with 0.3% formic acid and 5 mM ammonium formate (solvent B)
at a flow rate of 0.4 ml min1.
The eluent gradient profile was as follows: 0 min: 5% B; 1 min:
50% B; 2 min: 72% B; 4 min: 80% B and 6 min: 90% B. Finally it was
back to 5% B in 0.2 min and maintained for 1.8 min for column
equilibration. The temperature of the column was 35 C and the
injection volume was 5 lL (full loop).
The MS was working with ESI in positive mode and under the
multiple reaction monitoring (MRM) conditions shown in Table 1,
which were optimised elsewhere (Arroyo-Manzanares et al., 2013).
The ionisation source parameters were: source temperature
500 C; curtain gas (nitrogen) 30 psi; ion spray voltage 5000 V;
and GAS 1 and GAS 2 (both of them nitrogen) were set to 50 psi.
Results and discussion
1. Optimisation of sample preparation
The sample treatment is based on an extraction/partitioning
process of the QuEChERS procedure, which allowed the determina-