11/02/2025 - Soil Preparation for Chromatography

8th February 2025

Experimentation: Preparing Unearthed Soil for Chromatography

This blog entry outlines my preparation for new soil chromatography experiments this week. I'll be working with unearthed soil samples collected during my recent trip to Danby on 8th February. My approach involves applying the soil onto small sections of filter paper and semi-submerging pre-coated fabric strips into trays containing a broken-down soil solution.

This will be my first time exploring soil chromatography in a non-traditional format, deviating from the typical circular filter paper method. I'm curious to see how the results will differ when the materials are 'dipped' rather than allowing the soil to naturally disperse from the centre. I wonder whether this method will still produce distinct soil reading patterns featuring spikes, channels, and clear colour separation.

To start, I separated each soil sample after removing them from their sealed bags. I spread the soil onto a foil-lined baking tray and dried it in the oven. I pre-heated the oven first, but switched it off when placing the soil inside to avoid any 'cooking.'

Once the soil had dried and cooled, I processed each sample individually to prevent cross-contamination. Using a heavy pestle and mortar, I ground each soil type into a fine powder. This step helps remove stones, twigs, and other debris while also making the soil easier to break down when mixed with the sodium solution.

Once the soil is ground into a fine powder (or as fine as possible), I leave it to sit in the pestle and mortar. There is no particular reason for this pause other than the need to move on to the next step in the process. That step involves preparing a sodium water solution in a 1000ml cylinder. I begin by filling the cylinder with 500ml of cold water, then add approximately 1 gram (about a teaspoon) of sodium salt. The sodium aids in breaking down the soil particles when mixed into the water.

The next step in the soil chromatography process involves using a sieve placed over the cylinder. Small amounts of the ground soil mix are carefully poured into the sieve to prevent any loss if the soil does not fully align with the cylinder opening. By gently tapping the sieve, the soil gradually sifts through into the sodium water solution. Patience is essential at this stage, as the process can be time consuming, but it ensures that any non-soil debris is effectively filtered out.

The next step requires patience, involving up to twelve hours of agitation. Those familiar with film development in a tank will recognise the process, though this is a more prolonged version without the need for a light-tight container. Agitation begins immediately with a one-minute shake, followed by agitation every minute for the next fifteen minutes. After this, the soil solution is left to react with the sodium solution for twelve hours, with occasional agitation every few hours.

In a standard soil chromatography process, the soil solution would typically be distributed into small petri dishes. However, since this experiment follows a different approach, I poured the solution into four large trays, each clearly marked to correspond with the specific soil collection sites. This labelling will aid in the analytical stage once the materials are dipped into the solution.

Later this week, I plan to transfer the soil solution onto the pre-coated light-sensitive materials. The final outcome should be visible within five to seven days, once fully exposed to natural daylight.