Table 4.

Compound pairs with a %RTD of 2 % or less that also had a min-max index of 100 or less, indicating similarity in their mass spectra. The %RTD and the min-max index are listed. Compound pairs are listed in order of increasing min-max indices.

Compound 1 (C1)	Compound 2 (C2)	%RTD (%)	Min-Max Index
m-methyl Cyclopropyl fentanyl	o-methyl Cyclopropyl Fentanyl	0.66	−12
Remifentanil	Remifentanil Acid	1.03	−2
p-fluoro Furanyl Fentanyl 3-furancarboxamide	p-fluoro Furanyl Fentanyl	0.79	−2
m-Methylfentanyl	o-Methylfentanyl	0.55	0
m-methyl Acetyl fentanyl	o-methyl Acetyl fentanyl	0.04	6
m-methyl Methoxyacetyl Fentanyl	o-methyl Methoxyacetyl Fentanyl	0.36	8
Octfentanil	m-fluoro Methoxyacetyl Fentanyl	1.03	9
o-Fluorofentanyl	m-Fluorofentanyl	1.81	10
o-methyl Furanyl fentanyl	m-methyl Furanyl fentanyl	0.15	13
o-Fluoroisobutyryl Fentanyl	m-Fluoroisobutyryl Fentanyl	0.65	13
N-(2C-T) Fentanyl	N-(2C-T-2) Fentanyl	0.71	26
o-Fluorobutyryl Fentanyl	m-Fluorobutyryl Fentanyl	1.60	26
o-fluoro Furanyl Fentanyl	p-fluoro Furanyl Fentanyl 3-furancarboxamide	1.51	28
2’,5’-dimethoxy Fentanyl	N-(2C-D) Fentanyl	1.31	33
Etodesnitazene	Isodesnitazene	1.46	39
N-(2,5-DMA) Fentanyl	N-(DOM) Fentanyl	0.77	41
N-(2C-T-4) Fentanyl	N-(2C-T-2) Fentanyl	1.68	49
N-(2C-T-4) Fentanyl	N-(2C-T) Fentanyl	0.96	49
N-(2C-iP) Fentanyl	N-(2C-E) Fentanyl	0.03	54
o-Fluorofentanyl	2’-fluoro-o-fluorofentanyl	0.14	59
N-(2C-P) Fentanyl	N-(2C-G) Fentanyl	1.69	75
N-(3,4,5-TMA) Fentanyl	N-(DOC) Fentanyl	0.05	75
N-(2C-TFM) Fentanyl	N-(2C-D) Fentanyl	1.17	76
N-(MDA) Fentanyl	N-(6-APB) Fentanyl	1.73	80
2’-fluoro-o-fluorofentanyl	m-Fluorofentanyl	1.67	88
N-(2-APB) Fentanyl	N-(MDA) Fentanyl	0.65	92