The GTP that I am using is trisodium salt obtained from sigma. To prepare the GTP solution, I am dissolving it in 50mM Tris, pH adjusted to 7.5. The solution is sterile filtered, aliquotted and flash freezzed.

Please do confirm if it is a proper way of preparing GTP solution and If not then what is the better way or any other recommendation. I checked the phosphate level of water as well as buffer used for the assay. The value comes less than 0.2, which according to protocol is ok.