Column, capillary thermostat

Equipment Hewlett Packard 6890 gas chromatograph equipped with a HP-5 0.25 gm, 30 mx 0.32 mm capillary column, a thermostat, three flasks for the reaction educts and products, microreactor setup according to Figure 12.15 with two microheat exchangers, a microreactor, three inlet/outlet modules, and a micromixer. Extra equipment for the experiments in a batch reactor, such as round-bottom flask equipped with a thermometer, a reflux cooler, a dropping funnel, and a mechanical stirrer, are necessary. 

The bulk of the SFE experiments performed to date were executed with systems typically consisting of a syringe or reciprocating pump, a high-pressure containing sample vessel comprised of HPLC column hardware, and a fused silica capillary restrictor. Extraction vessel temperatures of 40-80°C were usually accomplished using a converted oven or with the use of a thermostatted tube heater (2,3). Instrument manufacturers now offer a variety of commercially available SFE systems that vary in design, operation, features, ease of operation, and limitations. 

I, sample injector 2, thermostat 3, multi-capillary column 4, ionization chamber 5, 63Ni source of beta radiation 6, field inlet 7, separation chamber 8, electrodes 9, drift voltage generator 10, electrometer and... 

The stationary phase consists of a thin layer (ca. 0.2 pm) of a non-volatile liquid, such as methylsilicone or methylphenylsilicone, tightly adsorbed to the inert surfaces of the column. The liquid stationary phases are classified according to their polarity, non-polar phases are used most often because they are easier to handle and are stable over a wide temperature range. The mobile phase is an inert carrier gas such as nitrogen, helium or hydrogen which flows at a constant, but adjustable rate through the column. Current capillary columns, with internal diameters between 0.1-0.6 mm, are constructed of fused silica, specially prepared from pure silicon tetrachloride, and formed into spirals up to 100 m long. Injectors, columns and detectors are located in separately thermostatable compartments. 

Fig. 17.14. (a) CEC. Separation of racemic propranolol on a poly(methacrylic acid-co-TRIM) CSP (75 pm x 350 mm capillary column) imprinted with (/ )-propranolol. The sample was injected electrokinetically (5 kV, 3 s) and was separated at a constant voltage of 30 kV. The electrolyte was CH3CN-acetate buffer (4 M, pH 3.0) (8 2). Detection at 214 nm. The capillary was thermostatted to 60°C and an overpressure of 7 bar was applied. (Adapted from [61], with permission from the American Chemical Society, USA.) (b) CE. Separation of racemic propranolol using 0.05% (w/v) />o/y(Af-acryloylalanine-co-EDMA) particles imprinted with (5)-propranolol as a chiral additive in the background electrolyte (100 pm X 470 mm capillary column). The sample was injected by a 3 s pressure injection and was separated at a constant voltage of 15 kV. The electrolyte was 5 mM phosphate buffer, pH 7.0. Detection at 210 nm. Temperature 25°C. (Adapted from [62], with permission from the Royal Society of Chemistry, UK.)... 

Gas sampling valves are usually mounted in the column oven, in a separately heated adjacent oven, or external to the column oven and connected to the column by a short length of capillary tubing. For the most accurate work it is generally recommended that the injection valve is thermostatted in its own oven. Since the valve materials are in contact with the sample they must be chemically and physically inert, free from outgassing products, gas tight at all temperatures, and operate without lubricants. 

Most instruments use a cassette design to position the separation capillary in the thermostat and to connect the column with the buffer reservoirs and detector. Columns can be purchased with a detection window located at the correct position for insertion into the cassette. Alternatively, a number of different types of ring heaters, optical splicers and microbumers are available for those who wish to prepare their own columns at a lower cost [294,315,317]. A detector window is prepared by vaporizing a small section of the polyimide coating to leave a transparent section of fused silica about 1-2 mm long at a fixed distance from the column outlet. Once the window is formed, the column is fragile, and must be handled carefully. It is also important that the column ends are cut square and free of debris since misshapen column ends can results in distorted peak shapes and poor quantitative precision. 

Usually treatments of membrane osmometry do not refer to the height of a liquid column that brings the pressure to the membrane under gravity. We take care of this aspect. However, we will not deal with capillary effects. We show a possible experimental design for membrane osmometry in Fig. 6.15. The apparatus consists of two subsystems System ( ) is a solvent (1) with a solute (2) that cannot pass the membrane, and system (") consists of a pure solvent (1). The systems are separated by a semipermeable membrane. The whole design is embedded in a thermostat and operated in vacuum. We will assume that the solvent has a vapor pressure that does not contribute to the total pressure that is exerted to the membrane by gravity that is pointing downward. 

Direct injection is used with wide bore capillary columns ( 0.32 mm) operated at relatively high flow rates of 5-15 ml min The injector consists of a thermostatted hot vaporization chamber with a direct connection between the liner and the column. Figure 4. Typically, a double gooseneck liner is used with the column fixed to the constriction at the bottom end (the seal is usually made between the poly-imide outer coating of the column and the inner glass surface of the liner). Using a liner with a single... 

Ice-water mixture (thermostat), calorimeter vessel, water, mercury, capillary with mercury column, ice, sample container... 

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