Table 1. Correlations between ESI response and molecular characteristics.

The investigated molecular descriptors were summarized as descriptors of basicity (pKa, pH of 4 mM solution, gas phase basicity, proton affinity, substituent’s electronegativity, and polarizability), polarity (logD, logP, polar/nonpolar/solvent accessible surface area), size (molecular and molar volume, molar mass) and volatility (boiling point, vapor pressure, vaporization enthalpy). A significant linear correlation of signal intensity or ratio with one of the molecular descriptors of each group (basicity, polarity, size and volatility) with a coefficient >0.4 is denoted with “+”, a coefficient >-0.4 with “-“.

	all compounds	anilines API	anilines Esquire	ortho	meta	para
	Signal intensity at pH 7 correlates with
signal pH 3	+	+	+		+	+
signal ratio	-	-	-	-		-
basicity	+	+	+	+	+	+
polarity	+	+	+	+	+	+
size						+
volatility
	Signal intensity at pH 3 correlates with
signal pH 7	+	+	+		+	+
signal ratio		-		+
basicity	+	+			+	+
polarity	+	+			+	+
size			+	-		-
volatility		+
	Signal ratio pH 7/ pH 3 correlates with
signal pH 7	-	-	-	-		-
signal pH 3		-		+
basicity		-		-*	+*	-
polarity		-	-	-		-
size						+
volatility	+	+	+	+

*… gas phase basicity only