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. Author manuscript; available in PMC: 2012 Feb 11.
Published in final edited form as: J Chromatogr A. 2010 Nov 16;1218(6):763–777. doi: 10.1016/j.chroma.2010.11.009

Table 4.

The Total Retention and Percent Cation Exchange Contributions on the HC-COOH Phase as a Function of pHa

pH Stationary phase Retention Acetophenone 3-methoxy tyramine Solutes Methcathinone Cathinone Ephedrine
4.0 HC-COOH k′total=k'RP+k'IEX,[SiOH]+k'IEX,[COOH] 4.21 0.33 0.97 0.73 0.82
HC-C8 k′total=k'RP+k'IEX,[SiOH] 5.57 0.22 0.90 0.65 0.74
%k ′ IEX,[COOH] b 0 0 0 0
4.5 HC-COOH k′total=k′RP+k'IEX,[SiOH]+k'IEX,[COOH] 4.30 0.68 1.74 1.33 1.45
HC-C8 k′total=k'RP+k'IEX,[SiOH] 5.59 0.34 1.21 0.87 1.00
%k ′ IEX,[COOH] b 35 27 29 26
5.0 HC-COOH k′total=k'RP+k'IEX,[SiOH]+k'IEX,[COOH] 4.32 1.31 3.22 2.48 2.73
HC-C8 k′total=k'RP+k'IEX,[SiOH] 5.61 0.50 1.67 1.22 1.38
%k ′ IEX,[COOH] b 53 46 48 47
5.5 HC-COOH k′total=k'RP+k'IEX,[SiOH]+k'IEX,[COOH] 4.26 2.38 6.04 4.64 5.20
HC-C8 k′total=k'RP+k'IEX,[SiOH] 5.51 0.73 2.36 1.70 1.94
%k ′ IEX,[COOH] b 65 60 62 61
6.0 HC-COOH k′total=k'RP+k'IEX,[SiOH]+k'IEX,[COOH] 4.23 4.35 11.10 8.11 9.93
HC-C8 k′total=k'RP+k'IEX,[SiOH] 5.59 1.06 3.51 2.50 2.85
%k ′ IEX,[COOH] b 73 68 68 71
a

The chromatographic conditions are the same as in Fig. 3.

b

The percentage of cation exchange contributions from carboxyl groups to the total retention at different pH calculated from Eq. 2.