Using the manufacturer of the unit and swabs is a good start. To answer your questions....
- How many samples we have to test?
This will be based on the frequency of cleaning and/or pre-operational inspections.
- Before and after cleaning?
You can perform before cleaning swabs to benchmark and see what levels are coming back as. After cleaning is the intended process to verify that your cleaning program is operating is achieving the desired results.
- How to identify the limits?
Since units and swabs can vary from one brand to another the best method is to establish limits through ongoing testing. Come up with a list of your equipment you would want to swab for ATP, start swabbing, and start to look at the RLU results. You are going to be performing this testing on a very frequent basis at first, directly after cleaning and before the sanitizing step. Once you have some data collected you can review and see what the max level RLU you are receiving from each piece of equipment or surface.