### XPS Detection Limits

In general, detection limits for XPS range from 0.1 to 1 atomic percent.  However there are cases where limits could be much better or much worse.  An article from Alexander Shard [1] gives an excellent look at detection limits in over 6000 binary systems for both Al and Mg X-ray sources.  In such systems a heavy element, such as gold, in a light element matrix, say carbon, would have detection limits closer to 0.01 atomic percent.  For the opposite situation, carbon in a gold matrix, detection limits for carbon would be around 3 atomic percent.  Spectral overlaps can also degrade detection limits significantly and are incorporated into the tables presented.  Overlaps with Auger peaks can be overcome by changing X-ray sources used (i.e. using Mg K instead of Al K).  One can also work with advanced curve-fitting techniques to overcome some of these overlap issues.

Reference:
[1] A.G. Shard, Surf. Interface Anal. 46 (2014) 175-185.