Measu ring Mass

In most analyses, an analytical balance must be used to measure masses with high accuracy. Less accurate laboratory balances are also used for mass measurements when the demands for reliability are not critical.

Types of Analytical Balances

An analytical balance is an instrument for determining mass with a maximum capacity that ranges from 1 g to a few kilograms with a precision of at least 1 part in 10⁵ at maximum capacity. The precision and accuracy of many modern analytical balances exceed 1 part in 10⁶ at full capacity. The most common analytical balances (macrobalances) have a maximum capacity ranging between 160 and 200 g. With these balances, measurements can be made with a standard deviation of ± 0.1 mg. Semimicroanalytical balances have a maximum loading of 10 to 30 g with a precision of ± 0.01 mg. A typical microanalytical balance has a capacity of 1 to 3 g and a precision of ± 0.001 mg (1 μg). The analytical balance has evolved dramatically over the past several decades. The traditional analytical balance had two pans attached to either end of a lightweight beam that pivoted about a knife edge located in the center of the beam. The object to be weighed was placed on one pan. Standard masses were then added to the other pan to restore the beam to its original position. Weighing with such an equal-arm balance was tedious and time consuming.

The first single-pan analytical balance appeared on the market in 1946. The speed and convenience of weighing with this balance were vastly superior to what could be realized with the traditional equal-arm balance. As a result, this balance rapidly replaced the latter in most laboratories. The single-pan balance is currently being replaced by the electronic analytical balance, which has neither a beam nor a knife edge. The single-pan balance is still used in some laboratories, but the speed, ruggedness, convenience, accuracy, and capability for computer control and data logging of electronic balances ensure that the mechanical single-pan analytical balance will soon disappear from the scene.