2.5. GC–NCI-MS–MS operating conditions
GC–MS–MS analysis was performed in NCI mode on Agilent Technologies 7890A GC system coupled to 7000A GC/MS Triple Quad. A DB-5MS capillary column (15 m × 0.25 mm i.d., 0.1 μm film thickness) containing 5% phenyl methyl siloxane was used with helium as carrier gas at constant flow of 1 mL min− 1. The temperature program was from 100 °C (held for 1 min) to 230 °C at 15 °C min− 1, then from 230 to 310 °C (held for 2 min) at 10 °C min− 1, using the splitless injection mode during 0.8 min. Inject volume was 3 μL. The inlet temperature was set at 275 °C and ion source temperature at 250 °C. Ammonia was used as reagent gas at 2.04 × 10− 4 Torr. More details on MS–MS condition and selected transitions were reported elsewhere (Feo et al., 2011).
2.6. Lipid content
Total milk lipid content was determined by crematocrit method (Mayans and Martell, 1994). However, due to the low breast milk volume available, lipid content was not calculated in all the collected samples, thus a median value was used for the calculation of pyrethroid concentrations.