Abstract: Different pretreatment methods may have a potential impact on the results of loess and palaeosol grain size analysis. Taking five samples from the S₀-L₁ section of the Luochuan profile as the subject of this study, four sets of comparative experiments were designed to systematically evaluate whether variations in the method and concentration of H₂O₂ addition, the amount of HCl used and reaction time, the solid-liquid separation method, and the ultrasonic dispersion method and duration affect the grain size analysis results. The study found that, for a 0.2 g loess-palaeosol sample, adding a sufficient amount of 10% H₂O₂ in a single step yielded better results than adding small amounts in multiple stages; appropriately increasing the amount of HCl and the reaction time can improve the accuracy of grain size analysis data; solid-liquid separation by centrifugation reduces the loss of fine-grain fractions more effectively than static sedimentation, with satisfactory results achieved after just 5 minutes of centrifugation; online ultrasonic dispersion for 5 minutes is the optimal choice, as excessive ultrasonication of palaeosols may cause agglomeration, leading to overestimated grain size values. Palaeosols are more sensitive to pretreatment methods than loess. It is recommended to weigh out approximately 0.2 g of the sample to be tested and place it in a 300 ml beaker. Add 50 ml of a 10 per cent H₂O₂ solution in a single batch and heat to react for 2 hours; increase the volume of the 10 per cent HCl solution to 50 ml and extend the reaction time to 2 hours; centrifuge at 4000 r/min for 5 minutes to separate the solid from the liquid; repeat the centrifugation twice, add 10 ml of a 10 per cent (NaPO₃)₆ dispersant, and then subject the sample to online ultrasonication for 5 minutes on a laser grain size analyser to complete the pre-treatment process. This study provides experimental evidence for improving the comparability of grain size data and reducing methodological errors in palaeoenvironmental reconstruction.

Key words: grain size analysis, pretreatment methods, loess-paleosols