Increase Of Acetonitrile Content Research Articles

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.

Enantioseparation of warfarin derivatives on molecularly imprinted polymers for (S)- and (R)-chlorowarfarin

Monodisperse molecularly imprinted polymers (MIPs) for warfarin (WF), 4ʹ-chlorowarfarin (CWF), (S)-CWF and (R)-CWF (MIPWF, MIPCWF, MIP(S)-CWF and MIP(R)-CWF, respectively) were prepared using 4-vinylpyridine (4-VPY) and ethylene glycol dimethacrylate (EDMA) as a functional monomer and a crosslinker, respectively, by multi-step swelling and polymerization. The molar ratio of a template molecule, 4-VPY to EDMA was 6:18:25 or 4:18:25. The retention and molecular recognition properties of MIPWF and MIPCWF were evaluated using a mixture of sodium phosphate buffer or ammonium formate and acetonitrile in reversed-phase LC. WF and CWF on these MIPs gave the maximal retentions at mobile phase pH 7, and those retentions were decreased with an increase of acetonitrile content. The retention and imprinting factors were in the order of WF < CWF < 4ʹ-bromowarfarin (BWF) on MIPWF and MIPCWF in neutral mobile phases. On the other hands, in acidic mobile phases the retention factors were in the same order with those in neutral mobile phases, while the imprinting factors of WF and CWF were higher on the respective MIPs. These results suggest that ionic or hydrogen bonding interactions, hydrophobic interactions and π-π interactions could work for the retention and molecular recognition of WF, CWF and BWF on these MIPs in a reversed-phase mode. Furthermore, MIP(S)-CWF and MIP(R)-CWF could separate WF, CWF and BWF enantiomers in acidic mobile phases.

Identification of the factors affecting the retention of weak acid solutes in hybrid micellar systems with cetyltrimethylammonium bromide

Retention behavior of ionized and unionized forms of ten weak acid solutes was investigated in hybrid micellar systems with varying cetyltrimethylammonium bromide concentrations (CTAB), acetonitrile (ACN) content and mobile phase pH range from 2.5 to 7.5. It was shown that observed retention patterns are significantly affected by CTAB concentration, ACN volume fraction and analytes' ionization state. The rationale and quantitative description for observed retention behavior was obtained by fitting k values to retention model and calculation of binding constants for both ionized and unionized species. The importance of interaction between analyte anions and positively charged CTAB molecules adsorbed onto stationary phase surface was confirmed. For all solutes, except salicylic acid and furosemide, binding to stationary phase is reduced upon ACN volume fraction increase since the solvent partially desorbs the adsorbed surfactant. Also, the interactions of analytes with micelles are diminished with increase in ACN content because it promotes decrease in micelle aggregation number and its capacity for analyte binding. The additional analysis to identify and interpret molecular descriptors which can best explain the experimental evidence and findings obtained was performed. These findings could provide a new and specific understanding of the interactions between all the components of the hybrid micellar chromatographic system and a good basis for further investigations suggesting the development of generally applicable predictors in structure-retention relationship studies in related chromatographic systems.

Molecularly imprinted polymer for glutathione by modified precipitation polymerization and its application to determination of glutathione in supplements

Molecularly imprinted polymers (MIP) particles for glutathione (GSH) with a narrow particle size distribution were prepared by modified precipitation polymerization using methacrylic acid as a functional monomer, divinylbenzene as a crosslinker and water as a co-solvent. The particle diameters of the MIP and non-imprinted polymer (NIP) prepared under the optimum conditions were 3.81±0.95 (average±standard deviation) and 3.39±1.22μm, respectively. The retention and molecular-recognition properties of the prepared MIP were evaluated using a mixture of acetonitrile and water as a mobile phase in hydrophilic interaction chromatography. With an increase of acetonitrile content, the retention factor of GSH was increased on the MIP. In addition to shape recognition, hydrophilic interactions seem to work for the recognition of GSH on the MIP. The MIP had a specific molecular-recognition ability for GSH, while glutathione disulfide, l-Glu, l-Cys, Gly-Gly and l-Cys-Gly could not be retained or recognized on the MIP. The effect of column temperature revealed that the separation of GSH on the MIP was entropically driven. Binding experiments and Scatchard analyses revealed that one binding sites were formed on both the MIP and NIP, while the MIP gave higher affinity and capacity for GSH than the NIP. Furthermore, the MIP was successfully applied for determination of GSH in the supplements.

Molecularly imprinted polymer for chlorogenic acid by modified precipitation polymerization and its application to extraction of chlorogenic acid from Eucommia ulmodies leaves

Molecularly imprinted polymers (MIPs) for chlorogenic acid (CGA) were prepared by modified precipitation polymerization using methacrylic acid as a functional monomer, divinylbenzene as a crosslinker and methanol or dimethylsulfoxide as a co-solvent. The prepared MIPs were microspheres with a narrow particle size distribution. Binding experiments and Scatchard analyses revealed that two classes of binding sites, high and low affinity sites, were formed on the MIP. The retention and molecular-recognition properties of the prepared MIP were evaluated using a mixture of water and acetonitrile as a mobile phase in hydrophilic interaction chromatography. With an increase of acetonitrile content, the retention factor of CGA was increased on the MIP. In addition to shape recognition, hydrophilic interactions seem to work for the recognition of CGA on the MIP. The MIP had a specific molecular-recognition ability for CGA, while other related compounds, such as caffeic acid, gallic acid, protocatechuic acid and vanillic acid, could not be recognized by the MIP. Furthermore, the MIP for CGA was successfully applied for extraction of CGA in the leaves of Eucommia ulmodies.

The effect of solvents on the electrochemical behavior of homogentisic acid

The electrochemical oxidation of homogentisic acid (HGA) as an important biological molecule has been studied in aqueous and mixed acetonitrile–water solutions using cyclic voltammetry. The effects of pH, HGA concentration, time window of the chosen electrochemical method and different solvents were studied to investigate the proton and electron transfer processes. The oxidation product of HGA in aqueous solution is stable in acidic, neutral and weakly alkaline media at the time scale of cyclic voltammetry. The electrooxidation process of HGA in aqueous solution follows Eq mechanism. In mixed acetonitrile–water solution, the electrooxidation process of HGA follows an EqCiEq mechanism. The experimental results indicate that the subsequent chemical reaction of dimerization is more probable for the oxidized form of HGA. It is shown that the separation of the cathodic and anodic peak potentials, ΔEp, in the mixture of acetonitrile–water is greater than that in aqueous solution and it increases with the increase of acetonitrile content in the mixture.

Monodisperse, molecularly imprinted polymers for creatinine by modified precipitation polymerization and their applications to creatinine assays for human serum and urine

Molecularly imprinted polymers (MIPs) for creatinine were prepared by modified precipitation polymerization using methacrylic acid as a functional monomer and divinylbenzene as a crosslinker. The prepared MIPs were monodispersed with a narrow particle size distribution. Binding experiments and Scatchard analyses revealed that two classes of binding sites, high- and low-affinity sites, were formed on the MIPs. The retention and molecular-recognition properties of the MIPs were evaluated by hydrophilic interaction chromatography using a mixture of ammonium acetate buffer and acetonitrile as a mobile phase. With an increase of acetonitrile content, the retention factor of creatinine was increased on the MIP. In addition to shape recognition, hydrophilic interactions seemed to enhance the recognition of creatinine on the MIP. The MIPs’ molecular-recognition ability was specific for creatinine; the structurally related compounds such as hydantoin, 1-methylhydantoin, 2-pyrrolidone, N-hydroxysuccinimide and creatine were not recognized. Furthermore, the creatinine concentrations in human serum and urine were successfully determined by direct injection of the deproteinized serum and diluted urine samples onto the MIP.

Monolithic columns containing sol–gel bonded octadecylsilica for capillary electrochromatography

A new method for preparing monolithic capillary columns is reported. A fused-silica capillary packed with porous octadecylsilica (ODS) particles using a CO 2 slurry was partially filled with a siliceous sol formed by hydrolysis and polycondensation of tetramethoxysilane and ethyltrimethoxysilane. After gelling and aging of the siliceous sol at room temperature, the column was dried with supercritical CO 2. The scanning electron micrograph of a cross-section of the capillary column revealed that the ODS particles were bonded to each other and to the column inner wall by the sol–gel, forming a monolith. The performance of the monolithic column was evaluated for capillary electrochromatography using small aromatic compounds and polycyclic aromatic hydrocarbons with Tris buffer in aqueous acetonitrile mobile phase. The electroosmotic flow velocity increased with a decrease in Tris buffer concentration from 10 to 5 m M. The electroosmotic flow velocity increased significantly with an increase in Tris buffer pH from 5 to 7.5, and then remained nearly constant with Tris buffer pH between 7.5 to 9.0. The electroosmotic flow velocity increased with an increase in acetonitrile content from 20 to 50%, and then remained nearly constant with acetonitrile content between 50 to 90%. No bubble formation was observed during CEC operation, and all of the test compounds eluted as symmetrical peaks. The logarithms of the retention factors of the aromatic compounds and polycyclic aromatic hydrocarbons decreased linearly with an increase in acetonitrile content. For a 21/29 cm×75 μm I.D. monolithic column containing 9% sol–gel bonded 5 μm ODS, approximately 2.7×10 4 theoretical plates (plate height 7.8 μm; 1.3×10 5 theoretical plates per meter) were measured. It was found that the resistance to mass transfer of unretained thiourea was small, which was attributed to partial filling of the small pores in the particulate packing and partial filling of the interstitial space by the porous sol–gel network. The procedure for column fabrication was simple, and three columns were prepared without failure.

Near-infrared studies of HDO in D2O + acetonitrile + Zn(ClO4)2 system

Abstract Isotopically diluted HDO in D2O + acetonitrile (AN) + Zn(ClO4)2 system have been investigated by near-infrared spectroscopy at 25°C. Measurements were carried out in the range of the first overtone of 2υ3(OH) stretching vibration and of υ3(OH) + υ3(OD) combination vibration bands of HDO at selected D2O + AN mixture compositions. Spectral results infinitely diluted solutions, in respect to HDO and Zn(ClO4)2, were interpreted. Spectra of HDO molecules affected by the solute and its respective hydration numbers were determined. Changes of the 2υ3(OH) band caused by Zn(ClO4)2 were transformed into changes of enthalpy of hydrogen bonds of water, using the Badger-Bauer rule. The results were discussed in the light of respective calorimetric data. It was stated that with the increase of AN content in the mixture, Zn(ClO4)2 becomes more and more effective in strengthening the structure of water in respect to the situation in the mixture and also in pure water. Preferential hydration of Zn(II) have been inferred from that. The obtained results are justified by the microheterogenic structure of water + AN mixture and cooperation of hydrogen bonds stimulated by the presence of Zn(II) in solution.