LC-MS
A purified sample has better chance of good identification. Because of signal suppression and ionization interferences samples analyzed by LC-MS should not contain alkali salts and non-volatile buffers, PEGs, plastics and plasticizers, detergents and other additives compete for ionization. Solid phase extraction (SPE) can be used for clean-up and concentration of desired analytes in contaminated samples.
GC-MS
Samples must not contain non-volatile contaminants (salts, metals, polymers, etc.) as well as grease and plasticizers. Derivation of polar compounds should be performed to make them volatile.