CONVEYOR-BELT APPARATUS FOR FINE GRINDING OF SOIL AND PLANT MATERIALS

Recent advances in instrumentation have provided the capability to determine total N and N-15 concentrations in milligram quantities of soil or plant material. Analytical precision with small samples is adversely affected by sample heterogeneity, however, and fine sample grinding is necessary. A grinding apparatus using a conveyor-belt assembly and operating as a roller mill was developed. The samples are ground and stored in the same bottle, reducing the risk of cross contamination, and up to 55 samples can be processed simultaneously. Corn (Zea mays L.) leaf, bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon], and soil were finely ground in 12 h or less, but longer grinding periods are recommended for hard-to-grind materials such as corn grain and corn cobs. Analytical precision for measurement of total N and N-15 concentrations by direct-combustion, continuous-flow mass spectrometry tended to increase with decreasing particle size.