Determination of trace element concentrations in tomato samples at different stages of maturation by ICP OES and ICP-MS following microwave-assisted digestion

Abstract

The concentrations of 15 elements (Al, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Se, Sn, Sr, V and Zn) were determined in three tomato species (Khaki, Cherry and Italy) at different stages of maturation by ICP OES and ICP-MS following microwave-assisted acid digestion. The digestion efficiency was evaluated on the basis of the determination of residual carbon content and trace element recoveries. Diluted nitric acid solutions were used for the efficient digestion of 300 mg of tomato samples, with a considerable reduction in the residual acidity when compared with a procedure that employed a concentrated nitric acid solution. The good agreement between the measured and certified concentrations of a National Institute of Standards and Technology (NIST) Certified Reference Material 1573a (Tomato Leaves) indicated that the developed analytical method was well suited to determine the trace elements contents in similar matrices. The analytical parameters, such as the limits of quantification, the accuracy and the precision of the overall procedure, were assessed statistically. Moreover, the measured trace element concentrations were used to distinguish between conventional and organic cultivation. According to the data, the species of tomato, the form of cultivation and the stage of maturation of the fruit influenced the concentrations of the trace elements that are found in the tomato samples. Tomatoes in the final stage of maturation showed higher concentrations of most of the elements that were measured in the three species studied. Regarding the type of cultivation, organic tomatoes contained higher levels of micronutrients and less contaminants when compared with conventionally grown tomatoes.

Highlights ► The concentrations of 15 elements were determined in three species of tomatoes by ICP OES and ICP-MS. ► The type of sample, form of cultivation and maturation influenced the concentrations of trace elements in tomato samples. ► Tomatoes in the final stages of maturation showed higher concentrations ​​for most elements that were measured. ► Organic tomatoes had higher levels of micronutrients and lower levels of contaminants.