Hello, fellow researchers. One of the methods for DNA isolation from blood in my laboratory is salting out. We use this to obtain a high-purity, highly concentrated DNA solution. We did this plenty of times during the last 10 years, and everything was fine, but since more or less 6 months, we met an obstacle. After the overnight incubation at 55 Celcius degree (protocol included) and adding NaCl solution, during the isopropanol/ethanol step, strange sediment started to appear (images included). This greatly affected the purity and concentration of obtained DNA. It looks like proteinase stopped working because samples are contaminated with proteins (according to the measurements of 260 and 280 ratio), which never happened before. We replaced all the chemicals (including proteinase K), made new solutions and adjusted the pH to the proper level (everything was done twice), but that did not solve the problem. I want to emphasise, that we performed this procedure countless times and everything was OK. We started to think that something was wrong with plastic tubes or blood. However, we performed isolation on fresh material and new plastics as well as on blood samples and plastic, which have been used in previous (successful) isolations. The same blood samples were used in KIT isolation procedure using spin columns with silica membrane and this went perfectly fine (but using salting out as you know we can obtain much more DNA). Have any of you faced this problem?