Fabrication of covalent organic frameworks modified nanofibrous membrane for efficiently enriching and detecting the trace polychlorinated biphenyls in water

Enriching and detecting the trace pollutants in actual matrices are critical to evaluating the water quality. Herein, a novel nanofibrous membrane, named PAN-SiO₂@TpPa, was prepared by in situ growing β-ketoenamine-linked covalent organic frameworks (COF-TpPa) on the aminated polyacrylonitrile (PAN) nanofibers, and adopted for enriching the trace polychlorinated biphenyls (PCBs) in various natural water body (river, lake and sea water) through the solid-phase micro-extraction (SPME) process. The resulted nanofibrous membrane owned abundant functional groups (-NH-, -OH and aromatic groups), outstandingly thermal and chemical stability, and excellent ability in extracting PCBs congeners. Based on the SPME process, the PCBs congeners could be quantitatively analyzed by the traditional gas chromatography (GC) method, with the satisfactory linear relationship (R²>0.99), low detection limit (LODs, 0.1∼5 ng L^-1), high enrichment factors (EFs, 2714∼3949) and multiple recycling (>150 runs). Meanwhile, when PAN-SiO₂@TpPa was adopted in the real water samples, the low matrix effects on the enrichment of PCBs at both 5 and 50 ng L^-1 over PAN-SiO₂@TpPa membrane firmly revealed the feasibility of enriching the trace PCBs in real water. Besides, the related mechanism of extracting PCBs on PAN-SiO₂@TpPa mainly involved the synergistic effect of hydrophobic effect, π-π stacking and hydrogen bonding.

Urinary volatile Organic compounds in non-alcoholic fatty liver disease (NAFLD), type two diabetes mellitus (T2DM) and NAFLD-T2DM coexistence

INTRODUCTION

Accumulating evidence have shown a significant correlation between urinary volatile organic compounds (VOCs) profile and the manifestation of several physiological and pathological states, including liver diseases. Previous studies have investigated the urinary metabolic signature as a non-invasive tool for the early discrimination between non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH), which nowadays represents one of the most important challenges in this context, feasible only by carrying out liver biopsy.

OBJECTIVES

The aim of the study was to investigate the differences in the urinary VOCs profiles of non-alcoholic fatty liver disease (NAFLD) patients, diabetes mellitus (T2DM) subjects and NAFLD/T2DM patients.

METHODS

Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was applied to profile the urinary VOCs. Urine samples were analysed both under acid and alkaline conditions, to obtain a range of urinary volatiles with different physicochemical properties.

RESULTS

Urinary VOCs profiles of 13 NAFLD patients, 13 T2DM subjects and 13 NAFLD/T2DM patients were investigated by multivariate and univariate data analysis techniques which allowed to identify 21 volatiles under alkaline conditions able to describe the NAFLD/T2DM group concerning the other two groups.

CONCLUSION

Our results suggest that VOCs signatures can improve the knowledge of the pathological condition where NAFLD coexists with T2DM and discovering new features that are not simply the sum of the two diseases. These preliminary findings may be considered as hypothesis-generating, to be clearly confirmed by larger prospective investigations.

Cryogenic trapping as a versatile approach for sample handling, enrichment and multidimensional analysis in gas chromatography

Cryogenic methods - those that employ cryogenic fluids/gases but also other approaches to generate reduced temperature - are versatile, functional and relatively easily implemented as part of a total gas chromatographic method. The general utility of a cold region is almost invariably as a trapping or focussing step, to collect analyte into a sharp zone. The success in effectively trapping analyte depends on analyte volatility and the temperature of the cold region. Analytes collection into a sorbent phase supported by cryotrapping usually provide a greater capacity trapping for the sorption step. Stripping analyte from a sample into a cryogenic trap, with subsequent introduction to GC as in a purge-and-trap method, sample introduction into an injector with incorporation of a cooling zone, manipulation and management of chromatographic bands during chromatography elution such as employed in multidimensional gas chromatography, and focussing analyte just prior to the detector, all have the same goal of concentrating the band, reducing its dispersion, and maximising response. This review summarises various approaches that demonstrate how cryogenic methods have been incorporated into gas chromatographic analysis.