C-18 extraction

A cleanup column from a commercial source can be used or can be constructed easily from a Pasteur pipette (see Figure 12.12). A small piece of cotton is placed in the bottom of the pipette. A suitable absorbant, such as a solid coated with or bonded to a high-molecular-weight hydrocarbon such as octadecanol (this is often simply called a C-18 extraction column), can be loaded into the pipette and covered with another small amount of a cotton ball. A list of common extract cleanup absorbants and their characteristics is given in Table 12.3. 

A novel device was designed to estimate the dislodgeability of dust-associated pesticide residues by skin contact (Edwards and Lioy, 1999). Called the EL Sampler , the device consists of a spring-loaded assembly that permits the sampling medium to be pressed lightly (12g/cm or 1160 Pa) onto the surface to be monitored. A 10-cm x 15-cm Empore C-18 extraction membrane was used for the sampling medium. The material was chosen after controlled experiments on particle adhesion showed it to pick up the same distribution of test dust particle sizes as the human hand. In studies in which the EL sampler was pressed onto polyethylene surfaces coated with house dust and then sprayed with a solution of pesticides in 2-propanol, the device was found to collect 35%, 31 %, 32% and 18 %, respectively, of chlorpyrifos, diazinon (0,0-diethyl 0-[6-methyl-2-(l-methylethyl)-4-pyrimidinyl] phosphorothioate), malathion and atrazine (6-chloro-A -ethyl-A -isopropyl-l,3,5-triazine-2,4-diamine). Parallel studies with human hand presses (full hand at 6.8 kg = ca. 6900 Pa) yielded collection efficiencies of 42 %, 29 %, 43 % and 21 %, respectively. 

The aqueous layer was extracted with diethyl ether. The combined ethereal solutions were dried over potassium carbonate, after which the greater part of the diethyl ether was distilled off at normal pressure through a 40-cm Vigreux column (bath temperature < 90°C). Careful distillation of the remaining liquid afforded the bis-ether, b.p. 47-49°C/18 mmHg, Op 1.4469, in 78% yield. 

A mixture of 10.0 grams of /3-dimethylaminoethanol and 1.9 grams of sodium in 90 cc of dry xylene was heated at for 5 hours. To the resulting solution was added at 30°C, 18 grams of 3-butyl-Tchloroisoquinoline. The solution, which turned very dark, was heated at 100°-125°C for 3.5 hours. The mixture was extracted with two 100 cc portions of 2 N... 

Ionic liquid -i- catalyst -i- Organic liquid (c) Product extraction with an 18... 

TIPSH (0.25 mol) was added to a mixture of anhydrous copper(n) chloride (0.55mol) and MeCN (250ml), resulting in a two-phase liquid system. This was heated under reflux for 16h, and then chilled to precipitate copper(i) chloride. The supernatant, consisting of a dark MeCN layer and a colourless phase of TIPSCl, was separated, and the MeCN phase was extracted with pentane. The pentane extract and the TIPSCl phase were combined, concentrated and distilled, to give the product (0.25 mol, 100%), b.p. 88-92 °C/18 mmHg. 

Supercritical fluid extraction (SFE) is generally used for the extraction of selected analytes from solid sample matrices, but applications have been reported for aqueous samples. In one study, recoveries of 87-100% were obtained for simazine, propazine, and trietazine at the 0.05 ug mL concentration level using methanol-modified CO2 (10%, v/v) to extract the analytes, previously preconcentrated on a C-18 Empore extraction disk. The analysis was performed using LC/UV detection. Freeze-dried water samples were subjected to SFE for atrazine and simazine, and the optimum recoveries were obtained using the mildest conditions studied (50 °C, 20 MPa, and 30 mL of CO2). In some cases when using LEE and LC analysis, co-extracted humic substances created interference for the more polar metabolites when compared with SFE for the preparation of the same water sample. ... 

Stalikas C. 2007. Extraction, separation, and detection methods for phenolic acids and flavonoids. J Sep Sci 30(18) 3268-3295. 

The fourth type of mediator-based cation optical sensing is using potential sensitive dye and a cation selective ionophore doped in polymer membrane. Strong fluorophores, e.g. Rhodamine-B C-18 ester exhibits differences in fluorescence intensity because of the concentration redistribution in membranes. PVC membranes doped with a potassium ionophore, can selectively extract potassium into the membrane, and therefore produce a potential at the membrane/solu-tion interface. This potential will cause the fluorescent dye to redistribute within the membrane and therefore changes its fluorescence intensity. Here, the ionophore and the fluorescence have no interaction, therefore it can be applied to develop other cation sensors with a selective neutral ionophore. 

Ou et al. [42] used methanol-ultrasonic extraction followed by clean-up with aluminium oxide, and enrichment with a C-18 SPE column for the determination of LAS in plant tissues by HPLC. Both efficiency and accuracy of the overall method were high, with a mean recovery of 89% (84-93% for LAS concentrations ranging from 1 to 100 mg kg-1) and a repeatability of 3% relative standard deviation for six replicate analyses. With a 2 g sample for analysis, LAS levels of 0.5 mg kg-1 in plants could be detected with the proposed method. 

B. 3-(Methoxymethoxy)-1 -butanol. A solution of 17.6 g (0.10 mol) of 1-acetoxy-3-(methoxymethoxy)butane in 100 mL of methanol is added to a solution of 35.0 g (0.253 mol) of potassium carbonate (Note 9) in 50 mL of water contained in an open 250-mL, round-bottomed flask equipped with a magnetic stirring bar. The resulting two-phase mixture is stirred vigorously at room temperature for 2 hr. The flask is then connected to a rotary evaporator and methanol is removed at 20-30°C (18 mm). The two-phase residue is extracted with four 20-mL portions of diethyl ether and the... 

Air reactions were run under a nitrogen atmosphere. Initial product isolation was accomplished by aqueous extraction of the reaction mixture followed by concentration of the organic phase. Azeotropic removal of water during the course of, the reaction did not affect the indicated results. °At 25 C and at 110 C. 18-Crown-6,... 

The concentration of DDT in solution (Table I) often exceeded the generally accepted water solubility of 2 ppb. Two factors may account for these differences. First, the water samples were not filtered before C 18 Sep Pak extraction. 

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