Table 1. Retention times of β ₂-AR specific ligands on different columns.

Ligand	Retention times (min)
	Exposed silica gel	Histidine coated gel	Immobilized β 2-AR
Salbutamol	1.65	1.62	5.0
Tobuterol	1.58	1.67	9.9
Clorprenaline	1.71	1.64	12.5
Bambuterol	1.56	1.59	49.1

Notes: All the capacity factors are determined triplicate at 37 °C. The void time is measured as 1.6 min using sodium nitrite as an injection.