The present disclosure concerns a method and detector (10) for detecting an analyte (1) in a sample volume (2), such as nitrosamine in an amine solvent. The method comprises measuring a resonance Raman spectrum (I1) with a first light beam (PI) matching an electronic transition of the analyte (1). The detection of the analyte is enhanced by measuring an off-resonance Raman spectrum (12) using a second light beam (P2) that is shifted in wavelength at least 10 nm away from the electronic resonance. The resonance Raman signal (S1) of the analyte (1) is isolated from the background (Q1, Q2) by a difference analysis between the resonance and off-resonance Raman spectra (I1, I2). The method and detector (10) can be employed for detecting nitrosamine in a carbon capture process or plant (20) that employs an amine solvent.