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Conventional film processing
Published in Damian Tolan, Rachel Hyland, Christopher Taylor, Arnold Cowen, Get Through, 2020
Damian Tolan, Rachel Hyland, Christopher Taylor, Arnold Cowen
True – the developer reduces exposed silver bromide to metallic silver.False – oxidation of developer shortens its life. Preservatives (e.g. sodium sulphite) are added to the developer to minimise oxidation and its effects.False – this acts as an accelerator. Most developers have a pH 10–11.5.True – this explains why timing of development is crucial. The addition of a restrainer, typically potassium bromide, helps the unexposed silver bromide crystals to maintain a barrier of bromide ions around them, thus preventing reduction and fog formation.True – these act synergistically, another example is metol/hydroquinone.
The effect of chamomile extract obtained in supercritical carbon dioxide conditions on physicochemical and usable properties of pharmaceutical ointments
Published in Pharmaceutical Development and Technology, 2018
Emilia Klimaszewska, Artur Seweryn, Anna Małysa, Małgorzata Zięba, Joanna Lipińska
A number of extraction methods have been developed for the purpose of extracting chemical compounds from plant-based substances (Azmir et al. 2013, p. 426). One of them is liquid extraction, mainly water- or alcohol-based. A currently available alternative to these methods is the process of extraction based on CO2 in supercritical conditions. Extracts obtained through this innovative extraction method are characterized by high quality and, importantly, contain exclusively active biological ingredients which are present in the raw material. The extraction process is conducted at relatively low temperatures (under 50 °C), and the main extracting agent is compressed carbon dioxide (at approximately 300 bar). The solvent is nontoxic, relatively easily accessible and inexpensive. On completion of the extraction process, CO2 escapes from the extract. Extracts obtained through this method have a very high level of purity (Reverchon & Senatore 1994, p. 154; Hamburger et al. 2004, p. 46; Reverchon & De Marco 2006, p. 146; Sahena et al. 2009, p. 240; Junior et al. 2010, p. 51; Yang et al. 2011, p. 2009; Jia et al. 2012, p. 533; Petroniho et al. 2012, p. 1; Sovova´ et al. 2013, p. 1151; Azmir et al. 2013, p. 426; Daut et al. 2015, p. 573; Mackėla et al. 2015, p. 291). The chemical composition of chamomile extracts obtained in supercritical CO2 by the following operational conditions (300 bar, 45 °C, flow rate of CO2 80 kg/h) was analogous to those reported by Scalia et al. (1999, p. 549) and Michorczyk et al. (2015, p. 1316). GC/MS chromatography (Scalia et al. 1999, p. 549; Michorczyk et al. 2015, p. 1316) shows that chamomile extracts obtained in supercritical CO2 conditions are a rich source of multiple compounds including thujone, camphor, metol, menthone, isomenthone, α-cubebene, nerolidol, bisabolol oxide B, chamazulene, etc.