COMPARISON OF 3 WET DIGESTION METHODS FOR THE DETERMINATION OF PLANT SULFUR BY INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROSCOPY (ICPAES)

Increased incidence of sulphur (S) deficiency in crops has led to a gr eater need for S determination in plant tissues. Among the methods ava ilable for measurement of S, inductively coupled plasma atomic emissio n spectrometry (ICP-AES) has been proved to be accurate and rapid. Thi s paper compares digestion with HNO3-HClO4, fuming HNO3-KNO3 and alkal ine NaOBr prior to the S measurement by ICP-AES. Both HNO3-HClO4 and f uming HNO3-KNO3 were found to give satisfactory results for five certi fied plant materials, with high accuracy and precision. The HNO3-HClO4 method involved a rigid temperature control, with slow ramp rates and a final temperature (190-degrees-C) lower than the boiling point of H ClO4, to minimise the possibility of gaseous losses of S. Both methods can also be used for the simultaneous determination of phosphorus (P) , calcium (Ca), magnesium (Mg), iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn), and additionally potassium (K) with HNO3-HClO4. In co ntrast, the alkaline NaOBr method was less suitable as a digestion pro cedure for S measurement by ICP-AES, because it involved a large dilut ion factor and produced high blank values.