Oven thermostats

The basic SFC system comprises a mobile phase delivery system, an injector (as in HPLC), oven, restrictor, detector and a control/data system. In SFC the mobile phase is supplied to the LC pump where the pressure of the fluid is raised above the critical pressure. Pressure control is the primary variable in SFC. In SFC temperature is also important, but more as a supplementary parameter to pressure programming. Samples are introduced into the fluid stream via an LC injection valve and separated on a column placed in a GC oven thermostatted above the critical temperature of the mobile phase. A postcolumn restrictor ensures that the fluid is maintained above its critical pressure throughout the separation process. Detectors positioned either before or after the postcolumn restrictor monitor analytes eluting from the column. The key feature differentiating SFC from conventional techniques is the use of the significantly elevated pressure at the column outlet. This allows not only to use mobile phases that are either impossible or impractical under conventional LC and GC conditions but also to use more ordinary... 

Drying, usually by physical methods, is one of the most common unit operations in both laboratory or industrial scale process chemistry, and since heating is usually employed to remove volatiles, thermally unstable materials may decompose if overheated. As a light-hearted example, when a faulty oven thermostat led to overheating of mercuric thiocyanate, a monstrous Pharaoh s serpent resulted. Drying moist cadmium propionate in an electric oven led to explosive ignition of the diethyl ketone vapour produced as an unforeseen by-product. Drying 3,5-dinitro-2-toluamide had more serious consequences. 

Veigh to the nearest mg a tall Kraft paper container 30 mm In dlam and 0.2 mm thick. Pack the container with the sample(l00 g) and reweigh. Tare to the nearest mg a piece of porous cardboard 5 5 cm square and 2 mm thick. Place the container on the cardboard and insert the ensemble In an oven, thermostatically maintained at 40 1° or 501 1°. After 21 days, reweigh the cardboard, the sample + container, and the empty container... 

The Mason jar was sealed with a screw cap and placed in an oven thermostatically controlled at 50°C. The increase in weight of this vial was monitored and the hydrolysis of the test sample measured as described above. 

Ovens, thermostatically controlled or other suitable equipment. 

Column oven thermostatically controlled enclosure for the chromatographic column, maintained to 0.1 °C, may be isothermal or temperature programmed. 

Cold on-column injection employs the direct introduction of the sample as a liquid into the oven-thermostatted column inlet or precolumn without prior vaporization in a heated external chamber [40,42,43,69,81]. The sample is subsequently vaporized from the liquid layer formed in the column inlet or precolumn. Cold on-column injection is the only technique in which the composition of the sample introduced into the column is identical to the original sample composition. Discrimination is virtually eliminated and quantification of components of different volatility is facilitated. Sample... 

Concurrent eluent evaporation is most commonly performed with the loop-type interface (Figure 4) the liquid is pushed into the oven-thermostatted precolumn by the carrier gas and stopped there by its... 

Electric ovens. The most convenient type is an electrically heated, thermostatically controlled drying oven having a temperature range from room temperature to about 250-300 °C the temperature can be controlled to within 1 -2 °C. They are used principally for drying precipitates or solids at comparatively low controlled temperatures, and have virtually superseded the steam oven. 

The column is enclosed in a thermostatically controlled oven so that its temperature is held constant to within 0.5 °C, thus ensuring reproducible conditions. The operating temperature may range from ambient to over 400 °C and for isothermal operation is kept constant during the separation process. 

It is seen that in order to measure retention volumes with a precision of 0.1%, the temperature control must be +/- 0.04°C. This level of temperature control on a thermostat bath is not difficult to achieve but it is extremely difficult, if not impossible, to return to a specific temperature to within +/- 0.04°C after prior change. To achieve a precision of retention volume measurement of 1%, the temperature control must be +/- 0.4°C. This is far more practical as most column oven temperature can be set to a given temperature to within +/-0.25°C. Although the data was obtained for three specific solutes, the results can be taken as reasonably representative for all solutes and phase systems. In most practical analyses, the precision limits of retention volume measurement will be about 1% but this will not include the reproducibility of the flow rate given by the pump. As... 

The column oven is generally a forced circulation air thermostat of sufficient size to allow comfortable installation of the longest columns normally used. In the design of a column oven it is important to ensure a uniform temperature throughout the column coil region. The temperature uniformity depends on the geometry of the oven, the Ideation of the heater and sensor, and the pattern of mixing and circulation of air. A temperature... 

A portion of each solution was retained for analysis of carb-oxylate content at zero time. Samples of the polymer solutions were weighed into glass jars, the pH adjusted to 8.5 and the jars were sealed with tightly fitting screw caps. The jars were placed in thermostatted ovens at 90°, 108°, and 120°C. After the appropriate time, the jars were removed, cooled and weighed to ensure no loss of contents, prior to analysis for hydrolysis. 

Within a fuzzy system, an inference engine works with fuzzy rules it takes input, part of which may be fuzzy, and generates output, some or all of which may be fuzzy. Although the role of a fuzzy system is to deal with uncertain data, the input is itself not necessarily fuzzy. For example, the data fed into the system might consist of the pH of a solution or the molecular weight of a compound, both of which can be specified with minimal uncertainty. In addition, the output that the system is required to produce is of more value if it is provided in a form that is crisp "Set the thermostat to 78°C" is more helpful to a scientist than "raise the temperature of the oven." Consequently, the fuzzy core of the inference engine is bracketed by one step that can turn crisp data into fuzzy data, and another that does the reverse. 

The oven temperature always drops a few degrees, owing to the cooling effect of the cold acid and the evaporation of a relatively large quantity of water. This drop in temperature is much less noticeable in a large oven than in a small one, and in one having thermostatic control in contrast to manual control. 

To ensure operation under reproducible conditions, the column is enclosed in a thermostatically controlled oven whose temperature can be held constant to within 0.1°C. Operating temperatures range from ambient to over 400°C and may remain constant during a separation - isothermal operation - or automatically increased at a predetermined rate to speed the elution process - temperature programming (p. 106). The latter is a form of gradient elution. Rapid temperature equili-... 

Most modern HPLC instruments include a column oven that can thermostat the column to at least 100°C. A typical HPLC analysis can be done in half the time by elevating the column temperature from ambient to 50 or 60°C. At temperatures above 100°C, it is not uncommon to decrease analysis time by a factor of 5.26 Also, re-equilibration time for the column is much shorter, so it is possible to achieve ultra-fast gradient analysis with HTLC. 

All solvents for these solution thermolysis reactions were freshly distilled and all reactions were done in sealed glass tubes heated in a thermostatted oven. Over a wide range of solvents (DMF, naphthalene, diphenylmethane, benzene, toluene, and decalin) there was no significant variation in either isomerization rate or product composition. Reactions were done at 125°C, 155°C and 195°C and the only limitation was that DMF could not be used as the solvent in reactions at 195°C it led to substantial substrate destruction (polymer forming reactions of substrate with DMF ). Isomer compositions were ascertained both by HPLC and by NMR. 

Small lab reactors are fiequently thermostatted, either by contact with the surroundings (a small beaker on a bench) or by placing them on a hot plate or in an oven. This is because in a lab reactor the wall area (where heat transfer occurs) is usually large compared to the reactor volume (where reaction heat is generated). 

The beaker containing the solvent is equilibrated in a thermostatically controlled oven at 95 C for about 15 minutes. 

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