A micro-sized PVC membrane Li+-selective electrode without internal filling solution and its medical applications

Optical determination of lithium therapeutic levels in micro-volumes of interstitial fluid

BACKGROUND

Long-term management of bipolar disorder (BD), characterized by mood fluctuating between episodes of mania and depression, involves the regular taking of lithium preparations as the most reliable mood stabilizer for bipolar patients. However, despite its effectiveness in preventing and reducing mood swings and suicidality, lithium has a very narrow therapeutic index and it is crucial to carefully monitor lithium plasma levels as concentrations >1.2 mmol/L are potentially toxic and can be fatal. Current methods of lithium therapeutic monitoring involve frequent blood tests, which have several drawbacks related to the invasiveness of the technique, comfort, cost and reliability. Dermal interstitial fluid (ISF) is an accessible and information-rich biofluid, and correlations have been found between blood and ISF levels of lithium medication.

METHODS

In the current study, we sought to investigate the optical determination of lithium therapeutic concentrations in samples of ISF extracted from porcine skin utilizing a microneedle-based approach. Monitoring of lithium levels in porcine ISF was achieved by employing a spectrophotometric method based on the reaction between the chromogenic agent Quinizarin and lithium.

RESULTS

The resulting spectra show spectral variations which relate to lithium concentrations of lithium in samples of porcine ISF with a coefficient of determination (R² ) of 0.9. This study has demonstrated successfully that therapeutic levels of lithium in micro-volumes of porcine ISF can be measured with a high level of accuracy utilizing spectroscopic techniques.

CONCLUSIONS

The results support the future development of a miniaturized and minimally-invasive device for lithium monitoring in bipolar patients.

Advances in Therapeutic Monitoring of Lithium in the Management of Bipolar Disorder

Since the mid-20th century, lithium continues to be prescribed as a first-line mood stabilizer for the management of bipolar disorder (BD). However, lithium has a very narrow therapeutic index, and it is crucial to carefully monitor lithium plasma levels as concentrations greater than 1.2 mmol/L are potentially toxic and can be fatal. The quantification of lithium in clinical laboratories is performed by atomic absorption spectrometry, flame emission photometry, or conventional ion-selective electrodes. All these techniques are cumbersome and require frequent blood tests with consequent discomfort which results in patients evading treatment. Furthermore, the current techniques for lithium monitoring require highly qualified personnel and expensive equipment; hence, it is crucial to develop low-cost and easy-to-use devices for decentralized monitoring of lithium. The current paper seeks to review the pertinent literature rigorously and critically with a focus on different lithium-monitoring techniques which could lead towards the development of automatic and point-of-care analytical devices for lithium determination.

Application of Potentiometric Sensors in Real Samples

Potentiometry is one of the most important electrochemical methods and potentiometric based sensors have been extensively studied by researchers for many years. The fact that potentiometric sensors have several advantages over other analytical devices is another reason for intensive research on the topic. In this area, hundreds of different sensors have been developed till today and introduced into the literature. The successful use of the developed sensors, particularly in real sample analysis, has made potentiometric sensors the center of attention. In this review, we highlight the studies which have been successfully applied to the developed drug samples and also to many real samples, with high recovery rates.

Measuring calcium, potassium, and nitrate in plant nutrient solutions using ion-selective electrodes in hydroponic greenhouse of some vegetables

Generally, the life cycle of plants depends on the uptake of essential nutrients in a balanced manner and on toxic elements being under a certain concentration. Lack of control of nutrient levels in nutrient solution can result in reduced plant growth and undesired conditions such as blossom-end rot. In this study, sensitivity and selectivity tests for various polyvinylchloride (PVC)-based ion-selective membranes were conducted to identify those suitable for measuring typical concentration ranges of macronutrients, that is, NO(3-), K(+), and Ca(2+), in hydroponic solutions. The sensitivity and selectivity of PVC-membrane-based ion-selective sensors prepared with tetradodecylammoniumnitrate for NO(3-), valinomycin for K(+), and Ca ionophore IV for Ca(2+) were found to be satisfactory for measuring NO(3-), K(+), and Ca(2+) ions in nutrient solutions over typical ranges of hydroponic concentrations. Potassium, calcium, and nitrate levels that were utilized by cucumber and tomato seedlings in the greenhouse were different. The findings show that tomato plants consumed less amounts of nitrate than cucumber plants over the first 2 months of their growth. We also found that the potassium intake was higher than other nutritional elements tested for all plants.

A paper-based potentiometric cell for decentralized monitoring of Li levels in whole blood

A novel approach to monitor Li levels in blood in decentralized (out of the lab) settings is presented. The approach uses a potentiometric cell fully made with filter paper as a support. Electrodes were built using carbon nanotubes ink to create a conductive path and a suitable polymeric membrane. Solid-state ion-selective electrodes for Li and a reference electrode were built and optimized. The results obtained on real samples of serum and whole blood are comparable with those obtained by conventional standard approaches. This platform shows an outstanding performance for the direct, fast and low-cost monitoring of Li levels in blood.

Solid-contact polyvinyl chloride membrane electrode based on the bis[(2-(hydroxyethylimino)phenolato]copper(II) complex for trace level determination of copper ions in wastewater

A miniaturized solid-contact polyvinyl chloride membrane electrode based on the bis[(2-(hydroxyethylimino)phenolato]copper(II) complex has been prepared for the determination of Cu(II) ion in real samples. The influence of coating membrane composition, pH, and possible interfering cations on the response of the ion-selective electrode was investigated. A number of membranes at different compositions were prepared and their Cu2+ sensing capabilities were investigated. The best results for Cu2+ sensing was obtained for the electrode membrane containing ionophore − 2-nitrophenyloctyl ether – polyvinyl chloride and potassium tetrakis(p-chlorophenyl)borate in a ratio of 4:65:30:1 (w/w, mg), respectively. The prepared electrode exhibited a near-Nernstian response (28.3 mV/decade) to Cu2+ in the concentration range from 1.0 × 10−6 to 1.0 × 10−1 mol/L with a limit of detection of 8.3 × 10−7 mol/L. The potentiometric response of the electrode was independent from the pH of the test solution in the pH range of 3.0–6.0. The electrode has a very short response time, about 15 s, and it can be used over a period of 3 months without any divergence in potential. The electrode has been successfully applied as an indicator electrode in potentiometric titration of Cu(II) ions with ethylenediaminetetraacetic acid and in the determination of Cu(II) in wastewater of the copper processing industry.