Photo stability

The application of isothermal microcalorimetry to photo-degradation studies, especially in relation to chemical stability, is gaining considerable interest 

There have been several successful attempts to construct photo-calorimeters, mainly to study rapid photo reactions, for example the rearrangement of rhodopsin [98]. The development of photo-calorimetry is progressing towards a differential instrument capable of studying relatively slow degradation reactions [99,100]. 

A number of miscellaneous uses for thermal analysis within the pharmaceutical sciences exist. The following sub-sections illustrate examples of such uses. By their nature, only selected examples are given. 

The interactions between drugs and excipients or polymers or between excipients are of vital importance to formulation. Under the assessment of compatibility by DSC or DTA it was suggested that 1 1 blends may be used to maximise any interaction between two materials. This is one of the major limitations of the technique. It does not seek to establish true equiibrium between the materials. A combination of DSC or DTA with HSM provides the best way of establishing the phase diagram. 

On first sight it might seem sensible to scan, by whichever method, physical mixes of the two materials. The initial melt on a DSC or DTA scan represents the solidus temperature of the phase diagram. The initial melt should be taken, not as the extrapolated onset temperature, but as the true onset. This creates 

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Ranby, B. and Rabek, J., Photo Degradation, Photo Oxidation and Photo Stabilization of Polymers, Wiley, New York, 1975, 75. 

Rubin HD, Arent DJ, Bocarsly AB (1985) The n-CdSe photoelectrochemical ceU Wavelength-dependent photo stability. J Electrochem Soc 132 523-524... 

In order to simplify the experimental problems involved in unravelling the mechanisms of UV protection by the piperidines, we have concentrated on the use of the simpler monopiperidine compounds. Although our findings are relevant to the photoprotection by the more complex multifunctional, commercial additives, some major differences may exist, and will be emphasized together with the very significant effects of the solid state on photo-stabilization. 

An unsubstituted hydroxylamine is a powerful hydroperoxide decomposer and peroxyl radical scavenger, and could play an important role in photo-stabilization even if present at only a low concentration after dark intervals. 

Despite their low (photo)stability, chlorophylls, or rather their derivatives, have found some applications, especially in the nutrition industry. In Europe the food additive E140 is chi, and E141 is chlorophyllin (a semisynthetic sodium/copper derivative of chlorophyll), and they are used in cakes, beverages, sweets, icecream etc. As color No 125 they find applications in toothpaste, as a soap pigment and in shampoos. The older literature also... 

Akimoto, K., Kurosaka, K., Nakagawa, H., and Sugimoto, I. (1988), A new approach to evaluating photo-stability of nifedipine and its derivatives in solution by actinometry, Chem Pharm. Bull., 36,1483-1490. 

ICH. Guidance for Industry Q1B Photo stability Testing of New Drug Substances and Products (Nov. 1996). 

International Conference on Harmonisation (ICH). GMP Guide for APIs (Nov. 2000). International Conference on Harmonisation (ICH). Guidance for Industry Photo stability Testing of Drug Substances (Nov. 1996). 

Both organic and inorganic polymer materials have been used as solid supports of indicator dyes in the development of optical sensors for (bio)chemical species. It is known that the choice of solid support and immobilization procedure have significant effects on the performance of the optical sensors (optodes) in terms of selectivity, sensitivity, dynamic range, calibration, response time and (photo)stability. Immobilization of dyes is, therefore, an essential step in the fabrication of many optical chemical sensors and biosensors. Typically, the indicator molecules have been immobilized in polymer matrices (films or beads) via adsorption, entrapment, ion exchange or covalent binding procedures. 

Thus, the electronic excitation energy is first spent on a chemical bond breaking (the relaxation of the electronically excited site) and, then, a certain part of the energy is released in the form of the heat during the reconstruction of the disrupted bond. The model proposed may explain the high photo stability of the E -centers in Si02. 

Hexsaazocyclanes (HZ), were taken as additives, which have the advanced circuit of interface, high photo stability and thermo stability. 

Luminescent UC materials are those excited by a long wavelength light source and give a short wavelength emission. Such materials have been known for over 50 years. The rare earth based UC materials, such as those codoped with and Er, exhibit high photo stability and... 

Figure 13 Influence of UV absorber type, concentration, and film thickness on the photo-stabilizing effect of transparent covers on prednisolone phosphate infusions (Suntest CPS-i-, 415 N/nf, window glass filter). 45pm film thickness ( ) without cover, (A) 0,5% UV B absorber, ( A) 0,5% UV A absorber, ( ) 0,5% mixture (1 1) 100pm film thickness ( O) 0,25% UV B absorber, ( ) 1,0% UV B absorber, ( r>) 1,0% UV A absorber, ( ) 1,0% mixture (1 1). Source From Ref. 32.

Habib MJ, Asker AF. Influence of certain additives on the photo-stability of colchicine solutions. Drug Dev Ind Pharm 1989 15(5) 845-849. 

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