Microwave digestion of plant samples for sulfur analysis

The goal was to develop an easy, fast, and economical procedure to produce plant digests that can be accurately analyzed by plasma emission spectrometry for foliar sulfur content. The closed vessel microwave procedure described requires less than 2 hours to produce 12 digested 0.5 gram samples from the point of weighing the samples to applying them to plasma emission spectrometry analysis. The procedure utilizes nitric acid and hydrogen peroxide as a predigestion. The predigested samples are then each microwaved for 2.25 minutes. With this procedure, sulfur levels are within an average of 1.27% of that reported for the NBS Citrus Standard, are within 102.25% to 99.44% of the values determined for wet ash digested materials and display recovery rates of 96 to 98% for known levels of sulfur in the range expected in plant foliage. (author)