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Note that this method should only be used on interstitial water (IW) squeezed from the core material by the titanium squeezers. The RHIZON samplers alter the pH and alkalinity of the IW samples and should not be analyzed for alkalinity or pH.
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To measure alkalinity, a pore water sample is titrated with an acid to an endpoint at which carbonate is converted to bicarbonate and bicarbonate is converted to carbonic acid. In seawater, this endpoint occurs at about pH = 4.2.
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Make sure to select a correct dispensing rate program for the standard in question. You can access the rates by selecting Edit Rates from the Main instrument panel.
Before any measurement, press the red STOP/FILL button on the titrator itself. This will fill the syringe pump and ensure you will not run out of acid during the titration.
To start creating a standard ratio correction, select STANDARDS from the Main instrument panel.
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The system is now calibrated, dispensing rate and standard ratio correction selected. Generally, start with the slowest dispensing rate, assuming the alkalinity will be around the value of IAPSO. Same with the standard ratio correction, start with the IAPSO standard ratio correction and adjust according to what is measured in the samples.
Before any measurement, press the red STOP/FILL button on the titrator itself. This will fill the syringe pump and ensure you will not run out of acid during the titration.
Select SAMPLE from the Main instrument panel.
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Select the sample (IWS) from LIMS tree. Alternatively, type or scan in a Text_ID. If you use 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 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.
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