Trace level determination of substance P using capillary electrophoresis and laser-induced fluorescence

An analytical method was developed to determine the undecapetide substance P (SP) based on capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection. SP was derivatized with the fluorogenic reagent 2,3-naphthalenedicarboxaldehyde (NDA) prior to injection into the CE-LIF system. The pre-column derivatization scheme combined with injection enhancement techniques extends the detectability of SP to the subnanomolar level. Limit of detection (LOD) of 100 pM was achieved without pre-concentrating the sample prior to injection. The reproducibility for six different preparations of a standard sample containing 5 nM of SP was 6.8% RSD and that of the CE migration time was 0.08% RSD. The method was used to determine SP in a saliva sample.