Hybrid materials based on deep eutectic solvents for the preconcentration of formaldehyde by SPME in coffee beverages

Coffee is one of the most widely consumed beverages. It can be prepared from green or roasted beans or from instant coffee. Unfortunately, in addition to the aroma obtained in the coffee roasting process, among others, formaldehyde can be produced. In this study, thin-film solid-phase microextraction was used to preconcentrate trace amounts of formaldehyde in different types of coffee with different roasting levels. For this purpose, 18 hybrid materials based on deep eutectic solvents were synthesized and tested as sorbents in thin-film solid-phase microextraction. The coffee samples were brewed, and then formaldehyde present in them was derivatized using the Nash reagent. The sample preparation procedure was optimized for selected DES-based sorbent using a central composite design method and validated. Formaldehyde was determined in almost all samples of second-crack coffee (roasted at 240 °C) at 0.17-0.75 ng mL^-1 and in darker-colored instant coffees at 0.18-0.54 ng mL^-1.