Influence of Acidic Eluent Selection on Organic Acid Analysis (KC-811)

RSpak KC-811 is an ion exclusion chromatography column for organic acid analysis. The packing material consists of styrene-divinylbenzene copolymer modified with strongly acidic sulfo groups. By using a diluted strong-acidic aqueous solution as an eluent, organic acids exist in equilibrium of dissociated and undissociated states. In ion exclusion chromatography mode, undissociated organic acids are retained by hydrophobic interaction with the packing material. Meanwhile, dissociated organic acids are retained less as they are electrostatically repelled by the functional groups. Thus, differences in pKa and polarity of organic acids make them separated from each other in the ion exclusion chromatography. Strong acids commonly used are phosphoric acid, perchloric acid and p-toluenesulfonic acid. This application introduces analyses of organic acids using 0.1 % phosphoric acid, 5-mM p-toluenesulfonic acid and 5-mM perchloric acid as an eluent. The same resolution level can be obtained under any of the eluent conditions. However, in the case of 0.1 % phosphoric acid with RI detector, quantification of citric acid may not be accurate since the system peak overlaps with its peak. On the other hand, p-toluenesulfonic acid is not a suitable eluent for organic acid analysis when used with a UV detector, as p-toluenesulfonic acid has high UV absorbance. For organic acid analysis, the post-column reaction method is another option. We recommend selecting an appropriate acidic eluent for each detection method.

Sample: 5 μL

  1. 1.Citric acid 1.3 %
  2. 2.Tartaric acid 1.3 %
  3. 3.Malonic acid 1.3 %
  4. 4.Succinic acid 2.0 %
  5. 5.Lactic acid 2.5 %
  6. 6.Formic acid 3.0 %
  7. 7.Acetic acid 3.0 %
Chromatogram of Organic acids
Column
Shodex RSpak KC-811 (8.0 mm I.D. x 300 mm)
Eluent
(a) 0.1 % H3PO4 aq.
(b) 5 mM p-Toluenesulfonic acid aq.
(c) 5 mM HClO4 aq.
Flow rate
1.0 mL/min
Detector
RI
Column temp.
40 ℃

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