LC-DAD separation of Kahweol and cafestol oleate and palmitate from coffee

Analysis of diterpene esters (kahweol oleate -KO; cafestol oleate -CO; kahweol palmitate -KP; cafestol palmitate -CP) by LC DAD in standards and coffees.

Separation conditions: 

Coffee brews were extracted using 5 mL of diethyl ether. The mixture was vortexed for 2 min, and after centrifugation, the upper phase was transferred to a clean test tube. Next, the aqueous solution was re-extracted using diethyl ether, and the combined ether phase was washed with 5mL of 2 M NaCl solution followed by centrifugation (4000 rpm, 10 min. Finally, the clean ether phase was dried under an azote stream. Samples were kept at –22ºC until analysis using LC–DAD. Separation was achieved using a Purospher STAR LichroCART RP 18 end-capped (250 × 4 mm, 5 µm) column attached. Before injection, the dried extract was dissolved in 2.5 mL of acetonitrile and filtered through 0.45 µm filter membrane (PTFE, VWR, USA). Twenty microliters of sample were injected, and the separation was achieved using isocratic conditions for 35 min with the mobile phase made of acetonitrile/isopropanol (70:30, v/v) and pumped at 0.4 mL/min. A diode array detector, in the range of 200–400 nm, was used. After each run, the acquisition software exported data as a comma-separated-values format (EZChrom Elite 3.1.6).

For the calibration curves, mixtures of the four diterpenes esters at similar concentrations were used in the range of 2 to 200 mg/L. Eight samples were prepared and run in duplicates

Files: 

Data.mat: Matlab structure with, as fields:
     <Time>                             : a 3751 length vector. Time axis in min
     <Wavelength>                    : a 201 length vector, Wavelength of detection
     <Names_calibration>          : Name of the samples for calibrations
     <Data_calibration>             : a 3751x201x16 matrix with in first dimension the retention time, in second dimension the wavelength for detection and third dimension the calibration samples.
     <Data_samples>                : a 3751x201x4 matrix with in first dimension the retention time, in second dimension the wavelength for detection and third dimension the coffee samples.
     <Names_Samples>             : Name of the samples
     <Concentrations_calibration>: Table with the real concentration (mg/L) used in the standard samples.