Choosing the right weigh boat for analytical balances
Choosing the right weigh boat is an important factor in making accurate measurements using an analytical balance. Before you order weigh boats and select one to use most often, consider all your choices. The difference between the right weigh boat and the wrong one is as simple as accurate versus inaccurate measurements.
Weigh paper is a popular option for weighing small amounts of dry granules or powders. Weigh paper often has a slippery or waxy feel to prevent the powder from sticking to it. Large pieces of weigh paper are unnecessary for measuring out milligram-scale quantities of powder so, if your weigh paper is gratuitously large, consider cutting it into smaller squares ahead of time for easy use.
To properly use weigh paper, make a single fold along the length of the paper about 1/3 of the way from an edge. Place the weigh paper on the analytical balance with the larger surface area face down and the folded edge up. Press the tare button to re-zero the machine. Next, weigh out your desired quantity of powder on the large face of the weigh paper.
After measuring the desired amount and allowing the balance to get an accurate reading, carefully pick up the paper and tilt the powder toward the folded margin. Align one end of that marginal fold with an open container and raise the opposite end of the paper so the powder all falls toward the groove and toward the container.
Plastic weigh boats come in many sizes and are excellent options for weighing out both powders and liquids. Plastic weigh boats, however, are not suitable for weighing out powders that succumb to the effects of static because plastic weigh boats easily develop static electricity charges across the surface.
When using a plastic weigh boat, it's still necessary to tare after placing the empty weigh boat on the analytical balance, but since there is no fold to direct the fall of the powder, sometimes it's necessary to bend the entire weigh boat into a large-mouthed container so no powder is lost.
Foil weigh boats are durable and suitable for weighing out liquids or powders, just as plastic weigh boats are. For reactive materials or for weighing out organic solvents, foil weigh boats are likely the ideal choice. Because foil doesn't easily bend in a directed fashion, it's useful to know how to get all weighed powder out of the weigh boat. One great way of doing this is, if the powder you're weighing out is destined to be added to a solution, use a transfer pipet to bring some of the solution to the weigh boat and redraw the solution, including the powder that has been weighed out back into the pipet and expel the contents of the pipet back into the container of the solution.
For more help with the best techniques and practices for weighing substances with accuracy, contact us.