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    • CommentAuthorjuruble
    • CommentTimeJun 21st 2007 edited

    This protocol explains how to: use the pH meter.

    Protocol revised: 3/12/2007

    Protocol written by: Julie Ruble (pictures by Dom Ippolito)

    1. Uncap 4, 7, and 10 standard solutions (Fig. 1).

      Fig. 1
      Figure 1. Standard solutions for calibrating the pH meter.

    2. Remove pH meter probe from storage vial and rinse with distilled water squirt bottle. Gently blot with kimwipe. Do not let probe dry out in air!
    3. Place probe in the 4 standard solution and press "Standardize." Wait until screen flashes 4.00 -- this means the pH meter has finished calibrating with this solution.
    4. Repeat step 3 with the 10 and 7 standard solutions, rinsing between each solution with distilled water and blotting with kimwipes.
    5. Once pH meter is completely calibrated, place probe in your solution (Fig. 2). When the meter stops drifting and you see the S on the screen, it has reached a stable reading.

      Fig. 2
      Figure 2. Placing pH meter into the solution. Notice the end of the probe is submerged, but not the entire probe.  Solution should still be mixing while you measure and adjust pH.

    6. If you need the solution to be more acidic, add HCl slowly (you can dilute the HCl to change the pH to a lesser degree). If you need the solution to be more basic, add NaOH slowly.
    7. When finished, rinse probe and blot. Return to storage vial (make sure there is still enough pH electrode storage solution in the vial to cover end of probe).