needed into a 100-mL volumetric flask.
Dilute to the line with chlorine-demand-free deionized water. Invert to
mix.
Method 2
a. Dilute 1 drop of 5% chlorine bleach in 1 liter of chlorine-demand-free
deionized water. Use this as the standard.
b. Verify the standard’s concentration using the Hach Free Chlorine
Method 8021.
c. Perform the chlorine dioxide test on the standard without adding
glycine.
d. For program 76, the chlorine dioxide reading should be 2.35 times greater
than the chlorine result. For program 77, the chlorine dioxide reading
should be 2.34 times greater than the chlorine result. If so, this verifies the
DPD and the instrument are functioning properly.
e. Repeat the chlorine dioxide test on the chlorine standard, including the
glycine addition. The reading should be less than 0.10 mg/L. This
verifies that the glycine is eliminating free chlorine interference.
Method Performance
Precision
Standard: 1.00 mg/L ClO
2
See Section 3.4.3 Precision on page 44 for more information, or if the standard
concentration did not fall within the specified range.
Sensitivity
See Section 3.4.5 Sensitivity on page 44 for more information.
Summary of Method
Chlorine dioxide reacts with DPD (N, N-diethyl-p-phenylenediamine) to the
extent of one-fifth of its total available chlorine content corresponding to
reduction of chlorine dioxide to chlorite to form a pink color. The color intensity
is proportional to the ClO
2
in the sample. Chlorine interference is eliminated by
adding glycine, which converts free chlorine to chloroaminoacetic acid, but has
no effect on chlorine dioxide at the test pH. Test results are measured at 530 nm.
Program 95% Confidence Limits of Distribution
76 0.95–1.05 mg/L ClO
2
77 0.95–1.05 mg/L ClO
2
Program Portion of Curve ∆Abs ∆Concentration
76 Entire range 0.010 0.04 mg/L ClO
2
77 Entire range 0.010 0.04 mg/L ClO
2