How do I determine the conversion factor for a phosphonate compound not listed in the procedure?

Document ID

Document ID TE363

Version

Version 2.0

Status

Status Published

Published Date

Published Date 27/05/2017
Question
How do I determine the conversion factor for a phosphonate compound not listed in the procedure?
Summary
Conversion factor for phosphonates
Answer
The phosphonate test converts all phosphonate compounds into phosphate, and then measures the increase in phosphate due to the phosphonates.

The conversion factor for a particular phosphonate is determined from the molecular weight of the phosphonate relative to phosphate, and the number of PO4 (or PO3) groups in the phosphonate molecule:
-Conversion factor = MW phosphonate/(MW PO4 x PO4 or PO3 groups)

Example:
What is the conversion factor for MDTP (2-methylene diamine tetrakis-(Methylene Phosphonic Acid))?

Answer:
-The molecular weight (MW) of MDTP is 490 g/mole
-The molecular weight of phosphate is 95 g/mole
-There are 4 PO3 groups per molecule of MDTP
-The conversion factor is: 490 / (95 x 4) = 1.29
-In this example, you would multiply the result displayed on your instrument by 1.29 to find the concentration of MDTP in your sample.