Thermo Fisher Scientific Ion Selective Electrodes Ammonia - Manual (Page 18)

Glassware
Clean glassware is essential for good measurement. Be sure to wash the glassware well with a mild
detergent and rinse very well with distilled or deionized water. Clean glassware will drain without
leaving water droplets behind.
Electrodes
The electrodes may be checked by using the procedure found in the section entitled Electrode
Slope Check.
1. Be sure to use either distilled or deionized water when following the procedures given in
Electrode Slope Check
.
2.
If electrode fails to response as expected, see the sections entitled
Electrode Assembly
and
Checking Membrane
. Repeat electrode slope check.
3.
If the electrode still does not perform as described, determine whether the ammonia
electrode inner body is working properly as directed in
Checking the Electrode Inner
Body.
4.
If the stability and the slope check out properly, but measurement problems persist, the
standards may be of poor quality, the sample may contain interference or complexing
agents, or the technique may be in error. (See
Standard, Sample and Technique sections
below.)
5.
Before replacing a "faulty" electrode, review the instruction manual and be sure to:
- Clean and rinse the electrode thoroughly.
- Prepare the electrode properly.
- Use proper filling solution, buffer, and standards.
- Measure correctly and accurately.
- Review
TROUBLESHOOTING HINTS.
Standards
The quality of results depends greatly upon the quality of the standards. ALWAYS prepare fresh
standards when problems arise. It could save hours of frustrating troubleshooting! Error may result
from contamination of prepared standards, accuracy of dilution, quality of distilled water, or a
mathematical error in calculating the concentrations.
The best method for preparation of standards is by serial dilution. This means that an initial
standard is diluted, using volumetric glassware, to prepare a second standard solution. The second
is similarly diluted to prepare a third standard, and so on, until the desired range of standards has
been prepared.
Sample
If the electrode works properly in standards but not in sample, look for possible interference,
complexing agents, or substances which could affect response or physically damage the sensing
electrode or the reference electrode. If possible, determine the composition of the samples and
check for problems. See
Sample Requirements and Interference .