Shop Electrodes by Application
Our products can be used in a wide range of applications. Our electrodes are manufactured accurately with first-class engineering and are ideal for quality results in various applications.
Ion Selective Electrode Application Methods: Determination of Sulphate in Water
This application note covers the determination of sulphate in water. As there is no ion selective electrode (ISE) for the direct measurement of sulphate, the analysis is performed using a sample subtraction technique with a lead ISE. The potential of a known concentration of lead can be measured before addition of an unknown concentration of sulphate. The decrease in measured potential of the lead standard will therefore be proportional to the amount of sulphate added. There is no limit to the concentration of sulphate being measured, provided that the concentration of lead standard used in the method, is greater than that of the sulphate in the sample. If the concentration of sulphate is greater than the range of the lead ISE, then some sample conditioning may be required.
Equipment Required
- pH/mV Analyzer or pH Meter with millivolt scale
- Lead Ion Selective Electrode
- 1000ppm Lead Standard Solution 500ml
- Glass Beaker 250ml
- Glass 10 and 100ml Pipettes
- Deionised water in a wash bottle
Probe Slope
To ensure the accurate determination of sulphate in water (or your sample) you will need to measure the slope of the lead ISE. To do this measure the mV values in 100ppm and followed by the 1000ppm lead standards. Subtract the value in 100ppm from the value in 1000ppm. The slope should be between 24 and 29mV.
Method
Pipette 100ml of a lead standard of known concentration into a clean glass beaker, 1000ppm standard would be suitable here. Place the lead ISE into the standard, gently stir and select mV mode, note the stable mV result (mV1). Pipette 10ml off the unknown sulphate sample into the standard, gently stir using the electrode and after approximately 1 minute note the stable mV result (mV2).
Remove the lead ISE, rinse thoroughly with deionised water and replace the protective cap.
Calculation
Calculate ΔE by subtracting mV2 from mV1. The unknown sulphate concentration can be calculated using the following equation:
Cu = Concentration of the unknown sulphate
Cs = Concentration of Pb2+
Vs = Volume of Pb2+ standard
Vu = Volume of the sulphate sample
ΔE = Change in electrode potential in mV (mV2-mV1)
S = Slope of the electrode in mV
For more information on this application contact our team.