SDS depletion efficiency is best described by quantifying the residual SDS, relative to the starting concentration. Liu et al. [12] described a tube gel electrophoresis strategy to deplete SDS, reported to remove 85% of the initial SDS. Such efficiency is sur- prisingly low, considering the approach makes use of the proven strategy of in-gel digestion. Placed into context, a starting concen- tration of 1% SDS generally requires a minimum 99% of the SDS to be removed to be compatible with LC–MS. Botelho et al. [6] have previously reported that protein precipitation in acetone will deplete 99.9% of the SDS. Sun et al. [19] describes a strong cation exchange approach that is 99.99% efficient at SDS depletion. Again, it is difficult to directly compare such values, given the influence of sample composition, or possibly also the methods used to quantify residual SDS. The methylene blue active substances assay (MBAS) [20] is the most widely reported approach to quantify SDS, but is highly susceptible to interferences from anionic components which also complex with the cationic dye and extract into chloroform. Other colorimetric assays exist (Stains-All) [21]. GC–MS has also been used following pyrolysis of the detergent [22], as has LC–MS, though not in the context of quantifying trace levels of detergent from protein-containing solutions.