Potentiometric Sensing of Nonsteroidal Painkillers by Acyclic Squaramide Ionophores

We report here a small library of a new type of acyclic squaramide receptors (L1-L5) as selective ionophores for the detection of ketoprofen and naproxen anions (KF- and NS-, respectively) in aqueous media. 1H NMR binding studies show a high affinity of these squaramide receptors toward KF- and NS-, suggesting the formation of H-bonds between the two guests and the receptors through indole and -NH groups. Compounds L1-L5 have been tested as ionophores for the detection of KF- and NS- inside solvent PVC-based polymeric membranes. The optimal membrane compositions were established through the careful variation of the ligand/tridodecylmethylammonium chloride (TDMACl) anion-exchanger ratio. All of the tested acyclic squaramide receptors L1-L5 have high affinity toward KF- and NS- and anti-Hofmeister selectivity, with L4 and L5 showing the highest sensitivity and selectivity to NS-. The utility of the developed sensors for a high precision detection of KF- in pharmaceutical compositions with low relative errors of analysis (RSD, 0.99-1.4%) and recoveries, R%, in the range 95.1-111.8% has been demonstrated. Additionally, the chemometric approach has been involved to effectively discriminate between the structurally very similar KF- and NS-, and the possibility of detecting these analytes at concentrations as low as 0.07 μM with R2 of 0.947 and at 0.15 μM with R2 of 0.919 for NS- and KF-, respectively, was shown.

Environmental Engineering Applications of Electronic Nose Systems Based on MOX Gas Sensors

Nowadays, the electronic nose (e-nose) has gained a huge amount of attention due to its ability to detect and differentiate mixtures of various gases and odors using a limited number of sensors. Its applications in the environmental fields include analysis of the parameters for environmental control, process control, and confirming the efficiency of the odor-control systems. The e-nose has been developed by mimicking the olfactory system of mammals. This paper investigates e-noses and their sensors for the detection of environmental contaminants. Among different types of gas chemical sensors, metal oxide semiconductor sensors (MOXs) can be used for the detection of volatile compounds in air at ppm and sub-ppm levels. In this regard, the advantages and disadvantages of MOX sensors and the solutions to solve the problems arising upon these sensors' applications are addressed, and the research works in the field of environmental contamination monitoring are overviewed. These studies have revealed the suitability of e-noses for most of the reported applications, especially when the tools were specifically developed for that application, e.g., in the facilities of water and wastewater management systems. As a general rule, the literature review discusses the aspects related to various applications as well as the development of effective solutions. However, the main limitation in the expansion of the use of e-noses as an environmental monitoring tool is their complexity and lack of specific standards, which can be corrected through appropriate data processing methods applications.

Synthesis and Characterization of New-Type Soluble β-Substituted Zinc Phthalocyanine Derivative of Clofoctol

In this work, we have described the synthesis and characterization of novel zinc (II) phthalocyanine bearing four 2-(2,4-dichloro-benzyl)-4-(1,1,3,3-tetramethyl-butyl)-phenoxy substituents on the peripheral positions. The compound was characterized by elemental analysis and different spectroscopic techniques, such as FT-IR, ¹H NMR, MALDI-TOF, and UV-Vis. The Zn (II) phthalocyanine shows excellent solubility in organic solvents such as dichloromethane (DCM), n-hexane, chloroform, tetrahydrofuran (THF), and toluene. Photochemical and electrochemical characterizations of the complex were performed by UV-Vis, fluorescence spectroscopy, and cyclic voltammetry. Its good solubility allows a direct deposition of this compound as film, which has been tested as a solid-state sensing material in gravimetric chemical sensors for gas detection, and the obtained results indicate its potential for qualitative discrimination and quantitative assessment of various volatile organic compounds, among them methanol, n-hexane, triethylamine (TEA), toluene and DCM, in a wide concentration range.

Selective Detection of Mg 2+ for Sensing Applications in Drinking Water

A new series of ligands containing the 2‐(2‐hydroxy‐3‐ naphthyl)‐4‐methylbenzoxazole (HNBO) fluorophore showed selectivity for Mg²⁺ ions, without the interference of Ca²⁺. The most promising representative L3 resulted the best performing sensor for Mg²⁺ both in solution and embedded in an all‐solid‐state optode, especially towards real samples of drinkable water.

Advances in Optical Sensors for Persistent Organic Pollutant Environmental Monitoring

Optical chemical sensors are widely applied in many fields of modern analytical practice, due to their simplicity in preparation and signal acquisition, low costs, and fast response time. Moreover, the construction of most modern optical sensors requires neither wire connections with the detector nor sophisticated and energy-consuming hardware, enabling wireless sensor development for a fast, in-field and online analysis. In this review, the last five years of progress (from 2017 to 2021) in the field of optical chemical sensors development for persistent organic pollutants (POPs) is provided. The operating mechanisms, the transduction principles and the types of sensing materials employed in single selective optical sensors and in multisensory systems are reviewed. The selected examples of optical sensors applications are reported to demonstrate the benefits and drawbacks of optical chemical sensor use for POPs assessment.

Keeping Track of Phaeodactylum tricornutum (Bacillariophyta) Culture Contamination by Potentiometric E-Tongue

The large-scale cultivation of microalgae provides a wide spectrum of marketable bioproducts, profitably used in many fields, from the preparation of functional health products and feed supplement in aquaculture and animal husbandry to biofuels and green chemistry agents. The commercially successful algal biomass production requires effective strategies to maintain the process at desired productivity and stability levels. Hence, the development of effective early warning methods to timely indicate remedial actions and to undertake countermeasures is extremely important to avoid culture collapse and consequent economic losses. With the aim to develop an early warning method of algal contamination, the potentiometric E-tongue was applied to record the variations in the culture environments, over the whole growth process, of two unialgal cultures, Phaeodactylum tricornutum and a microalgal contaminant, along with those of their mixed culture. The E-tongue system ability to distinguish the cultures and to predict their growth stage, through the application of multivariate data analysis, was shown. A PLS regression method applied to the E-tongue output data allowed a good prediction of culture growth time, expressed as growth days, with R² values in a range from 0.913 to 0.960 and RMSEP of 1.97–2.38 days. Moreover, the SIMCA and PLS-DA techniques were useful for cultures contamination monitoring. The constructed PLS-DA model properly discriminated 67% of cultures through the analysis of their growth media, i.e., environments, thus proving the potential of the E-tongue system for a real time monitoring of contamination in microalgal intensive cultivation.

The Long-Lasting Story of One Sensor Development: From Novel Ionophore Design toward the Sensor Selectivity Modeling and Lifetime Improvement

The metalloporphyrin ligand bearing incorporated anion-exchanger fragment, 5-[4-(3-trimethylammonium)propyloxyphenyl]-10,15,20-triphenylporphyrinate of Co(II) chloride, CoTPP-N, has been tested as anion-selective ionophore in PVC-based solvent polymeric membrane sensors. A plausible sensor working mechanism includes the axial coordination of the target anion on ionophore metal center followed by the formed complex aggregation with the second ionophore molecule through positively charged anion-exchanger fragment. The UV-visible spectroscopic studies in solution have revealed that the analyte concentration increase induces the J-type porphyrin aggregation. Polymeric membranes doped with CoTPP-N showed close to the theoretical Nernstian response toward nitrite ion, preferably coordinated by the ionophore, and were dependent on the presence of additional membrane-active components (lipophilic ionic sites and ionophore) in the membrane phase. The resulting selectivity was a subject of specific interaction and/or steric factors. Moreover, it was demonstrated theoretically and confirmed experimentally that the selection of a proper ratio of ionophore and anionic additive can optimize the sensor selectivity and lifetime.

Smartphone coupled with a paper-based optode: Towards a selective cyanide detection

A low-cost on-paper sensor based on 5,10,15-tritolylcorrolatocobalt(III) triphenylphosphine, CoTTCorr(PPh3), was developed for cyanide detection in aqueous solutions. The sensor was coupled to a smartphone and used a home-written color intensity analysis software in order to record and interpret the colorimetric response. The detection of cyanide was possible down to 0.053 mg/L, an order of magnitude lower than the value of 0.5 mg/L set by the World Health Organization (WHO) for safe short-term exposure of cyanide in potable water. The colorimetric sensor had selectivity toward cyanide ions over the anions Cl-, Br, F-, NO2, SCN-, OA[Formula: see text]-,ClO4-, H2PO4- and HCO3- while the influence of NO3- ions on the sensor optical response towards cyanide was overcome by optimization of the ionophore/anion-exchanger ratio inside the sensing material. The best performance was obtained for the optode with an ionophore to exchanger ratio of 1:3. The optimized optodes were employed for quantification of cyanide content added to potable water and saliva.

Potentiometric E-Tongue System for Geosmin/Isoborneol Presence Monitoring in Drinkable Water

A potentiometric E-tongue system based on low-selective polymeric membrane and chalcogenide-glass electrodes is employed to monitor the taste-and-odor-causing pollutants, geosmin (GE) and 2-methyl-isoborneol (MIB), in drinkable water. The developed approach may permit a low-cost monitoring of these compounds in concentrations near the odor threshold concentrations (OTCs) of 20 ng/L. The experiments demonstrate the success of the E-tongue in combination with partial least squares (PLS) regression technique for the GE/MIB concentration prediction, showing also the possibility to discriminate tap water samples containing these compounds at two concentration levels: the same OTC order from 20 to 100 ng/L and at higher concentrations from 0.25 to 10 mg/L by means of PLS-discriminant analysis (DA) method. Based on the results, developed multisensory system can be considered a promising easy-to-handle tool for express evaluation of GE/MIB species and to provide a timely detection of alarm situations in case of extreme pollution before the drinkable water is delivered to end users.

N2S2 pyridinophane-based fluorescent chemosensors for selective optical detection of Cd2+ in soils

A fluorescent sensor array for the quantitative determination of Cd²⁺ in soils based on two N₂S₂ pyridinophane chemosensors is presented.

Chemical traffic light: A self-calibrating naked-eye sensor for fluoride

We report a low-cost sensing platform for effective naked-eye detection of fluoride ion in aqueous media. The sensor is based on silicon complex of 5,10,15-tritolylcorrole (SiTTCorr) deposited on paper support and designed in a particular way that permits it to perform in a unique sensing event an internal sensor self-calibration and subsequent analysis of fluoride ion in a concentration range from 20 [Formula: see text]g/L to 200 mg/L with a LOD 9 [Formula: see text]g/L, much lower than the WHO guideline value of 1.5 mg/L for fluoride in drinking water. The influence of tetradodecylammonium chloride (TDACl) anion exchanger addition to the performance of SiTTCorr-based sensors was studied and the sensor with optimal ionophore: exchanger [Formula: see text] 2:1 ratio demonstrated the highest sensitivity. The evident color variation of SiTTCorr-based optode from dark pink to intense green occurred upon addition of increasing concentrations of fluoride. A smartphone application equipped with home-written color intensity analysis software as a detector of developed sensor output permitted fluoride content quantification in bottled water and toothpaste samples. Moreover, since at the quantification step the SiTTCorr color variation was significant for the red component of visible light and increase of fluoride content evidently changed this color from red to yellow and then to green, the developed optode was compared to a kind of chemical traffic light, able to detect the presence of fluoride in permitted, borderline or dangerous concentrations, respectively.

Response Standardization for Drift Correction and Multivariate Calibration Transfer in "Electronic Tongue" Studies

The procedures for response standardization in "electronic tongue" (ET) studies are described. The construction of reliable multivariate calibration for "electronic tongue" requires the analysis of a large number of representative samples both with ET and reference techniques. This is a laborious and expensive process. Long-term sensor array operation leads to the changes in sensor response characteristics and thus invalidates the multivariate predictive models. Moreover, due to the individual parameters of each sensor in different sensor arrays, it is not possible to use the calibration model for one system together with the data acquired by another system, even if they have the same sensors. Both of these issues lead to the necessity of frequent sensor array calibration which would be ideal to avoid. Instead of recalibration, these two problems can be handled using mathematical methods intended for sensor response standardization. This chapter describes two popular methods of standardization which can be used for both drift correction and calibration transfer. Thus, significant efforts on measuring representative sample sets for sensor array recalibration can be avoided.

Electronic Tongue for Brand Uniformity Control: A Case Study of Apulian Red Wines Recognition and Defects Evaluation †

The potentiometric electronic tongue system has been tested as a potential analytical tool for brand uniformity control of monoculture Apulian red wines (Primitivo and Negroamaro). The sensor array was composed of eight porphyrin coatings obtained by electrochemical polymerization process and was employed for both wines discrimination and quantitative detection of wine defect compounds: "off-odour" 3-(methylthio)-propanol; isoamyl alcohol fusel oil; benzaldehyde (marker of the yeast activity) and acetic acid (marker of vinegar formation). PLS-DA applied to Electronic tongue output data has permitted a correct discrimination of more than 70% of analysed wines in respect to the original brand affiliation. Satisfactory PLS1 predictions were obtained in real wine samples; with R² = 0.989 for isoamyl alcohol and R² = 0.732 for acetic acid. Moreover; the possibility to distinguish wine samples on the base of permitted levels of fault compounds content was shown.

A Fluorescent Sensor Array Based on Heteroatomic Macrocyclic Fluorophores for the Detection of Polluting Species in Natural Water Samples

The development of a novel all-solid-state optical sensor array based on heteroatomic macrocyclic fluorophores (diaza-crown ether, metallocorrole and pyridinophans) for the photographic analysis of liquid media, is presented. The sensitivity of the new optical system toward a number of different species (cations: Li⁺, K⁺, Na⁺, NH4+, Mg²⁺, Ca²⁺, Co²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺ and anions: NO2-, NO3-, Cl⁻, Br⁻, HCO3-) was evaluated both in single selective sensor mode and in multisensory arrangement. The satisfactory PLS1 regression models between sensor array optical response and analyte concentration were obtained for Cd²⁺, Cu²⁺, Zn²⁺, and NO2- ions in all the range of tested concentrations. Among these species the highest attention was focused onto detection of cadmium and nitrite ions, for which the detection limits, DL, estimated by 3σ method were found 0.0013 mg/L and 0.21 mg/L respectively, and these values are lower than the corresponding WHO guideline values of 0.003 mg/L (Cd²⁺) and 2 mg/L (NO2-). The suitability of the developed sensors implemented with familiar devices for signal acquisition (Light Emitting Diode, LED, as light source and a digital camera as a signal detector), and chemometric methods for data treatment to perform fast and low-cost monitoring of species under interest, in real samples of environmental importance, is demonstrated.

Non-enzymatic portable optical sensors for microcystin-LR

We report a selective non-enzymatic optical sensor for fast and low-cost detection of microcystin-LR and POCT estimation of water toxicity.

β-Pyrazino-fused tetrarylporphyrins

A novel method for the preparation of β-fused porphyrin dyads was developed that exploits a one-pot reaction of 2,3-diaminoporphyrins with diethyl oxalate. This approach provides good yields of the zinc β-fused dyad and the corresponding free-base, opening the way for preparation of several metal derivatives to permit modulation of optoelectronic characteristics for commercial applications.

Corrole-based ion-selective electrodes

Different corrole derivatives have been exploited as ionophores for the development of ion-selective electrodes (ISEs). The compounds used are free-base 5,10,15-triphenylcorrole, the corresponding Mn and Fe chloride complexes, the Cu complex of 5,10,15-tris(4-tert-butylphenyl)-corrole and the Fe chloride complex of 2,3,17,18-tetraethyl,7,8,12,13-tetramethylcorrole. Corroles have been dispersed in the polyvinyl chloride polymeric matrix and different plasticizers have been used for the preparation of selective membranes. The developed ISEs have been tested for the detection of model analytes and the working mechanism has been investigated in detail. In the case of free-base corrole, the results showed that it is difficult to obtain high selective ISEs, due to the macrocycle high sensitivity to the background solution pH. On the other hand, Mn derivative are shown to be highly selective for chloride ion detection, with performances superior to the corresponding Mn porphyrin-based ISEs. Finally both Cu and Fe derivatives are very promising ionophores for the detection of hydrophilic anions, such as carbonate and monohydrogen phosphate ion.

Potentiometric Polymeric Film Sensors Based on 5,10,15-tris(4-aminophenyl) Porphyrinates of Co(II) and Cu(II) for Analysis of Biological Liquids

Novel carbonate-selective potentiometric sensors based on 5,10,15-tris(4-aminophenyl)-20-phenyl porphyrinates of Cu(II) and Co(II) have been developed. Ionophore functioning mechanism and possible source of carbonate sensitivity have been evolved. Potentiometric properties of Co(II)- and Cu(II)TATPP-based sensors were compared with common carbonate-ISEs containing trifluoroacetophenone derivatives. The analytical utility of newly developed sensors has been demonstrated by measuring the bicarbonate content in human blood plasma.

Clinical analysis of human urine by means of potentiometric Electronic tongue

The Electronic tongue (ET) composed of different kind of potentiometric chemical sensors has been applied for the detection of urinary system dysfunctions and creatinine levels. The creatinine contents evaluated by ET were compared with those obtained by automated Jaffe's method and GC-MS, obtaining a satisfying agreement for both methods. Partial least square regression discriminate analysis (PLS-DA) and feed forward back-propagation neural network (FFBP NN) classified 51 urine specimens from healthy volunteers in four classes, according to the creatinine content, showing that both techniques can satisfactorily differentiate urines according to this parameter. The best accuracy result of 92.2% correct classification of unknown samples was achieved with FFBP NN. Moreover, the possibility of ET system to distinguish between urine samples of healthy patients, and those with malignant and non-malignant tumor diagnosis of bladder has been shown.

Metalloporphyrin - based Electronic Tongue: an Application for the Analysis of Italian White wines

An Electronic Tongue system (ET) composed of "all-solid-state" potentiometricsensors was developed and applied for the identification of white wines. The sensingproperties were due to the PVC based membranes doped with several metallo-porphyrinsdeposited on the surface of glassy carbon working electrodes; potentiometric responsetowards several ions in a concentration range from 10-5 M to 10-1 M were studied and cross-sensitivity of sensors was estimated. The sensor array was applied both for the classificationand quantitative analysis of "Verdicchio D.O.C." Italian dry white wines produced by ninecantinas. Peculiar parameters of white wines (namely alcoholic degree, volatile acidity, SO₂,L-Malic Acid, L-Lactic Acid and Total Polyphenols) individuated by standard analyticalmethods were compared with the values evaluated by metalloporphyrin-based ET. Thesystem satisfactory discriminates between an artificial wine control and analyzed winescoming from different cantinas and produced in different years. A satisfactory correlationbetween results of wine analysis performed by certified methods and ET response has beenobtained for SO₂, L-Malic Acid, and Total Phenols content. The developed procedureallows the monitoring of the acetic acid amount in wines and hence to control wine volatileacidity, so indicating the initial steps of wine spoilage process.

Determination of oceanic carbon dioxide using a carbonate-selective electrode

Potentiometric properties of the PVC membrane-based electrodes prepared with molecular tweezer-type neutral carriers, 3,12-bis(TFAB)CA and deoxy-3,12-bis(TFAB)CA, and trifluoroacetyl-p-decylbenzene (TFADB) were measured in buffered electrolytes (0.1 M Tris-H2SO4, pH 8.6 and 8.0) and artificial seawater. It was observed that the deoxy-3,12-bis(TFAB)CA-based electrode provides greatly enhanced carbonate selectivity over chloride (log K(CO3(2-), Cl-)POT approximately -6) and other minor anions present in seawater. Thus, we explored the possibility of applying this new carbonate-selective electrode for direct determination of oceanic carbon dioxide. The total carbon dioxide (TCO2) level in surface Yellow Sea water was determined with the deoxy-3,12-bis(TFAB)CA-based electrode, Severinghaus-type CO2 gas sensor, and the traditional potentiometric titration methods. The results showed that the carbonate-selective electrode provides accurate oceanic TCO2 determination comparable to that obtainable with the other two methods. The analytical procedure based on a carbonate-selective electrode is clearly advantageous over other conventional methods: it does not require any sample pretreatment and extra reagents other than the standard calibration solutions, while providing the measured results directly and immediately.