It is known that phosphate at certain concentrations can precipitate iron, and now I'm planning a trial having a final concentration of 5 mM of phosphate and a final pH of 5.7. The final concentration of FeNaEDTA is 100 µM... do you think that iron could sequestrate iron? Should I increase the final concentration of FeNaEDTA?
I start with the assumption that your solution contains mostly Fe3+, since at pH 5.7 3+ is prevalent compared to 2+; 5 mM phosphate will bind and precipitate Fe2+, which will lead to conversion of 3+ to 2+ and further precipitation; pretty soon you will deplete your solution of Fe, and if you increase Fe concentration above 5 mM you will deplete your buffer as well. IMHO you should stay away from phosphate and switch to one of Goods buffers buffering in your required pH range.
Iron in my solution is binding to NaEDTA complex.
Thank for your answer!
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