I can use HCl to dissolve CaHPO4.2H2O (CaHPO4.2H2O was created from Ca(OH)2 and H3PO4 with ratio 1:1, respectively) and use photometry method to determine PO43-. But Ca2+, how to determin Ca2+? If I titration by EDTA that use murexide, pH = 10, Ca3(PO4)2 will be precipitated. If Ca2+ was precipitated by H2C2O4, after that precipitation filter (CaC2O4) and titration C2O42- in CaC2O4 by KMnO4. But I think It is not very accurate.
Thank Sebastian Schmitt for your answer, CaHPO4.2H2O is not pure. CaHPO4.2H2O was created from Ca(OH)2 and H3PO4 with ratio 1:1, respectively. And, I want to determine Ca2+ content by chemistry method.
I think you have a number of possibilities:
- AAS
- ICP
- IC
For the first two, dissolve the solid in HNO3 and then proceed with the measurements.
For the latter, you will have to see what columns and instrument you have available at your institute / department. Depending on the column's ion exchange capacity you will have to decide on dilution and injection volume.
I have to admit, I am a bit weak on the titration side, but wouldn't compexometric titration be an alternative, as well?
My two cents.
Hope this helps.
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