Another paper describes how imidazole propionate serum levels were measured: https://www.nature.com/articles/s41467-020-19589-w

"""Imidazole propionate serum measurements

ImP was quantified using ultra-performance liquid chromatography coupled to tandem mass spectrometry according to previous work. Briefly, serum samples were extracted with 3 volumes of ice-cold acetonitrile containing internal standards (13C3-labeled ImP and urocanate). After derivatization to butyl esters using 5% hydrochloric acid in butanol, the samples were separated on a C18 column using a gradient consisting of water and acetonitrile. Quantification was made using an external calibration curve16."""

So yes, but no.