Figure 4

Monitoring ion suppression (post column infusion method). The TIC of all immuno-suppressants when injected in methanolic solution, 1:3, 1:11 and 1:21 diluted sample-matrix respectively are shown. A: valve switch to methanolic buffer (97% methanol). B: valve switch to aqueous buffer (10% methanol; reconditioning of SPE column). C: strong loss of ions during straight forward elution of aqueous buffer from SPE column. D: second loss of signal during assumed elution of sample matrix (2.15 - 2.45 min).