at the following link you will find a recent and detailed review article on the analysis of polyphosphates in life science (Anal. Chem. 2020, 92, 6, 4167-4176):
https://doi.org/10.1021/acs.analchem.9b05144
You may find information here that can help you in your research.
thank you for posting this very interesting technical question on RG. In addition to the very helpful literature reference suggested by Florian Morsbach please also have a look at the following potentially useful review article:
Polyphosphate: an ancient molecule that links platelets, coagulation, and inflammation
Article Polyphosphate: An ancient molecule that links platelets, coa...
Methods The review comprises a section entitled "Methods for preparing and analyzing polyP" with numerous references to original research papers. This article has not yet been posted as public full text on RG, but one of the authors has an RG profile (https://www.researchgate.net/profile/James-Morrissey). Thus you can easily request the full text directly from this author via RG (provided that it is of interest to you).
The isolation and analysis of polyphosphate has also been described in the following Open Access article:
Polyphosphate exerts differential effects on blood clotting, depending on polymer size