As stated by the manufacturer, the cartridge removes over 95% of detergents. From Fig. 2, when applied to intact proteins, SDS depletion approached the 99% removal threshold – well above the manufacturer specifications, though still less than other deple- tion protocols. A lower level of residual SDS observed for the
0.1 g/L E. coli protein test solution may be attributed to the high variance in the Of the eight methods assessed, the highest detergent removal efficiency was observed with FASP II (30 kDa membranes). From Fig. 2, with all four test solutions, FASP II consistently depleted SDS to levels below the limit of quantitation of our LC–MS/MS assay. This corresponds to well over 99.99% SDS depletion. Using 10 kDa filters, the residual SDS was slightly higher (between 3 and 4 g), though still among the better performing SDS depletion protocols, and well below the 10 g cutoff permitting LC–MS analysis. Wis- niewski has previously shown that larger MWCO filters are more efficient at SDS depletion [28]. An exceptional level of SDS depletion was also observed through in-gel digestion of the BSA test sam- ples, though detectable levels of SDS were observed with the E. coli
test samples. With E. coli, a larger (∼1 cm) gel band was excised
to recover the full E. coli proteome from the gel. We also note the
shorter resolving period, which may not be sufficient to isolate the higher concentration of SDS from the sample loading buffer. It can therefore be stated that FASP II is as effective as a conventional in-gel digestion protocol in terms of SDS depletion