Spectrometry
NomenclCI ture
W e have compiled the following list of terms, their definitions, and abbreviations, which occur most frequently in papers on spectrometry. The list indicates our preferred usages in an attempt to obtain some consistency in a field where much discrepancy exists. Sources used in this compilation were: ASTM Committee E-1 3 on Absorption Spectroscopy (1 959 revision of tentative definitions); H. K. Hughes et a/. [ANAL. CHEM.24, 1 3 4 9 (1 9 5 2 ) 1; and Chemical Abstracts. Our advisory board members considered the terms and the following list includes their suggestions.
Absorbance, A .
( r o t optical density, absorbancy, or extinction.) Logarithm t o the base 10 of the reciprocal of the transmittance A = log10 (l/Z').
Absorptivity, a. (Not k.)
(Not absorbancy index, specific extinction, or extinction coefficient.) Absorbance divided by t h e product of the concentration of the substance (in g./l.) and the sample path length (in cm.), a = -A
be
C. (Not molar absorbancy index, molar extinction coefficient, or molar absorption coefficient.) Product of t h e absorptivity, a, and the molecular weight of the substance.
Absorptivity, Molar,
a.)
Angstrom, A.
(Not Unit of length equal t o 1/6438.4696 of wavelength of red line of Cd. For cm. practical purposes, it is considered equal to
Instrument with a n entrance slit and dispersing device t h a t uses photography to obtain a record of spectral range. T h e radiant power passing through the optical system is integrated over time, and the quantity recorded is a function of radiant energy.
Spectrograph.
Spectrometer, Optical. Instrument with a n entrance slit,
a dispersing device, and with one or more exit slits, with which measurements are made at selected wavelengths within the spectral range, or by scanning over t h e range. The quantity detected is a function of radiant power.
Branch of physical science treatin measurement of spectra.
Spectrometry.
Spectrometer with associated equipment, so t h a t i t furnishes the ratio, or-a function of the ratio, of t h e radiant power of two beams as a function of spectral wavelength. These two beams may be separated in time, space, or both.
Spectrophotometer.
2'. (Kot transmittancy or transmission.) T h e ratio of the radiant power transmitted by a sample to the radiant power incident on the sample.
(Representing Beer-Lambert law.) Absorptivity of a substance is a constant with respect t o changes in concentration.
Transmittance,
Quantity of the substance contained in a unit quantity of sample. (In absorption spectrometry i t is usually expressed in grams or moles per liter.)
Ultraviolet.
Beer's Law.
Concentration, c.
Frequency.
Number of cycles per unit time.
T h e region of the electromagnetic spectrum extending from approximately 0.78 to 300 microns.
Infrared.
Micron, p .
Unit of length equal to
Millimicron, mp.
of a micron. angstroms.
meter,
Unit of length equal t o one thousandth Almost b u t not exactly equal t o 10
(Not 1 or d.) Internal cell or sample length, usually given in centimeters.
Sample Path Length, b.
1968
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ANALYTICAL CHEMISTRY
the
The region of the electromagnetic spectrum from approximately 10 to 380 mp. The term without further qualification usually refers to the region from 200 to 380 mp.
Pertaining to radiant energy in the electromagnetic spectral range visible to the human eye (approximately 380 t o 780 mp).
Visible.
(One word.) The distance, measured along the line of propagation, between two points t h a t are in phase on adjacent waves-units A., mp, and p ,
Wavelength.
(One word.) Number of waves per unit length. The usual unit of wavenumber is the reciprocal centimeter, cm.-l I n terms of this unit, the wavenumber is the reciprocal of the wavelength when the latter is in centimeters in vacuo.
Wavenumber.
