IUPAC Recommendations Research Articles

Covalent and Non-covalent Noble Gas Bonding Interactions in XeFn Derivatives (n = 2–6): A Combined Theoretical and ICSD Analysis

A noble gas bond (also known in the literature as aerogen bond) can be defined as the attractive interaction between any element of group-18 acting as a Lewis acid and any electron rich atom of group of atoms, thus following the IUPAC recommendation available for similar π,σ-hole interactions involving elements of groups 17 (halogens) and 16 (chalcogens). A significant difference between noble gas bonding (NgB) and halogen (HaB) or chalcogen (ChB) bonding is that whilst the former is scarcely found in the literature, HaB and ChB are very common and their applications in important fields like catalysis, biochemistry or crystal engineering have exponentially grown in the last decade. This article combines theory and experiment to highlight the importance of non-covalent NgBs in the solid state of several xenon fluorides [XeFn]m+ were the central oxidation state of Xe varies from +2 to +6 and the number of fluorine atoms varies from n = 2 to 6. The compounds with an odd number of fluorine atoms (n = 3 and 5) are cationic (m = 1). The Inorganic Crystal Structural Database (ICSD) strongly evidences the relevance of NgBs in the solid state structures of xenon derivatives. The ability of Xe compounds to participate in π,σ-hole interactions has been studied using different types of electron donors (Lewis bases and anions) using DFT calculations (PBE1PBE-D3/def2-TZVP) and the molecular electrostatic potential (MEP) surfaces.

Terminology of electrochemical methods of analysis (IUPAC Recommendations 2019)

Abstract Recommendations are given concerning the terminology of methods used in electroanalytical chemistry. Fundamental terms in electrochemistry are reproduced from previous PAC Recommendations, and new and updated material is added for terms in electroanalytical chemistry, classification of electrode systems, and electroanalytical techniques.

Application of PVC Membrane and Modified Carbon Nanotubes Paste as Electrochemical Sensors for Potentiometric Determination of Loperamide Hydrochloride

Objectives: The main purpose of this work is to design a simple, sensitive, accurate and precise potentiometric membrane ion selective electrodes for selective determination of loperamide hydrochloride in bulk powder and in pharmaceutical preparation. Methods: Electrochemical behavior of loperamide hydrochloride were investigated using PVC membrane and modified carbon nanotubes paste sensors. The linearity of this developed method was established in the concentration range of 10-5 - 10-2 M and10-6 - 10-2 M shows a Nernstian slope of 57.38 mV and 58.74 mV for PVC and Carbon paste sensor, respectively. Results: Validation parameters such as specificity, linearity, accuracy, precision, stability, limit of detection were found to be within the acceptance limit as studied according to IUPAC recommendation data. Conclusion: Both sensors are successfully applied for potentiometric determination of loperamide hydrochloride in its pure form and pharmaceutical formulations.

Nomenclature for boranes and related species (IUPAC Recommendations 2019)

Nomenclature for boranes and related species (IUPAC Recommendations 2019)

Nomenclature and terminology for linear lactic acid-based polymers (IUPAC Recommendations 2019)

Nomenclature and terminology for linear lactic acid-based polymers (IUPAC Recommendations 2019)

Validated Potentiometric Sensors for Determination of Ramipril in Pharmaceuticals and Biological Fluids using in situ Screen Printed and Carbon Paste Electrodes

In this study, electroactivity and performance characteristics of in situ screen printed (ISPEs) and carbon paste (ICPEs) electrodes with different types of ion pairing agents were studied in order to evaluate ramipril (RAM) concentrations in pure solutions, pharmaceutical formulations and biological fluids. The surface analysis of the electrodes was carried out using scanning electron microscopy and energy dispersive X-ray analyzer. The electrodes showed linear responses with good Nernstian slopes of 59.6 ± 0.6 and 58.8 ± 0.8 mV/decade over the concentration range from 5 × 10–7 to 1 × 10–2 M for ISPE and ICPE modified with phosphomolybdic acid (PMA) (electrodes I and III), respectively. At the same time, for ISPE and ICPE modified with phosphotungstic acid (PTA) (electrodes II and IV) slope values of 59.3 ± 0.9 and 58.3 ± 0.9 mV/decade, respectively, were obtained. Also, the two types of electrodes modified with PMA and PTA provided response times of about 5 s for ISPEs and 6 s for ICPEs and exhibited lifetimes of 99 and 92 days for electrodes I and II, respectively, and 68 days for the both paste electrodes (III and IV) in the pH range from 2 to 5 for all the proposed electrodes. They showed high thermal stability where the isothermal coefficients were found to be 0.5 × 10–3 and 1.0 × 10–3 V/grad for electrodes I and II, respectively, and 0.8 × 10–3 and 0.9 × 10–3 V/grad for electrodes III and IV, respectively. Selectivity coefficients of RAM sensors relative to a number of potential interfering materials were investigated. The direct potentiometric determination of ramipril using the prepared sensors gave recoveries between 99.4−99.6, 99.5−99.8, 99.3−99.5 and 99.5−99.6% using electrodes I, II, III and IV, respectively. The developed method was found to be simple, precise and accurate when compared to the reported methods. Method validation parameters were optimized according to IUPAC recommendations.

Brief guide to the nomenclature of organic chemistry (IUPAC Technical Report)

Abstract This IUPAC Technical Report is one of a series that seeks to distil the essentials of IUPAC nomenclature recommendations. The present report provides a succinct summary of material presented in the publication Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013. The content of this report will be republished and disseminated as a four-sided lift-out document (see supplementary information) which will be available for inclusion in textbooks and similar publications.

Carbon thick sheet potentiometric sensor for selective determination of silver ions in X-ray photographic film

Innovative screen-printed electrode (SPE) based on Alizarin Red S (ARS) for Ag (I) ion determination was developed. The ionophore content was varied and optimized which indicated that the ink incorporating 30 mg of Alizarin Red S reflects the best experimental performance exhibiting monovalent Nernstian slope value of 59.95 mV decade−1 over a considerable spacious concentration range from 5.0 × 10−7 to 1.0 × 10−2 mol L − 1 with a lower detection limit value of 5.0 × 10−7 mol L − 1. Additionally, the developed sensor stable for more than 112 days without any significant drift in potential exhibited a fast response time (7 s). The interaction between Ag (I) ions and ARS ionophore at the electrode surface was investigated and elucidated using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and FTIR spectra measurement. The proposed sensor achieved constant potentiometric response in pH range of 4–8 and thermally stable to 50 ͦ C. The developed sensor indicates discriminating capability toward Ag (I) ions with regard to most common transition metal ions. The new developed sensor used for determination of Ag (I) ion in x-ray photographic film and can be applied as indicator electrode in precipitation titrations. Furthermore, the method was validated according to IUPAC recommendation parameters.

IUPAC Provisional Recommendations

Abstract Provisional Recommendations are preliminary drafts of IUPAC recommendations. These drafts encompass topics including terminology, nomenclature, and symbols. Following approval, the final recommendations are published in IUPAC’s journal Pure and Applied Chemistry (PAC) or in IUPAC books. During the commentary period for Provisional Recommendations, interested parties are encouraged to suggest revisions to the recommendation’s author.

Nomenclature for boranes and related species (IUPAC Recommendations 2019)

Abstract An appraisal of the current IUPAC recommendations for the nomenclature of boranes and related systems has been undertaken. New developments in the field have been investigated and existing nomenclature systems have been adapted to accommodate these new developments. The principal areas considered are stoichiometric and structural nomenclature (including heteroatom and metal-atom subrogation, as well as substitution of hydrogen), conjoined-cage species, supra-icosahedral systems, and sub-icosahedral non-standard structures. Elements of substitutive, additive, and replacement nomenclature systems have been integrated into individual names to address contentious problems in boron nomenclature that have been around for a long time.

Establishing Meaningful Limits of Detection for Ion-Selective Electrodes and Other Nonlinear Sensors.

Although IUPAC has recommended a probabilistic approach to determining limit of detection (LOD) based on false-positive and false-negative rates for more than 20 years, the LOD definition for ion-selective electrodes (ISEs) long predates these recommendations and conflicts substantively with them. Although it is well known that the ISE LOD definition does not follow best practice, it continues to be used due to simplicity and a lack of available methods for estimating LOD for nonlinear sensors. Here, we use ISEs as a model system for estimation of LOD for nonlinear sensors that is consistent with broad IUPAC recommendations and justified using statistical theory. Using freely available software, the new approach and updated definition is demonstrated through theory, simulation, and an environmental application. The results show that the current LOD definition for ISEs performs substantially worse than the proposed definition when assessed against IUPAC recommendations, including ignoring sensor noise and LOD uncertainty, leading to bias of an order of magnitude or more. Further, the environmental application shows that the new definition, which includes estimates of LOD uncertainty, allows more objective assessment of sensor response and fitness for purpose. The growing demand for ultrasensitive sensors that operate in complex matrices has pushed the boundaries of traditional calibration approaches. These sensors often operate near their limit of detection (LOD), with additional challenges created if their response is nonlinear. These challenges are amplified when assessing new sensors, since they may be less reproducible and noisier than benchmark techniques.

Nomenclature and terminology for linear lactic acid-based polymers (IUPAC Recommendations 2019)

Abstract Lactic acid enantiomers and cyclic lactic acid dimers, the latter referred to as lactides, are sources of degradable aliphatic polymers that are composed of chiral constitutional repeating units. The different synthesis routes and the various combinations of chiral units result in a multitude of chiral structures and of corresponding properties. Distinctive structural identification is often crucial, especially for applications as degradable polymers. This document provides recommendations for the nomenclature, abbreviations, and terminology related to lactic acid-based polymers in order to allow consistent comparison between polymers of different origins and between data collected within different disciplines.

Green monitoring of bromhexine oxidative degradation kinetics

Kinetics studies are important in quality control to assure the safety and efficacy of the pharmaceutical compounds. Recently, potentiometric ion-selective electrodes (ISEs) breakthrough kinetics study due to their ability to provide real-time measurements which meet “green analytical chemistry” (GAC) principles. A polyvinyl chloride (PVC) matrix membrane was fabricated to monitor bromhexine (BR) oxidative degradation kinetics using tetraphenylborate as a cation exchanger. At-line monitoring of the oxidative degradation kinetics of BR was performed; by continuous measuring the decrease in the sensor potential over time. So a real-time observation and a continuous profile were obtained for the oxidation of BR under various H2O2 concentrations and temperature. This kinetic study determines the oxidation activation energy that was 6.4 kcal mol−1. To expand the application of this sensor, BR was determined in bulk powder and dosage form in the presence of both co-formulated drug (acefylline piperazine) and dosage form additives. The proposed sensor had been characterized according to IUPAC recommendations and a linear dynamic range was 5 × 10−6 to 1 × 10−3 M and other sensor parameters had been calculated.

IUPAC Provisional Recommendations

Abstract Provisional Recommendations are preliminary drafts of IUPAC recommendations on terminology, nomenclature, and symbols, made widely available to allow interested parties to comment before the recommendations are finalized and published in IUPAC’s journal Pure and Applied Chemistry (PAC). Full text is available online.

Nomenclature and terminology for dendrimers with regular dendrons and for hyperbranched polymers (IUPAC Recommendations 2017)

Nomenclature and terminology for dendrimers with regular dendrons and for hyperbranched polymers (IUPAC Recommendations 2017)

Cost-effective and green synthesized electroactive nanocomposite for high selective potentiometric determination of clomipramine hydrochloride

Cost-effective, scalable and efficient electroactive material for ion-selective electrode was developed. Facile nanocomposite composed from montmorillonite clay layers and polyaniline nanofibers (PANI-NFs) was facilely prepared at ambient condition. The polyaniline nanofibers were polymerized on the surface of montmorillonite clay. Then the prepared nanocomposite was used as efficient electroactive modifier for developing new sensitive and selective modified carbon paste electrodes (CPE) for potentiometric determination of Clomipramine hydrochloride (CLO-HCl) in pure and pharmaceutical formulations. Effects of experimental parameters such as paste composition, response time, selectivity, pH and temperature on the potential response of CLO-HCl electrode were investigated. The paste incorporating 5 (electrode I) and 10 (electrode II) mg of developed nanocomposite (MT-PANI-NF) showed the best experimental performance, exhibiting the best Nernstian slope values of 60.30 ± 0.28 and 60.00 ± 0.22 mV decade−1 over a considerable spacious concentration range from 1.0 × 10−5 to 1.0 × 10−2 mol L−1 over pH range from 3.5 to 7.5. Additionally, a fast dynamic response time of 9 and 7 s for electrode I and II, respectively, was achieved. The proposed sensors displayed good discriminating capability toward CLO-HCl with regard to a number of interfering materials. The interaction between MT-PANI-NF nanocomposite and CLO-HCl drug at the electrode surface was studied through scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The results were obtained using those electrodes were in a good agreement with those which were obtained using the official method. The method was validated according to IUPAC recommendation parameters.

Aluminum(III)-Selective Screen Printed Sensor Based on Methyl Red

Modified screen printed electrode (MSPE) with 2-[[4-(dimethyl amino) phenyl] diazenyl] benzoic acid (Methyl Red) was prepared for determination of aluminum ions in water and pharmaceutical (Maalox and Epicogel) samples. The MSPE reveals linear response over a wide concentration range of 5.0 × 10–6–1.0 × 10–2 mol L–1 of aluminum at 25°C with a trivalent cationic slope of 20.4 ± 0.5 mV decade–1 with detection limit 5.0 × 10–6 mol L–1 in pH range 3–5. Moreover, the mechanism of chemical reaction between Methyl Red and aluminum ions on the sensor surface was studied using IR spectra, energy dispersive X-ray analysis (EDX) and scanning electron microscope (SEM). The prepared sensor also showed reproducible and stable response over a period of 14 week with fast response time about 5 s. The proposed potentiometric method was validated according to the IUPAC recommendations. The results obtained from the proposed sensor were comparable with those obtained with inductively coupled plasma mass spectrometry (ICP–MS).

Comparative study between two fabricated potentiometric sensors to enhance selectivity towards ferrous ions

Electroanalytical methods are highly selective for measuring electrical quantities including the charge, potential and current with their relation to chemical parameters. They are widely applied in various fields such as biochemical analysis, industrial quality control and environmental monitoring. They have many advantages over other techniques in that they are not time consuming and are specific for certain oxidation states of certain elements which give these techniques high selectivity and sensitivity features. This paper is based on two parts: the first part describes the fabrication of screen‐printed electrodes (SPEs) modified with methyl red as electroactive material, while second part describes the preparation and characterization of Fe(II)–methyl red complex using various spectroscopic tools, the complex being used for the construction of carbon paste electrodes (CPEs). The two proposed electrodes were successfully applied for the determination of Fe(II) in water and pharmaceutical (pharovit) samples. The electrodes under investigation show potentiometric response for Fe(II) in the concentration range 8.0 × 10−7–1.0 × 10−2 and 5.0 × 10−7–1.0 × 10−2 M at 25°C for SPE and CPE, respectively, and the electrode response is independent of pH in the range 1.5–7.0. These sensors show Nernstian slopes of 29.1 ± 0.2 and 29.7 ± 0.16 mV decade−1 with detection limit values of 8.0 × 10−7 and 5.0 × 10−7 M for SPE and CPE, respectively. These electrodes show fast response time of 6 and 4 s and exhibit a lifetime of 100 and 30 days for SPE and CPE, respectively. The mechanism of chemical reaction between modifier and Fe(II) on the SPE surface was studied using infrared spectra, scanning electron microscopy and energy‐dispersive X‐ray analysis. The proposed potentiometric method was validated according to the IUPAC recommendations. The results obtained using the proposed sensors were comparable with those obtained with inductively coupled plasma analysis.

A green stability indicating ISE-potentiometric method for the monitoring of chlorhexidine in the presence of its rapidly absorbed toxic degradation product; a kinetic study

Chlorhexidine (CHX) is an antiseptic and disinfectant used in several antimicrobial preparations. In the current study an environmentally friendly ISE-potentiometric method was developed for the determination of CHX, measurements were carried out directly in the aqueous solution of the sample without pretreatment. Four PVC-membranes were fabricated using dioctylphthalate as a solvent mediator along with different cation exchangers, namely; sodium tetraphenylborate, sodium phosphotungstate tribasic, sodium phosphomolybdate and ammonium reineckate. Responses were compared and that containing ammonium reineckate illustrated the best near-Nernstian slope through a wide linear range (3.85 × 10−6–1 × 10−3 M). The sensor was able to determine CHX in colored and turbid solutions without prior extraction, pretreatment, filtration or derivatization steps. This method enabled in-site stability study without interference of para-chloroaniline (PCA) the most common and carcinogenic degradation product by monitoring the degradation kinetics of CHX at different pH values (3.5, 4.0 and 5.0). The sensor was able to provide a reliable in-line monitoring of the process without the need for frequent sample withdrawal at time intervals or sample pretreatment steps which saved time. Sensor response characteristics were calculated according to the IUPAC recommendations and the method was validated as per the ICH recommendations. The proposed method provided a green eco-friendly method that saves cost, time and effort, and consumes the least amount of chemicals.

Ecofriendly Long Life Nanocomposite Sensors for Determination of Carbachol in Presence of Choline: Application in Ophthalmic Solutions and Biological Fluids.

Several emerging nano scale forms of carbon are showing great promise in electrochemical sensing such as graphene and multi-walled carbon nanotubes (MWCNTs). Herein we present an ecofriendly method to fabricate long life and sensitive ion selective sensors based on graphene and MWCNTs nanocomposites with no need for volatile organic solvents. Both sensors were fabricated, for the analysis of carbachol in ophthalmic solutions, plasma and urine where ion- association complex was formed between cationic carbachol and anionic Sodium tetra phenyl borate (NaTBP) in a ratio 1:1. Both sensors were evaluated according to the IUPAC recommendation data, revealing linear response in the concentration range 10−7 M to 10−2 M with near Nernstian slopes 50.80 ± 5 and 58.14 ± 3 mV/decade and correlation coefficients 0.9992 and 0.9998 for graphene and MWCNTs based sensors, respectively. Both sensors were successfully applied as stability indicating method for the analysis of carbachol in presence of its metabolite choline, in ophthalmic preparations, in plasma and urine showing good recovery percentage values. MWCNTs based sensor showed some advantages over graphene sensor regarding lower limit of detection (LOD), longer life time and higher selectivity towards carbachol. Statistical comparison of the proposed sensors with the official method showed no significant difference for accuracy and precision.