eutech-instruments ammonia gas Manuale Utente
Instruction Manual
Ammonia Gas-sensing Electrode
4
3.
Adjust the meter to the concentration of the standard and fix the value in the memory
according to the meter manufacturer's instructions.
according to the meter manufacturer's instructions.
4.
Rinse the electrodes with distilled water and blot dry.
5.
To another 150 ml beaker, add 100 ml of the higher value standard and 2 ml of ISA. Place
the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode
tips into the solution.
the beaker on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode
tips into the solution.
6.
Adjust the meter to the concentration of the standard and fix the value in the memory.
7.
Read the electrode slope according to the meter manufacturer's instructions. Correct
electrode operation is indicated by a slope of 90-100%. See
electrode operation is indicated by a slope of 90-100%. See
TROUBLESHOOTING section
if the slope is not within this range.
MEASUREMENT
Measuring Hints
Samples should be measured immediately after collection. Samples should be stored according to
the directions given in
Sample Storage
if immediate measurement is not possible.
The ratio of a surface area to volume in the beaker should be minimized. Beakers containing the
samples or the standard should be kept covered between measurements.
The ammonia ISA, 10M NaOH, should be added just before measurement. All samples and
standards should be at the same temperature for precise measurement. A difference of 1
o
C in
temperature will result in approximately a 2% error. All samples must be aqueous.
Always rinse the electrode with distilled water and blot dry between measurements. Use a clean,
dry tissue to prevent cross-contamination.
Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can
generate sufficient heat to change solution temperature. To counteract this effect, place a piece of
insulating material, such as gauze or styrofoam, between the beaker and the magnetic stirrer.
Always check to see that the membrane is free from air bubbles after immersion into standard or
sample.
Always rinse the electrode with distilled water and blot dry between measurements. Use a clean,
dry tissue to prevent cross-contamination.
Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can
generate sufficient heat to change solution temperature. To counteract this effect, place a piece of
insulating material, such as gauze or styrofoam, between the beaker and the magnetic stirrer.
Always check to see that the membrane is free from air bubbles after immersion into standard or
sample.
Sample Storage
Samples should be measured immediately after preparation or collection, if possible. Wait only long
enough for temperature equilibration between the sample and the electrode. If stirring a 100 ml
basic solution in a 150 ml beaker, the rate of ammonia loss at room temperature is about 50% in six
hours. The loss of C0
2
increases with increasing temperature.
If the samples cannot be measured immediately, add 0.5 ml of 1M HCl to each liter of sample to
make them slightly acidic (pH 6) and store in tightly capped vessels. Prior to measurement, add
10M NaOH to make the samples slightly basic.