Characterization of Inductively Coupled Plasma Time-of-Flight Mass Spectrometry in Combination with Collision/Reaction Cell Technology–Insights from Highly Time-Resolved Measurements
There are two methods to reduce the contribution of interfering ions in inductively coupled plasma mass spectrometry (ICP-MS): high mass resolving power or collision/reaction cell technology. High mass resolving power (<10 000) is a feature of magnetic sector-field instruments, whereas collision/reaction cell technology is mostly applied in quadrupole-based instruments and facilitates interference reduction by either chemical reactions or kinetic-energy discrimination. icpTOF instruments combine both features; moderate mass resolving power and collision/reaction cell technology. This combination provides more flexibility in method design for a variety of challenging applications, such as detection of trace amounts of Fe, K, Ca.
In this paper, the capabilities of icpTOF instruments in combination with a collision/reaction cell technology are described for the first time. Application of H2, He, or the mixture of both were tested in standard and high-spatial-resolution laser ablation analysis and for the analysis of single microdroplets which simulate single nanoparticles.
The major findings of this study can be summarized as follows:
• Hydrogen can attenuate Ar+ ions to the level where the application of the notch filter becomes unnecessary. This improves the detection of neighboring ions, which are otherwise affected by the notching process.
• Selective suppression of Ar-based ions enables the detection of the most abundant isotopes of Ca and Se, significantly improving their detection limits. Detection limits of Ca and Se were improved by three and one order of magnitude, respectively.
• Application of flow rates <4 ml/min of H2, He, or the mixture of both gases enhances the sensitivity by a factor of 1.5-2 and mass resolving power by up to 16%. In this study, the instrument was tuned in standard mode and not retuned when applying the gas. The retune, however, might help to boost either the sensitivity or the mass resolution even further
• In LA experiments, quantification quality was not affected by utilization of the collision/reaction cell with a few exceptions
• Signal broadening observed with microdroplets was not the issue for the high-spatial-resolution LA analysis, which could still be performed at relatively high repetition rates