Semimicro scale, operations

XII,2. SOME TYPICAL OPERATIONS ON THE SEMIMICRO SCALE 1. Distillation at atmospheric pressure.—A simple apparatus is shown in Fig. XII, 2, 1 the pear-shaped distilling flask with long side... 

II.4 SEMIMICRO APPARATUS AND SEMIMICRO ANALYTICAL OPERATIONS The essential technique of semimicro analysis does not differ very greatly from that of macro analysis. Since volumes of the order of 1 ml are dealt with, the scale of the apparatus is reduced it may be said at once that as soon as the simple technique has been acquired and mastered, the student will find it just as easy to manipulate these small volumes and quantities as to work with larger volumes and quantities in ordinary test-tubes (150 x20 mm) and related apparatus. The various operations occupy less time and the consumption of chemicals and glassware is reduced considerably these two factors are of great importance when time and money are limited. Particular care must be directed to having both the apparatus and the working bench scrupulously clean. 

Distillation is a widely used technique in chemical analysis for characterizing materials by establishing an index of purity and for separating selected components from a complete matrix. The technique is even more widely used in preparative chemistry and throughout manufacturing industry as a means of purifying products and chemical intermediates. Distillation operations differ enormously in size and complexity from the semimicro scale to the thousands of tons per annum production operations. For analytical purposes the scale employed is usually bench-level. 

The scale of the recrystallisation envisaged in group (1) means that the operations are carried out in the conventional manner but in apparatus of reduced size. Thus small conical flasks (5 to 20 ml), pear-shaped flasks (5 to 20 ml), semimicro test tubes (75 x 10mm or 100 x 12mm) or centrifuge tubes (1 to 5ml)... 

In micro analysis the scale of operations is reduced by a factor of 0-01 as compared with macro analysis. Thus whereas in macro analysis the weights and volumes for analysis are 0-5—1 g and about 10 ml, and in semimicro analysis 50 mg and 1 ml respectively, in micro analysis the corresponding quantities are about 5 mg and 0-1 ml. Micro analysis is sometimes termed milligram analysis to indicate the order of weight of the sample employed. It must be pointed out that whilst the weight of the sample for analysis has been reduced, the ratio of weight to volume has been retained and in consequence the concentration of the individual ions, and other species, is maintained. A special... 

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