Potentiometric Surfactant Sensor Based on 1,3-Dihexadecyl-1H-benzo[d]imidazol-3-ium for Anionic Surfactants in Detergents and Household Care Products.

A 1,3-dihexadecyl-1H-benzo[d]imidazol-3-ium-tetraphenylborate (DHBI-TPB) ion-pair implemented in DHBI-TPB surfactant sensor was used for the potentiometric quantification of anionic surfactants in detergents and commercial household care products. The DHBI-TPB ion-pair was characterized by FTIR spectroscopy and computational analysis which revealed a crucial contribution of the C-H∙∙∙π contacts for the optimal complex formation. The DHBI-TPB sensor potentiometric response showed excellent analytical properties and Nernstian slope for SDS (60.1 mV/decade) with LOD 3.2 × 10-7 M; and DBS (58.4 mV/decade) with LOD 6.1 × 10-7 M was obtained. The sensor possesses exceptional resistance to different organic and inorganic interferences in broad pH (2-10) range. DMIC used as a titrant demonstrated superior analytical performances for potentiometric titrations of SDS, compared to other tested cationic surfactants (DMIC > CTAB > CPC > Hyamine 1622). The combination of DHBI-TPB sensor and DMIC was successfully employed to perform titrations of the highly soluble alkane sulfonate homologues. Nonionic surfactants (increased concentration and number of EO groups) had a negative impact on anionic surfactant titration curves and a signal change. The DHBI-TPB sensor was effectively employed for the determination of technical grade anionic surfactants presenting the recoveries from 99.5 to 101.3%. The sensor was applied on twelve powered samples as well as liquid-gel and handwashing home care detergents containing anionic surfactants. The obtained results showed good agreement compared to the outcomes measured by ISE surfactant sensor and a two-phase titration method. The developed DHBI-TPB surfactant sensor could be used for quality control in industry and has great potential in environmental monitoring.

Recent Advances in (Bio)Chemical Sensors for Food Safety and Quality Based on Silver Nanomaterials.

There is a continuing need for tools and devices which can simplify, quicken and reduce the cost of analyses of food safety and quality. Chemical sensors and biosensors are increasingly being developed for this purpose, reaping from the opportunities provided by nanotechnology. Due to the distinct electrical and optical properties of silver nanoparticles (AgNPs), this material plays a vital role in (bio)sensor development. This review is an analysis of chemical sensors and biosensors based on silver nanoparticles with application in food and beverage matrices. It consists of academic research published from 2015 to 2020. The paper is structured to separately explore the designs of two major (bio)sensor classes: electrochemical (including voltammetric and impedimetric sensors) and optical sensors (including colourimetric and luminescent), with special focus on the type of silver nanomaterial and its role in the sensor system. The review indicates that diverse nanosensors have been developed, capable of detecting analytes such as pesticides, mycotoxins, fertilisers, microorganisms, heavy metals, and various additives with exceptional analytical performance. Current trends in the design of such sensors are highlighted and challenges which need to be overcome in the future are discussed.

A novel amperometric method for antioxidant activity determination using DPPH free radical.

A new method for the determination of antioxidant activity based on the amperometric reduction of 2,2-diphenyl-1-picrylhydrazyl (DPPH) at the glassy carbon electrode is proposed. All experiments were done in three-electrode electrochemical cell at 140 mV vs. Hg(2)Cl(2) | 3 M KCl using ethanolic solution (phi=40%) and 0.033 M KCl in 0.033 M phosphate buffer, pH=7.4. The linear range obtained for Trolox in 100 microM DPPH ethanol-water solution was up to 30 microM, with a limit of detection of 0.05 microM. The developed method was applied for the evaluation of antioxidant activity of some water or ethanol soluble pure compounds of antioxidants and of the samples of tea, wine and some other beverages. The good correlation of measurements (R(2)=0.9993) expressed as Trolox equivalent was obtained between the proposed amperometric method and classic spectroscopic method.

The study of some possible measurement errors in clinical blood electrolyte potentiometric (ISE) analysers.

The understanding of the most important sources of error in potentiometric blood analyser which might contribute to better instruments measurement repeatability is very often marginalized in fabrications and daily operation of some commercial blood analysers. In this paper ISEs-potentiometric measurements were performed and validated in Clinical Institute of Laboratory Diagnosis of the Zagreb University School of Medicine and Clinical Hospital Centre, using a carefully designed and constructed fully automated (computerised) homemade ISE-based blood electrolyte analyser constructed with an in-line five-channel flow-through measuring cell. The influence of electrolyte concentration of the salt bridge is reported. Special attention has been paid to the reference electrode design, and constructions which can operate in open liquid junction and membrane restricted liquid junction modes are described.

Hydrothermal synthesis and thermal evolution of carbonate-fluorhydroxyapatite scaffold from cuttlefish bones.

Phase composition, crystal structure and morphology of carbonated fluor/hydroxyapatite synthesized hydrothermally from aragonitic cuttlefish bones were studied by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). The product of synthesis has been characterized as carbonated fluor/hydroxyapatite with carbonate incorporated inside channel (A-type) and substituted for the PO4(3-) group (B-type). The vibration band at 874 cm(-1) assigned to bending (ν2) mode undoubtedly confirmed carbonate substituted for PO4(3-) group, while the band at 880 cm(-1) was attributed to A-type carbonate substitution. The additional sharp and intense band at 865 cm(-1) considered as "non-apatitic" carbonate substitution is not assigned with certainty so far. Evolution of CO2 from tetrahedral (PO4(3-)) sites with the increase in heat-treatment temperature is evident by the changes in tetrahedral bond lengths and angles, as obtained by the Rietveld structure refinement. Also, changes in the isotropic temperature parameters for the 2a site point to A-type carbonate incorporation as well.

A novel biamperometric biosensor for urinary oxalate determination using flow-injection analysis.

A biosensor for determination of oxalate concentration in urine has been developed by immobilisation of oxalate oxidase and peroxidase on the surface of an interdigitated gold electrode. Enzyme immobilisation was performed using BSA and glutaraldehyde. Biamperometric measurements were made in flow conditions both in aqueous oxalate solutions (tested concentration range between 50 microM and 10 mM) and in real urine samples (tested measuring range between 5 and 100 microM). Optimal working conditions were examined for flow-injection analysis, and good correlation was achieved between added oxalate quantity and the one measured by biosensor in urine matrix (R(2)=0.9983). The influence of some interferences (ascorbic acid, uric acid, paracetamol, acetylsalicylic acid) was also studied using biamperometric measurement mode.

Chromogenic radical based optical sensor membrane for screening of antioxidant activity.

Solid-state optical sensor membranes based on immobilised chromogenic radicals for the assessment of antioxidant activity have been studied. Two stable lipophilic chromogenic radicals, DPPH (2,2-diphenyl-1-picrylhydrazyl radical) and galvinoxyl radical, GV, (2,6-di-tert-butyl-alpha-(3,5-di-tert-butyl-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy radical), were immobilised in plasticised PVC films and screened for suitability as indicators of antioxidative activity. The spectrophotometric characterisation of the polymer films containing immobilised free radicals was performed, and the response of the immobilised free radicals toward standard antioxidants was studied. It has been demonstrated that the immobilised radicals retain their reactivity towards antioxidants and the results suggest that the reactivity of immobilised radicals is comparable to standard solution-based DPPH assays. Polymer films containing immobilised DPPH radical respond to standard antioxidants in aqueous solutions by changing colour irreversibly from purple (absorption maximum at 520nm) to yellow. The initial slopes of the response curves to the phenolic antioxidant gallic acid, obtained in the 1-50mM concentration range, gave a linear calibration plot in a 1min exposure cuvette test. The polymer films were used to screen antioxidative activity of beverage and food samples known to contain antioxidants, such as black and green tea, coffee, red wine, fruit juice, olive oil and sunflower oil. It has been demonstrated that a rapid and simple qualitative screening test of untreated samples is possible using a test strip based on immobilised DPPH radical.

A novel method for flow injection analysis of total antioxidant capacity using enzymatically produced ABTS*+ and biamperometric detector containing interdigitated electrode.

Application of interdigitated array microelectrodes as electrochemical sensors for determination of antioxidant capacity is reported. Electrochemical measurements with interdigitated electrodes (IDE) were studied in both stationary solutions and the flow system. The method is based on biamperometric measurements using ABTS(*+)|ABTS redox couple in phosphate buffer solution, pH 7.40. During analysis, the ABTS radical cation was enzymatically produced by peroxidase in a tubular flow-through reactor. The performance of bioreactor was tested at different concentrations of immobilized enzyme, ABTS and hydrogen peroxide. The influence of flow rate on proper operation of the bioreactor was also studied. The results of antioxidant activity were determined using Trolox as a standard. The applied IDE detector accomplished good sensitivity of 0.3nA/microM of Trolox and offered linear range between 20 to 500microM of Trolox. The comparison of results (R(2)=0.9915) for antioxidant activity between spectroscopic and FIA biamperometric measurements by interdigitated electrodes confirmed the applicability of the proposed method for determination of antioxidant capacity.

Evaluation of the antioxidant activity by flow injection analysis method with electrochemically generated ABTS radical cation.

A Trolox equivalent antioxidant capacity (TEAC) decolourisation assay was adapted to a flow injection analysis (FIA) system and a simple and rapid method for antioxidant activity evaluation was developed. To avoid the time consuming step of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS) radical cation preparation by chemical oxidation of ABTS, as in the original TAEC assay, and hence, to shorten the analysis time, the ABTS radical cation was generated on-line by electrochemical oxidation of ABTS in the flow-through electrolysis cell forming a part of the FIA system. The proposed method was optimised with respect to a flow rate, injection volume and ABTS radical cation/carrier ratio. Under the optimised conditions linear calibration graphs for Trolox were obtained over the range 10-100 microM, with a limit of detection 1.6 microM. Good reproducibility (relative standard deviation 1.95%) and sample throughput (32 samples per hour) were achieved. The developed method was applied to the evaluation of the antioxidant activity of pure compounds and samples of some common beverages. In both cases a good correlation between the results obtained by the proposed method and TEAC values evaluated by the classic TAEC decolourisation assay was obtained (r(2)= 0.996 for pure compounds and r(2)= 0.957 for beverage samples).