Sample / solvent stability in a limit test


I’m working with a limit test to prove the absence of protein in my samples. It’s a simple limit test, my standard is my LOD - it’s a yes or no result. The method has been validated (specificity and LOD), but I’d like to show sample / buffer stability, so we don’t need to prepare everything freshly. And here I’m kind of lost - since I don’t get any ‘real’ results - we don’t quantify anything - I cannot compare two measurements (fresh sample buffer vs ols sample buffer) - both measurements would just show the samples are below LOD (I guess). What would be the best way to prove that my buffer solutions are safe to store for a few weeks, i.e. give the same results as fresh buffers?
Any help with that matter is greatly appreciated, thanks in advance!

Make two buffers. Label the buffers A and B. Set an initial time zero and test with both buffer A and B. Record your results. Store buffer A and discard buffer B. Set up a time schedule for the next test. Record your schedule in lab notebook or protocol. At next time interval repeat your test with the same sample from time zero. Prepare fresh buffer B. Perform test with Store buffer A and fresh buffer B. Document visual observations and results (Pass/Fail). Discard buffer B. Continue to repeat until you get to the desired time i.e. 3wks, 4wks etc. Each time prepare fresh buffer B, use the same sample and test with both A and B buffers. Document ,over whatever time interval you decide, that you did not observe any difference in result from Store buffer A and Fresh buffer B.