First, recent advances in the field of single particle inductively coupled plasma mass spectrometry (spICP-MS) will be briefly reviewed with a focus on the characterization of engineered nanomaterials (ENMs) and environmental applications [1].
Second, our recent efforts to push the limits in spICP-MS for the detection of ENMs in the aquatic environment will be discussed. While the fundamental concepts of spICP-MS were established long ago, off-the-shelf quadrupole-based mass spectrometers are still limited in hardware and software capabilities for ideal nanoanalysis. Specifically, the instruments' hardware is typically limited in data acquisition speed and maximum measurement time. We have shown earlier with a custom-built high-speed data acquisition (DAQ) unit [2] that signals from discrete nanoparticle ion clouds in the ICP can be acquired continuously with a time resolution of five microseconds and 100% duty cycle. In addition, our data processing approach allows the quantification of both the NP size distribution and the concentration of dissolved ions. Poisson statistics are used to determine thresholds to identify the beginning and end of NP signal events. In doing so, NPs can be detected even in the presence of a significant concentration of ionic background (e.g. ¹⁰⁷Ag⁺ up to 1.000,000 cps) [3]. Detection of small NPs usually requires utilization of the pulse counting signal, which entails the risk of nonlinear response for larger NPs (cf. non-linearity in the raw signal in Fig. 1). The development of a dead time correction approach to microsecond time-resolved spICP-MS data allowed us to increase the maximum number of counts tolerated per particle [4]. All of these advances mentioned above enabled us to study ENMs in aquatic environments [5]. Selected examples and future challenges will be discussed.

<b>Figure </b><b>1</b><b>:</b> Microsecond time-resolved dead time correction improves the linear response of spICP-MS and helps to expand particle size coverage [4].

Figure 1: Microsecond time-resolved dead time correction improves the linear response of spICP-MS and helps to expand particle size coverage [4].

Ingo Strenge

Appearances