During studies on the dcgradativc changes in synthetic l~olymctaphosphatcs by ultrasonic irradiation', it was ncccssary to estimate the small amounts of orthophosphate originally prcscnt and also any orthophosphate found during the cxposurc. Colorrmctric methods where hrgh concentrations of sulfuric acid and molybdatc am usecl~-3 were inapplicable bccausc of the labrlc nature of metaphosphate. 'I'hc method of LOWRY AND LOPEZ", whrch is widely employed to estimate orthophosphatc in the prcsencc of acicl-labile phosphate esters, was then tried. Thcrc was no color formation when fresh solutions of polymctaphosphatcs were tested, but after subjecting to ultrasonic vihratron at 25 kc/set for ~0450 min in a stainless steel vessel, thcrc was a significant color clcvclopmcnt when the solutions were rcanalyzccl. It was found that the color formation due to orthophosphatc was supprcsscd by high concentrations of polymctaphosphate.
This inhibition was overcome partially, or nearly completely, by the addition of certain metal ions. 'lhc isobutanol estraction method of UERENBLUM AND C&IAIN*, in contrast to the drrcct calorimetric method of LOWIXY-LOPEZ, was found to be suitable for the accurate assay of the orthophosphate in the prcscncc of a large excess of conclenscd phosphates. With this method the orthophosphate content of the exposed solution was practtcally the same as that of the unexposed solution.
A study has been made of the influence of various condensed phosphates on the estimation of orthophosphate by the LOWRY-Lorrzz mcthocl, and of the addition of microquantities of copper and other metallic ions in prcvcnting the inhibition.