Improvements to Single Particle ICPMS by the Online Coupling of Ion Exchange Resins

Single particle ICPMS (SP-ICPMS) is becoming a very promising technique for nanoparticle detection and characterization, especially at very low concentrations (similar to,10(-12)-10(-10) M). Nonetheless, the ability of the technique to detect smaller nanoparticles is presently limited by the setting of threshold values for the discrimination of nanoparticles from the dissolved metal background. In this study, a new approach to attaining lower particle size detection limits has been developed by the online coupling of an ion exchange column (IEC) with SP-ICPMS (IEC-SP-ICPMS). The IEC effectively removes the continuous signal of dissolved metal, allowing for both lower detection limits and an improved resolution of solutions containing multiple particles. The feasibility and the efficiency of this coupling were investigated using silver nanoparticles in the presence of various concentrations of Ag+ and other major ions (Mg2+, Ca2+, Na+, K+, and Cl-). The online elimination of the dissolved metal made data processing simpler and more accurate. Following the addition of 1 to 4 mu g L-1 of Ag+ spikes, symmetric particle size distributions were obtained using IEC-SP-ICPMS, whereas the use of SP-ICPMS alone led to asymmetric distributions, especially for nanoparticle sizes below 60 nm. Although this proof of principle study focused on nanosilver, the technique should be particularly useful for any of the metal based nanoparticles with high solubilities.