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KIRTLAND AIR FORCE BASE ALBUQUERQUE, NEW MEXICO ...

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APPENDIX B<br />

SOP B5.1<br />

pH<br />

The following procedure is used for measuring groundwater pH with a pH meter:<br />

The instrument and batteries should be checked and calibrated in the laboratory prior to<br />

initiation of the field effort.<br />

The accuracy of the buffer solutions used for field and laboratory calibration should be<br />

checked. Buffer solutions need to be changed due to degradation upon exposure to the<br />

atmosphere. The date of preparation of each buffer should be included on the bottle label.<br />

Immerse the tip of the electrodes in water overnight. If this is not possible due to field<br />

conditions, immerse the electrode tip in water for at least an hour before use. The electrode<br />

tip may be immersed in a rubber or plastic sack containing buffer solution for field transport<br />

or storage. This is not applicable for all electrodes as some must be stored dry.<br />

Make sure all electrolyte solutions within the electrode(s) are at their proper levels and that<br />

no air bubbles are present within the electrode(s).<br />

Immerse the electrode(s) in a pH-7 buffer solution.<br />

Adjust the temperature compensator to the proper temperature (on models with automatic<br />

temperature adjustment, immerse the temperature probe into the buffer solution).<br />

Alternately, the buffer solution may be immersed in the sample and allowed to reach<br />

temperature equilibrium before equipment calibration. It is best to maintain buffer solution<br />

at or near expected sample temperature before calibration.<br />

Adjust the pH meter to read 7.0.<br />

Remove the electrode(s) from the buffer and rinse well with deionized water. Immerse the<br />

electrode(s) in pH-4 (for water with pH of 1 to 7) or pH-10 (for water with pH of 7 to 12)<br />

buffer solution and adjust the slope control to read the appropriate pH. At least three<br />

successive readings during calibration, one minute apart, should be within +0.1 pH unit. For<br />

best results, the standardization and slope adjustments should be repeated at least once daily<br />

before use.<br />

Immerse the electrode(s) in the unknown solution, slowly stirring the probe until the pH<br />

stabilizes. Stabilization may take several seconds to minutes. If the pH continues to drift,<br />

the sample temperature may not be stable, a chemical reaction (e.g., degassing) may be<br />

taking place in the sample, or the meter or electrode may be malfunctioning. This must be<br />

clearly noted in the log book.<br />

Read and record the pH of the solution, after adjusting the temperature compensator to the<br />

sample temperature. pH should be recorded to the nearest 0.1 pH unit. Also record the<br />

sample temperature.<br />

Rinse the electrode(s) with deionized water.<br />

Keep the electrode(s) immersed in water when not in use.<br />

Kirtland AFB<br />

SOPs for Field Investigations B-125 April 2004

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