Amino AcidTMSderivative Slope(μM-1) Responseaxisintercept R2 Calculated concentration in the standardsolution(μM) Notreviewed Reviewed Nor2TMS 1.095E-02 5.547E-01 0.999 101.4 accepted Leu2TMS 1.058E-02 5.375E-01 0.999 101.6 accepted Ala2TMS 7.45E-03 3.848E-01 0.999 103.3 accepted Gly2TMS 2.30E-03 1.075-01 0.971 93.4 rejectedsee text Gly3TMS 3.00E-03 1.436E-01 0.986 95.6 rejectedsee text Val2TMS 8.71E-03 4.55E-01 0.995 104.5 accepted Ile2TMS 9.16E-03 5.33E-01 0.999 103.5 accepted Pro2TMS 9.18E-03 4.108E-01 0.997 89.5 96.8 Ser3TMS 6.95E-03 3.302E-01 0.997 95.0 accepted Thr3TMS 3.333E-03 1.583E-01 0.994 95.0 accepted Met2TMS 4.87E-03 2.295E-01 0.998 94.2 accepted Asp2TMS 5.86E-03 3.029E-01 0.993 103.4 accepted PyroGlu2TMS 9.70E-03 5.274E-01 0.995 108.7 103.9 Glu3TMS 3.06E-03 1.63E-02 0.993 10.65 rejectedsee text Phe1TMS 1.25E-03 7.093E-02 0.998 113.4 rejectedsee text Phe2TMS 4.16E-03 1.448E-01 0.997 69.6 rejectedsee text Lys2TMS ME 6.57E-3 2.36E-1 0.949 71.84 rejectedsee text Cys3TMS 1.48E-3 1.89E-01 0.949 255.4 rejectedsee text Tyr2TMS 6.99E-03 2.46E-01 1.000 70.39 rejectedsee text Trp2TMS 1.015E-03 2.201E-02 0.983 43.4 rejectedsee text

Table 2: Equations of the regression line through the (TargetIonRR, AddedConc) experimental points in the standard additions plots and calculated concentrations of the standard 100 μM solution of amino acids (data from the main basic experiment in Figure 1). Only concentrations which are affected by an uncertainty (evaluated from the standard additions plot) which does not exceed the set threshold of ± 6% have been accepted.