Mass spectrometry is used to evaluate sequence biomolecules, combinatorial libraries and help in exploring single cells or objects from space. It is an essential analytical tool in biochemistry, chemistry, medicine, pharmacy, and many other scientific fields.
What Is Mass Spectrometry
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Mass spectrometry is an analytical technique used to calculate the charge-to-mass ratio of one or more molecules in a sample. These types of measurements are frequently used for calculating the exact molecular mass of the sample components.
With mass spectrometry, you can analytically find out the molecular mass of a compound and indirectly contribute to the identification of the isotopes. The environmental and forensic analyses, structure explanation of unknown substances, quality control of foods, drugs, and polymers all rely on mass spectrometry to a great extent.
Principle of Mass Spectrometry
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A mass spectrometer produces multiple ions from the sample undergoing investigation, separates them based on their specific mass-to-charge ratio (m/z), and records the relative abundance of each type of ion.
In the very first step of mass spectrometric analysis of compounds, the gas phase ions of the compound are generated primarily through electron ionization. This molecular ion gets fragmented. After that, each primary production obtained from the molecular ion is fragmented in turn and so on. In the mass spectrometer, ions are separated based on their mass-to-charge ratio and detected in proportion to their abundance. As a result, the molecule’s mass spectrum is generated.
Mass Spectrometry Instrumentation
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The primary components of the mass spectrometry instrumentation are as follows:
Sample Inlet: Samples are gradually streamed into the ionization chamber at low pressure through a pinhole called “molecular leak”.
Ionizer: In an ionizer, positively charged ions are generated by bombarding the samples with a beam of electrons. The electrons in the ionizer pass between cathode and anode. When the sample moves through the stream of electrons between the cathode and anode, the high-energy electrons knock out the electrons from the sample and result in the formation of ions.
Accelerator: In this component, the positively charged sample ions move through three slits having voltages in decreasing order. Acceleration ensures that the kinetic energy of all the ions is the same.
Deflector: The applied magnetic field deflects the ions due to mass differences. An ion is least deflected if it is heavy or has two or more positive charges and most deflected if it is light or has only one positive charge.
Detector: The ions which have the correct mass and charge move to the detector. And the ion that hits the detector is used to analyse the mass-to-charge ratio.
Working of Mass Spectrometry
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Following steps are involved in the working of the mass spectrometry.
Step 1: First, the sample is ionized in the gas phase.
Step 2: Then, the sample ions are accelerated through an electric field. After acceleration, all the ions emerge with a velocity proportional to their mass-to-charge ratio.
Step 3: The ions move into a field-free region.
Step 4: After that, the ions get deflected by a magnetic field.
Step 5: Finally, ions are moved through the mass analyser which determines the arrival time of the sample ions and records the mass spectrum.
Applications of Mass Spectrometry
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There are numerous applications of mass spectrometry. Whether in pure or applied research, mass spectrometry is used for both qualitative and quantitative analysis of macromolecules and low molecular weight compounds in almost every discipline of science. Given below are some of the most important applications of mass spectrometry.
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Determination of the molecular mass of biomolecules like proteins, carbohydrates, and nucleic acids.
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Determination of biopolymer sequences such as nucleic acids, oligosaccharides, and polypeptides.
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To determine the structure of a protein.
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Identification of elements and their isotopes.
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Testing toxins and pesticide residues in food.
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Analysing air, water, and soil quality to monitor the environment and climate change.
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Observing patients’ metabolic gas exchange during surgery.
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Determining the composition of rock and soil and carbon dating of samples.
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Analysis of quality control in the chemical and petrochemical industries.
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Research on particles in aerosols such as perfumes.
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Determination of drug abuse cases by analysing drug abuse metabolites in saliva, urine, and blood.
Advantages of Mass Spectrometry
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It utilizes a small sample size.
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It is faster.
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It is capable of differentiating isotopes.
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It is extremely sensitive ( parts per million)
- It is the perfect tool to identify the presence or absence of a substance in a given sample.
Limitations of Mass Spectrometry
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- It does not offer direct structural information and cannot tell apart between optical and geometric isomers.
- It requires pure samples.
- It is not suitable for non-volatile compounds and cannot be used to identify hydrocarbons.
Things To Remember based on Mass Spectrometry
- Mass spectrometry is an analytical technique used to calculate the mass-to-charge ratio of one or more molecules in a sample.
- It is useful in the environmental and forensic analyses where the structure explanation of unknown substances can be done.
- A mass spectrometer is extremely sensitive and uses a small sample to identify the substances.
- Mass spectrometers cannot be used for the detection of hydrocarbons and structural isomers.
Sample Questions based on Mass Spectrometry
Ques. Explain the basic principle of mass spectrometry. (2 marks)
Ans. A mass spectrometer produces multiple ions from the sample undergoing investigation, separates them based on their specific mass-to-charge ratio (m/z), and records the relative abundance of each type of ion.
Ques. How are samples converted into ions in Mass Spectrometry? (5 marks)
Ans.
- Electronic Ionization: The sample is hit by a high-energy electron beam. When an electron collides with a sample molecule, it removes an electron from the molecule, resulting in the formation of a cation.
- Chemical Ionization: An ionised reagent gas is mixed with the sample molecules. The collision between the sample molecules and ionized reagent gas ionizes the latter by proton transfer, electron transfer, and adduct formation.
- Electrospray Ionization: The sample is dissolved in a polar, volatile solvent and dispersed electrostatically through a narrow capillary, resulting in an aerosol of droplets that are highly positively charged.
- Desorption Ionization: In this, the sample is dissolved in an appropriate matrix. A sample is ionised using the short laser light pulse and then released into a vacuum system from the matrix for further analysis.
Ques. Describe the role of mass accuracy in mass spectrometry. (2 marks)
Ans. The difference between the measured mass/charge of an ion and that it's true, exact m/Q is defined as mass precision. For each of the three input calibration ions, the DAQ records mass accuracy in parts per million (ppm).
Ques. What is the importance of mass spectrometry? (2 marks)
Ans. Mass spectrometry is a technique for determining the mass of ions (electrically charged particles), molecules, or atoms formed from them. It is used to explain fundamental atomic and molecular processes as well as immediate interest in cell events.
Ques. Name the type of radiation used in mass spectrometry? (2 marks)
Ans. Photoionization can be used in experiments that use mass spectrometry to solve chemical kinetics processes and isomeric materials branching. In these types of cases, a high-energy photon either UV or X-ray is used to separate stable gaseous molecules from Argon or Helium carrier gas.
Ques. Why is the particle first ionized in a mass spectrometer? (2 marks)
Ans. Mass spectrometry accurately measures the mass of different molecules within a sample. and to do so, it turns the atoms into ions (electrically charged atoms with either too few or too many electrons). Then it separates the ions, bypassing them first through an electric field, then through a magnetic field, so they fan out into a spectrum. A computerized detector tallies the ions in different parts of the spectrum and you can use this information to figure out what kinds of atoms were originally in the sample.
So, in working with a mass-spectrometer, ionization is the first step.
Ques. What are some of the applications of mass spectrometry? (3 marks)
Ans.
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Determination of the molecular mass of biomolecules like proteins, carbohydrates, and nucleic acids.
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Determination of biopolymer sequences such as nucleic acids, oligosaccharides, and polypeptides.
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To determine the structure of a protein.
-
Research on particles in aerosols such as perfumes.
-
Determination of drug abuse cases by analysing drug abuse metabolites in saliva, urine, and blood.
Ques. What are some of the limitations of mass spectrometry? (2 marks)
Ans.
- It does not offer direct structural information and cannot tell apart between optical and geometric isomers.
- It requires pure samples.
- It is not suitable for non-volatile compounds and cannot be used to identify hydrocarbons.
Ques. What is the use of ionizer in mass spectrometry? (2 marks)
Ans. In an ionizer, positively charged ions are generated by bombarding the samples with a beam of electrons. The electrons in the ionizer pass between cathode and anode. When the sample moves through the stream of electrons between the cathode and anode, the high-energy electrons knock out the electrons from the sample and result in the formation of ions.
Ques. Describe the working of mass spectrometry? (3 marks)
Ans. Step 1: First, the sample is ionized in the gas phase.
Step 2: Then, the sample ions are accelerated through an electric field. After acceleration, all the ions emerge with a velocity proportional to their mass-to-charge ratio.
Step 3: The ions move into a field-free region.
Step 4: After that, the ions get deflected by a magnetic field.
Step 5: Finally, ions are moved through the mass analyser which determines the arrival time of the sample ions and records the mass spectrum.
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