By Anonymous on Sunday, March 10, 2002 - 07:36 am:
I determine lactic acid by HPLC using Aminex HPX-87,300mm X 7.8mm (catalog:125-0140), Column temp.=35Co , Mobil phase : 5mM sulphuric acid, Flow Rate 0.5ml/min, detection by UV detector at wavelength 220nm ,detection time 20min , but The retention time of lactic acid changes all over the run ,even with the same bottle of mobial phase.
By Anonymous on Sunday, March 10, 2002 - 11:14 am:
Did you check the flow rate?
By mmaxxxx on Friday, June 14, 2002 - 03:52 am:
Don't loose your time and use the following conditions (read them in the instruction manual of the column):
mobile phase: H2SO4 0.0065M + 2% CH3CN
flow: 0.6 mL/min
no guard column (centrifuge your samples at 6000rpm or filter them through .45mcm
most important: column temperature = 65°C (thermostat, water bath as well).
Prepare 3x of mobile phase needed for analysis, start your HPLC system at 0.1mL/min at 30°C, then increase the temperature by steps of 10°C every 10 minutes, then increase the flow rate by steps of 0.1mL/min every 10 minutes.
Let the system work all night long prior to routine work.
Choose the best wavelenght for your analyte (no problem to work at 210nm, some other organic acids have better lambda).
To have an idea: formic tr=13min, propionic 17,sorbic 57, fumaric 11, citric 7.
No way if you're thinking about ascorbic acid.
By Anonymous on Friday, June 14, 2002 - 02:16 pm:
stoneage
By mmaxxxx on Monday, June 17, 2002 - 02:53 am:
Well, I use to sign my messages: "anonymous" means having no identity, this is not my situation.
Anyway, please let me know some "new" methods for lactic acid analyses, since I've got some routine work to do: changing HPX-87H column with some other RP colums in the same HPLC system is not very quick and comfortable.
CG and/or enzymatic methods would be appreciated.
Thanks.
Have a good day.
MMAXXXX
By chris knutsen on Tuesday, June 18, 2002 - 12:56 am:
If lactic acid is the only acid in the mixture you can just do a titration. Here is the method from the USP.—
Otherwise, have you checked the AOAC methods for lactic acid-or the food chemical codex (FCC)? I do not have these available to me right now, but good luck
To about 2.5 mL of Lactic Acid, accurately weighed in a tared 250-mL flask, add 50.0 mL of 1 Nsodium hydroxide VS, and boil the mixture for 20 minutes. Add phenolphthalein TS, and titrate the excess
alkali in the hot solution with 1 N sulfuric acid VS. Perform a blank determination (see Residual Titrationsunder Titrimetry á 541 ń). Each mL of 1 N sodium hydroxide is equivalent to 90.08 mg of C 3H 6O 3.Auxiliary Information—
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