We routinely use this method for measuring samples which require extraction from a reactor containing a solution. For example, microbial cultivation experiments or sediment slurries. The approach is relateively easy, however it typically results in longer measurement time because filters block easily, learing to unsatisfactory amounts of Fe in a sample.

Prior to taking samples, prepare the filter housing unit:

• You will need:
  • 1 x luer lock compatible end
  • 1 x white O-ring
  • 1 x screw cap to close filter unit
  • 1 x filter paper (1 cm²; 0.44 µm pore size is recommended)
• Take the luer lock end compatible end of the filter and place a white O-ring inside.
• Remove a filter from the box and ensure it is clear from the protective blue paper.
• Place the white filter inside the luer lock compatible end of the filter.
• Screw in the cap to close the filter unit and it is now ready for sampling.

• Prepare 2 pieces of kapton tape.
• Put 1 piece of kapton tape with the sticky side facing up.
• Take ~2ml of sample (adjust volume depending upon your Fe concentration) with needle and luer lock syringe.
• Remove the needle and attach the syringe to the filter unit.
• Push the contents of the syringe through the filter, however if the syringe plunger becomes too hard to push, then stop pushing as the filter already has enough material.
• Carefully unscrew the filter unit and using tweezers remove the filter paper and put it on to a piece of tissue paper to soak up excess liquid.
• If the white O-ring is still on the filter then carefully try to remove if possible so you can reuse it, otherwise leave it in place.
• Put the filter paper onto the kapton tape (with sticky side up) and then lower the second piece of kapton on top (with sticky side down).
• Push the air out of the kapton tape using the back of a pair of tweezers (do not press onto the sample itself) but leave a small channel to allow any air to be squeezed out. Once most of the air is squeezed out, close the channel with the back of the tweezers.
• LABEL the kapton-filter-kapton sandwich.
• Put the sample into a container and store frozen (-20 °C or lower) until measurement.
• The filter housing unit can be reused by soaking in oxalic acid (0.5 %) for 2-3 days to remove all traces of Fe. Rinse with DI water and dry

• This preparation method can be done within a glovebox, but make sure to only remove the sample within a well sealed anoxic container.
• Does not require samples to be dried
• Can measure sorbed iron
• Filters block easily, can require multiple layers
• Only works below room temperature

We routinely use this method for measuring samples which have been air dried and freeze dried. The holder is a custom design which was produced in our workshop, but in general it should be possible to make your own version.

Prepare the sample holder:

• You will need:
  • 1 x Outer plexiglas part
  • 1 x Inner plexiglas part
  • 1 x small piece of parafilm
• The inner part will sit inside the outer part, but it is worth testing before you add any samples that both parts fit smoothly together and can be separated without excessive force.

• Make sure your sample is well grounded to make a homogenous powder. Your sample should be a powder with the consistency close to talcum powder
• Weigh out your sample into the Outer par (the desired mass depends on the density of your sample and Fe content. A general rule of thumb is that you should use ~30-40 mg in case you have pure Fe oxide. If your Fe content is much lower then you will need to add more sample, but usually 150-200 mg is the absolute upper limit of material you can add to the holders and still get a decent spectrum.
• Spread the powder within the holder so it creates a relatively even layer.
• Gently place the Inner part into the Outer part.
• Rotate the Inner part within the Outer part to ensure that the sample is spread thinly and evenly.
• Hold the sample holder up to the light to look for any holes. If there is any holes in the power, continue to rotate the inner part clockwise and anticlockwise until the hole closes. You may need to remove the Inner part and spread the powder again.
• When satisfied, carefully wrap the parafilm around the edge of the holder so that the Inner and Outer parts remain firmly stuck together.
• Store sample in an appropriate place until time for measurement
• After you have finished measurement, the holder can be reused by removing the sample and soaking in oxalic acid (0.5 %) for 2-3 days to remove all traces of Fe. Rinse with DI water and dry

• This preparation method can be done within a glovebox, but make sure to only remove the sample within a well sealed anoxic container.
• You can mix your sample with glucose or boron nitride if sample content is low
• Works at all temperatures
• Straightforward and quick sample preparation
• Samples can undergo transformation during dehydration

We very rarely use this appraoch except for samples which cannot be filtered or dried. We have custom designed Teflon caps which were made in our workshop.

Prepare the sample holder:

• You will need:
  • 1 x Teflon cap
  • 1 x piece of kapton tape

• Place the cap on a flat surface
• Add your sample into the cap. In general, the volume to add depends on the Fe content of your sample, but we find that 150 µl works ok.
• Carefully wrap the top of the cap with a layer of kapton tape
• Whilst ensuring that the cap remains completely flat, place into the freezer overnight.
• Store frozen (-20 °C or lower) until measurement.

• This preparation method can be done within a glovebox, but make sure to only remove the sample within a well sealed anoxic container.
• Can be an option if filtration and drying cannot be used to prepare sample.
• Only works below room the freezing temperature of the sample.
• Difficult to estimate best volume to add to holder without knowledge of Fe content.