squiggly
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The meters work by measuring the charge through a reference electrode. The membranes on these devices actually attract ions to them, and when this happens the flow of charge which arises is measured. The membrane attracts these ions more or less strongly according to their concentration.
There are some problems though:
1. The instrument has a fairly high detection limit.
2. The instrument can become saturated along it's membrane, and give a measurement that is lower than what should be found.
3. Some ions will not interact with some membranes. The best method to use here are ion specific meters (to detect fluorine concentration, or sodium concentration--for instance).
4. The kinetics of attraction (the number of ions which will be attracted) are severely affected by different solution compositions. For instance. A solution of only one ion will give more accurate readings than one with, two, three, or four. When you get beyond 4 the kinetic picture is so hard to predict that the meter becomes basically useless.
There are some problems though:
1. The instrument has a fairly high detection limit.
2. The instrument can become saturated along it's membrane, and give a measurement that is lower than what should be found.
3. Some ions will not interact with some membranes. The best method to use here are ion specific meters (to detect fluorine concentration, or sodium concentration--for instance).
4. The kinetics of attraction (the number of ions which will be attracted) are severely affected by different solution compositions. For instance. A solution of only one ion will give more accurate readings than one with, two, three, or four. When you get beyond 4 the kinetic picture is so hard to predict that the meter becomes basically useless.