Acetonitrile Content Research Articles

Evaluation of the Adsorption-Accessible Surface Area of MIL-53(Al) using Cannabinoids in a Closed System.

Cannabinoids are important industrial analytes commonly assayed with high-pressure liquid chromatography (HPLC). In this study, we evaluate the suitability of MIL-53(Al), a commercially available metal-organic framework (MOF), as a stationary phase for cannabinoid separations. The suitability of an MOF for a given separation is hypothesized to be limited by the ability of a given molecule to enter the pore of the MOF. To evaluate the extent of possible adsorptive interactions between cannabinoids and the interior surface area of MIL-53(Al), the radii of gyration (Rg) and solvent-accessible surface areas were calculated for three cannabinoids, namely, cannabidiol, cannabinol, and Δ9-tetrahydrocannabinol, as well as the MOF. These values were used to calculate the theoretical adsorption capacity of the MOF, using four competing adsorption models. The Rg of cannabinoids (4.1 Å) is larger than one MOF pore aperture dimension (4.0 × 5.0 Å). The adsorption capacity was measured by relating a decrease in the cannabinoid concentration in acetonitrile when exposed to 100 mg of MOF. The cannabinoid uptake by the MOF was estimated using the relative standard deviation (RSD) of the soaking solution assay, as the decomposition-corrected RSD as uptake (DCRU). The DCRU was calculated as 0.007 ± 0.004 μgcannabinoids/mgMOF. These findings indicate that most of the MOF surface area was inaccessible for adsorption by cannabinoids due to size-exclusion effects. The implication of this work is that the suitability of an MOF for adsorptive separations, such as liquid chromatography, must have an upper limit for the size of the analyte. Additionally, MOFs may generally be more suitable for separations in the gas phase, where adsorbates are not hindered by the presence of a solvation shell.

Interaction behaviour of acetonitrile in the presence of acetylacetone: FTIR studies and DFT calculations

ABSTRACT FTIR spectral signatures of acetonitrile (AN), acetylacetone (AcAc) and their binary solutions at various mole fractions of AN/AcAc have been recorded to investigate the interaction of AN with AcAc. In the binary solutions, the intensity of AN stretching bands gets reduced much while that of the AcAc bands suffer minor changes. AN dimers dissociate into monomers even in the binary solution with the AcAc concentration of one fourth of AN concentration. The gets red-shifted and remain more or less at the same wavenumber in all the solutions. The nature of shift in AN bands shows that AN – AcAc non-classical H – bonds are weaker than AN – AN interactions. The red shift in is the indication of formation of H – bonds which are stronger than interactions. Using DFT calculations, the interactions in the 1:1 complexes have been analysed.

Development of liquid chromatographic and UV-visible spectrophotometric methods for determination of pKa values of folic acid antimetabolites

In this study, the values of ionization/protonation constants (pKa) of pemetrexed and raltitrexed, which are folic acid antimetabolites, were determined by reversed-phase liquid chromatography (RPLC) and UV-visible spectrophotometric methods at 25 °C. The pKass values were evaluated by retention time (tR) in binary acetonitrile-water mixtures with acetonitrile (ACN) contents of 13%, 15%, 17% and 20% (v/v) for the RPLC method and 13%, 15% and 17% (v/v) for the spectrophotometric method. The aqueous pKa values (pKaww) of the studied compounds were calculated from the pKass value using the macroscopic parameters (mole fraction and dielectric constant), which play an important role in solvent properties. In addition, the degree of ionization of pemetrexed and raltitrexed was calculated using the pKaww values.

Utilization of Experimental Design for the Establishment and Optimization of RP-HPLC Method for the Estimation of Two Selective Serotonin Reuptake Inhibitors/benzodiazepines Combinations in the Presence of their Related Compounds

Background: Design of experiment (DOE) is considered the most powerful tool to identify factors that affect variation and improve the response by tuning these factors. In the present work, DOE was applied to establish an innovative, sensitive and precise HPLC method for the simultaneous determination of Escitalopram oxalate, Paroxetine hydrochloride hemihydrate and Clonazepam in presence of their related compounds in drug substance and drug products. Methods: Buffer molarity, % organic modifier (acetonitrile content) at the beginning/end of the gradient, flow rate at the beginning/end of the gradient, pH of the mobile phase, and column temperature were screened using Plackett-Burman design (PBD) model. The main effect plot showed that % organic modifier at the beginning/end of gradient and flow rate at the beginning of gradient were statistically significant variables influencing peaks resolution (p<0.05). Box-Behnken design (BBD) was then used as an optimization model in order to achieve the highest possible resolution with the least possible experimental trials through studying the interaction and quadratic effects of these three factors. Finally, the optimum condition for predicated peak resolution could be achieved by the desirability function. Results: After optimization, chromatographic separation was attained on Agilent Zorbax SB C18 (4.6×250mm, 5µm) column using gradient elution of mobile phase: (A) potassium dihydrogen phosphate (pH 2.7; 0.025M) and (B) acetonitrile at ambient column temperature with the last eluted compound at less than 17 min. The flow rate was maintained at 1/2.3 mLmin-1 with UV detection at 245/210 nm using time programming. Conclusion: The optimized chromatographic method was used for stability indicating assay of the cited drugs in presence of their related compounds according to ICH Q2R1 guidelines.

Chromatographic method development for the simultaneous assay of pseudoephedrine hydrochloride and chlorphenamine maleate in oral dosage formulations

Common cold medicines usually present as multi-component products and constitute one of the largest groups of ‘over-the-counter’ medicines marketed in Ghana. Due to their wide patronage and easy accessibility, their quality control is of utmost importance to medicine consumers. In this study, the Design of Experiment (DOE) concept is adopted to develop a chromatographic method for the simultaneous assay of pseudoephedrine hydrochloride and chlorphenamine maleate in commercially available products. The separation of the drugs was achieved on an Agilent Eclipse Plus C18 analytical column (4.6 × 150 mm; 5 µm) and detected at 252 nm, while maintaining column temperature at 30 oC. The method parameters, including acetonitrile concentration in the mobile phase, mobile phase pH and flow rate were optimized using a Central Composite Design study, while monitoring the method attributes, asymmetric factors, selectivity, retention times, and resolution. The outcome showed a good correlation between experimental and predictive values throughout the modeled Design Space, with a Desirability of 1.000. The conditions optimized included a mobile phase containing acetonitrile, 50 mM aqueous acetate buffer solution (pH = 3.19) and triethylamine (15.34:84.65:0.01 v/v/v), and a flow rate of 1.437 mL/min. The method was then validated following the International Council for Harmonization Q2(R) guidelines to establish linearity and range, accuracy, precision, robustness, and stability of the test solution. The developed method was successfully applied to estimate pseudoephedrine hydrochloride and chlorphenamine maleate contents in single and fixed-dose formulations commercially available (N = 38).

Characterization and applications of a trioctyl(3/4-vinylbenzyl)phosphonium stationary phase for use in capillary liquid chromatography

The morphology, composition, and selectivity of a silica-based monolithic stationary phase, grafted by a layer of trioctyl(3/4-vinylbenzyl)phosphonium chloride ([P888VBn]Cl), is presented. The results of elemental analysis confirmed that the prepared stationary phase contains 38.8 at.% of silicon, 60.2 at.% of carbon, and 1.0 at.% of phosphorus. Capillary columns (150 × 0.1 mm) for liquid chromatography were evaluated using alkylbenzenes, monosubstituted benzenes, polyaromatic compounds, substituted benzene regioisomers, and aromatic carboxylic and amino acids. The prepared ionic liquid (IL)-based stationary phase exhibits hydrophobic, hydrophilic, and electrostatic interactions, as confirmed by experiments on the evaluation of the effect of the mobile phase composition (content of acetonitrile and ammonium formate) on the isocratic chromatographic separation. Thus, the IL-based capillary column demonstrates a unique separation selectivity compared to Phenyl-, C8-, and C18-stationary phases, and high efficiency for an expanding number of structurally diverse compounds.

Development and Validation of HPLC-DAD Method with Pre-Column PMP Derivatization for Monomeric Profile Analysis of Polysaccharides from Agro-Industrial Wastes.

The instrumental analysis of complex mixtures of sugars often requires derivatization to enhance the method’s selectivity and sensitivity. 1-Phenyl-3-methyl-5-pyrazolone (PMP) is a common sugar derivatization agent used in high-performance liquid chromatography (HPLC). Although many C18 column applications for PMP–sugar derivative analysis have been developed, their transferability is not straightforward due to variations in column chemistry and preparation technology. The aim of this study was to develop and validate an application for Zorbax Extend C18 columns for the analysis of 8 neutral and 2 acidic sugars commonly found in plant polysaccharides. The method was further compared to well-established alditol acetates and m-hydroxydiphenyl methods and employed for sugar profiling of selected agro-industrial wastes. The most influential separation factors were the mobile-phase pH and acetonitrile content, optimized at 8.0 and a 12–17% gradient, respectively. The method showed excellent linearity, repeatability and intermediate precision. High sensitivity was achieved, especially for neutral sugars, with an accuracy error range of 5–10% relative standard deviation. The sugar profiling results were highly correlated to the reference method for neutral sugars. The HPLC method was highly applicable for the evaluation of polysaccharides in selected wastes and showed advantages in terms of simplicity, accuracy in acidic sugar determination and suitability for their simultaneous analysis with neutral sugars.

Modification of magnetite-doped NH2-MIL-100(Fe) with aliphatic C8 carbon chain for feasible protein purification in reversed-phase mode

NH2-MIL-100(Fe) is a stable Metal-Organic Frameworks (MOFs) possessing numerous tunable properties. In this study, we have successfully modified NH2-MIL-100(Fe) with aliphatic C8 carbon chain to create a hydrophobic surface distribution. The detailed characterizations of NH2-MIL-100(Fe)-C8 were performed to demonstrate its attractive properties, such as unique MOF architecture, sufficient surface area, and surface hydrophobicity. In addition, the NH2-MIL-100(Fe)-C8 exhibited the distinctive hydrophobic interaction with an individual protein under a specific concentration of acetonitrile, and was able to separate the protein from a mixture with a good resolution. It has a binding capacity of 6.25 μg of BSA/mg particle. Since we have introduced Fe3O4 to NH2-MIL-100(Fe)-C8 to provide with excellent magnetization, the target protein could be easily collected by a magnet and the NH2-MIL-100(Fe)-C8 could be regenerated over 15 times without significant loss of its capacity. Therefore, NH2-MIL-100(Fe)-C8 provides researchers with a convenient and affordable tool for protein separation and purification in reversed-phase mode.

Electrocatalytic H2 evolution promoted by a bioinspired (N2S2)Ni(II) complex.

A bioinspired (N2S2)Ni(II) electrocatalyst is reported that produces H2 from CF3CO2H with a turnover frequency (TOF) of ∼1250 s-1 at low acid concentration (<0.043 M) in MeCN. A mechanism for the H2 production by this electrocatalyst is proposed and its activity is benchmarked against those of other reported molecular Ni H2 evolution electrocatalysts. The involvement of a hemilabile pyridyl group of the N2S2 ligand is proposed to mimic the role of a cysteine residue involved in the biological proton reduction performed by [NiFe] hydrogenases.

Ion channels in sulfonated copolymer-grafted nanoparticles in ionic liquids.

The use of ionic liquids as solvents for polymers or polymer-grafted nanoparticles provides an exciting feature to explore electrolyte-polymer interactions. 1-Hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIm-TFSI) can have specific interactions with the polymer through ion-dipole forces or hydrogen bonding. In this work, poly(methyl methacrylate)-b-poly(styrene sulfonate) (PMMA-b-PSS) copolymer-grafted Fe3O4 nanoparticles with different sulfonation levels (∼4.9 to 10.9 mol% SS) were synthesized, and their concentration dependent ionic conductivities were reported in acetonitrile and HMIm-TFSI/acetonitrile mixtures. We found that conductivity enhancement with the particle concentration in acetonitrile was due to the aggregation of grafted particles, resulting in sulfonic domain connectivity. The ionic conductivity was found to be related to the effective hopping transfer within ionic channels. On the contrary, the conductivity decreased or remained constant with increasing particle concentration in HMIm-TFSI/acetonitrile. This result was attributed to the ion coupling between ionic liquids and copolymer domains.

Spectrophotometric determination of acid dissociation constants of some arylpropionic acids and arylacetic acids in acetonitrile-water binary mixtures at 25ºC

The acid dissociation constant of drug active compounds (arylpropionic and aryl acetic acids) were determined in acetonitrile and water binary mixtures (corresponding volume fractions of 0.40, 0.45, 0.50, and 0.55) by using a multi-wavelength spectrophotometric method. Drug active compounds, which were slightly soluble in water, were studied in these binary mixtures. The dissociation constants of drug active compounds are important in drug design studies and in any research of the biopharmaceutical and physicochemical properties of drugs. The STAR program was used for the determination of dissociation constants. The acidity constants of arylpropionic and aryl acetic acids were correlated with the Kamlet and Taft solvaatochromic parameters. Aqueous pKa values of these arylpropionic and aryl acetic acids were determined from pKa values obtained from acetonitrile and water binary mixtures with varying volume fractions. The studied drugs had a pKa value corresponding to base functional group. Results showed that the acid dissociation constant values of the drug active compounds increased with an increase in acetonitrile content in the medium.

Mixed-acidic cation-exchange material for the separation of underivatized amino acids

Mixed-acidic cation-exchange (MCX) columns with both strongly (SCX) and weakly (WCX) acidic functional groups were developed for the separation of standard amino acids. The resins were prepared by carboxylation of highly crosslinked monodisperse poly(styrene-divinylbenzene) copolymer particles with performic acid and subsequent sulfonation with sulfuric acid. The degree of functionalization was varied independently for each processing step and controlled by measuring pH dependent retention of the obtained resins. A series of mixed-acidic resins with different SCX/WCX-ratios was chromatographically characterized by variation of formic acid and acetonitrile concentration in the aqueous eluent. The overall cation-exchange capacity was varied from 33 to 68 µmol/mL. The comparison with two commercial columns (Metrohm Metrosep C6, WCX and Hamilton PRP X-200, SCX) revealed the additive character of the different functional group properties within MCX columns and a unique selectivity which can be adjusted by both eluent composition and SCX/WCX-ratio of the resin. The retention window between neutral and basic amino acids was altered by varying the amount of sulfonic acid groups attached to the polymer. Orthogonality plots demonstrated constant selectivity for neutral amino acids. Correlating the retention data with log P data demonstrated the influence of non-ionic hydrophobic and π-π-interactions for the separation of amino acids on PS/DVB-based cation-exchangers. An isocratic IC-ESI-MS method was developed to separate and quantitate 20 underivatized standard amino acids within 30 min. Limits of detection were between 4 and 64 nmol L−1 and a high linearity of calibration curves was obtained for all analytes. The method was validated by comparing a certified reference standard with external calibration data.

Inactivation of SARS-CoV-2 in clinical exhaled breath condensate samples for metabolomic analysis

Exhaled breath condensate (EBC) is routinely collected and analyzed in breath research. Because it contains aerosol droplets, EBC samples from SARS-CoV-2 infected individuals harbor the virus and pose the threat of infectious exposure. We report for the first time a safe and consistent method to fully inactivate SARS-CoV-2 in EBC samples and make EBC samples safe for processing and analysis. EBC samples containing infectious SARS-CoV-2 were treated with several concentrations of acetonitrile. The most commonly used 10% acetonitrile treatment for EBC processing failed to completely inactivate the virus in samples and viable virus was detected by the assay of SARS-CoV-2 infection of Vero E6 cells in a biosafety level 3 laboratory. Treatment with either 50% or 90% acetonitrile was effective to completely inactivate the virus, resulting in safe, non-infectious EBC samples that can be used for metabolomic analysis. Our study provides SARS-CoV-2 inactivation protocol for the collection and processing of EBC samples in the clinical setting and for advancing to metabolic assessments in health and disease.

The effect of reagents solvation on change in the stability of coordination compounds of silver(I) ion with pyridine in mixed methanol–acetonitrile solvents

In this study, potentiometric titration was used to determine the stability constants of mono- and bis(pyridine) complexes with silver(I) in mixed methanol–acetonitrile solvents. Gibbs free energies of transfer of pyridine from methanol to methanol–acetonitrile mixtures were determined by the method of distribution between two immiscible phases. The effect of solvent composition on change in the solvation state of pyridine was analyzed. The replacement of methanol by acetonitrile leads to the desolvation of pyridine. The resolvation of pyridine occurs predominantly due to the resolvation of the nitrogen atom at the concentration of acetonitrile >0.5 mol fr. The enthalpic contribution was shown to have a major contribution in ΔtrG0(Py)MeOH→(MeOH-AN). The effect of reagents solvation on the stability of [AgPy]+ and [AgPy2]+ complexes upon the change of the solvent composition was investigated. The resolvation of silver(I) was established to be a key factor controlling the stability of both complexes in MeOH-AN mixtures. The possibility of predictive calculation of the stability constants [AgPy]+ in individual and mixed non-aqueous solvents through the change in the Gibbs free energy of the solvation of the complexing ion was shown. Proper data are compared with data reported in the literature.

Separation of some vitamins in reversed-phase thin-layer chromatography and pressurized planar electrochromatography with eluent containing surfactant

The separation of some water- and fat-soluble vitamins via micellar systems of reversed-phase high-performance thin-layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC) was subjected to research. Hence, the influence of the mobile phase composition (surfactant and acetonitrile concentration, eluent buffer pH) on the migration distances and zone separation of some vitamins (thiamine, riboflavin, niacin, pyridoxine, cyanocobalamin, folic acid, ergocalciferol and α-tocopherol) was investigated. Our results indicated that the applied technique has an impact on the solute order. Comparing the system capacity of HPLC and PPEC (measured as height of the theoretical plate) for the mobile phase systems with and without surfactant shows differences, especially for fat-soluble vitamin. The variances and reproducibilities (% RDS) values of the vitamin are less in PPEC than in TLC. Moreover, the migration distances of water-soluble vitamins are longer than fat-soluble ones. Overall, eluent consisting of 50% acetonitrile, 18.75 mM SDS, the buffer of pH 6.99 via the PPEC technique was most appropriate for determining the investigated vitamins in the artificial mixture and the two commercially available vitamin combinations.

Preparation of liquid crystal-based molecularly imprinted monolith and its molecular recognition thermodynamics

液晶分子印迹聚合物(MIPs)因刚性液晶单体的加入而在超低交联度水平下也能印迹和识别模板分子,有效解决了传统MIPs因高交联度造成的位点包埋、结合容量低、传质慢等问题。尽管液晶MIPs具有如此独特的优势,但却面临着由于交联度的大幅度降低而导致印迹效果下降的问题。为了研究液晶MIPs的结合特性,制备具有良好印迹效果的低交联液晶MIPs,该文通过二次接枝聚合,制备了一系列不同交联度的液晶分子印迹整体柱,用高效液相色谱法研究了聚合参数与印迹整体柱亲和性的关系。实验中选用三羟甲基丙烷三甲基丙烯酸酯(TRIM)为交联剂,以甲苯和十二醇为致孔剂合成整体柱骨架,并在此基础上以(S)-萘普生为模板,加入液晶单体4-氰基苯基单环己基乙烯(CPCE)进行二次聚合接枝。实验中系统考察了流动相中乙腈比例及缓冲液pH值对色谱保留的影响,结果发现液晶单体的加入使得MIPs对萘普生保留控制机制由原来的氢键作用变为了疏水作用;通过动态吸附实验得到的突破曲线经前沿分析及对吸附等温线Langmuir、Freundlich和Scatchard分析拟合,发现交联度为15%时液晶MIPs印迹因子最大(3.78)、非均一性最强,且特异性吸附量高于非特异性吸附量。液晶MIPs的计量置换模型(SDM-R)分析表明,液晶印迹整体柱对模板分子的总亲和力(ln A=0.645)明显高于其类似物;而从空间匹配程度看,与液晶印迹整体柱空间匹配程度最高的是酮洛芬而非模板分子,但液晶印迹整体柱对酮洛芬的总亲和力(ln A=0.242)不及模板分子的一半,表明在本低交联液晶印迹系统中,空间效应不是决定印迹系统识别能力的主要因素。进一步的分离热力学研究发现,低交联液晶印迹柱的|ΔΔH|<T|ΔΔS|,而交联度为70%的非液晶MIPs柱的|ΔΔH|>T|ΔΔS|,表明液晶MIPs的分离过程是一个熵控制过程,而常规无液晶MIPs的分离过程是一个焓控制过程。上述结果表明,液晶单体的加入改变了MIPs的识别机制,适当的低交联度可显著提高液晶MIPs的识别性能,因此液晶MIPs这些特质有望使其成为新一代的MIPs。

Concentration dependence study of non-coincidence effect (NCE) on C[dbnd]O stretching and NH2 bending modes of formamide in acetonitrile: A comparative study

The isotropic and anisotropic parts of Raman spectra corresponding to CO stretching and NH2 bending modes of formamide (HCONH2) in different acetonitrile (CH3CN) concentration were investigated in the region 1500−1800 cm−1 to study the non-coincidence effect. The experimentally obtained values of NCE with varying solvent concentrations were explained using three different models namely, Mirone-Fini model, Mirone-McHale model, and Logan model respectively. The experimentally measured values of non-coincidence splitting, Δνnce, for neat HCONH2 in the modes corresponding to CO stretching and NH2 bending are ∼21 and ∼11.38 cm−1 which then reduces to a very low value of 1.26 and 0.5 cm−1 at mole fraction, ϰf=0.1 respectively. It has been observed that Mirone-McHale model and Logan model reproduces better experimental results of NCE of the CO stretching mode whereas Mirone-Fini model gives accurate results to explain the experimental results of NCE of the NH2 bending mode.

Feasibility of supercritical fluid extraction-supercritical fluid chromatography mass spectrometry for the determination of polycyclic aromatic hydrocarbons in particulate matter samples.

There has been an increased interest in the development of green analytical methods for polycyclic aromatic hydrocarbons in environmental samples due to their toxicity and ubiquitous nature. In this work, the feasibility of on-line supercritical fluid extraction-supercritical fluid chromatography-tandem mass spectrometry was investigated for rapid and automated determination of the 16 United States Environmental Protection Agency priority polycyclic aromatic hydrocarbons in particulate matter samples. Three specialty polycyclic aromatic hydrocarbons columns with different stationary phases were screened and an octadecyl-silica column was selected for method development. Enhanced extraction efficiency was achieved using an extraction program with gradient flow rate and gradient concentration of acetonitrile as a modifier. The method was evaluated by analyzing standard reference materials of urban dust and diesel particulate matter from the National Institute of Standards and Technologies. Possible reasons for the unsatisfactory recoveries with certain polycyclic aromatic hydrocarbons are discussed.

Determination of amoxicillin and cotrimoxazole concentrations in sputum of patients with cystic fibrosis.

In the management of cystic fibrosis, treatments against Staphylococcus aureus and Haemophilus influenzae such as amoxicillin or cotrimoxazole have to be prescribed and the antibiotherapy's efficacy may be linked to the concentration that reaches the infected site. As cystic fibrosis patients present disturbed pharmacokinetics parameters, drug monitoring would be relevant to assess the lung distribution of antibiotics and to optimize dosing regimens. In this context, the aim of the study was to develop and validate HPLC-based methods for the determination of both antibiotics in bronchial sputum from cystic fibrosis patients, in order to assess the distribution of the drugs into the lungs. Plasma proteins were precipitated by acetonitrile and amoxicillin concentrations in sputum were determined by HPLC coupled with tandem-mass spectrometry. Following liquid extraction with ethyl acetate, cotrimoxazole was quantified by HPLC using ultraviolet detection. Both methods were rapid, specific, accurate and reproducible. The method was applied to patient samples. In three treated patients, concentrations of amoxicillin in sputum were similar and below the lower limit of quantification (0.1 μg/g) and in six patients, sputum concentrations up to 11.1 and 6.4 μg/g were measured for sulfamethoxazole and trimethoprim, respectively.

Chromatographic Separation and Determination of Anthocyanins under Conditions of Reversed Phase Chromatography, When Used As Mobile Phases of Acetonitrile–Formic Acid/Phosphoric Acid–Water Systems

A study is performed of the effect of composition of the mobile phases of acetonitrile–formic acid/phosphoric acid–water systems and the concentrations of acetonitrile and acid have on the chromatographic behavior of anthocyanins under the conditions of reversed phase HPLC.