By Markus Christ on Thursday, March 1, 2001 - 06:39 am:
Does anyone have a method or experience with the
determination of gluconic acid in water. I have
the following problem: When I dissolve K-gluconate
in water I will get two species: gluconic acid
and the lactone of gluconic acid.
How can I shift the equillibrium to gluconic acid?
I use KH2PO4 (50 mM, pH 3.0) as eluent and a Prontosil C18-AQ column. Detector is a DAD (202 nm).
By Uwe Neue on Thursday, March 1, 2001 - 04:25 pm:
I have never worked with this. but I would bet that the equilibrium is pH dependent. How about going to pH 7? We may have to struggle to get retention, but it is a start.
I assume that this is the mobile phase, and that there is no organic in it. The next step is then to increase retention, for example by adding a LARGE amount of salt.
By Jaime Villanueva on Thursday, March 1, 2001 - 05:57 pm:
I have done gluconic acid analysis by ion chromatography using a conductivity detector, a Brownlee PolyPore H column 25 cm and a .002 N sulfuric acid mobile phase with flow rate of 0.6 ml/min. the gluconic acid comes on pretty early right after the water peak. This method is also for organic acids. Believe it or not I still use a Wescan Instument: Probaly the only one still alive.
By B.Buglio on Wednesday, March 7, 2001 - 08:03 pm:
A basic solution will prevent lactonization and
the open chain salt will predominate. In this
regard a CE method for gluconic acid has been
reported (J Chromatogr B Biomed Appl 1996, May 31;
681(1) 87-97) which employs an electrolyte having
a pH of 12.2 and indirect detection at 222nM. It
should be possible to obtain a nonsilica-based
anion exchange column such as the Wescan anion/R
column, develop a method using an aqueous,
strongly basic mobile phase and monitor at 210nM.
By Merlin on Tuesday, April 10, 2001 - 03:44 pm:
Try 0.005% heptylamine in your mobile phase. It will give you your basic solution suggested by B.Buglio (pH 9.4). It will also ion pair with the acid, and increase the retention on your RP column. You may even need to use 5-10% MeCN. If you need higher pH to fully inhibit the lactonization, increase HA up to 0.1% (pH~12), but you may need to switch to a polymeric RP column.
You may be able to use far UV detection, <210 nm, but sensitivity will not be very good. This molecule would be more suited to an ELS detector
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