Cobalt has been confirmed in samples taken from 13 horses trained by Darren Smith and one from the Paul Murray stable.

Racing NSW stewards said on Tuesday they had received certification from two official racing laboratories of the concentration of cobalt taken from Smith's horses between February 7 and May 21.

Stewards interviewed Smith on May 29 and visited his stables near Newcastle the following day after which they placed an embargo on all horses in his care.

Clearing samples were subsequently taken from a number of horses and they were transferred to other licensed trainers to continue their race programs.

Tests on samples from the Murray-trained Alma's Fury taken after his win in the Apollo Stakes in February 2013 and his second in the Doncaster Prelude on April 13 that year, also confirmed the concentration of cobalt.

In June this year, stewards visited Murray's Kembla Grange stables and confiscated an injectable bottle of an unknown fluid and sent it for analysis.

Both Smith and Murray will front inquiries at dates to be determined.