Acetonitrile Content Research Articles

Quality by Design oriented development of hydrophilic interaction liquid chromatography method for the analysis of amitriptyline and its impurities

This paper presents integration of Quality by Design concept in the development of hydrophilic interactions liquid chromatographic methods for analysis of amitriptyline and its impurities (A, B, C, and F). This is the first time that HILIC method for amitriptyline and its impurities is developed. Using QbD concept, it is possible to design a robust method and incorporate quality directly into its development. QbD concept in combination of Design of Experiments methodology (DoE) enables creation of well-defined design space. In this study, for method optimization a Box-Behnken design was used to test the effect of acetonitrile content, buffer concentration and pH of water phase on critical system responses such as retention factor of impurity A, resolution between impurity B and impurity C, amitriptyline peak asymmetry factor and retention time of last eluted impurity F. The defined mathematical models and Monte Carlo simulations were used to identify the design space. For robustness testing, fractional factorial design was applied. Optimal chromatographic conditions were the analytical column ZORBAX NH2 (250 mm x 4.6 mm, 5 μm particle size); mobile phase consisted of acetonitrile-water phase (60 mM ammonium acetate, pH adjusted to 4.5 with glacial acetic acid) (92.5:7.5 v/v); column temperature 30 °C, mobile phase flow rate 1 mL min−1, wavelength of detection 254 nm. Finally, method was fully validated and applicability of the method in tablet analysis was confirmed.

Simultaneous Determination of Aminoglycoside Residues in Livestock and Fishery Products by Phenylboronic Acid Solid-Phase Extraction and Liquid Chromatography-Tandem Mass Spectrometry.

A rapid and simple method has been developed for simultaneous determinations of the concentrations of nine aminoglycosides (AGs) in livestock and fishery products using phenylboronic acid (PBA) solid-phase extraction (SPE) clean-up. Unlike the widely employed SPE approaches, based on cation-exchange, PBA SPE relies on the reversible formation of covalent bonds with the analytes. The advantage of using PBA lies in the fact that this compound strongly and stably retains analytes, and the pH of the loading solution can be easily adjusted using a high-concentration buffer. The clean-up conditions, such as the pH of the loading solution and the acetonitrile concentration in the elution and wash solvents, were optimized. The degree of recovery measured for nine AGs in six samples (bovine muscle, bovine liver, milk, chicken egg, fish and shrimp) were in the 73 - 98% range, and the values for the relative standard deviation were 9.3% or less.

Acetonitrile as adjuvant to tune polyethylene glycol + K3PO4 aqueous two-phase systems and its effect on phenolic compounds partition

Aqueous two-phase systems (ATPS) have been proposed as platforms for the purification of biomolecules, and the application of adjuvants to tune the properties of ATPS phases and their ability to extract and separate biological products investigated. This work addresses, for the first time, the use of acetonitrile (ACN) as adjuvant in ATPS composed of polyethylene glycol (PEG) of different molecular weights (from 400 to 20,000 g·mol−1) and potassium phosphate. The effect of ACN concentration (at 0.25, 2.5, 5 and 7.5 wt%) in the liquid-liquid equilibrium is here studied by measuring the phase diagrams, the composition of the phases in equilibrium and their Kamlet-Taft parameters. The results obtained demonstrate that the ACN presence increases the biphasic region of PEG-K3PO4 ATPS and its distribution between the coexisting phases is dependent on its concentration and ATPS composition. The difference in the dipolarity/polarizability of the coexisting phases is significantly affected by the presence of ACN in the ternary mixture. The partition of two phenolic compounds – protocatechuic acid and gallic acid – was studied, showing that ACN improves the partition of these molecules to the salt-rich phase, and that the system selectivity can be significantly improved by changing the concentration of the phase forming compounds.

Determination of Some Physicochemical Properties of Mebendazole with RPLC Method

In this study, the retention behavior of benzimidazole anthelmintic drug mebendazole (MBZ) was investigated with a liquid chromatographic method. Influence of acetonitrile (ACN) concentration prese...

CENTRAL COMPOSITE DESIGN APPLIED IN HPLC OPTIMIZATION FOR ANALYSIS OF TARTRAZINE AND AURAMINE O IN POWDER DRINKS

Objective: This study was intended to optimize reversed-phase high-performance liquid chromatography (RP-HPLC) method for the determination of Tartrazine (TAR) and Auramin O (AUO) in powder drinks using experimental design of central composite design (CCD) approach.
 Methods: TAR and AUO in powder drink product has same properties, therefore both analytes were analysed using C18 column (XBridge Shield RP 18 250 mm x 4.6 mm i.d., 5 µm) using Shimadzu LC 20AD chromatograph equipped with photo-diode array (PDA) detector at 300-650 nm. Some factors responsible for RP-HPLC separation of TAR and AUO including the concentration of buffer, the ratio of mobile phase and flow rate were optimized using CCD. The responses evaluated were peak area, retention time, and tailing factor. The mobile phase used was acetonitrile and ammonium acetate buffer, and acetonitrile composition was optimized at 84-86% for separation of TAR and AUO, delivered at a flow rate of 0.8–1.2 ml/min, using ammonium acetate buffer at 19-21 mmol.
 Results: CCD showed that separation of TAR and AUO was influenced by flow rate, the ratio of acetonitrile and ammonium acetate concentration. These factors affected significantly to retention time, peak area, and tailing factor. The optimal condition obtained based on CCD was flow rate of 1.2 ml/min, the ratio of acetonitrile 86%, and ammonium acetate concentration of 19 mmol.
 Conclusion: CCD can be used to get optimum condition for analysis of TAR and AUO in powder drink product.

Evaluating the Adsorbed Water Layer on Polar Stationary Phases for Hydrophilic Interaction Chromatography (HILIC)

The water-rich liquid layer immobilized on the surface of the polar stationary phases is critical to the retention of polar compounds in hydrophilic interaction chromatography (HILIC). Although the presence of the adsorbed water layer has been investigated and confirmed by multiple techniques, there is a lack of quantitative measures that can be easily determined and linked to chromatographic parameters. This study proposes a simple measure termed volume ratio (the ratio of the adsorbed water layer volume and the mobile phase volume) that can be easily determined using toluene elution volume. The volume ratio values measured using the proposed method indicate that the volume of the adsorbed water layer varies in a wide range in the stationary phases commonly used in HILIC separation. It was observed that the volume ratio increases with the acetonitrile content and ammonium acetate concentration in the mobile phase. In addition, increasing the column temperature had the effect of reducing the volume ratio and diminishing the adsorbed water layer.

Multivariate optimization and validation of a procedure to direct determine acetonitrile and ethanol in radiopharmaceuticals by GC-FID

A fast and simplified analytical procedure was developed and validated for the direct determination of organic solvents (acetonitrile and ethanol) in radiopharmaceuticals samples ([18F]FMISO, [18F]FES and [18F]FLT) by gas chromatography coupled with flame ionization detection (GC-FID). Optimization studies were performed with the aid of two-level full factorial design. The optimum conditions were located using Derringer's desirability function. Procedure validation assured the compliance of the assay to Brazilian regulatory agencies standards (ANVISA and INMETRO). Values for LOD and LOQ were commensurate with the level at which the impurities must be controlled. Good linearity was achieved (R ≥ 0.990) for acetonitrile and ethanol concentrations ranging from 0.003 to 0.09% (w/v) and 2.1 to 11.0% (v/v), respectively. Accuracy and precision assessments were performed using samples fortified with standards (spiked samples). The developed procedure proved to be selective, sensitive, accurate (95.9–117.8% of nominal values) and precise (RSD ≤ 9.7%). The validated procedure was successfully used to assess organic solvents levels in a Brazilian radiopharmaceuticals samples manufactured by Radiopharmaceutical Research and Production Unit of Nuclear Technology Development Center (CDTN), in Belo Horizonte (Brazil). The analytes could be well resolved in 1.5 min and accurately determined in three different types of radiopharmaceuticals. This procedure is applicable to samples even with high ethanol content up to 11% (v/v). Other advantages include no sample preparation, short chromatographic separation time and minimum manual operation. As results, the proposed procedure can be useful in the routine analysis for the determination of acetonitrile and ethanol in radiopharmaceutical samples.

Tyrocidine A interactions with saccharides investigated by CD and NMR spectroscopies.

Tyrocidines are a family of cyclic decapeptides produced by the soil bacterium, Brevibacillus parabrevis. These antibiotic peptides can be used to prevent infections in agriculture and food industry but also to prepare antimicrobial lozenges, creams, and dressings for medical applications. It has been observed that the tyrocidines interact with saccharides such as cellulose from their soil environment, as well as sugars in culture media and glycans in fungal cell walls. Here, we investigated the interactions of tyrocidines with glucose, sucrose, and cellotetraose (as cellulose model) in a quantitative fashion utilising CD and NMR spectroscopy. The CD and NMR spectra of tyrocidine A (TrcA) were analysed as a function of solvent composition, and the spectral properties agree with the formation of oligomeric structures that are governed by β-sheet secondary structures once the acetonitrile content of the solvent is increased. Saccharides seem to also induce TrcA spectral changes reverting those induced by organic solvents. The CD spectral changes of TrcA in the presence of glucose agree with new ordered H-bonding, possibly β-sheet structures. The amides involved in intramolecular H-bonding remained largely unaffected by the environmental changes. In contrast, amides exposed to the exterior and/or involved in TrcA intermolecular association show the largest 1 H chemical shift changes. CD and NMR spectroscopic investigations correlated well with TrcA-glucose interactions characterized by a dissociation constant around 200μM. Interestingly, the association of cellotetraose corresponds closely to the additive effect from four glucose moieties, while a much higher dissociation constant was observed for sucrose. Similar trends to TrcA for binding to the three saccharides were observed for the analogous tyrocidines, tyrocidine B, and tyrocidine C. These results therefore indicate that the tyrocidine interactions with the glucose monosaccharide unit are fairly specific and reversible.

Preparation and evaluation of highly hydrophilic aptamer-based hybrid affinity monolith for on-column specific discrimination of ochratoxin A

Nonspecific adsorption is a challenge of specific recognition on aptamer-based affinity monoliths. Here, a novel highly hydrophilic polyhedral oligomeric silsesquioxane (POSS)-containing aptamer-based hybrid-silica affinity monolith with a good recognition nature was prepared and used for specific discrimination of ochratoxin A (OTA). A homogeneous polymerization mixture consisted of POSS chemicals, hydrophilic monomers and aptamer solution was directly polymerized via the “one-pot” method. Preparation and characterization of the resultant affinity monolith were studied in detail. A highly hydrophilic nature was obtained and the typical hydrophilic interaction liquid chromatography (HILIC) was observed when acetonitrile (ACN) content in mobile phase was 25%, which reached the highest hydrophilicity of POSS-based hybrid monoliths. By using OTA as model analyte, the nonspecific adsorption was effectively suppressed. The recovery of the analogue ochratoxin B (OTB) was only about 0.1% even if the content of OTB was 50 times more than OTA, which was much better than other POSS-containing monoliths and polar siloxane-based hybrid monoliths. Applied to beer samples, the adsorption of background materials was drastically resisted, and efficient recognition of OTA was obtained with the recoveries of 94.9–99.8%. Much less disturbance was observed than that occurred in hydrophobic POSS-based affinity monolith. It lights an attractive implement with high hydrophilicity and specificity for online selective recognition of OTA.

Systematic evaluation of selected supercritical fluid chromatography diol‐ and diethylamine‐based columns for application in hydrophilic interaction liquid chromatography

AbstractHydrophilic interaction liquid chromatography has become a useful method for separation of polar and hydrophilic analytes, i.e. compounds that are difficult to separate in reversed‐phase chromatography. The retention mechanism in hydrophilic interaction liquid chromatography is rather complex. Different types of interactions contribute to retention, depending on the properties of stationary phase, mobile phase and nature of analytes. Many columns for hydrophilic interaction liquid chromatography are available and the new stationary phases are still under development. In our study systematic examination to describe two novel columns, intended for supercritical fluid chromatography, as potential stationary phases for hydrophilic interaction liquid chromatography was performed. The supercritical fluid chromatography columns contained polar diethylamine ligand and diol ligand bonded to ethylene bridged hybrid particles. The retentivity and selectivity of the stationary phases were evaluated using a variety of test compounds. The impacts of acetonitrile content, buffer pH and concentration on the retention were investigated. Distinct mixed‐mode behavior of the diethylamine column was observed; significant contribution of anion‐exchange interaction to retention was confirmed. The DIOL phase has neutral character and retained analytes predominantly by hydrophilic interaction liquid chromatography mechanism.

Post-Column Make-Up Flow (PCMF) Enhances the Performance of Capillary-Flow PGC-LC-MS/MS-Based Glycomics.

Deep characterization of biologically relevant glycans remains challenging. Porous graphitized carbon-liquid chromatography tandem mass spectrometry (PGC-LC-MS/MS) enables the quantitative elucidation of glycan fine structures. However, the early PGC-LC elution of smaller glycans (tri-, tetra-, and pentasaccharides) at low organic solvent content hampers their detection. In efforts to improve the glycan profiling sensitivity and accuracy, we present a new capillary-flow PGC-LC-MS/MS-based configuration comprising a post-column make-up flow (PCMF) that supplies an ion-promoting organic solvent to separated glycans prior to their detection by MS. The analytical performance of this setup was systematically evaluated against our existing capillary-flow PGC-LC-MS/MS platform (Jensen et al., Nat. Protoc. 2012, 7, 1299). Specifically, the ion intensities and signal-to-noise ratios of various classes of nonderivatized glycans from N- and O-glycoproteins and fructooligosaccharide mixtures were compared using methanol (MeOH)-, isopropanol (IPA)-, and acetonitrile (ACN)-based PCMF at various concentrations. In particular, ACN- and IPA-based PCMF dramatically increased the signal response across all glycan types (30- to 100-fold), improved the MS/MS spectral quality, and reduced the quantitative glycoprofile variation between replicates. In particular, the detection of the early eluting glycans benefitted from the PCMF. The highest sensitivity gains were achieved with the supplements of 100% ACN and IPA (equating to 57% (v/v) net concentration at the ion source) while neither compromising the favorable PGC-LC properties including the high peak capacity and glycan isomer separation nor changing the MS detection behavior. In conclusion, PCMF-based PGC-LC-MS/MS dramatically improves the glycomics sensitivity, coverage, and quantitative accuracy not least for the difficult-to-detect early eluting and low-abundance glycans detached from N- and O-glycoproteins.

Elucidation of retention behaviors in reversed-phase liquid chromatography as a function of mobile phase composition

Various retention models have been widely used for understanding the retention mechanisms of solutes in reversed-phase chromatography systems. The models have been used to interpret the often-observed linear plots of the logarithms of retention factor k versus the solvent modifier concentration CM and ln k versus ln⁡CM. In this study, the retention behaviors of nine solutes as a function of acetonitrile (ACN) concentration were systematically investigated using a commercially available C18 column. The thermodynamic properties of solute adsorptions in neat water, determined using van’ t Hoff plots, were investigated. Slightly concave upward and downward retention curves were identified for the plots of ln k versus CACN and ln k versus ln CACN, respectively. A three-equilibrium-constant stoichiometric displacement retention model was used to interpret the retention behaviors of the solutes. The model was demonstrated to account for the nonlinearity of the retention curves. The linear fits of the ln k versus ln⁡CACN and ln k versus CACN plots were implied to be more suitably used for high and low ACN concentration ranges, respectively. The model fitted the experimental data satisfactorily over a full range of ACN concentrations; thus, the nonlinearity of ln k versus ln⁡CACN plots was implied to mainly be attributed to the weak ACN–sorbent interactions. U-shaped retention curves were observed for acetone, tetrahydrofuran, tert-butanol, and benzyl alcohol at high ACN concentrations, indicating that the retention behaviors of these solutes may involve two types of interactions, with complementary effects on solute retention factor with increasing ACN concentration.

Preparation and Evaluation of Molecularly Imprinted Polymers for Promazine and Chlorpromazine by Multi-step Swelling and Polymerization: the Application for the Determination of Promazine in Rat Serum by Column-switching LC.

Molecularly imprinted polymers (MIPs) for promazine (PZ) and chlorpromazine (CPZ), MIPPZ and MIPCPZ, were prepared by multi-step swelling and polymerization using methacrylic acid as a functional monomer and ethylene glycol dimethacrylate as a crosslinker. The retention and molecular-recognition properties of MIPPZ and MIPCPZ were evaluated using a mixture of potassium phosphate buffer and acetonitrile, or a mixture of ammonium formate and acetonitrile as the mobile phase in LC. PZ and CPZ gave the maximal retentions on MIPPZ and MIPCPZ at an apparent pH 8.2 using a mixture of potassium phosphate buffer and acetonitrile as the mobile phase. The retentions of PZ and CPZ decreased with an increase of acetonitrile contents from 70 to 90 vol% using a mixture of ammonium formate and acetonitrile as the mobile phase. The template molecules (PZ and CPZ, respectively) were recognized the most on the respective MIPs, and the imprinting factor of PZ was higher on MIPCPZ than on MIPPZ. These results indicate that in addition to shape recognition, ionic and hydrophobic interactions seem to work for the retention and molecular-recognition of PZ and CPZ on the MIPs. MIPCPZ was successfully utilized for the selective extraction of PZ in rat-serum samples in column-switching LC with fluorescence detection.

Analysis of amino acids in blood by combining zeolitic imidazolate framework-8-based solid phase extraction and capillary electrophoresis

Detection of amino acids (AAs) in blood is helpful to diagnose some diseases. In this work, a method is developed for determination of trace amounts of AAs in bovine blood by combining solid phase extraction (SPE) and capillary electrophoresis (CE). Zeolitic imidazolate framework-8 (ZIF-8) nanoparticles are prepared and used as adsorbents to simultaneously extract three AAs (tryptophan, tyrosine, phenylalanine). Under the optimum extraction conditions, the extraction efficiencies of ZIF-8 for AAs are 95.1% (tryptophan), 91.1% (tyrosine), and 90.1% (phenylalanine), respectively. Interestingly, ZIF-8 demonstrates good extraction ability for AAs in high concentration of acetonitrile (ACN) aqueous solutions. Thus, they can be directly used to extract AAs from the deproteinized blood sample using ACN. An α-cyclodextrin-mediated cation selective exhaustive injection-sweeping CE method is developed for analysis of the extracted AAs. The detection limits for AAs range from 0.13 to 0.37 μg mL−1 using the SPE/CE method. Standard addition method is used to evaluate the feasibility of the method in bovine blood samples. The standard addition curves demonstrate good linearity with determination coefficient > 0.9912.

Raman spectroscopic study of nonlinear modulation on Fermi resonance of acetonitrile by hydrogen-bonding network

Raman spectra of acetonitrile-water mixtures are measured in different acetonitrile concentration fractions. The nitrile stretch (v2) and the combination (v3 + v4) modes are coupled by Fermi resonance. We extract the Fermi resonance parameters and find that the frequency separation shows non-linear dependence as a function of acetonitrile concentration fractions. v2 ~ v3 + v4 Fermi doublets intensity ratio exhibits nonlinearity, which is accelerated with the decreasing of the Fermi coupling strength. The OH stretching region is also investigated in order to reveal the variation of the water structure. Our data show that there are strong relationships between the intensity of ~3225 cm−1 band and the v2~v3 + v4 Fermi resonance. Because the nitrile stretch and Fermi resonance are very environmental sensitive, the nonlinear modulation on Fermi resonance and the non-regular intensity ratio are attributed to the change of water hydrogen-bonding network. The results provide useful structural and spectral insights for the design of new experiments and the molecular structure modeling.

Comparison of the Partition Efficiencies of Multiple Phenolic Compounds Contained in Propolis in Different Modes of Acetonitrile⁻Water-Based Homogenous Liquid⁻Liquid Extraction.

Homogeneous liquid–liquid extraction (HLLE) has attracted considerable interest in the sample preparation of multi-analyte analysis. In this study, HLLEs of multiple phenolic compounds in propolis, a polyphenol-enriched resinous substance collected by honeybees, were performed for improving the understanding of the differences in partition efficiencies in four acetonitrile–water-based HLLE methods, including salting-out assisted liquid–liquid extraction (SALLE), sugaring-out assisted liquid–liquid extraction (SULLE), hydrophobic-solvent assisted liquid–liquid extraction (HSLLE), and subzero-temperature assisted liquid–liquid extraction (STLLE). Phenolic compounds were separated in reversed-phase HPLC, and the partition efficiencies in different experimental conditions were evaluated. Results showed that less-polar phenolic compounds (kaempferol and caffeic acid phenethyl ester) were highly efficiently partitioned into the upper acetonitrile (ACN) phase in all four HLLE methods. For more-polar phenolic compounds (caffeic acid, p-coumaric acid, isoferulic acid, dimethoxycinnamic acid, and cinnamic acid), increasing the concentration of ACN in the ACN–H2O mixture could dramatically improve the partition efficiency. Moreover, results indicated that NaCl-based SALLE, HSLLE, and STLLE with ACN concentrations of 50:50 (ACN:H2O, v/v) could be used for the selective extraction of low-polarity phenolic compounds. MgSO4-based SALLE in the 50:50 ACN–H2O mixture (ACN:H2O, v/v) and the NaCl-based SALLE, SULLE, and STLLE with ACN concentrations of 70:30 (ACN:H2O, v/v) could be used as general extraction methods for multiple phenolic compounds.

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.

Chiral separation of aliphatic primary amino alcohols as o-phthaldialdehyde/mercaptoethanol derivatives on polysaccharide-based chiral stationary phases.

A sensitive chiral high performance liquid chromatography (HPLC) method for the determination of aliphatic primary amino alcohol isomers with o-phthaldialdehyde/mercaptoethanol precolumn derivatization has been developed and validated. Seven chiral columns were tested in a reversed phase mode. Excellent enantioseparation with the resolution more than 2.0 was achieved on Chiralcel OJ-3R. The effect of various chromatographic conditions including column temperature, acetonitrile content in the mobile phase, buffer pH, buffer concentration, and buffer type in the mobile phase on the retention and the selectivity was investigated. The final mobile phase consisted of binary mixture of 20mM ammonium formate solution with acetonitrile (75:25; v/v). The analyses were performed at mobile phase flow rate of 1.0mL/min and the column temperature of 40°C. The fluorescence detection was performed at excitation wavelength of 345nm and emission wavelength of 450nm. The developed method was fully validated in terms of linearity, sensitivity, accuracy, precision, intermediate precision, and selectivity according to International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use guidelines using internal normalization procedure. The proposed chiral method was proved to be highly sensitive, simple, and rapid and was successfully applied to the determination of D-Valinol content in commercially available samples of L-Valinol.

Enantioseparation of N-acetyl-dl-cysteine as o-phtaldialdehyde derivatives obtained with various primary aliphatic amine additives on polysaccharide-based chiral stationary phases

A sensitive and rapid high-performance liquid chromatography (HPLC) method was developed to enantioseparation of N-acetyl-dl-cysteine after precolumn derivatization using o-phthaldialdehyde and primary aliphatic amines. Seven polysaccharide-based chiral columns were tested in a reversed phase mode. Under the optimal chromatographic conditions, N-acetyl-dl-cysteine derivatives were completely enantioseparated on Chiralcel OZ-3R column with the resolution more than 2.5. The impact of various primary aliphatic amine additives as co-reagents (ethyl-, 1-propyl-, 1-butyl-, 1-pentylamine, (R)-sec-butylamine, tert-butylamine, isobutylamine, cyclopropyl-, cyclobutyl-, cyclopentyl and cyclohexylamine) used in precolumn derivatization step on the retention behavior (retention factor, selectivity and column efficiency) of N-acetyl-dl-cysteine derivatives was investigated. The effect of chromatographic conditions including acetonitrile content in the mobile phase, mobile phase pH, salt concentration in the mobile phase and column temperature on the retention and selectivity was investigated. The developed method was properly validated in terms of linearity, sensitivity (limit of detection and limit of quantification), accuracy, precision, intermediate precision and selectivity according to International Council for Harmonisation (ICH) of Technical Requirements for Pharmaceuticals for Human Use guidelines using internal normalization procedure. Proposed HPLC method was successfully applied to the determination of optical purity in commercially available N-acetyl-L-cysteine samples.

Comparative Study of Quinolines and Tetrahydroquinolines Sorption on Various Sorbents from Water-Acetonitrile Solutions.

The retention of 16 quinoline and tetrahydroquinoline derivatives was investigated under liquid chromatography conditions using porous graphitized carbon (PGC), octadecyl silica (ODS) and hypercrosslinked polystyrene (HCLP) stationary phases. For most of the analytes, retention on PGC was greater than on ODS, while retention on HCLP was even greater than on both ODS and PGC. The non-linearity of retention dependencies on acetonitrile content in the eluent was observed for compounds containing carboxy, hydrazo and methoxy groups. The relationships between quinolines structure and their retention factors were investigated. It was found that sorption on different sorbents correlated with different descriptors. Retention on ODS was found to be highly correlated with lipophilicity only while on HCLP it depended on both lipophilicity and polarizability of the sorbates. The feature of PGC was a good correlation of retention factors with topological and geometrical parameters. Additionally, ability of PGC to form OH…π bonds with hydroxymethylquinolines was found. The observed regularities allow one to rationally optimize the chromatographic analysis of structurally similar compounds, which is very important for bioactive substances.