Mass Spectrometry Flashcards

Flashcards based on the Instrument Technician Mass Spectrometry apprenticeship module.

What is mass spectrometry?

A technique that measures the atomic and molecular masses of atoms and molecules.

What three parameters of positively charged ions are measured in mass spectrometry?

Mass (m) of each ion, number of positive charges (z) on each ion, and the number of ions.

What is the purpose of mass spectrometers?

Analyze gas mixtures and determine their composition by identifying the names of the compounds (qualitative analysis) and finding the relative amount or concentration of each compound (quantitative analysis) in the gas mixture.

What do mass-to-charge ratio (m/z) values identify?

The original atom or molecule.

What is the function of the inlet system in a mass spectrometer?

Prepares the sample (clean, dry gas or vapor) to enter the high vacuum system of the analyzer.

What is the function of the ion source in a mass spectrometer?

Gives the gas molecules a positive charge and may also break the bonds of some of the ionized molecules, creating positively charged ion fragments.

What is the function of the mass analyzer section?

It separates the ions (including the fragments) according to their mass-to-charge (m/z) ratio.

What is the function of the ion detectors?

Detect the separated ions as weak electrical currents, which are then amplified. The detector signals are proportional to the number of ions hitting the ion detector.

What pressure must be maintained inside the mass spectrometer, and why?

Below 10^-6 mmHg; otherwise, air molecules interfere with the movement of the ions through the instrument.

What is the purpose of a roughing vacuum pump?

Reduces pressure from atmospheric pressure to about 0.1 mmHg when the instrument starts up, before the high vacuum system overtakes it.

What is the function of the data handling section?

Identifies the names of the sample compounds from their ion m/z ratios and calculates their concentrations from the detector signal currents.

List four types of mass analyzers used in process mass spectrometers.

Fixed magnetic sector deflection, variable magnetic sector deflection, quadrupole mass filter, and time-of-flight.

How does a fixed magnetic sector deflection analyzer work?

Incoming ions must all have the same velocity, achieved via a velocity selector, so that their trajectories through a magnetic field are affected based on mass. Detectors are at precise locations to detect different mass fragments.

How does a variable magnetic sector deflection analyzer work?

An electromagnet provides a variable magnetic field. By increasing the magnetic field, ions of increasing mass hit the detector.

How does a quadrupole mass filter work?

Applies direct current (dc) and high frequency alternating current (ac) voltages between each pair of connected rods or poles to filter ions with increasing m/z ratios to pass between the rods to the detector.

How does a time-of-flight mass spectrometer work?

Uses differences in transit time through a drift region to separate ions of different masses; lighter ions have a higher velocity than heavier ions, so they reach the detector in less time.

What is the function of a Faraday cup detector?

Measures process sample component concentrations in the range of 0.1% to 100%.

What is the function of a electron multiplier detector?

It can detects low concentrations found in environmental samples, typically 0.1% to ppm.

What is the purpose of a roughing pump?

To remove high volumes of air when first starting up, reducing pressure to about 0.1 mmHg.

What is the purpose of a high vacuum pump?

To remove the remaining traces of gas, reducing the pressure to its operating value of less than 10^-6 mmHg.

What are two common types of high vacuum pumps?

Turbomolecular pump and the ion pump.

What is the function of a turbomolecular pump?

The angle of the fast moving rotating blades directs gas molecules through the pump. Must exhaust into the inlet of a backing pump.

How does an ion pump work?

It ionizes gas molecules then captures and stores them on the metal walls of the pump.

What is the function of ionization vacuum gauges?

To monitor high vacuum (less than 10^-6 mmHg pressure).

What is the function of thermal vacuum gauges?

Monitor low vacuum from roughing vacuum pumps and pressure reduction during the initial start-up of a mass spectrometer to a lower limit of 10^-3 mmHg pressure.

In industrial applications, what do mass spectrometers perform and what is its purpose?

Rapid sample analysis; data can be used for process control by using one analyzer to provide data from multiple sample points.

What is a mass spectrum?

A plot of a mass spectrometer's detector output against the mass-to-charge ratio (m/z). It is like a unique fingerprint of the unknown compound which can be compared against those of known compounds.

What gases are typically monitored in hydrocarbon processing using mass spectrometers?

Hydrocarbon and inorganic gases (typically carbon dioxide, oxygen, nitrogen, and hydrogen sulfide).

What is measured during iron and steel production?

Gases above molten iron and steel, providing data to control quality and information on hydrogen content.

What is monitored in biotechnology applications?

Composition of gases above the liquids contained in fermenters and bioreactors.

What is commonly sampled when mass spectrometer is used for Environmental Applications?

Volatile organic compounds (VOCs) are carbon-containing chemicals that evaporate into the surrounding air, such as organic solvents and gasoline.

What range of gas mixture component concentrations do environmental mass spectrometers measure?

0.1% to 1 ppm.

What are two common stream selectors used with mass spectrometers?

Manifold systems and rotary stream selectors.

What is the purpose of purging and pressurizing the instrument enclosure?

Prevent the entry of flammable gas into the instrument enclosure.