Screen-printed sensor for batch and flow injection potentiometric chromium(VI) monitoring

Abstract

A disposable screen-printed electrode was designed and evaluated for direct detection of chromium(VI) in batch and flow analysis. The carbon screen-printed electrode was modified with a graphite-epoxy composite. The optimal graphite-epoxy matrix contains 37.5% graphite powder, 12.5% diphenylcarbohydrazide, a selective compound for chromium(VI), and 50% epoxy resin. The principal analytical parameters of the potentiometric response in batch and flow analysis were optimized and calculated. The screen-printed sensor exhibits a response time of 20 +/- 1 s. In flow analysis, the analytical frequency of sampling is 70 injections per hour using 0.1 M NaNO(3) solution at pH 3 as the carrier, a flow rate of 2.5 mL.min(-1), and an injection sample volume of 0.50 mL. The sensor shows potentiometric responses that are very selective for chromium(VI) ions and optimal detection limits in both static mode (2.1 x 10(-7) M) and online analysis (9.4 x 10(-7) M). The disposable potentiometric sensor was employed to determine toxicity levels of chromium(VI) in mineral, tap, and river waters by flow-injection potentiometry and batch potentiometry. Chromium(VI) determination was also carried out with successful results in leachates from municipal solid waste landfills.

Potentiometric Screen‐Printed Bisensor for Simultaneous Determination of Chromium(III) and Chromium(VI)

“…In addition, the amount of graphite in the composite matrix must be optimized to obtain stable materials which present good mechanical properties and electrical conductance. Following the results obtained in previous works 11, 12 and in order to obtain the maximum electrical conductance without loss of stability and hardness of the cured material and the best potentiometric response of the bisensor, the graphite‐epoxy composites were prepared in both cases with 50 % (w/w) epoxy resin, 37.5 % (w/w) graphite powder and 12.5 % (w/w) DPC or DPHE.…”

“…The influence of pH on the potentiometric response for screen‐printed sensors modified with graphite‐epoxy composites containing DPC has been studied 12. The results showed that the pH dependence of the sensor in presence and in absence of chromium(VI) solution is probably due to the nature of the graphite‐epoxy composite matrix.…”

“…These electrodes consist of two elliptic carbon working electrodes (maximum length 3‐mm, maximum width 1‐mm) and a pseudo silver reference electrode present in a strip. The pseudo silver reference electrode is covered with a PVC membrane to obtain a stable reference electrode potential 12, 24, 25. The membrane was prepared by mixing and dissolving PVC, o ‐nitrophenyloctyl ether, and potassium tetrakis( p ‐chlorophenyl)borate in tetrahydrofuran to obtain a membrane composition of 66 % (w/w) PVC, 33 % (w/w) o ‐nitrophenyloctyl ether, and 1 % (w/w) potassium tetrakis ( p ‐chlorophenyl)borate.…”

“…Then, the surfaces of carbon screen‐printed bielectrodes were covered with the corresponding modified graphite‐epoxy composite. The compounds chosen as modifiers of the graphite‐epoxy composites had been previously used by our research group to prepare carbon paste electrodes 10, 11 and chromium(VI) screen‐printed sensors with successful results 12. In this work the design, develop and application of a new device to determine both chromium species in the same sample at the same time using sample volumes lower than 1 mL is performed.…”

Opportunities and challenges of using ion-selective electrodes in environmental monitoring and wearable sensors

“…Among the limits fixed by the Water Framework Directive [3] for four heavy metals, i.e., lead, cadmium, mercury and nickel, it appears that research on ISEs has been largely focused on lead at the required nano-molar level [77,81], and potentiometric detection at these levels for other important toxic ions, e.g., manganese and arsenate, has so far not been reported [93] or it is below the environmental policy requirements, e.g., Cr(VI) [94]. In this regard it is worthwhile to note that the measurement of cadmium at 1 ppb levels, i.e., compatible with some water regulation policies, in concentrated NaCl samples (simulating sea water) with ISE was reported [95].…”