Semimicro analysis

Janak, J. Chromatographic semimicro-analysis of gases, IV. and V. Separating and analysis of gaseous hydrocarbons. VI. The analysis of inert gases. Collection Czech. 

For these, and also other, reasons many laboratories now employ semimicro analysis, particularly for the elementary courses. Both macro and semimicro procedures will be given separately in this book in order that the requirements of all types of students may be met. Nevertheless, when the semimicro technique is adopted, students are recommended to read the sections dealing with macro technique. It may be said that when the general technique of semimicro analysis has been mastered and appreciated, no serious difficulty should be encountered in adapting a macro procedure to the semimicro scale. Apart from drop reactions, few applications of the micro technique will be described in the text. 

Qualitative analysis utilizes two kinds of tests, dry reactions and wet reactions. The former are applicable to solid substances and the latter to substances in solution. Most of the dry reactions to be described can be used with only minor modifications for semimicro analysis. Dry tests appear to have lost their popularity in certain quarters they do, however, often provide useful information in a comparatively short time and a knowledge as to how they are carried out is desirable for all students of qualitative analysis. Different techniques are employed for wet reactions in macro, semimicro, and micro analysis. 

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. 

Several types of centrifuge are available for semimicro analysis. These are ... 

Wash bottles For most work in semimicro analysis a 30 or 60 ml glass stoppered bottle is a suitable container for distilled water the latter is handled with a reagent dropper. Alternatively, a bottle carrying its own dropper (Fig. II. 14a or b) may be used. A small conical flask (25 or 50 ml) may be used for hot water. For those who prefer wash bottles, various types are available (Fig. 11.19) a is a 100 or 250 ml flat-bottomed flask with a jet of 0-5-1 mm diameter, and is mouth-operated b is a hand-operated wash bottle (flask, 125 ml rubber bulb, 50 ml) c is a Pyrex 50 ml graduated wash bottle, and d is a polythene bottle, from which the wash solution can be obtained by squeezing. 

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... 

For the cations, a limited number of preliminary reactions should be studied first, followed by an analysis of a mixture or solution containing a member or members of each group. This will give practical experience in the routine operations of semimicro analysis and also provide practice from the very outset in the use of Group Separation Tables. Particular attention should be paid to ... 

VI.3 SYSTEMATIC ANALYSIS ON THE SEMIMICRO SCALE. GENERAL CONSIDERATIONS The object of systematic qualitative analysis on the semimicro scale is not only to detect the constituents of a given mixture, an equally important aim is to ascertain the approximate relative amounts of each component. For this purpose about 0-2 g of material is usually employed for the analysis the relative magnitudes of the various precipitates will provide a rough guide as to the proportions of the constituents present. Systematic semimicro analysis is carried out in the following steps ... 

The size of the sample is often used to classify the type of analysis performed. As shown in Figure 8-1, the term macro analysis is used for samples of mass more than 0.1 g. A semimicro analysis is performed on a sample in the range of 0.01 to O.lg, while the samples for a micro analysis are in the range 10 to 10 g. For samples whose mass is lower than 10 g, the term ultramicro analysis is sometimes used. 

Alexeyev, Qualitative Chemical Semimicro Analysis Mir Publishers (ed.), Moscow, 1975, p. 475. 

Qualitative analysis may be carried out on various scales. In macro analysis the quantity of the substance employed is 0.1 to 0.5 g and the volume taken for analysis is about 20 ml. In what is usually termed semimicro analysis these quantities are reduced by a factor of 10-20, i.e. about... 

Droppers 3. Droppers for handling liquids in semimicro analysis, a dropper (also... 

Transferring of precipitates in some cases precipitates can be transferred from semimicro test-tubes with a small spatula (two convenient types in nickel or monel metal are shown in Fig. 2.20). This operation is usually difficult, particularly for centrifuge tubes. Indeed, in semimicro analysis it is rarely necessary to transfer actual precipitates from one vessel to another. 

T. D. Parks and L. Lykhen "Reduced-Scale Methods for Micro and Semimicro Analysis. Part II" Petrol. Refiner 29 No. 9, 112-14 (1950). 

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