Fullerenes c 60

Toluene, methanol, isopropanol and acetonitrile (Biosolve, Valkenswaard, The Netherlands) were all analytical grade (LC-MS). Fullerenes C 60 (CAS: 99685-96-8) and C 70 (CAS: 115383-22-7) standards were purchased by Sigma-Aldrich (Steinheim, Germany). Stock solutions of the individual fullerenes, at the concentration of 5 mg/L, were prepared in Toluene and placed on an orbital shaker (Laboshake orbital shaker, Gerhardt, K€ onigswinter, Germany) in the dark overnight. Further solutions needed for the experiments, were obtained by dilution of the stock solutions, and stored at 4 C in the dark and sonicated for 2 min before use (Bransonic 12, Branson, Danbury CT, United States).

Toluene (analytical grade), methanol (ULC/MS grade) and acetonitrile (LC-MS grade) were obtained from Biosolve B.V. (Valkenswaard, The Netherlands). Fullerenes C 60 (purity >99.9%, CAS: 99685-96-8) and C 70 (purity >99%, CAS: 115383-22-7) were purchased from Sigma-Aldrich (Steinheim, Germany). Stock solutions of the individual fullerenes were prepared in toluene at a concentration of 500 mg/L and placed on an orbital shaker (Laboshake orbital shaker, Gerhardt, K€ onigswinter, Germany) in the dark overnight. Further solutions needed for the experiments were obtained by dilution of the stock solutions and stored at 4 C in the dark and sonicated for 2 min before use (Bransonic 12, Branson, Danbury CT, United States). Quartz sand (silicon dioxide, SiO 2 ) was purchased from Sigma-Aldrich (Zwijndrecht, the Netherlands). The sandy soil consisted of a fullerenes free top-soil (top 10 cm) collected in a natural park in Oude Schulpweg, Castricum, the Netherlands (52 32 0 39.689 00 N, 4 39 0 5.623 00 E). This soil had previously been characterized by our group and had no detectable fullerenes (Carboni et al., 2016b) and 0.2% organic carbon (Carboni et al., 2016a) . The soil was placed in an oven at 65 C for one week in order to remove traces of water and then sieved with a 1.68 mm mesh.