Time of Flight Mass Spectrometry (TOF MS)

Flashcards covering the key concepts of Time of Flight Mass Spectrometry (TOF MS), including the stages, ionization methods, equations, and important conditions.

Time of Flight Mass Spectrometry (TOF MS)

A technique used to identify elements by determining the isotopes present in a sample.

Conditions for Mass Spectrometry

Must be kept under a high vacuum to prevent ions from colliding with air molecules.

Electrospray Ionization

A method where a sample is dissolved in a volatile and polar solvent, injected at high pressure through a fine needle with a high voltage, causing the sample to gain a proton (H+) from the solvent.

Electrospray Ionization Equation

X(g) + H+(g) → XH+(g), where X is any molecule.

Use of Electrospray Ionization

Used for analyzing large organic molecules because it does not cause fragmentation.

Electron Impact Ionization

A method where a vaporized sample is injected at low pressure and bombarded with high-energy electrons, causing an outer electron to be knocked out and forming a 1+ ion.

Electron Impact Ionization Equation

X(g) → X+(g) + e-, where X is any element.

Use of Electron Impact Ionization

Used for elements and substances with low formula mass, as it causes fragmentation of larger molecules.

Acceleration Stage in TOF MS

Positive ions are accelerated to a constant kinetic energy by an electric field towards a negatively charged plate. Lighter ions travel faster.

Ion Drift and Detection

Positive ions pass through a hole in a negatively charged plate, forming a beam, and travel through the flight tube to a negatively charged detector. They gain an electron and produce a current.

Current Produced in Detection Stage

The amount of current produced is proportional to the abundance of the ion.

Data Analysis in TOF MS

Involves analyzing the current produced and the flight tube times to produce a spectra with relative abundance vs. mass charge ratios.

Kinetic Energy Equation

K = ½ mv², where K is kinetic energy (J), m is mass (kg), and v is velocity (m/s).

Time of Flight Equation

t = d/v, where t is time of flight (s), d is distance or length of flight tube (m), and v is velocity (m/s).

Unique Unit of Mass for TOF MS

Mass must be converted from grams to kilograms for calculations.