A simple roller-mill grinding procedure for plant and soil samples

Obtaining finely ground, homogeneous plant and soil samples for chemical analysis without cross contamination is a major concern when using direct combustion procedures for determination of total nitrogen (N), total carbon (C), and isotope-ratio analysis. A rollermilling device, using square glass bottles instead of round grinding bottles, was evaluated. Rotation of the square bottles on the roller mechanism increased the milling action by the stainless steel rods inside the bottles. The roller-milling device with square grinding bottles resulted in a sample with smaller particles (99.2% <100 mesh) than with a ball-milling device (83% <100 mesh). The roller-mill provided acceptable results (soil and plant samples ranging from 1.6-43.8% C, 0.5-2.3% N, and 0.3777-1.038 atom% N-15 (isotopic ratio analysis) had coefficients of variation ranging from 0.44-1.78, to 0.97-1.60, and 0.09-1.43, respectively) while providing an economical approach to grinding large numbers of samples to achieve finely ground, homogeneous samples with minimal labor and equipment costs.