Spherical Lignin-Derived Activated Carbons for the Adsorption of Phenol from Aqueous Media.

In this work, a synthesis and activation path, which enabled the preparation of spherical activated carbon from a lignin precursor, characterized by high adsorption capacity in the removal of phenolic compounds from water, was successfully developed. Two industrial by-products, i.e., Kraft lignin and sodium lignosulfonate, were used to form spherical nanometric lignin grains using pH and solvent shift methods. The obtained materials became precursors to form porous activated carbons via chemical activation (using K2CO3 or ZnCl2 as activating agents) and carbonization (in the temperature range of 600-900 °C). The thermal stabilization step at 250 °C was necessary to ensure the sphericity of the grains during high-temperature heat treatment. The study investigated the influence of the type of chemical activator used, its quantity, and the method of introduction into the lignin precursor, along with the carbonization temperature, on various characteristics including morphology (examined by scanning electron microscopy), the degree of graphitization (evaluated by powder X-ray diffraction), the porosity (assessed using low-temperature N2 adsorption), and the surface composition (analyzed with X-ray photoelectron spectroscopy) of the produced carbons. Finally, the carbon materials were tested as adsorbents for removing phenol from an aqueous solution. A conspicuous impact of microporosity and a degree of graphitization on the performance of the investigated adsorbents was found.

The Use of an Acylhydrazone-Based Metal-Organic Framework in Solid-Contact Potassium-Selective Electrode for Water Analysis.

A solid-contact ion-selective electrode was developed for detecting potassium in environmental water. Two versions of a stable cadmium acylhydrazone-based metal organic framework, i.e., JUK-13 and JUK-13_H2O, were used for the construction of the mediation layer. The potentiometric and electrochemical characterizations of the proposed electrodes were carried out. The implementation of the JUK-13_H2O interlayer is shown to improve the potentiometric response and stability of measured potential. The electrode exhibits a good Nernstian slope (56.30 mV/decade) in the concentration range from 10-5 to 10-1 mol L-1 with a detection limit of 2.1 µmol L-1. The long-term potential stability shows a small drift of 0.32 mV h-1 over 67 h. The electrode displays a good selectivity comparable to ion-selective electrodes with the same membrane. The K-JUK-13_H2O-ISE was successfully applied for the determination of potassium in three certified reference materials of environmental water with great precision (RSD < 3.00%) and accuracy (RE < 3.00%).

3D-printed manifold integrating solid contact ion-selective electrodes for multiplexed ion concentration measurements in urine.

Urinalysis is a simple and non-invasive approach for the diagnosis and monitoring of various health disorders. While urinalysis is predominantly confined to clinical laboratories the non-invasive sample collection makes it applicable in wide range of settings outside of central laboratory confinements. In this respect, 3D printed devices integrating sensors for measuring multiple parameters may be one of the most viable approaches to ensure cost-effectiveness for widespread use. Here we evaluated such a system for the multiplexed determination of sodium, potassium and calcium ions in urine samples with ion-selective electrodes based on state of the art octadecylamine-functionalized multi-walled carbon nanotube (OD-MWCNT) solid contacts. The electrodes were tested in the clinically relevant concentration range, i.e. ca. 10-4 - 10-1 mol L-1 and were proven to have Nernstian responses under flow injection conditions. The applicability of the 3D printed flow manifold was investigated through the analysis of synthetic samples and two certified reference materials. The obtained results confirm the suitability of the proposed system for multiplexed ion analysis in urine.

3D-printed flow manifold based on potentiometric measurements with solid-state ion-selective electrodes and dedicated to multicomponent water analysis.

A 3D-printed flow manifold dedicated to potentiometric simultaneous determination of potassium, sodium, calcium and chloride in water is presented. The method is based on application of miniature solid-contact ion selective electrodes with a special design obtained with the use of 3D printing. The electrodes offer many attractive advantages including short response time and miniaturization feasibility. The use of the proposed novel electrodes enables performance of rapid potentiometric measurements in flow-injection technique and registration of many injection peaks in a short time. One of the advantages of using a special 3D-printed flow vessel for potentiometric measurements was miniaturization of electrodes and the possibility of integrating several (from three up to six) ion selective electrodes in one module enabling realization of multi-component analyses in the same time. Thanks to that the volume of each solution and measurement time were significantly reduced during multi-component analysis. In order to find out if the proposed manifold works properly, three multi-component synthetic samples and four certified reference materials were analyzed. The presented study shows that the proposed 3D-printed flow manifold with solid-state ion-selective electrodes could be an effective tool in a modern multi-component analysis meeting the requirements of green analytical chemistry.

Reliable calibration by nonlinear standard addition method in the presence of additive interference effects.

ABSTRACT: The possibility of adapting the Standard Addition Method (SAM) to calibration in very difficult analytical conditions, namely when there is a need to determine an analyte with the use of nonlinear calibration graph and in the presence of matrix components causing additive interference effect, is investigated. To this aim the SAM in the common version and the Chemical H-point Standard Addition Method (C-HPSAM) realized by the flow injection technique were applied. Specifically, a flow manifold was used for construction of a set of nonlinear calibration graphs in different chemical conditions. As the graphs were intersected indicating both the additive interference effect and the analytical result free of this effect, the analyte concentration in the sample was able to be obtained with improved accuracy. The applicability of this approach was verified on the example of spectrophotometric determination of paracetamol in pharmaceuticals and of total acidity in wines. The C-HPSAM method enabled complete compensation of the additive effect and obtaining analytical results at a relative error not exceeding 6.0%.

Application of gradient ratio flow-injection technique to implementation of the Chemical H-point Standard Addition Method.

A new gradient ratio approach to Chemical H-point Standard Addition Method (C-HPSAM) was developed in flow injection analysis with spectrophotometric detection. C-HPSAM is based on an idea to use SAM for calibration in several different chemical conditions in order to correct unspecific (additive) interferences in samples with unknown matrix. The approach proposed in this paper employs the gradient ratio flow-injection technique to generate a continuous change of chemical conditions. By doing so a set of two-point SAM calibration curves with different slopes are possible of registering that are intersected in a common point indicating the values of both unspecific interferences and analyte concentration in a sample. The applicability of the approach was verified on the examples of spectrophotometric determinations of ascorbic acid and paracetamol. Ascorbic acid was determined in soft drinks and juices basing on reduction of Fe(III) to Fe(II) and reaction of the latter ion with o-phenantroline to form the ferroin complex absorbing at 512 nm. Paracetamol determined in pharmaceuticals was nitrificated in reaction with sodium nitrite in acidic medium and then the formed derivative species was converted into a more stable compound in reaction with sodium hydroxide, for which absorbance was recorded at 430 nm. All analytical results were obtained within the confidence interval of the values obtained by capillary electrophoresis and the relative errors were below 6%. It was proved that the developed method is readily applicable to analysis of real samples of complex unknown matrices. As it is additionally effective, low-cost and green, it can be considered as a helpful analytical tool.