Determination of Potassium in Water

This is a method for determining the concentration between 0.1-1000 ppm potassium in ground water, drinking water and wastewater.

 

Equipment Required

1. pH/Ion analyzer (recommended) or pH meter with millivolt scale
2. Potassium combination ion selective electrode

 

Reagents Required

1. Ionic strength adjustment buffer, 10M TEAC
2. Standard potassium solution, 1000 ppm

 

Ionic Strength Adjustment Buffer (ISAB) Preparation

Dissolve 183.79g of tetraethyl chloride in distilled water and dilute to 1000 ml (10M TEAC)

 

Potassium Standard Solution

Dissolve 1.91 g of potassium chloride in distilled water and dilute to 100ml (1000 ppm as potassium). Prepare 100, 10, 1, 0.1 ppm standards by serial dilution of the 1000 ppm standard.

 

Method

Calibration Procedure:

 

To 100 ml of each standard solution add 1 ml of ISAB.

• Ion Analyzer: Immerse electrodes into the .1 ppm standard/ISAB solution and record the mV reading according to the Analyzer manual. Repeat this operation for each standard (wiping the electrode between measurements and rinsing the electrode with distilled water afterwards) in increasing concentrations. A straight line with a slope 56 ⁺/_- 3 mV / decade at 25 ⁰C should result.
• pH meter: Plot the calibration curve, mV reading vs. concentration, on semi-log paper.

 

Measurement:

 

To 100 ml of sample add 1 ml of ISAB, immerse electrode and record the mV reading.

 

Calculation

As both sample and standards have been diluted by the same amount, the potassium concentrations are read off the calibration curve directly (if pH meter is used, read off the calibration curve directly).