Acetonitrile-water Mixtures Research Articles

The molecular nature of the eliminating azeotropy in water–acetonitrile system by ionic liquid entrainer using FTIR and DFT calculations

This study focused on investigating the structure and hydrogen-bonding characteristics of 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc])-water-acetonitrile mixtures aiming at revealing the molecular intrinsic of the azeotropy breaking by ionic liquid entrainer. Our approach combined FTIR with density functional theory (DFT) calculations applying the CN stretching vibration region as the responsive indicator of the microenvironment to discern the structural and hydrogen-bonding properties of the H2O‒CH3CN and [EMIM][OAc]‒CH3CN binary systems and [EMIM][OAc]−H2O−CH3CN ternary systems. Distinct interaction models were observed between [EMIM][OAc] and CH3CN compared to those in water and CH3CN system, leading to different influences on the CN stretching vibration region. Excess peaks associated with H2O−CH3CN, CH3CN self-aggregator, and IL−CH3CN interaction complexes were identified. The interaction strength between [EMIM][OAc] and CH3CN was notably more potent than that between water and CH3CN. Consequently, IL had the ability to disrupt the interaction complex of water-acetonitrile with the formation of the IL−CH3CN complex. This species transformation during the mixing process elucidated the characteristics of phase equilibrium shift in the azeotrope system.

Understanding the relationship between preferential interactions of peptides in water-acetonitrile mixtures with protein-solvent contact surface area.

The influence of polar, water-miscible organic solvents (POS) on protein structure, stability, and functional activity is a subject of significant interest and complexity. This study examines the effects of acetonitrile (ACN), a semipolar, aprotic solvent, on the solvation properties of blocked Ace-Gly-X-Gly-Nme tripeptides (where Ace and Nme stands for acetyl and N-methyl amide groups respectively and X is any amino acid) through extensive molecular dynamics simulations. Individual simulations were conducted for each peptide, encompassing five different ACN concentrations within the range of χACN = 0.1-0.9. The preferential solvation parameter (Γ) calculated using the Kirkwood-Buff integral method was used for the assessment of peptide interactions with water/ACN. Additionally, weighted Voronoi tessellation was applied to obtain a three-way data set containing four time-averaged contact surface area types between peptide atoms and water/ACN atoms. A mathematical technique known as N-way Partial Least Squares (NPLS) was utilized to anticipate the preferential interactions between peptides and water/ACN from the contact surface areas. Furthermore, the temperature dependency of peptide-solvent interactions was investigated using a subset of 10 amino acids representing a range of hydrophobicities. MD simulations were conducted at five temperatures, spanning from 283 to 343K, with subsequent analysis of data focusing on both preferential solvation and peptide-solvent contact surface areas. The results demonstrate the efficacy of utilizing contact surface areas between the peptide and solvent constituents for successfully predicting preferential interactions in water/ACN mixtures across various ACN concentrations and temperatures.

Automatic immunomagnetic beads cleanup and isotope dilution-based liquid chromatography tandem mass spectrometry for the determination of aflatoxins in feed and feedstuff

In this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method based on immunomagnetic bead cleanup and isotope dilution was established for the simultaneous detection of four aflatoxins (aflatoxins B1, B2, G1, and G2) in feed and feedstuff. The samples were extracted with an acetonitrile–water mixture (84 + 16, v/v), purified using automatic immunomagnetic beads, and detected by LC-MS/MS. Under the optimal LC-MS/MS conditions, the four mycotoxins had a linear relationship in the concentration range of 0.5–50 µg/kg, and the correlation coefficients were all greater than 0.99. The limits of detection of the four aflatoxins ranged from 0.075–0.17 µg/kg, and the limits of quantification ranged from 0.25–0.5 µg/kg. The average spike recoveries of the four common feed and feedstuff matrices (corn, soybean meal, pig compound feed, and chicken compound feed) at three spiked levels (2, 10, and 50 µg/kg) ranged from 80.8–118.3 %, and the relative standard deviations (RSDs) were all less than 7.80 %. Thirty-two actual feed samples were analyzed for the four aflatoxins. Aflatoxin B1 was detected in nineteen samples (0.11–6.39 µg/kg); aflatoxin B2 was detected in four samples (0.12–0.43 µg/kg); aflatoxin G1 was detected in four samples (0.19–0.57 µg/kg), and aflatoxin G2 was not detected. The immunomagnetic beads cleanup system could automatically remove each of the four aflatoxins in feed and feedstuff and realize batch sample processing in 20 min. The established LC-MS/MS method has high accuracy and repeatability, and it can be used for the rapid and simultaneous determination of four aflatoxins in feed samples.

Four new diarylheptanoids and two new terpenoids from the fruits of Alpinia oxyphylla and their anti-inflammatory activities

Four previously unreported diarylheptanoids (1a/1b-2a/2b), one undescribed sesquiterpenoid (8), one new diterpenoid (12), and twelve known analogs were isolated from the fruits of Alpinia oxyphylla. The structural elucidation of these compounds was achieved through a comprehensive analysis of spectroscopic data, single-crystal X-ray diffraction, electronic circular dichroism (ECD), and modified Mosher's method. Enantiomeric mixtures (1a/1b, 2a/2b, 3a/3b, 4a/4b, and 5a/5b) were separated on a chiral column using acetonitrile-water mixtures as eluents. Among them, compounds 3a/3b and 4a/4b were isolated as optically pure enantiomers in the initial chiral separation. Furthermore, most of the isolates were evaluated for their inhibitory effects against the production of nitric oxide (NO) and interleukin-6 (IL-6) in lipopolysaccharide (LPS)-induced RAW264.7 macrophages. Interestingly, 2 and 4 showed significant inhibitory activities against NO production with IC50 values of 33.65 and 9.88 μmol·L-1 (hydrocortisone: IC50 34.26 μmol·L-1), respectively. Additionally, they also partially reduced the secretion of IL-6.

Extractive distillation using salt-based deep eutectic solvent as entrainer for separating acetonitrile-water mixture

Salt-based deep eutectic solvents (DESs) have been proposed in this work for the separation of the azeotrope of acetonitrile and water (H2O). The vapor–liquid equilibrium experiments indicated that (ChCl:U:CaCl2)1:2:0.36 exhibits an higher selectivity among all of the entrainers investigated and eliminates the azeotropic point of acetonitrile and water mixture. Moreover, the calculated values by NRTL model coincide well with the experimental data for the systems (acetonitrile + H2O + (ChCl:U:CaCl2)1:2:0.36). Based on the thermodynamic study, the conceptual process design was established to evaluate the competitiveness of the suggested entrainers for the separation of acetonitrile and water. It was determined that the thermodynamic efficiency (η) in the extractive distillation (ED) process utilizing the new salt-based DESs entrainers increases 60.31 % compared with the benchmark entrainer ethylene glycol (EG). Conversely, the ED process using (ChCl:U:CaCl2)1:2:0.36) entrainer can reduce the total annual cost (TAC) by about 7.81 % and the CO2 emissions (ECO2) by 14.74 %. The ED process using (ChCl:U:CaCl2)1:2:0.36) as entrainer shows the high energy efficiency, low economy cost and low CO2 emissions with a great industrial application prospect when compared to the bench marked process.

Analysis of the separation of acetonitrile-water mixture

Analysis of the separation of acetonitrile-water mixture

Comparison between acetonitrile-water separation by betaine and betaine hydrochloride

Acetonitrile and water are miscible solvents. This study compares their separation by betaine and betaine hydrochloride. Acetonitrile is a hydrogen (H) bond acceptor and so is betaine, because of its -CO and -CO- groups. Therefore, betaine competes with acetonitrile for interactions with the hydrogens of water molecules, as indicated by attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR). Therefore, when added to acetonitrile-water mixtures, betaine displaces acetonitrile. Separation into bulk phases occurs with 5–10 wt% betaine (relative to water), for acetonitrile concentrations between 50 and 80 wt% (relative to the aqueous phase). At lower acetonitrile concentrations (e.g., 1 wt%), betaine separates acetonitrile from water to yield emulsified acetonitrile droplets, detected by light scattering. With 1 wt% acetonitrile and betaine, acetonitrile droplets in water are negatively charged due to the -CO- group of betaine, as shown by electrophoretic measurements. In the case of betaine hydrochloride, the negative charge of the -CO- group is shielded by a proton, and interactions with water are weaker. As a result, bulk separation is not observed. Nonetheless, betaine hydrochloride also competes against acetonitrile for interactions with hydrogen atoms of water molecules, albeit not as effectively as betaine. This is shown by ATR-FTIR. Therefore, betaine hydrochloride emulsifies acetonitrile in water into sub-micron droplets. These droplets are positively charged, owing to the positively charged nitrogen atom of betaine hydrochloride. Acidifying mixtures of betaine, acetonitrile and water (with HCl) impedes bulk separation. This result confirms the importance of electrostatic interactions between the hydrogens of water and the unshielded, negative -CO- group of betaine.

Determination of ionization/protonation constant values of some guanine derivative drugs by traditional/ green RPLC and UV–Vis spectrophotometric methods

In this study, the greenreverse-phase liquid chromatography (RPLC) method was used in addition to the traditional RPLC method to determine the ionization/protonation constants (pKa) of the guanine derivatives ganciclovir, valacyclovir, and valganciclovir. The determination of these values was carried out in binary acetonitrile–water mixtures (for the traditional RPLC method), ethanol–water binary mixtures (for the green RPLC method), and in aqueous solution of a micelle-forming surfactant (for pure micellar chromatography). The pKa values sspKa of the compounds were calculated using the linear solvation energy relationship (LSER) method in the studied hydro-organic and micellar solvent-free mixtures. Moreover, the UV–Vis spectrophotometric method was used to compare the sspKa values of ganciclovir, valaciclovir, and valganciclovir obtained in a acetonitrile–water medium using another method. The pKa values ​​of the examined compounds in water were calculated using the linear relationship between the sspKa values ​​determined in hydroorganic mixtures and some macroscopic values ​​of acetonitrile and ethanol. Additionally, wwpKa values ​​were determined in the micellar solvent-free mobile phase. Subsequently, the wwpKa values calculated by these direct and indirect methods were compared and the agreement between them was excellent. By using the wwpKa value calculated for each compound, the ionization percentages were calculated at different pH (1–12) values with the Henderson-Hasselbalch equation. The environmental impact of the RPLC methods used in this study was assessed using the green metrics tools GAPI and AGREE. The result of the investigation was that the environmental suitability of the green methods is satisfactory.

Revisiting Textbook Azide-Clock Reactions: A "Propeller-Crawling" Mechanism Explains Differences in Rates.

An ongoing challenge to chemists is the analysis of pathways and kinetics for chemical reactions in solution, including transient structures between the reactants and products that are difficult to resolve using laboratory experiments. Here, we enabled direct molecular dynamics simulations of a textbook series of chemical reactions on the hundreds of ns to μs time scale using the weighted ensemble (WE) path sampling strategy with hybrid quantum mechanical/molecular mechanical (QM/MM) models. We focused on azide-clock reactions involving addition of an azide anion to each of three long-lived trityl cations in an acetonitrile-water solvent mixture. Results reveal a two-step mechanism: (1) diffusional collision of reactants to form an ion-pair intermediate; (2) "activation" or rearrangement of the intermediate to the product. Our simulations yield not only reaction rates that are within error of experiment but also rates for individual steps, indicating the activation step as rate-limiting for all three cations. Further, the trend in reaction rates is due to dynamical effects, i.e., differing extents of the azide anion "crawling" along the cation's phenyl-ring "propellers" during the activation step. Our study demonstrates the power of analyzing pathways and kinetics to gain insights on reaction mechanisms, underscoring the value of including WE and other related path sampling strategies in the modern toolbox for chemists.

Non-destructive chromatographic determination of surface area in reverse phase chromatographic columns

One of the critical but underutilized parameters that affect chromatographic separation is an adsorbent surface area (S.A.). We introduce a concept of direct determination of the total surface area of chromatographic columns by utilizing a nondestructive measurement of eluent component excess adsorption isotherm measurement and the application of the Standard Excess Adsorption Isotherm from acetonitrile-water and methanol-water binary mixtures for direct determination of the S.A. in chromatographic columns. This nondestructive technique was used to determine the surface area of five commercial columns, including three core-shell particle type columns (Kinetex-C18, Ascentis C18, and Hallo C18) and in-housemade C18 columns. The traditional low-temperature nitrogen adsorption (LTNA) technique was compared to the novel chromatographic method of nondestructive surface area determination for adsorbents modified with octadecylsilanes. The chromatographically determined surface area was in good agreement with the conventional techniques for all columns used. The difference between the three techniques is less than 10%. Columns were characterized in terms of adsorbent geometry (e.g., pore volume, column void volume, interparticle volume), ligands bonding density, and the amount of the packing material in a chromatographic column.

The method of determination for 2, 3-Butanedione in the air of workplace by high performance liquid chromatography with derivatization

Objective: To establish a method for the determination of 2, 3-Butanedione (BUT) in the air of workplace, which including the process of collection by absorption in phosphoric acid aqueous solution and the process of analysis and detection by high performance liquid chromatography with derivatization. Methods: In October 2022, a porous glass plate absorption tube containing 10 ml of 0.01% phosphoric acid solution was used to collect BUT in the air of the workplace at a flow rate of 0.2 L/min. The absorption solution was derived by 2, 4-dinitrophenylhydrazine for 75 min and separated on a SB-C18 column (250 mm×4.6 mm, 5 μm) . At the column temperature of 30 ℃, the mixture of acetonitrile-water (V∶V, 1∶1) was eluted at the flow rate of 1.0 ml/min. It was detected by UV detector (λ=365 nm) , qualitatived by retention time and quantitatived by external standard. Results: It showed that BUT in phosphoric acid aqueous solution could be stored for at least 7 d at 4 ℃. There was a linear relationship within the determination range of 0.05-6.00 μg/ml, the linear regression equation was y=89.610x+0.133, r=0.9999. The sampling absorption efficiencies were 98.33%-100.00%, the detection limit of the method was 0.005 μg/ml, the minimum detection concentration was 0.016 mg/m(3) (based on V(0)=3.0 L) . The recovery rates were 95.96%-102.44%, the intra batch precision were 4.36%-7.78%, and the inter batch precision were 4.96%-6.06%. Conclusion: The method has the advantages of simple operation, high sensitivity and good accuracy. It can prevent the loss and degradation of BUT. It can be used for the determination of BUT in the air of workplace.

Quantification of Arbortristoside-A isolated from Nyctanthes arbor-tristis using HPLC: Method development and pharmaceutical applications

Arbortristoside-A (Arbor-A) is a naturally occurring iridoid glycoside and herbal-based lead molecule with proven medicinal potential. Aiming at the development of an efficient analytical tool for the quantification of Arbor-A in pharmaceutical dosage forms, in the presented work, we developed an economical, fast, and sensitive RP-HPLC-UV method and validated the procedure as per the ICH guidelines, Q2(R1). The chromatographic separation was accomplished under the optimised experimental conditions using an HPLC system with an LC-2010 autosampler, a PDA detector, and a Phenomenex C18 column with the mobile phase composed of a 70:30 (v/v) water-acetonitrile mixture eluting isocratically at a flow rate of 1 mL/min at ambient temperature, and UV detection at 310 nm. Arbor-A showed a sharp peak at the retention time of 5.60 min and exhibited linearity (R2 = 0.9988) with LOD and LOQ of 0.50 μg/mL and 1.50 μg/mL, respectively. The accuracy of the method was 98.33–101.36 % with acceptable intra-day and inter-day precisions as well as robustness (<2% RSD). To ratify the applicability of the presented approach in emerging pharmaceuticals, a nanoformulation loaded with Arbor-A was designed and analysed utilising the provided methodology. The method has also enabled to determine the degradation kinetics of Arbor-A under stress conditions, etcetera, employing forced degradation and short term stability studies.

Phosphonate-substituted porphyrins as efficient, cost-effective and reusable photocatalysts.

Recent advances in visible light photocatalysis represent a significant stride towards sustainable catalytic chemistry. However, its successful implementation in fine chemical production remains challenging and requires careful optimization of available photocatalysts. Our work aims to structurally modify bioinspired porphyrin catalysts, addressing issues related to their laborious synthesis and low solubility, with the goal of increasing their efficiency and developing reusable catalytic systems. We have demonstrated the catalytic potential of readily available meso-tetrakis[4-(diethoxyphosphoryl)phenyl]porphyrins (M(TPPP)). Novel metal (Pd(II), Co(II) and In(III)) complexes with this ligand were prepared in good yields. These chromophores were characterized in solution using spectroscopic (NMR, UV-vis, fluorescence) and electrochemical methods. The introduction of phosphonate groups on the phenyl substituents of meso-tetraphenylporphyrins (M(TPP)) improves solubility in polar organic solvents without significantly altering the photophysical properties and photostability of complexes. This structural modification also leads to easier reductions and harder oxidations of the macrocycle for all investigated complexes compared to the corresponding TPP derivatives. The free base porphyrin, zinc(II), palladium(II), and indium(III) complexes were studied as photocatalysts for oxidation of sulfides to sulfoxides using molecular oxygen as a terminal oxidant. Both dialkyl and alkyl aryl sulfides were quantitatively transformed into sulfoxides under blue LED irradiation in the acetonitrile-water mixture (10 : 1 v/v) with a low loading (0.005-0.05 mol%) of porphyrin photocatalysts, where H2(TPPP) and Pd(TPPP) were found to be the most efficient. The reaction mechanism was studied using photoluminescence and EPR spectroscopies. Then, to access reusable catalysts, water-soluble derivatives bearing phosphonic acid groups, H2(TPPP-A) and Pd(TPPP-A), were prepared in high yields. These compounds were characterized using spectroscopic methods. Single-crystal X-ray diffraction analysis of Pd(TPPP-A) reveals that the complex forms a 3D hydrogen-bonded organic framework (HOF) in the solid state. Both H2(TPPP-A) and Pd(TPPP-A) were found to catalyze the photooxidation of sulfides by molecular oxygen in the acetonitrile-water mixture (1 : 1 v/v), while only Pd(TPPP-A) resulted in selective production of sulfoxides. The complex Pd(TPPP-A) was easily recovered through extraction in the aqueous phase and successfully reused in five consecutive cycles of the sulfoxidation reaction.

Determination of 2,4-dimethylhydroxybenzene by chromatographic methods in forensic toxicological research of biological material

Is to develop a method for determining 2.4-dimethylhydroxybenzene (2.4-DMHOB) in biological material. The analytical methods used in the experiments were extraction, column chromatography of normal pressure, TLC, GC-MS and HPLC. To extract the analyte from the bioactive matrix, maceration with the binary insulating agent acetone-ethyl acetate (3:7) was used, observing the 2:1 mass ratio of the «insulating agent-matrix». Optimal conditions of semi-preparative analyte chromatography were achieved in column (150×10 mm) of «Silasbor» S-18 sorbent in elution with a mixture of acetonitrile-water (7:3), which was used in the proposed cleaning scheme, combining extraction and reversed-phase column chromatography. The application of the mobile phase of tetrachloromethane-dioxane (9.5:0.5) has been substantiated for the selective determination of 2.4-DMHOB by TLC («Sorbfil» plates). The expediency of confirming identification of the analyte in the form of 2.4-dimethyltrymethylsilylphenol using GC-MS (DB-5MS EVIDEX column (25.000×0.2 mm), stationary phase (5%-phenyl)-methylpolysiloxane, carrier gas - helium) has been shown. The group of characteristic particles in the mass spectrum of trimethylsilyl analyte derivative was represented by 45; 59; 73; 82; 91; 105; 119; 135; 149; 163; 179; 194 m/z ions. HPLC (Discovery C18 250×4.6 mm column, eluting liquid - acetate buffer solution with pH 5.5 - acetonitrile, 50:50) was used to confirm the identification and quantification of 2.4-DMHOB. A method for determining 2.4-DMHOB by the HPLC method in biological material (liver tissue) is proposed, which corresponds to the criteria of linearity, selectivity, accuracy, precision and stability. The minimum detectable quantity of 2.4-DMHOB in the bioactive matrix is 0.5 µg/g, the minimum determined quantity is 1.2 ug/g.

Dinuclear tricarbonylrhenium(I) complexes: impact of regioisomerism on the photoluminescence properties.

Dinuclear Re(I) complexes have proportionally been much less studied than mononuclear analogues. In particular, very little information is available about their solid-state emission properties. In this work, two structural isomers of dinuclear complexes (Bi-Re-metaPhe and Bi-Re-paraPhe), which differ by the relative position of the coordination spheres on a central phenyl ring, were synthesized and compared with each other and with the parent mononuclear compound (Mono-Re-Phe), from a theoretical and experimental point of view. In solution, the electronic, electrochemical and spectroscopic properties of the dinuclear complexes were almost identical, and rather close to those of the monomer. In the solid state, the photoluminescence (PL) efficiency of dimers was not higher than that of the monomer, but a clear mechanoresponsive luminescence (MRL) effect appeared only for the former ones. The positional isomerism influenced the amplitude of this effect, as well as the aggregation-induced emission (AIE) properties in a water-acetonitrile mixture. This study reveals the importance of positional isomerism to modulate the emission properties in the solid state. It also shows the advantage of dinuclear structures to access new MRL-active materials.

Ultra-clean pure shift NMR with optimal water suppression for analysis of aqueous pharmaceutical samples.

Pure shift NMR experiments greatly enhance spectral resolution by collapsing multiplet structures into singlets and, with water suppression, can be used for aqueous samples. Here, we combine ultra-clean pure-shift NMR (SAPPHIRE) with two different internally encoded water suppression schemes to achieve optimal performance for small molecule and macrocyclic peptide pharmaceuticals in water and acetonitrile-water mixtures.

Electrochemical water oxidation reaction by dinuclear Re(V) oxo complexes with a 1,4-benzoquinone core via the redox induced electron transfer (RIET) process.

We report two dinuclear rhenium(V) oxo complexes 1 and 2 types, [ReV(O)(Cl)3(L2-)ReV(O)(Cl)3][NBu4]2 (1, L2- = dianionic 2,5-dihydroxy 1,4-benzoquinone (DBQ2-)) and (2, L2- = dianionic chloranilic acid (CA2-) ligands), as a homogeneous electrocatalyst for water oxidation reactions in the acetonitrile-water mixture. The evolution of dioxygen gas at the anode was confirmed by a GC-TCD study. In controlled potential electrolysis (CPE), oxidation at 1.30 V (vs. Ag/AgCl) at neutral pH, 1 and 2 afforded 1+ [ReVI(O)(Cl)3(DBQ˙3-)ReVI(O)(Cl)3]- and 2+ [ReVI(O)(Cl)3(CA˙3-)ReVI(O)(Cl)3]- ions, respectively, via the redox induced electron transfer (RIET) process. Electrochemically generated species of 1+ and 2+ could be isolated in dry acetonitrile. 1+ and 2+ ions give strong EPR signals in fluid solution as well as under frozen glass conditions due to the [ReVI(O)(Cl)3(L˙3-)ReVI(O)(Cl)3]- ↔ [ReVI(O)(Cl)3(L2-)ReV(O)(Cl)3]- (where L2- = DBQ2- and CA2-) equilibrium. However, the continuation of the CPE study (1.30 V vs. Ag/AgCl) in the presence of acetonitrile-water mixture oxidised the in situ generated species of 1+ and 2+ to higher valent ReVIO species. These species (1+ and 2+) bound water through the water nucleophilic attack (WNA) to produce peroxide intermediate species of [ReV(OOH)(Cl)3(DBQ2-)ReV(OOH)(Cl)3] (A1) and [ReV(OOH)(Cl)3(CA2-)ReV(OOH)(Cl)3] (A2) for catalysts 1 and 2, respectively. Interestingly, A1 and A2 were authenticated and analysed by ESI mass spectrometry and infrared spectroscopy and were the active precursors of this water oxidation process. The extent of current generation under similar conditions suggested that complex 1 is superior to complex 2 for the water oxidation reaction. Notably, the maximum turnover frequency (TOFmax) of catalysts 1 and 2 were 2.1 and 1.6 s-1 at 0.27 V and 0.24 V over potential, respectively, which is very significant in WOR.

Isotopic internal standard correction for the determination of diludine residue in animal-derived matrix samples using enhanced matrix removal-lipid clean-up combined with ultra-performance liquid chromatography-tandem mass spectrometry

A robust method has been established for the successfully determination of diludine (DHP) levels in animal-derived matrix samples, utilizing enhanced matrix removal-lipid clean-up (EMR-lipid) combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC–MS/MS). DHP-13C4 was employed as an isotopically labeled internal standard to estimate the recovery, matrix effect, and process efficiency. The water-acetonitrile mixture was utilized to extract the edible tissues (muscle, fat, kidney, and liver) of cattle and chicken, while the salting out method was employed for extracting egg and milk. The extracts were then mixed with water and acetonitrile to a constant volume, and subjected to clean-up via cartridge. Subsequently, the analytes were transferred onto a reversed-phase C18 analytical column and quantified by triple-quadrupole tandem mass spectrometry in multiple-reaction monitoring mode. Quantification was accomplished using a solvent calibration curve in conjunction with an internal standard method. The proposed method showed good linearity in the range of 0.5–50 ng mL−1 (R2 ≥ 0.999), high sensitivity (the limit of detection was 2.5 μg kg−1, and the limit of quantification was 5 μg kg−1), a high spiked recovery rate (between 82.6% and 109.4%), and repeatability (the relative deviation within the batch and the relative deviation between batches were ≤ 7.5%).

Simple and robust LC–MS/MS method for quantification of colistin methanesulfonate and colistin in human plasma for therapeutic drug monitoring

A rapid, simple, and robust LC–MS/MS method was developed and validated for the quantitation of colistin and colistin methanesulfonate (CMS) in human plasma. The method also prevented overestimation of colistin concentration by establishing the stability of CMS under sample preparation conditions, including blood and plasma storage conditions. Polymyxin B1 was used as an internal standard, and positive-ion electrospray ionization in multiple reaction monitoring mode was used for quantification. Chromatographic separation was achieved using a Zorbax eclipse C18 column (3.5 µm, 2.1 mm i.d. × 100 mm), with a flow rate of 0.5 mL/min, 5 μL injection volume, and gradient elution with a mixture of acetonitrile-water (containing 0.1 % trifluoroacetic acid). The method had a quantifiable range of 0.043–8.61 and 0.057–11.39 μg/mL for colistin A and B in human plasma, respectively, under a total runtime of 6.0 min. Further, it demonstrated appropriate extraction efficiency, no significant interference from co-eluting endogenous compounds, and satisfactory intraday and interday precision and accuracy. The proposed procedure for sample preparation successfully addressed the issue of CMS instability, consequently diminishing the probability of overestimating the concentration of colistin. Therefore, this simple and robust LC-MS/MS method for CMS and colistin quantification in human plasma is a valuable tool for clinicians to accurately monitor colistin treatment in patients with infections caused by multidrug-resistant (MDR) Gram-negative bacteria.

Synthesis of Cu (II) and Zn (II) Complexes of a Quinoline Based Flexible Amide Receptor as Fluorescent Probe for Dihydrogen Phosphate and Hydrogen Sulphate and Their Antibacterial Activity.

A novel 8-hydroxy quinoline-derived amide receptor, in conjunction with its Cu (II) and Zn (II) complexes, has been strategically developed to function as remarkably efficient fluorescent receptors with a distinct capability for anion sensing. The comprehensive characterization of the synthesized compounds were achieved through UV-Vis, IR, NMR, and HRMS spectroscopic techniques. Among the Cu (II) and Zn (II) complexes, the latter exhibits superior selectivity for anions, specifically dihydrogen phosphate and hydrogen sulfate, as their tetrabutylammonium salts in a 9:1 acetonitrile-water (v/v) mixture. The Cu (II) complex demonstrates enhanced anion binding compared to the amide ligand, albeit with reduced selectivity. Furthermore, the affinity was evaluated using the Benesi-Hildebrand plot. The binding constants and Limit of Detection (LOD) for both complexes were precisely quantified. The Job plot illustrates a clear 1:1 binding interaction between the metal complexes and the guest anions. Significantly, both metal-complex receptors display a broad spectrum of antibacterial activity, against both gram-positive and gram-negative bacteria. It is worth highlighting that the Zn (II) complexed receptor outperforms the Cu (II) complexed receptor, as evidenced by its considerably lower Minimum Inhibitory Concentration (MIC) value against both bacterial strains.