Comparison of laser diffractometry and pipetting methods for particle size determination: A pilot study on the implications of result discrepancies on soil classification.

In recent decades, the determination of particle size distribution (PSD) using thelaser diffraction method (LDM) has become increasingly common, supplanting tra-ditional sedimentation techniques. Advances in everything from sample preparationto software settings have been realized globally, whether through recommendationsfrom laser diffraction (LD) manufacturers or through user experiences. These devel-opments seek to enhance accuracy and diminish the uncertainties associated withnew methodologies. Particularly in the determination of PSD using LDM on variousLD instruments and in comparison with the sieve–pipette method (SPM), discrep-ancies in PSD frequently arise. This article aims to mitigate these discrepancies bypredefining parameters, specifically through the adjustment of LD software settingsand sample preparation (employing a uniform set of dispersed samples in potassiumhydroxide) on two widely used LD instruments for soil measurements: Mastersizer3000 and Analysette 22. Additionally, these samples were analyzed using the tradi-tional SPM (ISO 11277, 1998), with the results from LDM and SPM subsequentlycompared. The paper also explores the impact, range of user options, and limitationsof predefined software settings on both LD instruments. Eighty soil samples wereanalyzed for PSD, collected from arable land in the cadastral area of Hrušky, dis-trict of Břeclav (Czech Republic), in spring 2022, from depths of 0- to 10-cm and10- to 20-cm. Significant differences in PSD were confirmed, although the trends ofthe grain size distribution curves were very similar to those of LDM. Results fromthe Mastersizer underestimated the clay fraction by an average of 17% comparedto SPM, at the expense of the sand fraction, whereas the silt fraction was underesti-mated by a maximum of 4%. Conversely, Analysette 22 overestimated the silt fractionby an average of 37% at the expense of the sand fraction, confirming only a slight difference in the clay fraction: 3%. Moreover, the quantity of sample entering the dis-persion unit was identified as a significant issue when comparing LD instruments,despite the obscuration value being nearly identical, that is, 20%–30%. Therefore, itwas not possible to achieve the same or similar weight when introducing suspensioninto circulation. The robustness of the obtained results underscores the importance ofunderstanding input parameters when interpreting results between different methods.