Anhydrous sodium sulphate

Samples were non-derivatized and derivatized for the GC-MS analysis. For derivatized samples, the preparation prior to GC-MS analysis was performed according to Semreen [18 (link)] methodology as follows: 30 mL from cell-free supernatants were extracted three times with 90 mL of chloroform (Fisher Scientific, Santa Clara, CA, USA). The chloroform layer was dehydrated over anhydrous sodium sulphate (Fisher Scientific), filtered, and followed by evaporation using a rotatory evaporator (Buchi, Essen, Germany). The residue collected from each extract was dissolved in 500 μL of chloroform prior to GC-MS injection. In addition, 100 µL of the chloroform extract was derivatized by adding 50 μL of N-trimethylsilyl-N-methyl trifluoroacetamide and trimethylchlorosilane (MSTFA + 1% TMS) followed by incubation at 50 °C for 30 min prior to GC-MS injection.

All chemicals and reagents were of reagent grade and were supplied by Sigma Aldrich, Poole, UK, unless otherwise indicated. 4APEG-NH₂ [Tetra-O,O,O,O-poly(ethyleneglycol-O-2- ethyleneimine), 2000 Da] was supplied by Jenkem Technology, Plano, TX, USA. Triethylamine (TEA) and anhydrous sodium sulphate were supplied by Fisher scientific, Loughborough, UK. Hydrochloric acid (HCl) was supplied by VWR International, Poole, UK. Deuterium oxide (D₂O) was supplied from Goss Scientific, Crewe, UK, and dialysis membrane (molecular weight cut off = 1 kDa) was supplied from Spectrum Chemical Manufacturing Corporation, New Brunswick, NJ, USA.