PASCO PS-2169 Water Quality MultiMeasure Sensor - Manual (Page 5)

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M o d e l N o . P S - 2 1 6 9 p H / IS E / O R P
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Measuring pH
The pH electrode produces a voltage proportional to the pH of the solution that it is
immersed in. This voltage is measured by the multi-sensor, which computes pH.
Unscrew and remove the storage bottle from the electrode (be careful not to spill the
storage solution). Push the O-ring and bottle cap up the electrode handle. Rinse the
electrode tip with distilled water. If you see bubbles in the electrode bulb, gently
shake the electrode downward (similar to shaking down a thermometer). Start data
collection. Place the tip of the electrode in the solution to be measured and wait for
the reading on your computer or interface to stabilize. Rinse the electrode with dis-
tilled water before measuring another solution.
pH Calibration
The pH measurement can be calibrated; however, for most applications calibration is
not necessary. Perform a two-point calibration with two buffer solutions of known
pH. For instructions on calibrating in DataStudio, see Appendix A. For instructions
on calibrating on the Xplorer GLX, refer to the Xplorer GLX Users’ Guide.
pH Electrode Maintenance and Storage
Cleaning
If the pH electrode becomes contaminated, use one of these methods to clean and
restore it. After any of these procedures, soak the electrode in a pH 7 buffer solution
for 30 minutes.
• General Contamination: Soak the electrode in 0.1 molar hydrochloric acid
(HCl) for 15 minutes.
• Protein Deposits: Soak the electrode in a solution of 1% pepsin in 0.1 molar
HCl.
• Inorganic Deposits: Rinse the electrode with 0.1 molar ethylene dinitric
tetra-acidic acid (EDTA) tetrasodium solution.
• Oil and Grease Film: Wash the electrode carefully in a mild detergent or a sol-
vent known to be effective for the particular film.
• Unknown Contamination: Soak the electrode alternately in 12 molar sodium
hydroxide (NaOH) and 1 molar HCl. Leave it in each solution for one minute.
Rinse completely between soakings. End with HCl. (The NaOH etches the glass
and the HCl reestablishes hydrogen ions on the surface.)
If these steps fail to improve the response of the electrode, replaced it.
Storage
Store the pH electrode in the included electrode storage bottle with one of the follow-
ing solutions. (Never store the electrode in distilled water.)
• Short-term (up to one week): pH 4 buffer solution or tap water.
• Long-term (over one week): pH 4 buffer solution with 1 g per 100 mL of potas-
sium chloride (KCl) added.