Receivers and fraction collectors

For micro- and semi-micro-distillation smaller flasks are frequently necessary. As a rule these are made with pointed bases, in order that distillation may be continued down to a small residue (Fig. 127). 

Flat-bottomed flasks have proved to be favourable (Fig. 315) since the evaporating surface remains almost constant down to the residue whereas in round-bottomed flasks the liquid surface decreases more and more as the level sinks. 

For continuous distillation a satisfactory arrangement consists of a flask provided with an overflow tube, which maintains a constant liquid level and through which the bottom product is continuously drawn off. 

In low-temperature distillation it is usual to employ cylindrical flasks which are generally placed inside a Dewar vessel (Figs. 173, 175, 176,180). Other forms of flask may sometimes be necessary, depending on the method of heating (section 7.7.2). 

For semi-technical plants of glass, short-necked round-bottomed flasks of capacities up to 41 and three-neck round-bottomed flasks of capacities up to 101 (TGL 10102) are available. The glassware manufacturers can now offer spherical distilling flasks and cylindrical vessels with capacities up to 200 and 3751, respectively. Connection pieces may be placed at the top, at the side or at the bottom. Cylindrical vessels are usually provided with caps which hold the connection pieces. 

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The components to be described next are the first and last links in the chain of distillation apparatus. The still pot contains the substance to be distilled and the receiver and the fraction collector take up the purified and fractionated distillate, respectively. 

The fraction collector 23 normally contains sixty 20 ml receiving tubes and is buUt into a vacuum desiccator with a wire-gauze safety cover. It can be employed at atmospheric pressure and at reduced pressures down to 1mm. After 30 tubes have been filled a signal sounds alternatively, the apparatus may be made to switch over automatically to the next circle of tubes. When all the tubes are full there is another signal and the reflux controller is switched off so as to stop the distillate take-off. 

Radiolabeled [l- C]18 3n-3 was purchased from Perkin-Elmer Life Sciences (Boston, MA). The free acid form of 24 5n-3 and 24 6n-3 were generous gifts from A. Spector and H. Sprecher. Human skin fibroblasts from normal controls and patients with peroxisomal or mitochondrial disorders were received from the Mental Retardation Research Center of the Kennedy Krieger Institute. Cells at 90% confluence were incubated with 0.05 pCi albumin-bound [1- C] 18 3n-3 in Dul-becco s modified Eagle s minimum essential medium supplemented with 10% fetal bovine serum for 3 d. At harvest, cells were removed and washed with Hanks solution. An aliquot of cells was removed for protein determination, and the remainder was used for analysis of fatty acids after conversion to their methyl esters (17). Radiolabeled fatty acid methyl esters were separated by reversed-phase high performance liquid chromatography (18), and collected by a fraction collector. The radioactivity was counted by liquid scintillation counting. 

In the case of effluent analysis, one possibility is to receive the effluent in a fraction collector, several types of which are available commercially, and to process individual portions. Alternatively, the effluent can be scanned continuously, in general by the use of optical methods with or without appropriate reagents. In gas chromatography, the effluent is scanned continuously by means of detectors of various types. 

After standing in reactor 12, the mixture is cooled there down to 30 °C and filtered in nutsch filter 16 from diethylaminochloride. The filtrate is sent into tank 17 for distillation, and the filter cake is washed with toluene to eliminate amidation products as completely as possible. After the filtrate has been loaded, cooler 18 is filled with water, and the tank agitator is switched on. A residual pressure of 40-55 GPa is created in the system and the tank jacket is filled with a heat carrier or vapour. First, receptacle 20 receives toluene (below 60-65 °C) after separating toluene, amidation products are distilled into fractions. Receptacle 21 receives the intermediate fraction (below 106 °C) the distillation is monitored by the refraction index. At no20 = 1.4210+1.4230 the target fraction, diethylaminomethyl-triethoxysilane, is separated into receptacle 19. The distillation is continued up to 140 °C. As it accumulates, the intermediate fraction from receptacle 21 is sent into apparatus 12 for repeated amidation, and the ready product, diethylaminomethyltriethoxysilane, is sent after additional filtering (in case there is a filter cake) from receptacle 19 into collector 22. 

Some authors suggest the criterion of no overshadowing between 9 a.m. and 3 p.m. (i.e., 3 hr on either side of solar noon). Others are more demanding, suggesting 4 hr before and after solar noon (i.e., 8 a.m. to 4 p.m.) yet others are more permissive, with limits of 10 a.m. and 2 p.m. (i.e., 2 hr). All of these limits would apply to the mid-winter day. Figure 21 shows a typical irradiance curve for a northfacing collector (located in the Southern Hemisphere) with a 9 a.m. and 3 p.m. cut-off (other periods are shown by dashed lines). It is obvious that most of the radiation is received around solar noon, and the fraction lost (outside these time limits) is not excessive. 

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