Validation of gravimetric method for determination of clay in soil

Abstract

The requirements for method validation are taken from the method ISO 11277:2020 Soil quality – determination of particle size in soil – by sieving and sedimentation method, Annex C table C.1 [1]. The validation was performed on soil samples and on soil reference material (old PT scheme). Validation includes checking the volume of the pipette i.e., calibration of the pipette, correction for the contribution of the dispersing agent, repeatability (RSDr), reproducibility (RSDR), recovery (R), checking bias from the used lab equipment and the bias from purity of use chemicals. As a final part of the validation, the combined measurement uncertainty (Uc) and expanded measurement uncertainty (U) with a confidence level of 95% were calculated. The pipette calibration error is 2.40%. The obtained results are RSRr = 1.38%, RSDR = 13.21%, Recovery = 100.66%, laboratory equipment bias is 2.66%, bias from used chemicals is 0.17%, combined uncertainty is 5.08% and expanded measurement uncertainty is 10.17% by gravimetric determination of clay content, using the pipette method.