The catalog 16316 kit measures peroxynitrite anion ONOO- in solution, the probe is not cell-permeable. However, both 16315 and 16317 kits are for intracellular peroxynitrite anion measurement, the probe is cell permeable. Kit 16315 is optimized for fluorescence microscopy and fluorescence microplate reader, and kit 16317 is optimized for flow cytometry. All the 3 kits are measured at excitation and emission with 490 and 525 nm (FITC filter sets).