I am trying to use PEG as a means of calculating the OSI of human milk after storing it at different temperatures (4C, -20C, -80C). Going forward, I will be testing a bunch of different donor human milk after various treatments. I want to standardize the assay in terms of negative control, positive control, temperature of heating block, air flow rate, etc. How do I go about standardizing these variables for something as variable as human milk? So far I am thinking of using PEG + DI water as the negative control as the samples to be tested would be PEG + Human Milk. What is a good positive control? TIA!!