Abstract
An automated turbidimetric method has been developed for the rapid and accurate determination of sulfate. The method is practical and useful for accurately measuring total sulfur in plant tissues, and extractable sulfate in soils and fertilizers. The principle of intermittent reagent addition is used, which eliminates drift and sensitivity changes caused by coating of BaSO4 on tubing and cell walls. Also, the appropriate chemistry is used to minimize coating and interactions of the wash with the sample at a sampling rate of 30/h. The sensitivity of the method is excellent with a working range of 0–15 ppm sulfur for soils. For plant and fertilizer digests, the sample solutions are diluted to 0–35 ppm S. The precision as determined by repeated analysis of a soil sample extract was 0.58% relative standard deviation (RSD) with a mean of 9.26 μg extractable sulfate sulfur. On another soil sample, using a different extractant and extraction procedure, the RSD was 0.64%, mean of 9.29 μg/g. Multiple automated sulfur analyses on a plant tissue digest resulted in an RSD of 0.41% for a sample containing 0.21% S. The average recovery of sulfate sulfur on 5 Magruder Fertilizer Check Samples by the automated turbidimetric method was 100.6%, range of 99.8 to 101.4%, as compared to gravimetric analysis. The automated turbidimetric method for sulfate has excellent precision and sensitivity in plant tissue and soil analyses where gravimetric BaSO4 assays are not practical. The method is rapid, precise, and accurate for analysis of sulfate sulfur in fertilizers.
Determination of Total Sulfur and Sulfate Sulfur in Geological Materials of Rocks, Soils, and Sediments by ICP-OES After Sample Digestion Using Alkali Flux
