Determination of 17 Elements in Breast Milk by Inductively Coupled Plasma Mass Spectrometry with Direct Dilution

A method for simultaneous determination of 17 elements including vanadium, chromium, manganese, cobalt, nickel, copper, zinc, arsenic, selenium, strontium, barium, molybdenum, cadmium, tin, antimony, mercury, and lead in breast milk by inductively coupled plasma mass spectrometry (ICP-MS) with direct dilution was proposed. 0.5 mL of breast milk was taken and made its volume up to 10 mL with 0.01% (volume fraction) Triton X-100 solution containing 2% (volume fraction) nitric acid and 0.01% (volume fraction) tetramethyl ammonium hydroxide. The mixture was vortex mixed evenly, and centrifuged at a rotational speed of 4 000 r·min⁻¹ for 5 min. The supernatant solution was passed through a 0.45 µm water phase filter membrane, 17 elements in the filtrate were determined by ICP-MS in kinetic energy discrimination (KED) mode, and 6 μg·L⁻¹ mixed internal standard solution, including scandium, germanium, rhodium, and bismuth was added online. As shown by the results, linear relationships between the ratios of the corresponding signal intensity to the internal standard signal intensity and mass concentrations of elements were found in definite ranges, with detection limits (3s) in the range of 0.019-0.768 μg·L⁻¹. This method was used for analysis of American national standard reference materials, and the determined values of other elements except zinc were found within the uncertainty range of the certified values, with coefficients variation of intra-day and inter-day less than 13%. Test for recovery was made by the standard addition method, giving results in the range of 81.3%-119%.