Alkaloids can also be extracted in the protonated form (after acidification to pH 2–4 with diluted acids such as phosphoric acid, sulfuric acid or citric acid) with water or alcohols (e.g., methanol). On the other hand alkaloids containing phenolic groups (e.g., morphine) are deprotonated at higher pH, and are thus not extracted by organic solvents under such conditions. Some alkaloids can only be extracted at higher pH (> 10) for example, tryptamine. Verpoorte, in Encyclopedia of Analytical Science (Third Edition), 2015 ExtractionĪlkaloids can be extracted under neutral or basic conditions (after basification of the plant material or biofluid to pH 7–9 with ammonia, sodium carbonate, or sodium hydrogencarbonate) as free base with organic solvents (e.g., dichloromethane, chloroform, ethers, ethyl acetate, alcohols). A major criticism of this method is that the pH is maintained at an unphysiological level which is associated with rising levels of serum gastrin and which could cause alterations in gastric acid secretion.Ī. The method is reproducible and is the simplest of the methods used to measure meal-stimulated gastric acid secretion. The amount of sodium hydrogencarbonate or hydroxide (in mmol h −1) required to keep the pH at 5.5 is equal to the rate of postprandial gastric acid secretion. Whenever the pH is observed to drop, sodium hydrogencarbonate or hydroxide is infused into the stomach to maintain the pH at 5.5. For a period of 4 h thereafter, frequent aspirations of 2–3 ml samples of gastric fluid are obtained, the pH is quickly determined and then returned to the stomach. A homogenized test meal, also with a pH adjusted to 5.5, is ingested or instilled through a nasogastric tube. The gastric pH is raised to 5.5 by the infusion of sodium hydrogencarbonate or hydroxide. This technique is used to measure the gastric acid secretory response induced by a meal. Koo, in Encyclopedia of Analytical Science (Second Edition), 2005 Continuous in vivo intragastric titration
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