Mass spectrometers are instruments that can determine the type of molecules in a sample by creating ions from the molecules in the sample. These ions are then accelerated by an electric field and then pass through a magnetic field, which classifies them according to their mass-charge ratio (m / z).
Thus, the work of analysis consists of comparing the reference data of “molecular weight” and “weight of the fragment” to determine the identity of the sample. This is possible because the mass spectrum of each substance is unique if the original mass matches the output correctly, or vice versa.
The main description of an Agilent 7850 ICP-MS Instruments is that it contains a sample inlet, an ionization source, an ion accelerator, a mass focuser, and a detector. More sophisticated instruments also use some type of energy filter in front of the mass focuser for more accurate mass determination.
The samples entering the mass spectrometer must be in the vapor phase, so to ensure that the sample to be analyzed remains as a gas, the sample inlet temperature must be higher than room temperature and sometimes up to 400 ° C.
The following steps illustrate:
1. The sample enters the ionization chamber, heats up, and turns into a gas.
2. At high voltage, the electron beam accelerates.
3. Using high-voltage electrons, the sample molecules are ionized and destroyed (forming well-defined fragments).
4. Each fragment is then sent to the accelerator as a “separate particle.”
5. Under the action of the acceleration voltage, the velocities of the charged particles in the acceleration chamber increase.
6. The ions enter a magnetic field, which allows only those ions with a certain charge-mass ratio to pass through. To detect different masses so that all debris reaches the detector, the magnetic field is changed. The ion collides with the detector, amplifying the original signal, which is sent to the computer for processing and analysis.
The result is displayed as a peak matrix on the graph; this is called the “mass spectrum”. Each “peak” is equivalent to the mass of the fragment. The more fragments found with a specific mass, the more intense the peak will be.
Under certain controlled conditions, each substance has a characteristic mass spectrum. This means that a sample can be identified by comparing its mass spectra with the mass spectra of known compounds. Only then is quantitative analysis possible by measuring the relative intensity of the mass spectra.
The peak in the mass spectrum representing the unfragmented molecule is called the “major ion or molecular ion” and is the highest mass detected, representing the molecular weight of the sample being analyzed. However, it is the other peaks observed in the mass spectrum that reveal the structure of the molecule. Sometimes the most difficult part during mass spectrometry analysis is determining the main peak and therefore the molecular weight of the sample.