COMPARISON OF SOME METHODS FOR THE DETERMINATION OF TOTAL SULFUR IN PLANT-TISSUES

There are several methods for determining total sulfur (S) in plant ma terials but few studies comparing several methods. In this study, we c ompared six methods, viz, dry ashing-inductively coupled plasma emissi on spectrometry (ICP), oxygen flask combustion - ICP, oxygen flask com bustion - ion chromatography (IC), automated combustion (LECO CNS-2000 ), and two variants of micro- wave-acid digestion (HNO3/HClO4 or HNO3/ H2O2/HCl) followed by ICP analysis. Six tissue types (citrus leaf, can ola seed, corn leaf, pine needle, red clover shoot, and wheat flour) w ere decomposed by the above methods in two batches (days) of three sub samples each. Average tissue S content as determined by the methods wa s: automated combustion = HNO3/H2O2/HCl -ICP > oxygen flask combustion = dry ashing > HNO3/HClO4-ICP. There was a small but significant meth od x tissue interaction, with some methods giving higher S values for certain tissue types and vice versa. Oxygen flask combustion followed by ICP or ion chromatographic analysis gave similar S values for all t issue types indicating complete oxidation of plant S to sulfate. Mean coefficients of variation ranged from 3.1 to 5. 5%. Both the HNO3/HClO 4 and the HNO3/H2O2/HCl microwave digestion-ICP methods were suitable to somewhat different degrees for multielemental analysis, but the tes ted dry ashing-ICP method was not suitable without modification.