Cellulose mixed ester filter membranes

Prior to the phytolith extraction nickel crucibles (99.6% Ni) were cleaned with 10% HCl and 10% H 2 O 2 for 1 h and subsequently heated up to 500 °C in a muffle furnace for one hour. Dried leaves of each of the three grasses (reference plants without artificial Ge treatment and plants treated with 50 lmol L -1 Ge) were placed inside the crucible and were calcined at 500 °C for 4 h. After cooling down the ash was transferred into sample tubes by adding 10 ml of 1% HNO 3 . The sample tubes were slowly shaken for one hour. The solutions were subsequently filtered through 200 nm cellulose mixed ester (CME) filter membranes (MERCK MILLIPORE). Each filter was washed three times with deionized water. A blank filter without ash was processed as reference. The membrane filters with the adhering phytoliths were dried at 60 °C for 48 h and weighed. After cooling, the filters of three out of four replicates were placed into microwave digestion tubes (Ethos plus 2, MLS) and totally dissolved by using a mixture of HNO 3 , H 2 O 2 and HF (Wiche et al. 2016) . The last remaining filter with adhering phytoliths was later used for microscopy and EDX measurements. Concentrations of Si and Ge in the resulting solutions and the filtrates were measured by ICP-MS using 10 lg l -1 rhodium and rhenium as internal standards.

Prior to the phytolith extraction nickel crucibles (99.6% Ni) were cleaned with 10% HCl and 10% H 2 O 2 for 1 h and subsequently heated up to 500 °C in a muffle furnace for one hour. Dried leaves of each of the three grasses (reference plants without artificial Ge treatment and plants treated with 50 lmol L -1 Ge) were placed inside the crucible and were calcined at 500 °C for 4 h. After cooling down the ash was transferred into sample tubes by adding 10 ml of 1% HNO 3 . The sample tubes were slowly shaken for one hour. The solutions were subsequently filtered through 200 nm cellulose mixed ester (CME) filter membranes (MERCK MILLIPORE). Each filter was washed three times with deionized water. A blank filter without ash was processed as reference. The membrane filters with the adhering phytoliths were dried at 60 °C for 48 h and weighed. After cooling, the filters of three out of four replicates were placed into microwave digestion tubes (Ethos plus 2, MLS) and totally dissolved by using a mixture of HNO 3 , H 2 O 2 and HF (Wiche et al. 2016) . The last remaining filter with adhering phytoliths was later used for microscopy and EDX measurements. Concentrations of Si and Ge in the resulting solutions and the filtrates were measured by ICP-MS using 10 lg l -1 rhodium and rhenium as internal standards.