Table 1. The online SPE-HPLC-MS/MS gradient elution and valve switching program.

Isocratic pump Mobile Phase C		Binary pump			Valve switching program
Time (min)	Mobile Phase C Flow rate (mLmin-1)	Time (min)	Mobile Phase A (%)	Mobile Phase B (%)	Valve position
0	2	0	90	10	I
1.5	2	2	90	10	II
1.51	0	3	30	70
6	0	4.5	30	70	I
6.01	2	4.6	0	100
		6	0	100
		6.01	90	10
		8	90	10