Česká společnost pro hmotnostní spektrometrii

(Česká konference hmotnostní spektrometrie 2023 - PL-1)
ICP-MS: the other mass spectrometry

Jan Kratzer ^1 *

1. Institute of Analytical Chemistry ASCR, v.v.i., Brno

Abstrakt

The aim of this lecture is to bridge the gap between the users and specialists in the field of organic mass spectrometry and the community working in inorganic (i.e. element) mass spectrometry employing the inductively coupled plasma mass spectrometry (ICP-MS) technique. ICP-MS is nowadays the most sensitive, multi-element and universal detector that allows detection of elements, especially metals, down to the pg·ml^-1 level. ICP-MS instrumentation has many similarities with organic mass spectrometers but it also shares many common features with other atomic spectrometric detectors used in trace element analysis. Analogously to other MS techniques, the ICP-MS consists of: 1) ion source, 2) mass analyzer and 3) the detector. ICP torch is the ion source realized by rf-driven (27 or 40 MHz) plasma sustained in argon at atmospheric pressure. This highly energetic plasma (8000 K, 1600 W) is responsible for atomization, excitation and finally ionization of analyte. The ions produced enter the low pressure environment of MS. They are separated according their mass to charge ratio (m/z) in a single quadrupole mass analyzer. Due to its low resolution (1 amu) strategies have been developed to avoid isobaric (on mass) interferences to distinguish between atomic ion of analyte and polyatomic ions as interferents having the same m/z, e.g. ⁷⁵As⁺ (analyte) versus ⁴⁰Ar³⁵Cl⁺ (interferent). For that purpose, the ICP-MS spectrometers are equipped with collision/reaction cells while their newest generation relies on triple quadrupole (ICP-MS/MS) configuration. The ions are subsequently detected by electron multiplier. Sample introduction is an inherent part of ICP-MS analysis affecting also the detector sensitivity. Like in other spectrometric detectors employed in element analysis liquid sample nebulization is the most common approach. Sample introduction efficiency is limited by the efficiency of the nebulizer (5-10%). Alternative approaches to sample introduction include solid sampling by laser ablation (LA) or gas phase sampling by vapor generation (VG). LA-ICP-MS is suitable for hard-to-degrade samples and enables also element imaging. VG-ICP-MS relies on selective analyte conversion from liquid to gas phase improving analyte introduction efficiency and decresing the risk of interferences due to matrix separation. Analysis of (metal) nanoparticles is also feasible by single particle (sp)-ICP-MS bringing information about their concentration and size distribution. ICP-MS is not only used to determine the total element content but it can be also applied to the speciation analysis, i.e. determination of different chemical species of the same element. Since ICP-MS is a ″destructive″ detector not preserving structure information about the species due to the atomization/ionization processes in the ICP torch, separation of the species by HPLC or GC have to precede their detection with speciation information derived from retention times. Applications of ICP-MS to trace element and speciation analysis in environmental and clinical samples will be discussed. Examples from the fields of metallomics will be demonstrated where both organic and inorganic MS can be combined as HPLC detectors to receieve simultaneously information on structure (ESI-MS) and ultratrace metal content (ICP-MS) in metalloproteins.

* Korespondující autor: jkratzer@biomed.cas.cz

Poděkování:

This work has been supported by the Czech Academy of Sciences, Institute of Analytical Chemistry (Institutional Research Plan no. RVO: 68081715).