Control of the stability

The stability is another critical aspect for RM use it has to be verified in relation to the purpose of the study, e.g. over the duration of an interlaboratory study, or over long-term storage periods (for CRMs). The (in)stability should be studied or known before the RM is produced and should be monitored on the batch of RM. Studies may be performed under accelerated ageing conditions, e.g. elevated temperatures, or at various temperatures over defined periods of time. The BCR has developed a strategy with respect to stability assessment which has been successfully used for a wide variety of chemical species as described later in this chapter. Full details on the organisation of such studies are described elsewhere (Quevauviller et al., 1996a Quevauviller, 1998b). 

Besides the preliminary stability study, regular checks should be carried out over the entire lifetime of the material. In some rare situations over the certification projects conducted under the BCR activities, examples of instability of substances in materials were demonstrated. A typical example was shown by the instability of TBT demonstrated in the CRM 462 (coastal sediment) at +40°C over a short-term period and at +4°C over 24 months which justified the withdrawal of the material from the market and its re-certification (Lamberty et at., 1998). 

When instability is detected at an earlier stage of study the material has to be immediately stored in adequate conditions. In addition a short-term stability study has to be performed to monitor the behaviour of the material during transport under possibly increased temperature conditions. Short-term drastic transport conditions maybe reproduced by storing the material under temperatures up to 40-50°C for 10 days. This covers the maximum real-time transport duration (normal surface transportation) under severe high temperatures (Quevauviller, 1998b). 

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Kinetics can also be applied to the optimization of process conditions, as in organic syntheses, analytical reactions, and chemical manufacturing. This last example constitutes an important aspect of chemical engineering. Yet another practical use of chemical kinetics is for the determination and control of the stability of commercial products such as pharmaceutical dosage forms, foods, paints, and metals. 

T.W. Hamann, N.S. Lewis, Control of the stability, electron transfer kinetics, and pH-dependent energetics of Si/H2 0 interface through methyl termination of Si(III) surfaces,/. Phys. Chem. B 110 (2006) 22291-22294. 

Control of the stability of the steroid hormone in the reference material. 

Fig. 4.7. Cell holder with temperature control, stirred sample cell (S), and flow cell arrangement. Q, high pressure mercury arc ST75 /q and /, measurement beam with attenuated intensity, PSl, PS2, shutters F, interference filter B, beam splitter in the irradiation pathway for the control of the stability of the arc by two photo diodes D1, D2.

These are many examples in the literature, concerning llie usefulness of clays for the control of the stability of pharmaceutical suspensions thus. Cordoba et al. (67) studied the effect of a natural sepioliie on the stability of sulfamethoxazole, Schott (70) analyzed mixtures of bismuth subnitrate and monunorillcmitc. and McGinity and Hanis (71) analyzed how the presence of montmorilicMiite can affect the dissolution rates of poorly soluble drugs. 

Figure 6.91 Control of the stability and reactivity of esters via <7 interactions with strained cyclopropyl C-C bonds.

Michel, R., Plostica, T., Abezgauz, L., Danino, D., Gradzielski, M. Control of the stability and structure of liposomes by means of nanoparticles. Soft Matter 9, 4167 177 (2013)... 

Microfibrillar cellulose (MFC) is a basic structural component of wood fibers, one of the most abundant biological raw materials on the planet. Recently, the potentialities of MFC as a renewable, abundant and biodegradable material have attracted increasing interest. Some examples of uses envisaged are MFC as a reinforcement material in composites, as a component in wood- and paper-based products with enhanced strength properties and built-in advanced functionalities, and as an additive for control of the stability and rheology of emulsions, suspensions and foams. 

The light-responsive aqueous solutions of macromolecules are intensively studied since they may be applied in sol-gel materials and in drug-deliveiy. Light is a rapid and clean trigger because no additives or stirring are necessary. Such materials may be used in design of functional viscosifiers, in control of the stability of emulsions and in solubilization of drugs or... 

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