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- Set your Stability Criteria for each step of the program: Measurement continues until Stability Criteria (mV/s) is satisfied.
- Select your Increment for each mV level (initial to 150, 150 to 220 and 220 to 240): How much acid is added in each increment.
- Set the Time Out for each step of the program: Seconds until rate program times out if Stability Criteria is not satisfied.
- Save To File.
Standard ratio correction
Calculating the standard ratio correction (estimated vs. actual alkalinity) for the anticipated range of alkalinity values accounts for measurement error in acid strength. Standard ratio correction 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). It is good practice to have IAPSO, 20 mM and 40 mM standard ratio corrections calculated before arriving at the first site. This prepares you for alkalinities up to 40 mM.
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The system is now calibrated, dispensing rates selected (generally start with the slowest rate, assuming that alkalinity will be around the value of IAPSO) and standard ratio correction selected (again, generally start with the IAPSO standard ratio and adjust accordingly according to what is measured in the samples).
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Select the sample (IWS) from the LIMS database. Use the tree or type in the Text_ID in the appropriate field. If you type in a Filter Code IWS, the software will only bring up the IWS sample, which can be handy if your IW has a lot of children.
Place 3 mL of the sample in the vessel. Add stir bar. Remove the electrode from the storage solution, rinse with DI water, and blot dry with a Kimwipe. Do not rub the electrode, as this can cause a static charge. Insert the electrode tip into the titration vessel (not touching the bottom of the cup or stir bar). Confirm that the frit is in the solution.
Select Continue.
Click START. The software will guide you through.
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Click Ok/Save to save the results to the LIMS database. The value saved to LIMS and the value you need to note in the blue book is the “Alkalinity Cor” value. This is the value your result with the standard ratio applied to it.