20
SAMPLE HANDLING
• Keep samples stored in tightly converted bottles to prevent ammonia loss or ammonia
contamination from other sources.
• Alkaline samples must be measured at once or acidified for storage. (HCl may be added to
bring pH to 6).
• Acidic samples such as wine or juice may require additional ISA quantity because the pH of
the sample should be arround 11 for measurement.
• Measure samples and standards quickly after adding ISA because ammonia gas will escape
from the solution.
• For solution containing oil, sluge and waste samples (which may contain surfactants), digest
sample first using a total Kjeldahl nitrogen (TKN) procedure.
• For samples found to penetrate or “wet” the membrane. Measurements may be made above
the sample in a small headspace of a closed system (flask). The system should be saturated
with water vapor, the membrane tip suspended in the vapor phase above the sample, and the
concentration of N-NH
3
greater than 10
-3
M. In this case a loger response time is expected.
• Reuse of standards with already added ISA is not advised, because loss of ammonia is expected.
CLEANING PROCEDURE
If the sensor slope just misses the suggested slope window, soaking the sensor in a standard for a
period of time may solve the problem (choose 10
-2
M or 1 000 ppm Ammonia standard).
Rinse in deionised water and blot dry.
• Slide electrode cap and spring down cable and screw top cap onto outer body until fully
engaged. Afterwards, unscrew top cap two times. Do not invert electrode. Keep the membrane
side down.
• Gently pull spring loaded cable back and slowly release to allow filling solution to migrate
between membrane and glass electrode inner body. Screw top cap onto outer body until fully
engaged.
• Install assembled electrode in gas sensor test vessel or in electrode holder and connect cable
connector to the meter.