Uncovering the interference from lipid fragments on the qualification and quantification of serum metabolites in matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis.

RATIONALE: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has exhibited great advantages in rapid analysis of metabolites. However, the influence of lipid fragments generated by in-source fragmentation (ISD) and/or post-source fragmentation (PSD) on the accurate qualification and quantification of metabolites has not been fully demonstrated. METHODS: Phospholipid standards and serum extract were analyzed by MALDI MS with both TiO2 nanoparticle (TiO2 NP) and 2,5-DHB matrices to illustrate the structures of lipid fragments and their influence on the qualitative and quantitative analysis of metabolites in biological samples. Monophasic and biphasic extraction methods were also compared for their efficiency in removing potential interferents. RESULTS: The fragment ions derived from the phosphocholine head group of phosphatidylcholines (PC) interfere with peaks of low molecular weight (LMW) metabolites at both the MS and MS2 levels. The biphasic extraction system with methanol/chloroform very efficiently removed the interference from PC fragments, and the metabolites choline and carnitine in serum were directly and accurately quantified by MALDI MS by using this biphasic extraction. CONCLUSIONS: The phospholipids could produce fragment ions through ISD and PSD in MALDI MS with both nanoparticle and organic matrices. The fragments exerted influence on the qualification and qualification of metabolites in serum. By choosing the proper extraction method, the interference from lipid fragments could be efficiently alleviated.