Efficient, Low-Cost, and High-Throughput Sodium Dodecyl Sulfate (SDS) Removal from Protein Digests Using Weak-Anion Exchange.

Abstract

Sodium dodecyl sulfate (SDS) plays a pivotal role in protein denaturation, tissue extraction, and protein mass-based electrophoretic separations. However, even modest concentrations of SDS can cause column overpressure, retention time shifts, and ionization signal suppression during liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. Thus, SDS removal is a critical step for LC-MS/MS analysis of protein digests containing SDS. This study describes an inexpensive and high-throughput method to remove SDS from protein digests using weak-anion exchange (WAX) resins in 96-well filter plates. Requiring less than 3 min, this method can reduce SDS concentrations from 0.1-0.4% to less than 5 ppm and from 0.6-1% to less than 100 ppm. After SDS removal, the recoveries of unmodified tryptic peptides and phosphorylated peptides (at 94.3 nM) were ∼90% and ∼70%, respectively. Additionally, when using aqueous 1% SDS to solubilize trastuzumab-spiked mouse serum and subsequently removing the SDS using the WAX resin, quantitation of trastuzumab exhibited excellent linearity (R² = 0.9996) together with a low coefficient of variation (<10%). Calculated concentrations were within 20% of the expected value for spiked standard samples (0.5, 1, and 2 μg/mL trastuzumab in mouse serum). The method is about 20× more cost-effective versus commercialized SDS removal kits and both the resin and filter plate are readily available, so the method should easily transfer to other laboratories.