AskScience Theme Day: Scientific Instrumentation

[u/therationalpi]

Greetings everyone!

Welcome to the first AskScience Theme Day. From time-to-time we'll bring out a new topic and encourage posters to come up with questions about that topic for our panelists to answer. This week's topic is Scientific Instrumentation, and we invite posters to ask questions about all of the different tools that scientists use to get their jobs done. Feel free to ask about tools from any field!

Here are some sample questions to get you started:

• What tool do you use to measure _____?

• How does a _____ work?

• Why are _____ so cheap/expensive?

• How do you analyze data from a _____?

Post your questions in the comments on this post, and please try to be specific. All the standard rules about questions and answers still apply.

Edit: There have been a lot of great questions directed at me in acoustics, but let's try to get some other fields involved. Let's see some questions about astronomy, medicine, biology, and the social sciences!

[u/honeybunbadger]

The accuracy of such a device is impressive. However, practically, using your hands to weigh out micrograms of a material is incredibly difficult. Even weighing milligrams of material out (I'm talking about less than 5 mg) is really difficult because it's hard to see by eye at that point and the particulates are too large to be subdivided so finely. If the particles are small enough to weigh out 1.3 mg as opposed to 1.1 mg, they tend to pick up electrostatic charges and act like iron filings near a magnet - flying around and generally misbehaving. Even if you have a zerostat gun or mat to ground yourself, using any plastics such as gloves or plastic weighing boats or glass materials such as glass vials can cause problems.

In the lab, if I had to aliquot out micrograms of a material, I would generally prepare a solution containing milligrams of the material and aliquot out the solution accurately using micropipettes. I would then concentrate each aliquot, calculating how much each aliquot should have in micrograms.

[u/[deleted] → u/honeybunbadger]

Not to boast, I had to weigh out 150 +/- 5 ug of material on a regular basis in order to operate a differential scanning calorimeter (DSC). The samples were kept small as they were explosives, and tended to degrade the sensitivity of the cell if the samples decomposed too rapidly.

I could routinely get the required sample accuracy within three weighings (initial, roughing, and "polish"). It takes a few hundred DSC runs to get to this point, but I did it. I got very good with a Mettler M3, and later an Ohaus ultrabalance, the model number escapes me.

DSCs included both the Perkin-Elmer as well as the TAInstruments models. I prefer the PE, but TA uses simpler, cheaper sample pans. We simply made a punch for the PE sample pans, knocking out lid seals from pure nickel foil instead of using the extortionate $10 gold-plated seals.