Preparations semi-micro

For an example of sublimation, see the preparation of anthra-quinone, p. 259 for semi-micro sublimation, see p. 69. 

All thermometers for semi-micro preparations must have very small bulbs. They may often be inserted into flasks through a short collar of rubber tubing in place of the customary corks. 

Preparations, By employing suitable apparatus as described above, the student is enabled to carry out the following semi-micro preparations. 

The preparations of all the derivatives, and all the hydrolyses of esters, anilides, etc., described in Part III, provide excellent practice in semi-micro manipulation. 

Standard Semi-micro Equipment. The authors have found, during many years, that a student provided with the following basic semimicro equipment will be enabled to carry out the majority of the small preparations described in this book. 

First, considerably greater emphasis has been placed on semimicro techniques and their application to preparations, separations, analysis and physical determinations such as those of molecular weight. We have therefore greatly expanded the section on Manipulation on a semi-micro scale which was in the Third Edition, and we have described many more preparations on this scale, some independent and others as alternatives to the larger-scale preparations which immediately precede them. Some 40 separate preparations on the semi-micro scale are described in detail, in addition to specific directions for the preparation of many classes of crystalline derivatives required for identification purposes. The equipment required for these small-scale reactions has been selected on a realistic basis, and care has been taken not to include the very curious pieces of apparatus sometimes suggested as necessary for working on the semi-micro scale. 

A notable change in methods of isolating alkaloids from plant materials has been described by Applezweig, depending on the use of a suitable ion-exchange material and capable of application on a semi-micro scale or for industrial use. It has been applied to the preparation of the total alkaloids of cinchona bark (totaquina) and according to Sussman, Mindler and Wood, is also used industrially for the recovery of hyoscine. 

The maximum injection volume depends on the volume of the sample loop in the injection valve. The reproducibility of manual injection depends on the skill of the operator. The use of a small sample loop and an overflow injection of the sample solution so that the loop is fully flushed with sample are basic requirements for quantitative analysis. The highest injection reproducibility can be obtained by an auto-injector with a fixed sample loop. The smallest reasonable injection volume is 1 (A. A nl-scale injection valve can be constructed however, the memory effect at the surface of contact parts affects quantitative analysis compared with the use of a /d-scale injection valve. For a semi-micro system, a low hold-up volume injection valve is desired. The minimum injection volume is 80 nl. For a preparative-scale injection, the sample loop can be easily replaced with a larger-volume loop, such as a 200 jA, instead of the standard 20 /A loop. 

In gel inclusion chromatography (GIC), the insoluble, swelling cyclodextrin polymers are utilized (24-26). For routine analytical purposes this method is too slow and time consuming, but some highly effective preparative separations including enantiomeric resolutions have been published. This approach seems to be very promising for semi-micro or laboratory scale preparative separations. 

Polyelectrolyte complexes are very promising materials for preparing semi-permeable membranes of definite permeability and selectivity The methods of preparation and the properties of membranes made of polyelectrolyte complexes based on strong polyelectrolytes, e.g. poly(sodium sterene sulfonate) and poly(vinylbenzyl-trimethyl ammonium chloride) were described These membranes may be applied for reverse osmosis in the desalting of sea-water, for dialysis and ultrafiltration in purifications and concentration of water solutions containing coUoids or micro-and macroparticles ... 

Brown, G. (1953) A semi-micro method for preparation of clays for X-ray study. Journal of Soil Science 4, 229-232. 

The cuvette rotor receives the reagent preparations of the samples, rotates the cuvettes for light measurements and places them under the washing station. The rotor is furnished with 45 semi-micro cuvettes —the odd number allows for simultaneous filling, measurement and aspiration. Only every second cuvette is filled. Every 8 s, each cuvette returns to its initial position after two turns. The minimum analysis time is therefore 6 min or a multiple of this. 

Chapter XII is concerned with Semimicro Technique. There can be little doubt that preparations on a smaller scale than has hitherto been customary have many advantages particular reference may be made to cost, time and bench space, all of which are important factors in teaching laboratories and also in training for research. Once the student has mastered the special technique, no difficulty should be experienced in adapting most of the preparations described in the book to the semi-micro scale. A few examples of small-scale preparations are included together with a suggested list of experiments for an elementary course. 

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