Poly(vinyl chloride)-based macrocyclic membrane sensors for magnesium.

Area of Science:

• Electrochemistry
• Materials Science
• Analytical Chemistry

Background:

• Development of ion-selective electrodes (ISEs) is crucial for accurate ion concentration measurements.
• Macrocyclic compounds offer potential as ionophores in ISE membranes due to their selective binding properties.
• Poly(vinyl chloride) (PVC) based membranes are widely used in ISEs due to their processability and stability.

Purpose of the Study:

• To develop and investigate novel magnesium (Mg2+) selective electrodes based on PVC membranes incorporating specific macrocyclic ligands.
• To optimize the membrane composition for enhanced sensitivity, selectivity, and operational stability.
• To evaluate the performance of the developed Mg2+ electrodes in various complex matrices and real-world applications.

Main Methods:

• Preparation of PVC-based membranes using two different macrocyclic ligands: 4,11-dimethyl-2,4,9,11-tetraethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (I) and 4,11-dioxa-2,9-dimethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (II).
• Incorporation of sodium tetraphenyl borate (STB) as an anion excluder and plasticizing solvent mediators including dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutylbutyl phosphonate (DBBP), and 1-chloronaphthalene (CN).
• Electrochemical characterization of the membranes, including potentiometric measurements, response time, pH range, selectivity studies, and stability tests.

Main Results:

• The membrane composition of (II)-PVC-STB-DBP in a 2:10:1:7 ratio exhibited optimal performance as a magnesium selective electrode.
• The optimized electrode demonstrated a wide working concentration range (1.9x10(-6) to 1.0x10(-1) M) with a Nernstian slope of 29 mV/decade over a pH range of 2.5-6.5.
• The electrodes showed excellent selectivity for Mg2+ over other cations, fast response time (15 s), good reproducibility (+/-0.2 mV), and stability for up to 3 months.
• Successful application in partially non-aqueous media, potentiometric titration of Mg2+ with EDTA, and in the presence of interfering anions (Cl-, SO4(2-)) and detergents.
• Accurate determination of Mg2+ in practical samples such as baby food products and soft drinks.

Conclusions:

• The developed PVC-based membrane sensor incorporating macrocycle (II) demonstrates high selectivity and sensitivity for Mg2+ detection.
• The optimized electrode offers a reliable and stable platform for potentiometric determination of magnesium ions.
• The sensor's practical applicability is validated through successful analysis of Mg2+ in diverse real-world samples, including food and beverages.