Single particle inductively coupled plasma mass spectrometry as screening tool for detection of particles

Single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) was evaluated and validated as a qualitative method for the assessment of the presence/absence of particles containing specific elements in a sample. The binary response (present/absent) obtained allows to use SP-ICP-MS as a screening tool for rapid classification of samples, which can be further submitted to more specific analysis. A metrological treatment of SP-ICP-MS as qualitative method is presented, providing solid criteria for identifying particle events in SP-ICP-MS measurements and the presence of particle in the samples by using the critical value (or limit of decision) concept. Based on theoretical and experimental evidences, a critical value for identification of particle events by using a 5σ criterion (σ: standard deviation of the baseline) is proposed to eliminate or minimize the occurrence of false positives, whereas a 2.33σ criterion (σ: standard deviation of the number of particles counted in blanks) is proposed for confirming the presence of particles larger than the minimum detectable size in a sample. Signal domain critical values can provide semiquantitative information as size and number concentration critical values. Size critical values of 25–30 nm were obtained for metallic, spherical and solid particle of gold and silver and 50–80 nm for aluminium, whereas number concentration critical values around 105 particles per liter could be achieved regardless the element for the total acquisition time selected (1 min). The screening approach was applied to the detection of particles from approved metallic additives in foods.