Design and optimization of a single-use optical sensor based on a polymer inclusion membrane for zinc determination in drinks, food supplement and foot health care products

A Novel Polymer Inclusion Membrane-Based Green Optical Sensor for Selective Determination of Iron: Design, Characterization, and Analytical Applications

The design, characterization, and analytical application of a green optical sensor for the selective determination of Fe(II) ions is proposed. The sensor is based on the immobilization of the chromogenic reagent picolinaldehyde salicyloylhydrazone (SHPA) within a polymer inclusion membrane. To reduce solvent usage, the reagent was synthesized using a green mechanochemical procedure. The components for sensor preparation were optimized with a sequential simplex method and the optimal composition was found to be 0.59 g cellulose triacetate (base polymer), 0.04 g SHPA (chemosensor reagent), 4.9 mL dibutyl phthalate (plasticizer), and 38 mL dichloromethane (solvent). The conditions of iron analysis were also optimized resulting in pH 6 for aqueous solution, 90 min exposure time and 10 min short-term stability. The optical sensor showed a linear range from the limit of detection (0.48 µmol L-1) to 54 µmol L-1 Fe(II). The precision of the method was found to be 1.44% and 1.19% for 17.9 and 45 µmol L-1 Fe(II), respectively. The characteristics of the sensor allowed the design of a Fe(II)/Fe(III) speciation scheme. The methodology was successfully applied to the determination of iron in food preservatives, food additives, and dietary supplement. Additionally, the Fe speciation scheme was successfully applied to an agricultural fertilizer.

Sensing Cd(II) Using a Disposable Optical Sensor Based on a Schiff Base Immobilisation on a Polymer-Inclusion Membrane. Applications in Water and Art Paint Samples

A disposable colour-changeable optical sensor based on an interesting polymer inclusion-membrane (PIM) was designed to determine Cd(II) ions in aqueous medium. The Schiff base 2-acetylpyridine benzoylhydrazone (2-APBH) immobilised on the polymer membrane was used as a sensing molecule. The amounts of the PIM components were optimised by a 3² fractional factorial design with two central points and two blocks. The best optical sensor composition consisted of 2.5 g of poly(vinylchloride) (PVC) as a base polymer, 3 mL of tributyl phosphate (TBP) as a plasticiser, and 0.02 g of 2-APBH as a reagent. The sensor showed a good linear response in the range from 0.02 mg L⁻¹ (limit of detection) to 1 mg L⁻¹ of Cd(II) under the following experimental conditions: pH 9.5 (adjusted using ammonium chloride buffer solution at 0.337 mol L⁻¹), 60 min of exposure time plus 2 min of sonication (pulses at 2 s intervals), and 10 min of short-term stability. The relative standard deviation of the method was determined to be 4.04% for 0.4 mg L⁻¹ of Cd(II). The optical sensor was successfully applied to the determination of Cd(II) in natural-water and art-paint samples.

All Silica Micro-Fluidic Flow Injection Sensor System for Colorimetric Chemical Sensing

This paper presents a miniature, all-silica, flow-injection sensor. The sensor consists of an optical fiber-coupled microcell for spectral absorption measurements and a microfluidic reagent injection system. The proposed sensor operates in back reflection mode and, with its compact dimensions, (no more than 200 µm in diameter) enables operation in small spaces and at very low flow rates of analyte and reagent, thus allowing for on-line or in-line colorimetric chemical sensing.

Assessment of potential health risk associated with the use of Cladophora fracta as mulch

In this study, cadmium, copper, nickel, zinc, chromium, manganese and lead were determined in Cladophora fracta present in Lake Hazar (Turkey). The health risks (non-carcinogenic and carcinogenic) of heavy metals associated with the use of Cladophora fracta as mulch were also determined. Bioconcentration factor (BCF) and metal pollution index (MPI) were calculated. When compared with reference value (1.5 mg/kg for Cr and 200 mg/kg for Mn), the highest accumulation by Cladophora fracta was seen in the month of June as 1442 ± 7.2% (23.13 mg/kg) for Cr and the lowest accumulation calculated in the month of July as 5 ± 0.2% (210 mg/kg) for Mn. In our study, the highest MPI value was 13.69 in September. The magnitude of MPI values of heavy metals determined during April to September appeared in the following order September > August > July > June > May > April. The HQ_ing (hazard quotient due to ingestion) and HQ_inh (hazard quotient due to inhalation) in all months were chidren > female > male while the order of HQ_der (hazard quotient due to dermal) was determined as male > female > children. Non-carcinogenic risk (HQ) and Hazard Index (HI) values in terms of ingestion, inhalation and dermal ways were lower than 1. Also, total HI values were < 1. As a result, there was not non-carcinogenic and carcinogenic risks associated with usage of Cladophora fracta as mulch.

A New «off-on» Fluorescence Zinc Ion Sensors Based on Iodo- and Bromosubstituted Dipyrromethenes

Monoiodo- and dibromsubstituted dipyrromethenes HL¹ - HL³ were described as a highly sensitive and selective «Off-On» fluorescent chemosensor for Zn²⁺ based on the chelation-enhanced fluorescence (CHEF) effect. Сoordination reactions of HL¹ - HL³ with Zn²⁺ cations are accompanied by a significant (124 to 215-fold) increase in fluorescence intensity against the background of other metal ions in the binary propanol-1/cyclohexane mixture (1:30). The fluorometric detection limit of Zn²⁺ ions using HL¹ - HL³ sensors is from 3.0∙10^-8 to 3.3·10^-9 mol/L. The presence of Na⁺, K⁺, Ca²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Co²⁺, Pb²⁺ cations does not interfere with the detection of Zn²⁺. Complexation reactions are accompanied by a visual change in the color of the solution from yellow-orange to pink-raspberry so that the HL¹ - HL³ ligands can also be used as a «naked-eye» indicators of the presence of Zn²⁺ ions.

Influence of Electrolyte Coextraction on the Response of Indicator-Based Cation-Selective Optodes

Here, we report on systematic investigation of the impact of coextraction of the aqueous electrolyte and anion interference on the response of cation-selective bulk optodes. It is evident that to deliberately manage the properties of chemical sensors and to apply them in routine analysis, one should have exhaustive insight into their operation mechanism. Despite the extensive research in the field of ionophore-based optodes and numerous attempts for their practical application, the understanding of how coextraction of an aqueous electrolyte influences its response characteristics has not been developed thus far. Meanwhile, the electrolyte coextraction determines the detection limits of analogous ion-selective electrodes. A theoretical model based on phase distribution equilibrium is proposed to quantitatively describe the effect of Donnan exclusion failure on the response of polymeric plasticized optodes. The theoretical conclusions are confirmed by the results obtained with Na⁺/pH-selective optodes based on a neutral chromoionophore as a model system in solutions containing anions of various lipophilicities (Cl^-, NO₃^-, I^-, SCN^-, and ClO₄^-). For the first time, it is shown that coextraction leads to a significant shift of the response range of the optodes as well as to nonmonotonic response curves due to the transition from cationic to anionic response. An approach to estimate the coextraction constants of electrolytes from the optode response curves is proposed. The limitations in the applicability of optodes due to co-ion interference are explored. It is found that neglecting anion interference can cause dramatic errors in the results of analyses with optical sensors.