Robotic Clay fraction Analysis


Classification of soil is important for environmental control and construction purposes. Soil classification is based on several factors such as absorption, the ability to shrink or swell, water retention and permeability. Most of these factors independently correlate with the particle size of the soil. The clay fraction, the smallest fraction (0-2 micron), is indispensable in assessing soil quality. The clay fraction is measured according to for instance ISO 11277 and allows the soil to be categorized within stated classes.

The analysis is carried out in three steps:

  1. Weighing the sample and separating the fractions


  1. Removal of Organic Matter and Carbonates
  2. Determination of the clay fraction

Skalar has developed a concept to automate the second and third step in this process using a Skalar Robotic analyzer. Automation of these steps is of particular interest because they  can now be carried out fully automatic and with precise timing and pick up heights.

A typical Organic Matter/Carbonates removal sequence:

Steps of Automation

  • Removal of Carbonates
  • Removal of Organic matter
  • Rinsing of the sample

After weighing, the samples are placed in a bottle. The bottles are placed in the Skalar SP50 Robotic analyzer and an amount of water is added. The bottles with sample are heated until the boiling point has been reached. A sample is boiled for 30 min. During heating and boiling every 30 min, 5 ml of hydrogen peroxide is added to remove the organic matter. Afterwards the sample is cooled down and the same process is started but now with the addition of hydro chloric acid to remove the carbonates. During the complete process water is added in intervals to avoid excessive boiling of the sample.

A typical Clay fraction analysis sequence:

Steps of Automation

  • Addition of pyrophosphate
  • Addition of dilution water
  • Sample homogenizing
  • Sample take up
  • Sample transferring
  • Sample dispensing
  • Sample drying in aluminum cup


The sample is transferred into a volumetric cylinder of 500/1000 ml. The system, a Skalar SP2000 robotic analyzer automatically adds Sodium pyrophosphate solution and brings the suspension to volume by adding distilled water. During a user-definable time, the sample is homogenized. After a settling period of several hours a fraction of the suspension is taken at a predefined depth from the cylinder and this fraction is transferred to an evaporation dish by the system. After drying the remainder of the sample is weighed and the Clay fraction is calculated via the software.

This procedure can also be performed unattended allowing for overnight operation. In addition, it is also possible to determine other fractions.