Alkaline extraction conditions

Some agrochemicals bind strongly to the soil component as bound residues, which cannot be extracted without vigorous extraction procedures. In this case, an acidic (e.g., hydrochloric acid, sulfuric acid) or alkaline solution (e.g., sodium hydroxide, potassium hydroxide) can be used as an extraction solvent, and also heating may be effective in improving the extraction of the residues. Analytical procedures after the extraction are the same as above, but a filtration procedure may be troublesome in some of these situations. However, these procedures are rare exceptions or are needed for specific chemicals that are stable under such harsh extraction conditions. 

Selectivity over other metallocyano species was poor, decreasing in the order tridecylamine > Primene 81R > Primene JMT. The best extraction conditions proved to involve neutral or slightly elevated pH.339 The addition of Cyanex 921, Cyanex 923, or TBP (Table 6) allowed extractions to be performed under more alkaline conditions and improved the selectivity over other metals.338... 

The late discovery of acetyl xylan and feruloyl esterases has been partly due to the lack of suitable substrates. Xylans are often isolated by alkaline extraction, in which ester groups are saponified. Treatment of plant materials under mildly acidic conditions, as in steaming or aqueous-phase thermomechanical treatment, leaves most of the ester groups intact. These methods, however, partly hydrolyze xylan to shorter fragments (63,69). Polymeric acetylated xylan can be isolated from delignified materials by dimethyl sulfoxide extraction (70). The choice of substrate is especially important in studies of esterases for deacetylation of xylans. The use of small chromophoric substrates (p-nitrophenyl acetate, a-naphthyl acetate, and methylumbelliferyl acetate) analogously to the assays of disaccharidases may lead to the monitoring of esterases unable to deacetylate xylan (33, 63, 64). 

No complete picture of biological materials can be given without reference to their original condition in their natural environment. Brief consideration will, therefore, be given to the biosynthesis of the hemicelluloses and to their relationship, in the plant, to cellulose and lignin. Since much of our present knowledge of the chemistry of the hemicelluloses is based upon examination of materials isolated by alkaline extraction from plant tissues which, in many cases, have been previously treated to remove lig-... 

Woods contain a number of acyl (mainly acetyl) groups, and it is probable that these are associated with the xylan components of the hemicellulose fraction. Evidence for the original esterification of aspen-wood xylan comes from the observation that the isolated xylan (obtained by alkaline extraction) is readily cleaved by periodate, whereas only a small proportion of the D-xylose residues in the wood itself are oxidized under similar conditions.66 Hemicelluloses still containing acyl groups may be extracted from wood holocelluloses by means of dimethyl sulfoxide, and further quantities... 

Test Condition Pulp = LDSP, After Mild Alkaline Extraction,... 

Under our experimental conditions, nitric acid dissolved iron pyrite but not the hematite which was formed during the alkaline treatment step. More rigorous alkaline treatment conditions were more effective than less rigorous conditions for converting the iron pyrite into hematite which could not be easily removed by the nitric acid. Consequently, when rigorous alkaline treatment conditions were applied to Lower Kittanning coal, the residual hematite more than made up for the other minerals which were extracted so that the overall reduction in ash content for the two-step process was no better than for HNO, leaching alone. 

To analyze free-form phenolic acids in fmit or vegetable juice, the sample preparation is straightforward and simple. The juice can be directly injected into an HPLC system after it is filtered to remove any insoluble particles. However, for a sample with a solid fraction containing both free and bound phenolic acids, the sample preparation is not as simple. A mechanical method is needed to physically break down the sample and release the free phenolic acids, which are blocked in the inner core of the sample matrix. Chemical (acid or alkaline) or enzymatic hydrolysis must be applied to break down linkages in the bound phenolic acids to release free phenolic acids. However, the recovery of total phenolic acids is significantly affected by hydrolysis and other extraction conditions. An intensive hydrolysis condition may increase the release rate of bound phenolic acids to free phenolic acids however, it can also cause degradation of some phenolic acids and lower... 

The chlorination tower lining is tile set in a polyester or vinyl ester mortar with a Portland cement grout backing. The hypochlorite and peroxide units do not need the resistance of the resin mortar, therefore, Portland cement mortar can be used. Caustic extraction towers are occasionally lined with tile set in Portland cement mortar even though the alkaline operating conditions may soften the tile. To minimize the softening effect, the tile should have an extremely tight, well fired body. 

Alkaline extraction of wood is usually carried out at or below room temperature for limited periods of time and in an atmosphere of nitrogen. Under these conditions, any changes in the xylan brought about by the alkali are kept at a minimum, excepting a complete de-O-acetylation. Whistler and Corbett found that a corncob xylan was stable in N sodium... 

The phenomena which have been observed on extraction of wood with aqueous sodium hydroxide - also occur, albeit to a smaller extent, with holocelluloses the restriction to dissolution is, in this case, mostly due to the fiber structure itself. In a study of the extraction of a chlorine holocellulose from European beech with sodium hydroxide solutions of various concentrations, Corbett and Ewart found that 87% of the (4-0-methyl-glucurono) xylan could be removed under mild conditions, and another 10% by extraction with hot alkali, but that 1.3% remained associated with the cellulose. The same authors have also described an apparatus suitable for the alkaline extraction of wood or holocellulose in an atmosphere of nitrogen. 

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