Most initial screens carry a 50 ng cutoff threshold. The confirmation GC/MS is at 15 ng.

A lot of people dont realize it, but a 50 ng assay screen is functionally equivalent to the 15 ng GC/MS. For more information, do a Forum Search using the terms "functionally equivalent metabolites".

With that being pointed out, if you fail a GC/MS, you wouldve failed the assay screen as well.