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. Author manuscript; available in PMC: 2014 Jan 4.
Published in final edited form as: J Chromatogr A. 2012 Nov 19;1271(1):71–85. doi: 10.1016/j.chroma.2012.11.024

Fig. 5.

Fig. 5

pH-zone-refining CCC of DNP-amino acids with (A) and without (B) spacer acids in the stationary phase. (A) Rectangular shape of DNP-amino acids are widely separated from each other by three spacer acids (acetic acid, propionic and n-butyric acid). (B) Elimination of these spacer acids resulted in fusion of all rectangular peaks with minimum overlapping as demonstrated by associated pH and partition coefficient values (Kstd). Experimental conditions are identical to those in Fig. 4 except that the sample size was increased from 1 mg to 100 mg for each DNP-amino acid. Kstd values were obtained by partitioning an aliquot of each fraction into the standard two-phase solvent system composed of chloroform–acetic acid–0.1 M HCl (2:2:1, v/v) used for the separation. SF: solvent front.