I used the bioanalyzer to determine RNA quality of samples extracted from fresh frozen postmortem brain tissue. I used an optimized phenol/chloroform extraction method with column purification to isolate miRs as well. My 260/280 ratios were at 2.0. However, the integrity of several samples were less than 6.0. I repeated the run without freezing the samples, and the RINS were not the same. There were no issues with my ladder, I performed all experiments on ice/metal block at 4 degrees C, I zapped everything, and the positive control did not read at the pre-determined RIN. I'm having difficultly trouble shooting.