Melamine, identification

Phenol, urea, and melamine are also obtained as intermediates on acid hydrolysis of the corresponding formaldehyde condensate resins and appropriate tests for phenol, urea, and melamine may be employed for identification purposes. 

A specific identification test for urea is the enzymatic reaction with urease. 50 mg of powdered resin or 0.1 ml of the resin solution is carefully heated in a test tube with a Bunsen burner until all formaldehyde has been removed (check odor ). After cooling and neutralizing with 10% sodium hydroxide using phenolphthalein as an indicator, 1 drop of 1 N sulfuric acid and 0.2 ml of a freshly prepared 10% urease solution are added. A moist piece of litmus paper is then attached to the upper rim of the test tube. After a short time, the blue coloration of the indicator paper demonstrates the presence of ammonia which is formed only by urea-containing resins and not by melamine resins. Hexamethylene tetramine is the only substance that may interfere with this reaction. 

Flirt et al. [51] have published an effective and rapid method for the detection of melamine by ultraviolet spectrophotometry. This method can be used for products containing MF. It makes use of the strong absorption of the melamine ion at 235 nm. The resin is extracted from comminuted MF samples by hydrolyzing to melamine by boiling under reflux in 0.1 N hydrochloric acid. Stafford [52] also gives a method for the identification of melamine in wet-strength paper. 

The analysis of MF resins as well as alkoxylated MF resins by chromatographic methods has been described vastly in the literature (119,120) and allows the separation and identification of oligomeric methylolated melamines by conventional UV- or refractive index based detection. The most direct method for the determination of methylolated melamines within a MF resin is the coupling between HPLC methods and Mass Spectrometry (qv), enabling the direct structural analysis by HPLC-MS methods on methoxylated (121-124) and butoxylated MF resins (see Chromatography, HPLC) (125). Favored ionization methods use ESI-MS ionization methods to achieve an efficient ionization process. The detection of up to pentameric melamine units can be achieved by this method. 

In this section, we discuss the identification process and the chemical structures of polymers as obtained from their infrared and Raman spectra. Many polymers have common features, and it is convenient to segregate polymers into groups, such that the characterization of the polymers in a group can be discussed together. A popular method for classifying polymers is by their modes of application. For instance, some polymers, such as polyvinyl acetate, polystyrene, and nylons, are classified as thermoplastics, while urea, melamine, and epoxide resins are classified as thermosets or thermosetting resins. In this chapter we will use a different approach to classify the polymers, based on their similarity of chemical structure. This enables us to utilize the correlation between the functional groups of polymers and their characteristic infrared and Raman frequencies. 

Costa, L. Camino, G. Luda di Cortemiglia, M.P. Mechanism of thermal degradation of fire-retardant melamine salts, in G.L. Nelson, Ed., Fire and Polymers Hazard Identification and Prevention. ACS Symposium Series, Vol. 425. American Chemical Society, Washington, DC, 1990, pp. 211-238. 

Identification (ID) test. The objective of an ID test is to confirm that the chemical species being analyzed is the correct species. An ID test must be able to discriminate the intended analyte from other related species, impurities, or matrix components that may be present this is termed method specificity. It is typically demonstrated for an LC method by measuring resolution between the anal5de of interest and other species that may be present. As illustrated by the heparin and melamine examples, the importance of method specificity should not be understated. 

Vail, T. M., Jones, P. R. and David Sparkman, O. Rapid and unambiguous identification of melamine in contaminated pet food based on mass spectrometry with four degrees of confirmation. /. Anal. Toxicol. 31 304-312, 2007. 

PJ Schmitz, JW Holubka, L Xu. Mechanism for environmental etch of acrylic melamine-based clearcoats Identification of degradation products. J Coatings Technology 72(904) 39-45, 2000. 

An example of the use of the computational capabilities of the data station to assist in the identification of a chemical substructure in a crosslinked polymers has been reported [37]. A mass spectrum from a melamine-based paint was obtained using a carbon dioxide laser. A peak at m/z 163.075700 was observed. Using a data station, a value of 163.075356 was calculated corresponding to a chemical formula of 0-2, C-10, H-1 1. Choices are limited by specifying that the chemical composition only... 

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