APstop Solution* （10X concentrate） is specially formulated for use with KPL colorimetric substrates for alkaline phosphatase detection in microwell applications, including BluePhos Microwell Phosphatase Substrate （Catalog Number 50-88-00）, FirePhos Microwell Phosphatase Substrate System （Catalog Number 50-87-20） and pNPP Microwell Substrate System （Catalog number 50-80-00）.  APstop Solution allows the user to stop the reaction at a specific point for consistent results from assay-to-assay.

*formerly named BluePhos Stop Solution