Updated project metadata. We improve on currently-available resources by describing a mass spectrometry (MS)-based strategy using stable isotope dynamic labelling of secretomes (SIDLS) that discriminates between authentic secretory proteins and intracellular proteins within the secretome of cultured cells. By monitoring the rate of incorporation of labelled amino acids into newly synthesised proteins as they appear in the media, we can differentiate those proteins that have been destined for secretion, and exhibit rapid labelling, from those with low rates of labelling or low turnover relative to the growth rate of the cells which is a feature of intracellular proteins. Part of the wet lab protocol for our analysis of secretomes, is the use of the resin, Strataclean (Agilent). In this Supplementary dataset to our main paper (also in PRIDE/ProteomeXchange), we characterise the linearity of capture of secreted proteins using Stracalean resin, by label-free quantitative mass spectrometry. We mix cell-coditioned culture media with 'virgin' media in different ratios and analayse the capture capacity of equal quantitites of StrataClean reagent.