There is ICP-OES and a newer ICP-MS. Apparently ICP-MS is much more accurate. Some reefing sites sell the MS as a single test for $65, but I found going to this site it was half the price (I haven’t used them though)is there two different test options for ATI?
Water Testing
We do ICP analysis on all types of water. We test for 50+ elements and provide results as low as 10 ppt
www.icp-analysis.com