OPAQUING AGENT

Numerous factors may be involved with the toxic substance itself. If the substance is a toxic heavy metal cation, the nature of the anion with which it is associated can be crucial. For example, barium ion, Ba2+, in the form of insoluble barium sulfate, BaS04, is routinely used as an x-ray opaque agent in the gastrointestinal tract for diagnostic purposes (barium enema x-ray). This is a safe procedure however, soluble barium salts such as BaCl2 are deadly poisons when introduced into the gastrointestinal tract. 

Titanium Dioxide. The recrystallization of titanium dioxide in a cover-coat glass is very important to the development of thin, highly opaque finish coats. Titania, Ti02, is the primary opacifying agent for white finish coats. Two polymorphic forms of titania, anatase and mtile, may be present in... 

Crystallisable polymers have also been prepared from diphenylol compounds containing sulphur or oxygen atoms or both between the aromatic rings. Of these the polycarbonates from di-(4-hydroxyphenyl)ether and from di-(4-hydroxy-phenyl)sulphide crystallise sufficiently to form opaque products. Both materials are insoluble in the usual solvents. The diphenyl sulphide polymer also has excellent resistance to hydrolysing agents and very low water absorption. Schnell" quotes a water absorption of only 0.09% for a sample at 90% relative humidity and 250°C. Both the sulphide and ether polymers have melting ranges of about 220-240°C. The di-(4-hydroxyphenyl)sulphoxide and the di-(4-hydroxy-phenyl)sulphone yield hydrolysable polymers but whereas the polymer from the former is soluble in common solvents the latter is insoluble. 

Alkanesulfonates are widely used as an internal antistatic agent for poly(vinyl chloride) (PVC). Since alkanesulfonates cause hazing of unplasticized PVC in the normally used quantities of 1.0 to 1.5 parts per hundred parts resin (phr), its main use is in the manufacture of opaque PVC-calendered film. To produce transparent unplasticized articles, the addition of alkanesulfonates should not exceed 0.3 phr. Figure 40 shows the antistatic effect of alkanesulfonates in PVC. 

In media selective for enterobacteria a surface-active agent is the main selector, whereas in staphylococcal medium sodium and lithium chlorides are the selectors staphylococci are tolerant of salt concentrations to around 7.5%. Mannitol salt, Baird-Parker (BP) and Vogel-Johnson (VJ) media are three examples of selective staphyloccocal media. Beside salt concentration the other principles are the use of a selective carbon source, mannitol or sodium pyruvate together with a buffer plus acid-base indicator for visualizing metabolic activity and, by inference, growth. BP medium also contains egg yolk the lecithin (phospholipid) in this is hydrolysed by staphylococcal (esterase) activity so that organisms are surrounded by a cleared zone in the otherwise opaque medium. The United States Pharmacopeia (1990) includes a test for staphylococci in pharmaceutical products, whereas the British Pharmacopoeia (1993) does not. 

With the exception of single-crystal transmission work, most solids are too opaque to permit the conventional use of ultraviolet/visible (UV/VIS) electronic spectroscopy. As a result, such work must be performed through the use of diffuse reflection techniques [8-10]. Important work has been conducted in which UV/VIS spectroscopy has been used to study the reaction pathways of various solid state reactions. Other applications have been made in the fields of color measurement and color matching, areas which can be of considerable importance when applied to the coloring agents used in formulations. 

Gastrointestinal transit time by hydrogen breath test and radio-opaque markers Gastrointestinal motiUty agents... 

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