Macro analytical balances

For many laboratory operations it is necessary to weigh objects or materials which are far heavier than the upper weight limit of a macro analytical balance, or small amounts of material for which it is not necessary to weigh to the limit of sensitivity of such a balance this type of weighing is often referred to as a rough weighing . A wide range of electronic balances is available for such purposes with characteristics such as, for example,... 

Weighing and measurements. The rough balances used for macro-scale preparative work are not adequate for senu-micro preparations. For the latter purpose, ordinary analytical balances should... 

Scale of Operation The scale of operation for precipitation gravimetry is governed by the sensitivity of the balance and the availability of sample. To achieve an accuracy of 0.1% using an analytical balance with a sensitivity of 0.1 mg, the precipitate must weigh at least 100 mg. As a consequence, precipitation gravimetry is usually limited to major or minor analytes, and macro or meso samples (see Figure 3.6 in Chapter 3). The analysis of trace level analytes or micro samples usually requires a microanalytical balance. 

Classical laboratory, manual methods conducted on a macro-scale where sample quantities arc in the range of grams and several milliliters. These are the techniques that developed from the earliest investigations of chemistry and which remain effective for teaching the fundamentals of analysis. However, these methods continue to be widely used in industry and research, particularly where there is alarge variety of analytical work to be performed. The equipment, essentially composed of analytical balances and laboratory glassware, tends to be of a universal nature and particularly where budgets for apparatus are limited, the relative modest cost of such equipment is attractive. 

Food Chemicals Codex tests and assays are designed for use with three types of analytical balances, known as micro-, semimicro-, and macro-. 

Basically, there is little difference between carrying out experiments on a semimicro (10 to 1,000 mg) scale or on a macro scale. For the smaller quantities, material must be weighed or measured more carefully (using an analytical or semimicro balance and a calibrated pipette), and one uses smaller apparatus. At the lower end of the range, reactions are conveniently carried out in test tubes, which will usually serve as satisfactory aircooled reflux condensers. A simple apparatus which will provide for stirring, the addition of liquid reagents, and drying is shown in Fig. 

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