Amy was a participant the Understanding Science project. She was interviewed when she had just started her A level (i.e. college) chemistry, and one of the topics that the course had started with was mass spectrometry. She gave me a very detailed account of what she had been taught, despite both casting doubt on the logic of parts of the account, and of the accuracy of her own recollection. The discussion, part of which is reported here, took place over a period of just over 40 minutes during an interview of about 80 minutes duration. Amy sets out an overview of the topic of mass spectroscopy
At the start of the discussion about mass spectrometry, Amy offered an overview of what she had learnt. Amy peppered her talk with conditionals (e.g. apparently, sounds stupid, sort of - see Amy's overview of mass spectroscopy) to imply that she was unsure of what she was imparting. However, a tidied-up account (sans the conditionals) seems pretty impressive for someone just introduced to the concept of mass spectrometry:
If you had like a piece of iron and then you put it through this machine thing…You need all the atoms to be free, so you’d like heat it until it becomes like vapour, like a gas, and then it goes into like this other thing, which is an electron gun, which has a filament , so it has electrons which are being attracted to this plate underneath it, and as the electrons from the filament are attracted to the plate they hit the iron em atoms causing an electron to be knocked off the iron atom making it into an iron positive ion. And then it passes through these sort of plates, and it’s deflected, and then there’s like an electromagnetic field which – depending on like the direction and the strength - the beam of ions that you’ve got will be deflected a different amount and so you can somehow measure
Amy seemed to be unconvinced, or at least surprised by a number of aspects of the material she had learnt about the mass spectrometer. So, for example, she found it strange that iron could be vaporised: iron turning into a gas sounded weird.
Amy's account suggested that she was not sure what the machine was called, and that suggested that she had "no idea" how the ions were measured at the end of the process. Yet further questioning suggested she knew more than she first realised (or, at least, revealed).
I: So what is it you’re measuring?
A: Erm, the mass of different sort of – ions, apparently.
I: Oh okay. So this I something that happens apparently, and sounds stupid?
A: Yeah.
I: and it happens in a machine?
A: Yeah.
I: but they haven’t told us what the machine’s called?
A: Yeah.
I: And I’m not surprised, because there’s so much to remember there.
A: I haven’t remembered it right?
I: Have you not. What do you think the machine might be called? If you had to call this machine something, what might you call it?
A: Oh wasn’t it a spect-rom-eter or something, something weird.
I: Something weird like a spectrometer, so this machine might be a spectrometer?
A: Or something weird like that.
I: Or something weird like that, okay. So you’ve got this, so you’ve taken me all through this process, and parts of it sound stupid, and parts of it happen apparently, and apparently means that you don’t really believe it or you’re not, you’re not quite convinced you believe it?
A: Well science is weird, all these weird things happen, so.
I: Mm. that’s true, that’s true. So somehow this helps you tell the mass of an ion?
A: Yeah.
I: But we’re not sure how?
A: Erm – well, no, apparently, erm, - like, you’ll have like heavier ions and lighter ones, erm, - which will sort of be deflected different amounts and so by changing the electromagnetic field you can sort of erm - I don’t know collect as it were the different - like the heaviest ions and then like the not so heavy ones, and then, yeah.
Whilst not being a completely detailed account, Amy's report seemed to have captured the gist of the process quite well, apparently.
Amy's explanation of the stupid-sounding bit: A visual teaching model of ionisation in the mass spectrometer.
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Dr Keith S Taber kst24@cam.ac.uk
University of Cambridge Faculty of Education