Single particle analysis of TiO₂ in candy products using triple quadrupole ICP-MS

Titanium dioxide (TiO₂) belongs to the materials that have gained great importance in many applications. In its particulate form (micro- or nanoparticles), it has entered a huge number of consumer products and food-grade TiO₂, better known as E171 within the European Union, represents an important food additive. Thus, there is an increasing need for analytical methods able to detect and quantify such particles. In this regard, inductively coupled-mass spectrometry (ICP-MS), in particular single particle ICP-MS (spICP-MS), has gained importance due to its simplicity and ease of use. Nevertheless, the number of applications for Ti nanoparticles is rather limited. In this study, we have applied the spICP-MS strategy by comparing different measuring modes available in triple quadrupole ICP-MS. First, single quadrupole mode using the collision/reaction cell system was selected for monitoring the isotope ⁴⁷Ti. Different cell gases like He, O₂ and NH₃ were tested under optimised conditions for its applicability in spICP-MS of standard suspensions of TiO₂. The determined analytical figures of merit were compared to those obtained by triple quadrupole mode using the ⁴⁷Ti or ⁴⁸Ti reaction products using O₂ and NH₃ as reaction gases. This comparison demonstrated that the triple quadrupole mode (TQ mode) was superior in terms of sensitivity due to the more efficient removal of spectral interferences. Particle size detection limits down to 26nm were obtained using the best instrumental conditions for TiO₂ particles at a dwell time of 10ms. Finally, the different measuring modes were applied to the analysis of chewing gum samples after a simple extraction procedure using an ultrasonic bath. The obtained results showed a good agreement for the detected particle size range using the different TQ modes. The size range of TiO₂ particles was determined to be between approximately 30 and 200nm, whereas roughly 40% of the particles were smaller than 100nm. For the determination of the particle number concentration in these real samples, we suggest CeO₂ particles as internal standard.