Field Equipment Calibration
PH, Temperature, Conductivity,
Turbidity, Dissolved Oxygen, Free & Total Chlorine
Yeggie Dearborn
CCSF
Objective
 Understand Equipments and Supply Needed
 Ensure QA/QC is in place for data collection
 Testing various water samples
-pH/Temp/Specific Conductance/Total Dissolved
Solids (TDS)
-Turbidity
-Dissolved Oxygen
- Total & Free Chlorine
Necessary Equipment & Supplies
 Turbidity
-<0.1-750 NTU standards for 4 point calibration
- Sample vial
- Chlorine Standards A & B
- DPD-Colormetric Determinant for Free and
total Chlorine
-TURBIDITY /Chlorine meter
 pH/temp/Electric Conductivity meter
-pH Electrode Storage Solution
-4.0 pH buffer
-7.0 pH buffer
-10.0 pH buffer
-Conductivity Standard
-multiparameter probe and meter
Dissolved Oxygen
-Dissolved Oxygen/Meter
Probe
Extra batteries for the meters
Extra Field data sheets
Beaker/ sample Container
Deionized water for cleaning probes,
vials
pH/Temperature Calibration
Probe must be submerged in the solution and allowed to stabilize
Calibration
 Three point calibrations
 Use pH 7.0, pH 4 & pH 10 for three point depending on the anticipated sample
pH. Slope should be 92-102% out side this range readings are not accurate
 pH is temperature dependent; most meters compensate for the temperature
effect (not as strong an effect as for EC)
 Measure Temperature of stabilized buffers
Buffers/standards
 pH measurements are only as accurate as the buffers used for calibration.
 Discard buffers after their expiration dates.
 Be careful not to contaminate stock solutions with used buffer, rinse water or
with a different buffer.
Conductivity (EC) Calibration
Probe must be submerged in the solution and allowed to
stabilize
Calibration Standards
 conductivity standards commonly used depend on the
instrument example :
- 12.88 mS/cm for Hanna Multiparameter probes
 A maximum of 20% error regardless of standard used
is acceptable. Beyond 20%, readings are not accurate
Turbidity Calibration
Sensor calibration
 Turbidity free water = zero (0 NTU) standard
 filtering either sample water or deionized water through a 0.2 um or
smaller filter to remove particles
or
 use deionized water that is degassed by sparging (bubbling) with
helium to minimize air bubbles that give false turbidity readings
Turbidity Standards
•Formazin -Opacity of Formazin Standards ( 0,
2,10,40 80, 400 NTUs) :
Higher opacity= higher turbidity
•Other Standards available that are more
environmentally friendly ! Most Portable meters
have their own Turbidity Standards (<0.1, 15,100
750 NTUs)
Turbidity Range & Calibration
 Standards range depends on anticipated sample values
 Drinking water - typically 0-20 NTU
 Lakes, streams and wetlands - 0-20, 0-50 or 0-100 NTU
 Wastewater; Storm water run off 0-750 NTU; sometimes>1000
NTU, require dilution
 2 standards typically adequate , but four point calibration is better
(response is linear)
 Most commonly use ready made standards <0.1 NTU, 15 NTU, 100
NTU and 750 NTU.
Total & Free Chlorine-Colorimetric Calibration
 Calibrate the meter with Calibration solution provided
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with the meter. Most meters have specific calibration
standards.
Sample is initially read without addition of colorimetric
solution
For Total or free Chlorine specific colorimetric test reagent
are added
Field Meters have an interface that converts Absorbance
recorded by instrument into ppm (part per million) or
mg/L of Total or Free Chlorine
Validated Range 0-5 ppm (instrument can read as low as
0.02 ppm)
Dissolved Oxygen-Sensor Probe Calibration
Hanna Instrument
 The probe is under polarization with a fixed voltage of approximately
800 mV.
 Probe polarization is essential for stable measurements with the same
recurring degree of accuracy.
 With the probe properly polarized, oxygen is continually "consumed" by
passing through the sensitive diaphragm and dissolving in the
electrolyte solution contained inside the probe.
 Calibration should be 100% in the air (at sea level)
 The Probe can measure Oxygen as % saturation in a solution or mg/ L
without recalibration, by simply pressing RANGE function,
 The mg/L readings make it possible to read the concentration of the
dissolved oxygen directly in ppm.
 Range: 0.00 to 45.00 mg/L O2 /0.0 to 300 % O2
Dissolved Oxygen-Sensor Probe Salinity,
Altitude Compensation
 Temperature is automatically compensated during the
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Probe sensor read out. Temperature has an impact on
amount of dissolved O2.
However, reading need to be adjusted manually for altitude
and salinity that will affect DO reading.
Adjustment charts are provided to compensate for change
in altitude or salinity in reference to sea level.
Salinity adjustment is required when measuring salt water.
Altitude compensation is required if above sea level.
Stabilization Criteria for each parameter
QA/QC
Reading must be stabilized within certain range for each
parameter calibrated and tested
Stabilization Criteria for each parameter is required as
part of QA/QC.
 Temperature +/- 0.2 deg C
 Conductivity
<100 mS/cm +/- 5%
>100 mS/cm +/-20%
 pH
+/- 0.1 unit
 DO
+/- 0.3 mg/L
 Turbidity
+/- 10%
Field Monitoring Exercise 1
 In groups 4-5 you will be calibrating equipments set up in
various stations in the lab
 Each group will analyze 2 separate water samples available
to whole class.
- One tap water ( sample A)
- On Unknown water (sample B)
 Each sample will be analyzed for pH, Conductivity/TDS,
Temperature, DO, Cl2 (total and Free) and Turbidity
 Record Data in the Field log sheet provided.
 Interpret your results based on Water quality limits
discussed for these parameters .