Hi, I have a problem in measuring soil pH. The soil is collected from a coastal sand dune and my extracting solution is made with the following procedure:
5g of soil + 25ml of distilled water
30min shaking
60min keeping it still
The problem is that pH meter shows unstable values. Every second I check pH meter it shows different values. For example, the meter shows 6.78 now but one second before, it was 6.79 and two more seconds before, it was 6.80. So it took almost 5min to get stable value.
I always do calibration and the meter has no errors. Is there any 'better' or 'right' way to get a stable value faster?
@ Lee, when a pH system is unstable, erratic, or the offset drifts, the most common problem is an electrical ground loop in the system, particularly if the tank and/or pipes are plastic. To verify this problem, remove the electrode and calibrate it in a known buffer in a beaker. Moreover, make sure that the electrode contains saturated KCL solution and some solid KCL.
This is normal problem which occurs in soil pH measurement. As you have taken 1:5 soil and water suspension, make sure that pH value of distilled water is 7 before adding in the soil and your pH meter is properly calibrated.
Follow the steps as:
(1) After complete stirring/shaking with stirring rod for 30 min, insert the probe immediately and take the initial reading of the solution (which is your desired soil pH) otherwise pH value of the solution will start to decrease/increase and will move towards 7 pH value of the distilled water because solution starts to become transparent.
2) Insert the probe almost more than half of the depth of the solution and above the bottom of the glassware.
Keon-Hak Lee
You can also try using a soil: solution ratio of 1:2.5 which is the international standard. In addition, you can try using 0.01M CaCl2 instead of water. Soil pH in CaCl2 is more stable as it is less affected by soil electrolyte concentration.
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