Table 1. Summary of seven alkanoic acids (R₂=H): the molecular properties and results of positive-ion APCDI mass spectra obtained by the Q-orbitrap MS.

Molecular properties					Results of positive-ion APCDI mass spectra: m/z, chemical formula, and relative intensities (%) of major ions
Analyte (M)	Molecular mass (nominal Da)	Formula	R1	R2	Protonated molecule, [M+H]+		NH4+ adduct, [M+NH4]+		H2O loss from protonated molecule, R1CO+
Acetic acid	60	C2H4O2	CH3	H	61.0283	100	78.0548	71.2	N.D.a
					C2H5O+		C2H8O2N+
Propanoic acid	74	C3H6O2	C2H5	H	75.0439	100	92.0703	24.2	57.0333	3
					C3H7O2+		C3H10O2N+		C3H5O+
Butanoic acid	88	C4H8O2	C3H7	H	89.0595	100	106.086	31.7	71.049	5
					C4H9O2+		C4H12O2N+		C4H7O+
Pentanoic acid	102	C5H10O2	C4H9	H	103.0751	100	120.1016	18.6	85.0646	3.3
					C5H11O2+		C5H14O2N+		C5H9O+
Hexanoic acid	116	C6H12O2	C5H11	H	117.0907	100	134.1171	37.6	99.0802	4.1
					C6H13O2+		C6H16O2N+		C6H11O+
Heptanoic acid	130	C7H14O2	C6H13	H	131.1058	100	148.1321	11.3	113.0953	2.5
					C7H15O2+		C7H18O2N+		C7H13O+
Octanoic acid	144	C8H16O2	C7H15	H	145.1221	100	162.1486	19.4	127.1116	3.4
					C8H17O2+		C8H20O2N+		C8H15O+

^aNot detected due to detection limit of m/z range.

APCDI, atmospheric pressure corona discharge ionization technique; MS, mass spectrometry.