Evaluation of mutual interference between bovine α-lactalbumin peptide and its isotope-labeled peptide in whey protein analysis using liquid chromatography-tandem mass spectrometry

Internal standard (IS) method is commonly used to correct the matrix effect of samples in the liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis of whey proteins. However, the presence of mutual interference between some peptides and their isotope-labeled peptides distorts the MS signals, requiring a fundamental evaluation to understand the phenomenon of signal variations. In this study, a simple strategy is proposed to evaluate the effects of sample pretreatment, materials and dilution of solutions on the MS signals of α-lactalbumin (VGINYWLAHK) and β-lactoglobulin peptides using two typical LC-MS/MS systems, Q-Trap and Q-Orbitrap. The strategy adapts the experimental MS data to optimize methods, thus providing meaningful solutions to suppress the mutual interference presented in the analysis of peptides. As a result, the strategy through the combination of 100-fold dilution and plastic injection vial improves the quantitation results of α-lactalbumin peptide significantly. While the β-lactoglobulin peptide presents different phenomenon of signal variations when compared with that of α-lactalbumin peptide, revealing that each peptide needs to be optimized individually. The calibration effect of different IS was also studied in fifteen infant milk powders to confirm the mutual interference impact to quantification result. These results indicated that a simple strategy through the combination of sample dilution and plastic injection vial could be well extended to quantitative analysis of any other peptide in the complex systems.