Eluents degassing

Eluent degassing is important due to trap in the check valve causing the prime loose of pump. Eoss of prime results in erratic eluent flow or no flow at all. Sometimes only one pump head will lose its prime and the pressure will fluctuate in rhythm with the pump stroke. Another reason for removing dissolved air from the eluent is because air can get result in changes in the effective concentration of the eluent. Carbon dioxide from air dissolved in water forms of carbonic add. Carbonic add can change the effective concentration of a basic eluent including solutions of sodium hydroxide, bicarbonate and carbonate. Usually degassed water is used to prepare eluents and efforts should be made... 

The sample and eluents must be filtered through at least a 0.45 pm filter, and the eluents degassed. 

Sephacryl gels were preswelled in H20(dest) -I- 0.01% Merthiolate. The diluted and degassed gels were then packed at medium pressure assisted by a pump-sucking eluent with a flow rate of approx 0.4 ml/min. 

The traditional HPLC instrument is composed of two different parts the first part separates the components of the sample and the other part accomplishes the detection of the components separated. The part of the HPLC carrying out the separation contains a column, an injection device and the eluent delivery system (pump with filters, degasser and transfer tubing, eventually a mixer for gradient elution). One or more detectors, a signal output device coupled with appropriate software, are responsible for detection and primary data evaluation. Pumps deliver the eluent or the different components of the eluent into the column with a precise, constant and reproducible flow rate. 

Degassing of the eluent is important for trouble-free operation and highly sensitive detection,2 otherwise the eluent may become supersaturated with air that is released as bubbles in the pump check valves or the detector flow... 

B. 1,3-Dimethyl-6H-benzo[b]naphtho[1,2-d]pyran-6-one (4). Under an argon atmosphere, a 250-mL, oven-dried, round-bottomed flask, equipped with a reflux condenser, is charged with freshly distilled N,N-dimethylacetamide (DMA, 130 mL), 3,5-dimethylphenyl 1-bromo-2-naphthoate (3, 3.24 g, 9.12 mmol), palladium(ll) acetate (205 mg, 0.913 mmol), triphenylphosphine (481 mg, 1.83 mmol), and sodium acetate (1.50 g, 18.3 mmol) (Notes 4 and 5). The orange suspension is degassed three times, placed in a preheated (130°C) oil bath (Note 5), and stirred at 130°C for 12 hr (Note 6). Removal of the solvent at 40°C (0.1 mbar, 0.075 mm) gives a black oily residue, which is Chromatographed (5 x 40 cm column, silica gel 0.063 - 0.2 mm, 170 g, 1 cm of charcoal at the top of the column eluent hexane / diethyl ether 5 1), to yield 2.00 g (80%) of the lactone 4 as a slightly yellow solid. Recrystallization from diethyl ether / hexane delivers 1.63 g (65%) of colorless or pale yellow crystals (Note 7). 

A simple and effective form of degassing is to hold a flask of mobile phase under a vacuum while agitating the contents in an ultrasonic bath (Fig. 3.7). The eluent is then transferred to the chromatograph for several hours of reliable operation, especially if the eluent is blanketed with an inert gas such as helium. This approach is particularly useful for clean solvents that readily absorb gases such as carbon dioxide from the atmosphere. The eluent should be degassed in the solvent storage container used for chromatography to minimize contact with the air. 

A mixture of Se-Vh selenoester (23.9 jxmol) and AIBN (1 mg) in dry benzene (6 ml) was degassed and substituted by argon gas. Benzene (2 ml) solution of Bu3SnH (29.8 p,mol) and AIBN (1 mg) was added dropwise to the refluxing mixture over 8 h. After the addition, the mixture was refluxed further 3 h. After removal of the solvent, the residue was chromatographed on silica gel (eluent ether and petroleum ether) to obtain a hepta-cyclic compound in 17% yield [322]. 

To a solution of 5 (30 mg, 0.114 mmol) in dry degassed CH2C12 (25 mL) was added, via syringe, a solution of ruthenium alkylidene catalyst G1 (5 mg, 0.006 mmol) predissolved in CH2C12 (6mL). The resulting purple solution was heated to 45 °C for 21 h and then concentrated under reduced pressure to afford an oily brown residue. Purification by MPLC [pre-packed silica gel column 2 x 50 cm, eluent ethyl... 

Representative procedure. To a solution of oxime 17 (1 equiv) and t-BuOH (2.5 equiv) in THF was added dropwise Sml2 (3 equiv) in anhydrous degassed THF under an argon atmosphere at -78 °C. The solvent was then evaporated at reduced pressure. The resulting residue was taken up in Et20 and filtered through a pad of Celite. The filtrate was concentrated in vacuo and the crude product was purified by column chromatography (EtOAc-hexanes eluent). 

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