Determination of benzoate in cranberry and lingonberry by using a solid-contact benzoate-selective electrode.

Benzoic acid is used as a preservative in processed food, and occasionally in cosmetics and pharmaceuticals, while benzoic acid occurs naturally in, e.g., cranberry and lingonberry. Therefore, the determination of benzoate is of interest for product quality assurance, food safety, and personal health. In this work, a solid-contact benzoate-selective electrode (benzoate-ISE) was developed by utilising poly(3,4-ethylenedioxythiophene) (PEDOT) as solid contact and a solvent polymeric membrane containing a 1,3-bis(carbazolyl)urea derivative as ionophore. The benzoate-ISE was characterised in parallel with an ionophore-free control-ISE by electrochemical impedance spectroscopy and potentiometry. The presence of the ionophore in the membrane improved the selectivity to benzoate. Benzoate-ISEs and control-ISEs were used further to determine the benzoate concentration in cranberry and lingonberry by standard addition. The results obtained with both types of ISEs were compared with those obtained by ion chromatography. The results obtained with benzoate-ISEs were consistent with those obtained with ion chromatography. On the contrary, the control-ISE (without ionophore) gave significantly higher benzoate concentrations, especially in the case of cranberry where the benzoate concentration was low (ca 0.2 g kg-1) compared to lingonberry (ca 1 g kg-1). Hence, the benzoate-selectivity of the ionophore was crucial to obtain a benzoate-ISE that was practically applicable for determination of benzoate concentrations in cranberry and lingonberry.

Improved pH measurement of mobile phases in reversed-phase liquid chromatography.

Mobile phase pH is a critically important parameter in reversed-phase liquid chromatographic (RPLC) separations involving analytes that display acidic or basic properties in the pH range used for the mobile phase. The main problem in measuring mobile phase pH lies in the fact that RPLC mobile phases are typically aqueous-organic mixtures. In addition to experimental difficulties, the pH values refer to different aqueous-organic compositions that cannot be correctly compared. Given this situation, the unified pH (wabspH, also termed as ) based on the absolute chemical potential of the solvated proton has been proposed as a rigorous way of characterising mobile phase acidity that is fully inter-comparable between mobile phases of any composition. Here we report the wabspH values of 78 reversed-phase liquid chromatography-mass spectrometry mobile phases that were carefully measured by potential differences in a symmetric cell with two glass electrode half-cells and almost ideal ionic liquid triethylamylammonium bis((trifluoromethyl)sulfonyl)imide [N2225][NTf2] salt bridge with multiple overlapping measurements. The system of altogether 300 ΔwabspH values was anchored to the pH value of standard pH 7.00 aqueous buffer solution. The consistency standard deviation of the whole set of measurements was 0.09 pH units. In addition to the differential potentiometric reference method, simpler measurement methods that use double junction reference or double junction combined electrodes were tested and were found suitable for routine laboratories if high accuracy is not required.

Laser-based analytical techniques in cultural heritage science - Tutorial review.

This tutorial review combines the fundamentals of the design and operation of lasers with their usage in applications related to conservation and cultural heritage (CH) science - as components of analytical devices for the study of the chemical composition of materials. The development of laser instruments and their fundamental physical background, including a short explanation of their properties and parameters, are briefly summarised, and an overview of different laser-based analytical techniques is given. The analytical techniques covered in this tutorial are divided into three groups based on their technical aspects and properties: (1) vibrational spectroscopy, (2) elemental analysis, and (3) different molecular mass spectrometric techniques.

Rigorous pH measurement in non-aqueous solution: measurement method and reference values in ethanol.

The recently introduced unified pH ([Formula: see text]) concept enables rigorous pH measurements in non-aqueous and mixed media while at the same time maintaining comparability to the conventional aqueous pH scale. However, its practical application is hindered by a shortage of reference [Formula: see text] values. In order to improve this situation, the European Metrology Research Project (EMPIR) UnipHied ("Realisation of a UnipHied pH scale") launched an interlaboratory comparison among highly experienced electrochemistry expert laboratories to assign the first such reference [Formula: see text] values by adopting an extensive statistical treatment of the reported measurement data: to phosphate buffer in water-ethanol mixture (50 wt% of ethanol) and ammonium formate buffer in pure ethanol. Two different measurement setups - one capable of being easily adopted in industrial applications - have been used to demonstrate the robustness of [Formula: see text] measurement. This is an important step towards wider adoption of the [Formula: see text] concept in practice, like liquid chromatography, biofuels analysis and electrocatalysis.

Chiral Carborane Acids Decorated with Binol-Based Phosphonates: Synthesis, Characterization, and Application.

The syntheses of hexabrominated closo-carborates decorated with different chiral Binol-derived phosphonates and their conjugate acids are described. X-ray diffraction analysis reveals a polymeric structure for the sodium salt with the anionic units connected by [B-Br-Na-O═P]+ linkages. For the acid, coordination of the proton to the phosphonate's P═O oxygen atom is assumed. The pKa value was estimated by combining experiments and computations. Application of these Brønsted acids as chiral catalysts in an imino-ene and a Mukaiyama-Mannich reaction was moderately successful.

Theoretical Study on Fluorinated Derivatives of Sulfolane, Cyclopentanone, and Gamma-Butyrolactone.

In this paper, fluorinated compounds based on sulfolane, cyclopentanone, and gamma-butyrolactone are studied computationally, focusing on their applicability in electrochemical devices and acid-base-related studies. Candidates for solvents with (1) high polarity, (2) good electrochemical stability, and (3) low basicity were searched for. Some of the compounds are studied here for the first time. Electrochemical stabilities, dielectric constants, boiling points, basicities, and lipophilicities were estimated using DFT and COSMO-RS methods with empirical corrections. The effect of fluorination on these properties as well as the bond parameters was studied. The possible synthesis routes of the proposed compounds are outlined. Some molecules display a combination of estimated properties favorable for a solvent, although none of the studied compounds are expected to surpass acetonitrile and propylene carbonate by the width of the electrochemical stability window.

The Unified Redox Scale for All Solvents: Consistency and Gibbs Transfer Energies of Electrolytes from their Constituent Single Ions.

We have devised the unified redox scale Eabs H2O , which is valid for all solvents. The necessary single ion Gibbs transfer energy between two different solvents, which only can be determined with extra-thermodynamic assumptions so far, must clearly satisfy two essential conditions: First, the sum of the independent cation and anion values must give the Gibbs transfer energy of the salt they form. The latter is an observable and measurable without extra-thermodynamic assumptions. Second, the values must be consistent for different solvent combinations. With this work, potentiometric measurements on silver ions and on chloride ions show that both conditions are fulfilled using a salt bridge filled with the ionic liquid [N2225 ][NTf2 ]: if compared to the values resulting from known pKL values, the silver and chloride single ion magnitudes combine within a uncertainty of 1.5 kJ mol-1 to the directly measurable transfer magnitudes of the salt AgCl from water to the solvents acetonitrile, propylene carbonate, dimethylformamide, ethanol, and methanol. The resulting values are used to further develop the consistent unified redox potential scale Eabs H2O that now allows to assess and compare redox potentials in and over six different solvents. We elaborate on its implications.

Ionization and lipophilicity in nonpolar media mimicking the cell membrane interior.

Ionization and lipophilicity may vary with the environment. Therefore, in this study we provide some insight in the performances of different experimental techniques (potentiometry, UV-vis, shake-flask and chromatography) to determine ionization and lipophilicity in more nonpolar systems than those commonly used in drug discovery. To this purpose a pool of 11 compounds of pharmaceutical interest was firstly submitted to a few experimental techniques to measure pKa in water, water/acetonitrile mixtures and pure acetonitrile. Then we measured logP/logD with shake-flask and potentiometry in octanol/water and toluene/water and also determined a chromatographic lipophilicity index (log k'80 PLRP-S) in a nonpolar system. Results show that ionization decreases for both acids and bases in a coherent, significant but not dramatical extent when water is present in the system, but the picture is completely different in pure acetonitrile. Lipophilicity may vary or not with the environment according to the chemical structure of the investigated compounds as also revealed by electrostatic potential maps. Since the internal core of cell membranes is largely nonpolar, our results support the need of extending the pool of physicochemical descriptors to be determined in the various stages of drug discovery programs and indicate some experimental strategies for their determination.

Multifunctional Organocatalysts - Singly-Linked and Macrocyclic Bisphosphoric Acids for Asymmetric Phase-Transfer and Brønsted-Acid Catalysis.

The linking of phosphoric acids via covalent or mechanical bonds has proven to be a successful strategy for the design of novel organocatalysts. Here, we present the first systematic investigation of singly-linked and macrocyclic bisphosphoric acids, including their synthesis and their application in phase-transfer and Brønsted acid catalysis. We found that the novel bisphosphoric acids show dramatically increased enantioselectivities in comparison to their monophosphoric acid analogues. However, the nature, length and number of linkers has a profound influence on the enantioselectivities. In the asymmetric dearomative fluorination via phase-transfer catalysis, bisphosphoric acids with a single, rigid bisalkyne-linker give the best results with moderate to good enantiomeric excesses. In contrast, bisphosphoric acids with flexible linkers give excellent enantioselectivities in the transfer-hydrogenation of quinolines via cooperative Brønsted acid catalysis. In the latter case, sufficiently long linkers are needed for high stereoselectivities, as found experimentally and supported by DFT calculations.

Non-invasive analysis of natural textile dyes using fluorescence excitation-emission matrices.

Multidimensional fluorescence spectroscopy was assessed as a non-invasive and non-destructive method for the analysis of components in natural textile dyes. Results demonstrate that components in the natural dyes fluoresce and wool's intrinsic fluorescence is, in many cases, not a considerable analytical interferent. In the case of some self-dyed reference yarns, like those dyed with northern and lady's bedstraws, wood horsetail, safflower, salted shield lichen, dyer's madder and cochineal, the fluorescence excitation-emission matrices (EEMs) are sufficiently characteristic for using them as a primary means of identification (or assignment to a family of dyes). With most of the studied yellow and green dyes (heather, silver birch, some bloodred webcap treatments, alkanet), however, the spectra can be used as additional information for identification. This study reports multidimensional fluorescence data for a collection of wools dyed with natural dyes (31 dyed wool yarn samples that were self-dyed with 18 different natural dyes) that were used as references in a case study of two historical textiles for which liquid chromatography-mass spectrometry was used as a confirmatory technique. Given its utility as a rapid and non-destructive/non-invasive method with information-rich multidimensional EEM output, the front-face fluorescence spectroscopy of surfaces using a fiber optic probe is a promising technique for the analysis of dyes on cultural heritage textiles.

Coumarin-based derivatization reagent for LC-MS analysis of amino acids.

In this paper, we report about the application of a sensitive fluorescent derivatization reagent Coumarin151-N-Hydroxysuccinimidyl Carbamate (Cou151DSC) for amino compounds using high-performance liquid chromatography (HPLC) compatible with ultraviolet (UV), fluorescence detector (FLD) and electrospray ionization - tandem mass spectrometry (ESI-MS/MS)-positive mode. We optimized derivatization procedure and validated an analytical method to determine 24 amino acids in Kvass drink using Norvaline as an internal standard. Compared to 6-Aminoquinolyl-N-Hydroxysuccinimidyl Carbamate (6-AQC), the derivatization with Cou151 DSC is faster and milder, for 5 min at 40°C instead of 15 min at 55°C. The limit of quantitation (LOQ, pmol on column) for 21 amino acids in this work is lower 1.1-30.0 times than values obtained with 6-AQC. The derivatives have excitation wavelength at 355 nm and emission wavelength at 486 nm. Their MS/MS fragmentation behaviors were examined together with 23 other amino compounds. We found three possibilities to lose a neutral group which can be Coumarin 151 isocyanate Cou151NCO (255 Da), amine Coumarin 151 (229 Da) or urea Cou151CONH2 (272 Da). The accuracy of the proposed method was within 83-107% with good relative standard deviations (RSDs) of equal or less than 6%. The recoveries were from 82 to 120% in four spiked concentrations, repeatability was between 0 and 14%. The intra- and inter-day precision are less than 13% and 18%, respectively.

Comparison of two azobenzene-based amino acid derivatization reagents for LC-MS/MS analysis in positive and negative ESI modes.

Derivatization reagents based on azobenzene containing different N-hydroxysuccinimidyl moieties- AzoB (carbamate) and AzoC (ester) - are proposed for the LC-ESI-MS analysis of free amino acids in fermented beverages and juices. A dual comparison between LC-MS/MS in positive and negative ESI modes in dynamic Multiple Reaction Monitoring (dMRM) and Neutral Loss Scan was investigated. The results indicate that the studied carbamate derivatization reagent, AzoB, can be employed for targeted analysis (MS/MS) but also for non-targeted analysis of derivatized amino acids thanks to its constant neutral loss (223 Da) that is the same in both ionisation modes. For amines, precursor ion scan can be used as identification tool. The derivatization properties of AzoB and AzoC were compared against other derivatization reagents, and they showed advantages such as fast derivatization reaction and good reactivity with secondary amines. AzoC also displayed a disadvantage -side products were formed that affect the quantitation. Free amino acids profile of Kvass (a fermented beverage from eastern Europe) was determined for first time, proline was found to be the most abundant amino acid.

Positive + negative is not equal to zero: Use of negative ionisation as analyte identity confirmation tool in LC-ESI-MS analysis.

In this study the use of negative electrospray ionisation mode as a confirmation tool for identifying derivatized amino acids using LC-ESI-MS, was evaluated. The derivatization reagent was based on azobenzene N-hydroxysuccinimide carbamate. The results indicate that even though negative ionisation mode produced less intense peaks, the ratio of peak area of quantifier ion (obtained in positive mode) to the qualifier (or identifier) ion measured in negative mode meets the requirements established by two prominent validation guidelines: SANTE/11312/2021 and 2002/657/EC. Therefore, the use of product ions obtained via negative transitions as qualifier ions, while using product ions from positive transitions as quantifier ions is a fruitful approach that widens the choice of transitions to choose from for obtaining suitable qualifier ions. This methodology was applied to the LC-ESI-MS/MS determination of amino acids in different beverages (tomato juice, watermelon juice, kvass).

One Hundred Carboxylate Receptors.

This work presents a compilation of binding constant (logKass) values in DMSO-d6/H2O (0.5% m/m) for a variety of receptors with 12 carboxylate anions (formate, acetate, lactate, pivalate, sorbate, hexanoate, benzoate, glyphosate, glucuronate, ibuprofen, naproxen, and ketoprofen). A total of 489 logKass values are listed for 100 anion receptor molecules. Most logKass values originate from previously published articles, along with some values for previously unpublished receptor molecules, spanning a workflow of 8 years. The purpose of this study is to serve as a comprehensive information source for selecting suitable receptor candidates to be used in practical carboxylate sensing applications, such as constructing ion-selective electrodes (ISE-s). To support such decision making, all receptors are presented together with lipophilicity (logPo/w) data.

On-off-on Control of Molecular Inversion Symmetry via Multi-stage Protonation: Elucidating Vibronic Laporte Rule.

The Laporte rule dictates that one- and two-photon absorption spectra of inversion-symmetric molecules should display alternatively forbidden electronic transitions; however, for organic fluorophores, drawing clear distinction between the symmetric- and non-inversion symmetric two-photon spectra is often obscured due to prevalent vibronic interactions. We take advantage of consecutive single- and double-protonation to break and then reconstitute inversion symmetry in a nominally symmetric diketopyrrolopyrrole, causing large changes in two-photon absorption. By performing detailed one- and two-photon titration experiments, with supporting quantum-chemical model calculations, we explain how certain low-frequency vibrational modes may lead to apparent deviations from the strict Laporte rule. As a result, the system may be indeed considered as an on-off-on inversion symmetry switch, opening new avenues for two-photon sensing applications.

A Chemically Fuelled Molecular Automaton Displaying Programmed Migration of Zn2+ Between Alternative Binding Sites.

A molecular system comprising a cationic zinc complex and an amino acid-derived ambident ligand having phosphate and carboxylate binding sites undergoes a series of rearrangements in which the metal cation migrates autonomously from one site to another. The location of the metal is identified by the circular dichroism spectrum of a ligated bis(2-quinolylmethyl)-(2-pyridylmethyl)amine (BQPA) chromophore, which takes a characteristic shape at each binding site. Migration is fuelled by the decomposition of trichloroacetic acid to CO2 and CHCl3 , which progressively neutralises the acidity of the system as a function of time, revealing in sequence binding sites of increasing basicity. The migration rate responds to control by variation of the temperature, water content and triethylamine concentration, while an excess of fuel controls the duration of an induction period before the migration event.

Comparison of the ionisation mode in the determination of free amino acids in beers by Liquid Chromatography tandem mass spectrometry.

A comparison of positive and negative ionization modes in LC-ESI-MS/MS was carried out for the analysis of derivatized amino acids in 15 different beer samples. 22 free amino acids were derivatized using Diethyl ethoxymethylenemalonate (DEEMM) and their content was determined. When using the DEEMM as derivatization reagent the negative ionization mode provided analytical performance equal to or in some cases even superior to the positive ionization mode. For 6 amino acids (Thr, ß-Ala, α-Ala, Met, Val and Orn) the negative mode led to lower LoQ values, while the positive mode offered lower LoQ values for 5 amino acids (Arg, Asp, Glu, GABA, and Pro). The remaining 11 amino acids showed similar LoQ values in both modes. Because of this, negative ionization mode allowed to detect and quantify amino acids such as: ß-Alanine, threonine, and ornithine whose concentrations were low in most of the analysed samples. The relative standard deviation (RSD) for the results in both modes were similar. The method's linearity was determined to be in the range of 1 to 130 ppb with r2 > 0.99. Recoveries ranged from 93 to 112%. Negative mode was less affected by matrix effects the main effect was signal enhancement. In contrast, the positive ionization mode suffered from signal enhancement as well as signal suppression.

Long-Time Evaluation of Solid-State Composite Reference Electrodes.

In this study, the performance and long-time evaluation of solid-state composite (SSC) reference electrodes were investigated. The stability of all the SSC reference electrodes was continuously monitored by using potentiometry and electrochemical impedance spectroscopy methods over a period of several months. A multi-solution protocol was used to study the influence of the ionic strength of the sample solution, ion charge, and mobility, and the sample pH values on the performance of the reference electrodes. The SSC reference electrodes were used in the calibration of commercial indicator electrodes for different ions at different temperatures. The concentrations of K+, Na+, Ca2+, and Cl- ions and pH values were measured in river water samples at different temperatures using the SSC reference electrodes. The obtained results for the same samples were compared with the results given by an independent laboratory specialized in routine water analyses. The agreement between the results was very good and even better than the case where commercial reference electrodes were used. Our study showed that the SSC reference electrodes exhibit good long-term stability and excellent performance, both in the calibrations and analyses of environmental samples.

Electrochemistry and Reactivity of Chelation-stabilized Hypervalent Bromine(III) Compounds.

Hypervalent bromine(III) reagents possess a higher electrophilicity and a stronger oxidizing power compared to their iodine(III) counterparts. Despite the superior reactivity, bromine(III) reagents have a reputation of hard-to-control and difficult-to-synthesize compounds. This is partly due to their low stability, and partly because their synthesis typically relies on the use of the toxic and highly reactive BrF3 as a precursor. Recently, we proposed chelation-stabilized hypervalent bromine(III) compounds as a possible solution to both problems. First, they can be conveniently prepared by electro-oxidation of the corresponding bromoarenes. Second, the chelation endows bromine(III) species with increased stability while retaining sufficient reactivity, comparable to that of iodine(III) counterparts. Finally, their intrinsic reactivity can be unlocked in the presence of acids. Herein, an in-depth mechanistic study of both the electrochemical generation and the reactivity of the bromine(III) compounds is disclosed, with implications for known applications and future developments in the field.

Measurements and Utilization of Consistent Gibbs Energies of Transfer of Single Ions: Towards a Unified Redox Potential Scale for All Solvents.

Utilizing the "ideal" ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol-1 over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent pe abs H 2 O - and the E abs H 2 O values that account for the electronating potential of any redox system similar to the pH abs H 2 O value of a medium that accounts for its protonating potential. This E abs H 2 O scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents' redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the E abs H 2 O scale.