How to weigh samples on the microbalance
Note: No flat samples, they get stuck in the carrousel.
Check required amount of sample with Lab personnel before starting to weigh!
We use a simple balance without the fancy electric doors, etc. It has proven to be very reliable. We get it checked once a year for accuracy.
Not to be confused with an analytical balance (digits to 0.0001g or 0.00001g), the microbalance has digits 0.001mg (0.000001g).
For elemental analysis (%NCHS) the higher the elemental percent, the more this kind of accuracy is critical.
|Make||Model||Readability (mg)||Capacity(g)||Pan size mm (inches)|
|Sartorius||M2P||0,001/0,002/0,005||0,5/1/2||Ø 22 (0,86)|
Note: Density of the sample material may affect the quantity of material able to fit in a particular size of capsule. Go up a size when necessary, but try not to exceed the weight limit for a size.
- Aluminium block for sample prep; good hard suface that is easy to keep clean
- Small angled spatula; micro spatulas are also handy for very small samples
- Blunt-ended forceps for squishing capsules without tearing or poking holes
- Fine-tipped angled forceps good for picking up capsules by top edge
- Flat forceps ("offset-tipped") with slight angle good for squishing air out of larger capsules before compressing
- Plastic tray with numbered wells to hold compressed capsules; with lid
Additional items: Kimwipes; (elastics or) tape to keep tray closed for storage and shipping. Beware: if elastics are too tight, the lid can bulge allowing samples out of their wells.
Using the fine angled forceps, place a tin capsule on the balance and Tare.
Remove the capsule from the balance and place on the aluminium block or some other smooth, clean surface.
Scoop the appropriate amount of sample material into the capsule; in most cases, this means having about 100µg of nitrogen, carbon or sulphur.
Place capsule back into balance; remove and adjust amount of material if necessary.
Record the weight (all digits).
NO FLAT SAMPLES: THEY GET STUCK IN THE CARROUSEL.
- Use blunt-ended forceps to close the top of the capsule.
- While holding the top closed, use flat-tipped forceps to squeeze out remaining air in the main portion of the capsule.
- While holding the main portion of the capsule, fold top of capsule down.
- Continue with blunt-ended forceps to fold capsule again if necessary, and form into a cube or a ball.
CAUTION: fine-tipped forceps and corners of flat-tipped forceps can puncture the capsule. Also, find a happy medium between getting all the air out and squeezing so hard the capsule breaks.
NOTE: if the capsule does crack, it is acceptable to slip it into a second capsule and close, except in the case of Elemental Analysis or significant loss of material.
These are some examples of the original vs. the final sizes of the different tin capsules.
How you squish the capsules is up to you; however, the final result must be a cube or ball
that does not leak.
- Store samples in a clean tray using the numbering system
A1, A2, A3, ... B1, B2, ...
- Fill out the submission form and e-mail it to the lab.