A design of experiments concept for the minimization of nonspecific peptide adsorption in the mass spectrometric determination of substance P and related hemokinin-1.

Substance P and hemokinin-1 were predominantly examined by immunoassays with their limitation to differentiate appropriately between both peptides. The use of liquid chromatography coupled with tandem mass spectrometry is a promising, highly selective alternative. Adsorption processes have been identified in preliminary experiments to play a crucial role in the loss of mass spectrometry intensity of both peptides. Therefore, a design of experiments concept was created to minimize nonspecific peptide adsorption. For this purpose, the most critical influencing parameters-(1) the composition of the injection solvent as well as (2) the most suitable container material-were systematically and concordantly investigated. The addition of modifiers, such as formic acid, dimethyl sulfoxide, and organic solvents, to the injection solvent led to a substantial gain of intensity of substance P and hemokinin-1 compared to the start gradient as an injection solvent. Furthermore, the systematic investigation underlined the high impact of the container material, demonstrating polypropylene as the most favorable material. A conjoint injection solvent optimum was found to determine both peptides simultaneously by the conduction of a sweet-spot analysis. The experimental design substantially reduced nonspecific peptide adsorption and enabled the simultaneous and selective determination of endogenous substance P and hemokinin-1 plasma levels.