13
XII. XII.
XII. XII.
XII.
Sample HandlingSample Handling
Sample HandlingSample Handling
Sample Handling
• Keep samples stored in tightly covered bottles to pre-
vent ammonia loss or ammonia contamination from
other sources.
• Alkaline samples must be measured at once or acidi-
fied for storage. (HCl may be added to bring pH to 6).
• Acidic samples such as wine or juice may require
addition ISA. Samples should be approximately pH
11 for measurement.
• Measure sample and standards quickly after adding
ISA because ammonia gas will escape from the solu-
tion.
• For solutions containing organically bound nitrogen
such as oil, sludge, waste, or samples which may
contain surfactants; digest sample first using a total
Kjeldahl nitrogen (TKN) procedure. This involves
oxidation with hot sulfuric acid which converts bound
nitrogen to ammonium ions. Consult Method 4500-
N
org
from Standard Methods for the Examination of
Water and Wastewater.
• For samples found to penetrate or “wet” the mem-
brane, measurements may be made above the sample
in a small headspace of a sealed system such as HI
4000-71 test vessel, provided the concentration of
NH
3
is greater than 10
-3
.
M. The headspace should be
saturated with water vapor and the membrane end of
the electrode suspended in the gas sample above the
sample with ISA added. Expect a longer response
time from the sensor when gas phase measurements
are made.
