Investigation of four digestion procedures for multi-element determination of toxic and nutrient elements in legumes by inductively coupled plasma-optical emission spectrometry

A simple and reliable multi-element procedure for determination of essential (Cr, Cu, Fe, Mg, Mn, Zn) and toxic (Al, Cd, Pb) elements in legumes by inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed. In this contribution, four different digestion procedures were thoroughly investigated and accurately evaluated with respect to their affect on the analysis of legumes. These included wet digestion with HNO3/H2SO4 and HNO3/H2SO4/H2O2, and dry ashing with Mg(NO3)2 and Mg(NO3)2/HNO3. Two calibrations (aqueous standard and standard addition) procedures were studied, and proved that standard addition was preferable for all analytes. ICP-OES operating parameters, such as radio-frequency (RF) incident power, sample uptake flow rate and nebulizer argon gas flow rate were optimized. The precision as repeatability, expressed as relative standard deviation (R.S.D.) for aqueous standard containing 250 μg l−1 of each analyte was in the range1.5–8.0%. The accuracy, expressed as relative error was generally varied in the range of 0.5–10% for all analytes, while the quantification limits were lower than 2.5 μg g−1. Although, acceptable results were obtained from all developed procedures, wet digestion method with HNO3/H2SO4/H2O2 is recommended for better recovery. The good agreement between measured and certified concentrations with respect to IAEA-331 and IAEA-359 (CRM's supplied by IAEA, International Atomic Energy Agency) indicates that the developed analytical method is well suited for determination of toxic and nutrient elements in legumes and possibly similar matrices.