Simple method to assess the maximum bio-accessibility of elements from food using flow injection and inductively coupled plasma mass spectrometry

Abstract

A quick and simple method was developed to assess the maximum bio-accessibility of elements, i.e., the maximum amounts of elements that can be released from food into artificial gastrointestinal fluids. The method is based on leaching of the food sample by, successively, artificial saliva, gastric juice and intestinal juice. It uses a single-line flow injection manifold to repeatedly inject 100-µL aliquots of a given reagent that is then pumped through a micro-column of food (maintained at 37 °C in a thermostated water bath), which is connected to the nebulizer of an inductively coupled plasma mass spectrometry (ICP-MS) instrument. This on-line leaching approach allows the continuous monitoring of the progressive release of elements by a given reagent. A proof of concept of this simple method was made using a micro-column of a standard reference material of corn bran (SRM-8433 from the National Institute of Standards and Technology). Quantitation of the bio-accessible fraction of Zn and Pb was done by calibration using 100-µL injections of standard solutions prepared in the reagent matrices. Internal standardization using As (which was added to the reagents and the standard solutions) was required for the determination of Zn to compensate for matrix-induced ICP-MS signal enhancement. Following consecutive leaching by the three reagents, total digestion of the sample remaining in the column was done to verify mass balance. The high sensitivity of ICP-MS allows the detection of trace elements as they are released from the food. Furthermore, the resulting leaching profiles simultaneously provide information on the fractionation of elements in the food, including the source of some elements (exemplified here by Pb) whose isotopic distribution varies in nature. In contrast to the batch method, the elements are continuously removed from the system, thereby driving the dissolution equilibrium to the right. As a result, the maximum amount of analyte that can be dissolved in a given reagent is measured, which allows a quick assessment of the worst-case scenario in the case of toxic elements (i.e., risk assessment).