Quantification of bitter compounds in Belgian endive: a comparative study. Supplementary material: MS1 and MS2 spectra of selected compounds in table format

Positive and negative electrospray spectra of Belgian endive (C. intybus) extract components in table format. Both MS1 and MS2 spectra are given.
Protocol:
Fresh Belgian endive heads are frozen by immersion in liquid nitrogen, and subsequently crushed to a fine powder in a pre-cooled blender. The powder is stored at -80 ˚C in plastic tubes (Falcon) tubes until use. For each sample 300 mg of crushed frozen leaves is weighed in a pre-cooled 2 mL plastic tube (Eppendorf). These tubes can also be stored at -80 ˚C for a few days before use. Care is taken to prevent thawing of the frozen material up until this point, by pre-cooling of all materials which comes in contact with the plant powder. Failure to do so causes a brownish discoloration in the subsequent steps which is symptom of oxidation.For the extraction, 1.4 mL of extraction solvent is added to each small plastic tube. Extraction solvent is prepared by adding 1 mL of formic acid and 100 µL of acetonitrile containing 20 mg·mL-1 of α-santonin to 1 L of HPLC water Extraction is performed under continuous shaking at 30 °C for 15 min in a Thermomixer (Eppendorf), followed by centrifugation at 2000 g at 4 °C for another 15 min. Exactly 1 mL of the supernatant is drawn with an insulin syringe and filtered through a 13 mm x 0.2 µm PTFE disc filter in a glass vial. Extractions are performed in batches of 12 samples, whose preparation can be overlapped. As an example, when the first batch is on the thermomixer, solvent addition to the second can be started; after the first moves to the centrifuge, the second goes to the thermomixer.HPLC-MS analysis is performed on an Waters 2695 Alliance coupled to a Micromass QTof Micro mass spectrometer. A Kinetex C18 column (2.1 mm I.D. x 150 mm length x 5 µm particle diameter, core shell silica) is used. The injection volume is 10 µL and the oven temperature 40 ˚C. The HPLC is operated with a constant flow of 0.2 ml∙min-1 in gradient mode according to the following protocol:•From 0 to 1 mins isocratic hold at 5 % acetonitrile•From 1 to 15 mins linear gradient to 50 % acetonitrile•From 15 to 19 mins isocratic hold at 50 % acetonitrile
The optimized values for the positive mode were as follows: capillary voltage: 3100 V, sample cone: 24 V, extraction cone 1 V, desolvation temperature: 450 ˚C, desolvation flow: 600 L∙h-1, no cone flow, source temperature: 110 ˚C, collision energy: 3 V. For the negative electrospray mode, the following not optimized source parameters were used: capillary voltage: 2500 V, sample cone: 20 V, extraction cone 1 V, desolvation temperature: 400 ˚C, desolvation flow: 400 L∙h-1, no cone flow, source temperature: 110 ˚C, collision energy: 3 V. Acquisition parameters were the same for both modes: scan time: 0.4 s , inter-scan time: 0.1 s , reference scan (leu-enkephalin): 60 s, centroid mode, centroid threshold: 1, minimum point: 5