Discolorants, analysis

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

A number of techniques are available for determining the composition of a solid surface. Since the surface plays an important role in many processes, such as oxidation, discoloration, wear, and adhesion, these techniques have gained importance. The choice of a surface analysis technique depends upon such important considerations as sampling depth, surface information, analysis environment, and sample suitability. Different... 

It turned out that meeting a 20 ppb limit was not excessively burdensome on major manufacturers of peanut butter and other peanut products, at least in the United States aflatoxin tended to concentrate in discolored or otherwise irregular peanuts, which, fortunately, could be picked up and rejected by modern electronic sorting machines. Manufacturers did, however, have to institute substantial additional quality control procedures to meet FDA limits, and many smaller manufacturers had trouble meeting a 20 ppb limit. An extensive USDA program of sampling and analysis of raw peanuts, which continues to this day, was also put into place as the first line of attack on the problem. 

Irradiation of sulfur by various means yields discoloration of elemental sulfur, but it is doubtful that these forms will ever lead to pure allotropes. Above 92°C, a-sulfur converts into monoclinic sulfur. The kinetics of the transformation depend on various factors. Thermal analysis of single crystals of a-sulfur shows that the conversion is so slow that a-sulfur can be heated to 112°C, where it melts, before j8-sulfur is formed (19). 

Ten of 12 workers experienced acute irritant contact dermatitis of the hands after 2 days of direct contact. In the most severe case, a woman with no previous skin problems, who wore latex gloves intermittently, had painful swelling of the fingers of both hands with redness and vesicles on the palms. The affected skin later became thickened and showed a brownish discoloration. Another worker noticed small vesicles on the forehead, probably due to scratching with contaminated fingers. All cutaneous reactions cleared within 3 weeks of termination of exposure. Gas chromatograph analysis of the NMP used at the factory did not reveal any contaminating compounds. 

Synthetic operations involving ozonolysis lead to formation of aldehydes, ketones or carboxylic acids, as shown in Scheme 16, or to various peroxide compounds, as depicted in Scheme 7 (Section V.B.5), depending on the nature of the R to R substituents and the prevalent conditions of reaction no effort is usually made to isolate either type of ozonide, but only the final products. This notwithstanding, intermediates 276 and 278 are prone to qualitative, quantitative and structural analysis. The appearance of a red-brown discoloration during ozonization of an olefin below — 180°C was postulated as due to formation of an olefin-ozone complex, in analogy to the jr-complexes formed with aromatic compounds however, this contention was contested (see also Section V1I.C.2). 

Werij, J. S., Kloosterman, B., Celis-Gamboa, C., de Vos, C. H., America, T., Visser, R. G., Bachem, C. W. (2007). Unravelling enzymatic discoloration in potato through a combined approach of candidate genes, QTL, and expression analysis. Theor. Appl. Genet., 115, 245-252. 

Meat discoloration studies typically involve a maximum of 5 days, with discoloration analy-sis being performed every day or on alternate days. The actual experimental time involved in the objective assessment of discoloration is not extensive and depends on the number of samples being analyzed. Colorimetric measurements with hand-held colorimeters are very rapid (three measurements per meat surface in < 1 min). Spectral scans of meat surfaces require 1 to 2 min. Extraction and analysis of ground meat products has the added step of homogenization and filtration prior to spectrophotometry, but relative to many laboratory procedures, this is relatively quick. Isolation and purification of preparative amounts of myoglobin requires only 2 to 3 days once appropriate preparations are made. Finally, metmyoglobin can be reduced to oxymyoglobin in 15 to 20 min. 

Phenolic compounds are of interest due to their potential contribution to the taste (astrin-gency, bitterness, and sourness) and formation of off-flavor in foods, including tea, coffee, and various fruit juices, during storage. Their influence on the appearance of food products, such as haze formation and discoloration associated with browning in apple and grape products, is also significant. Furthermore, analysis of these phenolic compounds can permit taxonomic classification of the source of foods. The importance of each phenolic compound and its association with the quality of various foods is described further in Sec. IV, on food applications. 

This hypothesis has been confirmed by the greatly improved thermal stability of PVC as a result of the formation of a graft copolymer of d -l,4-polybutadiene onto poly (vinyl chloride). The improved thermal stability is demonstrated by the almost total absence of discoloration on molding the graft copolymer into a film at 200°C in air, the reduced rate of dehydrochlorination on heating in an inert atmosphere at 180°C, and higher onset and peak temperatures for hydrogen chloride evolution as determined by differential thermal analysis. 

The discoloring is likely to be caused by the photoreduction of silver chloride and/or silver phosphate in the skin. X-ray dispersive analysis of skin and other tissues reveals that the granules consist of silver complexed with sulfur and/or selenium. The photoreduced deposits are not removed by the body, and there are no clinical means of removing them. 

The addition of bromine to 2,3,4,6-tetra-0-acetyl-(2-hydroxy-D-glucal) conforms closely to that required by one double bond. Maurer1 found values which were some 4 to 8 % low. However, the analysis is complicated by evolution of hydrogen bromide and rapid discoloration of the... 

Diepoxyethylbenzene was first prepared by Everett and Kon (3) as a liquid which evidently was not pure because analysis showed a difference of 4% in the carbon content. Our product was a white crystalline mass with melting point 79°C. and boiling point 95°C. at 0.06 mm. Catalytic hydrogenation gave the theoretical absorption. The stabilizing effect in PVC mixtures was about 30% of dibutyltin laurate—i.e., 3.3 times more of the stabilizer is necessary to obtain the same discoloration as dibutyltin laurate in a plasticized mixture of PVC with 30% dioctylph-thalate at 200°C. for 20 minutes. 1,3,5-Triacetylbenzene was prepared by the two methods mentioned above. 

The resultant dried pellet should be whitish in color, but light brown to light red pellets are also sometimes obtained. Discolored pellets are of high enough purity that they are almost always good targets for PCR or RFLP analysis. The pellet should be resuspended in from... 

---