A mass spectrometer measures atoms and molecules’ masses and relative concentrations. Triple Quadrupole ICP-MS is an analytical technique that uses charged particles’ mass-to-charge ratio to identify a compound’s chemical composition. Using electric and magnetic fields, a mass spectrometer sorts ions by their masses. A detector measures the value of some indicator quantity to calculate the abundances of each ion fragment present.
Mass spectrometers work by generating ions from a sample’s molecules. These ions are then accelerated by an electric field and then magnetized to determine their mass to charge ratio (m/z). Creating ions often breaks molecules into charged fragments that are unique to the original substance. The mass spectrum of the compound can then be used to identify each component qualitatively.
The ‘original molecule’ can be reconstructed using the fragment masses of the molecules.
The sample’s identity is determined by comparing the molecular mass’ and the’mass of fragments’ to reference data. It’s possible because each substance’s mass spectrum is unique, and the parent mass matches the output mass.
A mass spectrometer has a sample inlet, ionization source, ion accelerator, mass focuser, and detector. Advanced instruments use an energy filter before the mass focuser to achieve more precise mass assignments. However, due to space constraints, we will focus on the most basic mass spectrometer.
Samples admitted to a mass spectrometer must be in the vapor phase, so the sample inlet is kept above ambient temperature, sometimes as high as 400o C.
The steps below show:
Enter the ionization chamber, heat up, and gasify the sample.
- A high voltage accelerates an electron beam
- High voltage electrons ionize and shatter sample molecules (producing well-defined fragments)
- Each fragment is then sent to the accelerator as a “particle.”
- The accelerating voltage increases the velocities of charged particles in the acceleration chamber.
In the magnetic field, only ions with a specific charge to mass ratio can pass. The magnetic field varies to detect different masses, so all fragments reach the detector. It collides with the detector, amplifying the original signal and sending it to a computer for analysis.
The output is a chart with peaks called the mass spectrum’. Each ‘peak’ represents a fragment mass. The rise will be more intense if there are more fragments found with one mass.
Each substance has a unique mass spectrum under certain conditions. That is, comparing a specimen’s mass spectrum to known compounds can identify it. Quantitative analysis requires measuring the relative intensities of mass spectra.
The parent ion or molecular ion is the highest detected mass in the mass spectrum and represents the sample’s molecular weight. The mass spectrum’s other peaks reveal the molecule’s structure. Finding the parent peak and thus the sample’s molecular mass can be complex in mass spectrometer analysis.
Modern mass spectrometry relies on computer hardware and software for both instrument control and spectral analysis.