Low-temperature chromatograph

In the earliest interface, a continuous moving belt (loop) was used onto which the liquid emerging from the chromatographic column was placed as a succession of drops. As the belt moved along, the drops were heated at a low temperature to evaporate the solvent and leave behind any mixture components. Finally, the dried components were carried into the ion source, where they were heated strongly to volatilize them, after which they were ionized. 

Separated from retinol by column chromatography on water-deactivated alumina with hexane containing a very small percentage of acetone. Also chromatographed on TLC silica gel G, using pet ether/isopropyl ether/acetic acid/water (180 20 2 5) or pet ether/acetonitrile/acetic acid/water (190 10 1 15) to develop the chromatogram. Then recrystd from propylene at low temperature. 

Although many attempts have been made to separate or exclusively synthesize one isomer of an unsymmetrically substituted phthalocyanine,72-89-296,297 the product mixture has been separated in only two cases.96 103,104 Besides the chromatographic separation of the statistical product mixture it is also possible to prepare exclusively the D4h isomer by use of steric hindrance of bulky substituents, e.g. 7-ferr-butylnaphthalene-l,2-dicarbonitrile only forms the respective An isomer of the tetra(to -butyl)-substituted 1,2-NcFe by heating in hexan-l-ol.73 Recently, some 1,8,1 5,22-substituted pure isomers have also been synthesized by the use of bulky substituents in 3-substituted phthalonitriles298,299 at low temperature (see Section 2.1.4.).94... 

To a solution of 6.99 g (25.3 mmol) of 2,3,4-trimethyl-4-(5-trimethylsilyl-3-pentynyl)-2-cyclohexenone in 150 mL of C HjClj are added at —78 C 5.1 mL (44 mmol) of TiCl4, and the resultant mixture is stirred for 30 min at —78 "C. The mixture is quenched at low temperature with 100 mL of water and extracted with three 50-mL portions of Ch,C12. The combined organic phase is washed with 150 ml, of brine and dried over MgS04. The solvent is removed in vacuo and the crude product is flash chromatographed (EtOAc/ petroleum ether 3 97) to give the pure product as a 2 1 mixture of diastcreomers yield 4.32 g (84%) d.r. 2 1. 

Rittenhouse, C.T., and Olesik, S.V., High performance liquid chromatographic evaluation of a low-temperature glassy carbon stationary phases, /. Liq. Chromatogr. Relat. Technol, 19, (17,18), 2997, 1996. 

Additional advances have been made in the use of leaving groups other than halide for the nonphosphorus component of the Michaelis-Arbuzov reaction. The sensitive species 3,5-d i-t-b u ty I -4-hydroxybenzyl acetate has been noted to undergo efficient reaction (75-85% isolated yields) with a series of trialkyl phosphites upon heating at relatively low temperature (95°C) without the use of excess phosphite or additional catalyst.138 Chromatographic analysis of the reaction mixture indicates virtually quantitative conversion in the process. 

Ethyl glycidate is a rather sensitive compound (it cannot be chromatographed on silica gel) and distillation at low temperature under high vacuum (0.1-2 mm) avoids the formation of undistillable residues resulting from polymerization. The product should be stored at 5°C (or lower) and is perfectly stable at this temperature. 

From all these results dinophysistoxin-3 was assigned to 7-0-acyl dinophysistoxin-1 (III). Dinophysistoxin-3 was extremely vulnerable to acid, alkali and exposure to air. Leaving a dried sample, even at low temperature, easily resulted in the loss of toxicity and production of multiple spots on TLC. The presnece of this component in the mussel and two species of the short-necked clams was evidenced by liquid chromatographic analysis of intact toxin and by gas chromatographic analysis of dinophysistoxin-1 and fatty acids in the hydrolyzates. 

Preparation of various enantiomerically pure sulfoxides by oxidation of sulfides seems feasible in the cases where asymmetric synthesis occurs with ee s in the range of 90% giving crystalline products which can usually be recrystallized up to 100% ee. Aryl methyl sulfides usually give excellent enantioselectivity during oxidation and are good candidates for the present procedure. For example, we have shown on a 10-mmol scale that optically pure (S)-(-)-methyl phenyl sulfoxide [a]p -146 (acetone, o 1) could be obtained in 76% yield after oxidation with cumene hydroperoxide followed by flash chromatographic purification on silica gel and recrystallizations at low temperature in a mixed solvent (ether-pentane). Similarly (S)-(-)-methyl o-methoxyphenyl sulfoxide, [a]p -339 (acetone, o 1.5 100% ee measured by HPLC), was obtained in 80% yield by recrystallizations from hexane. 

To make sure of identical background and other conditions all sampling were done at the same time in the greenhouse. Twelve pots, four with plants of the barley cultivar Etu, four with barley cultivar Tellus, and four with soil only, were placed on a table with holes for the pots. The bottom of the pot was then easily accessible for all the necessary connections. Two samples from each pot and in all twenty-four samples in each set were obtained. After sampling, all tubes were stored in screw-capped glass tubes under inert conditions (low temperature and helium atmosphere) until gas chromatographic analysis. 

The extraction technique can play an important role in the recovery of volatiles, resulting in different profiles of volatiles for the same variety [67]. The direct extraction of Cucumis melo L. var. cantaloupensis with Freon 11 under low temperature was capable of recovering compounds never found before in melons [26]. The authors attributed this to the non-destructive extraction at low temperatures and the very efficient capillary chromatographic system used for the analysis. 

For the synthesis of atorvastatin we developed an efficient process that allows for direct cyanation of lactone 2 [21] to cyanomethyl lactone 3 to finally afford the well known atorvastatin precursor 5 (Scheme 6.3) [22]. It is worth pointing out that the two synthetic routes to the advanced statin intermediates 5 and 6 described here avoid ultra-low temperature chemistry, heavy metal catalysts, metal-organic species, and chromatographic purification steps. The DERA-catalyzed chemistry to form the six-carbon chiral unit is cost competitive and operated on a commercial scale. 

The gas chromatograph has an oven with sufficient volume to hold the column easily and which can be heated to the desired temperature (between 40 and 450 °C, stabilised to within 0.1 °C). The atmosphere inside the oven, which usually has a very small thermal inertia, is constantly agitated by forced ventilation. Using a cryogenic valve through which nitrogen or carbon dioxide can be introduced, the oven can be regulated at low temperatures. 

A method is presented for obtaining the diffusion coefficients of Ci to C4 hydrocarbons on H and Na mordenite by analysis of their chromatographic curves. It is shown that in such a transient device the role of the intercrystalline diffusion may be important for the estimation of the total mass-transfer resistance. The diffusion coefficients decrease with increase in the number of carbon atoms. They are about one order of magnitude smaller on mordenite in the Na form than in the H form. The energies of activation are higher for intracrystalline diffusion than for intercrystalline diffusion. The resistance from intercrystalline diffusion makes an important contribution to the total mass-transfer resistance at low temperature. 

To produce impressive linearity measurements, it helps to (a) use easily chromatographed compounds, like propane, (b) use minimum oven temperature, low-loaded columns, low temperature injection port and detector, (c) use fast, very sharp peaks,... 

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