In general you can make the product of g ( rcf) x time equal between centrifuges but this does not mean that techniques will work. You do not say what you are separating but many separations ( eg sub cellular fractions )simply will not work at low g forces however long you spin for so be careful. If you are just spinning down  precipitated denatured products from , for instance , a DNA prep then if both centrifuges are delivering above about 2000g then both will work equally well at removing the residue and you should report this accurately giving the g force ,spin time,, rotor type and machine type for both machines as the point of methodology is to ensure that others can replicate your results accurately if necessary

I agree with Mr. Rutland.

For point 1) For certain procedures (e.g. clarifying E. coli lysates prior to HPLC protein purification) there is no replacement for high-Gs. In contrast, I bet you could get away with a conventional centrifuge for certain other steps (e.g. an ammonium sulfate cut, spermidine precipitation, etc.). Certainly, for most nucleic acid precipitations the performance difference between an ultra- and a conventional centrifuge must be vanishingly close to 0 after a reasonably long spin.

As to point 2) You should accurately report the method or methods used when the data does to publication. If necessary, you can usually include excruciating details in a supplemental. If someone really want to reproduce your work, they'll likely dig deep enough to find those details. There is nothing unethical about using multiple, similar procedures in an experiment if they are accurately reported.

 Hi,

I am trying to isolate a sulfated polysaccharide precipitated from a water extract that has been treated with volumes of ethanol. Our ultra centrifuge can be set at 18500 x g while I found out that our other centrifuge that can work on 120mL (12 place rotor of up to 10mL each) of extract at a given time has a maximum of 3400 x g.

My plan is to use the 120mL (12 place rotor x 10mL each) capacity centrifuge during the final centrifugal step to recover as many isolate as possible with ease of scooping out the isolate (precipitate) without loosing much. The ultra centrifuge uses micro tube of up to 1.5mL and thus would cause much of a hardship to scoop out the isolates.

The question that arises then, is whether shifting from 18500 x g to 3400 x g is still ethical.

Thanks!

If it works and you report it accurately I don't see a problem with switching methods, or using data from both methods in a publication. If you're going against the grain of your field by changing the method I might pause to consider if the time saved procedurally will be worth the risk of irritating some nitpicky reviewer. It's possible they'd ask you to redo some experiments to confirm the different methods were indeed comparable in their performance, but I lack the expertise to say whether this is likely to be the case for your extraction and precipitation. I often played it fast-and-loose with pelleting bacteria and DNA in my cloning work, since it had no impact on the final product and since every lab does it's cloning a bit differently anyway.

i do worry about the difference between 18500g and 3400 g that there would still be some fine suspension left in the supernatant at 3400g. I suppose you could try spinning at 3400 g then spinning the supernatant again at 18500g to see if any more material spins down and if it does not then the slower spin may be sufficient but if the established methodology suggests a spin of 18500g I would have to recommend staying with that figure unless you are prepared to run tests proving that there is no difference between the methods which would need quite a lot of work proving that all of your material spins down at 3400g. It does also depend on whether you are just spinning down material to prove that it is present in which case complete sedimentation is possibly not needed or if you are spinning down to measure the amount of material present in which case sedimenting most of the material will not be sufficient.. It is not a question of ethics more a question of whether it works properly or not.

You can use the k factor formula to calculate the time. The k-factor is a measure of the sedimentation efficiency, which is inversely proportional to the time required for a particle to reach equilibrium in a centrifugal field. The smaller the k-factor, the faster the pelleting efficiency: https://lab.plygenind.com/compensate-lower-centrifuge-speed-increasing-time