> Repeat all steps in exactly the same way, but use distilled water.

But how do you know your source of distilled water isn't also contaminated?

▲ mattkrause 2 days ago | parent | next [-]

The point is that blank lets you measure that level of "background" contamination, which you then use to correct the measurements made on actual samples.

Suppose you measure around 100 plastic particles per unit in your blank and 1000 in a sample of A. This suggests that A enriches (sheds, etc) microplastic particles. On the other hand, if you found (say) 101 particles/unit in a sample of B, you'd conclude B doesn't do that.

▲ 2 days ago | parent | next [-]

[deleted]

▲ vel0city 2 days ago | parent | prev [-]

But in your example you still don't know if it was your testing process that shed 100 plastic particles or if your distilling process shed 100 plastic particles, meaning you don't actually know if B was or was not the source of the plastic particles. Was it your testing process that introduced those 100 particles, was it the distilling process that introduced them, 50/50, or something else?

B would be inconclusive against what you'd hope to be some kind of background, as its not significantly more but one couldn't conclude the source didn't shed that 100 because you don't actually know if in the blank the 100 particles of contamination was definitely your testing process or the source material genuinely having 100 particles of contamination.

I do agree though, in the A case one could pretty easily conclude whatever generated that sample is adding way more particles than an attempt at a baseline/background.

	▲	godelski 19 hours ago \| parent [-]
		`> B would be inconclusive against what you'd hope to be some kind of background` Correct. And this is why scientists use null hypothesis testing. You disprove things in science, not prove them. I think that's why you're confused. In the first situation you disproved that it comes from the background

▲ godelski 2 days ago | parent | prev [-]

You continue reading the comment and use the other version of a blank

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vel0city 2 days ago | parent [-]

So why even bother mentioning the distilled water? And if you're testing an aqueous process don't you pretty much need some fluid to put through the process?

	▲	godelski 20 hours ago \| parent [-]
		I gave the second example to try to avoid this type of response. It's not that hard to grasp. You don't need some fluid