1. Scope
1.1 This test method covers the measurement of the ultraviolet absorption of a variety of petroleum products. It covers the absorbance of liquids or the absorptivity of liquids and solids, or both, at wavelengths in the region from 220 to 400 nm of the spectrum.
1.2 The use of this test method implies that the conditions of measurement - wavelength, solvent (if any), sample path length, and sample concentration - are specified by reference to one of the examples of the application of this test method in the annexes or by a statement of other conditions of measurement.
1.3 Examples of the application of this test method are the determination of the absorbance of white mineral oil, the absorptivity of refined petroleum wax, and the absorptivity of USP petrolatum.
1.4 The values stated in SI units are to be regarded as the standard. The values stated in Fahrenheit, feet, and inches, indicated in parentheses, are for information only.
1.5 Warning - Mercury has been designated by EPA and many state agencies as a hazardous material that can cause central nervous system, kidney, and liver damage. Mercury, or its vapor, may be hazardous to health and corrosive to materials. Caution should be taken when handling mercury and mercury-containing products. See the applicable product Material Safety Data Sheet (MSDS) for details and EPA's website for additional information. Users should be aware that selling mercury or mercury-containing products, or both, in your state may be prohibited by state law.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warning statements, see 7.3.1, 7.3.3, and 13.4.
2. Referenced Documents
2.1 ASTM Standards:
D1193 Specification for Reagent Water
E 131 Terminology Relating to Molecular Spectroscopy
E 169 Practices for General Techniques of Ultraviolet-Visible Quantitative Analysis
E 275 Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
3. Terminology
3.1 Definitions of terms and symbols relating to absorption spectroscopy in this test method shall conform to Terminology E 131. Terms of particular significance are the following:
3.2 Definitions:
3.2.1 radiant energy, n - energy transmitted as electromagnetic waves.
3.2.2 radiant power, P, n - the rate at which energy is transported in a beam of radiant energy.
3.2.3 transmittance, T, n - the molecular property of a substance that determines its transportability of radiant power, expressed by:
where:
P = the radiant power passing through the sample and
Po = the radiant power incident upon the sample.
3.2.4 absorbance, A, n - the molecular property of a substance that determines its ability to take up radiant power, expressed by:
A = log10(1/T) = -log10T
where T is the transmittance as defined in 3.2.3.
3.2.4.1 Discussion - Absorbance expresses the excess absorption over that of a specified reference or standard. It is implied that compensation has been affected for reflectance losses, solvent absorption losses, and refractive effects, if present, and that attenuation by scattering is small compared with attenuation by absorption.
3.2.5 dilution factor, f, n - the proportion of solvent increase made to reduce the concentration and thus the absorbance of a solute, expressed by the ratio of the volume of the diluted solution to the volume of original solution containing the same quantity of solute as the diluted solution.
3.2.6 absorptivity, a, n - the specific property of a substance to absorb radiant power per unit sample concentration and path length, expressed by:
a = Af/bc
where:
A = the absorbance defined in 3.2.4,
f = the dilution factor defined in 3.2.5,
b = sample cell path length, and
c = the quantity of absorbing substance contained in a volume of solvent.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 sample cell pathlength, b, n - the distance in centimetres, measured in the direction of propagation of the beam of radiant energy, between the surface of the specimen on which the radiant energy is incident and the surface of the specimen from which it is emergent.
3.3.1.1 Discussion - This distance does not include the thickness of the cell in which the specimen is contained.
3.3.2 concentration, c, n - the quantity of absorbing substance in grams per litre.