New ionophores for vitamin B1 and vitamin B6 potentiometric sensors for multivitaminic control

Electrochemical sensor based on Ni-exchanged natural zeolite/carbon black hybrid nanocomposite for determination of vitamin B6

The utilization of environmentally friendly nanoporous natural zeolite exchanged with Ni²⁺ ions (NiZ) and conductive carbon black (CB) in the fabrication of a novel and selective voltammetric sensor of vitamin B₆ (VB₆) is presented. The used clinoptilolite-rich zeolite material and CB were characterized in terms of morphology and textural properties. The superior properties of Ni-zeolite/carbon black modified glassy carbon electrode (NiZCB-GCE), arising from the synergistic effect of combining the unique features of zeolite and conductive carbon black, were confirmed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. In the determination of VB₆ with the use of differential pulse voltammetry (DPV), the optimization of the pH value of supporting electrolyte and instrumental parameters, as well as the interference study were performed. Under optimized conditions, the oxidation peak current at the potential +0.72 V vs. Ag | AgCl | 3 M KCl reference electrode was linear to the VB₆ concentration in the range 0.050 to 1.0 mg L⁻¹ (0.30–5.9 μmol L⁻¹) (R = 0.9993). The calculated limit of detection (LOD, S/N = 3), equal to 15 μg L⁻¹ (0.09 μmol L⁻¹), was much better compared to chemically modified electrodes with other carbon-based materials. The RSD for 0.5 mg L⁻¹ was in the range 2.5–5.4% (n = 4). The developed NiZCB-GCE was successfully applied to the determination of VB₆ in commercially available multivitamin dietary supplements, food, and water samples. The obtained recoveries ranged from 95 to 106%.

Ionophore-based potentiometric sensors for the flow-injection determination of promethazine hydrochloride in pharmaceutical formulations and human urine

Plasticised poly(vinyl chloride)-based membranes containing the ionophores (α-, β- and γ-cyclodextrins (CD), dibenzo-18-crown-6 (DB18C6) and dibenzo-30-crown-10 (DB30C10) were evaluated for their potentiometric response towards promethazine (PM) in a flow injection analysis (FIA) set-up. Good responses were obtained when β- and γ-CDs, and DB30C10 were used. The performance characteristics were further improved when tetrakis(4-chlorophenyl) borate (KTPB) was added to the membrane. The sensor based on β-CD, bis(2-ethylhexyl) adipate (BEHA) and KTPB exhibited the best performance among the eighteen sensor compositions that were tested. The response was linear from 1 × 10⁻⁵ to 1 × 10⁻² M, slope was 61.3 mV decade⁻¹, the pH independent region ranged from 4.5 to 7.0, a limit of detection of 5.3 × 10⁻⁶ M was possible and a lifetime of more than a month was observed when used in the FIA system. Other plasticisers such as dioctyl phenylphosphonate and tributyl phosphate do not show significant improvements in the quality of the sensors. The promising sensors were further tested for the effects of foreign ions (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Co²⁺, Cu²⁺, Cr³⁺, Fe³⁺, glucose, fructose). FIA conditions (e.g., effects of flow rate, injection volume, pH of the carrier stream) were also studied when the best sensor was used (based on β-CD). The sensor was applied to the determination of PM in four pharmaceutical preparations and human urine that were spiked with different levels of PM. Good agreement between the sensor and the manufacturer’s claimed values (for pharmaceutical preparations) was obtained, while mean recoveries of 98.6% were obtained for spiked urine samples. The molecular recognition features of the sensors as revealed by molecular modelling were rationalised by the nature of the interactions and complexation energies between the host and guest molecules.

Potentiometric Multisensory Systems with Novel Ion-Exchange Polymer-Based Sensors for Analysis of Drugs

This paper examines potentiometric multisensory systems that consist of novel cross-sensitive PD-sensors (Potential Donnan-sensors). The analytical signal of PD-sensors is the Donnan potential at the ion-exchange polymer/electrolyte test solution interface. The use of novel sensors for the quantitative analysis of multicomponent aqueous solutions of amino acids, vitamins and medical substances is based on protolytic and ion-exchange reactions at the interfaces of ion-exchangers and test solutions. The potentiometric sensor arrays consist of PD-sensors and ion-selective electrodes. Such systems were developed for the multicomponent quantitative analysis of lysine monohydrochloride, thiamine chloride and novocaine hydrochloride solutions that contained salts of alkaline and alkaline-earth metals, as well as for mixed solutions of nicotinic acid and pyridoxine hydrochloride. Multivariate methods of analysis were used for sensor calibration and the analysis of the total response of sensor arrays. The errors of measurement of the electrolytes in aqueous solutions did not exceed 10%. The developed multisensory systems were used to determine the composition of a therapeutic “Mineral salt with low content of sodium chloride” and to determine concentrations of novocaine in sewage samples from a dental clinic.

Vitamin B6: a molecule for human health?

Vitamin B₆ is an intriguing molecule that is involved in a wide range of metabolic, physiological and developmental processes. Based on its water solubility and high reactivity when phosphorylated, it is a suitable co-factor for many biochemical processes. Furthermore the vitamin is a potent antioxidant, rivaling carotenoids or tocopherols in its ability to quench reactive oxygen species. It is therefore not surprising that the vitamin is essential and unquestionably important for the cellular metabolism and well-being of all living organisms. The review briefly summarizes the biosynthetic pathways of vitamin B₆ in pro- and eukaryotes and its diverse roles in enzymatic reactions. Finally, because in recent years the vitamin has often been considered beneficial for human health, the review will also sum up and critically reflect on current knowledge how human health can profit from vitamin B₆.