Our endotoxin detection assays are optimized to work with samples with a pH range of 6-8. If the pH of your sample falls outside of this range you can adjust it with a buffer, or HCl or NaOH. Make sure the buffer you are using is endotoxin free by running it as a sample in your assay. A good choice is Lonza's 50 mM Tris Buffer which is tested to contain less than 0.005 EU/ml.