Quantifying Sphingomyelin in Dairy through Infusion-Based Shotgun Mass Spectrometry with Lithium-Ion-Induced Fragmentation

• Published in: Journal of agricultural and food chemistry 2022-10, Vol.70 (42), p.13808-13817
• Main Authors: Magnuson, Andrew D., Bukowski, Michael R., Rosenberger, Thad A., Picklo, Matthew J.
• Format: Article
• Language: English
• Subjects: Omics Technologies Applied to Agriculture and Food
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/acs.jafc.2c04587

Quantifying sphingomyelin (SM) species by infusion-based mass spectrometry (MS) is complicated by the presence of isobaric phosphatidylcholine (PC) species, which generate a common m/z 184 product ion in the presence of ammonium ions as a result of the phosphocholine headgroup. Lithium ion adducts of SM undergo a selective dehydration [Li + H2O + (CH3)3NC2H4PO4] with a corresponding neutral loss of −207 Da. This neutral loss was employed to create a SM-selective method for identifying target species, which were quantitated using multiple reaction monitoring (MRM). SM-selective fragments in MS3 were used to characterize the sphingosine base and acyl chain. These methods were used to identify 50 individual SM species in bovine milk ranging from SM 28:1 to SM 44:2, with d16:1, d17:1, d18:1, d19:1, and d20:1 bases, and acyl fatty acids ranging from 10 to 25 carbons and 0–1 desaturations. Spiked SM standards into milk had a recovery of 99.7%, and endogenous milk SM had