Low energy electron stimulated desorption of ions from whole human blood

We present the results of experiments on positive and negative ion desorption, from whole dried samples of human blood and red blood cell (RBC), induced by the impact of electrons with energies below 70 eV. Such bombardments induce a rich fragmentation pattern of cations in comparison to that for negative ions. The threshold for desorption of cations is observed around 20 eV, whereas anions can be formed with electron energy as low as 2 eV. The electron energy dependence of ion yields for all detected anions (H−, CH3−/NH−, O−/NH2− and OH−) exhibits resonant structures attributed to the dissociative electron attachment process. The similarity between the line shapes of the ion yield functions of O− desorption from the blood sample and a pure oxygen molecular film suggests that this anion originates from the (Fe–O2) unit in hemoglobin. Additionally, from the observed shift of peaks in the O− yield, the binding energy of the oxygen molecule to iron is estimated to be approximately 1.2 eV.