Dried milk spots: a viable approach for assessing the chemical exposome in mothers and their infants by targeted LC-MS/MS

Abstract Breast milk is a key matrix for assessing early-life exposure. Dried milk spots (DMS) and microsampling devices are convenient low-volume sampling alternatives. Here, a sample preparation protocol and LC-MS/MS method for (semi-)quantitatively assessing 216 xenobiotics in DMS were optimized and evaluated. Two extraction solutions were compared. Both approaches performed similarly, with about 50% of analytes falling within the assigned acceptance range for matrix effects (60%–140%), and about 80% fulfilling the proposed extraction recovery criteria (42%–134%). In a proof-of-principle study, the method was applied to a pooled Austrian milk sample as well as to the NIST standard reference material SRM 1954 (pooled breast milk from US donors). A total of 30 exposure compounds were identified in SRM 1954, 22 of which were also determined in the Austrian pooled milk sample. Compounds were mostly detected at very-low trace levels and included air pollutants (cotinine), plastics-related chemicals (phthalates, bisphenols), flame retardants (TBBPA, TCBPA), perfluoroalkyl substances (PFOA, PFOS), personal care products ingredients (parabens) and pharmaceuticals (acetaminophen, fluconazole). The stability of analytes was assessed in DMS at −20, 4, 18 and 37°C for up to 2 months. No significant changes were observed during storage at −20°C regardless of storage time, while short-term stability was confirmed for approximately 80% of all tested exposure chemicals even at more elevated temperatures. A comparison between DMS and Mitra volumetric absorptive microsampling devices showed similar performance but differences in background contamination. Of the 24 compounds detected in the paper blank, 19 were also present in the Mitra tips, though at concentrations up to ten times lower. The developed assay is fit-for-purpose, enabling broad exposome-type population studies for investigating early-life exposure patterns.