McKesson, OPA Concentration Indicator McKesson OPA/28 Pad 50 Test Strips Bottle Single Use, Count of 1Product Description McKesson OPA 28 Test Strips To verify the efficacy of McKesson OPA 28 Solution, user should test for the minimum effective concentration (MEC) prior to each use. 3 second dip time 90 seconds read time Large, easy to read indicator pad. Definitive color identification comparison chart on each bottle. 18 month shelf life (unopened bottle), 6 month shelf life from date of opening. Not Made with Natural Rubber Latex. Packaged: 50