Analytical Balances

Balances and scales used in laboratories today come 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, precision scales, and moisture analyzers.

Spring balances are the simplest type, consisting of a coiled spring suspended from a fixed point with a pan at the other end. Beam balances are used to weigh solids, liquids, powders, and even animals, generally with a capacity from 610 g to 2,610 g; they are often used in classroom situations due to low cost, ease of use, and durability.

Analytical balances are designed for great precision in quantitative chemical analysis. They yield readability to four decimal places to the right of the decimal point (up to .0001 g). They are extremely sensitive and, since air currents can affect their measurement, must be covered by a draft shield. They are used for samples up to about 320 g. Top-loading balances, which can measure objects up to 200 g, are less expensive but less exacting than analytical balances. They are considered semi-analytical balances, with a readability of up to three decimal places to the right of the decimal point (up to .001 g). Precision balances have a readability of 0.01 g. They produce steady readings in a wider range of environmental conditions than analytical balances, being less sensitive to temperature fluctuations. They can have a capacity from 600 g to 34,000 g.

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 places to the right of the decimal point (.0000001 g). Moisture balances measure the moisture content in a material sample by using halogen heating with precise weighing technology.

Electronic scales and balances can provide weights in more than a dozen units, including grams, kilograms, pounds, newtons, grains, and ounces, and often in several operating languages. Application modes can be set for statistics, formulation, differential weighing, density determination, pipette calibration, parts counting, animal weighing, check weighing, percent weighing, filling, gross-net-tare weighing, and statistical quality control. Hence, it’s important to choose a balance that can report the information specified by the laboratory protocols and quality control systems.

Balances today can be connected to a PC, a data printer, an analytical instrument, or a laboratory robot using serial, parallel, or USB cables. The newest models are equipped with Bluetooth technology, to enable wireless communication. High-contrast backlit displays improve readability and allow accurate readings even in brightly lit conditions. When choosing scales and balances for their laboratories, users should understand that it may be more advantageous to purchase several scales and balances designed for specific applications than to try to find one that can handle all of their needs. They should consider the capacity, resolution, weight, containers, and size of their samples, as well as the speed at which results are needed.

The environment of the lab, operating temperature, humidity, vibration, and ventilation currents can all affect performance. Consequently, it’s important to keep the balance inside an enclosed space, keep it clean, make sure it is leveled correctly, and make sure it is regularly maintained and serviced. There are also personnel considerations that need to be monitored, such as who will operate and maintain the device and the type of training they have received. Finally, as with any other piece of equipment, it is best to always follow the manufacturer’s operating instructions, calibration frequency, and maintenance recommendations.

Shimadzu
The AUW series analytical and semi-micro balances feature fully automatic span calibration, an easy-to-use weighing chamber and level adjustment gauge, and prominent backlit display. They feature a weighing capacity of 82g at 0.01mg and up to 220g at an accuracy of 0.1mg. A number of powerful weighing applications, including piece counting, auto print, choice of display units, and specific gravity measurement, are included. A data capture function sends weighing data and GLP, GMP and ISO compliant calibration reports to printers or computers. The high-performance UniBloc measuring cell ensures stable temperature characteristics, excellent response time, stable corner-load performance, and a long operational life. The AUW series also features Windows®Direct communication, which requires no software installation to integrate Shimadzu balances with existing lab or business software.
www.ssi.shimadzu.com

Adam Equipment
With all-metal casing and large LCD readout with date and time, PGL balances combine the solid construction and fundamental features of a high-precision top loader with the simple operation of a portable balance. They come with ShockProtect™ overload, three-point protection that safe guards the balance from over loads, application modes for parts counting, percentage weighing, specific gravity/density determination and check weighing as well as 9 weighing units including one custom unit. The standard RS-232 allows communications to printers and computers and the keypad has color-coded keys for quick recognition. A built in rechargeable battery pack allows the balance to be used wherever and whenever needed.
www.adamequipment.com

Mettler Toledo
The XP6U top level ultra-microbalance features a 61 million digit resolution. The XP2U ultra-microbalance has a resolution of 21 million digits. Combined with all other XP related characteristics such color touch-screen display, customized screen programming, intelligent user guidance and hands-free infrared draft shield, these micro and ultra-microbalances are incomparable in terms of accuracy and flexible use of tare vessels. The XS3DU, the first microbalance to be offered in the Excellence product line, is designed to boost efficiency and reproducibility of work in basic research labs or academic institutions. It offers fundamental functionality with superb weighing performance in an 800 mg fine range with 1 μg readability.
www.mt.com

A&D Weighing
The Phoenix (GH) series of semi-micro analytical balances offer a variety of advanced features at highly affordable prices. An internally installed weight allows for quick and reliable one-step calibration, ensuring measurement accuracy. Phoenix balances automatically adjust their settings to compensate for changes in the environment. Anti-static glass is an additional standard feature which virtually eliminates the effect of static electricity on weighing performance. Capacities range from 120 grams to 320 grams with resolution from 0.1 mg to 0.01 mg.
www.andweighing.com

Sartorius
The Cubis premium balance series features a modular design that can be custom-configured to the changing requirements of different applications. Q-Level provides the option of fully automatic, motorized leveling at the touch of a key. A motorized draft shield enables the balance to be adapted to any work environment and a built-in ionizer eliminates interfering electrostatic charges on samples or on sample containers. This standard toploading semi microbalance features full resolution all the way up to 220 g. Its footprint takes up to 25% less space compared with conventional lab balances of the same resolution. The Q-Pan compensates for errors caused when a sample is off-centered on the pan and an extra-large weighing pan means reliable and repeatable results in a larger working area.
www.sartorius-usa.com

Tanuja Koppal, PhD, is a freelance science writer and consultant based in Randolph, N.J.