Basically, I'm performing a lab investigation to determine calcium content in different milk sorts. Since my school didn't have any EDTA, I'm using Sodium Oxalate to form a precipitate with Calcium Oxalate. However, the source I have says that the best way to make these two things react is by centrifuging, a tool which my school lacks. How could I do this without centrifuging for 5 minutes on 1500 RPM? Can I just wait or heat up increase the rate of reaction? Any tips?
If your "source" claimed that a centrifuge increased the reaction rate, then you need to find a better source. (I admit that it is possible that the compressive work a centrifuge does causes heating which for high speed centrifuges can be significant, but it isn't likely to be a factor here with small analytical amounts at relatively low speeds, <300 g's, imho) Without some calibration, you really need to find a method you can follow closely. If you have some knowns, say some calcium phosphate and some dietary calcium supplements, then you may be able to validate any deviations from the given method by showing that both highly insoluble salts and highly bioabsorbable calcium (usually calcium carbonate, acidified with HCl to the Ca++ ion) both can be analyzed with the modified method. (I also would guess that the centrifuge wouldn't "push down" other suspended (colloidal) material in the milk (which might either also contain calcium or improve the precipitation rate or amount of the calcium oxalate).)