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4.3 Choosing calibration standards
For best results, choose a calibration standard whose value is close to what you expect to see in the field. For
example, calibrate with a 1413 μS/cm
specific conductance standard if you expect to see specific conductance
readings between 500 and 1000 μS/cm in the field.
Calibrating with a sea water standard or a very low
standard would not be appropriate in that case. Similarly, if your waters tend toward the acidic, calibrate with
a 4-buffer instead of a 10-buffer.
If you are moving your multiprobe across wide ranges of water conditions, you may wish to recalibrate to
match the new situations. For instance, if you are measuring a clear lake during the morning and a high-
sediment stream in the afternoon, you might consider recalibrating at noon with a high-range turbidity
standard.
The table below shows common calibration practices.
Sensor
Standard method of calibration Available calibration solutions
Comments
Temperature
never requires calibrating
N/A
pH / pH reference
2 or 3 points
pH 4, pH 7, pH 10
pH 7, pH 10 most common
ORP
1 point
ORP Standard 200 mV
Conductivity
1 point
CD Standard, 0.5 Molar, 58670 Micro S
CD Standard, 0.1 Molar, 12856 Micro S
CD Standard, 0.01 Molar, 1412 Micro S
CD Standard, 0.001 Molar,147 Micro S
brackish/saltwater borderline
brackish typical freshwater very
pure fresh/glacial
Reference
Electrode
calibration not required
N/A
replace pH electrolyte solution
at routine calibration
Depth
adjust for barometric pressure
N/A
recalibrate at deployment site
for best accuracy
Turbidity
2 points
0 NTU, 10 NTU, 100 NTU, 400 NTU
calibrate near expected value
HDO
(Optical
DO)
calibrate at 100% saturated
water
DI water -shake vigorously to
oxygenate
set BP before calibrating, recal
at deployment site for best
accuracy
Chlorophyll
2 points
secondary solid or 40µg/L solution
or lab sample
Rhodamine
2 points
secondary solid standard or
rhodamine
Blue
Green
Algae
2 points
secondary solid standard or lab
sample
Ammonium
(NH4+)
2 points
Lo 4.63 mg/l; Hi 46.3 mg/l
Nitrate
(NO3+)
2 points
Lo 4.62 mg/l; Hi 46.2 mg/l
Chloride
(CL-)
2 points
CD Standard 147 Micro S
CD Standard 1412 Micro S
enter 34.3 during calibration for
low
enter 319.3 mg/l for high
