A Dilute-and-Shoot ICP-MS Method for Analysis of Selenium in Liquid Infant Formula

Proper determination of the amount of selenium (Se) in infant formula is important to maintain the health of non-breastfed babies. A simple dilute-and-shoot method using inductively coupled plasma mass spectrometry (ICP-MS) to determine Se in liquid infant formula was developed and validated in single- and cross-laboratory validations. Samples were diluted in an aqueous solution containing a surfactant and acetic acid and then directly introduced to ICP-MS without microwave digestion. For ICP-MS detection modes, the no-gas mode was preferable to the helium mode. In the single-laboratory validation, the developed method indicated excellent linearity (R2 = 0.998), satisfactory limit of quantification (instrumental 0.03 ng/mL, method 0.075 μg/100 mL), and acceptable accuracy (relative standard deviation = 1.8–6.6%, recovery = 87–101%) in a recovery test at three spike levels. Furthermore, the result of a certified standard reference material (SRM 1849a) suggested good trueness (115%). In the cross-laboratory validation between two laboratories, the reproducibility of the dilute-and-shoot method was comparable with the authentic microwave digestion method based on the AOAC official method. The ratios of observed Se by the dilute-and-shoot method to that of the microwave digestion method ranged from 81 to 113%. These data suggest that the method presented here is a reliable method to determine Se content in liquid infant formula.