Screening of polyphenols in grape marc by on-line supercritical fluid extraction - Flow through sensor

An on-line supercritical fluid extraction continuous flow manifold includin g a flow through sensor was used and applied to the quantitative determinat ion of total polyphenols in grape mare samples. A clean, highly selective s upercritical fluid extraction (SFE) method for the isolation of phenols fro m grape marc samples was optimised. Dried, ground, and sieved grape marc (0 .1 g) were subjected to SFE with CO2 modified with 5% methanol at 350 bar a nd 50 degreesC (CO2 density 0.9g ml(-1)) for 15 min at a liquid flow-rate o f 4 ml min(-1). Diatomaceous earth was used to reduce the void volume of th e extraction vessel. The analytes were concentrated on a PorapackQ or ODS t rap and subsequently eluted with methanol. The influence of extraction vari ables such as modifier content, pressure, temperature, flow-rate, extractio n time, and collection/elution variables, were studied. Total phenol extrac ts were determined by using a direct measurement at 270 mn as screening met hod.