The ProteinWorks™ μElution SPE Clean-up Kit (p/n 186008304) combines Oasis® MCX μElution technology with an optimized, broadly applicable protocol for the post-digestion peptide clean-up of directly digested or immunopurified plasma/serum samples. The protocol was developed to yield high recoveries of various tryptic peptides following mixed-mode cation-ion exchange SPE of digested protein samples, while removing digest reagents, minimizing matrix interferences, and improving specificity and sensitivity. The μElution format was specifically chosen as it allows one to load up to 375 μL of sample (prior to dilution) and elute in as little as 25 μL, providing up to a 15x concentration factor (often necessary to reach required detection limits), without evaporation and reconstitution. The ability to elute in small volumes eliminates potential peptide losses during evaporation due to adsorption to the walls of collection plates or instability. In addition, an entire Oasis 96-well Plate can be processed manually in under 30 minutes, or less than 20 seconds per sample, significantly increasing throughput.