Study of nutrients and toxic minerals in rice and legumes by instrumental neutron activation analysis and graphite furnace atomic absorption spectrophotometry

Instrumental neutron activation analysis (INAA) is one of the high metrological techniques for mineral determination. Nevertheless, it has some limitations for minerals with low detection limits, such as lead and cadmium, for which graphite furnace atomic absorption spectrophotometry (GF-AAS) provides reliable outcomes. This study was conducted to determine nutrients and toxic elements in four varieties of rice and six varieties of legumes. Rice and legume samples were collected from Talad-Thai and Yoawarat markets, which were representatives of rural and Bangkok areas, respectively. INAA was used for determination of various minerals whereas GF-AAS was used to determine Cd and Pb. In-house reference materials (RMs: white jasmine rice and soybeans) were prepared and their mineral contents were assigned, along with certified reference materials, by INAA and GF-AAS with standard addition technique. The INAA and GF-AAS methods were validated by various certified reference materials which showed a fairly good accuracy, 0.7–4.5% bias for INAA; 1.54 and 6.06% bias for AAS. The precision of INAA and GF-AAS, relative standard deviation (RSD) of all studied minerals was good (RSD less than 8.9%). All varieties of rice and legume seeds contain high amounts of Ca, K and Mg, whereas trace amounts of Al, Br, Cl, Fe, Mn, Zn. Cr, Cu, I, Mo, Se and Sn were found. Trace amounts of As (0.029–0.181 mg/kg) and Cd (0.010–0.025 mg/kg) were detected in all varieties of rice, but not detected in legume seeds, except that slightly higher level of Cd were found in soybeans and peanut (0.022 and 0.085 mg/kg, respectively). Low levels of Hg, ranging from 0.196 to 0.352 mg/kg, were detected in all studied sample, whereas level of Pb less than LOD (1 mcg/100 g) was found. To improve the quality of analytical mineral data, these in-house reference materials can be used as a reference material for internal and external quality control systems.