The RPC method adopts the low ligand density HSS (high strength silica) T3 (C18) stationary phase (Waters Corp., Milford MA, USA) and mobile phase conditions previously employed by others including Wong et al and later Want et al for the metabolic profiling of urine, proving highly suitable for the retention of smaller and more hydrophilic analytes in highly aqueous environments as well as moderately hydrophobic analytes including drugs and drug metabolites. The adapted method substitutes a 150 mm column in place of the thenconventional and ubiquitously used 100 mm columns, improving the separation of early eluting metabolites. This expanded column length was paired with a higher 0.6 mL/min flowrate, producing sharp peaks (approximately 1.5 seconds at baseline) across the gradient. This method, eventually published in 2016 after extensive testing and use, was important in establishing a new benchmark and "convention". It is used with both positive and negative mode ion detection.