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

Improving greenness and sustainability of standard analytical methods by microextraction techniques: A critical review

Since environmental awareness has increased in analytical chemistry, the demand for green sample preparation methods continues to grow. Microextractions such as solid-phase microextraction (SPME) and liquid-phase microextraction (LPME) miniaturize the pre-concentration step and are a more sustainable alternative to conventional large-scale extractions. However, the integration of microextractions in standard and routine analysis methods is rare, although these applications are used most frequently and have a role model function. Therefore, it is important to highlight that microextractions are capable to replace large-scale extractions in standard and routine methods. This review discusses the greenness, benefits, and drawbacks of the most common LPME and SPME variants compatible with gas chromatography based on the following key evaluation principles: Automation, solvent consumption, hazards, reusability, energy consumption, time efficiency, and handling. Furthermore, the need to integrate microextractions into standard and routine analytical methods is presented by using method greenness evaluation metrics AGREE, AGREEprep, and GAPI applied to USEPA methods and their replacements.

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

Headspace solid-phase microextraction (HSSPME) is one of the simplest and cost-efficient sample preparation approaches for determination of volatile organic compounds (VOCs) in soil. This study was aimed at the development of the model for numerical optimization of HSSPME of volatile organic compounds from dry soil samples by porous coatings using COMSOL Multiphysics (CMP). ‘Transport of Diluted Species in Porous Medium’ physics was used for modeling. Effect of sample mass, pressure, fiber-headspace and soil-headspace distribution constants on extraction profiles and time of 95% equilibrium has been studied using the developed model. Equilibrium extraction under atmospheric pressure (1 atm) can take up to 97 min, while under vacuum (0.0313 atm) – 2.3 min. Equilibration time under vacuum was 42-43 times lower than under 1 atm at all studied distribution constants and sample masses. The developed model was modified for optimization of pre-incubation time using ‘Transport of Diluted Species’ physics. According to the obtained plots, 95% equilibration time can reach 13.3 min and depends on both sample mass and soil-headspace distribution constant of the analyte. The developed model can be recommended for optimization of pressure, preincubation and extraction time when fiber-headspace and soil-headspace distribution constants, soil porosity and density are known.

Vacuum-assisted headspace thin-film microextraction: Theoretical formulation and method optimization for the extraction of polycyclic aromatic hydrocarbons from water samples

The thin films used in headspace thin-film microextraction (HS-TFME) enable higher sensitivity and superior extraction rates compared to other microextraction approaches, largely due to their greater surface area-to-volume ratio and extraction-phase volume. Nonetheless, analytes exhibiting a low affinity for the headspace and/or large partitioning between the extraction phase and headspace will still require more time to reach equilibrium. In this paper, we detail the development of a new method, termed as vacuum-assisted HS-TFME (Vac-HS-TFME), and we demonstrate how its use of vacuum conditions can accelerate the extraction kinetics of analytes with long equilibration times. The pressure-dependence of the extraction process was formulated and related to improvements in gas-phase diffusivity when lowering the total pressure. Four low-molecular-weight polycyclic aromatic hydrocarbons (PAHs) were used to experimentally verify the improvements in extraction efficiencies enabled by Vac-HS-TFME (vs. HS-TFME). To this end, the effects of temperature and extraction time on Vac-HS-TFME were investigated, with the results being compared to those obtained via regular HS-TFME. Furthermore, the use of a high-capacity sorbent in TFME allowed the positive effects of temperature and vacuum conditions to be combined successfully. Extraction-time profiles constructed at 30 and 50 °C revealed substantial acceleration in the overall extraction kinetics when sampling under vacuum conditions. At 50 °C, all of the analytes extracted via Vac-HS-TFME reached equilibrium within 45 min, whereas only two reached this state under atmospheric pressure. Vac-HS-TFME's analytical performance was evaluated under optimized conditions, and the results were compared to those obtained with regular HS-TFME. The findings revealed that for the two lighter PAHs, the performance of the two methods was similar since they were extracted close or at equilibrium. However, the calibration models for the two heavier PAHs tested here were linear over a wider concentration range (50-10000 ng L^-1) when using Vac-HS-TFME, had superior intra-day repeatability (7.4% and 6.7% vs. 11% and 9.3% with regular HS-TFME), and the limits of detection were lower compared to regular HS-TFME (15 and 11 ng L^-1 compared to 136 to 100 ng L^-1 with regular HS-TFME). Finally, the analysis of spiked wastewater effluent samples showed that the matrix did not affect extraction. The proposed Vac-HS-TFME approach combines the advantages of low-pressure sampling and high-capacity sorbent, and has a great potential for future applications in food, flavour, environmental, and biological analyses.

Hyphenated Mass Spectrometry versus Real-Time Mass Spectrometry Techniques for the Detection of Volatile Compounds from the Human Body

Mass spectrometry (MS) is an analytical technique that can be used for various applications in a number of scientific areas including environmental, security, forensic science, space exploration, agri-food, and numerous others. MS is also continuing to offer new insights into the proteomic and metabolomic fields. MS techniques are frequently used for the analysis of volatile compounds (VCs). The detection of VCs from human samples has the potential to aid in the diagnosis of diseases, in monitoring drug metabolites, and in providing insight into metabolic processes. The broad usage of MS has resulted in numerous variations of the technique being developed over the years, which can be divided into hyphenated and real-time MS techniques. Hyphenated chromatographic techniques coupled with MS offer unparalleled qualitative analysis and high accuracy and sensitivity, even when analysing complex matrices (breath, urine, stool, etc.). However, these benefits are traded for a significantly longer analysis time and a greater need for sample preparation and method development. On the other hand, real-time MS techniques offer highly sensitive quantitative data. Additionally, real-time techniques can provide results in a matter of minutes or even seconds, without altering the sample in any way. However, real-time MS can only offer tentative qualitative data and suffers from molecular weight overlap in complex matrices. This review compares hyphenated and real-time MS methods and provides examples of applications for each technique for the detection of VCs from humans.