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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%.Graphical abstract

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The implementation of a new calibration approach, termed the Signal Increment Standard Addition Method (SI-SAM), to the potentiometric determination of potassium in the synthetic samples and certified reference materials, is investigated. SI-SAM is a modification of SAM that is based on the change in the way in which the extrapolation is carried out. The calibration graph is extrapolated to the intersection with the signal of the first standard solution, not to the abscissa. Potentiometry is the method of choice due to its simplicity, rapid measurements, wide linear range and fulfilment of green analytical principles. However, careful attention is required to the calibration procedure because various versions of the standard addition method, which are commonly used in potentiometry, may create some problems leading to serious systematic analytical errors. The present work proves that SI-SAM allows for the elimination of this drawback and, consequently, for the determination of the considered analyte with improved results, especially in terms of accuracy and precision.

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%).

Photoactive TiO2 materials based on a C@TiO2 core-shell structure synthesized according to the bottom-up strategy using a spherical resin core were presented in relation to commercial TiO2 (P25) used as a reference material. The studied TiO2 materials were modified with Ag nanoparticles using two alternative methods: impregnation and precipitation. Depending on the deposition technique used, different distributions of the Ag modifier were achieved within the TiO2 structure. As confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements, the precipitation technique resulted in the formation of almost twice smaller, highly dispersed Ag nanoparticles compared to impregnation. Furthermore, the effect of the performed modification on the textural properties (low-temperature N2 adsorption) and surface composition (X-ray photoelectron spectroscopy) was determined. The phase composition of the TiO2 support as well as the dispersion of the Ag modifier significantly affected the energy gap determined from UV–Vis spectra and, consequently, their performance in the process photodegradation of 4-nitrophenol tested as a model molecule. In the case of the @TiO2 material modified with highly dispersed Ag, significantly higher photoactivity in the visible light range was observed than in the presence of analogous P25-based materials.

As is known, the calibration method most commonly used in analytical practice is the calibration curve method (CCM). However, the main drawback of this approach is that it leads to the analytical results being affected by serious systematic error when the interference effect occurs. In this work it is shown how the CCM can be modified in order to eliminate the additive interference effect. The concept, termed H-point calibration curve method (HPCCM), is based on the measurements of both the standard solutions and the samples at two different conditions (e.g. wavelengths) selected in such a way to change the signals for an analyte keeping the signal for the interferents constant. Under such conditions the analyte in a sample may be determined with the use of two calibration graphs much more accurately than using a single calibration graph. It has been shown that HPCCM is equally effective but more time-efficient than the alternative approach known in the literature, i.e. the H-point standard addition method. The method was verified on the example of the spectrophotometric determination of Fe(II) in the presence of Fe(III) in various water samples. Graphical abstract