What is the minimum mass difference needed to distinguish two approximately 100 KD proteins?
The biggest limitation in resolving two 100 kD proteins is the width of the isotope profile which at 100 kD is approximately 50 mass units wide (Yergey, J., Heller, D., Hansen, G., Cotter, R. J., and Fenselau, C., Anal. Chem.1983, 55, 353-356). Therefore to detect two approximately 100 kD proteins the mass difference between the two proteins should be at least 50 Da. This mass difference can be detected with an instrument resolving power of ~ 2,000 which, for instance, is within the instrument resolving power of about 10,000 on the Micromass Q-Tof API in the Keck Laboratory. Note also the subtle difference between the term resolution; which is the smallest separation, in m/z or dalton, between two peaks such that they can be distinguished; versus resolving power, which is m/Dm, in which Dm is the line width at 50% maximum peak height. Another factor that needs to be considered is that to detect the smallest difference in mass, the concentrations of the two proteins should be similar. A
