Single-particle inductively coupled plasma-mass spectrometry (SP-ICP-MS) is used for elemental analysis of single particles and biological cells. Time-of-flight (TOF) mass analyzers are widely used for multiple element analysis of individual particles. Owing to the sequential nature of the mass analyzer, quadrupole-based ICP-MS generally gives poor analytical performance when more than one element are being monitored. In this study, we present the first accurate and precise dual-mass measurement of individual particles using quadrupole-based ICP-MS, with the assistance of oxygen collision gas. Simultaneous measurement of the intensity of 107Ag and 109Ag of Ag nanoparticles (AgNP) showed particle recovery of 100% and Pearson correlation coefficient of 0.97, indicating proper sampling of all particles in the ICP. This technique gives good measurement precision (RSD <8%) and high accuracy in size measurement (error <3%). This technique was further applied to determine the elemental content and isotope ratios of particles and to study cell viability after Cisplatin staining. The results are comparable to that of existing TOF and multi-collector ICP-MS, indicating that quadrupole-based ICP-MS can be a cost-effective alternative for simultaneous measurement of two isotopes. Acquisition with longer integration time and shorter settling time is also proposed to further improve the sensitivity and number of isotopes monitored. This study will potentially open up more possibilities of using quadrupole based ICP-MS in biomedical research as quantification of multi-elements in single cells is far more informative. Other possible applications include classification of cancer subtypes according to the abundance of several biomarkers, as well as elemental bio-imaging of transcripts and proteins in tissues by laser ablation.
Keywords: Cell viability; Dual-mass; Isotope ratio; Nanoparticles; Single particle ICP-MS.
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