The biogeochemistry of arsenic is complex and includes various adsorption and desorption processes. Non-uniform pore geometries often lead to differences in adsorption and desorption pathways within a capillary. At equilibrium, the rate of adsorption equals the rate of desorption. This technique is similar to secondary ion mass spectrometry and plasma desorption mass spectrometry. An alternative ionization approach following laser desorption is a plasma. Matrix-assisted laser desorption/ionization (MALDI) is a soft ionization technique. "k" are constants of forward adsorption reaction and backward desorption reaction in the above reactions. Damage may result from oxide desorption or trapped charge following ionization. PAINT works by maintaining a balance between the dye adsorption/absorption and photobleaching/desorption rates. For more variations of soft ionization methods go to Soft laser desorption or Ion source. DESI is a combination popular techniques, such as, electrospray ionization and surface desorption techniques. DESI is a combination of electrospray (ESI) and desorption (DI) ionization methods. It is a variation of matrix-assisted laser desorption/ionization (MALDI). The term "sorption" encompasses both processes, while "desorption" is the reverse of it. Herbicides contribute to arsenic desorption through mobilisation and transportation of the contaminant.