Hot extraction method

The hot extraction method is a variation of this procedure. The aqueous pigment suspension, prepared as above, is refluxed for a certain time, usually 5 minutes, cooled rapidly, and filtered. A known amount of extract is then dried by evaporation and the weight of the residue determined, or the extracted pigment weighed and the dissolved portion determined by calculating the difference. 

The initial acidity or alkalinity of paper is measured conventionally by the pH of the water extract or by the total titratable acidity or alkalinity of the water extract (TAPPI T428 and ASTM D548). The extract for measurement of pH may be prepared as the cold water extract (TAPPI T509) or as the hot water extract (TAPPI T435 and ASTM D778). In the absence of hydrolyzable salts, it may be expected that hot and cold extraction methods will give approximately the same results. If hydrolyzable acid salts (particularly alum) are present, the hot extraction method yields a lower pH because of hydrolysis promoted at the higher temperature to yield free acids. 

ISO 787 specifies two methods of determination of matter soluble in water. The Part 3 gives the hot extraction method. The material is boiled in water for 5 min, cooled to room temperature. Altered, extract is evaporated, and soluble matter determined gravimetrically. In Part 8, the cold extraction method is specified. Extraction is done at room temperature for 1 h. The next steps are the same as in hot extraction method. 

The ASTM method is the same as hot extraction method in ISO procedure. ... 

Part 13 of ISO 787 determines water-soluble sulfates, chlorides and nitrates. The sample extract can be prepared by either cold or hot extraction method described in Section 4.28. The sulfates in the extract are determined by precipitation with barium chloride, the chlorides are determined by titration with silver nitrate, and the nitrates are determined by a colorimetric method using Nessler reagent." Part 19 gives an alternative method of determination of nitrates by a salicylic acid method. 

The solubility of the polymer-modified binders depends largely on the temperature of the solvent. This can lead to considerable differences between the results of cold and hot extraction methods. 

CO2 extraction has been prevalent for the isolation of essential oils and other natural lipophilic pigments like carotenoids. Hot water and superheated water extraction methods are used for analytical preparation of polar pigments. The technique is commonly referred to as subcritical water extraction because the practitioners of this approach come from SEE backgrounds. 

Figure 3 Size fractionation of EDTA-soluble polyuronides from Rutgers and transgenic fruit juice processed by cold- and hot-break methods. Pectin from processed juice was extracted as ethanol-insoluble solids and size fractionated on a Sepharose CL4B column. Under the same chromatographic conditions, elution of the branched dextrans with average molecular mass 2000, 500, 252, 151, 40 and 17.7 kD-peaked in fraction number 46, 50, 54, 62, 67 and 72, respectively. Modified from Thakur et al. [23].

Conventional methods of polymer extraction use large quantities of solvents as in shake-flask extraction or a Soxhlet extraction apparatus. For all classical extraction methods, solvent selectivity, in general, is low, i.e. solvents with high capacity tend to have low selectivity. In reflux extractions, which are still quite popular in polymer applications, the polymer is refluxed with a hot solvent, which disperses it to provide a solvent phase containing additives. In these conditions solvents are at their atmospheric boiling point. These methods are lengthy and labour intensive. Fractional extraction is based on solvents with increasing solvent power (cf. also [81]). 

The classical Soxhlet extraction technique has seen some improvements, mainly in the submersion of the whole extraction thimble into the boiling extraction solvent, degree of automation, and in reduction of solvent volume. In a recently introduced universal extraction system (Biichi) four SLE methods are contained in one device Soxhlet Standard, Soxhlet warm, hot extraction and continuous flow. It is possible to use solvents with boiling points of up to 150 °C inert gas can be supplied during the extraction process. 

Desrosiers [23] has dared ranking extracting methods as follows (in order of preference) SFE, US, hot block or MAE, Soxhlet (to be phased out as quickly as possible). Munteanu [556] has evaluated extraction techniques for additives from polymers prior to chromatographic analysis (up to 1990). The analytical extraction of additives from polymers has recently critically been reviewed with emphasis on SFE, MAE and ASE [92]. Dean [272] compared modem extraction techniques, with focus on environmental analysis. 

Askari et al. [15] have compared purge and trap, methanol immersion and hot solvent extraction methods for the determination of volatile organic compound in aged soil. These workers found that hot solvent extraction is much more effective than the US Environmental Protection Agency approved purge and trap technique [7, 8]. 

Obviously to remove large amounts of asphaltic materials, substantial quantities of clay would be required in both the percolation and hot contacting methods, and the adsorption process then may become uneconomical in the treating of raw residua. With the exception of residual oils containing low concentrations of asphalts, oils to be treated with clay generally receive some pretreatment—for example, with sulfuric acid followed by neutralization of the acid oil, or selective solvent extraction. 

Pressurised hot water extraction has been used to isolate polycyclic aromatic hydrocarbons from soil [104,105]. Ramos et al. [106] reported an rapid (ten minutes) miniaturised pressurised liquid extraction method using only 100 pi solvent for extracting polycyclic aromatic hydrocarbons from soil. 

Treated papers should maintain at a pH in the range 7 and 8.5. The pH should not be higher than 8.5 to prevent alkaline hydrolysis of cellulose. The acidity or alkalinity may be determined as the amount of water-soluble acidity or as the hydrogen ion concentration (pH) of the paper extract. The pH is more indicative of the stability of paper than is the total acidity. The pH can be determined by either a hot or cold extraction method. In the cold extraction method,... 

Method. Apply 25 li1 of the reference solution to the first column of each of three plates. Divide the basic extract from the solvent extraction method, or the remainder of the column extract, equally between the three plates. Develop one plate in a tank containing 100 ml of methanol strong ammonia solution (100 1.5) (System TA, p. 167). Develop the other two plates in a tank containing ethyl acetate methanol strong ammonia solution (85 10 5) (System TE, p. 168). After development, remove Ihe plates from the tanks and dry under a stream of cold air until they no longer smell of ammonia. Avoid using a hot-airblower as methadone may volatilise. 

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