ctrornetry Nomenclature W e have compiied the following list of terms, their definitions, and abbreviations, which occur most frequently in papers The list indicates our preferred usages in an attempt to obtain some consistency in a field where much i§crepan~yexists. Sou d in this compi(ationwere: ASTM Committee E-1 3 on Molecular Spectroscopy (1 966 revision wghes et a?. [Anal. Chem., 24, 1 3 4 9 (1 9 5 2 ) ] ; and Chemical Abstracts. This list is approved of the ACS Division of Analytical Chemistry.
om spectrometry.
~ b s o r b ~ n cAe .~ (Kot optical density, absorbancy, or extinction.) Logarithm to the base 10 of the reciprocal of the transmittance A = log,, ( l / T ) .
or^^^^^^^^ a.
(Not k ) . (Not absorbancy index, specific extinction, or extinction coefficient.) Absorbance divided by the product of the concentration of the substance and the sample path length,
a = -A bc
olar, E. (Not molar absorbancy index, tion Coefficient, or molar absorption coefficient.) Product of the absorptivity, a, and the molecular weight of the substance. Knit of length equal t o 1/6438.4696 of of red line of Cd. For practical purposes, it is considered equal to cm. eer’s Law. (Representing Beer-Lambert law.) Absorptivity of a substance is a constant with respect to changes in concentration. o ~ c e n ~ r ~ t ~c.o nQuantity , of the substance contained in ti unit quantity of sample. (In absorption spectrometry it is usually expressed in grams per liter.) ~
~
q
Number ~ e nof cycles ~ ~per ~unit time.
fared. The region of the electromagnetic spectrum extending from approximately 0.78 to 300 micrometers. equal t o 10-6 meter. ~ ~ ~ o p m~. ~Unit t eof ~length , (Do not use micron.) a ~ o ~ e nm. ~ ~ rEnit , of Jength equal t o (Do not use millimicron.)
meter.
ath Length, 6. (Not I or d.) Internal cell or sample length, usually given in centimeters.
P
ures
Spectrograph. Instrument with a n entrance slit and dispersing device t h a t uses photography t o obtain a record of spectral range. The radiant power passing through the optical system is integrated over time, and the quantity recorded is a function of radiant energy. Spectrometer, Optical. Instrument with an 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 the range. The quantity detected is a function of radiant power. Spectrometry. Branch of physical science treating the measurement of spectra. Spectrophotometer. Spectrometer with associated equipment, so that it furnishes the ratio, or a function of the ratio, of the radiant power of two beams as a function of spectral wavelength. These two beams may be separated in time, space, or both. Transmittance, 2’. (Iiot transmittancy or transmission.) The ratio of the radiant power transmitted by a sample t o the radiant power incident on the sample. Ultraviolet. The region of the electromagnetic spectrum from approximately 10 to 380 nm. The term without further qualification usually refers to the region from 200 t o 380 nm. Visible. Pertaining to radiant energy in the electromagnetic spectral range visible to the human eye (approximately 380 to 780 nm). Wavelength. (One word.) The distance, measured along the line of propagation, between two points that are in phase on adjacent waves-units k ,pm, and nm. Wavenumber. (One word.) Number of waves per unit length. The usual unit of wavenumber is the reciprocal centimeter, cm.-’ I n terms of this unit, the wavenumber is the reciprocal of the wavelength when the latter is in centimeters in vacuo.
recision an
ccuracy
It is important to know what an author means when he writes of precision and accuracy. The following definitions are applicable when one operator provides a series of test results and no prior information on the method i s used. They are endorsed YTlCAL CHEMISTRY-after careful study by members of its Advisory Board and on advice of qualified statistkiansssted when results reported are suitable for statistical treatment (based on 5 or more determinations). Series. A number of test results which possess common properties that identify them uniquely. an. The sum of a series of test results divided by the numer in the series. Arithmetic mean is Understood. cision Data. Measurements which relate to the variation among the test results themselves-i.e., the scatter or dispersion of a series of test results, without assumption of any prior information. The following measures apply: VARIANCE. The sum of squares of deviations of the test results from the mean of the series after divisions by one less than the total number of test results. ~ T A N D A R DDEVIATION. The square root of the variance. RELATIVE STANDARD DEVIATION.The standard deviation of a series of test results as a percentage of the mean of
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0
ANALYTICAL CHEMISTRY, VOL. 42,
this series. This term is preferred over “coefficient of variation.” RANGE.The difference in magnitude between the highest test result and the lowest test result in a series. Accuracy Data. Measurements which relate to the difference between the average test results and the true result when the latter is known or assumed. The following measures apply: ME~N ERROR. The average difference with regard to sign of the test results from the true results. Also equal to the difference between the average of a series of test results and the true result. RDLATIVE ERROR. The mean error of a series of test results as a percentage of the true result.
NO. 14, DECEMBER 1970
