How Does a Mass Spectrometer Work?
Mass spectrometry, often abbreviated to mass spec, is a technique used to accurately determine the mass of different molecules in a sample. A mass spectrometer is a device used to perform this measurement.
The first mass spectrometer was built in 1912 by J.J. Thomson. Originally called a parabola spectrograph, the device was used to provide definitive evidence of nonradioactive isotopes.
Through the years, the mass spectrometer has become one of the most useful devices found in most labs. It has been used to produce dozens of scientific breakthroughs. Without it, we would not have discovered isotopes, precise atomic weights, and the characterization of molecular structure. It is used in virtually every scientific field and industry.
What is a Mass Spectrometer?
Since that very first device, different types of mass spectrometers have been developed to address a wide variety of scientific research. Specifically, a mass spectrometer is any device that produces a mass spectrum read-out by measuring the individual mass spectra in a sample. Today, mass spectrometers are commonly used in life science research to analyze peptides, amino acids, and proteins. Mass spectrometers are also used to facilitate DNA sequencing and analyze intact viruses. They are used in environmental science labs, forensic labs, drug manufacturing facilities, and cosmetic research.
What Does a Mass Spectrometer Measure?
Mass spectrometers detect the speed at which positively charged ions move through a vacuum chamber toward a negatively charged plate. The speed of the ions is determined by the weight. This process allows researchers to apply analytical techniques to determine the composition of the sample.
For example, using a mass spectrometer, a researcher might analyze a blood sample to find out if a person has lead poisoning or test a water source for contamination. The versatility of this device offers unlimited uses, making it one of the most common lab devices used by scientists all over the world.
How a Mass Spectrometer Works
While there are many variations on methods used to accomplish the steps, there are just three basic components to mass spectrometry: an ion source for ionizing the sample, a magnetic sector to separate the ionized particles by mass-to-charge ratio (m/z), and an ion detector plate.
1. Molecule Ionization
A sample material is often vaporized (heated to a gas phase) or combined with a matrix material. Sample molecules are ionized using an ion source such as a chemical or electrospray ionization, or an electric field. This produces charged ions.
2. Acceleration and Deflection
The charged ions retain kinetic energy. The sample is moved into a vacuum chamber and the positive ions react by moving toward a negatively charged detector plate. The detector plate is also called an electron multiplier. How fast the ions move/their speed is determined by the molecular mass of positive ions. Deflection is accomplished using a magnetic field and the deflection rate also depends on mass.
As the ions move through the chamber, the mass analyzer records the speed and relative abundance of ions to produce a visual read-out or mass spectrum. Different compounds in the sample will have a different mass. The readout enables researchers to determine the composition of a sample by comparing the results to known elements.
Types of Mass Spectrometers
There is a large variety of mass spectrometers on the market today, each employing different methodologies to achieve results based on the type of materials being analyzed. Here are a few of the most common mass spectrometers available, but certainly not the only variations or configurations.
Liquid Chromatography Mass spectrometry (LC–MS)
LC-MS combines two scientific techniques. Liquid chromatography is used to separate mixtures containing various compounds, and mass spectrometry then identifies the structural identity of the individual components by analyzing their molecular weight with high specificity and detection sensitivity. This dual approach can be used to analyze biochemical, organic, and inorganic compounds. Due to the versatility of the combined technique, LC-MS is used in a wide variety of applications, including food analysis, environmental testing, biotechnology, pharmaceutical analysis, and cosmetic development.
Gas Chromatography Mass Spectrometry (GC-MS)
GC-MS is an analytical technique used to separate, quantify, and identify volatile organic compounds such as benzenes, alcohols and aromatics, and simple biomolecules that include steroids, fatty acids, and hormones.
The GC-MS method begins by vaporizing the sample to a gas phase and separating components with a capillary column. An inert carrier gas such as nitrogen or argon is used to propel the resulting compounds. As they separate, the compounds elute from the column at different times. The time it takes to elute is called retention time.
When the compounds detach from the column, they are ionized with electron or chemical ionization sources and accelerated through the mass spectrometer analyzer, typically a quadrupole or ion trap. The mass-to-charge ratios, or m/z values, of the ions are detected and measured to produce a mass spectrum read-out. Researchers identify the individual compounds in the sample using a known mass of compounds and analytes.
Triple Quadrupole Mass Spectrometer (TQMS)
A dual mass spectrometer with two quadrupole mass analyzers works in tandem sequence. Between them, a (non-mass-resolving) radio frequency (RF) quadrupole acts as a buffer for collision-induced dissociation. Coupling two mass analyzers in tandem improves sensitivity, resolution, and mass accuracy.
The TQMS configuration, also known as the QqQ configuration (Q1 and Q2 are the mass filters and q is the collision cell/buffer) is designed to perform four different scans: a precursor ion scan, neutral loss scan, product ion scan, and selected reaction monitoring. Though the mass resolution and mass range isn’t the best available, it is affordable, efficient, and easy to use.
The TQMS method is most commonly used for drug metabolism, pharmacokinetics, environmental studies, and biological analyses.
Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS)
MALDI-TOF MS is a combination of two highly effective techniques to analyze and identify large molecules without destroying fragile organic molecules such as polymers and dendrimers.
Using MALDI methodology, a sample is mixed with a matrix material and spread on a metal plate. Laser pulses are used to irradiate the sample, which causes ablation and desorption of the sample and matrix substance. The analyte molecules are then ionized using electrospray ionization. The sample molecules are accelerated into a TOF MS (Time-of-Flight Mass Spectrometry) to be analyzed.
TOF MS employs a technique to measure the molecular weight of a substance. An electric field charges the ions, then they are released in a vacuum chamber. The ions retain a kinetic energy charge, which accelerates the ions toward a detector. Mass is calculated by the speed with which the atoms reach the detector. Lighter ions travel more quickly. TOF MS provides a highly accurate mass weight measurement.
Cost to Buy Mass Spectrometers
Depending on your needs and purposes, purchasing a mass spectrometer for your lab can be alarmingly expensive. Units can range from under $10,000 to nearly $100,000. If you’re working on a budget, this one piece of essential equipment can really break the bank. This is why you should consider leasing your lab equipment.
Leasing vs. Buying a Mass Spectrometer
Leasing expensive lab equipment is a workable and economic solution to fully equip your lab quickly and with minimal expense. With leased equipment, you’re assured of a high-quality mass spectrometer for a fraction of the purchase price. With our equipment, you won’t blow through your lab funding before you get started, and you’ll have a bigger budget left over for staff and operating costs.