Ultrafast tandem ICP mass spectrometer for interference-free and high-sensitivity monitoring of transient signals (ICP-MS/MS)

ICP mass spectrometry (ICP-MS) is a particularly powerful technique for the determination of elements at trace and ultrasonic levels. When using a quadrupole filter to separate the ions from each other according to their mass-to-charge (m/z) ratio, only modest mass resolution is obtained. Ions differing by less than half an atomic mass unit are not separated from each other, so spectral interference occurs. To avoid spectral interference, a tandem ICP-MS (ICP-MS/MS) device is equipped with a collision/reaction cell (CRC) preceded by a quadrupole filter (Q1). In an MS/MS mode, Q1 selects ions of a well-defined mass and admits them into the CRC. In the CRC, selective reaction(s) occur between the ions and the gas molecules. The second quadrupole filter (Q2) then selects at which m/z to measure finals.
On the one hand, the reaction(s) in the CRC may aim to remove the interfering ions so that on-mass (at the original mass of the analyte nuclide) can be measured. On the other hand, the analyte nuclide can also be involved in a reaction so that it can be measured as a reaction product ion interference-free at a different m/z.
This particular device is also characterized by a fast detection system with a minimum measurement time of only 0.2 ms. This makes the device extremely suitable for single-event applications. Where traditionally liquid samples or solutions are measured, single-event ICP-MS measures suspensions containing individual small entities. These entities are e.g. nanomaterial particles, cells or microplastics. Each time such individual particle enters the ICP, a cloud of ions is formed, which is observed as a short transient signal.
This technique is used e.g. for the determination of the particle concentration to and size of nanoparticles, the concentration of exogenous (e.g. from the use of a drug) and endogenous elements in individual (bacterial, plant, animal and human) cells (down to sub-femtogram level) and the particle concentration to and size of microplastic particles.