Weighing: the environmental impact
10 Feb 2023
Labs are used to taking account of the effect of their processes on the environment but on a smaller scale it can affect them adversely too, as in the case of weighing results. However, there are some straightforward steps to counter this...
It goes without saying that achieving precision in weighing for the laboratory is of key importance.
And the three most important factors, state weighing, measurement and sample processing experts OHAUS, are achieving the correct high quality balance, understanding how to use it, and mitigating environmental factors.
Controlled and stable environments are essential when setting up and employing the balance if one is to achieve optimal performance. Therefore, advises the firm, begin with a checklist of influences that can adversely impact weighing results. These will include temperature, humidity, air flow, electrostatic charges and vibrations, but also the maintenance of stable power supply to prevent voltage changes influencing readings.
Materials such as metals and adhesives are susceptible to changes of temperature and humidity that may be imperceptible but cause sufficient expansion and contraction. Constant ambient temperature and humidity should be the aim and technicians should take care to readjust the balance when changes occur to these factors.
Likewise, says the company, sunlight, draughts and heating or cooling vents contribute to unstable readings. HVAC vents, fans, windows, cryogenic refrigerators muffle furnaces, and doorways all are potential sources of air movement. A poorly insulated room may present other, less obvious draft sources. Balances should be kept at a distance from air movement sources and laboratory workers should be mindful of opening events that could create a wind tunnel.
Static charge build-up is another concern during high-precision weighing employing analytical and semi-micro balances. Increasing the relative humidity, adjusting sample storage, using glass containers more resistant to static rather than plastic and static ionisers can help, advises the company.
Surface stability is another essential to avoid vibration effects. A dedicated table that adjoins another or butts up against a wall is more likely to create vibration. Foot traffic, HVAC equipment, and other machinery or instruments, including centrifuges, are other sources.
So, provide a stable environment or react effectively to changes within it. Then consider the preferred balance. OHAUS recommends analytical balances for small mass samples, power samples, or USP reference standard, as these can measure samples up to 320g with readability to 0.01mg accuracy. Precision balances measuring samples up to 35kg and offering readability up to 1mg are preferred for higher capacity.
The firm addresses the final factor – correct use of equipment – in its own weighing guide that outlines good practice for users. This includes basic explanation, terminology, installation, troubleshooting for accuracy, calibration weights and legal aspects.
