Extraction

• Weigh out 5 g of homogenized sample into a 50 mL amber centrifuge tube
• Add 5 µL of internal standard solution (β = 1 µg/mL Malachite Green-d5 and Leucomalachite Green-d5 each in acetonitrile)
• Add 25 µL of standard solution (β = 200 ng/mL Malachite Green, Leucomalachite Green, Leucocrystal Violet, Crystal Violet each in acetonitrile) for determining recovery rate
• Add 5 mL water and shake
• Add 10 mL 1 % acetic acid in acetonitrile and shake
• Add the extraction mix QuEChERS Mix II
• Shake vigorously for 30 s and cool down the mixture in an ice bath
• Centrifuge the mixture at 4500 rpm, for 5 min at 4 °C

Clean-up

• Put 5 mL acetonitrile supernatant in a 15 mL amber centrifuge tube
• Add the clean-up mix QuEChERS Mix III
• Shake vigorously for 30 s
• Centrifuge the mixture at 4500 rpm, for 5 min at 4 °C
• Dilute the extract 1:1 with an aqueous solution of 5 mmol/L ammonium acetate + 1 mL/L formic acid and filter through a syringe filter (CHROMAFIL Xtra PET-20/13, REF 729222)