How Analytical Balances Are Used In The Lab

An analytical balance is used to measure mass to a very high degree of precision and accuracy, because unlike spring scales their accuracy is not affected by differences in the local gravity. A change in the strength of the gravitational field caused by moving the balance will not change the measured mass, because the moments of force on either side of the balance beam are affected equally by the pull of gravity.

The weighing pans of a high precision (.01 mg or better) balance are inside a transparent enclosure with doors so that dust does not collect and so any air currents in the room do not affect the balance's operation. The use of a vented safety enclosure with an analytical balance which has uniquely designed acrylic airfoils, allows a smooth, turbulence-free airflow that allows weighing of masses of as little as 1 micro gram without fluctuations or loss of product. Samples should be at room temperature to prevent natural convection from forming air currents inside the enclosure, which could affect the weighing process.

Analytical precision is achieved by maintaining a constant load on the balance beam, by subtracting mass on the same side of the beam to which the sample is added. The final balance is achieved by using a small spring force, rather than subtracting fixed weights. This allows the weight to be added as a fine adjustment.

An analytical balance or scale used in laboratories may be in various shapes and sizes. Although often used interchangeably, scales and balances have different uses. A balance compares the mass of two sets of objects, while a scale determines the mass of an object or set of objects. The most common types in use today are beam balances, spring balances, top-loading balances, analytical balances and precision scales.

Chemical analysis is an area where these balances are often used, since it is designed for great precision which is useful in quantitative chemical analysis. Top-loading balances, which can measure objects up to 200 g, are less expensive but also offer less resolution than do some other types of balance. A top-loading balance is considered to be a semi analytical balance, with a readability of up to three decimal places (up to .001 g). A precision balance has a readability of 0.01 g. It produces steady readings in a wider range of environmental conditions than an analytical model, being less sensitive to temperature fluctuations.

Microbalances and ultra-microbalances are used to weigh the smallest samples. They offer a capacity of up to 6 g with readability up to seven decimal (.0000001 g). Electronic scales and balances can provide weights in more than a dozen units, including grams, kilograms, pounds, newtons, grains, and ounces.

Many things can affect the precision of an analytical balance. The environment of the lab, operating temperature, humidity, vibration and ventilation currents can all affect performance. Consequently, it is important to keep the balance inside an enclosed space, keep it clean and make sure it is leveled correctly. It is equally important to make sure it is regularly maintained and serviced. There are also personnel considerations that need to be observed. It is useful to know who will be operating and maintaining the device and the type of training they have received.

Finally, it is best to always follow the manufacturer's operating instructions, calibration frequency and maintenance recommendations for the analytical balance.