Extension of a dynamic headspace multi-volatile method to milliliter injection volumes with full sample evaporation: Application to green tea

Abstract

An extension of multi-volatile method (MVM) technology using the combination of a standard dynamic headspace (DHS) configuration, and a modified DHS configuration incorporating an additional vacuum module, was developed for milliliter injection volume of aqueous sample with full sample evaporation. A prior step involved investigation of water management by weighing of the water residue in the adsorbent trap. The extended MVM for 1mL aqueous sample consists of five different DHS method parameter sets including choice of the replaceable adsorbent trap. An initial two DHS sampling sets at 25°C with the standard DHS configuration using a carbon-based adsorbent trap target very volatile solutes with high vapor pressure (>10kPa) and volatile solutes with moderate vapor pressure (1–10kPa). Subsequent three DHS sampling sets at 80°C with the modified DHS configuration using a Tenax TA trap target solutes with low vapor pressure (<1kPa) and/or hydrophilic characteristics. After the five sequential DHS samplings using the same HS vial, the five traps are sequentially desorbed with thermal desorption in reverse order of the DHS sampling and the desorbed compounds are trapped and concentrated in a programmed temperature vaporizing (PTV) inlet and subsequently analyzed in a single GC–MS run. Recoveries of 21 test aroma compounds in 1mL water for each separate DHS sampling and the combined MVM procedure were evaluated as a function of vapor pressure in the range of 0.000088–120kPa. The MVM procedure provided high recoveries (>88%) for 17 test aroma compounds and moderate recoveries (44–71%) for 4 test compounds. The method showed good linearity (r2>0.9913) and high sensitivity (limit of detection: 0.1–0.5ngmL−1) even with MS scan mode. The improved sensitivity of the method was demonstrated with analysis of a wide variety of aroma compounds in brewed green tea. Compared to the original 100μL MVM procedure, this extension to 1mL MVM allowed detection of nearly twice the number of aroma compounds, including 18 potent aroma compounds from top-note to base-note (e.g. 2,3-butanedione, coumarin, furaneol, guaiacol, cis-3-hexenol, linalool, maltol, methional, 3-methyl butanal, 2,3,5-trimethyl pyrazine, and vanillin). Sensitivity for 23 compounds improved by a factor of 3.4–15 under 1mL MVM conditions.