Chromatographic Behavior of Uric Acid and Methyl Uric Acids on a Diol Column in HILIC

Tetraethylenepentamine-derived carbon dots and tetraethylenepentamine co-immobilized silica stationary phase for hydrophilic interaction chromatography

In this work, tetraethylenepentamine (TEPA) was used as precursor and reaction medium to prepare tetraethylenepentamine-functionalized carbon dots (TEPACDs), the resultant mixture was subsequently silanized and then grafted on the surface of bare silica. The obtained tetraethylenepentamine-functionalized carbon dots and tetraethylenepentamine co-modified silica stationary phase (Sil-TEPA/CDs) was characterized by multiple ways, such as Fourier transformed infrared spectroscopy (FTIR), elemental analysis and transmission electron microscope, which revealed the successful preparation of the mixed stationary phase and higher density of functional groups on co-modified stationary phase than precursor single-modified stationary phase. The synergistic effect of TEPACDs and TEPA was proved by comparing the separation performance of Sil-TEPA/CDs and Sil-TEPA toward amino acids, nucleosides, and nucleobases, which distinctly enhanced the selectivity of Sil-TEPA/CDs. Thus, 12 nucleosides and nucleobases and 11 amino acids was nicely separated on Sil-TEPA/CDs. By study the influences of the changes of mobile phase composition, mobile phase buffer concentration and buffer pH on the retention behaviors of Sil-TEPA and Sil-TEPA/CDs, it was found that both hydrophilic partitioning and adsorption of analytes on Sil-TEPA/CDs were enhanced benefit from the co-existence of TEPA and TEPACDs, which provided the analytes better separation performance. By comparing the column quality of Sil-TEPA/CDs with four commercially available columns, Sil-TEPA/CDs exhibited the best peak asymmetry of 0.98, and second best column efficiency of 43895 m-1 using guanosine as analyte. The RSD (n = 9) of the retention times of five selected analytes on Sil-TEPA/CDs were within 0.30-0.61% during 40 h of continuously elution, which implied excellent stability of prepared packing material.

Experimental design in HPLC separation of pharmaceuticals

Design of Experiments (DoE) is an indispensable tool in contemporary drug analysis as it simultaneously balances a number of chromatographic parameters to ensure optimal separation in High Pressure Liquid Chromatography (HPLC). This manuscript briefly outlines the theoretical background of the DOE and provides step-by-step instruction for its implementation in HPLC pharmaceutical practice. It particularly discusses the classification of various design types and their possibilities to rationalize the different stages of HPLC method development workflow, such as the selection of the most influential factors, factors optimization and assessment of the method robustness. Additionally, the application of the DOE-based Analytical Quality by Design (AQbD) concept in the LC method development has been summarized. Recent achievements in the use of DOE in the development of stability-indicating LC and hyphenated LC-MS methods have also been briefly reported. Performing of Quantitative structure retention relationship (QSRR) study enhanced with DOE-based data collection was recomended as a future perspective in description of retention in HPLC system.

Chemometric-assisted method development in hydrophilic interaction liquid chromatography: A review

With an enormous growth in the application of hydrophilic interaction liquid chromatography (HILIC), there has also been significant progress in HILIC method development. HILIC is a chromatographic method that utilises hydro-organic mobile phases with a high organic content, and a hydrophilic stationary phase. It has been applied predominantly in the determination of small polar compounds. Theoretical studies in computer-aided modelling tools, most importantly the predictive, quantitative structure retention relationship (QSRR) modelling methods, have attracted the attention of researchers and these approaches greatly assist the method development process. This review focuses on the application of computer-aided modelling tools in understanding the retention mechanism, the classification of HILIC stationary phases, prediction of retention times in HILIC systems, optimisation of chromatographic conditions, and description of the interaction effects of the chromatographic factors in HILIC separations. Additionally, what has been achieved in the potential application of QSRR methodology in combination with experimental design philosophy in the optimisation of chromatographic separation conditions in the HILIC method development process is communicated. Developing robust predictive QSRR models will undoubtedly facilitate more application of this chromatographic mode in a broader variety of research areas, significantly minimising cost and time of the experimental work.

Thiol–ene click chemistry for the design of diol porous monoliths with hydrophilic surface interaction ability: a capillary electrochromatography study

Thiol–ene click chemistry provides an efficient surface grafting strategy for designing diol monoliths meant for hydrophilic interaction capillary electrochromatography.

Five different columns in the analysis of basic drugs in hydrophilic interaction liquid chromatography

Five different columns (two silica, two cyanopropyl and one diol) were investigated in hydrophilic interaction liquid chromatography (HILIC). For the assessment of columns behavior in HILIC mode, six basic drugs (lamotrigine, thioridazine, clozapine, chlorpheniramine, pheniramine and sulpiride) were chosen. The assessment of the influence of the concentration of organic modifier on analytes’ retention on each column was provided by fitting the retention data into theoretical models. Utilizing the statistical analysis, the selection of the model that provides better prediction of the retention behavior was enabled. Dual RP-HILIC mechanism was suggested on cyanopropyl and diol columns, therefore the transition points between the two mechanisms on these columns were calculated. Furthermore, in order to investigate the impact of three factors simultaneously on the retention behavior of the analyzed substances on Betasil Silica column, chemometrically-aided empirical models were built. The experiments were conducted according to the matrix of Box-Behnken design and on the basis of the retention data, six quadratic models were obtained and their adequacy was confirmed using ANOVA test. The obtained coefficients of quadratic models enabled the elucidation of both single factor and factor interactions influence. This was also graphically presented in 3D response surface plots.

Development and evaluation of new zwitterionic hydrophilic interaction liquid chromatography stationary phases based on 3-P,P-diphenylphosphonium-propylsulfonate

New zwitterionic stationary phases were synthesized by covalently bonding 3-P,P-diphenylphosphonium-propylsulfonate to silica gel. The resulting materials possess both a negatively charged sulfonate group and a positively charged quaternary phosphonium group, which means that there is no net charge over a wide pH range. The retention mechanism and chromatographic behavior of polar solutes under HILIC conditions were studied on these zwitterionic phases. Compared to the commercial ZIC-HILIC column and a bare silica gel stationary phase, the newly synthesized zwitterionic stationary phases provided greater retention, higher peak efficiency and better peak symmetry in the HILIC mode. The analytes examined included: β-blockers, nucleic acid bases and nucleosides, salicylic acid and its analogues, and water soluble vitamins. Factors, such as the type of organic modifiers, solvent composition, pH and the buffer concentration of the mobile phase, have been considered as potential variables for controlling the chromatographic retention of polar analytes.

Recent and potential developments in the analysis of urine: a review

Analysis of urine is a widely used diagnostic tool that traditionally measured one or, at most, a few metabolites. However, the recognition of the need for a holistic approach to metabolism led to the application of metabolomics to urine for disease diagnostics. This review looks at various aspects of urinalysis including sampling and traditional approaches before reviewing recent developments using metabolomics. Spectrometric approaches are covered briefly since there are already a number of very good reviews on NMR spectroscopy and mass spectrometry and other spectrometries are not as highly developed in their applications to metabolomics. On the other hand, there has been a recent surge in chromatographic applications dedicated to characterising the human urinary metabolome. While developments in the analysis of urine encompassing both classical approaches of urinalysis and metabolomics are covered, it must be emphasized that these approaches are not orthogonal - they both have their uses and are complementary. Regardless, the need to normalise analytical data remains an important impediment.