Hexane recovery column

Based on the experimental results obtained with the laboratory setup, a full-scale plant was designed as shown in Figure 73. In addition to the polyazeotropic column on the left-hand side, it is seen to feature a hexane recovery column in the middle, and a finishing column on the right-hand side. In the latter, the raw diketones produced in the polyazeotropic column are separated into diacetyl and 2,3-pentanedione, both of these products being withdrawn as side streams. Their separation is straightforward since they exhibit ideal behavior as shown in Figure 74. 

Add 20 mL of hexane to Column 2, and elute until the hexane level is just below the top of the alumina. Do not discard the eluted hexane, but collect in a separate flask and store it for later use, as it may be useful in determining where the labeled analytes are being lost if recoveries are less than 50 percent. 

Microwave extraction realized at 120 °C for 30 min with Hexane -Acetone (3 2 V/V) as the extraction solvent was identified as the most effective extraction procedure for isolation of TPH from biotic matrices. The aim of this research is to develop a silica gel and alumina fractionation procedure for plant sample extraction. Column chromatography with two solvents (chloroform and hexane dichloromethane) as a mobile phase were used for clean-up of extract. In this research the efficiency of recovery received from chloroform as a mobile phase. 

The stopping solution composition was based on experiments showing that lowering the pH from 9 to 5 to 1 reduced formation of cis-DMNM, perhaps because this prevented elution of the amine from the column, and that addition of ammonium sulfamate lowered cis-DMNM formation, relative to the situation where ascorbate alone was used as a nitrite trap. The hexane wash of the column was introduced to remove a large peak near the solvent front in the GC-TEA, perhaps due to neutral fats. Using the described procedure, the recovery of 70-160 ng NMOR added to 2 g semisynthetic diet was 92 + 19% (mean + S.D. for 13 measurements). The recovery of 227 ng NMOR from 5-8 g whole mouse homogenate using the Iqbal method was 101 + 57% for 7 measurements. 

The liquid-liquid partition procedure described above can be substituted by using a Chem Elut column. After concentrating the extract derived from Section 2.2 to 20 mL, the concentrate is applied to a Chem Elut column and charged at room temperature for 5-10 min. Naproanilide, propanil and mefenacet are eluted with 80 mL of n-hexane when using the Chem Elut column. The recoveries are in the range 96-110% (personal data). 

Theobromine was determined by GC in various foods (bitter chocolate, milk chocolate, chocolate cake, cocoa powder, chocolate milk), and results are given in graphs and tables.27 Homogenized samples were boiled in alkaline aqueous media, then fat was extracted with n-hexane. The aqueous layer was acidified with diluted HC1 and NaCl was added. Theobromine was extracted from this treated aqueous solution with dichloromethane and the extract was evaporated to dryness. The residue was redissolved in dichloromethane containing an internal standard. GC analysis was performed on a column packed with 1% cyclohexane dimethanol succinate on Gaschrom Q, with FID. Average recoveries were 99 to 101%, coefficient of variation was less than 3% and the limit of detection for theobromine in foods was about 0.005%. 

Fish tissue is homogenized with a Polytron apparatus using methanol as a solvent, or extracted in a ball mill with hexane. The extracts are evaporated to dryness, dissolved in ethyl acetate toluene, and cleaned up on a gel permeation column followed by an alumina column. Analysis is performed by GC/NPD (Muir et al. 1981). Recovery is acceptable (79-97%) and limit of detection is 10 ng/g (Muir et al. 1981). 

Musty and Nickless [353] used Amberlite XAD-4 for the extraction and recovery of chlorinated insecticides and PCBs from water. In this method a glass column (20 x 1 cm) was packed with 2 g XAD-4 (60 - 85 mesh), and 1 litre of tap water (containing 1 part per 109 of insecticides) was passed through the column at 8 ml/min. The column was dried by drawing a stream of air through, then the insecticides were eluted with 100 ml ethyl ether-hexane (1 9). The eluate... 

Millar et al. [371] carried out experiments to study a method for the recovery of 18 organochlorine pesticides and seven PCBs from water. Extractions with dichloromethane, and 15% dichloromethane in hexane, at pH 2,7, and 10, and liquid-solid column chromatography using columns of Florasil or alumina, produced excellent results. An investigation was also made into the effects of... 

PCBs in biological samples are usually extracted by a Soxhlet column and with a nonpolar solvent such as hexane. The sample is first mixed with sodium sulfate to remove moisture. The extraction of PCBs from sediments was tested with sonication, with two sonications interspersed at a 24-h quiescent interval, with steam distillation, or with Soxhlet extraction (Dunnivant and Elzerman 1988). Comparison of the recoveries of various PCB mixtures from dry and wet sediments by the four techniques and the extraction efficiency of four solvents showed that the best overall recoveries were obtained by Soxhlet extraction and the two sonication procedures. In comparisons of solvent systems of acetone, acetonitrile, acetone-hexane (1+1), and water-acetone-isooctane (5+1.5+1), recoveries of lower chlorinated congeners (dichloro- to tetrachloro-) were usually higher with acetonitrile and recoveries of higher chlorinated congeners (tetrachloro- to heptachloro-) extracted with acetone were superior (Dunnivant and Elzerman 1988). The completeness of extraction from a sample matrix does not seem to discriminate against specific isomers however, discrimination in the cleanup and fractionation process may occur and must be tested (Duinker et al. 1988b). 

Since both n-hexane and ethyl ether have almost no similarities in structure with the adsorbent and with the molecules to be extracted, a very good recovery cannot be expected. The results obtained with the mixture of column A (Table 9.6), the one adopted, are fully comparable with those obtained by using a separatory funnel extraction (column FI) but the amount of solvent required is about ten times less. 

Japenga et al. [56] determined polychlorinated biphenyls and chlorinated insecticides in River Elbe estuary sediments by a procedure in which the sediments were pretreated with acetic acid, mixed with silica and Soxhlet-extracted with benzene/hexane. Humic material and elemental sulphur were removed by passing the extract through a chromatographic column containing basic alumina, on which sodium sulphite and sodium hydroxide were adsorbed. Silica fractionation was followed by gas chromatography to analyse chlorinated pesticides, polychlorinated biphenyls and polyaromatic hydrocarbons. Recovery experiments with standard solutions gave recoveries of 90-102%. 

Traditional column chromatography has also been employed for the extraction of carotenoids from palm oil. Separations were carried out on silica columns, carotenoids were eluted with n-hexane while the free fatty acids of the oil were removed from the stationary phase with ethyl acetate. The recovery of the method was 45 per cent and the purity of the cartotenoid fraction about 20 per cent w/w [23],... 

Gustavson et al. (2000) developed a convenient and novel solid phase extraction (SPE) method for the removal of methyl oleate from SPMD dialysates containing PAHs. A small SPE column (1 g or 0.5 g) containing a dual-zone silica (normal phase)-based restricted-access sorbent (Diazem, Midland, MI, USA) is used for the separation. The capacity of this sorbent to remove methyl oleate is about 1.8% (lipid/sorbent wt wt ). The PAHs are eluted with 19 mL of hexane and methylene chloride (97 3 VV ) and recoveries of all PAHs are typically >72%. 

Recently, three papers have reported the determination of risperidone and its active metabolite 9-hydroxyrisperidone using LLE and SPE technologies. The analytical columns used to separate these compounds were C4 or C18 bonded phases of 3 pm or 5 pm particle sizes with UV/VIS detection. Mobile phases consisted of phosphate bufiers (pH 3-4) in acetonitrile. The sample volumes used ranged from 200 pi to 1 ml, with extraction recoveries averaging 90%. The limits of quantitation ranged from 0.5 to 10 ng/ml in human plasma (Nagasaki et al., 1999 Avenso et al., 2000 Titier et al., 2002). A study by Titier showed the simultaneous determination of clozapine, olanzapine, haloperidol, risperidone, and its active metabolites by RP-HPLC in human plasma. The assay involved LLE with a hexane/isoamyl alcohol mixture... 

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