Direct analysis of 4-methylimidazole in foods using paper spray mass spectrometry

Rapid qualitative and quantitative analysis of 4-methylimidazole (4-MEI) in caramel and beverage samples is demonstrated using the paper spray form of ambient ionization mass spectrometry. The minimum level of pure 4-MEI detectable using multiple reaction monitoring (MRM) in a triple quadrupole instrument was 3 pg μL⁻¹ in neat solvent and 5 pg μL⁻¹ in a matrix containing caramel. This method was used to analyze 11 caramel samples for 4-MEI. After implementing effective quality control protocols, average relative standard deviations for paper spray triple quadrupole MS were less than 15% and the linear dynamic range was three orders of magnitude. Results obtained on three different days by two different analyst groups agreed closely. An ion trap tandem MS method of approximate quantitative analysis is also described and it gave similar precision to the triple quadrupole experiment when fluctuations in ion currents were cancelled by simultaneously isolating the analyte and internal standard and fragmenting both in an ion trap simultaneous MRM experiment. As another alternative, a rapid qualitative screening method based on the use of high-resolution measurements instead of tandem mass spectrometry using an Orbitrap was also tested and found to give a detection limit of 100 pg μL⁻¹.