Sodium dodecyl sulfate removal during electrospray ionization using cyclodextrins as simple sample solution additive...

Sodium dodecyl sulfate (SDS) removal is a vital procedure in SDS-assisted bottom-up proteomics because SDS affects the quality of the data in electrospray ionization mass spectrometry (ESI-MS). SDS removal methods provide efficient removal of SDS and improved peptide analysis, but would usually require time, specialised devices, and experienced analysts. Here, by simple addition of γ-cyclodextrin (γ-CD) to the solution at concentrations 1 to 2x the SDS in the sample, the SDS related signals in positive ionization ESI-MS can be significantly removed (70-99% reduction), without an additional sample manipulation step of extraction or purification. The mechanism for removal is based on the formation of tightly bound CD-SDS inclusion complexes, which hampered the generation of positively charged SDS multimers during ESI. For a sample with peptides (glu-val-phe, tyr-tyr-tyr, and bradykinin) and 3 mM SDS where 6 mM γ-CD was added, the %signal recoveries of peptides calculated by comparison with signals from standard samples without SDS were 49-59%. The space charge effect by SDS on bradykinin was also reduced, increasing the signal for bradykinin 12x in the presence of γ-CD. For a protein (bovine serum albumin, BSA) digest with 3 mM SDS, which is an expected concentration in trypsin treated samples, a noticeable 7-fold improvement in the peptide to SDS signal ratio and a 91% reduction of SDS signals were observed upon addition of 6 mM γ-CD. However, there were only small changes in the ESI-MS intensities for the BSA peptides (compared to without addition of γ-CD). This new approach to SDS signal removal using CDs in ESI-MS may find use in proteomic studies.