Experimental validation of variance capture in sample splitting for heterogeneity tests

Accurate particulate analysis in industries such as mining, agriculture and pharmaceuticals depends critically on representative sample division. While rotary splitters are widely recognized for their practical efficiency and representativeness, their systematic nature is theoretically incompatible with the randomness required for calibrating Gy's Fundamental Sampling Error formula in heterogeneity studies. This paper experimentally investigates whether a rotary splitter suppresses compositional variance compared to the conventional riffle splitter when operated at different split ratios. Using a seeded basalt lot with tracer additives of varying densities, the performance of a Rocklabs Boyd Elite Rotary Sample Divider was evaluated at split ratios from 5% to 25% and benchmarked against both a vibratory feeder (worst-case heterogeneity) and a 20-vane riffle splitter. Results demonstrate that the rotary splitter significantly suppresses variance at higher split ratios (≥15%), reducing particle count variability by 40–50% compared to the riffle splitter. This variance suppression is attributed to the larger sample mass and the high number of incremental cuts (∼246 vs. 20), which more effectively average out local segregation. The study concludes that while rotary splitting is unsuitable for Fundamental Sampling Error calibration due to its non-random mechanism, it is a superior tool for routine sample preparation where compositional representativeness is the primary goal, provided it is operated at an appropriate split ratio.