Quantification of lactose content in human and cowʹs milk using UPLC–tandem mass spectrometry

A sensitive, accurate, and specific quantitative UPLC–MS/MS method was developed for lactose measurement of cowʹs and human milk and validated with cowʹs milk samples certified by an external laboratory. The new method employs only a dilution of raw cowʹs and human milk for simple preparation with no need to remove protein and fat prior to analysis with UPLC–MS/MS. It was operated in negative mode to detect lactose molecules and labeled 13C12-lactose with the highest sensitivity. The principle advantages of the new LC–MS/MS method were: completed lactose determination in 5 min, absolute recovery of 97–107%, lower limit of detection <5 ng/L, and 99% linearity over the concentration range of 0.7–4.4 mg/L for both cowʹs and human milk. The mean lactose concentration of 51 human milk samples was measured as 56.8 ± 5.5 g/L ranging from 43 to 65 g/L. The described method represents validated lactose analysis with high accuracy and precision for a routine lactose determination in raw human milk.