[fabian]

Hi!...really need help with this problem. I am doing a final year project right now. I am trying to determine the aluminium content in the antacids.

Problem 1: i am using Edta as the titrant and Eriochrome Black T as the indicator. I found out that using a pH 10 buffer soln will ensure that the magnesium EDTA complex is stable at pH 10 and so, enable me to calculate just how much magnesium is in that soln. But problem is,how can i do the same with aluminium at the same pH?

Would i require another buffer soln at a diff pH to determine the aluminium content? I read somewhere that aluminium EDTA complex isnt stable at pH 10.

Porblem 2: i need to determine the Al and Mg content together using the EDTA as titrant. Is that even possible if the two metal complexes are not stable at the same pH?

Problem 3: Is there a simple alternate way to determine Al in antacid in the presence of Mg?

thanks

[AWK]

http://www.metrohm.com/company/metrohminfo/2001/pdf_e/mi2001_3e_07.pdf

[labrat41]

Hi!...really need help with this problem. I am doing a final year project right now. I am trying to determine the aluminium content in the antacids.

Problem 3: Is there a simple alternate way to determine Al in antacid in the presence of Mg?

thanks

Yes, there is, but you're going to need a thermometric titrator to do it. It relies on a little known reaction to form an insoluble salt, elpasolite, NaK2AlF6. The reaction is:

Al+++ + Na+ + 2K+ +6F- <-> NaK2AlF6

The titrant is 1mol/L NaF, the Al has to be present as Al+++, and the titration is carried out at ~pH4.5 in the presence of an acetate buffer. The buffer is composed of NaOAc, KOAc and HOAc, which also provides the excess of Na and K required to drive the reaction. The titration is capable of high precision (<0.1%rsd) due in part to the fact that 6 moles of titrant are required to react with 1 mole of Al. Here's the link to the Metrohm application note:
http://www.metrohm.com/infocenter/download.php4?doc=applications/notes/pdf/h053.pdf

You can also check out www.titrotherm.com for more information