Evaluation of the Electrostatic Contribution to the Retention of Modified Nucleosides and Nucleobases by Zwitterionic Hydrophilic Interaction Chromatography

Table 1

Parameters of the equation for the second-order polynomial fitting of the experimental retention factors (𝑘_exp) versus the inverse of the salt concentration ([M⁺]⁻¹)^(a).

Modified nucleosides and nucleobases	𝑘exp=𝑎/[M^+]^2+𝑏/[M^+]+𝑐
	M^+: Ammonium perchlorate
	𝑅^2	𝑎	𝑏	𝑐
9mGua	0.9538	−4𝐸−5	0.3	1.3667
1mGua	0.9681	−3𝐸−5	0.2	1.3969
7mGua	0.9782	−1𝐸−4	0.7	1.5624
	M^+: Potassium perchlorate
	𝑅^2	𝑎	𝑏	𝑐
9mGua	0.9392	−5𝐸−5	0.3	1.3109
1mGua	0.9127	−7𝐸−5	0.4	1.1628
7mGua	0.9574	−1𝐸−4	0.8	1.3724

(a) Isocratic elution: 80% ACN: 20% formic acid (2.6 mM, _wwpH=3.1) with variable concentrations of ammonium or potassium perchlorate. Temperature: 20°C. Flow: 0.5 mL min⁻¹. Injection: 50 μL in CAN.