Application of solid-phase extraction to brewed coffee caffeine and organic acid determination by UV/HPLC

A solid-phase extraction (SPE) method was adapted to perform brewed coffee sample clean-up for seven organic acids (acetic, citric, formic, malic, pyruvic, quinic and succinic) and caffeine determination by reversed-phase UV high performance liquid chromatography (RP/UV-HPLC). For all analytes the method showed good precision and linearity and, as an application, 20 brewed coffee samples from the two types of coffee (robusta vs. arabica) were tested. Brewed coffee samples were prepared according to ISO 6668 [1991. Green coffee—preparation of samples for use in sensory analysis] and the results were compared to sensory evaluation obtained from a panel of coffee tasters. Robusta coffee demonstrated the highest content of caffeine. Total acid content varied with coffee type and also with the geographic origin of the green coffee. Roasting conditions also seem to affect final acidity in brewed coffee for both coffee types analysed.