Practical investigations
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I'm doing the investigation on wines and for the indicator on the back titration method I've been given N-phenylanthranilic acid to use instead of the sodium diphenylamine sulphonate. However, I'm struggling to find any useful information about how it works: I've found that I should expect it to change from purple-red to colourless, but I have no information on the reaction. I'd imagine that it would work in a fairly similar way to the sodium diphenylamine sulphonate but I'd like some clarification please.
Igloo writes
N-phenylanthranilic acid is a pH-independent redox indicator (as is sodium diphenylamine sulphonate) and the theory underlying its use is certainly highly complex. Via Google, using “N-phenylanthranilic acid indicator” as a search phrase I came up with several web links, one of which is to a 28K download:
Visual indicators
You will need to read through the whole article very carefully to get anything useful out of it, but the relevant section is on page 5 of the pdf under “6.4.3 Redox Indicators”.
I’ve not been able to find anything about what happens to the molecule during redox, but I strongly suspect that its function is linked to the secondary amine linkage between the two benzene rings.
Perhaps you should try and access a few more of the web links via Google to see if there is anything more out there.
I assume that you have all the practical details as to how this indicator is made up. You should know that it is normally made up in sodium hydroxide solution, yet your dichromate back titration is obviously being carried out in strongly acidic conditions. Might this cause a problem? The advantage of sodium diphenylamine sulphonate is that it is often made up in acidic solution or in water.
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Risk assessment
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updated: 03 March 2006
