Column chromatography, determination

Gel-filtration column chromatography Determination of average molecular weight and the NH7-terminus... 

SI Huang, MJ Caldwell, KL Simpson. Reverse phase open column chromatography determination of urinary riboflavin. Int J Vitam Nutr Res 63 217-222, 1993. 

The separation of xanthates by ion-interaction reversed-phase column chromatography is described for the determination of eight different xanthates in reagents commonly used in flotation plants. The separated species were detected spectroscopically at a wavelength of 305 nm (96). 

Bi-functional radio-analytical scheme, based on exchange and extraction column chromatography, which provides the reliable information on molybdenum and uranium contents in biological materials has been elaborated. The contribution of uranium fission reaction has been strictly monitored. The uncertainty of the results of Mo determination by the presented method is very low. 

MICROWAVE-ASSISTED SOLVENT EXTRACTION AND A NEW METHOD FOR ISOLATION OF TOTAL PETROLEUM HYDROCARBONS (TPH) FROM PLANTS WITH COLUMN CHROMATOGRAPHY (SILICA GEL AND ALUMINA) AND DETERMINATION WITH SPECTROFLUOROPHOTOMETRY... 

Into a suspension of 8 g of sodium acetate m 400 mL of a solution of 1 part acetic acid and 10 parts fluorotnchloromethane is passed at -75 C a stream of fluonne diluted to 10% with nitrogen The reacuon is stirred with a Vibromixer A solution of 4-methylacetanilide (20 mmol) in a mixture of dichloromethane and fluorotnchloromethane cooled to -75 °C i s added to 20 mmol of acetyl hypofluonte as determined by titration with potassium iodide After 5 min the mixture is poured into water, and the orgamc layer is washed with sodium bicarbonate soluaon and dried over anhydrous magnesium sulfate After concentrauon and column chromatography over silica gel and elution with chloroform, 2-fluoro-4-methylacetanilide IS obtained m 85% yield... 

Showa Denko K.K. started the Shodex HPLC business in 1973 by developing columns to determine the molecular weight distributions of polymers produced at its petrochemical plant. Since then, more than 600 items of columns have been developed to achieve various kinds of analyses. Among them are several series of columns that can be used for size exclusion chromatography. The abundant variety of columns is one of the important characteristics of Shodex. Any kind of analytical requirements can be satisfied by choosing the appropriate column supplied by Showa Denko. 

To a solution of 1.44 g (3 mmol) of MAD in 10 mL of toluene are added 154 mg (1 mmol) of 4-rerr-butyl-cyclohexanone (3) at — 78°C. Butyimagnesium bromide (3 mmol) in btzO is added and the reaction mixture is stirred at — 78 C for 2 h. After quenching with 1 N HCI and extraction with Et20, the combined extract is dried and concentrated. The crude product is purified by column chromatography on silica gel (Et20/hex-ane) yield 142 mg (67%) d.r. 100 0 [determined by capillary GC (column PEG-HT, 0.25 mm x 25m temp. 130"C) by comparison with authentic samples]. 

To 158 mg (1 mmol) of 2-formyl-jVJV,3-trimcthylbutanamide in 5 ml, of CH2C12 are added at 0°C 2 mL of 1.0 M (dichloro)methylaluminum (2 mmol) in hexane. The reaction mixture is stirred at 25 °C for 2 h, then quenched with 1 M HC1. After extraction with CHCI,/EtOH (3 1), the combined organic layer is dried over Na,So4 and concentrated in vacuo. The crude product is purified by silica gel column chromatography yield 106 mg (62%) d.r. [(26, 35 )/(25, 3R )] 99 1 (determined by capillary GC). 

At 03C, a solution of 120 mg (1.2 mmol) of phenylacetylene in 2 mL of dry Et20 is treated with 0.45 mL (1.2 mmol) of 2.6 M BuLi in hexane, The mixture is stirred for 30 min, then a solution of 290 mg (1.3 mmol) of anhyd zinc bromide in 2 mL of Et20 is added. After cooling to —78 C, 100 mg (0.6 mmol) of 2-(ben-zyloxy)propanal (7) are added and the reaction mixture is allowed to warm to 0 C over a 2-h period. The reaction is quenched with sat. aq NH4C1. The organic layer is separated, dried over Na2S04 and concentrated. The residual oil is purified by column chromatography on silica gel yield 154 mg (95%) d.r. (syn/anti) 95 5 (determined by HPLC). 

Determined on the crude product by NMR. b After purification by column chromatography always d.r. >99 1. 

A solution of 0.858 g (5.5 mmol) of 4-(1-methyl-l-butenyl)morpholine and 0.75 g (5.0 mmol) of ( )-(2-ni-troethenyl)benzene in 10 mL of diethyl ether is kept at r.t. for 4d. The solution is then evaporated and treated with a mixture of 13 mL of ethanol and 15 mL of 10% aq hydrochloric acid for 1 h at 25 C. The solution is extracted with CH2C12 and the organic phase is washed with aq Nall CO, then with water and dried over MgSO . Evaporation gives 1.04 g of an oil which is purified by column chromatography (silica gel. hexanc/cthyl acetate 10 1) to give the pure title compound as an oil yield 0.90g (77%). The diastereomeric ratio is determined by HPLC (methanol/water 4 1, reverse phase RP8) to be 93 7. 

Analysis of sulfonic acid species in sulfonated olefins. Kupfer and Kuenzler [108] reported the determination of acid species following partition between a 6.5% hydrochloric acid solution in 40% ethanol and a 1 1 (v/v) propan-2-ol-hexane mixture. The organic fraction contains alkenesulfonic and hydroxy-alkanesulfonic acids and the aqueous phase disulfonic acids and sulfato-sulfonates. The monosulfonic acids were converted to methyl esters and separated by column chromatography. To determine sulfatosulfonates the aqueous fraction was hydrolyzed and then partitioned and chromatographed. The separation is controlled using IR spectroscopy. 

Analysis of neutral product for active species. The di- and poly sulfonates present in AOS have been isolated from monosulfonates by column chromatography using silanized silica gel by Puschmann [109]. The content of mono-and disulfonates in the fractions obtained were determined gravimetrically. 

We reacted 2 first with bromine in chloroform at 10 C. iH NMR studies have revealed that the reaction mixture was very complex and consisted of six products. This mixture was submitted to silica gel column chromatography. Careful repeated chromatography followed by fractional crystallization allowed us to isolate ten products (Scheme 3). IR analysis indicated that a hydroxyl group was incorporated in compounds lfi-19. Therefore, we assume that these products have been formed by partial hydrolysis of compounds lfl-14. Structural determination of compounds lfl-19 revealed that the barrelene skeleton was rearranged completely. 

Because of the instability of many of the compounds involved, it is necessary to determine the chemical recoveries in all cases. This requires the use of macro quantities (10 mg up to several hundred mg) of carriers and target compounds. This, in turn, makes it impractical to use the various thin-layer methods, such as paper and thin-layer chromatography and paper electrophoresis, although such methods have proved useful in identifying products and in checking the purity of fractions. The separation methods now most commonly used are column chromatography and sublimation. 

It is fruitless to attempt detailed study of a phenomenon whose products are not well identified. It is unfortunately frequently noted in the literature, especially in cases of column chromatography, that fractions are only identified as to the chemical operations which brought them to light. Fractions are identified, for example, only by the solvent used. Speculations as to the composition of the radioactive solutes in such solutions can seldom be really reliable, and the presence of an unexpected radioactive species is in such cases undetectable. It is also important in reading the literature to watch out for cases in which the chemical yields of the carriers have not been measured. Extensive decomposition can often occur on silica gel and alumina columns, especially when photosensitive or moisture sensitive compounds are used. For these reasons much of the information now existing in the literature must be regarded as only exploratory, awaiting the development of better analytical methods for separation, purification, identification and determination of the products —known or expected. 

Detection of the PSP toxins has proven to be one of the largest hurdles in the development of analytical methods. The traditional means, and still in wide use today, is determination of mouse death times for a 1 mL injection of the test solution. There are a variety of drawbacks to utilization of this technique in routine analytical methods, that have prompted the search for replacements. In 1975 Bates and Rapoport (3) reported the development of a fluorescence technique that has proven to be highly selective for the PSP toxins, and very sensitive for many of them. This detection technique has formed the basis for analytical methods involving TLC (77), electrophoresis (72), column chromatography (7J), autoanalyzers (7 ), and HPLC (5,6,7). 

After It has been determined which chain In the variant Is aberrant, specific structural studies are required. Several procedures are available which differ from one laboratory to the other and Include chain separation by column chromatography, modification of the sulfhydryl groups through reaction with... 

In order to achieve a true comparison between both catalytic systems, colloidal and molecular, which display very different reaction rates, a series of experiments were carried out with the homogeneous molecular system, decreasing the catalyst concentration in the studied allylic alkylation reaction. The reaction evolution is monitored taking samples at different reaction times and analysing each of them by NMR spectroscopy (to determine the conversion) and HPLC chromatography with chiral column (to determine the enantioselectivity of I and II). For molecular catalyst systems, the Pd/substrate ratio was varied between 1/100 and 1/10,000. For the latter ratio, the initial reaction rate was found comparable to that of the colloidal system (Figure 2a), but interestingly the conversion of the substrate is quasi complete after ca. 100 h in... 

In optintization of systems for preparative column chromatography, besides the choice of optimnm conditions enabling satisfactory resolution in a short time, load-ability determination also seems to play an important role. TLC and PLC are usually used for the search of system selectivity for individual purposes. 

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