A highly porous fiber coating based on a Zn-MOF/COF hybrid material for solid-phase microextraction of PAHs in soil

This study involved the development of a novel adsorbent by combining a Zn-based MOF with a melamine-based COF, resulting in the formation of a hybrid material known as Zn-MOF/COF. The adsorbent was characterized using FT-IR, SEM, XRD, EDX, and BET analysis techniques. The resulting Zn-MOF/COF sorbent was employed to prepare solid-phase microextraction (SPME) fibers for the extraction and enrichment of polycyclic aromatic hydrocarbons (PAHs) in contaminated soil samples, after coupling with GC-FID. A Box-Behnken design (BBD) was used to optimize key variables of SPME conditions. Under optimal conditions of 85 °C for 30 min extraction with 23 μL g-1 sample's moisture level, linear responses of six PAHs were ranging from 1 to 20000 ng g⁻1 with determination coefficients greater than 0.99. Limits of detection (LODs) were over the ranges of 0.1-1 ng g-1. The RSDs for intra-fiber and inter-fiber analyses were obtained 2.2-6.6% and 5.2-11.6%, respectively. Relative recoveries values for real soil samples were found to be 91.1-110.2%. The results showed lower cost and higher extraction efficiency for the Zn-MOF/COF fiber, compared with commercial and homemade adsorbents.

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.

Nylon 6-cellulose composite hosted in a hypodermic needle: Biofluid extraction and analysis by ambient mass spectrometry in a single device

This study proposes a hypodermic needle (HN) as a sorbent holder and an electrospray (ESI) emitter, thus combining extraction and analysis in a single device. A novel nylon 6-cellulose (N6-Cel) composite sorbent is proposed to extract methadone from oral fluid samples. The cellulosic substrate provides the composite with high porosity, permitting the flow-through of the sample, while the polyamide contributes to the extraction of the analyte. The low price of the devices (considering the holder and the sorbent) contributes to the affordability of the method, and their small size allows easy transportation, opening the door to on-site extractions. Under the optimum conditions, the analyte can be determined by high-resolution ambient ionization mass spectrometry at a limit of detection (LOD) as low as 0.3 μg/L and precision (expressed as relative standard deviation, RSD) better than 9.3%. The trueness, expressed as relative recovery (RR), ranged from 90% to 109%. As high-resolution mass spectrometers are not available in many laboratories, the method was also adapted to low-resolution spectrometers. In this sense, the direct infusion of the eluates in a triple quadrupole-mass spectrometry provided an LOD of 2.2 μg/L. The RSD was better than 5.3%, and the RR ranged from 96% to 121%.

Nanomaterial-assisted thread-based isotachophoresis with on-thread solute trapping

This research describes a nanomaterial-assisted TB-ITP setup for the clean-up, preconcentration, and trapping of alkaloids in biological fluids, followed by their on-thread DESI-MS determination.

Chromium-Based Polypyrrole/MIL-101 Nanocomposite as an Effective Sorbent for Headspace Microextraction of Methyl tert-Butyl Ether in Soil Samples

The performance of headspace solid-phase microextraction (HS-SPME) was upgraded by easy and low-cost preparation of a new nanocomposite fiber. A polypyrrole/chromium-based metal–organic framework, PPy@MIL-101(Cr), nanocomposite was electrochemically synthesized and simultaneously coated on a steel wire as a microextraction sorbent. The morphology and chemical structure of the prepared nanocomposite was characterized by Fourier-transform infrared spectrometry (FT-IR), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX) techniques. The microsorbent was used for sampling of methyl-tert-butyl ether (MTBE) in solid samples, through an HS-SPME sampling strategy, followed by GC-FID measurement. The optimal experimental conditions, including extraction temperature, extraction time, and GC desorption conditions, were evaluated and optimized. The proposed procedure showed good sensitivity (limit of detection was 0.01 ng·g⁻¹) and precision (relative standard deviation was 8.4% for six replicated analyses). The calibration curve was linear over the range of 5–40,000 ng·g⁻¹, with a correlation coefficient of 0.994. The limit of quantification was 0.4 ng·g⁻¹. The fabricated fiber exhibited good repeatability and reproducibility for the sampling of MTBE, with average recovery values of 88–114%. The intra-fiber and inter-fiber precisions were found to be 8.4% and 19%, respectively. The results demonstrated the superiority of the PPy@MIL-101(Cr)-coated fiber in comparison with handmade (polypyrrole, PPY) and commercial fibers (polyacrylate, PA; polydimethylsiloxane, PDMS; and divinylbenzene/carboxen/polydimethylsiloxane, DVB/CAR/PDMS) for the analysis of solid samples. The developed method was successfully employed for the analysis of MTBE in different soil samples contaminated by oil products.

Preparation of Carbotrap/silica composite for needle trap field sampling of halogenated volatile organic compounds followed by gas chromatography/mass spectrometry determination

BACKGROUND

A needle trap device (NTD) was packed with Carbotrap/silica composite sorbent and applied for field sampling of halogenated volatile organic compounds (HVOCs) followed by gas chromatography/mass spectrometry (GC/MS) separation and determination.

METHODS

Carbotrap B, as a highly pure surface sorbent, was prepared using sol-gel method to improve its surface properties for adsorption/desorption of the target analytes. The effects of important experimental variables on the sampling and determination of trichloroethylene (thrCE) and tetrachloroethylene (tetCE) using the proposed NTD-GC/MS strategy were evaluated and optimized.

RESULTS

The results showed that sampling temperature and relative humidity interfered with sampling efficiency of the developed method and peak area responses of the analytes decreased with increasing temperature and relative humidity. The peak areas of the analytes increased with raising desorption temperature from 180 to 250 °C, and increasing desorption time from 1 to 3 min. The carryover experiments showed that the carryover effect disappeared after 3 min of desorption time. The Limits of Detection (LODs) and Limits of Quantitation (LOQs) of the analytes were in the range 0.01-0.03 and 0.05-0.09, respectively.

CONCLUSIONS

The results indicated that the developed NTD-GC/MS procedure can be used as a technology with high sensitivity for the field sampling and determination of HVOCs.