For calibration solutions, 15 lL, 35 lL, 75 lL, 155 lL and 395 lL of the EC stock solution were given into five 25 mL volumetric flasks which were then filled to volume using a freshly prepared 13% vol. ethanol solution (simulating a table wine matrix) and stored at 3 ± 1 C. For matrix effect assessment, the ethanol solution was replaced by wine sample W04 (the lowest in terms of EC concentration found in a previous round of analyses).