Letter 3907

Gluconate Analysis for Caustic Etch 

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Does anybody know of an analytical technique for gluconate in the caustic etch used for aluminum? I need something for a plant floor that does not use complex equipment or techniques. Involving a pH meter or colorimeter is OK, but not HPLC, extractions, etc.

Paul Schultz - Alcoa Technical Center - Alcoa Center, PA

Gluconate is a complexing agent, so how about adding dropwise amounts of ferric chloride or some other compound to a known quantity of sample. Ideally, the iron would become complexed only by the gluconate, in stoichiometric amounts, and perhaps even be its own endpoint?


Tom Pullizzi
- Levittown, PA

Gluconate is a good complexor of transition metals, but it also complexes the aluminum dissolved by the etch (it is there to complex the Al and help prevent the Al sludge from precipitating like concrete). Therefore, titration with iron or other metals would only work if the gluconate complexes the iron or other metal much more strongly than aluminum. Does anyone know if that is the case? Or, is there a way to tie up the aluminum and do a simple acid-base titration for the gluconate endpoint?

Paul Schultz - Alcoa Center PA

Paul, If you add a certan ammount of Na glucoheptonate to tie up the Aluminum than I do believe you can proceed w/ Tom's suggestion of adding known ammounts of Ferric chloride to determine the so called "free gluconate" in your bath. I'd run a blank w/ and without the glucoheptonate.

One other suggestion would be straight titration w/ perchloric acid however you need to make the solution neutral This procedure can be found on the American Pharmacopea for Gluconate - Just follow the bouncing ball.

Good Luck

Domingos J C Spinelli - SurTec do Brasil Ltda. - SB Campo SP Brazil

Gluconate can be titrated by periodat (marplade titration). Take 0.5 cc of filtered etch bath dilute by 100cc dw add fk and by CLH nurilize it by phenolphetalein.any s or so2 from your etch will be removed , then make solution s lightly acidic to prepare for periodate titration . Titration is the same for glycerotitration is blank type.

Hadi Khosravi
- Tehran, Iran

Analysis method for sodium gluconate concentration. I'm looking for an analysis method for determining the concentration of sodium gluconate in a mixture with sodium hydroxide. The sodium gluconate is to be 25 to 50 g/l and the sodium hydroxide is to be 75 to 150 g/l.

William L. Glass
ST&I INC. - Paramont, CA, USA

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