Liquid Partitioning

Van Den Dool, H. and P.D. Kratz (1963), Generalization of the retention index system including linear temperature programmed gas-liquid partition chromatography . J. Chromatogr, Vol. 11, p. 463. 

Where larger quantities (upwards of Ig) are required, most of the impurities should be removed by preliminary treatments, such as solvent extraction, liquid-liquid partition, or conversion to a derivative (vide supra) which can be purified by crystallisation or fractional distillation before being reconverted to the starting material. The substance is then crystallised or distilled. If the final amounts must be in excess of 25g, preparation of a derivative is sometimes omitted because of the cost involved. In all of the above cases, purification is likely to be more laborious if the impurity is an isomer or a derivative with closely similar physical properties. 

Somatostatin [38916-34-6] M 1637.9, [a]p -36 (c 0.57, 1% AcOH). A tetradecapeptide which is purified by gel filtration on Sephadex G-25, eluting with 2N AcOH, and then by liquid partition chromatography on Sepahdex G-25 using n-BuOH-AcOH-H20 (4 1 5) and has Rp= 0.4. It is a brain growth hormone releasing-inhibiting factor which has also been synthesised. [Burgus et al. Proc Natl Acad Sci USA 70 684 1973, Sorantakis and McKinley Biochem Biophys Res Commun 54 234 1973 Hartridt et al. Pharmazie 37 403 1982.]... 

Where FCl is the solute gas-liquid partition coefficient, r is the tendency of the solvent to interact through k- and n-electron pairs (Lewis basicity), s the contribution from dipole-dipole and dipole-induced dipole interactions (in molecular solvents), a is the hydrogen bond basicity of the solvent, b is its hydrogen bond acidity and I is how well the solvent will separate members of a homologous series, with contributions from solvent cavity formation and dispersion interactions. 

Column Chromatography. Liquid-liquid partitioning has been used by several investigators for several pesticides, including pyrethrum (1,2,3,5,10,13). The most useful procedure allows the... 

In gas-liquid partition chromatography (GLPC), the stationary phase is a liquid that coats the particles in the tube or the walls of the tube. Often the tube itself is very narrow and long, perhaps 100 m, and has to be coiled (Fig. 4). Solutes are separated, as in liquid chromatography, by their relative solubility in the gas and liquid phases. In... 

Solution The phase in which reaction occurs will be denoted by the subscript /, and the other phase wiU be denoted by the subscript g. Henry s law constant will be replaced by a liquid-liquid partition coefficient, but will still be denoted by Kh- Then the system is governed by Equations (11.29) and (11.30) with = —kai and ( ) = 0. The initial conditions are... 

Other modes of LC operation include liquid-liquid partition chromatography (LLC) and bonded phase chromatography. In the former, a stationary liquid phase which is immiscible with the mobile phase is coated on a porous support, with separation based on partition equilibrium differences of components between the two liquid phases. This mode offers an alternative to ion exchange in the fractionation of polar, water soluble substances. While quite useful, the danger exists in LLC that the stationary phase can be stripped from the column, if proper precautions are not taken. Hence, it is typical to pre-equil-ibrate carefully the mobile and stationary phases and to use a forecolimn, heavily loaded with stationary phase 9). 

It is useful to conclude with several examples from our laboratory. We have applied the procedure of ion pair partition chromatography to the separation of biochemically important mixtures (47,48). In this method of liquid-liquid partition, the basic distribution process can be written as... 

Typically lipids, chlorophyll, and phenolic acids can be separated by liquid-liquid partition. Lipids and chlorophyll can be removed from acetone-water extracts by chloroform while phenolic acids have higher affinities for ethyl acetate at a pH close to nentral and water. °°... 

Tswett s initial column liquid chromatography method was developed, tested, and applied in two parallel modes, liquid-solid adsorption and liquid-liquid partition. Adsorption ehromatography, based on a purely physical principle of adsorption, eonsiderably outperformed its partition counterpart with mechanically coated stationary phases to become the most important liquid chromatographic method. This remains true today in thin-layer chromatography (TLC), for which silica gel is by far the major stationary phase. In column chromatography, however, reversed-phase liquid ehromatography using chemically bonded stationary phases is the most popular method. 

The P scale of solvent polarity is based on a combination of gas-liquid partition coefficients reported by Rohrschneider [43]. 

Berthod, A., Carda-Broch, S. Determination of liquid-liquid partition coeffidents by separation methods./. Chromatogr. A 2004, 1037, 3-14. 

L. A. Predicfion of the solubility, activity coefficient and liquid/liquid partition coefficient of organic compounds. QSAR Comb. Sci. 2004, 23, 709-720. 

Initial purification is the rough purification (considered by many people as isolation) to prepare a feed for subsequent high-resolution steps. In initial purification steps the goal is to obtain concentration with partial purification of the product, which is recovered as a precipitate (precipitation), a solution in a second phase (liquid-liquid partitioning), or adsorbed to solids (adsorption, chromatography). 

The methods EN 1528 1996 and EN 12393 1998 comprise a range of old multiresidue methods of equal status, which are widely accepted throughout Europe. These are, e.g., the Luke method and the German Deutsche Forschungsgemeinschaft (DFG) methods S8 and S19 ° (all based on extraction with acetone), the Association of Official Analytical Chemists (AOAC) method 970.52 (using acetonitrile extraction and liquid-liquid partition combined with Horisil column cleanup) and the Dutch ethyl acetate extraction combined with GPC. All methods have been subjected to inter-laboratory studies, although not with all pesticide/matrix combinations, which would be impossible to achieve. 

The extent of cleanup needed depends on the target analyte, the quality of the sample extract, the method of detection and sensitivity. Liquid-liquid partition (LLP) and solid-phase extraction (SPE) columns such as the Cig cartridge and macroporous diatomaceous column are the cleanup method of choice. 

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). 

Analytical methods for parent chloroacetanilide herbicides in soil typically involve extraction of the soil with solvent, followed by solid-phase extraction (SPE), and analysis by gas chromatography/electron capture detection (GC/ECD) or gas chromatog-raphy/mass spectrometry (GC/MS). Analytical methods for parent chloroacetanilides in water are similarly based on extraction followed by GC with various detection techniques. Many of the water methods, such as the Environmental Protection Agency (EPA) official methods, are multi-residue methods that include other compound classes in addition to chloroacetanilides. While liquid-liquid partitioning was used initially to extract acetanilides from water samples, SPE using... 

The aqueous layer (CNP-NH2 layer) collected by liquid-liquid partitioning is transferred into a separatory funnel containing 20 mL of 4 M KOH aqueous solution and 100 mL of n-hexane, and shaken vigorously for 5 min. The n-hexane layer is collected. A further 100 mL of n-hexane are added to the aqueous layer and shaken again. The n-hexane layers are collected, dried with ca 50 g of anhydrous Na2S04, concentrated to dryness carefully, and n-hexane solution of the residue is prepared for GC analysis. 

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