Hach DR/850, Procedures Manual, Page: 113 / 460

113
Summary of Method
The range of analysis using the DPD method for total chlorine
can be extended by adding more indicator in proportion to sample
volume. Thus, a larger fill powder pillow of DPD Total Chlorine
Reagent is added to a 5-mL sample portion.
The combined chlorine oxidizes iodide in the reagent to iodine.
The iodine reacts with DPD (N,N-diethyl-p-phenylenediamine)
along with free chlorine present in the sample to form a pink
color which is proportional in intensity to the total chlorine
concentration.
Instrument Setup
The following procedure will add this method as a new Hach
program to a DR/800 instrument.
1. Turn on the instrument by pressing the
ON
key.
2. Press the
SETUP
key.
3. Press the
DOWN
arrow key until the prompt line shows
USER.
4. Press the
ENTER
key.
5. Enter “8138”, followed by
ENTER
.
6. Key the number in the “Enter” column corresponding to line
number 1 on the display. Press
ENTER
. Repeat for lines 2–56
on the display.
Manganese, oxidized (Mn
4+
,
Mn
7+
) or Chromium, oxi-
dized (Cr
6+
)
1. Adjust sample pH to 6–7.
2. Add 2 drops Potassium Iodide (30 g/L) to a 5-mL sample.
3. Mix and wait 1 minute.
4. Add 2 drops of Sodium Arsenite (5 g/L) and mix.
5. Analyze the treated sample as described in the procedure.
6. Subtract the result from this test from the original analysis to obtain the
correct chlorine concentration.
Ozone Interferes at all levels
Peroxides May interfere
Extreme sample pH or highly
buffered samples Adjust the sample pH to 6–7 with Sulfuric Acid or Sodium Hydroxide
Interfering Substance Interference Levels and Treatments
CHLORINE, TOTAL, Ultra-High Range, continued