High-sensitivity quantitation of a Nanobody® in plasma by single-cartridge multidimensional SPE and ultra-performance LC–MS/MS

his article is available for members, for free, to celebrate Nico van der Merbel being awarded the BOSCA – Excellence in research. Background: A major challenge in protein quantitation based on enzymatic digestion of complex biological samples and subsequent LC–MS/MS analysis of a signature peptide is dealing with the high complexity of the matrix after digestion, which can reduce sensitivity considerably. Results: Using single cartridge multidimensional SPE, sufficient selectivity was introduced to allow quantitation in 50 µl of plasma down to 10.0 ng/ml (˜0.3 nM). An inhouse prepared 18O-labeled signature peptide was used as the internal standard. The procedure was...