Table 1. Acids Tested on the Reverse-Phase System Coupled to ESI(−)-MS and CADa,b.
| name | exact mass | formula | number of carboxylic acid groups | log P | relative response factor alone (TAC/μg) × 106 | relative response factor diluted in SRFA (TAC/μg) × 106 | relative enhancement in SRFA |
|---|---|---|---|---|---|---|---|
| 1,4-cyclohexanedicarboxylic acid | 172.074 | C8H12O4 | 2 | 0.5 | 2.69 ± 0.16 | 1.12 ± 0.16 | 0.41 |
| hippuric acid | 179.058 | C9H9NO3 | 1 | 0.3 | 3.11 ± 0.19 | 3.18 ± 0.27 | 1.02 |
| aspirin | 180.042 | C9H8O4 | 1 | 1.2 | 2.09 ± 0.13 | 0.00 ± 0.00 | 0.00 |
| cyclohexylsuccinic acid | 200.105 | C10H16O4 | 2 | 2 | 5.11 ± 0.21 | 16.32 ± 1.39 | 3.20 |
| ibuprofen | 206.131 | C13H18O2 | 1 | 3.5 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 |
| (5-formyl-2-methoxyphenoxy) acetic acid | 210.053 | C10H10O5 | 1 | 0.4 | 3.59 ± 0.22 | 3.33 ± 0.31 | 0.93 |
| sinapic acid | 224.068 | C11H12O5 | 1 | 1.5 | 1.61 ± 0.11 | 0.85 ± 0.07 | 0.53 |
| 2,5-dihydroxy-1,4-benzenediacetic acid | 226.048 | C10H10O6 | 2 | 0.1 | 3.17 ± 0.08 | 1.62 ± 0.12 | 0.51 |
| 3-ethyl-3-phenyl glutaric acid | 236.105 | C13H16O4 | 2 | 2.1 | 4.88 ± 0.22 | 9.77 ± 0.77 | 2.00 |
| benzene-1,3,5-triacetic acid | 252.22 | C12H12O6 | 3 | 0.3 | 2.74 ± 0.23 | 0.03 ± 0.03 | 0.01 |
| 2-(4-(2,2-dicarboxy-ethyl)-2,5-dimethoxy-benzyl-malonic) acid | 370.09 | C16H18O10 | 4 | 1 | 3.98 ± 0.39 | 5.24 ± 0.69 | 1.32 |
| fusidic acid | 516.345 | C31H48O6 | 1 | 5.5 | 1.86 ± 0.16 | 3.30 ± 0.53 | 1.78 |
| carbenoxolone | 570.356 | C34H50O7 | 2 | 6.4 | 0.99 ± 0.07 | 3.27 ± 0.60 | 3.31 |
| glycyrrhizic acid | 822.404 | C42H62O16 | 1 | 3.7 | 1.13 ± 0.08 | 0.00 ± 0.00 | 0.00 |
| median | 2.7 | 2.4 | |||||
| mean | 2.6 | 3.4 | |||||
| standard deviation | 1.5 | 4.6 | |||||
| standard error | 0.4 | 1.2 |
a
In addition to the exact mass, chemical formula, and number of carboxylic acid groups, the log P calculated by XLogP3 3.0 (PubChem release 2019.06.18) is given. The result for the relative ESI(−)-MS response factor is displayed as counts × time/μg injected, both in clean solution and after dilution in SRFA. The relative enhancement in relative response factor after dilution is shown as a ratio in the final column.
b
The error stated for the relative response factors is the uncertainty of the slope at 95% confidence level.