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Apparatus, supplies and reagents

Laboratory apparatus

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Figure 1. Metrohm Autotitrator (Note: dispenses 0.1 M HCl).

Hardware and software

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Figure 1. Metrohm Autotitrator (Note: dispenses 0.1 M HCl).

Supplies

Laboratory reagents

Dry reagents

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1. Set your Stability Criteria for each step of the program: Measurement continues until Stability Criteria (mV/s) is satisfied.
2. 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.
3. Set the Time Out for each step of the program: Seconds until rate program times out if Stability Criteria is not satisfied.
4. Save To File.

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Figure 4. Selecting a dispensing rate.

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-         40 mM standard = 38–42 mM

Generating standard values

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.

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To start creating a standard ratio correction, select STANDARDS from the Main instrument panel and enter the information for the standard in question.

Figure 5. Entering standard information.

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1. Place 3 ml of standard in vessel. Add stir bar and immerse electrode in vessel. Confirm that the frit is in the solution. Check that your Drift Span is 30.
2. Select Continue.  
3. Click START.
4. Insert the acid dispensing probe when prompted.
5. When finished, clean vessel and electrode. Repeat steps 1–4 until you have at least three consistent measurements per standard.
   Now go to the
   

Managing standard values

Select STND Manager

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from the Main instrument panel.

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Figure 7. Averaging standard measurements.

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1. Select the three measurements you want to average and click Average.
2. The small window shows the next step in which you can save the new standard ratio correction or replace an old one. Usually we save as a new ratio (e.g. 371_13august). The window showing the name creation is not shown.Click Done.
   
   
   

   To select a To select a standard ratio correction for subsequent measurements go to Setup in the main Main alkalinity interface.

   
   

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Figure 9. Selecting the standard ratio correction file to use.

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This window also shows the electrode calibration values, the path to the datalog file, the default setting for the Drift Span and where to select the standard ratio correction.

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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 useful if your IW has a lot of children.

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Figure 13. Reminders before starting the pH measumentmeasurement.

After completing all the steps in the guide boxwindow, click GO. The pH measurement will commence.

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Once the pH measurement is complete, you will see a guide box againbe reminded about the acid dispenser.

Figure 15. Acid dispenser reminder prior to starting the alkalinity measurement.

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The Gran-Method window appears with the results of the titration. Write the pH and the Alkalinity Cor value in the blue book. This Alkalinity Cor is the alkalinity with the standard ratio correction applied to it. Confirm that your MUT uploader is active. Click Ok/Save. This will upload the result to LIMS assuming the MUT uploader is active.

When finished, transfer the residue into a labeled 5 ml cryo vial. Clean the vessel, the stir bar, the electrode and the acid dispensing probe.

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Outlier Gran factor points can be deleted from the linear portion of the curve to improve the accuracy of sample results as follows.:

1. When the titration is complete, the Alkalinity Calculation screen Calculations window opens. Unlock the Gran factor axis.
2. Zoom in on the Gran factor points.
3. Select the cursor and move to the point to be deleted.
4. Click Delete Data and then click . This will only delete the selected point. Click Ok - Save when finished.

Figure 19. Editing Gran factor points.

Data reports

Data reports are not available at the instrument, but data can be viewed by selecting View Datalog (Figure 20) from the Main instrument panel. Also, the software appends the alkalinity results to the DAT file C:\ProgramData\IODP\Alkalinity. The best way to view the alkalinity values to be used in graphs and reports is via LIMS Reports. It is also highly recommended to record the alkalinity and pH values in the blue laboratory notebook to protect against inadvertent data loss.

Figure 20. Datalog.

Quality assurance/quality control

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Calibration/calibration verification

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Precision Precision

Precision

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