Hamburger phenomenon deals with the following:

Chloride shift (Hamburger phenomenon) the HCO3- diffuses out of the RBCs into the plasma, the inside of the cells become less negatively charged. Because the RBC membrane is relatively impermeable to cation, so in order to neutralize this effect, negatively charged chloride ions diffuse from the plasma into the RBCs to replace the HCO3-. The movement of chloride ions into the RBCs is called chloride shift or Hamburger phenomenon. Ref: Essentials of Medical Physiology By Khurana, 2008, Page 256.