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1. | Heat reagent water in a glass beaker while adding Bis and stirring. |
2. | When precipitation is observed (saturation), add HCl until pH = 7 as tested with pH paper. |
3. | Cool solution (a gel forms in the beaker), then decant the water and place in a warm oven until dry. |
4. | Scrape dry remains from the bottom of the beaker and place in a vacuum desiccator to cool. |
5. | Take first weight quickly upon removal from desiccator when making up the buffer. See ODP Tech Note 15 for complete instructions on making up the powdered buffer. |
6. | Redry in oven and cool in desiccator each time prior to weighing. |
7. | Make new Bis buffer at the beginning of each expedition. |
Main instrument panel
Instrument calibration
Instrument calibration
To ensure accuracy of sample measurements, the titrator settings must be optimized. Calibration of the system includes calibrating the electrode, selecting a dispensing rate program and calculating a standard ratio.
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Before the titrator can be used to measure samples, the electrode must be calibrated against pH buffers in the range expected in samples. Generally, calibration at pH 4, 7 and 10 covers the necessary range.
Figure 2. Electrode Calibration.
- Select Calibrate Electrodes from the main Alkalinity interface.
- Enter your range of buffers (4, 7, 10).
- Select your Drift Span. A drift span of 30 (default) indicates that a minimum of 30 measurements will be taken after each addition of titrant (acid). The difference between the first and last measurement is compared to the drift tolerance specified in the rate program.
- Place 3 mL of the first buffer solution in the vessel. Add stir bar and immerse electrode in vessel.
- 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.
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1. | Open the Rates & Standard Corrections tab in the Alkalinity main menu (Figure 3). |
2. | Under Rates, select a predefined rate from the list. These rates are multistep rate programs such as the 3 mV rate example in the previous section. |
3. | Click Load This Rate to use the predefined rate program. |
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Figure 3. Selecting a Predefined Dispensing Rate Program.
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1. | Open the Alkalinity/Standard tab in the Alkalinity main menu (Figure 4). |
2. | Edit the Rates fields for each step in the rate program as follows: |
| –Level (mV) up to which this rate is applicable (150 in the example shown below). |
| –Acid (mL) to add in each increment (0.030 mL = 30 µL as below). |
| –Drift tolerance (mv/s) for acid increment (0.02 as below). Measurement continues until drift tolerance is satisfied. |
| –Seconds until rate program times out (timeout(sec)) if drift tolerance is not satisfied (180 as below). |
3. | Click Save This Rate. |
4. | Enter a rate program name in the dialog box and click OK. |
Figure 4. Creating a New Dispensing Rate Program.
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