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Gluconate Analysis for Caustic Etch

Q. 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 Center, Pennsylvania

A. Gluconate is a complexing agent, so how about adding dropwise amounts of ferric chloride [on eBay or Amazon affil link] 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 monitor   tom pullizi signature
Tom Pullizzi
Falls Township, Pennsylvania

Q. 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 [returning]
- Alcoa Center Pennsylvania

A. Paul, If you add a certain amount of Na glucoheptonate to tie up the Aluminum than I do believe you can proceed w/ Tom's suggestion of adding known amounts of ferric chloride[on eBay or Amazon affil link]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 Pharmacopoeia for Gluconate - Just follow the bouncing ball.

Good Luck

Domingos J C Spinelli
- SP Brazil

A. Gluconate can be titrated by periodat (marplade titration). Take 0.5 cc of filtered etch bath dilute by 100 cc dw add fk and by CLH neutralize it by phenolphetalein. Any S or SO2 from your etch will be removed , then make solution slightly acidic to prepare for periodate titration . Titration is the same for glycerotitration is blank type.

Hadi Khosravi
- Tehran, Iran

Q. 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
- Paramount, California, USA

Q. Does anybody know of an analytical technique for gluconate in the caustic (sodium hydroxide)

vahida huseljic
- Tuzla, Bosnia and hercegovina
January 27, 2009

Q. What is needed is a method for determining the non-aluminum chelated gluconate. The free gluconate. In order to accomplish this we would need a complexing agent weaker than the aluminum gluconate complex. I'm wondering if that can be done using a known calcium chloride solution with ammonium oxalate as the indicator? I'm planning to check this procedure out but if anyone already knows that answer please let me know.

Charles Hawes
Consultng Chemist - Sparta, Tennessee USA
April 24, 2018

A. Another method for determining free un-chelated sodium gluconate would be to run an aluminum content of the bath converting that to the chelated gluconate level then subtracting that from the original sodium gluconate content. That calculation would give the amount of un-chelated sodium gluconate in the bath.

Charles Hawes [returning]
Mid South Laboratories - Sparta, Tennessee USA
April 26, 2018

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