ASTM D 2743-2010 Determination of Uniformity of Solid Paints for Road Sign Paints by Spectrophotometry and Gas Chromatography

Meaning and Purpose
All the methods provided involve a comparison between the spectra or chromatograms of the control and test samples to determine if they show significant differences. Quantitative limits cannot be established to guide whether spectral or chromatographic differences are truly significant. Of course, it is important to test for the presence of moderate or strong peaks in the sample, which are not evident in the reference. There is a significant difference in the ratio of the two peaks of a spectrum compared to the reference sample. In summary, some judgments need to be made in this regard, and it is recommended to refer to published IR or gas chromatographic data in order to determine, where feasible, the likely overall nature of the dopants or their functional groups that may lead to different comparative spectra.

Method A is fast and the most convenient of the procedures given. It should first be used to detect the inhomogeneity of the test sample. A significant spectral difference from the reference sample can be seen as an indication of adulteration, in which case no other method is required. As a general rule. Method A is sufficient to detect severe or severe adulteration of carrier solids. However, if Method A does not show significant spectral differences, it cannot be assumed that the test samples are fully acceptable because variations in dry oils, polyols, and certain diacid types in alkyd resins, addition of certain aliphatic or nonfunctional hydrocarbon resins, and many minor adulterations may not always show characteristic IR spectral differences. Therefore, in this case, it is recommended to follow the other tests given in methods B and C, or to proceed directly to Method D.

ASTM D 2743-2010 Determination of Uniformity of Solid Paints for Road Sign Paints by Spectrophotometry and Gas Chromatography

Method B can be used to detect the adulteration of an unsaponifiable substance, or an adulteration with an unsaponifiable component that escapes detection in Method A only because the amount of the adulterant may be so small that its powerful spectral peak may have been masked by the rest of the carrier solids. Care should be taken in interpreting the spectral differences in Method B to avoid the erroneous conclusion that the test samples are unacceptable because they differ in their spectra. Obvious but untrue differences may occur due to incomplete saponification, failure to remove all saponifiable materials and the presence of unsaponifiable substances in the carrier solids which are partially contaminated with sterols and other substances to different degrees. Having established that genuine spectral differences do exist, there is no need for further testing, unless it is wise to resort again to the published literature on infrared in an attempt to determine the likely nature of the adulterant. While methods A and B represent the acceptability of the test sample, it is still not always possible to exclude adulteration caused by changes or modifications in the saponification fraction (i.e., types of fatty acids, diacids and polyols). In such cases, it is recommended to continue using method C for the determination of oleic acid and to continue using other gas chromatographic methods for polyols and dibasic acids where such equipment is available.

Method C is very sensitive in detecting adulteration and changes in the oil or fatty acid portion of the carrier solid. For example, it can detect whether linseed, coconut, oiticica, etc. have been replaced by soybean oil and vice versa, or whether fish oil or tall oil has partially or completely replaced other dry oils, etc. Therefore, when the results of methods A and B indicate that the test sample is acceptable and a dry oil component is known to be present, method C should be used in addition to more fully guarantee the uniformity of the product. If the results of method C and the results of methods A and B indicate product uniformity, it is fairly safe to assume that the product has not changed significantly.

ASTM D 2743-2010 Determination of Uniformity of Solid Paints for Road Sign Paints by Spectrophotometry and Gas Chromatography

Method D is intended as an alternative to methods B and C, where the results of method A indicate product acceptability. By using quantitative UV spectral absorbance data, Method D is a very sensitive procedure for detecting complete or even partial adulteration of test samples. However, great care needs to be taken in the initial pre-drying of the carrier solids, since at this stage the composition is very sensitive to oxidative changes. Even small oxidative changes can seriously affect the absorbance data obtained in UV spectroscopic analysis and may give the impression that the two samples being compared are different, when in fact they are identical. When these considerations are specified and the comparative spectra in methods D and A are the same, then the sample can be assumed to be acceptable. There is A significant difference in the spectrum from Method D, indicating product inhomogeneity even though method A may not reveal this inhomogeneity.

ASTM D 2743-2010 Determination of Uniformity of Solid Paints for Road Sign Paints by Spectrophotometry and Gas Chromatography

Scope of
1.1 These practices provide general information on instrumental techniques for detecting the adulteration or inhomogeneity of the chemical properties of vehicle solids in a large number of traffic paints by using infrared and ultraviolet spectroscopy and gas chromatography, either alone or in combination. The procedure given applies if the selection and purchase of traffic paints is made on the basis of a prequalified laboratory or road performance test or both and a reference sample of the original paint so assessed and selected is retained and compared with a test sample representing a subsequent purchase and delivery lot of such paint and is required to be identical to the original reference sample.

1.2 Although these practices are not specified, the methodology given can also be used for appropriate modifications to assess the acceptability of traffic paints purchased according to compositional specifications. In this case, the application is limited to previous vehicle solids and the availability of a suitable standard or range of standards representing acceptable vehicle solids and will be compared with samples from subsequent delivery batches.

1.3 The technology provided is fully adequate to detect severe adulteration of carrier solids, where completely different dry oils, resins or polymers or a combination of these have been substituted for those originally included in the reference sample. These methods have been found to be sufficient to detect vehicle solids, adulteration, or modifications as low as % of vehicle solid weight in cases where there is less adulteration or modification.

1.4 These techniques, developed in collaboration with alkyd, chlorinated rubber alkyd, and poly (vinyl toluene) type coatings, involve the detection of inevenness when foreign materials such as rosin, fish oil, hydrocarbon resins, and chlorinated paraffins are added. The procedures given may be, but are not necessarily fully applicable to all other types of vehicle solids or foreign additions, or both.

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