Fabrication and evaluation of a portable low-pressure headspace solid-phase microextraction device for on-site analysis

A comprehensive theory for vacuum-assisted headspace extraction of solid samples

Vacuum-assisted headspace extraction (VA-HSE) has proven to be an efficient solution for the rapid and effective extraction of volatile and semi-volatile species. The research has been mainly focused on liquid samples by considering differences in Henry's constants, while the accelerating effect of vacuum is more significant and practically more important in solid samples with complex matrices. Nevertheless, the lack of a comprehensive theory for VA-HSE in solid samples, based on the adsorption/desorption phenomena, is quite evident. This research was done with the aim of modeling VA-HSE of solid samples from a thermodynamic point of view. To understand the impact and mechanism of reduced pressure, the sampling space was divided into three separate areas including the solid matrix (the surface and cavities of the solid sample), the headspace of the sample, and the extraction phase (the surface and cavities of the adsorbent). The effects of vacuum on the movement of analyte molecules in all three areas were investigated and included in a comprehensive equation. According to the theoretical model, when a solid sample is subjected to vacuum conditions, the enthalpy of the analytes in their free state decreases. As a result, the analytes become more volatile. Additionally, vacuum reduces the thickness of the boundary layer in solid samples. This facilitates the diffusion of analyte molecules into the cavities within the solid material and eventually into the headspace of the sample. A similar effect is observed on the extractive phase side when vacuum is applied. The reduction in boundary layer thickness promotes the adsorption of analytes onto the extractive phase, thereby facilitating a quicker equilibrium of analyte concentration in the extraction phase. The proposed model was validated by correlating it with the experimental data found in the literature. The results of this analysis have shown a robust correlation between the theoretical model and the experimental data, bolstering the reliability of the model, and highlighting its practical relevance.

An automated micro solid phase extraction gas chromatography-mass spectrometry (μSPE-GC-MS) detection method for geosmin and 2-methylisoborneol in drinking water

Geosmin and 2-methylisoborneol (2-MIB) are amongst the most common earthy and musty taste and odour (T&O) compounds found in drinking water. With low odour threshold detection limits below 10 ng L^-1, and the complexity of raw water matrices, these two compounds provide a significant challenge for water companies globally. In this research, for the first time, a novel and fully automated micro-solid phase-extraction (μSPE) method coupled with gas chromatography (GC)-mass spectrometry (MS) has been developed for the detection of geosmin and 2-MIB for drinking water analysis. The new automated method described herein is environmentally friendly requiring low raw water sample volumes, of 25 mL, and only 50 μL of elution solvent. Our μSPE-GC-MS method exhibits excellent linearity for both compounds (R² > 0.999) and low limits of detection of 2.0 ng L^-1 and 4.3 ng L^-1 for geosmin and 2-MIB, respectively. The method showed excellent recovery rates (95.1-100.1%) and good precision (RSD < 7%) in raw sample matrices. Our approach is fully automated onto a robotic workstation which can be readily integrated into a laboratory workflow for routine water analysis. Furthermore, the method has excellent potential to be incorporated within a portable system for onsite analysis.

Quantification of trace transformation products of rocket fuel unsymmetrical dimethylhydrazine in sand using vacuum-assisted headspace solid-phase microextraction

Quantification of unsymmetrical dimethylhydrazine transformation products in solid samples is an important stage in monitoring of environmental pollution caused by heavy rockets launches. The new method for simultaneous quantification of unsymmetrical dimethylhydrazine transformation products in sand samples using vacuum-assisted headspace solid-phase microextraction without addition of water followed by gas chromatography-mass spectrometry is proposed. Decreasing air evacuation time from 120 to 20 s at 23 °C resulted in increased responses of analytes by 25-46% and allowed obtaining similar responses as after evacuation at -30 °C. The best combination of responses of analytes and their relative standard deviations (RSDs) was achieved after air evacuation of a sample (m = 1.00 g) for 20 s at 23 °C, incubation for 30 min at 40 °C, and 30-min extraction at 40 °C by Carboxen/polydimethylsiloxane (Car/PDMS) fiber. The method was validated in terms of linearity (R²=0.9912-0.9938), limits of detection (0.035 to 3.6 ng g^-1), limits of quantification (0.12-12 ng g^-1), recovery (84-97% with RSDs 1-11%), repeatability (RSDs 3-9%), and reproducibility (RSDs 7-11%). It has a number of major advantages over existing methods based on headspace solid-phase microextraction-lower detection limits, better accuracy and precision at similar or lower cost of sample preparation. The developed method was successfully applied for studying losses of analytes from open vials with model sand spiked with unsymmetrical dimethylhydrazine transformation products. It can be recommended for analysis of trace concentrations of unsymmetrical dimethylhydrazine transformation products when studying their transformation, migration and distribution in contaminated sand.