Why don't PromoCell specify in the instructions how long the primary cells should be trypsinized?

The time needed to detach our primary cells depends on many different factors like the cell type; cell density; lot #; trypsin concentration; the efficiency of the washing step before adding the trypsin and the trypsinization temperature. For most cell types we recommend trypsinization at room temperature and direct observation of detachment under the microscope. This way; you can find out your individual trypsinization time and keep the contact time between cells and trypsin to a minimum. Most cells detach after 2-8 min. Please refer to the instructions in the Manual. For some cell types; trypsinization at 37°C or the use of Accutase or another Detachment Solution is recommended.