Apparatus, assembling small scale

Semimicroscale Columns. An alternative apparatus for small-scale column chromatography is a commercial column, such as the one shown in Figure 19.8. This type of column is made of glass and has a solvent-resistant plastic stopcock at the bottom. The stopcock assembly contains a filter disc to support the adsorbent column. An optional upper fitting, also made of solvent-resistant plastic, serves as a solvent reservoir. The colunm shown in Figure 19.8 is equipped with the solvent reservoir. This type of column is available in a variety of lengths, ranging from 100 to 300 mm. Because the column has a built-in filter disc, it is not necessary to prepare a support base before the adsorbent is added. 

Although apparatus employing ground-glass joints is excellent for work on a macro scale, it is not always suitable for very small-scale work as the joints are often disproportionately large compared with the rest of the assembly. The semi-micro apparatus described on pp. 59-72 can therefore be considered as being of general utility for this scale of work, especially as the use of corks has been reduced to a minimum. 

The apparatus is dried in an oven and assembled under dry nitrogen. Alternatively it can be flamed dry in a stream of dry nitrogen. A magnetic stirrer can be utilized for small scale experiments. 

Due to the viscous nature of the bunker C oil, a large amount is left on the flotation cells wall and impeller assembly (axis and baffles). This fact explains the relatively low overall recovery of hydrocaAons (35%), although 99% of this substance is separated along with the froth. These losses are a result of the small-scale of the laboratory apparatus. In a properly designed continuous process, no significant hydrocarbon or solid losses will occur. 

In addition to the engineering skills and the access to the full range of supporting laboratory capabilities (bench development, in-process, analytical, physical chemistry, microbiology), scaling-up requires a variety of measurement apparatus (e.g., compressibility cell to measure flows through beds of solids at different compression), as well as the frequent assembly of dedicated apparatus or pilot units (e.g., units to measure fouling rates of surfaces over short-term test, small-scale... 

When dealing with small volumes, a fairly common approach has been to take the glass vessel and reduce its size to 100-200 mL, and to also scale down the size of the paddle shaft or basket shaft and baskets accordingly (Fig. 11.1). In most cases, the modified and smaller vessels are configured within the standard dissolution tester. Table 11.1 provides a comparison between standard USP dissolution Apparatus 2 and minidissolution assembly. Because the minidissolution assembly is not compendial, chemical and mechanical calibration procedures should be developed for performance verification. 

The checker reports that standard filtration techniques can be substituted for the centrifugation steps. The reaction of hydrous niobium (V) oxide is done in a 100-ml. round-bottomed flask fitted with an outer standard-taper joint. The solution of niobium(V) chloride in thionyl chloride is filtered by attaching a filter tube (having a standard-taper inner joint at each end) with a medium-porosity sin-tered-glass filter to the neck of the reaction flask, attaching another 100-ml. round-bottomed flask to the opposite end of the filter tube, and inverting the assembly. The residue can be washed with small aliquots of thionyl chloride. With this kind of apparatus the synthesis can be scaled up by a factor of 10 or more. 

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