Hi, I'm trying to use LIBS technique to figure out elemental analysis of human nails. But every time i run the experiment, i get the emission line of metal instead. The sample holder is indeed made up of metal. What should I do to overcome this problem? Since i have small size sample, I'm using focusing lens with fl 15cm to focus the laser but there's no spark. Should i stop using lens? or should i use lens with different fl? Thanx!