Acetonitrile-dimethyl Sulfoxide Research Articles

A novel sample-preparation method for the generic and rapid determination of pesticides and mycotoxins in tea by ultra-performance liquid chromatography–tandem mass spectrometry

A rapid, simple, and generic analytical method for the simultaneous determination of 140 undesirable low-weight pesticides and mycotoxins from different chemical classes in black tea was developed. The method involved swelling the sample in ammonium acetate buffer, extraction with acetonitrile–dimethyl sulfoxide, cleanup by dual dispersive solid-phase extraction (D-SPE) with the assistance of low-temperature centrifugation, and analysis by ultraperformance liquid chromatography coupled with electrospray ionization tandem mass spectrometry using multiple reaction monitoring mode. The interferences in the extract were eliminated by the combination of dual d-SPE using only C18 sorbent and anhydrous magnesium sulfate, which maintained the chromatographic column under the ideal condition for a long time and enabled satisfactory recoveries of hydrophobic and hydrophilic analytes simultaneously. Matrix-matched calibration curves were obtained for most target compounds with linear regression coefficients above 0.9900. The limits of quantification (LOQs) ranged within 0.5–10.0 μg/kg, which were usually sufficient to verify the compliance of products with legal tolerances. Satisfactory recoveries of 64.5%–138.1% were obtained in black ta samples with the relative standard deviation (RSD) values between 1.8 and 25.9%. The inter-day precision ranged within 2.2%–24.9%. For over 90% of the analytes, the recoveries were between 70% and 120%, with RSD values below 15.0%. The application of this method in routine monitoring programs can drastically reduce effort and time.

Ionic equilibrium in mixtures of polar protophobic and protophilic non-hydrogen bond donor solvents: Acids, salts, and indicators in acetonitrile with 4 mass % dimethylsulfoxide

Acetonitrile (AN) and dimethylsulfoxide (DMSO) belong to the so-called polar non-hydrogen bond donor solvents, in accordance with Bordwell's classification. At that, according to Kolthoff, AN is a protophobic, and DMSO is an expressed protophilic solvent. This article presents a study of the acid-base and related equilibria in a binary AN – DMSO solvent system with mass ratio 96: 4, which corresponds to the molar fraction xDMSO = 0.021. Owing to the aforesaid property of DMSO, the utilization of this binary mixture makes it possible to neglect the interfering influence of water traces, which is difficult to overcome in pure AN. As result, in the solvent under study, the proton is solvated first of all by DMSO despite predominance of AN. The solvent composition was chosen basing on the pKa values of the picric acid, which were determined via UV–visible spectroscopy at different AN – DMSO ratios. The interfering influence of water traces was checked. An operational paH+∗ scale was developed using a quinhydrone electrode in a concentration cell with liquid junction, basing on a picrate buffer solution with paH+∗ = 3.27. The cation-anion association constants of a set of salts were determined using the conductance method, the pKa values of the buffer acids (benzoic, salicylic, 2,4- and 2,6-dinitrophenols) were calculated, and the constants KAHA−f of homoassociation (A− + HA ⇄ AHA−) were estimated. The response of the glass electrode to the acidity of the solutions was proved within the range of 2.5 ≤ paH+∗ ≤ 15.5 (slope = 59.69), the paH+∗ values of 16 picrates of organic bases were determined, and the pKas of 7 indicators, nitrophenols and sulfonephthaleins, were obtained spectroscopically in the solvent under study. The dissociation constants of salts, acids, and indicators in AN–DMSO (96:4) mixed solvents were compared with those in other non-hydrogen bond donor solvents. Basing on some reliable assumptions, the values of the Gibbs energy of the H+ transfer from the binary solvent to AN and DMSO were estimated as ΔGtro = +44 ± 3 and −22.6 ± 3 kJ mol−1, respectively.

Generic and rapid determination of low molecular weight organic chemical contaminants in protein powder by using ultra-performance liquid chromatography-tandem mass spectrometry

A rapid, simple, and generic analytical method that could simultaneously determine 291 undesirable low molecular weight chemical contaminants from different drug families in protein powder, such as veterinary drugs and pesticides, etc, had been developed. This method comprised the extraction with acetonitrile-dimethyl sulfoxide (DMSO), clean-up through dispersive solid phase extraction (D-SPE) and low temperature filtration, and analysis by ultra-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry at multiple-reaction monitoring mode. Acetonitrile-DMSO was more generic than acetonitrile or methanol for the extraction of large-scale organic chemical contaminants with different polarities in protein powder. Most interferences in the extract were eliminated by the combination of D-SPE and low temperature filtration, which simultaneously provided satisfactory recoveries of both hydrophobic and hydrophilic analytes. In particular, besides the purification function, the sorbent of D-SPE also played an important role in grinding samples to improve extraction efficiency during homogenization. This streamlined approach allowed the processes of extraction and the main purification were carried out in one-step, and dramatically reduced sample preparation turnaround times and solvent consumption. For quantification, matrix-fortified calibration curves showed competent linearity for most of the target compounds with linear regression coefficients (r) higher than 0.9900, except for two analytes. The limits of quantification ranged from 0.1 μg/kg to 50 μg/kg, which was usually sufficient to verify the compliance of products with legal tolerances. The average recoveries for spiked protein powder ranged from 65.6% to 142.2% with associated RSD values between 0.5% and 28.5%. For over 90% of the analytes, the recoveries were between 70% and 120% with RSD values in the range of 1%–15%. Applying this method in routine monitoring programs would drastically reduce both effort and time.

Influence of Non-Aqueous Solvents on Complexation and Selectivity of Complexes Formed Between 18-crown-6 with La3+, Ce3+, Pr3+ and Nd3+ cations in pure acetonitrile, pure dimethyl sulfoxide and acetonitrile-dimethyl sulfoxide binary mixtures at 298.15K, 308.15K and 318.15K using conductometric method

Influence of Non-Aqueous Solvents on Complexation and Selectivity of Complexes Formed Between 18-crown-6 with La3+, Ce3+, Pr3+ and Nd3+ cations in pure acetonitrile, pure dimethyl sulfoxide and acetonitrile-dimethyl sulfoxide binary mixtures at 298.15K, 308.15K and 318.15K using conductometric method

Flavonoid oxidation kinetics in aqueous and aqueous organic media in the presence of peroxidase, tyrosynase, and hemoglobin

The kinetics of oxidation reactions of flavonoids, quercetin, dihydroquercetin, and epicatechin has been studied in the presence of biocatalysts of different natures: horseradish peroxidase, mushroom tyrosinase, and hemoglobin from bull blood. Comparison of the kinetic parameters of the oxidation reaction showed that peroxidase appeared to be the most effective biocatalyst in these processes. The specificity of the enzyme for quercetin increased with increasing the polarity of the solvent in a series of ethanol–acetonitrile–dimethyl sulfoxide.

Quantitative structure—retention relationships of some steroid and phenanthrene derivatives on cyano-, reversed-phase, and normal-phase thin-layer chromatography stationary phases

In the presented study, quantitative structure—retention relationships (QSRR) methodology was used to investigate the relationship between the chemical structures of steroids and phenanthrene derivatives, their physicochemical properties, and the chromatographic retention. Normal-, reversed-phase and cyano-bonded silica stationary phases were tested with five binary mobile phases (acetonitrile—water, acetonitrile—dimethyl sulfoxide (DMSO), acetonitrile— methanol, acetone—petroleum ether, and acetone—water). The study was based on multiple linear regression, and the results are presented as QSRR equations. Additionally, principal component analysis and cluster analysis were performed. They have been carried out based on retention parameters and molecular descriptors, which were calculated from the optimized structures by use of HyperChem and ChemAxon software. The high correlation coefficients (r), F-values, and low values of the standard deviation indicate that the obtained QSRR equations present well the...

Conductometric studies on complexation of Ag+ cation by C-thiophene calix[4]resorcinarene in pure and mixed non-aqueous solvent systems

The present work relates to the complexation reaction between a new ionophore C-thiophenecalix[4]resorcinarene (C-TC[4]R) with Ag+ cation in pure acetonitrile (ACN), methanol (MeOH), ethanol (EtOH), dimethylformamide (DMF) and dimethylsulfoxide (DMSO) and their binary mixtures by conductometric method. The conductance data showed that the stoichiometry of the complexes formed in pure as well as binary solvent mixtures was 1:1 (Ag+: C-TC[4]R). The stability of C-TC[4]R complexes with Ag+ metal ion was observed to be sensitive to the nature of the solvent system. The results obtained show that the selectivity of C-TC[4]R for Ag+ cation in pure solvents followed the order MeOH > DMF > EtOH > DMSO > ACN. In binary solvent systems, there was a linear change in log K f values for all the binary mixtures (ACN–DMF, ACN–DMSO, MeOH–DMF, EtOH–DMF and EtOH–DMSO) except MeOH–DMSO. The results show that the complexation reactions were spontaneous and entropy (∆S°) as well as enthalpy (∆H°) stabilized in all the solvent systems except EtOH–DMSO, in which the complexes were entropy destabilized. A linear relationship between ΔH° and ΔS° values indicate the existence of entropy–enthalpy compensation in the formation of [Ag–C-TC[4]R]+ complex in all the solvent systems studied.

Conductometric Studies of the Thermodynamics for Complexation of 1,1-Diethyl-3-(4-methoxybenzoyl)thiourea and Cobalt(II) Cation in Aqueous Binary Mixtures of Polar Organic Solvents

The complexation reaction of Co2+ (M) and the 1,1-diethyl-3-(4-methoxybenzoyl)thiourea (L) ligand in the binary mixtures: acetonitrile–dimethylsulfoxide (MeCN–DMSO), acetonitrile–dichloromethane (MeCN–DCM), water–dimethylsulfoxide (H2O–DMSO) and acetonitrile–water (MeCN–H2O), was investigated using a conductometric method at temperatures of (288.15, 298.15, 308.15 and 318.15) K. In all cases, the conductance data showed that the stoichiometry of the neutral complex formed between M and L is 1:3 [M:3L], which indicates that the Co2+ ion was oxidized to Co3+ during the reaction. The best estimate of the stability constant, log10 K f, = 3.31 for the [CoL3] complex, was observed with the MeCN–DCM (20:80 %) binary mixture at 298.15 K. The values of the thermodynamic parameters (i.e., $$ \Delta G_{\text{c}}^{^\circ } $$ and $$ \Delta S_{\text{c}}^{^\circ } $$ ) for the formation of the [CoL3] complex were obtained from the temperature dependence of the stability constant via van’t Hoff plots. The results show that, in most cases, the [CoL3] complexes are enthalpy destabilized but entropy stabilized. The values and signs of the thermodynamic parameters are affected by the nature and composition of the mixed solvents but are independent of the temperature.

Thermodynamics of Na+ Cl− ion – pair association in acetonitrile–dimethyl sulfoxide mixtures

Molecular dynamics simulations of Na+ Cl− ion pairs in acetonitrile–dimethyl sulfoxide mixtures have been performed as a function of salt concentration and the composition of mixtures. Temperature dependence of the potentials of mean force (PMFs) is studied to assess the enthalpy and entropy contributions to the PMFs. Stability of contact ion pair increases with increase in temperature and decreases with the salt concentration. In higher salt concentrations, free energies of contact ion pair formation seem to approach a limiting value. Formation of the ion pairs is governed by the entropy irrespective of concentration of salt and mixture compositions.

A conductivity study of preferential solvation of lithium ion in acetonitrile-dimethyl sulfoxide mixtures

The electrical mobility of LiPF6 in acetonitrile–dimethyl sulfoxide (ACN–DMSO) mixtures, a potential electrolyte in oxygen cathodes of lithium-air batteries, has been studied using a very precise conductance technique, which allowed the determination of the infinite dilution molar conductivity and association constant of the salt in the whole composition range. In the search for preferential Li+ ion solvation, we also measured the electrical conductivity of tetrabutylammonium hexafluorophosphate (TBAPF6), a salt formed by a bulky cation, over the same composition range. The results show a qualitative change in the curvature of the LiPF6 molar conductivity composition dependence for ACN molar fraction (xACN)∼0.95, which was not observed for TBAPF6. The dependence of the measured Li/Li+ couple potential with solvent composition also showed a pronounced change around the same composition. We suggest that these observations can be explained by Li+ ion preferential solvation by DMSO in ACN–DMSO mixtures with very low molar fractions of DMSO.

Effect of the composition of a solution on the enthalpies of solvation of piperidine in methanol-acetonitrile and dimethylsulfoxide-acetonitrile mixed solvents

Heat effects of dissolution of piperidine (ppd) are measured by calorimetry at 298.15 K over the range of composition of acetonitrile-methanol (AN-MeOH) mixed solvents. Based on the ΔsolH○(ppd)AN-MeOH values obtained using the literature data on ΔsolH○ (ppd) in acetonitrile-dimethylsulfoxide (AN-DMSO) mixed solvents and the vaporization enthalpy of ppd, the enthalpies of solvation of amine in AN-MeOH and AN-DMSO binary mixtures are calculated. A rise in the exothermicity of solvation of piperidine is observed upon the transition from AN to DMSO and MeOH, due mainly to the enhanced solvation of the amino group of ppd as a result of changes in the acid-base properties of the mixed solvent.

The influence of composition of acetonitrile-dimethyl sulfoxide solvent on stability of silver(I)-ethylenediamine complexes

The influence of the composition of acetonitrile-dimethyl sulfoxide solvent on shifting complexation equilibrium between silver(I) and ethylenediamine was studied potentiometrically at 298.15 K. The stability of the monoethylenediamine complex with silver(I) was found to increase with increasing acetonitrile content in the mixed solution, while the stability of bis-complexes changes only insignificantly. A decrease in the Gibbs energy of formation of [AgEn]+ ion was found to be caused by resolvation of the monoligand ion and a reduced stability of the solvation complex of silver(I). The Gibbs energy for the second coordination step remained constant due to the mutual compensation for the solvation contributions from all reagents.

Spectroscopic and DFT study of solvent effects on the electronic absorption spectra of sulfamethoxazole in neat and binary solvent mixtures

The solvatochromic behavior of sulfamethoxazole (SMX) was investigated using UV–vis spectroscopy and DFT methods in neat and binary solvent mixtures. The spectral shifts of this solute were correlated with the Kamlet and Taft parameters (α, β and π*). Multiple lineal regression analysis indicates that both specific hydrogen-bond interaction and non specific dipolar interaction play an important role in the position of the absorption maxima in neat solvents. The simulated absorption spectra using TD–DFT methods were in good agreement with the experimental ones. Binary mixtures consist of cyclohexane (Cy)-ethanol (EtOH), acetonitrile (ACN)-dimethylsulfoxide (DMSO), ACN–dimethylformamide (DMF), and aqueous mixtures containing as co-solvents DMSO, ACN, EtOH and MeOH. Index of preferential solvation was calculated as a function of solvent composition and non-ideal characteristics are observed in all binary mixtures. In ACN–DMSO and ACN–DMF mixtures, the results show that the solvents with higher polarity and hydrogen bond donor ability interact preferentially with the solute. In binary mixtures containing water, the SMX molecules are solvated by the organic co-solvent (DMSO or EtOH) over the whole composition range. Synergistic effect is observed in the case of ACN–H2O and MeOH–H2O, indicating that at certain concentrations solvents interact to form association complexes, which should be more polar than the individual solvents of the mixture.

Preparation of a novel potassium ion imprinted polymeric nanoparticles based on dicyclohexyl 18C6 for selective determination of K+ ion in different water samples

This work reports the first application of the ion imprinting technology for determination of potassium ion by precipitation polymerization method. Ion imprinted polymeric (IIP) nanoparticles were prepared by using dicyclohexyl 18C6 (DC18C6) as a K+ ion selective crown ether, in the acetonitrile–dimethylsulfoxide (3:1; v/v) mixture as porogen. The imprint potassium ion was removed from the polymeric matrix using 0.5M HNO3. The scanning electron microscopy (SEM) micrographs showed colloidal nanoparticles of 60–90nm in diameter and slightly irregular in shape. The obtained ion-imprinted particles for K+ showed selective recognition with rapid adsorption and desorption processes. It was found that imprinting results in increased affinity of the material toward K+ ion over other competitor metal ions with the same charge and/or close ionic radius. The synthesized IIP nanobeads were shown to be promising for solid-phase extraction coupled with flame photometry for determination of trace K+ ion in different water samples.

Thermochemistry of the silver(I) complexation with 18-crown-6 ether in binary acetonitrile—dimethylsulfoxide solvents

The effect of acetonitrile-dimethylsulfoxide solvents on the enthalpy of silver(I) complexation with 18-crown-6 ether is studied by means of calorimetry. It is found that an increase in the concentration of dimethylsulfoxide leads to an increase in the reaction exothermicity. It is shown that the determining factor in the change in the reaction enthalpy is the solvation effect of the ligand.

Competitive 7Li NMR study of complexation of different metal ions with tetraethyleneglycol-bis(8-quinolyl) ether in acetonitrile–dimethylsulfoxide and nitromethane–dimethylsulfoxide binary mixtures

7Li NMR spectroscopy was used to determine the stoichiometry and stability of the Li + ion complex with tetraethyleneglycol-bis(8-quinolyl) ether ( L) in acetonitrile–dimethylsulfoxide (97.2:2.8, w/w) and nitromethane–dimethylsulfoxide (97.2:2.8, w/w) binary mixtures. A competitive 7Li NMR spectroscopy was also employed to probe the complexation of Na +, Ag +, Ca 2+, Mg 2+, Zn 2+, Cd 2+, Pb 2+ and UO 2 2+ ions with L in the same solvent systems. The 7Li chemical shift data indicated that all studied cations form 1:1 complexes with the ligand and all the resulting 1:1 complexes in nitromethane–dimethylsulfoxide are more stable than those in acetonitrile–dimethylsulfoxide solution. In both solvent systems, the stability of the resulting complexes was found to vary in the order Ag + > Pb 2+ > Na + > Cd 2+ > Zn 2+ > Li + > Ca 2+ > UO 2 2+ > Mg 2 +.

Extraction and analysis of colourful eggshell pigments using HPLC and HPLC/electrospray ionization tandem mass spectrometry

The literature on the pigments of avian eggshells is critically reviewed. Methods using methanolic sulfuric acid or hydrochloric acid to extract eggshell pigments are unsuitable to detect the occurrence of zinc protoporphyrin or zinc biliverdin because they demetallate these compounds. Extraction methods are described here using EDTA and acetonitrile-acetic acid or acetonitrile-dimethyl sulfoxide, which do not demetallate zinc protoporphyrin. Such extracts were prepared from eggshell of the common nighthawk, Chordeiles minor, and from another six bird species. Protoporphyrin and biliverdin were identified and fully characterized by HPLC/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) in all samples, but none contained zinc protoporphyrin. The zinc complex of biliverdin, claimed to be an additional pigment responsible for eggshell background colours, was labile to EDTA and acid pH and if occurring naturally could not be extracted intact by the published or the modified protocols. An explanation is advanced for the exceptional report that all porphyrins from uroporphyrin to protoporphyrin were found in eggshells of the fowl Gallus domesticus.

Effect of the composition of an acetonitrile-dimethyl sulfoxide solvent on stability of the silver(I) complexes with 18-crown-6 ether

The effect of the composition of an acetonitrile-dimethyl sulfoxide (AN-DMSO) mixed solvent on the stability of silver(I) complexes with 18-crown-6 ether (18C6) is studied by potentiometry. An insignificant increase in the stability of [Ag18C6]+ (0.34 log units) is observed on going from acetonitrile to dimethyl sulfoxide. The effect of solvation on the shift of complex formation equilibrium is considered.

Influence of the composition of acetonitrile-dimethyl sulfoxide solvent on the thermodynamics of silver(I) complexation with piperidine

The influence of the composition of the acetonitrile-dimethyl sulfoxide solvent on the main thermodynamic characteristics (ΔG°, ΔH°, ΔS°) of the complexation between silver(I) and piperidine was studied by the calorimetric and potentiometric methods. Analysis of the obtained experimental material was carried out using the solvation approach based on the thermodynamic solvation characteristics of the reactants.

FT-Raman spectroscopic evidences for the preferential solvation of sodium tetrafluorobrate in acetonitrile-based mixed solvents

Solutions of sodium tetrafluorobrate in acetonitrile–dimethylformamide, and acetonitrile–dimethylsulfoxide mixtures have been studied by FT-Raman spectroscopy for three solvent compositions, respectively. New bands due to solvent molecules in the first solvation shell of Na + were detected in the region of the O C N deformation and CH 3 rocking mode for amide and of the S O and C S stretching modes for sulfoxide. The individual solvation numbers of sodium cation in different environment were deduced. In all the cases, it is found that the sodium ion was preferentially solvated by DMF or DMSO in respective binary solvents. This result was further supported by ab initio calculations.