Core-shell Stationary Phase Research Articles

Overcoming the Strong Sample Solvent Effect for Sustainability Measurement Challenges in Liquid Chromatography. Example for Bisphenol-A.

This paper describes an approach to achieve low parts per billion (ppb) concentration level detection using a reversed-phase ultrahigh-performance liquid chromatographic ultraviolet absorbance detection method with large-volume feed injection (FI) for analytes in dichloromethane (DCM). FI is a novel technology that allows sample injection at a defined speed into the LC mobile phase. We demonstrate this approach for a mixture of bisphenol A and its diglycidyl ether derivatives in DCM. DCM is a very strong injection solvent at reversed-phase LC conditions and is typically immiscible with a starting reversed-phase gradient mobile phase containing a high percentage of water. As a result, reduced separation performance and even peak splitting are seen with classic flow-through injection. The method setup comprised an octyl-bonded core-shell stationary phase (150 × 4.6 mm i.d., 2.7 μm particle size) with a water/acetonitrile mobile phase gradient and an exceptionally high injection volume of 45 μL of DCM solution using FI. Optimization of feed speed (1%) and isocratic hold duration (4 min) was crucial for final separation conditions. FI delivered more than a 20-fold improvement in the limit of detection (LOD) compared to standard flow-through injection while maintaining peak resolution. The LOD of the final method ranged between 1 and 10 ppb in the polymer resin. This methodology has high potential for trace analysis in a large variety of applications that suffer from the "strong solvent effect".

A comprehensive undergraduate experiment: preparation and chromatographic evaluation of a core-shell stationary phase based on a covalent organic framework

Continuously promoting new curriculum standards is a key aim of the Ministry of Education of China. With this in mind, this paper introduces a comprehensive teaching experiment for undergraduate instrumental analysis courses that aims to improve students' material-preparation and instrumental-analysis skills through practice. Herein, a covalent organic framework-based core-shell stationary phase material (SiO2@COFTTA-DHTA) is prepared via a one-pot method and characterized in detail, after which its chromatographic properties are evaluated by high performance liquid chromatography (HPLC). The experimental process includes material synthesis and characterization, as well as studying the chromatographic-retention behavior and chromatographic-separation performance of the material. By the combining theoretical science and experimental teaching, this experiment not only deepens students' understanding of the properties of functional materials and their applications, but also improves their experimental-design and critical-thinking skills. This experiment not only cultivates students' interests in scientific research, but also exercises their experimental, operational, innovative-thinking, and practical abilities, while concurrently enhancing their sense of social responsibility and historical mission, thereby delivering the all-round educational goals of experimental teaching.

Novel PEI/Zein core–shell composite as mixed-mode stationary phase for high performance liquid chromatography

Based on the adhesion of polyethyleneimine (PEI), a novel PEI/zein co-modified core-shell stationary phase (PEI/Zein@SiO2) was prepared by doping zein to form a composite modification layer. The stationary phase achieved effective separation of nucleosides, bases and antibiotics in hydrophilic interaction mode on account of the hydrophilic groups of composite coating. With the hydrophobicity of zein, the flavones could be separated in reversed-phase mode. In short, the separation and analysis of hydrophilic/hydrophobic compounds were accomplished excellently by the PEI/Zein@SiO2 column with mixed double mode. The prepared chromatographic stationary phase not only avoided the dissolution of zein, but also covered the strong adsorption of some analytes caused by silica hydroxyl groups on the surface of silica spheres. The morphological structure and specific surface area of the material were reflected by various characterization techniques. Hydrophilic/hydrophobic compounds were used as tested analytes to research separation performance and retention mechanisms of PEI/Zein@SiO2 column. The stability and reproducibility of the PEI/Zein@SiO2 stationary phase were satisfied. Therefore, the modification of zein could improve the separation selectivity of stationary phase effectively for complex samples, which had the potential to be one of the significant potential application materials in stationary phase packing.

Optimization of a Solid-Phase Extraction Coupled with a High-Performance Liquid Chromatography and Diode Array Ultraviolet Detection Method for Monitoring of Different Antibiotic Class Residues in Water Samples.

The increased use of cephalosporin antibiotics in the last few years as well as the detection of their residues in wastewater treatment plants and hospital wastewater poses a risk for infiltration of their residues into environmental water samples. A simplified, sensitive, and convenient solid-phase extraction (SPE) procedure coupled with either HPLC or fast HPLC methods with diode array detection was developed and validated to screen the residues of six different cephalosporin antibiotics: cefoperazone, cefipime, ceftazedime, ceftriaxone, cefdinir, and cefotaxime, along with amoxicillin, levofloxacin, and ciprofloxacin in water samples. An HPLC-diode array detector (HPLC-DAD) method and a fast HPLC method, based on a core-shell stationary phase, were developed for the fast screening of the antibiotic compounds. In addition, the SPE step was optimized to enable the extraction of the studied drugs with high accuracy of the recovered amounts of residues. The method sensitivity was enhanced by the coupling of SPE with HPLC-DAD and fast HPLC to achieve low LODs; from 0.2 to 3.8 ng/mL and from 0.65 to 12.2 ng/mL, respectively. The developed methods were augmented by LC-MS/MS determination for confirmation of identity and quantity of any positively identified sample. The method was applied to the analysis of water samples collected from a rural site. In Addition, an example application of cleaning validation of cefotaxime-contaminated stainless-steel surfaces was provided. The method's simplicity and high sensitivity encourage its application in monitoring of antibiotic residues in different types of water samples such as environmental samples and samples from cleaning validation activities. HPLC-DAD and fast HPLC methods were developed for separation of nine different antibiotics. The combination with the SPE procedure achieved low detection limits; from 0.2 to 3.8 ng/mL for SPE-HPLC-DAD and from 0.65 to 12.2 ng/mL for SPE-fast HPLC.

Synthesis of hierarchically porous zirconium-based metal-organic framework@silica core-shell stationary phase through etching strategy for liquid chromatography

Metal organic frameworks (MOFs) show promise to be employed as stationary phase for high performance liquid chromatography (HPLC), however, the microporous structures of MOFs seriously restrict the diffusion and mass transfer of solute molecules, leading to a low column efficiency. In this paper, the fabrication of hierarchically porous UiO-66@SiO2 (HP- UiO-66@SiO2) core-shell microspheres via H2O2 etching has been proposed as a viable approach to enhance the separation performance of MOFs-based columns for HPLC. Through the direct treatment of the preliminary prepared UiO-66@SiO2 microspheres with H2O2 etching, HP-UiO-66@SiO2 core-shell microspheres were successfully synthesized with an enlarged pore size of up to 9 nm, facilitating efficient mass transfer in chromatographic separation. The prepared HP-UiO-66@SiO2 core-shell microspheres were then explored as stationary phase in HPLC to separate the nonpolar alkyl benzene homologues, the polar aromatic alcohol homologues and the xylene isomers. The results indicated that the baseline separations of these solutes were achieved successfully with narrow peak width and higher resolution than the UiO-66@SiO2 column. The HP-UiO-66@SiO2 column exhibited superior separation performance, reaching a maximum plate number of 134,459/m for fluorene, and showing good reproducibility. As a result, this template-free approach suggests that the fabrication of hierarchically porous MOFs@silica core-shell microspheres is a successful approach to enhance the column efficiency of MOFs-based columns in HPLC.

A composite hydrogel modified silica stationary phase for mixed‑mode liquid chromatography

A novel composite hydrogel functionalized silica core-shell stationary phase was prepared by the surface modification of silica sphere. The successful synthesis of the new stationary phase (T-Sil@PAM/SA/UiO-66-NH2) was proven by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), etc. Due to the coexistence of amide, hydroxyl, long carbon chain and UiO-66-NH2 in composite hydrogel shell, the obtained stationary phase can be used in hydrophilic/reversed-phase liquid chromatography with multiple retention mechanisms, such as hydrophilic, hydrophobic and π - π interactions. The chromatographic retention behavior of T-Sil@PAM/SA/UiO-66-NH2 demonstrated that the new stationary phase showed excellent separation performance for both polar analytes (such as alkaloids, saccharides, etc.) and nonpolar analytes (such as substituted benzene and polycyclic aromatic hydrocarbon (PAHs), etc.). Furthermore, compared with NH2 column and commercial C18 column, the T-Sil@PAM/SA/UiO-66-NH2 exhibited a certain superiority. Moreover, the relative standard deviation (RSD) of PAHs’ retention time with eight replicates consecutive elution was found to range from 0.03% to 0.17%. Therefore, the successful use of T-Sil@PAM/SA/UiO-66-NH2 in mixed‑mode liquid chromatography expanded the potential applications of hydrogels in the field of separation.

Simple Preparation Method of Silica Core–Shell Spheres for HPLC in Undergraduate Chemistry

High-performance liquid chromatography (HPLC) experiments are an important part of the undergraduate analytical instrumentation laboratory courses and usually use commercial C18 silica-packed reversed-phase columns. In this experiment, a simple method of preparing SiO2 core–shell packed columns was developed to enable students to master the whole process of HPLC experiment from stationary phase preparation and column packing to separation experiments, just as they do for gas chromatography. Nonporous SiO2 particles with a particle size of approximately 2.2 μm were prepared by a three-step dilution reaction using the sol–gel method. The product yield was 92.1%. Monodisperse and spherical SiO2 core–shell particles (SiO2@dSiO2) with a particle size of about 2.4 μm were prepared by a one-step hydrothermal method using the prepared SiO2 spheres as the core. The product yield was 83.3%. The prepared SiO2@dSiO2 particles were derivatized with n-octadecyldimethylchlorosilane and then packed into a stainless steel chromatography column. A high column efficiency of 83,188 theoretical plates per meter was obtained for fluorene in reversed-phase mode for the separation of a mixture of polycyclic aromatic hydrocarbons. The column efficiency obtained with this method is the same as that of a commercial column packed with fully porous particles of the same particle size. The SiO2 core–shell stationary phase preparation method developed in this experiment has the advantages of simple process, high yield, and good repeatability. The experiment can be designed to be completed over a period of 1–3 weeks. Inorganic material synthesis is another important aspect of this experiment.

ZIF-8 Assisted Polyacrylamide Functionalized Silica Core-Shell Stationary Phase for Hydrophilic Interaction Liquid Chromatography

A novel ZIF-8 assisted polyacrylamide functionalized silica polar stationary phase was prepared by a facile method of adding ZIF-8 nanoparticles and silica into polyacrylamide (PAM) aqueous solution, and then stirring the mixture until the solution was evaporated absolutely with the help of mechanical agitator. Interestingly, the prepared stationary phase (PAM-Sil@ZIF-8/PAM) showed favorable hydrophilicity, as demonstrated by good separation performance and strong retention ability toward several types of polar compounds, such as amino acids, saccharides, and alkaloids. In addition, PAM-Sil@ZIF-8(50 mg)/PAM showed better separation performance compared with amino-modified silica and Sil/PAM stationary phase due to the addition of ZIF-8. Furthermore, it was demonstrated that the addition of ZIF-8 improved the specific surface area and provided extra interaction sites for the stationary phase and analytes, which is beneficial for the separation of samples. In addition, the column efficiency can reach 7861.9 plates/m for colchicine. Moreover, it exhibited good stability and reproducibility under our operation conditions. In short, a novel stationary phase, which can be used for hydrophilic interaction liquid chromatography, was obtained and proved that the separation performance of polymer modifying silica stationary phase can be greatly improved by the addition of MOF nanoparticles.

Preparation and characterization of glucose-based covalent organic polymer coated silica as stationary phase for high-performance liquid chromatography

Carbohydrate is a renewable, sustainable, hydrophilic, and biodegradable natural product, which is widely used in the field of adsorption. In this study, a glucose-based covalent organic polymer (COP) coated silica was fabricated by facile solvent knitting reaction between tetrabenzylglucose and silica-phenyl with anhydrous aluminum trichloride as catalyst, forming a core-shell stationary phase (donated as SiO2@COPBn-glu) for high performance liquid chromatography. The prepared SiO2@COPBn-glu was characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectrometry, solid-state 13C nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy, and N2 adsorption-desorption experiments. Owing to the coexistence of benzene units and alkyl, hydroxyl and ether groups in the skeleton of COPBn-glu shell, the developed chromatographic packing exhibited reversed-phase/hydrophilic interaction mixed-mode with multiple retention mechanisms, such as hydrophobic, π-π, hydrogen bonding, and electron donor-acceptor interactions. The results revealed that the SiO2@COPBn-glu column demonstrated excellent selectivity and retention behavior for both hydrophilic and hydrophobic compounds with good repeatability and stability. Meanwhile, the chromatographic performance of the prepared SiO2@COPBn-glu column was compared with a C18 column to assess the role of the coating COPBn-glu shell. Therefore, the development of the SiO2@COPBn-glu stationary phase expands the potential application of COPs in separation field.

Chromatographic Regulation by the Building Blocks for Triazine Polymer-Based Core–Shell Stationary Phases

Two versions of reversed-phase/hydrophilic interaction mixed-mode core–shell stationary phases for high-performance liquid chromatography using porous organic polymers as the shell material were investigated. The stationary phase named SiO2@CTPCC-TPB using triazine-triphenylbenzene-based porous organic polymers as the shell material has been reported previously. To regulate chromatographic performance, heptazine–biphenyl moieties with fewer benzene rings and higher nitrogen content were used as organic building blocks to grow a porous shell on the surface of silica to acquire a core–shell stationary phase, namely, SiO2@CHPCy-DB. Various techniques were used to characterize the developed core–shell microsphere, and nonpolar/polar solutes were utilized as probes to investigate the chromatographic behavior of the stationary phase. The results revealed that SiO2@CHPCy-DB exhibited reversed-phase/hydrophilic interaction mixed-mode with multiple retention mechanisms. Meanwhile, the separation behavior of the two homemade columns and a commercial column was compared to assess the role of the building blocks in porous organic polymers in regulating and improving separation. The successful determination of drugs of abuse in urine via the SiO2@CHPCy-DB column indicated its potential for the determination of trace analytes in complex samples.

Core shell stationary phase for a novel separation of some COVID-19 used drugs by UPLC-MS/MS Method: Study of grapefruit consumption impact on their pharmacokinetics in rats

A sensitive and selective UPLC-MS/MS method was developed for the synchronized determination of four drugs used in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), namely, azithromycin, apixaban, dexamethasone, and favipiravir in rat plasma. using a Poroshell 120 EC-C18 column (50 mm × 4.6 mm, 2.7 m) with a high-resolution ESI tandem mass spectrometer detection with multiple reaction monitoring. We used an Agilent Poroshell column, which is characterized by a stationary phase based on non-porous core particles. With a remarkable improvement in the number of theoretical plates and low column backpressure. In addition, the developed method was employed in studying the potential food-drug interaction of grapefruit juice (GFJ) with the selected drugs which affects their pharmacokinetics in rats. The LC-MS/MS operated in positive and negative ionization mode using two internal standards: moxifloxacin and chlorthalidone, respectively. Liquid- liquid extraction of the cited drugs from rat plasma was accomplished using diethyl ether: dichloromethane (70:30, v/v). The analytes were separated using methanol: 0.1 % formic acid in water (95: 5, v/v) as a mobile phase in isocratic mode of elution pumped at a flow rate of 0.3 mL/min. A detailed validation of the bio-analytical method was performed in accordance with US-FDA and EMA guidelines.Concerning the in vivo pharmacokinetic study, the statistical significance between the results of the test groups receiving GFJ along with the cited drugs and the control group was assessed demonstrating that GFJ increased the plasma concentration of azithromycin, apixaban, and dexamethasone. Accordingly, this food–drug interaction requires cautious ingestion of GFJ in patients using (SARS-CoV-2) medications as it can produce negative effects in the safety of the drug therapy. A potential drug–drug interaction is also suggested between those medications requiring a suitable dose adjustment.

Isocyanate derivatization coupled with phospholipid removal microelution-solid phase extraction for the simultaneous quantification of (S)-metoprolol and (S)-α-hydroxymetoprolol in human plasma with LC–MS/MS

A sensitive liquid chromatography-tandem mass spectrometry (LC–MS/MS) assay was developed and validated for the quantification of (S)-metoprolol (MET) and its main metabolite, (S)-α-hydroxymetoprolol (OH-MET). Human plasma samples (50 μL) were spiked with both analytes and their deuterated internal standards (IS) (S)-MET-(d7) and α-OH-MET-(d5). Phospholipid removal microelution-solid phase extraction (PRM-SPE) was performed using a 4-step protocol with Oasis PRiME MCX μElution 96-well cartridges. The eluates were reconstituted in 100 μL of acetonitrile with 50 μg/mL (S)-α-methylbenzyl isocyanate (MBIC) for chiral derivatization. After 60 min at room temperature, the reaction was quenched using 100 μL of water 2 % formic acid. Chromatographic separation of the derivatized analytes was performed on a Kinetex phenyl-hexyl core-shell stationary phase with an elution gradient. Mobile phases were composed of a mixture of water and methanol, with ammonium formate and formic acid as buffers. Total runtime was 15 min. Analyte detection was performed by an AB/SCIEX 4000 QTRAP mass spectrometer with multiple reaction monitoring. Chromatograms showed MBIC successfully reacted with racemic MET, α-OH-MET, and their respective IS. Detection by positive electrospray ionization did not reveal derivatized by-products. Quantification ranges were validated for (S)-MET and (S)-α-OH-MET between 0.5–500 and 1.25−500 ng/mL, respectively, with correlation coefficients (r2) >0.9906. The PRM-SPE assay showed low matrix effects (86.9–104.0 %) and reproducible recoveries (69.4–78.7 %) at low, medium, and high quality control (QC) levels. Precision and accuracy were all comprised between 85–115 % for all three QCs, and between 80–120 % for the lower limit of quantification, for intra- and inter-day values (n = 6, 3 consecutive days). Non-derivatized analytes were stable at room temperature, after 3 freeze-thaw cycles, and stored for 30 days at −80 °C (n = 4). Reinjection reproducibility of a previously validated batch was achieved after 8 days under auto-sampler conditions, indicating the stability of (S)-MET and (S)-α-OH-MET derivatives. Its clinical use was established in a cohort of 50 patients and could be used to further investigate the clinical impact of (S)-MET concentrations.

Design and evaluation of novel MOF-polymer core-shell composite as mixed-mode stationary phase for high performance liquid chromatography.

A general method was developed for preparing ametal-organic framework-polymer composite coated silica core-shell stationary phase. Silica microspheres were comodified with metal-organic framework and polyvinylpyrrolidone rather than the in situ method of silica modification by original metal-organic framework particles. Metal-organic framework particles and polyvinylpyrrolidone on silica surface were beneficial to suppress silanol activity and enhance composite material tolerance, as well as increasing the water compatibility of the original metal-organic framework-based stationary phases. The stationary phase exhibited superior hydrophilic and hydrophobic performance in terms of separation for various analytes including seven alkaloids, six sulfonamides, five antibiotics, and five polycyclic aromatic hydrocarbons. Moreover, the composite material also showed excellent stability with the relative standard deviation of the retention time of 0.4 to 0.7%. The separation performance with real samplesproved that the column has good practical application potential. In summary, the poposed method provides a general way for preparing metal-organic framework-polymer composite material and changed the current status of original metal-organic framework particles modified silica as a single mode chromatographic stationary phase.

MOF-74@SiO2 core-shell stationary phase: Preparation and its applications for mixed-mode chromatographic separation

The development of versatile mixed-mode stationary phase materials is of important meanings for solving the increasing demands for real sample analysis. Herein, with 2,5-dihydroxyterephthalic acid as the organic ligand and nickel as the metal centre, MOF-74 nanocrystal materials were facilely grafted on the surface of carboxyl-functionalized silica gel via layer-by-layer assembling technique. The structures of the monodisperse MOF-74@SiO2 material were proved by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, elemental analysis, thermogravimetric analysis, and Brunauer-Emmett-Teller specific surface area and pore size analyzer, respectively. Because the introduced 2,5-dihydroxyterephthalic acid is of hydrophilic carboxyl and hydroxyl groups, the packed MOF-74@SiO2 column reveals hydrophilic interaction/reversed-phase mixed-mode retention properties. Compared with commercial C8 column or silica-based column, the MOF-74@SiO2 column shows distrinct separation selectivity in short separation time for polycyclic aromatic hydrocarbons, phenolic compounds and polar sulfonamide compounds. The developed MOF-74@SiO2 column was further successfully applied for the separation and detection of illegal addition of glucocorticoid in children’s face cream as well as sulfonamides veterinary drug residues in pure milk. The research provides a simple and convenient approach to prepare multifunctional MOFs-based stationary phase materials.

The preparation of a core–shell stationary phase by the in situ polymerization of a hydrophilic polymer on the surface of silica and its chromatographic performance

A method for the in situ polymerization of polymers on a silica surface was developed.

Theoretical Analysis of Efficiency of Multi-Layer Core-Shell Stationary Phases in the High Performance Liquid Chromatography of Large Biomolecules.

Modern analytical applications of liquid chromatography require columns with higher and higher efficiencies. In this work, the general rate model (GRM) of chromatography is used for the analysis of the efficiency of core-shell phases having two porous layers with different structures and/or surface chemistries. The solution of the GRM in the Laplace domain allows for the calculation of moments of elution curves (retention time and peak width), which are used for the analysis of the efficiency of bi-layer particles with and without a non-porous core. The results demonstrate that bi-layer structures can offer higher separation power than that of the two layers alone if the inner layer has smaller surface coverage (retentivity) and the pore size and pore diffusion of the outer layer is either equal to or higher than that of the inner layer. Even in the case of core-shell phases, there is an increase in resolution by applying the bi-layer structure; however, we can always find a mono-layer core-shell particle structure with a larger core size that provides better resolution. At the optimal core size, the resolution cannot be further improved by applying a bi-layer structure. However, in case of the most widely produced general-purpose core-shell particles, where the core is ∼70% of the particle diameter, a 15–20% gain of resolution can be obtained by using well-designed and optimized bi-layer core-shell phases.

The Benefits of Ultra-High-Performance Supercritical Fluid Chromatography in Determination of Lipophilic Vitamins in Dietary Supplements

Nine tocopherol derivatives including four tocopherols, four tocotrienols, and one esterified form of α-tocopherol acetate were analyzed using ultra-high-performance supercritical fluid chromatography (UHPSFC) with diode array detection. The separation was carried out on BEH 2-EP column using shallow gradient elution of 1–4% methanol and CO2 in 5 min. Complementary ultra-high-performance liquid chromatography method was developed using Ascentis Express F5 core–shell stationary phase and isocratic elution with 75% acetonitrile/methanol (1:1) and 25% water. This separation took 12 min that is the shortest liquid chromatography run in analysis of all tocopherol derivatives reported so far. However, our UHPSFC method resulted in more than two times faster analysis, and allowed direct injection of heptane solutions and extracts from liquid–liquid extraction. These features made UHPSFC a method of choice for subsequent analysis of dietary supplements containing different forms of vitamin E. Sample preparation methods were optimized for individual dosage forms of drops, capsules, tablets, and granulate.

Stability Indicating Hplc Method using Core Shell Stationary Phase for the Determination of Related Substances in Levocetirizine Dihydrochloride Oral Solution

Stability Indicating Hplc Method using Core Shell Stationary Phase for the Determination of Related Substances in Levocetirizine Dihydrochloride Oral Solution

Mixed-Mode Liquid Chromatography on Core Shell Stationary Phases based on Layer-By-Layer Nanodiamond/Polyamine Architecture

Background: The use of diamond as a chromatographic stationary phase has been studied for more than 45 years now. Detonation nanodiamonds (DND) have been regularly used to increase the low specific surface area of these non-porous stationary phases. Recently, core-shell particles with multiple layers of polyallylamine (PAAm) and DND have been reported for liquid chromatographic separations and solid phase extractions. However, retention mechanisms and selectivity of such core-shell particles are not well -understood due to their complex architecture. Objective: The objective of this work was to perform a detailed evaluation of the mixed mode behavior of three structural analogues of new nanodiamond (ND)/polyamine based core-shell stationary phases. Method: Particles were composed of a glassy carbon core coated with poly(allylamine) (PAAm) and ND, deposited using a layer-by-layer (LbL) approach, with the outer PAAm layer treated with a mixture of a hydrophobic cross-linker and modifier to introduce C8/C18 functional groups. Three types of the core-shell stationary phases having different shell thicknesses and purity of NDs were investigated. Type II was prepared with fewer PAAm/ND bilayers as compared to Type I, whereas Type III was prepared with a same number of bilayers but with an additionally purified form of ND as compared to Type II. Ion-exchange interactions of the phases were tested with a set of model anionic, cationic and ampholytic analytes at different eluent pHs. The relative degree of anionexchange and hydrophobic interactions was also evaluated using a set of dansylated amino acids (Dns-AAs) at varied mobile phase buffer concentrations and organic solvent contents. Results: Anion-exchange properties were noted for all phases at low pH, with the Type I phase exhibiting stronger retention of anionic analytes due to higher PAAm content in its shell. Typical reversed-phase behaviour was observed for the hydrophobic Dns-AAs (Phe, Ile, Leu, Trp, Val and Pro), while the retention selectivity for hydrophilic Dns-AAs (Gln, Asn, Thr, Ser) indicated mixed mode mechanism. Values of methylene selectivity obtained for homologues of carboxylic acids indicated relatively low hydrophobicity for all studied phases. Conclusion: All three columns demonstrated low to medium hydrophobicity, and the solute selectivity was dominated by their ion-exchange property. These nanodiamond columns result in lower performance as compared to conventional analytical columns, however, the inherently stable nanodiamond platform ascertains that nanodiamond columns offer better stability at extreme conditions.

Stability Indicating HPLC Method Using Core Shell Stationary Phase for the Determination of Related Substances in Levocetirizine Dihydrochloride Oral Solution

Abstract: Rationale: Levocetirizine (LCZ) is a new generation antihistamine drug used for the allergic symptoms resulting from various diseases. The present research work focuses on the development of a simple and precise HPLC method for the effective separation and quantitative determination of LCZ and its impurities. Experimental: Eight potential related impurities of LCZ were separated and identified in the bulk drug as well as oral solution dosage form. The separation was achieved on a core shell stationary phase Kinetex bipheyl (250, 4.6×5 μm) column with mobile phase of sodium perchlorate in water and acetonitrile in a gradient elution. Results:The results were monitored and analytes were quantified at 230 nm. The method was validated as per ICH guidelines for specificity, linearity, precision, accuracy and robustness. The proposed method finds its application in the routine analysis of LCZ in bulk drug and various dosage forms. Key words: HPLC, Core shell, Related Substances, Levocetirizine dihydrochloride.