Dichloromethane extractables from distribution

Herbicides are components with relatively low Kow values and high solubilities. This means that they can be extracted from soil with a water/acetone mixture. To enable the measurement of low concentrations, the herbicides have to be transferred to a volatile solvent, which is not miscible with water, like petroleum ether or dichloromethane. If the original acetone/water extraction medium is concentrated (evaporation), the water percentage will increase during the concentration and the extracted components will precipitate or adsorb to the equipment. It is therefore necessary to add a solvent like petroleum ether to the system. There will be a distribution between the soil and the acetone/water mixture and one between the acetone/water mixture and the petroleum ether. If the water content is low the system is very effective for non-polar components. With a higher water content it will be more effective for more polar components. With a too high water content the accessibility increasing properties of acetone are lost and the efficiency of the extraction process decreases. 

Another RP-HPLC procedure was applied for the study of the distribution and stability of steryl chlorin esters in copepod faecal pellets from diatom grazing. Pigments were sonicated for 15 min with acetone at 0°C and the procedure was repeated until the extract became colourless. The organic phase was evaporated and the fraction containing the free alcohols was separated by TLC (silica stationary and dichloromethane mobile phases) and analysed by gas chromatography. RP-HPLC measurements were performed in an ODS... 

Percentage Extraction, % , and, in Brackets, Distribution Ratios, D, for Lanthanides and Thorium Nitrates by Narrow-Rim Calixarenes CMPO from 1 M HN03 into Dichloromethane T = 20°C, CM = 10 4 M... 

In a typical experiment, styrene (180 mg, 1.74 mmol) was admixed with clayfen or clayan (300 mg) in a glass tube. The reaction mixture was placed in an oil bath for 15 min or irradiated for 3 min in an alumina bath inside an unmodified household microwave oven (900 W) at its medium power. On completion of the reaction, followed by TLC examination (hexane-EtOAc, 4 1, v/v), the product was extracted into dichloromethane (45 mL), the combined organic extract dried with anhydrous sodium sulfate and solvent removed under reduced pressure. The relative amounts of product distribution were calculated from GC-MS analysis. Alternatively, the crude material was chromatographed on a silica gel column and eluted with hexane-EtOAc (4 1, v/v) to afford the pure product (147 mg, 57%). 

Kinetic studies have demonstrated that uptake of compounds into leaves is best represented by a two-compartment process a rapid distribution into the outer leaf surface, followed by a slower diffusion into the interior of the leaf. This is illustrated by studies of the uptake of DDE in spmce needles." A 10-year old spruce tree was placed in a chamber and exposed to air containing 50 ng m of DDE. It can be seen from Eigure 3.25 that DDE concentration increased more rapidly in a soluble cuticular lipid fraction than in the needle remaining after extraction. The former was obtained by extraction with dichloromethane and was considered to be representative of the lipophylic needle surface. Note that introducing the tree into the exposure chamber reduced the concentration of the DDE in the air. When the tree was transferred to a clearance chamber , DDE was lost rapidly from the extracted lipid fraction and only slowly from the remaining needle. A two-compartment model has been developed to simulate DDE uptake and release. Based on this response, if needles were to be used for monitoring, it is important to recognize that one portion of the needle reacts within hours to atmospheric concentrations, whereas the needle as a whole could take months to achieve some steady state. 

The Ni(II) and VO(II) complexes of etioporphyrins and deoxophylloerythroetio-porphyrins from fuel and crude oils were studied on an aminopropyl column (A = 400 run, ex 620 nm, em) using a 25-min 45/55/0—20/30/50 toluene/ hexane/dichloromethane gradient [617]. A chromatogram of four neat metal-porphyrin standards and four crude oil extracts are shown. Due to the very large number of possible homologs of the porphyrins, a manifold of peaks was obtained. These distributions were distinctly different for each crude oil sample. Tentative identification, as related to the retention of the neat standards, is given. 

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