by
lmh » Wed Dec 02, 2020 5:48 pm
… oh yes, and going wildly off topic, you've reminded me of many happy hours extracting trichloroacetic acid from aqueous samples by mixing with water-saturated ether and pipetting off the ether. Problem was, the first wash would have so much TCA in the ether that sometimes (but not always) the ether would be the denser phase instead of the lighter. Or in some cases the two phases would be rather undecided as to who should be on top...
Also of a story from an instrument engineer, who'd gone to fix a system with a blocked needle. While he was fixing it, another instrument in the same organization got reported as having a blocked needle, so he moved on to that one... and on to a third instrument...
What was happening was that someone had a method in which they simply centrifuged a revoltingly particulate sample in an injectable vial, so that the solids landed up on the bottom of the vial, and the injection was supposed to be taken from the liquid above. But unfortunately if you've got bottom-sensing on your needle, so the needle first pushes on the bottom of the vial and then moves upwards.... And of course if the user thinks the first system's blocked so they go looking for a second system to run their sample, and hey, by some coincidence that's blocked too, so they go looking for a third system....