Glossary

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A

Angstrom

An angstrom (A) is one ten millionth of a meter (10-10m). An angstrom is an non SI unit that is still in use as it is approximately the size of an hydrogen atom.

See also angstroms(10^-10 m), centimeters (10^-2m), millimeters (10^-3m), micrometers (10^-6m), nanometers (10^-9m).

Atom % - Mass Spectrometry

The Atom percent is the relative abundance of one isotope relative to the sum of all the isotopes.

E.g. for N with the 15N and 14N isotopes, the natural abundance of the isotopes in air is, atom% 15N = 0.366 and atom% 14N = 99.634.

See also: Atom % MS, Atom % Excess MS, Delta.

Atom % - X-ray Analysis

This is the molar ratio between the elements expressed as a percentage.

E.g. for H₂O the atom% H = 66%, and the weight% H = (2 / (16+2)) *100 / 1 = 11%

Atom % Excess MS

The atom% excess is the amount of that isotope in excess of the chosen standards isotope atom% concentration. E.g. for a compound with an atom% 15N 0.4660 it would be 0.1 atom% Excess compared to natural abundance of 0.366 atom% 15N.

See also: Atom % MS, Atom % Excess MS, Delta.

Atomic Mass / Weight

The atomic mass is the mass of an isotope relative to the mass of the Carbon 12 (12C) Isotope which by definition has an amu of 12. The atomic weight used in a periodic table is generally the average of the mass of the elements natural abundance isotopes. In mass spectrometry this unut is also referred to as a Dalton.

Atomic Mass Number (A)

The atomic mass number is the sum of the number of protons and neutrons within an atom.

Atomic Number (Z)

The atomic number is the number of protons within an atom.

B

Backscattered Electron

A backscattered electron is an electron that originates from the elastic scattering of the primary electron beam after it interacts with the sample. These electrons by definition have energies greater than 50eV, and the number of BE's produced is related to the average atomic number of the atom, the sample density, and depending on detector configuration and geometry to topography at the point of the electron beam impact.

C

Carbon

Carbon has three isotopes, the more common 12C and the minor isotope 13C and 14C. Carbon 12 contains 6 protons and 7neutrons, while Carbon 13 is slightly heavier with 6 protons and 7neutrons and Carbon 14 is heavier again with 6 protons an 8 neutrons. Importantly all there have the same electron orbital structure and hence they will behave the same chemically. The natural abundances are 13C = 1.1080 Atom % ; 12C = 98.8920 At% and 14C = 1e-10 At %. In Pee Dee Belemnite (Vienna PDB - a standard reference material) the isotope abundances are 13C = 1.1112 At% 12C = 98.8888. Carbon 12 and Carbon 13 are stable isotopes, while Carbon 14 is radioactive.

See also Carbon, Nitrogen, Oxygen, Sulfur.

Centimetre

A centimetre (cm) is one hundredth of a meter (10-2m).

See also: angstroms(10^-10 m), centimetres (10^-2m), millimetres (10^-3m), micrometres (10^-6m), nanometres (10^-9m).

D

Delta

A measure of isotopic abundance, defined as a ratio of the isotopic abundances to the ratio of a predefined isotopic standard. A delta of zero means that the sample has the same isotopic abundances as the standard; a positive delta means that the sample is enriched relative to the standard and a negative value is depleted relative to the standard.

The delta is a dimensionless unit and is sometimes termed “per mil” as it is a small difference multiplied by 1000.

Delta = 1000 ( ( (%Minor Isotope/ %Major Isotope)Sample / (%Minor Isotope / % Major Isotope) Standard ) – 1 )

See also: Atom % MS, Atom % Excess MS, Delta.

E

Electron

An electron is fundamental particle of negative charge. The amount of electrons moving is proportional to the electric current; and the energy of an electron as it moves is proportional to the voltage.

F

G

H

I

Isotope

Isotopes are an atom that has the same number of protons, but a different number of neutrons. Since the numbers of protons within the isotopes are the same, then the electron structure will also be the same, and hence they will exhibit the same chemical behavior. However because of the differences in mass between isotopes, which is a consequence of the different number of neutrons, there may be different degrees of isotopic fractionation associated with chemical and biological processes. The degree of fractionation can be measured and used to identify what processes are occurring.

Stable Isotopes - are isotopes that do not undergo radioactive decay.

Radioactive Isotopes - under go some form of radioactive decay.

J

K

L

M

Mass to Charge Ratio

The mass to charge ratio (m/Q) is the ratio of the molecular mass of an ion to the charge of the ion, the unit of mass to charge is kg/coulomb. The mass to charge ratio is used in many areas of physics involving ions.

In Mass Spectrometry the ratio m/z is often used as the M to C ratio, where m is the mass of the ion and z is the charge number of the ion. An N2 molecular ion with a charge of +1 would have and m/z ratio of 28.

Micrometer

A micrometer (um) is millionth of a meter (10-6m), or if you prefer one thousandth of a millimeter. A red blood cell for a human is on average about 7 micrometers in diameter and bacteria about 2 micrometers.

See also angstroms(10^-10 m), centimeters (10^-2m), millimeters (10^-3m), micrometers (10^-6m), nanometers (10^-9m).

Millimeter

A millimeter (mm) is one thousandths of a meter (10-3m). A human hair is about 0.1 millimeters in diameter.

See also angstroms(10^-10 m), centimeters (10^-2m), millimeters (10^-3m), micrometers (10^-6m), nanometers (10^-9m).

N

Nanometer

A nanometer (nm) is one thousandth millionth of a meter (10-9m). Viruses have diameters approximately 10 to 100’s of nanometers in size.

See also angstroms(10^-10 m), centimeters (10^-2m), millimeters (10^-3m), micrometers (10^-6m), nanometers (10^-9m).

Neutron

A neutron is a fundamental particle of zero charge, which makes up part of the nucleus of an atom. The mass of a neutron is approximately equal to that of the sum of the masses of a proton and an electron.

Nitrogen

Nitrogen has two isotopes, the more common 14N and the minor isotope 15N. Nitrogen 14 contains 7 protons and 7 neutrons, while Nitrogen 15 is slightly heavier with 7 protons and 8 neutrons. Importantly both have the same electron orbital structure and hence they will behave the same chemically. The natural abundances in air which is also a standard refernce material are 15N in air is 0.3663 Atom % ; 14N 99.6337 Atom %.

See also Carbon, Nitrogen, Oxygen, Sulfur.

O

Oxygen

Oxygen has three isotopes, the more common 16O and the minor isotope 17O and 18O. Oxygen 16 contains 8 protons and 8 neutrons, while Oxygen 17 has 8 p 9n and Oxygen 18 has 8 protons and 10 neutrons. Importantly all have the same electron orbital structure and hence they will behave the same chemically. The natural abundances are 16O = 99.7590 Atom % ; 17O = 0.0374 At% and 18O = 0.2039 At %. Oxygen 16, 17O and 18O are stable isotopes.

See also Carbon, Nitrogen, Oxygen, Sulfur.

P

Proton

A proton is a fundamental particle of positive charge, which makes up part of the nucleus of an atom.

Q

R

S

Secondary Electron

A secondary electron is an electron that originates from the inelastic scattering of the primary electron beam after it interacts with the sample. These electrons by definition have energies less than 50eV, and the number of SE's produced is related to the number of electrons in the outer shell of the atom and the local topography at the point of the electron beam impact.

Sulfur

Sulfur has five isotopes, the more common 32S and the minor isotope 33S, 34S, 35S and 36S. Sulfur 32 contains 16 protons and 16 neutrons, while 33S has 16p 17n, 34S has 16p 18n, 35S has 16p 19n and 36S has 16p 20n. Importantly all have the same electron orbital structure and hence they will behave the same chemically. The natural abundances are 32S = 95.0180 Atom % ; 33S = 0.76 At%, At% 34S = 4.2150 At%, 35S = synthetic, 36S = 0.0140 At %. Sulfur 32, 33S, 34S and 36S are stable isotopes, while Sulfur 35 is radioactive.

See also Carbon, Nitrogen, Oxygen Sulfur.

T

U

V

W

Weight Percent - X-ray Analysis

The weight percent of an element (or compound i.e. H₂O) is the percentage weight, of one element in a compound, relative to the sum of the weights of all the elements in that compound.

E.g. for H₂O the atom% H = 66%, and the weight% H = (2 / (16+2)) *100 / 1 = 11%

X

Y

Z

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