Extraction modifiers

Almost all solvent solutions used in solvent extraction processes require treatment, either before their initial use or after being stripped of the extracted species. After preparation of the solvent by mixing appropriate amounts of extractant, modifier, and diluent, the solution is treated by contacting with an appropriate aqueous solution before entering the extraction stage. Such pretreatment is generally referred to as equilibration of the solvent. 

Soluble loss of a reagent (extractant, modifier, or diluent) from the solvent phase is an inherent part of the solvent extraction process, since all organic compounds are soluble, to some extent, in water. The conditions prevailing in the system can also promote solubility, which can be a particular problem if the composition and properties of the aqueous phase are inflexible. For example, the solubility of alkylphosphoric acid and carboxylic acid extractants is dependent on temperature, pH, and salt concentration in the aqueous phase. 

McIntosh, J.L. (1969) Bray and Morgan soil test extractants modified for testing acid soils from different parent materials. Agronomy Journal 61, 259-265. 

Solvent extraction, Ag+ TLC Folch and Rose Gottlieb extraction (modified) + SPE (LC-SI, lg/6mL)... 

While there is no doubt that free lipids can facilitate the formation of hemozoin in model systems, their potential biological role must be placed in the appropriate context. The vast majority of these lipids are involved in cellular structures (organism membrane, organelles, etc.), not freely soluble in the cytoplasm. The methods of extraction modified from Bligh and Dyer [35] by Cohen [36] were designed to extract all of the available... 

A protocol on lipid extraction modified from the pioneering work of Folch et al. (1957) is included in this unit for convenience (see Support Protocol). The authors laboratory uses this protocol for virtually all kinds of samples, and have found it to be effective with reproducibly high recoveries. Another very popular lipid extraction technique is the Bligh and Dyer method, which uses a 1 1 (v/v) mixture of chloroform/methanol (Bligh and Dyer, 1959). For more information on lipid extraction, the discussion by Nelson (1991) on solvent selection and extraction efficiency is recommended. 

FIGURE 22.7 Half-life values of insulin and calcitonin in homogenates or extracts of freshly isolated rabbit mucosae (in the absence of any inhibitors), (a) In homogenates, and (b) in extracts. (Modified from Sayani, A.P. and Chien, Y.W., Crit. Rev. Ther. Drug Carrier Syst. 13, 85, 1996.)... 

Category Targets Process Extractants Modifier Crown Ether, Calix-Crown Diluent Remarks... 

C. acuminata aqueous extract modified 12 proteins in tomato roots, decreasing the majority of them. The 23 amino acids of the N-terminal of protein 5 of tomato (37.5 kDa, 100% increase) showed 95% similarity to the glutathione S-transferases of other Solanaceae. In plants, GSTs play roles in normal cellular metabolism, as well as in the detoxification of a wide variety of toxic compounds. GSTs have been involved in numerous stress responses, including pathogen... 

Fig. 8.18. Hymenolepis diminuta rate of secretion of neutral red-positive material from the penetration glands of newly hatched hexacanths in Tyrode s solution alone (—) and in Tyrode s + adult Tenebrio molitor midgut extract (—). (Modified from Lethbridge Gijsbers, 1974.)...

SC-C02 extraction modified by 10% ethanol is more efficient (Baumann et al., 2000), but the high operating pressure creates problems. Microwave-assisted extraction (MAE) technique for selective and rapid extraction of curcuminoids is also possible. 

Extraction properties, including efficiency, selectivity, water coextraction, and temperature dependence, are strongly affected by the properties of the extracting medium. These depend on the amine concentration and on the diluent used. In a nonpolar solvent, charged species such as ion pairs tend to stabilize by aggregation. Polar and particularly protic solvents solubilize ion pairs, reduce their aggregation, and substantially enhance their extraction efficiency. The effects of diluents are in many cases so strong that they are frequently refered to as extractant modifiers or enhancers. 

The use of pre-extraction spiking is particularly important when the presence of matrix co-extractives modifies the response of the analyte as compared with analytical standards. It is increasingly common in methods for veterinary drug residues in foods to base the quantitative determination on a standard curve prepared by addition of standard to known blank representative matrix material at a range of appropriate concentrations that bracket the target value (the analytical function). Use of such a tissue standard curve for calibration incorporates a recovery correction into the analytical results obtained. 

Velazquez, D.V., H.S. Xavier, J.E. Batista, and C. de Castro-Chaves. 2005. Zea mays L. extracts modify glomerular function and potassium urinary excretion in conscious rats. Phytomedicine 12(5) 363-369. 

To the flask equipped with a dropping funnel and a Soxhlet extracter (modified for constant return of the extract) and protected by a drying tube was added 5.0 g magnesium turnings and 50 mL dry ether, followed by a crystal of iodine and a few drops of a... 

Table 2 Metal concentrations of extract (modified Table 3 of reference 18)...

Yamaguchi Y, Matsuno S., Kagota S., Haginaka J., Kunitomo M. Oxidants in cigarette smoke extract modify low-density lipoprotein in the plasma and facilitate ath-erogenesis in the aorta of Watanabe heritable hyperlipidemic rabbits. 2001 156 109il7. 

The injection of moderate amounts of an anterior pituitary extract modifies the thyroid in such a way that it produces more thyroid hormones. Soon after injection, the gland grows, the cells enlarge and proliferate, iodine uptake is accelerated, and thyroglobulin synthesis and thyroxine release through proteolysis are increased. It now seems likely that all these effects result from the action of several hormones, some of which are still not known. 

---