An MRI-free non-destructive on-line system for detecting a presence of a material in a sample. The system includes a flow conduit encompassed by a tunable RF coil and having an input duct and an output duct; a flow of the sample through the flow conduit; a signal detector that detects frequency-dependent output signals as a function of a frequency variation of the RF tunable coil within a frequency range of an RF resonant frequency of a standard sample of the substance; and a processing unit.