Trace-level monitoring of a synthetic opioid API during cleaning process validation, on an ARION® C8, 3 µm column (150 mm × 4.6 mm, ARI-5734-IK46). Isocratic elution with 0.23 % perchloric acid : ACN (6:4 v/v) at 1.0 ml/min, ambient temperature and UV detection at 206 nm. The chromatogram shows a sample at the limit of quantification, where the analyte is still clearly distinguishable at about 8 minutes, well away from the solvent and matrix disturbances at the start of the run.