Comparison of DL-Amino Acid Labeling Kit and Achiral Labeling Reagents

A comparison of the below labeling reagents was performed using pre-column derivatization.

  1. #19942-74: DL-Amino Acid Labeling Kit
  2. #10427-91: Dabsyl Chloride
  3. #27810-44: o-Phthalaldehyde

Optical separation of DL enantiomers

Labeled DL-phenylalanine was analyzed using a C18 column. The labeling reagent in the DL-Amino Acid Labeling Kit has a chiral carbon, resulting in the labeled D and L forms being diastereomers. This makes them separable on C18 columns.

chromatogram showing optical separation of DL-amino acids

* Generally, fluorescence detection is used for amino acids labeled with o-phthalaldehyde.

Detection sensitivity with mass spectrometry (MS)

Detection sensitivity was compared using labeled L-phenylalanine as the sample. Both the DL-Amino Acid Labeling Kit and dabsyl chloride had high MS sensitivity, due to their easily ionizable structures.

chromatogram showing increased sensitivity with LC-MS using this kit

Stability of labeled samples

Labeled L-phenylalanine was analyzed by HPLC 1, 3, and 7 days after labeling. The sample labeled with o-phthalaldehyde was not stable, and therefore should not be labeled manually, but rather using online analysis within the instrument.

Days after labeling DL-Amino Acid Labeling Kit Dabsyl chloride o-Phthalaldehyde
1 100% 100% 100%
3 113% 95% 0%
7 106% 96% 0%

* Analysis conditions are as in "Optical separation of DL enantiomers". The peak area measured after 1 day was taken as 100%. Samples were stored refrigerated.