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Pharmacist weights sample on a precision balance

Precision and Capacity in Laboratory Balances

A wide array of precisions, capacities, and features add up to balance options for every type of laboratory

Brandoch Cook, PhD

There are a few pieces of equipment that every lab needs regardless of its size or the application in which it is engaged. A laboratory balance resides around the top of this list. For research labs, the integrity and quality of every buffer is dependent upon the balance’s accuracy and usability. For analytical labs, identification and characterization are only possible if starting quantities are dependable. For pharma labs and drug discovery, compliance and adaptability to evolving regulatory standards and guidelines are as essential as the ability to detect changes in mass at infinitesimal scales. 

Laboratory balances fall into three broad categories that differ in configuration, sensitivity, and capacity: top loading, precision, and analytical. Top loading balances employ an open configuration with a large pan to accommodate various weigh boats. They have the highest capacity with the lowest precision of readability, usually differences of 0.01 gram (10 milligrams). They are the workhorses of research labs and used to create most buffers, requiring dissolution of tens or hundreds of grams of powder. When an investigator prepares reagents for agarose gels and western blotting experiments, the top loading balance is a relevant piece of equipment. Although most have capacities of five to 10 kilograms, there are specialized high-capacity instruments that can measure weights up to 70 kilograms, convenient for taring large vessels before anything goes into them. The undersides of some balances reveal an underhook that can be used to weigh magnetic materials by dangling them, avoiding interference with the force restoration mechanisms used in contemporary high-quality balance design.

It is true for all balances that as capacity increases, sensitivity decreases. Although analytical and precision balances are similar to each other in outward design, they typically differ by an order of magnitude of readability, 0.0001 compared to 0.001 gram (1 milligram), respectively. Precision balances are, therefore, often called “milligram scales.” The outward characteristics that distinguish both from toploaders are smaller weigh pans and draft shields that isolate samples and powders from interference during weighing. In terms of utility, however, they are both adept at handling much smaller tasks. Analytical balances often have maximum capacities of 220 grams or less and are useful for constituting solutions containing less than a few grams in less than a few milliliters, for instance, cytokine and small molecule inhibitor stock solutions. For those invested in the seriously small, there are ultra-micro balances with capacities of two grams that read accurately at the nanoscale, although prices increase accordingly. Nonetheless, there is a wide variety of precision and analytical balances that can include features like automated draft shields, internal calibration that accounts for latitude and altitude, and the ability to report weights in many different international and commercial units.

These and other options can drive purchasing decisions that are unique to each type of laboratory. Internal calibration and lock-out with user authentication can strengthen an audit trail and facilitate regulatory compliance. Increased connectivity to external devices via USB ports allows investigators to streamline analytical procedures. The latest technology in balances also allows custom configuration, including draft shields with ionizers to reduce static electricity while weighing precious powders. With a vast array of precisions, capacities, and features, there is a perfect balance for every laboratory.