≥99% [TLC]. Free PNP < 500ppm.
Chromogenic substrate for E. coli: M. Kilian and P. Bulow, Acta Pathol. Microbiol. Scand. Sect. B, 87, 271 (1979): W. Hansen and E. Yourassowsky, J. Clin. Microbiol., 20, 1177 (1984): M.R. Adams et al., Appl. Environ. Microbiol., 56, 2021 (1990).