In method 8007 for phosphonates, how can a conversion factor be determined for a phosphonate compound not listed in the method?

Document ID

Document ID TE363

Version

Version 4.0

Status

Status Published

Published Date

Published Date 07/31/2018
Question
In method 8007 for phosphonates, how can a conversion factor be determined for a phosphonate compound not listed in the method?
Summary
Conversion factor for phosphonates
Answer
Phosphonate method 8007 uses a UV-catalyzation oxidation to convert all phosphonate compounds in the sample into orthophosphate and then measures the resulting orthophosphate concentration.

The conversion factor for a particular phosphonate is determined from the molecular weight (MW) 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 number of PO4 or PO3 groups)

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

Answer:
-The molecular weight of MDTP is 490 g/mole
-The molecular weight of orthophosphate 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.

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