Measuring gas-liquid partition coefficients of aroma compounds by solid phase microextraction, sampling either headspace or liquid

Abstract

Hydrophobic compounds are important odorants and nutrients in foods and beverages, as well as environmental contaminants and pharmaceuticals. Factors influencing their partitioning within multi-component systems and/or from the bulk liquid phase to the air are critical for understanding aroma quality and nutrient bioavailability. The equilibrium partitioning of hydrophobic analytes between air and water was analyzed using solid phase microextraction (SPME) in the headspace (HS-SPME) and via direct immersion in the liquid (DI-SPME). The compounds studied serve as models for hydrophobic aroma compounds covering a range of air-water partition coefficients that extends over four orders of magnitude. By varying the total amount of analyte as well as the ratio of vapor to liquid in the closed, static system, the partition coefficient, K(vl), can be determined without the need for an external calibration, eliminating many potential systematic errors. K(vl) determination using DI-SPME in this manner has not been demonstrated before. There was good agreement between results determined by DI-SPME and by HS-SPME over the wide range of partitioning behavior studied. This shows that these two methods are capable of providing accurate, complementary measurements. Precision in K(vl) determination depends strongly on K(vl) magnitude and the ratio of the air and liquid phases.

Simultaneous determination of free and bonded forms of odor-active carbonyls in wine using a headspace solid phase microextraction strategy

“…This minimum alteration should be reconciled, however, with the need for sensitivity. Because of this, a HS-SPME sampling method has been chosen together with conditions in which the displacement of the equilibrium toward free forms should be minimal [28]. Those conditions include incubation of the sample at 45 • C for 10 min and short extraction (10 min) of the headspace over the unstirred sample with a PDMS/DVB fiber.…”

“…For instance, several authors have proposed the direct headspace extraction [27] or the SPME extraction of headspaces using short extraction times to assess the degree of interaction of aroma compounds with the matrix [28][29][30]. These approaches, however, require the previous knowledge of the total concentration of the analyte and need to be complemented by a second method and may have sensitivity problems.…”

Partitioning, solubility and solubilization of limonene into water or short‐chain phosphatidylcholine solutions

“…× 14 mm I.D. × 0.13 mm, Metro Gasket, Kansas City, MO), aluminum foil (Reynolds, Richmond, VA), and a PTFE septum of 3 mm thickness inserted into a bimetal (Sn/Al) crimp cap (Restek, Bellefonte, PA) (Lloyd, Dungan, & Ebeler, 2011a). Vials were mixed in an agitator (Gerstel, Linthicum, MD) equipped with temperature control at 300 rpm.…”

“…From the headspace concentration, vapor/water and water/micelle partition coefficients, as well as dissolved concentrations in water, could then be determined, given known amounts of total solute and surfactant. We have shown in previous work that such methods are well‐suited for quantifying solute distributions between vapor and water in the absence of surfactant (Lloyd, Dungan, & Ebeler, 2011a), and for measuring solute partitioning into micelles over a wide range of compositions (Lloyd, Kardaras, et al, 2011b), without the need to significantly alter the overall system equilibria. In addition, earlier studies have demonstrated that vapor phase measurements of volatile hydrophobic compounds are effective at accurately and non‐invasively assessing their concentration distribution within aqueous micellar solutions (Christian et al, 1981; Vane et al, 2000).…”

Origins of Grape and Wine Aroma. Part 2. Chemical and Sensory Analysis

“…The SPME extraction time chosen will depend on the method objectives. If sampling of only volatiles in the headspace is desired, without influencing the partitioning of the volatiles from the liquid phase into the headspace, then short sampling times are used (~1 to 5 min) (Lloyd et al 2011). Sampling under these conditions is similar to a static HS extraction (Jung and Ebeler 2003).…”