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- Select Calibrate Electrodes from the main Alkalinity interface.
- Enter your range of buffers (4, 7, 10).
- Select your Drift Span. The default drift span is 30.
- Place 3 mL of the first buffer solution in the vessel. Add stir bar and immerse electrode in vessel. Confirm that the frit is in the solution.
- Select Cal 1 and then Start.
- When finished, clean vessel and the electrode.
- Repeat steps 4–6 with each calibration buffer, selecting Cal2 and Cal3 when appropriate.
- When all three buffers have been run, select OK-Save to save the calibration.
Dispensing rate
The rate at which the titrator dispenses the acid into the sample can be adjusted according to the expected alkalinity value. Higher alkalinities may require faster dispensing rates. The dispensing rate can be selected from a list of predetermined programs, or a new dispensing rate program can be created.
Select Edit Rates from the main alkalinity interface.
Standard ratio
Calculating the standard ratio (estimated vs. actual alkalinity, “fudge factor”) for the anticipated range of alkalinity values accounts for measurement error in acid strength. Standard ratio can be calculated using borax solution, sodium bicarbonate solution, or IAPSO standard seawater, as necessary, to most closely match alkalinity values (within 5 mM, to preserve the first-order transfer function) of the unknown samples. Generally, IAPSO standard seawater is used to establish this ratio, and additional calibration standards are used if samples deviate >5 mM from the alkalinity of IAPSO (~2.325 mM). The measurement is repeated until at least 3 consistent measurements are obtained within 5% of actual value for each standard:
- IAPSO = 2.21–2.44 mM
- 20 mM standard = 19–21 mM
- 40 mM standard = 38–42 mM
To start creating a standard ratio, select STANDARDS from the main alkalinity interface.
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