A comparison of X‐ray fluorescence spectrometry and chemical methods for determining sulphur in plant material

A rapid method for determining total S in plants by X‐ray fluorescence spectro‐metric analysis of ground pelletised plant material is compared with chemical methods using titrimetric, flame photometric and turbidimetric methods of sulphate determination. Errors in the chemical methods were caused by incomplete oxidation of organic sulphur and by non‐reproducibility of the turbidimetric determination of sulphate. A method incorporating the oxidation of the sample with HNO3 and Mg(NO3)2 and titration of the reduced sulphate by mercuric acetate gave recoveries accurate to a mean of 1% when determining the sulphur content of sulphur compounds. Taking the results for plant materials determined by the titrimetric method as standard, XRF gave sulphur values with a mean difference of 4%; the flame photometric determination of sulphate after HNO3 + Mg(NO3)2 oxidation gave results with a mean difference of 12%. The effect of absorption of S radiation by silicon is noted.