Hello Alun,

I don't know of specific pure compounds being used for this purpose.

There are certified botanical and soil reference materials, but the certificate is generally for total constituents.  For plants and soils the organic- P generally constitutes about half the total. This statement will probably bring out plenty of non-conforming examples.

Paul

 Mr. Alun and Dr.Paul,It is  a difficult topic to address.During my doctoral programme I determined organic P by ignition method,thinking that the extraction procedures are cumbersome and equally not so accurate.In  seeds P is present as phytic acid(phytate) and is estimated colorimetrically using  Phytic acid dodeca sodium salt from maize Sigma P-8810 from Sigma chemicals Co.as standard.In soil organic P may range from 20-80 percent and average may be 50% as mentioned by Dr.Paul.It is believed that at least 50%of soil organic P is in phytate form.But the phytate may not be more than 30%,the other forms known  are  phospholipids and nucleic acids.But their quantities are small.Almost 50% of organic P is not properly characterized.Scientists attempted phytate estimation in soil and manure using calcium and sodium phytate standard from Sigma chemicals Co.Now our understanding of organic P in soil is changing fast because of two reasons .1.Use of phytase enzyme in animal production system is changing the nature P in manure.2.The use of 31P nuclear magnetic resonance spectroscopy to determine the species of organic P in soil extracts.Current studies  showed that the Phytate P may not exceed 30% and  in the rest of unknown P most of it could be(61-73% ) in supra-/macro-molecular structure,may be P associated with humic matter.So using a standard P compound in organic P estimation may be difficult.I solicit responses from colleagues who have worked in this line for better appreciation of the subject.

Only one more thing I could add, i.e. that acid digests of soils give pseudo totals and 'real' totals require fusion in an alkaline flux.  If yuo are lucky you will find somebody who pours 'beads' from the flux and measures P using X ray fluorescence.

Phosphorus (total) standard solution traceable to SRM from NIST

You can use this standard by subjecting it to the same treatment as the samples to calculate the chemical yield and then in addition to your samples (at different concentrations) to see if there are to matrix interferences