44
Calibration
ISEs: Ammonium, Nitrate, & Chloride
Before performing the calibration, review Calibration setup (pH, ORP, ISE, conductivity, turbidity) on page 33.
The ISE sensors can be calibrated to one, two or three points. A 2-point calibration without chilling a third calibration
solution is extremely accurate and is the preferred method. However, if there is a large temperature variation during
sampling, a chilled third calibration point is recommended.
Higher calibration accuracy can be obtained if the standards used have a least one order of magnitude difference
between them. For example, 1 mg/L and 10 mg/L or 10 mg/L and 100 mg/L.
mV information for the ISE calibration
Ammonium mV values
• NH
4
1 mg/L = 0 mV +/- 20 mV (new sensor only)
• NH
4
100 mg/L = 90 to 130 mV > 1 mg/L mV value
• The mV span between 1 mg/L and 100 mg/L values should be ≈ 90 to 130 mV. The slope should be 45 to 65 mV
per decade.
Nitrate mV values
• NO
3
1 mg/L = 200 mV +/- 20 mV (new sensor only)
• NO
3
100 mg/L = 90 to 130 mV < 1 mg/L mV value
• The mV span between 1 mg/L and 100 mg/L values should be ≈ 90 to 130 mV. The slope should be -45 to -65 mV
per decade.
Chlroide mV values
• Cl 10 mg/L = 225 mV +/- 20 mV (new sensor only)
• Cl 1,000 mg/L = 80 to 130 mV < 10 mg/L mV value
• The mV span between 10 mg/L and 1000 mg/L values should be ≈ 80 to 130 mV. The slope should be -40 to -65
mV per decade.
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