Handbook of ICP-QQQ Applications using the Agilent 8800 and 8900 (Primer)

Agilent Technologies launched its 8800 Triple Quadrupole ICP-MS (ICP-QQQ) at the 2012 Winter Conference on Plasma Spectrochemistry in Tucson, Arizona, USA. By the time the first ICP-QQQ was launched, ICP-MS had already been around for almost three decades and was widely praised for its low limits of detection. In fact, it was considered as the technique-par-excellence for multi-element (ultra-)trace analysis in a wide variety of fields. However, spectral interferences were still causing concern in some applications. Significant progress had been made in providing ICP-MS users with adequate tools to cope with spectral overlaps compared to the early commercial instruments introduced in 1983. By using a double-focusing sector-field mass spectrometer instead of a quadrupole filter for mass analysis, many spectral interferences can be resolved, but this approach requires expensive instrumentation. Quadrupole-based instruments could be equipped with a multipole-based collision/reaction cell (CRC), which alleviated spectral interferences to a significant extent, for instance, by using a non-reactive collision gas such as helium to slow down polyatomic interfering ions to a larger extent than the atomic analyte ions, such that the former could be selectively discriminated against on the basis of their lower kinetic energy. The analytical community first saw Agilent’s 8800 ICP-QQQ instrumentation as an improved version of a quadrupole-based ICP-MS equipped with a CRC. But the unique applications being performed using Agilent ICP-QQQ instruments installed in hundreds of laboratories across industry, research and academia clearly demonstrates that it is much more than that. In Agilent’s ICP-QQQ, an octopole CRC is preceded by an additional quadrupole, enabling double mass selection, i.e. before the ions enter the CRC and afterwards. When the first quadrupole is used as an ion guide only, the ICP-QQQ system can be used as a “traditional” quadrupole-based ICP-MS instrument. This mode could be useful for carrying out routine analysis not significantly challenged by spectral interferences. When operated in tandem or MS/MS mode, however, the double mass selection only allows the analyte ion and the interfering ion(s) with the same mass-to-charge ratio to enter the CRC; all ions with a different mass-to-charge ratio are removed at this stage. Consequently, the control over the processes in the cell is greatly improved as the reaction of other (e.g. matrix) ions with the cell gas no longer hinders the desired reaction process. In case of a mass-shift reaction—i.e. chemical conversion of the analyte ion into a reaction product ion that can be measured interference-free at another mass-to-charge ratio—the absence of other ions at the new “location” of the product ion in the mass spectrum is guaranteed. As a result, interesting but challenging elements, such as S and P in biochemical applications, As and Se in environmental and food applications, or Si in nanoparticle applications can be easily assayed, interference-free. Profiting from the analytical advantages offered by MS/MS functionality, some ICP-QQQ users have demonstrated a larger degree of creativity by using very reactive gases such as NH3 or CH3 F in the CRC and monitoring reaction product ions at much higher mass-to-charge ratios than could be adequately exploited previously. Although this might initially sound complicated, the ICP-QQQ’s software offers tools like product ion scanning, precursor ion scanning and differential mass scanning that provide the user with a clear insight into the reactions proceeding in the cell and allow the product ion that will provide the best, often unprecedented limits of detection to be easily identified. This level of freedom and ease of use leads to a situation in which every type of spectral overlap – whether caused by a polyatomic ion, doubly charged ion or isobaric nuclide – can be successfully overcome. Moreover, ICP-QQQ users have also been charmed by the additional advantages provided by this type of instrumentation, such as the unparalleled abundance sensitivity, which is an added benefit of double mass selection. In 2016, the 8800 ICP-QQQ was replaced by the Agilent 8900 ICP-QQQ series. While maintaining the performance to resolve spectral interferences, this second generation ICP-QQQ instrument provides enhanced sensitivity and a faster detector system with a 100 µs minimum dwell time. The latter feature is of specific importance in single-nanoparticle analysis, a rapidly emerging type of application, and in handling fast transient signals, such as those generated via laser ablation systems equipped with ultra-fast ablation cells. In my opinion, ICP-QQQ has not only fulfilled its initial promises, but has greatly surpassed the anticipations of the diverse community of ICP-MS users. Za odpiranje dokumenta
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