The loading capacity and extraction recovery of multi-StageTip microcolumns. (a-c) Recovery (%) of 3H-labelled CK standards in the first elution step (50 μl 0.5 M NH4OH in 60% MeOH) applied onto multi-StageTips using Empore sorbents in different combinations, C18/SDB-RPS (a), C18/Cation-SR (b), C18/SDB-RPS/Cation-SR (c) without (0 mg FW) and with plant matrices (1 or 2 mg FW). (d) Representative test of loading capacity and extraction recoveries at different steps during the purification protocol described in Figure2 for 1 mg FW of A. thaliana seedlings extracted. For all experiments, tritium-labelled standards (105 dpm) were dissolved and the extracts were prepared in Bieleski buffer. Values are means ± SD (n = 4); [3H]c Z, black bars; [3H]t ZR, white bars; [3H]iPR, square bars.