Carbon composite-PVC based membrane coated platinum electrode for chromium determination

Modified carbon paste ion selective electrode for determining Cr(iii) ions in aqueous solutions and some real samples using tetragonal zirconia nanoparticles

Tetragonal zirconia (t-ZrO₂) nanoparticles (ionophore) are used in newly designed and improved ion selective electrodes for chromium ion detection as an alternative, low-cost, high-precision, and selectivity method. Tetragonal zirconia nanoparticles were synthesized using a modified co-precipitation technique and calcined at 1000 °C for an hour. The phase composition, surface area, microstructure, pore size and particle size of synthesized t-ZrO₂ nanoparticles were examined using the X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM) and scanning electron microscopy (SEM) attached with an EDAX unit, respectively. Results from XRD showed that the t-zirconia was synthesized and have nanocrystallites size about 20.2 nm. The nano size of t-ZrO₂ was confirmed by the SEM and TEM (the particle size between 26.48 and 40.4 nm), the mesoporous character (average pore size about 4.868 nm) and large surface area (76.2802 m² g^-1) was confirmed by BET analysis. The paste composition with 67.3 : 30.5 : 2.7 (wt%) graphite, t-ZrO₂, and TCP, respectively, exhibited the best results. With a detection limit of 1.0 × 10^-8 mol L^-1, the electrode displayed a good Nernstian slope of 19.50 ± 0.10 mV decade^-1 over the concentration range from 1.0 × 10^-2 to 1.0 × 10^-8 mol L^-1 of Cr(iii) ions. The built-in sensor displayed a quick response time (7 s), was highly thermally stable in the range of 10 to 60 °C without departing from Nernstian behaviour and could be used for about 60 days in the pH range of 2.0 to 6.0. The electrode demonstrated excellent selectivity for the Cr(iii) ion towards a variety of metal ions. For chromium ion determination, numerous spiked real samples, including honey, water, tea, coffee, milk, cheese, and cosmetics, were used. Validation methods were used, and the results showed that there is no significant difference between the two methods (ICP and ISE) at a 95% confidence level. In several real water samples, the estimated limits of detection, limits of quantification, percent recovery, standard deviation, and relative standard deviation showed the effectiveness of the proposed electrode in the potentiometric detection of Cr(iii) ions.

Chromium measurement in pharmaceutical samples: a comparative study of three new membrane electrodes with different electron-ion exchangers

The present study deals with synthesis of N-(thiazol-2-ylcarbamothioyl) benzamide. It was utilized as a neutral ionophore for designing three types of chromium(III) sensors including coated wire ion selective electrodes (CW-ISEs), ion selective electrodes with liquid internal electrolyte (LIE-ISEs), and solid-state ion selective electrodes (SS-ISEs). UV-visible spectrophotometry was used to confirm the affinity of N-(thiazol-2-ylcarbamothioyl) benzamide to chromium(III). It was found that a membrane with a composition of 2% NaTPB, 8% ionophore, 60% DBP, and 30% PVC showed the best performance and a Nernstian slope of 21.6 mV per decade. Scanning electron microscopy was used to assess the PVC membrane morphology. The existence of chromium(III) in the liquid membrane matrix was proved by energy-dispersive X-ray spectroscopy. Detection limits for SS-ISE (1 × 10^-6 M) and CW-ISE (1 × 10^-6 M) were enhanced relative to LIE-ISE (1 × 10^-5 M). All three electrodes showed a response time of about 5 s. The sensors' applicable pH range was 4.0-6.0. Fourier transform infrared spectra recorded through the electrode membrane showed that chromium(III) ion can interact with sulfur, nitrogen and oxygen atoms of N-(thiazol-2-ylcarbamothioyl) benzamide. The sensors were utilized as indicator electrodes in chromium(III) potentiometric titration with ethylenediaminetetraacetic acid and for directly measuring chromium(III) in some pharmaceutical samples.

Ecological effects, remediation, distribution, and sensing techniques of chromium

Chromium is detected in most ecosystems due to the increased anthropogenic activities in addition to that developed from natural pollution. Chromium contamination in the food chain results due to its persistent and non-degradable nature. The release of chromium in the ecosystem accretes and thereafter impacts different life forms, including humans, aquatic and terrestrial organisms. Leaching of chromium into the ground and surface water triggers several health ailments, such as dermatitis, eczematous skin, allergic reactions, mucous and skin membrane ulcerations, allergic asthmatic reactions, bronchial carcinoma and gastroenteritis. Physiological and biological treatments for the removal of chromium have been discussed in depth in the present communication. Adsorption and biological treatment methods are proven to be alternatives to chemical removal techniques in terms of cost-effectiveness and low sludge formation. Chromium sensing is an alternative approach for regular monitoring of chromium in different water bodies. This review intended to explore different classes of sensors for chromium monitoring. However, the spectrochemical methods are more sensitive in chromium ions sensing than electrochemical methods. Future study should focus on miniaturization for portability and on-site measurements without requiring a large instrument provides a good aspect for future research.

Simple hydrothermal approach for synthesis of fluorescent molybdenum disulfide quantum dots: Sensing of Cr3+ ion and cellular imaging

Nowadays, fluorescent molybdenum disulfide quantum dots (MoS₂ QDs) have proven to be potential candidates in the sensing and bioimaging areas owing to their exceptional intrinsic characteristics. Here, a simple hydrothermal strategy was explored for the preparation of MoS₂ QDs using ammonium heptamolybdate and 6-mercaptopurine (6-MP) as precursors. The emission peak of MoS₂ QDs was significantly quenched in the presence Cr³⁺ ion due to the selective surface chemistry on the surfaces of MoS₂ QDs. The designed fluorescent MoS₂ QDs showed a linear fluorescence quenching response with increasing concentration of Cr³⁺ ion (0.1-10 μM), allowing to detect Cr³⁺ ion even at 0.08 μM. This fluorescent MoS₂ QDs were utilized for the quantification of Cr³⁺ ion in real samples (water and biological samples). Interestingly, the synthesized MoS₂ QDs exhibited negligible cytotoxicity on NRK cells and acted as good candidates for imaging of Trichoderma viride fungal cells.

Colloidal gold nanoparticle probe-based immunochromatographic assay for the rapid detection of chromium ions in water and serum samples

An immunochromatographic assay (ICA) using gold nanoparticles coated with monoclonal antibody (McAb) for the detection of chromium ions (Cr) in water and serum samples was developed, optimized and validated. Gold nanoparticles coated with affinity-purified monoclonal antibodies against isothiocyanobenzyl-EDTA (iEDTA)-chelated Cr(3+) were used as the detecting reagent in this completive immunoassay-based one-step test strip. The ICA was investigated to measure chromium speciation (Cr(3+) and Cr(6+) ions) in water samples. Chromium standard samples of 0-80 ng mL(-1) in water were determined by the test strips. The results showed that the visual lowest detection limit (LDL) of the test strip was 50.0 ng mL(-1). A portable colorimetric lateral flow reader was used for the quantification of Cr. The results indicated that the linear range of the ICA with colorimetric detection was 5-80 ng mL(-1). The ICA was also validated for the detection of chromium ions in serum samples. The test trips showed high stability in that they could be stored at 37°C for at least 12 weeks without significant loss of activity. The test strip also showed good selectivity for Cr detection with negligible interference from other heavy metals. Because of its low cost and short testing time (within 5 min), the test strip is especially suitable for on-site large-scale screening of Cr-polluted water samples, biomonitoring of Cr exposure, and many other field applications.