1. Take replicate samples (2-5 ml) of the cell culture and measure the optical density. (for Nannochloropsis OD at 750 nm).
2. Wash equipment with 10% HCl and set it up as followed: Use an Erlenmeyer flask connected to a vacuum pump, place a rubber stopper with a filter inserted in the middle of it, on the Erlenmeyer flask.
3. The precombusted (at 400°C and stored at -23°C) Whatman GF/F glass fibre filter are picked up with a tweezer, cut in three pieces and put on top of the filter system. The glass funnel is put on top of the filter and tighten with a blue clip.
4. Filter the sample and make sure the cells are collected on a circular surface of the filter and don’t suck the filter dry, cells could get burst.
5. To remove inorganic carbon, the filtered samples (taken with a tweezer) were fumigated 30 min with HCl (37%) by placing them in a box (the inside of the box should be covered in aluminium foil in advance), together with a cup of 37 % HCl.
6. Take out the filters (still use a tweezer and gloves), and cut out the area with cells using a circular cutter. Fold the resulting filter circle in half, and roll it together and place it in a tin capsule (in a microtiter plate).
7. Dry the samples at 60°C for 24 h before they are analyzed on an ECS 4010 Costech Instruments element analyzer.