Reduction of interferences in the determination of lanthanides, actinides and transition metals by an octopole collision/reaction cell inductively coupled plasma mass spectrometer – Application to the analysis of Chios mastic

Abstract

Lanthanides, actinides and transition metals have demonstrated the ability to be used as fingerprint for the specification of the authenticity and geographical origin of food commodities. Therefore, the existence of analytical methods for their determination is of great importance, since both producers and consumers could benefit. An inductively coupled plasma mass spectrometric (ICP-MS) method was developed and validated for the determination of these elements in a Protected Designation of Origin product, the Chios mastic gum. A multivariate strategy for the microwave digestion of mastic was carried out. Five factors were studied and optimized. Hold time, temperature and HF volume, were found to be the most critical factors, so further optimization was performed. Molecular oxide (MO+, MO2+) and hydroxide (MOH+) interferences were investigated. The capability of an octopole collision/reaction cell ICP-MS to attenuate or remove these interferences was studied. The effect of instrumental parameters on MO+/M+, MOH+/M+ and MO2+/M+ ratios was studied to ensure that observed changes were a result of alteration of the parameter and not due to random fluctuations. Moreover, the effect of kinetic energy discrimination to suppress these species was demonstrated. The energy losses of ions were measured from stopping curves and the estimation of collision cross sections was done. Efficiencies of He and H2 gases were compared and H2 was finally selected for all elements. The calculated recoveries were ranged between 70 and 70% and 104% and the relative standard deviations (intermediate precision) were generally under 16%. The limits of detection were 0.07ngg−1 (Dy, Th) – 1.4ngg−1 (Ce).