Yes — a good used laboratory balance from eBay can be an excellent choice, particularly compared with inexpensive new “milligram” pocket scales.
For weighing 50 mg (0.050 g) of fluorescein diacetate, ideally your balance should have:
- 0.001 g (1 mg) readability at minimum; 0.0001 g (0.1 mg) is substantially better.
- A draft shield, because air movement can noticeably affect milligram measurements.
- A proper calibration function and suitable calibration weight.
- Good repeatability — weighing the same test weight several times should give essentially the same result. Professional 1-mg balances typically specify repeatability around 1–2 mg. (Laboratory Balances)
If yours reads to 0.001 g, then 0.050 g = 50 mg will show directly on the display.
Yes. For weighing quantities around 50 mg, I’d look on eBay UK for a genuine older laboratory balance rather than a cheap new pocket scale. A 1 mg (0.001 g) balance is adequate, while a 0.1 mg (0.0001 g) analytical balance would be excellent.
Good model numbers/search terms include:
- Mettler PM200 — 200 g × 0.001 g. A very suitable older professional balance. (LabX)
- Mettler Toledo PB303-S — 310 g × 0.001 g. Another excellent choice. (BIOMEDevice)
- Mettler Toledo AB54 — 51 g × 0.001 g; plenty of capacity for your purposes. (LabX)
- Ohaus GT410 — 400 g × 0.001 g. (BIOMEDevice)
- Sartorius 2358 — around 320 g × 0.001 g. (LabX)
- Mettler AE200 — 200 g × 0.0001 g (0.1 mg). This is a true analytical balance and would be a particularly nice find. (BIOMEDevice)
- Mettler Toledo AG204 — 210 g × 0.0001 g. Excellent, but likely considerably more expensive. (BIOMEDevice)
- Ohaus AP210S — another older analytical balance worth watching for; used examples are still traded. (LabX)
For you, I’d particularly hunt for Mettler PM200, PB303-S, AB54, or Ohaus GT410. You don’t really need an expensive 0.1-mg analytical balance to weigh 50 mg of FDA.
For example, with a 1-mg balance:
0.050 g = 50 mg, so your desired quantity occupies 50 display increments. That’s quite reasonable for preparing microscopy solutions.
When looking at eBay listings, I’d strongly favour one that’s demonstrated powered up and weighing, includes its original mains adapter, has an intact pan/draught shield, and can be returned if faulty. Professional used Mettler, Sartorius and Ohaus instruments are commonly recommended over inexpensive nominal “milligram” scales. (Reddit)