Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Considering that illegal admixture of robusta coffee into high quality arabica coffee is an important task in coffee analysis, we evaluated the use of direct infusion electrospray ionization-mass spectrometry (ESI-MS) data combined with the partial least squares (PLS) multivariate calibration technique as a fast way to detect and quantify arabica coffee adulterations by robusta coffee. A total of 16 PLS models were built using ESI(+/-) quadrupole time-of-flight (QTOF) and ESI(+/-) Fourier transform ion cyclotron resonance (FT-ICR) MS data from hot aqueous extracts of certified coffee samples. The model using the 30 more abundant ions detected by ESI(+) FT-ICR MS produced the most accurate coffee blend percentage prediction, and thus, it was later successfully employed to predict the blend composition of commercial robusta and arabica coffee. In addition, ESI(+/-) FT-ICR MS analysis allowed for the identification of 22 compounds in the arabica coffee and 20 compounds in the robusta coffee, mostly phenolics.601742534258Embrapa CafeConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)Brazilian National Petroleum Agency (ANP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)