Hach DR/850 - Page 87

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6. Obtain a recent lot of Chlorine Solution Ampules,
50–70 mg/L, and note the actual free chlorine concentration
for this lot.
7. Calculate the amount of Chlorine Solution to be added to the
ammonia standard using the following equation:
8. Open an ampule and, using a glass Mohr pipet, add the
calculated amount of Chlorine Solution slowly to the
ammonia standard, while mixing at medium speed on a
stir-plate.
9. Allow the monochloramine solution to mix for 1 minute after
all Chlorine Solution is added.
10. Quantitatively transfer the monochloramine solution to a
clean 100-mL Class A volumetric flask. Dilute to the mark
with organic-free water, cap, and mix thoroughly. This is a
nominal 4.5 mg/L (as Cl
2
) monochloramine standard.
Use this standard within 1 hour of preparation.
Method Performance
Precision
In a single laboratory, using a monochloramine standard solution
of 2.10 mg/L Cl
2
and representative lots of reagent, a single
operator obtained a standard deviation of ±0.12 mg/L Cl
2
.
Estimated Detection Limit
The estimated detection limit for Method 10171 is 0.05 mg/L Cl
2
.
For more information on the estimated detection limit, see
Section 1 of the Procedure Manual.
Interferences
The following have been tested for interference and found not to
interfere up to the indicated levels:
mL chlorine solution required
455
free chlorine concentration
----------------------------------------------------------------=
Table 9 Non-interfering Substances
Substance Maximum Level Tested
Alanine 1 mg/L N
Aluminum 10 mg/L
Bromide 100 mg/L Br
–
CHLORAMINE, MONO, Low Range, continued