Determination of Cations and Anions in Environmental Samples by HPLC: Review

Reverse-Polarization High-Performance Layer Electrochromatography-A New Approach to Anion Separation

High-performance layer electrochromatography (HPLEC) combines the advantages of overpressured-layer chromatography (OPLC) and pressurized planar electrochromatography (PPEC) while overcoming some of their limitations. HPLEC equipment can work in various HPLEC, OPLC, and PPEC modes. The equipment enables HPLEC analysis also with an electroosmotic effect directed against the hydrodynamic flow of the mobile phase. The change in the electric field direction in the separation system does not result in a change in either the direction of the mobile phase flow or the direction of solute migration. The hydrodynamic flow generated by the pump dominates the electroosmotic effect and enables separation against the direction of the latter. Reversed-polarization HPLEC may be advantageous for the analysis of anionic compounds, as it facilitates faster and more selective separation than OPLC performed in similar conditions. This separation mode provides a new possibility to develop and optimize separation methods by performing separation against the electroosmotic effect and without need of any modification of the adsorbent surface. A drawback of this separation mode is the increase in the backpressure at the mobile phase inlet and the limitation of the mobile phase flow rate. Currently, contrary to the single-channel mode, multi-channel reverse-polarity HPLEC still requires some technical and methodological improvements.

Recent progress in micro/nano biosensors for shellfish toxin detection

Shellfish toxins, as one kind of marine toxin, have attracted worldwide attention due to their severe threat to food safety and human health. Therefore, it is highly essential and urgent to develop a low-cost and convenient method to detect these toxins. With the rapid advance in microfabrication processes, micro/nano biosensors provide novel approaches to address this issue. In addition to their features of low cost, portability, easy operation, high efficiency and high bioactivity, micro/nano biosensors have great potential to realize on-the-spot, rapid detection of shellfish toxins. This review focuses on the most recent advances in the development of micro/nano biosensors for shellfish toxin detection. These biosensors are mainly classified into five categories according to their transducer detection principles, which include optical devices, electrochemical sensors, electrochemiluminescence, field-effect transistors, and acoustic devices. Sensor strategies, toxin analytes, biosensitive elements, coupling methods and field detection performance are highlighted to discuss the applications of shellfish toxin detection. With advances in sensor technology, biomaterials, microfabrication and miniaturized electronics, micro/nano biosensors applied to in-field fast detection of shellfish toxins are expected to play a critical role in food safety, environmental monitoring, and foreign trade in the foreseeable future. Finally, the current challenges and future development trends of micro/nano biosensors for shellfish toxin detection are discussed.

Inorganic oxidizer detection from propellants, pyrotechnics, and homemade explosive powders using gradient elution moving boundary electrophoresis

Advancement in rapid targeted chemical analysis of homemade and improvised explosive devices is critical for the identification of explosives-based hazards and threats. Gradient elution moving boundary electrophoresis (GEMBE), a robust electrokinetic separation technique, was employed for the separation and detection of common inorganic oxidizers from frequently encountered fuel-oxidizer mixtures. The GEMBE system incorporated sample and run buffer reservoirs, a short capillary (5 cm), an applied electric field, and a pressure-driven counterflow. GEMBE provided a separation format that allowed for continuous injection of sample, selectivity of analytes, and no sample cleanup or filtration prior to analysis. Nitrate, chlorate, and perchlorate oxidizers were successfully detected from low explosive propellants (e.g., black powders and black powder substitutes), pyrotechnics (e.g., flash powder), and tertiary explosive mixtures (e.g., ammonium nitrate- and potassium chlorate-based fuel-oxidizer mixtures). Separation of these mixtures exhibited detection without interference from a plethora of additional organic and inorganic fuels, enabled single particle analysis, and demonstrated semiquantitative capabilities. The bulk counterflow successfully excluded difficult components from fouling the capillary, yielding estimated limits of detection down to approximately 10 μmol/L. Finally, nitrate was separated and detected from postblast debris collected and directly analyzed from two nitrate-based charges.

C3V symmetric tripodal molecular pocket for linear anions: Selective colorimetric detection of azide through N4-Cu-π···hole interactions

Tris(3-amino propyl)amine (TRPN) based C₃v symmetric tripodal molecular pocket, L has been prepared and mono copper complex of L, (1) having Cu-N₄-π··· hole as recognizing elements, becoming a potential and selective colorimetric chemo sensor for perfect linear recognition of N₃^-, generate a Cu-NNN- π··· hole unit inside the tripodal pocket. Systematic spectrometric and naked-eye colorimetric studies reveal that, this chemo sensor is also colorimetrically recognizing the cyanide ion by its cavity via Cu-N₄-π···hole interactions; nevertheless, when azide anion is entering as a guest into the molecular pocket of 1 which is already hosted cyanide anion, then host displaces cyanide ion, subsequently azide is getting inside the cavity. The strength of the copper complex, 1 towards azide and cyanide are found to be 2.36 × 10³M^-1, and 1.87 × 10³ M^-1 respectively in 7:3 acetonitrile:water solvent medium. Further, the ability of cyanide displacement by azide in complex 1 is found to be 2.53 × 10³ M^-1. To the best of our knowledge, this is the first example of naked-eye detection of azide via cyanide displacement assay by a tripodal receptor.

Elucidating sensing mechanisms of a pyrene excimer-based calix[4]arene for ratiometric detection of Hg(ii) and Ag(i) and chemosensor behaviour as INHIBITION or IMPLICATION logic gates

This article reports the synthesis and characterisation of two lower rim calix[4]arene derivatives with thiourea as spacer and pyrene or methylene-pyrene as fluorophore. Both derivatives exhibit a fluorimetric response towards Hg²⁺, Ag⁺ and Cu²⁺. Only methylene-pyrenyl derivative 2 allows for selective detection of Hg²⁺ and Ag⁺ by enhancement or decrease of excimer emission, respectively. The limits of detection of 2 are 8.11 nM (Hg²⁺) and 2.09 nM (Ag⁺). DFT and TD-DFT computational studies were carried out and used to identify possible binding modes that explain the observed response during fluorescence titrations. Calculations revealed the presence of different binding sites depending on the conformation of 2, which suggest a reasonable explanation for non-linear changes in fluorescence depending on the physical nature of the interaction between metal centre and conformer. INHIBITION and IMPLICATION logic gates have also been generated monitoring signal outputs at pyrene monomer (395 nm) and excimer (472 nm) emission, respectively. Thus 2 is a potential primary sensor towards Ag⁺ and Hg²⁺ able to configure two different logic gate operations.