Carefully unwind the tape and remove the probe from the protective glass tube.  Only the bulbous tip is sensitive to potassium.  For best results, soak the tip of the electrode in 0.1 N KCl solution for 24 hours prior to use.

Meter requirement:  Any research grade pH meter with millivolt mode capability.  Set meter to millivolt mode.

The MI-442 is standardized using pure potassium chloride (KCl) solutions and again in solutions containing possible interfering ions ( if appropriate).  The pure KCl solutions are used to determine probe function.  In pure solutions, a 55 mv difference (approximate) will occur between each tenfold change in concentration.  For example, test in 0.001 N KCl, 0.01 N KCl and 0.1 N KCl.

Standardization in solutions containing possible interfering ions is done in order to simulate the actual samples to be analyzed.  For example, if your samples contain a known sodium background such as 150 millimoles NaCl then your calibrating standards should also have this background.  These  are some possible mixtures you could use:  0.001N KCl-0.15 N NaCl,  0.01N KCl-0.15 N NaCl,  0.1N KCl-0.15 N NaCl.  The data are then plotted on semilog paper (See Sample Calibration Curve).

(Insert calibration curve)

Remember!  For best results, do the following:

1.  Always use standards that bracket the concentration range that you expect to have in your samples.

2.  Always mix your standards to closely match the composition of your samples.

3.  Always calibrate using the same volume of standard that you will have as a sample. Example:  samples = 50 microliters then standards = 50 microliters.

Handling

Always handle the electrode with the same care you would use with other electrodes.

Cleaning

When using the electrodes in solutions containing protein, the MI-442 and the reference electrode should be rinsed with an enzyme cleaning solution such as Terg-a-zyme (Alconox, Inc.) after each use for a couple of minutes to remove protein from the membrane and reference junction.  This will prolong the useful life of the electrodes.

Storing

Always clean the electrodes before storing:

Long- term (over 2 weeks):  Return the electrode to its original container and prepare it in the same condition is which you received it.  Usually this means simply moistening the sponge located in the bottom of the protective glass tube with distilled water.

Short-term:  The electrode can be left in a 0.1 N KCl solution.

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