L. Levine, J. Gordon, and W. Jenks 43 studied the chemical denaturation of T4 bacteriophage DNA at constant buffer composition and temperature in the presence of different denaturants. The authors mainly used the immunological method 51 that determines only denatured DNA. The authors found a critical concentration for each denaturant needed to create 50% DNA denaturation. M Xu, T Dai, Y Wang, and G Yang 52 used UV spectrophotometry to study the denaturation of DNA with high and low molecular weight in the absence and presence of different concentrations of dimethyl sulfoxide (DMSO). They also analyzed changes in the configuration of DNA using atomic force microscopy (AFM technique) and dynamic light scattering (DLS). Each stage of AFM treatment of DNA samples was performed at a constant temperature, so this method of investigating the denaturation process has to be classified as the chemical, not the thermal type.