The goal of EAB users is to obtain an accurate, precise, and reliable weight-measurement of the chosen sample. This goal begins with three basic steps which include the:
1) Selection of the appropriate EAB
2) Installation of the EAB in the most suitable laboratory location
3) Calibration of the EAB in its laboratory location.
Routinely checking the sensitivity and repeatability of the EAB in between calibrations by using known reference weights ensures accurate daily weight-measurements. And finally, the establishment of standard operating procedures (i.e., SOPs) for all weight-measurements improves the efficiency and accuracy of the weighing process because different users operate the EAB differently.
Sample types that require precise weight-measurements vary widely and include but are not limited to the following: routine chemical reagents (e.g., NaCl to make saline solutions), early pharmaceutical drug derivatives in the form of lyophilized dry powder, sampling filters used to measure particulate matter pollution in the air, differential weighing, density determination, pipette testing, precious samples available only in minute amounts, and filling gas tanks.
In most of the above-mentioned sample types, samples handling remains quite basic, requiring only a clean spatula/forceps and a clean EAB. The one proviso is that some samples are difficult to weigh (e.g., electrostatic samples) which is covered in more detail in my previous article, “Electronic-Analytical Balances (EABs) and Weighing Difficult Samples”.
However, one must be cognizant that sample handling may have a serious impact on the weight-measurement as discussed in the two examples below.
- Surgeons during reduction mammoplasty make judgments based on the intra-operative weight (i.e., wet weight) of resected breast tissue while insurance companies base their reimbursement on the pathology weight of resected breast tissue. In this situation, the pathology weight is less than the intra-operative weight (732g vs 780g, respectively; 48g less).1 The decreased pathology weight is due to fluid loss, desiccation from air exposure, and contact with towels during handling. Insurance companies often set predetermined criteria for reimbursement (e.g., removal of ›500g of breast tissue). Awareness of the above-mentioned discrepancy between intra-operative weight and pathology weight due to sample handling of resected breast tissue can help surgeons and patients avoid unnecessary reimbursement complications.
- Coffee roasters know that the temperature and speed of the roasting process affects CO2 release and this determines the freshness, shelf life, and taste of the brewed coffee. In order to quantify the CO2 release over time (i.e., a volatile sample), special handling of the sample is required. In this case, a chamber was designed with a fitted capillary to allow CO2 release2. CO2 release over time was measured by weighing the weight loss of the chamber filled with coffee beans after various roasting processes. In this situation, sample handling required the design of a special chamber to obtain an accurate weight-measurement of the CO2 release over time.
References
- Zeiderman MR et al; Eplasty 17:e32, Oct 2017
- Smrke S: J Agricultural and Food Chemistry 66(21), 5293-5300, 2018