How can the accuracy of the alkalinity result be checked?

Document ID

Document ID TE114

Published Date

Published Date 27/05/2017
Question
How can the accuracy of the alkalinity result be checked?
Summary
Checking the accuracy of alkalinity methods
Answer
Accuracy of any method can be verified by using a standard of known concentration in place of a sample.  However, in the case of samples where an interference is suspected, a sample spike (standard additions test) should be performed.  This procedure is slightly different depending on the method being used:

Method 8203-Digital Titrator Method:
1. Use the test procedure to measure the concentration of the sample.
2. Add 0.1 mL of alkalinity standard part number 1427810 to the titrated sample.
3. Titrate the spiked sample to the endpoint.  Record the number of digits on the counter.
4. Add one more 0.1 mL addition of the alkalinity standard to the titrated sample. 
5. Titrate the spiked sample to the endpoint.  Record the number of digits on the counter.
6. Add one more 0.1 mL addition of the alkalinity standard to the titrated sample. 
7. Titrate the spiked sample to the endpoint.  Record the number of digits on the counter.
8. Compare the actual result to the correct (calculated) result.  The correct result for this titration is 25 digits of the 1.600N Sulfuric Acid Titration Cartridge or 250 digits of the 0.1600N Sulfuric Acid Titration Cartridge for each 0.1 mL addition of the standard solution.  If much more or less titrant was used, there can be a problem with the user technique, reagents, apparatus or an interference.

Method 8221-Buret Titration
1. Use the test procedure to measure the concentration of the sample.
2. Add 0.1 mL of alkalinity standard part number 1427810 to the titrated sample.
3. Titrate the spiked sample to the endpoint.  Record the mL of titrant added.
4. Add one more 0.1 mL addition of the alkalinity standard to the titrated sample. 
5. Titrate the spiked sample to the endpoint.  Record the mL of titrant added.
6. Add one more 0.1 mL addition of the alkalinity standard to the titrated sample. 
7. Titrate the spiked sample to the endpoint.  Record the mL of titrant added.
8. Compare the actual result with the correct (calculated) result.  The correct result for this titration is 2.5 mL of titrant for each 0.1 mL addition of the standard solution.  If much more or less titrant was used, there can be a problem with user technique, reagents, apparatus or an interference.