Study of the stability

The composition of the material and the parameters investigated should remain unchanged over the entire period of use of the material. The study of the material s stability in time will mainly depend on its role. If the material is foreseen to be used in a short term interlaboratory study the stability has to be monitored only over the real duration of the exercise and additionally mimic situations which may be encountered during its short lifetime e.g. transport under severe climatic conditions. Stability studies may vary from some days to several years. The sources and risk of (in)stability should be studied or known before the RM is produced. They should be monitored on the batch of (C)RMs. This study can only be performed by scientists aware of the type of material and its potential sources of instability. Consequently, collaboration with the end-users is mandatory. 

In both situations the stability or instability is verified by an analytical method. As for the verification of the homogeneity, the reproducibility of this method is of crucial importance. It makes no sense to be concerned about degradations of some few percent of an analyte if the method does not allow one to detect differences of less than 10%  

Therefore, for some well-known matrices and some perfectly stable substances or elements, common sense is often better than any measurement. Also linked to the precision of the analytical method, it is always better to look for the appearance of degradation products with a method with optimised sensitivity rather than checking for the disappearance of few percent of a highly concentrated substance. Unfortunately, degradation products are not always known or they may already exist naturally in the sample at high concentration levels. Nevertheless, it is sometimes possible to find cases where degradation products are of help e.g. degradation of p,p -DDT into p,p -DDE in BCR-CRM 115 [12] and in BCR-CRM 598 [14] or arsenobetaine into dimethyl arsinic acid in BCR-CRM 627 [1,2]. 

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Deoxy-sugars. Part XVI. A Study of the Stabilities of Some Phosphoric Acid Derivatives of D-Galactose and 2-Deoxy-D-Gaiactose, A. B. Foster, W. G. Overend, and M. Stacey, /. Chem. Soc., (1951) 987-991. 

Studies of the stability and stabilization of anthocyanins are still required, based on the extreme importance of those pigments for food colors. Modem HPLC-MS equipment also allows us to easily follow the copigmentation reactions in detail, calculate their kinetic and thermodynamic parameters, identify the products formed during the reactions, and thus shed new light on the stability and stabilization of these pigments. Since anthocyanins play important roles as natural colorants for... 

Peters, W. J., Jackson, R. W. Smith, D. C. (1974). Studies of the stability and toxicity of zinc polyacrylate cements (PA2). Journal of Biomedical Materials Research, 8, 53-60. 

Lambeety a, Schimmel H, Pauwels J (1998) The study of the stability of reference materials by isochronous measurements. Fresenius J Anal Chem 360 359-361. 

An initial use of reflectance spectroscopy in the characterization of pharmaceutical solids concerned studies of the stability of coloring agents in tablet formulations. With the description of a device that enabled the surface of intact tablets to be studied [14], the photostability of various dyes and lakes in tablets was followed [15,16]. Exposure of formulations to both normal and exaggerated light conditions was investigated, and the kinetics of the photodegradation evaluated. In most cases, the photoreactions appeared to follow first-order kinetics. 

The study of the stabilizing effect of the nitrone group in cumyl radical (205) (Scheme 2.72) (362) and cumyl cation (206) (Scheme 2.73) (363) has shown that the nitrone group appears to be a super radical stabilizer and, at the same time, a weak cation stabilizer. ... 

An exhaustive study of the stability of aspirin in polyethylene glycols (substituted, unsubstituted and esterified), as well as other polyhydric alcohols, was undertaken by Whithworth and collaborators 79-183... 

Bradley, J.S. et al., Surface spectroscopic study of the stabilization mechanism for shape-selectively synthesized nanostructured transition metal colloids, J. Am. Chem. Soc., 122, 4631, 2000. 

The thermal and photochemical stability of both organic dyes and nanocrystals are influenced by an extremely broad variety of conditions that need to be considered excitation wavelength and intensity, matrix or microenvironment, label concentration, and, in the case of nanoparticles, surface chemistry. Therefore, the individual study of the stability of a chromophore under the conditions required can usually not be avoided. 

Astaxanthin was detected at 480 nm. The chromatographic profiles of microencapsulated and free astaxanthin after eight weeks of storage are shown in Fig. 2.36. It was concluded from the results that the method is suitable for the study of the stability of miroencapsulated astaxanthin. The HPLC data proved that microencapculated as (ax an h tin did not suffer isomerization or chemical decomposition under the experimental conditions [79],... 

Wang L., Duan Y., Shortle R., Imperiali B. and Kollman P. A. Study of the stability and unfolding mechanism of BBA1 by molecular dynamics simulations at different temperatures. Proteins Science (1999) 8 1292-1304. 

Archer C, Vance D (2002) Large fractionation in Fe, Cu and Zn isotopes associated with Archean microhially-mediated sulphides (abstr.). Geochim Cosmochim Acta (suppl.) 66 A26 Archibald SM, Migdisov AA, Williams-Jones AE (2002) An experimental study of the stability of copper chloride complexes in water vapor at elevated temperatures and pressures. Geochim Cosmochim Acta 66 1611-1619... 

Bosikova, Z., Klouhkova, 1., and Tesafova, E., Study of the stability of promethazine enantiomers by liquid chromatography using a vancomycin-bonded chiral stationary phase, J. Chromatogr. B, 770, 63, 2002. 

Tou, J.C. and Kallos, G.J. Kinetic study of the stabilities of chloromethyl methyl ether and bis(chloroethyl) ether in humid air. Anal Chem., 46(12) 1866-1869, 1974. 

S. Carda-Broch, J. Esteve-Romero and M.C. Garca-Alvarez-Coque, Furosemide assay in pharmaceuticals by micellar liquid chromatography study of the stability of the drug, J. Pharm. Biomed. Anal., 23(5), 803-817 (2000). 

Hensen B. J. and Green D. H. (1973). Experimental study of the stability of cordierite and garnet in pelitic compositions at high pressures and temperatures. Contrib. Mineral Petrol, 38 151-166. 

Although metal vinylidene complexes are quite abundant [4-18], heavier group 14 analogs of metal vinylidene complexes containing M=C=E or M=E=C moiety (E = heavier group 14 elements) have not yet been found. A recent theoretical study of the stability of the heavier Group 14 analogs of vinylidene complexes... 

Varea et al. described a study of the stability of procaine hydrochloride in cardioplegie solutions, prepared from Ringer s solution and electrolytes (both un-buffered, or buffered with sodium bicarbonate) [156], The content of the drug was measured by ultraviolet speetrophotometry, and the was found to follow pseudo-first order kinetics. The stability of the drug entity in buffered solutions was estimated to be approximately 5-7 days. 

Ellin, R.I. 1957. Studies of the stability of pyridine-2-aldoxlme methiodide (2-PAM). In Conference on Oxime Research, CWLTM 20-10. 

Kondritzer, A.A. 1958. Studies of the stability of therapeutic agents used in the treatment of nerve gas casualties. In Research Staff Conference, CWLTM 20-15. 

Finlayson-Pitts, B. J., J. N. Pitts, Jr., and A. C. Lloyd, Comment on A Study of the Stability of Methanol-Fueled Vehicle Emissions in Tedlar Bags, Environ. Sci. Technol., 26, 1668-1670(1992). 

Systematic study of the stability of metal complexes in nonaqueous systems and their reactivity with thiols, free radicals, etc., is required for a fuller understanding of their complex effects on the co-oxidation reaction. 

Study of the stability of these ketonucleoside derivatives in alkaline media has shown that they can readily revert to the starting ketone. 

The first study of the stability of nitrocellulose seems to be that of de Luca [2], It is described below (p. 307). 

The decisive factor for the catalytic activity is the metal-carbon monomer molecule has to be inserted. Essential content of the present work is the study of the stability of this metal-carbon bond as a function of the electron donor-acceptor properties of the ligands. Thus the activity of the catalytic center can be tailored. Furthermore, it could be shown experimentally, that the coordination of the monomer molecule to the free site of the active species provokes an additional destabilization of the metal-carbon bond. 

In milk, the important interfaces are those between the liquid product and air and between the milk plasma and the fat globules contained therein. Studies of the surface tension (liquid/air) have been made to ascertain the relative effectiveness of the milk components as depressants to follow changes in surface-active components as a result of processing to follow the release of free fatty acids during lipolysis and to attempt to explain the foaming phenomenon so characteristic of milk. Interfacial tensions between milk fat and solutions of milk components have been measured in studies of the stabilization of fat globules in natural and processed milks. 

Most known monocyclic 1,2,3-triazines and 1,2,3-benzotriazines are stable at room temperature. No detailed study of the stability of monocyclic 1,2,3-triazines towards water, aqueous acids or bases has been published, but one can assume from the reaction conditions used in the preparation of monocyclic 1,2,3-triazines, by oxidation of (V-aminopyrazoIes, that they are stable to water, aqueous acids or bases at room temperature, at least for a short time. Treatment of triaryl-1,2,3-triazines with aqueous hydrochloric acid at higher temperatures leads to hydrolysis of the ring and formation of 1,3-dicarbonyl compounds (Scheme 3) (60TL(13)19,76UP21800). 

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