Lead-selective fluorescent optode membrane based on 3,3′,5,5′-tetramethyl-N-(9-anthrylmethyl)benzidine

Development of a microplate-format direct optode sensor for ultra-high-throughput environmental and wastewater monitoring of Pb2

Although many Pb²⁺-selective optodes have been developed so far, methods using optical sensor membranes have not become widespread in environmental analytical practice. In order to create a bulk optode sensor, which can overcome all of the main drawbacks in the application of conventional optode membranes, - i.e., pH-dependence, long response time and the leakage of the ionic components - unusually thick PVC membrane was developed, embedded in microtiter plates and operated on a novel concept. This is the first reported work, which applies a plate-format optode as well as a direct optode-type sensing membrane for determination of Pb²⁺. We reported here also the first example for the application of an ionic component-free bulk optode membrane to avoid the membrane leakage, improve the regenerability and extend the lifetime of the membrane. The reported sensor has a LOD above 4.0 × 10^-7 M (∼83 μg L^-1), thus it is unsuitable for the effective monitoring of drinking waters, but considered to be a promising method for monitoring contamination episodes. On the other hand, the widest pH-independent working range of 4.3 < pH < 7.0 among bulk optodes reported in the literature was realized and an unprecedentedly fast response time of <10 s was achieved. The effectiveness of the applied method was investigated by measuring Pb²⁺-spiked multicomponent aqueous solutions as simulated environmental or wastewater samples containing near equimolar amounts of Ag⁺, Ca²⁺, Co²⁺, Cu²⁺, K⁺, Mg²⁺, Na⁺ and Zn²⁺ as acetate salts. In the presence of these potential competing ions with a concentration not greater than the typical ionic strength of surface freshwaters (∼10^-3 M) the reported sensor proved to be appropriate for the selective detection of Pb²⁺ without any preparation of the samples (e.g., preconcentration, buffering, addition of excipients, etc.) with a required sample volume of only 100 μL. An outstanding analytical performance could be achieved within an average time of less, than 5 s/sample. The reported fluorescent probe is considered to be a promising method for replacing atomic absorption spectroscopy- (AAS), anodic stripping voltammetry- (ASV) or inductively coupled plasma- (ICP) based techniques as well as conventional ion-selective bulk membranes in high-throughput preliminary environmental monitoring of Pb²⁺, as it provides a cheap and unprecedentedly fast qualitative analysis of contaminated surface and wastewaters.

Sensitive and visual detection of p-phenylenediamine by using dialdehyde cellulose membrane as a solid matrix

A novel method was developed for the sensitive and visual detection of p-phenylenediamine (PPD) via immobilizing the target specie PPD on dialdehyde cellulose membrane (DCM) followed by the reaction with salicylaldehyde. The obtained solid fluorescent membrane (S-PPD-DCM) emitted yellow fluorescence under 365 nm UV light. DCM was not only used as a solid matrix but also played a vital role in the enrichment of PPD. Experimental variables influencing the fluorescence signal were investigated and optimized. Under the optimum conditions, a detection limit of 5.35 μg L^-1 was obtained and two linear ranges were observed at 10-100 and 100-1000 μg L^-1, respectively. Moreover, the fluorescence of the resultant membrane can still be visualized by naked eye when PPD concentration was 50 μg L^-1. The detection of PPD was hardly affected by the coexistence of 1 mg L^-1 of o-phenylenediamine, m-phenylenediamine or phenylamine, exhibiting good selectivity. The developed method involved in a two-step Schiff base reaction and enhanced the fluorescence emission via blocking nonradiative intramolecular rotation decay of the excited molecules. It was applied to determine the PPD in spiked hair dye with satisfactory results.

A 3D origami paper-based analytical device combined with PVC membrane for colorimetric assay of heavy metal ions: Application to determination of Cu(II) in water samples

Microfluidic paper-based analytical devices (μPADs) as a potentially powerful analytical platform have recently gained significant attention for on-site monitoring of heavy metal ions, which are one of the most significant environmental concern because of non-degradability and high toxicity. The commonly applied μPADs suffers from some defects, such as heterogeneous deposition of reagent, resulting in poor detection limits and low sensitivity. So, in this work, a three-dimensional origami μPAD combined with PVC Membrane was developed, which can manage problems of movement of colored products or leaching out the dye and leading to color heterogeneity in the detection zones. Furthermore, a waste layer was added to μPAD for loading of more amounts of the analyte, which results in improvement of detection limit. As a proof of concept, the μPAD was used for the analysis of Cu²⁺ ion. For this purpose, pyrocatechol violet and chrome azurol S as colorimetric reagents were doped into PVC membrane and injected in the detection zone. The proposed μPAD was presented good linearity in the ranges of 5.0-1400.0 and 5.0-200.0 mg L^-1, and the limits of detections of 1.7 and 1.9 mg L^-1 in presence of chrome azurol S and pyrocatechol violet, respectively.

Electrochemical sensor based on lead ion-imprinted polymer particles for ultra-trace determination of lead ions in different real samples

In this paper, a self-manufactured lead(ii)-selective electrode, which was based on the use of lead(ii) ion imprinted polymer particles (IIPs) to detect lead ions, was studied using differential pulse voltammetry.

Ionophore-based optical sensors

This review provides an overview of the key aspects of designing ionophore-based optical sensors (IBOS). Exact response functions are developed and compared with a simplified, generalized equation. We also provide a brief introduction into less established but promising working principles, namely dynamic response and exhaustive exchange. Absorbance and fluorescence are the main optical readout strategies used in the evaluation of a sensor response, but they usually require a robust referencing technique for real-world applications. Established referencing schemes using IBOS as well as those from other optical sensors are also discussed. Finally, the power of recently developed photoresponsive ion extraction/release systems is outlined and discussed in view of dynamically switchable IBOS or regenerative exhaustive exchange IBOS.

Preparation of nano-sized Pb2+ imprinted polymer and its application as the chemical interface of an electrochemical sensor for toxic lead determination in different real samples

In this work, a new nano-structured ion imprinted polymer (IIP) was synthesized by copolymerization of methacrylic acid-Pb(2+) complex and ethylene glycol dimethacrylate according to the precipitation polymerization. Methacrylic acid acted as both functional monomer and complexing agent to create selective coordination sites in a cross-linked polymer. A carbon paste electrode modified with IIP-nanoparticles was used for fabrication of a Pb(2+) sensitive electrode. Differential pulse stripping voltammetry method was applied as the determination technique, after open circuit sorption of Pb(2+) on the electrode and its reduction to metallic form. The IIP modified electrode showed a considerably higher response, compared to the electrode embedded with non-imprinted polymer (NIP). This indicated that the suitable recognition sites were created in the IIP structure in the polymerization stage. Various factors, effective on the response behavior of the electrode, were investigated and optimized. The introduced sensor showed a linear range of 1.0 × 10(-9) to 8.1 × 10(-7)M and detection limit of 6.0 × 10(-10)M (S/N=3). The sensor was successfully applied for the trace lead determination in different samples.

Determination of terbium in phosphate rock by Tb3+-selective fluorimetric optode based on dansyl derivative as a neutral fluorogenic ionophore

For the first time a highly sensitive and selective fluorimetric optode membrane was prepared for determination of trace amounts of Tb(III) ions in phosphate rock samples. The Tb(III) sensing system was constructed by incorporating 5-(dimethylamino)-N'-(2-hydroxy-1-naphthoyl) naphthalene-1-sulfonohydrazine (L) as a neutral Tb(III)-selective fluoroionophore, in the plasticized PVC membrane containing sodium tetraphenyl borate as a liphophilic anionic additive. The response of the optode is based on the strong fluorescence quenching of L by Tb(3+) ions. At a pH value of 5.0, the optode displays a wide concentration range of 1.0 x 10(-7) to 1.0 x 10(-2)M, with a relatively fast response time of less than 45 s. In addition, to high stability and reproducibility, the sensor shows a unique selectivity towards Tb(3+) ion with respect to common cations. The optode was applied successfully to the trace determination of terbium ion in binary mixture and water samples and the determination of Tb(3+) in phosphate rock samples.

Highly selective optical-sensing film for lead(II) determination in water samples

An optical sensor is described for a sensitive and selective spectrophotometric determination of Pb(II) ions in aqueous solution. A sensor membrane based on 4-hydroxy salophen has been developed for the determination of Pb(II) ions that displays excellent performance. The membrane responds to lead(II) ions, giving a color change from colorless to yellow in a buffer solution (pH 3.1). The optode has a linear range of 1.0 x 10(-3)-1.0 x 10(-7) mol L(-1) Pb(II) ions with a detection limit of 8.6 x 10(-8) mol L(-1) Pb(II). The response time is within 10 min depending on the concentration of Pb(II) ions such that it can quantitatively detect Pb(II) even at concentration levels of 8.6 x 10(-8) mol L(-1) Pb(II) (0.018 ppm). The optode developed here is found to be stable, cost effective, easy to prepare, and efficient for direct determination of Pb(II) in a variety of aqueous samples using spectrophotometry. However, it is for one time use only as the reaction of Pb(II) with 4-hydroxy salophen is irreversible. The optode was successfully used for measuring Pb(II) ions in different water samples and in SRM sample.

Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration range of 1.0 x 10(-2) to 1.0 x 10(-6) M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.

Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydrpxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration rang of 1.0 x 10(-2) to 1.0 x 10(-6) M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.