Comparison of two automated solid phase extractions for the detection of ten fentanyl analogs and metabolites in human urine using liquid chromatography tandem mass spectrometry.

•Two automated SPE methods were developed for analysis of fentanyl analogs and metabolites.•On- and off-line SPE methods were shown to have comparable sensitivity and selectivity.•Both methods suitable for detection of exposure to seven fentanyls in human urine.