A new method for separation and determination of Cr(III) and Cr(VI) in water samples by high-performance liquid chromatography based on anion exchange stationary phase of ionic liquid modified silica

A visual and reversible nanoprobe for rapid and on-site determination of hexavalent chromium and lysine based on dual-emission carbon quantum dots coupled with smartphone

A straightforward, largely instrument-free, smartphone-based analytical strategy for hexavalent chromium and lysine (Lys) on-site detection via exploitation of dual-emission carbon quantum dots (DECQDs) has been demonstrated. DECQDs show dual-emission peaks at 439 and 630 nm with the excitation at 375 nm. As a dual-mode detection probe, the fluorescence and ultraviolet adsorption spectra of DECQDs vary with hexavalent chromium concentrations. Most importantly, Lys can restore the fluorescence of the hexavalent chromium added DECQD nanoprobe and change the color of the probe under natural light. At the same time, based on the participation of smartphones, the prepared DECQD probes favor the establishment of visual smart sensors that can also be used for the in-situ detection of targets. The on-site quantitative analysis exhibited a linear range of 5.3-320 μM with a detection limit of 1.6 μM towards Cr(VI) and the differentiation of Lys variation from 1 to 75 mM with a detection limit of 0.3 mM. The probe has been applied for the first time to enable vision-based colorimetric in complex samples such as water, milk and egg. The recoveries of Cr(VI) and Lys in real samples were between 90 and 104%, and the relative standard deviation (RSD) was as low as 0.4%. This work offers new perspectives for fundamental understanding and new design of functional luminescent materials that are applicable for food-safety and rapid and intelligent inspection. A straightforward, large instrument-free, smartphone-based analytical strategy with dual-emission carbon quantum dots was developed for hexavalent chromium and Lys on-site detection via fluorescent and colorimetric twofold readout measure.

Effective separation of chromium species in technological solutions using amino-immobilized silica prior to their determination

Amino-immobilized (poly(4,9-dioxadodecane-1,12-guanidine, polydiallyldimethylammonium, hexadimethrin bromide, polyhexamethylene guanidine) silicas were proposed for chromium speciation for the first time. Adsorbents surface was characterized by TGA-DSC, FT-IR, CHN, XRD and SEM analysis. Polyamines were strongly fixed on the silica surface and were not washed off with solutions of 3М HNO₃ and 20 g L^-1 NaCl. Аmino-immobilized silica quantitatively removed (R ≥ 99%) Cr(VI) from solutions at pH 4-7. Cr(III) was not recovered in this pH range, which makes it possible to separate Cr(VI) from Cr(III). The separation factor (К_{Cr(VI)/Cr(III)}) was ≥ 1∙10⁴. Silica-based adsorbents layer-by-layer immobilized with polyamines and 2-(1,8-dihydroxy-3,6-disulfo-2-naphthylazo)benzenearsonic acid were proposed for quantitative removal of Cr(III) from aqueous solutions with pH 4-6 at 90 °C. A system of sequentially connected columns filled with selective adsorbents was used to separate the chromium species in stream at рН= 5 and a flow rate of 1 mL min^-1. Chromium was determined after its elution with 5 mL of 2 M HNO₃ at a flow rate of 1 mL min^-1 using ICP-OES or ICP-MS. The pre-concentration factors for Cr(VI) and Cr(III) was 60. A two-column system was used for chromium speciation in technological solutions. The efficiency of chromium speciation was confirmed by state standard procedure.

Polyhydroquinoline nanoaggregates: A dual fluorescent probe for detection of 2,4,6-trinitrophenol and chromium (VI)

Fluorescent polyhydroquinoline (PHQ) derivative was fabricated utilizing one-pot engineered course. The PHQ derivative indicated aggregation induced emission enhancement (AIEE) with arrangement of nanoaggregates of size 11-13 nm in 95% watery DMF medium. The fluorescence emission of PHQ nanoaggregates was extinguished by including TNP and Cr (VI). They indicated prevalent fluorescence quenching towards both TNP and Cr (VI) over other meddling nitro-compounds and metal particles. In light of results got we presumed that both photo-induced fluorescence quenching of PHQ nanoaggregates by TNP, while Inner Filter Effect (IFE) was in charge of fluorescence quenching of PHQ nanoaggregates by Cr (VI). The PHQ nanoaggregates empowered identification of TNP and Cr (VI) down to 0.66 μM (TNP) and 0.28 μM (Cr (VI)). The use of PHQ nanoaggregates were reached out for location of TNP and Cr (VI) in genuine water tests.

New composite sorbent for speciation analysis of soluble chromium in textiles

Micrometer-sized silica spheres coated with a layer of Cr(VI) imprinted methylimidazolium ionic liquid were synthesized and applied for fast and selective determination of leachable Cr(VI) in fabrics. The silica cores were synthesized via original seeded growth procedure. Formation of ionic liquid layer onto their surface was simultaneously combined with CrO42− imprinting. The sorbent characterization was accomplished by SEM/ EDS, elemental microanalysis, and thermogravimetry. Excellent separation of Cr(VI) from Cr(III) was achieved at pH 3 for 10 minutes in a batch mode. A mixture of ascorbic and nitric acids was found to be the most efficient eluent. The adsorption equilibrium data were best represented by the Langmuir isotherm model. The sorbent was applied for quantification of Cr(VI) in textile extracts in accordance with international standard ISO105-E04. The analytical procedure developed (LOD 0.015 μg/g (measured by ETAAS), RSD 3−8% for concentration levels of Cr(VI) 0.015-0.5 μg/g) completely meets the requirements of the international textile regulations.

Preparation of polyacrylonitrile nanofibers decorated by N-doped carbon quantum dots: application as a fluorescence probe for determination of Cr(vi)

This study presents a new method to synthesize a fluorescence probe using an N-doped carbon quantum dot decorated polyacrylonitrile nanofiber (N-CQD@NF) nanocomposite.