Melting point tubes packing

Apparatus Capillary melting-point tubes, packing tube, and melting-point apparatus. 

Figure 9.6 shows two simple methods of evacuating a packed tube. Method A uses an ordinary melting-point tube, and method B constructs the melting-point... 

Melting points are important for determining the purity of solid products. A small amount of sample is packed into the closed end of a capillary tube with a wire or small glass rod. It is then attached to a thermometer, keeping the sample next to the bulb as shown (see Figure 19). Next submerge into oil filled tube, keeping setup in the middle of tube (do not touch the sides or bottom). Watch for temperature at which solid sample melts. 

All IR spectra were measured using an FT-IR spectrometer, JASCO FT/IR-420. All concentrations of Cl-MIT were measured by HPLC, using a column (0.6 cm x 15 cm), packed with YMC PAC ODS-A. Some 20 vol. % aqueous solution of acetonitrile was used as solvent (flow rate 1.0 ml min-1, detection UV spectrophotometer 273 nm). All melting points were measured with the sample packed in a capillary tube. 

Obtain a melting point capillary tube. One end of the tube will be sealed. The tube is packed with solid in the following way ... 

Some commercial melting-point instruments have a built-in vibrating device that is designed to pack capillary tubes. With these instruments, the sample is pressed into the open end of the capillary tube, and the tube is placed in the vibrator slot. The action of the vibrator will transfer the sample to the bottom of the tube... 

The melting point of the crystalline solid is determined by heating the packed capillary tube until the solid melts. Some representative devices for measuring melting points are presented in Figures 2.17-2.19. The most reproducible and accurate results are obtained by heating the sample at the rate of about 1-2 °C/min to ensure that heat is transferred to the sample at the same rate as the temperature increases and that the mercury in the thermometer and the sample in the capillary tube are in thermal equilibrium. 

Packed Columns. These columns are usually constructed of stainless steel tubing with diameters of 1 /8 in. (3 mm) or 1 /4 in. (6 mm) and lengths of from 4 to 12 feet. The column is packed with a liquid or low-melting solid as the stationary phase distributed on a solid support material. The stationary phase must be relatively nonvolatile, that is, it should have a low vapor pressure and a high boiling point. Some typical stationary phases used with packed columns are listed in Table 22.1. Typical support materials are shown in Table 22.2. The most common support material consists of diatomaceous earth (Chromosorb). 

A schematic flow diagram of the unit is shown in Figure 3-33. A solution of 48 wt% potassium hydroxide is added to the contaminated diethanolamine before it enters the top of a packed tower where it is contacted with superheated steam rising from the reboiler. Essentially all of the amine and water is vaporized, and the product is withdrawn at a point below the packed section into a condenser, which is held at a slightly lower pressure than that prevailing in the reboiler. A steam jet is used to maintain the required pressure. The salts drop into the reboiler and melt at 420 to 440°F, and any residual diethanolamine is flashed off. The temperature of the diethanolamine-water vapor withdrawn is 300 to 375°F. The temperatures in the column and reboiler are sufficient to vaporize practically all the amine without decomposition. Heat is supplied by circulating oil at 600°F through the reboiler tubes. Recovery of 90% of reusable diethanolamine is claimed. 

Figure 3 (A) The classic fibre optic probe for fluorescence spectroscopy is based on two or more fibres. Hexagonal packing is a dense arrangement and allows the selection of multiple fibres for different excitation sources and collection channels. A quartz shields permits the overlap of excitation and collection areas. The parts are (a) excitation fibres (b) collection fibres (c) tubing (d) carbon filled glue (e) sleeve (f) shield. (B) Atypical fluorescence probe for single point sampling (a) excitation fibres (b) collection fibres (c) sleeve. (C) A hexagonal fibre bundle with a melted and compressed arrangement allows excellent illumination and interrogation overlap. Reproduced by permission of Innova Quartz Inc.

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