The effect of vacuum: an emerging experimental parameter to consider during headspace microextraction sampling

Abstract

The effect of vacuum is an emerging experimental parameter to consider during optimization of a variety of headspace microextraction methodologies. The positive effect of vacuum was initially demonstrated for headspace solid-phase microextraction and was recently expanded to single-drop microextraction and higher capacity sorbents i.e. stir bar sorptive extraction. In all cases, sampling under vacuum greatly accelerated the extraction kinetics of analytes exhibiting long equilibration times under atmospheric pressure. At the same time, the extraction of analytes that reached equilibrium fast was not affected. In all optimized methods, extraction times were greatly reduced and/or sampling temperatures were lower to those reported with the standard methodology under atmospheric pressure. This work succinctly overviews the effect of vacuum on the different headspace microextraction technologies reported so far. The fundamental concepts describing the pressure dependence of each methodology are pulled together and presented in a simplified manner. The latest findings on the combined effects of vacuum and several selected experimental parameters typically examined during method optimization are then presented and the practical aspects of past outcomes are highlighted. The discussion also includes the air-evacuation step and the analysis of complex matrices. This article is intended for readers who are either new to the field of vacuum headspace microextraction sampling or its use and want to exploit this powerful approach.

Optimization of headspace solid-phase microextraction of volatile organic compounds from dry soil samples by porous coatings using COMSOL Multiphysics

“…At Kfh = 150,000, Ksh = 100,000 and 1000,000, t0.95 linearly decreases from 69.8-71.5 min to 52.3-54.0 min with the increase in ms from 1 to 10 g. At Kfh = 150,000 and Ksh = 10,000, t0.95 linearly decreases from 74.0 to 59.8 min with the increase in ms from 2 to 10 g. At Kfh = 8,300, t0.95 values are not higher than 6 min meaning that equilibrium extraction can be conducted at any ms with low time expenses (Figure 3B). The trends are similar to those at Kfh = 150,000, except at Ksh = 100: t0.95 increases when increasing ms from 1 to 5 g followed by the decrease when ms is increased to 10 g. At Kfh = 150,000 and Ksh = 1000, t0.95 increases when increasing ms from 1 to 5 g followed by a slight decrease when ms is increased to 10 g. faster [31][32][33][34]. This is mainly caused by the decreased diffusion coefficients in headspace under vacuum conditions [35].…”

The role of sample preparation in multidimensional gas chromatographic separations for non‐targeted analysis with the focus on recent biomedical, food, and plant applications

“…In the quest for greener, miniaturized, faster, selective/universal, and robust sampling strategies, it will be interesting to see how some recently developed sampling alternatives (vacuum‐based, thin‐film, paper‐based, freeze‐concentration, or solvent‐assisted SPe techniques [116–119]) will perform with GC×GC.…”

Comparing π‐complexation capabilities of ionic liquids containing silver(I) and copper(I) ions by headspace single drop microextraction in combination with high‐performance liquid chromatography

“…These solvents were selected as they possess lower volatility than water and acetonitrile under the conditions of the HS‐SDME experiments, as can be observed in Table S2. However, analyte standard solutions spiked into the EG/TEG mixtures were prepared at approximately five times higher levels since the enhanced viscosity of the solution (compared to the water/acetonitrile mixture) lowered the diffusion of the analytes from the liquid solution to the HS [45–47]. A mixture of EG and TEG (99:1, v/v) containing 5–50 mg/L of the analytes was found to successfully facilitate silver(I) ion‐aromatic complexation and follow a linear correlation with the [Ag + ][NTf 2 − ] concentration in the [C 10 MIM + ][NTf 2 − ] IL microdroplets, as shown in Figure 2.…”