Compositional analysis by spark emission is a very accurate method of measuring the composition of metals.
The surface of the material is sparked with high voltage which releases x-rays from the surface, resulting in a spectrum. The instrument detects these x-rays and then is able to determine the weight percent of each element in the material.
We use this to accurately measure the composition of steels, stainless steels, aluminium and its alloys, copper and its alloys, zinc and its alloys and cast irons. We can detect the light elements such as carbon phosphorous silicon and sulphur in all these alloys to four decimal places as well as all the metallic elements.
We have a hand held XRF which can non destructively test any material but has the limitation of testing the very light elements. However it can be used for on site PMI (positive material identification).