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Daniel W. Armstrong and Szabolcs Fekete are the winners of the 13th annual LCGC Lifetime Achievement and Emerging Leader in Chromatography Awards, respectively. Here, we review their achievements.
Daniel W. Armstrong and Szabolcs Fekete are the winners of the 13th annual LCGC Lifetime Achievement and Emerging Leader in Chromatography Awards, respectively. Here, we review their achievements.
Daniel W. Armstrong and Szabolcs Fekete are the winners of the 13th annual LCGC Lifetime Achievement and Emerging Leader in Chromatography Awards, respectively. Armstrong and Fekete will be honored in a symposium as part of the technical program at the Pittcon 2020 conference in Chicago on March 3, 2020.
The Lifetime Achievement in Chromatography Award
The Lifetime Achievement in Chromatography Award honors an outstanding and seasoned professional for a lifetime of contributions to the advancement of chromatographic techniques and applications.
Daniel W. Armstrong, the 2020 winner, is the R.A. Welch Distinguished Professor of Chemistry & Biochemistry at the University of Texas at Arlington (UTA). He has worked on an extremely broad range of separation techniques, including high performance liquid chromatography (HPLC), gas chromatography (GC), supercritical fluid chromatography (SFC); micellar LC (MLC), thin-layer chromatography (TLC); countercurrent chromatography (CCC); capillary electrophoresis (CE); and field flow fractionation (FFF), among others. He developed the theory and mechanistic background behind many of the practical advances in these techniques. Further, he advanced the use of separations techniques as a means to obtain important physico-chemical data. His most recent work in ultrafast separations and signal processing is driving fundamental changes in the field.
Among Armstrong’s greatest contributions is his work in the field of enantiomeric separations. He published a seminal paper in Science in 1986 that described in detail the mechanism of chiral recognition by cyclodextrins in aqueous and hydro-organic solvents. This was also the first example of small molecule molecular modeling. This study indicated the necessity of chromatographic enantiomeric separations for purity assessment and pharmacokinetic and pharmacodynamic studies and provided impetus that led the U.S. Food and Drug Administration (FDA) to issue new guidelines in 1992 for the development of stereoisomeric drugs. This changed the way that the pharmaceutical industry operated worldwide, and these changes still reverberate today.
Armstrong’s group was the first to introduce macrocyclic glycopeptide chiral selectors in HPLC, SFC, and CE as well as cyclofructan chiral selectors in HPLC, GC, SFC, and CE. Chromatographic columns possessing these stationary phases were commercialized and adopted as the leading chiral stationary phases because they exhibited wide chiral selectivity for a broad set of chiral molecules. In 2014, the European Space Agency’s Rosetta mission soft-landed its Philae probe on comet 67P/Churyumov-Gerasimenko, and one of the instrument packages on the lander contained a chiral GC column (Chiraldex G-TA) invented by Armstrong. This column has proven invaluable in the specific mission to separate small chiral molecules representing potential organic precursors in the search for life on the comet.
Another important contribution is Armstrong’s development of comprehensive solvation and characterization models for room-temperature ionic liquids as stationary phases in GC. In a 1999 paper, it was shown that ionic liquids exhibit a unique “dual nature” retention selectivity toward polar and nonpolar molecules. In 2002, he published a comprehensive model that relates the solvation properties of ionic liquids to their unique structural features that comprise the make-up of both the cation and anion within the ion pair. This was quickly followed by the development of methods to design analyte-specific stationary phases that could be employed at high temperatures. These stationary phases have subsequently been commercialized and have been an important contribution to the field, particularly in multidimensional GC where ionic liquids exhibit very unique selectivity compared to most other commercially available stationary phases.
Armstrong is considered the “father” of micelle and cyclodextrin-based separations. He elucidated the first chiral recognition mechanism by cyclodextrins, was the first to develop macrocyclic antibiotics as chiral selectors, and is one of the world’s leading authorities on the theory, mechanism, and use of enantioselective molecular interactions. More than 30 LC and GC columns that were originally developed in his laboratories have been commercialized or copied worldwide. His work and columns were in part responsible for the chromatography- and electrophoresis-led revolution in chiral separations over the last two and a half decades. The columns, chiral selectors, and techniques he developed still dominate the work of analytical
He has developed the most effective way to characterize the solvent properties of room temperature ionic liquids (RTILs). His approach has proven to be an essential and effective way to explain the effect of RTILs on organic reactions, and in various analytical methodologies. His group demonstrated surfactant aggregation to form normal micelles in RTILs. The first matrix-assisted laser desorption–ionization–mass spectrometer (MALDI-MS) matrices and high stability GC stationary phases based on RTILs were developed in his laboratories and were recently commercialized by Supelco/SigmaAldrich (now MilliporeSigma). The new enhanced MS technique of paired ion electrospray ionization (PIESI) was developed in his laboratory and is one of the most sensitive methods for ultratrace anion analyses and speciation. He developed the first high-efficiency CE separation approach for microorganisms (bacterial, viruses, fungi, and so forth). This development is extending the realm of separation science into the mainstream of biology and colloid science.
Armstrong’s impact derives not only from his research, but also from the more than 175 former graduate students, post-doctoral fellows, and visiting scientists who have studied and trained under his guidance. Armstrong’s former students are making contributions in academia in six countries and throughout most pharmaceutical companies worldwide, as well as in many petrochemical and polymer companies and federal agencies. He is the longtime Separations Associate Editor of the ACS journal Analytical Chemistry. He has more than 700 publications, including 32 book chapters, one book (Use of Ordered Media in Chemical Separations) and 33 patents. He has been named by the Scientific Citation Index as one of the world’s most highly cited scientists, and he has given ~580 invited, keynote, or plenary lectures and colloquia worldwide. His work has been cited more than 43,000 times, having a Hirsch (h-) index of 105 by Google Scholar. He also founded or cofounded two companies focused on the production of novel separation media and their use in difficult analyses.
Key Recent Publications
In his most recent work, Armstrong was, for the first time, able to give a description of the endogenous levels of free L-and D-amino acids in cultured human breast cancer cells (MCF-7) and non-tumorigenic human breast epithelial cells (MCF-10A) (1). This work revealed that D-Asp and D-Ser, which are co-agonists of the N-methyl-D-aspartate (NMDA) receptors, showed significantly elevated levels in MCF-7 cancer cells compared to MCF-10A cells. This demonstrated that these D-amino acids may regulate N-methyl-D-aspartate (NMDA) receptors and promote proliferation of breast cancer. It was noted that L- and D-amino acids levels are useful as cell malignancy indicators (MIs) for breast cancer epithelial cells (MCF-10A). Based on this work, a simple malignancy indicator (MI) test has been devised to detect breast cancer.
In other recent work, Armstrong described a novel method to synthesize spherical, porous, and high surface area geopolymer particles for use as a reversed-phase LC stationary phase (2). Geopolymer particles demonstrate excellent peak shape definition and improved selectivity compared to silica columns.
Armstrong and team captured and identified dicationic ionic liquid thermal decomposition products, specifically for 15 bis-/dicationic ionic liquids, to examine their thermally induced molecular and atomic structural changes and whether volatilization occurs before these changes (3). These compounds are useful for their ability to dissolve different compounds, for their low volatility and their molecular stability at high temperatures. They are also known to have infinitely variable (or “tunable”) molecular structures, which exhibit variable properties. It was found that thermolytic decomposition occurs most often at the heteroatom-carbon single bonds.
In groundbreaking work toward providing fundamental information on the role of D-amino acid oxidase (DAO) in the brain, which is potentially relevant for drug development related to DAO regulation, baseline analysis of L- and D-amino acids in the brains of mice having variable DAO activity (ddY/DAO+/+, ddY/DAO+/−, and ddY/DAO−/−) was carried out (4). For this research, a highly effective analytical method was developed to measure these amino acids in brain tissue samples. These amino acids are recognized for playing essential roles in brain health and for enhancing neurotransmission.
In 2018, Armstrong and his students developed a rapid method for optimizing enantiomeric separations of 150 amines using a stationary phase of superficially porous particles (SPPs) (5). For this work, four different chiral stationary phases (CSPs) of SPPs were used for enantiomeric separations of chiral amines, including a different structural and drug class amines. These molecules are of great importance in forensics and in pharmaceutical drug development. A cyclodextrin-based CSP (CDShell-RSP), a cyclofructan-based CSP (LarihcShell-P), and macrocyclic glycopeptide-based CSPs (VancoShell and NicoShell) were all used for this study. This method that was able to simultaneously baseline separate all 150 amines in a single LC–MS analysis. These CSPs were shown to be multimodal and can be used with solvents compatible with mass spectrometry.
Additional work published in 2018 demonstrated the high value of separations-based methods to prepare samples for use with analyte-specific chemical sensors, by removing matrix effects and interferents found within typical samples (6). Until this study, separation techniques were considered too slow for traditional chemical sensors (1 to 20 s for a single analyte). This work demonstrated that core–shell particle beds of optimal geometry can be used in an ultrahigh-flow regime and can provide subsecond separations of up to 10 analytes. Stainless steel columns of various compositions and geometries were optimized for subsecond analysis, providing quantitation of multiple chiral and achiral species, including plant hormones, acids, nucleotides, amino acid derivatives, and drugs, such as sedatives; these subsecond separations were reproducible with 0.9% RSD for both retention times and reduced plate height in van Deemter curves.
In a 2017 paper, Armstrong and colleagues described a set of fundamental and practical methods and insights into the processes involved in packing modern high-efficiency analytical and capillary columns (7). They provided logical approaches and strategies to optimize column packing in terms of the variable set of slurry solvents, stationary phases, and hardware designs. Such an approach is essential to bypass typical trial-and-error approaches to column construction and method development. The authors note, “The science of packing columns with stationary phases is one of the most crucial steps to achieve consistent and reproducible high-resolution separations.”
Peak detection, shapes, and analysis are key aspects of quantitation using chromatographic methods. Classical tests for peak symmetry or asymmetry indicate only skewness in excess (tail or front) and not the presence of both. Thermodynamic factors, kinetic factors, and variability in flow cause chromatographic peak shapes to depart from linearity. Two tests, the derivative test and the Gaussian test, are used to analyze peak shapes in GC, LC, SFC, and CE (8). The derivative test uses the symmetry of the inflection points along with the minimum and the maximum derivative values. The Gaussian test uses a constrained curve-fitting approach with residuals analysis. In this work, a number of examples are shown, and the utility of these approaches is demonstrated.
In another study, the analysis of D-amino acid levels was shown for the first time in perfused mouse brain tissue and blood; this method eliminates artifacts due to endogenous blood (9). A comparative study quantifying D- and L-amino acid levels in the hippocampus, cortex, and blood samples from NIH Swiss mice was also reported. The regulation and function of specific D-amino acids are discussed, and their essential biological and neurological roles are examined based on analytical results.
Another recent paper reported an investigation into the use of ultrafast chiral chromatography as a second dimension for 2D chromatographic separations (10). In this study, excellent selectivity, repeatability, and peak shape were achieved by combining achiral and chiral narrow-bore columns in the first dimension with columns packed with highly efficient chiral selectors in the second dimension. Both dimensions use 0.1% phosphoric acid in acetonitrile as eluents. The developed method was successfully applied to the analysis of complex mixtures including chiral and achiral drugs and metabolites, constitutional isomers, stereoisomers, and organohalogenated species representing quite similar pharmaceuticals and synthetic intermediates.
It is well understood that column technology is ahead of existing chromatographic instrument systems, and this was examined by Armstrong and his students in 2016 (11). In this study the idiosyncrasies of instrumental issues that affect the performance of ultrafast chiral and achiral sub SFC is addressed. One key aspect of instrument artifacts is indicated when the chromatographic output does not indicate the true peak profile occurring inside the column. Ultrafast SFC demonstrates unexpected affects not observed in ultrafast LC. A variety of instrumental affects, peak tests, and data processing methods in ultrafast SFC are applied and the results demonstrated.
In another publication, a method is described for the determination of trace water content in complex petroleum and petroleum-based product matrices (12). A simple, rapid, automated headspace GC (HSGC) method requiring ionic liquid stationary phases with modified instrumentation was tested. Water in the concentration range of ~12–3300 ppm was measured in 3 National Institute of Standards and Technology (NIST) reference materials and 12 petroleum product samples. The described approach appeared not to be affected by the complexities of the matrixes.
Key Career Publications: Most Cited
Armstrong and students have produced papers with large numbers of citations, with several papers receiving over 800 reference citations (according to Google Scholar). A leading paper, with over 1150 citations, described research using a linear free energy approach for room-temperature ionic liquid (RTIL) characterization (13). RTILs are used as solvents for organic synthesis and liquid−liquid extraction; in MALDI–MS, and as stationary phases in GC. This specific research determined the distinct multiple solvation interactions with probe solute molecules for 17 RTILs, providing interaction and property data for the various applications.
A second paper, with over 950 citations, describes the replacement of organic solvents with ionic liquids in multiple areas of separation science (14). Topics elucidated include the use of ionic liquids as “green solvents” for various chromatographic methods, extractions, and supported liquid membrane processes.
The use of stable RTILs for reaction solvents is discussed in another highly cited paper, with more than 800 citations (15). This work explains how RTILs are capable of solubilizing both cyclodextrins and glycopeptides, which are highly complex polar molecules. RTILs may also be coated onto fused silica capillaries due to their viscosity and wetting ability. In this study, 1-butyl-3-methylimidazolium hexafluorophosphate and its analogous chloride salt were demonstrated as stationary phases for GC. By applying inverse GC, the nature of RTILs was studied via their interactions with a variety of compounds, and the Rohrschneider-McReynolds constants were measured and computed for both ionic liquids and a commonly used commercial polysiloxane stationary phase.
Another Armstrong study with more than 800 citations used HPLC to evaluate representative macrocyclic compounds that were covalently linked to silica gel for their stability, loadability, and ability to resolve racemic mixtures (16). It was determined that more than 70 compounds were resolved while achieving some separations not previously reported on any other CSP. These CSPs were observed to be multimodal, useful for both normal-phase and reversed-phase modes, with no observed deleterious effects to the stationary phases or any irreversible changes in the enantioselectivity when alternating from one mode to another.
Over the years, Armstrong has become well known for his many collaborative research projects. One longtime collaborator is Ján KrupÄík, a professor at the Institute of Analytical Chemistry in the Faculty of Chemical and Food Technology at Slovak University of Technology in Slovakia. The collaboration between KrupÄík and Armstrong began 1998, resulting in 52 joint research papers and a close friendship. In 2018, Armstrong was awarded a Doctor Honoris Causa degree at the Slovak University of Technology in recognition his extensive research collaboration with the institution.
Another collaborator is Alain Berthod, the Emeritus CNRS Research Director at the Institute of Analytical Sciences at the University of Lyon in France. He first encountered Armstrong when he was reviewing a paper Armstrong had submitted to Analytical Chemistry. Berthod noticed an issue and contacted Armstrong personally. “Prof. Armstrong checked my equations and immediately responded telling me that he withdrew his article to rewrite it including my theoretical part and adding my name as coauthor,” he said. “That was the beginning of a lifetime of scientific collaboration and friendship,” he said. Since then, Armstrong has invited Berthod every other year to come during the summer (for collaboration on chiral separations. “We became close friends,” he said.
Jared Purnendu “Sandy” K. Dasgupta, the Hamish Small Chair in Ion Analysis at the Department of Chemistry and Biochemistry at The University of Texas at Arlington, has known Armstrong for a long time and says that collaboration is a key aspect of Armstrong’s personality. “We have authored a few papers together but perhaps more importantly have often sought each other out when we were particularly excited about something and wanted to talk to someone who would understand and appreciate it,” Dasgupta said. “I have known Dan for close to 40 years and I am still impressed by his zeal, his enthusiasm for his latest love, and his creativity. There is no one I can think of who has contributed to so many aspects of the separation sciences and continues to get into new frontiers-the LCGC lifetime achievement award is most befitting.”
Zachary Breitbach, a Principal Research Scientist in Analytical R&D for AbbVie, Inc. in North Chicago, Illinois, has a typical Armstrong scientific collaboration story. Breitbach was a graduate student of Armstrong’s from 2005 to 2010 and worked with him for the next six years to cofound a small HPLC column company and contract analytical group called AZYP Separations and Analytics. “We currently still work together teaching chiral separations short courses at conferences and are cochairing the 2021 Chirality Conference,” Breitbach says. “We have also become close friends.”
Given the impact and breadth of Armstrong’s work, others find it hard to say which of his achievements have been the most significant. KrupÄík, for example, says that there are many areas that can be cited as Armstrong’s greatest work. “His fundamental research in chiral recognition and enantiomeric separations (in LC and GC) revolutionized drug development and the pharmaceutical industry,” he said. KrupÄík adds that other notable research work includes introducing micelles to separations and deriving the three-phase model of separations, which has been widely applied in LC, GC, solid-phase microextraction (SPME), and more; and in developing and characterizing high-stability ionic liquids as the first new class of GC stationary phases in more than 40 years. “His very recent work on gas chromatography–molecular rotational resonance spectroscopy (GC-MRR) could be the most important development in instrumental analysis in decades,” he said.
Berthod considers Armstrong’s greatest contributions to separation science to be in two main areas: the development of the macrocyclic glycopeptide chiral selectors, and the use of dicationic ionic liquids as stationary phases in capillary columns for GC.
Jared Anderson is the Alice Hudson Professor of Chemistry at Iowa State University. He started working in Armstrong’s group as a graduate student in 2000 and graduated with his PhD in 2005. “The impact of his work can be felt in many sectors of industry ranging from food science, agriculture, to the pharmaceutical industry,” Anderson said. “One of the aspects that I have admired most about Dan is his ability to work in numerous areas and to make impactful contributions in whatever he does.” Anderson believes that Armstrong’s greatest contributions have been in chiral chromatography. “When Dan first started in chiral chromatography, there were very few chiral selectors among the various chromatographic techniques,” he said. “He pioneered the development of many new classes of chiral selectors that revolutionized the way in which chiral compounds can be separated.” Anderson noted that many fields in chemistry that work in the area of asymmetric catalysis rely heavily on the chiral columns developed in Armstrong’s laboratory to characterize the enantiomeric purity of their products.
Breitbach feels there is a long list of contributions to cite. “Some of the most important and impactful would have to be the invention, development, and commercialization of cyclodextrin and macrocyclic glycopeptides-based chiral selectors for GC, HPLC, and CE,” he says. “There are few who have advanced the field of chiral separations as much as Professor Armstrong,” he added, citing the many materials, analytical methods, techniques, publications, and instrument developments Armstrong has produced.
“There is little doubt that the Dan’s work on cyclodextrin and ionic liquid based chromatographic phases stands out,” said Dasgupta.
Teacher and Mentor
In addition to noting Armstrong’s impressive scientific contributions, many have also commented on his impact as a teacher and mentor, and as a person.
Anderson, for example, attributes his motivation in science to Armstrong. “My passion for the analytical sciences, especially in chromatography, was largely ignited by Dan,” he said. “There are few scientists that I’ve met who have the same insatiable love for science than he does!” Anderson also appreciates the excellent training he received Armstrong. “As a former student and now a mentor myself, I respect the high expectations he sets for his graduate students and postdocs-ensuring that they will be well-trained in science as well as in oral and written communication,” he said.
Breitbach agrees with that assessment. “In addition to the many methods, techniques, and materials developed by Professor Armstrong, it is his ability to teach those topics to conferees, readers of his publications, and his students that has been hugely impactful to the field. This is where his true legacy lies,” he said. Breitbach added that Armstrong is a leader who is inspiring and passionate about science. “I consider myself lucky to have spent many years working with Professor Armstrong; it was the most rewarding part of my career,” he said “He has made a lasting positive impact on me, my family, many other researchers, and the chromatographic community”
Others shared experiences of Armstrong’s personal concern for their well-being. Berthod recalls an incident when he was injured, and Armstrong took care of him for a full week. “Dan has the character trait of being dedicated to others,” he said.
KrupÄík agrees. “Dan is an excellent scientist and teacher as well as a very good father and grandfather,” he said.
A Broad Impact
Dan Armstrong’s impact on the field of chromatography is vast, encompassing mobile and stationary phases, column design, instrument and detector design, and data analysis; mass spectrometry; enantiomeric separations; ionic liquids, including synthesis, characterization and applications; ordered media, including micelles and macrocyclic compounds; molecular recognition, specifically chiral and isomeric types; and drug, environmental, and food analysis.
Dasgupta appreciates his contributions in a personal way, as a colleague, and as a member of the broader separations science community. “He is an asset to this department and this university,” Dasgupta said. Indeed, he is an asset to the field he has devoted his life to,” he said. “I am just fortunate that he is my colleague and my friend.”
The Emerging Leader Award
The Emerging Leader in Chromatography Award recognizes the achievements and aspirations of a talented young separation scientist who has made strides early in his or her career toward the advancement of chromatographic techniques and applications.
Szabolcs Fekete, the 2020 winner, earned his PhD degree in 2011 from Technical University of Budapest, Hungary, and is currently a scientific collaborator at the University of Geneva. His work focuses on six major areas. The first two are the characterization of therapeutic proteins and advancing protein analysis using reversed-phase LC, ion-exchange chromatography (IEC), size-exclusion chromatography (SEC), hydrophobic interaction chromatography (HIC), and hydrophilic interaction chromatography (HILIC). The others are LC column technology; LC method development, optimization, and retention modeling; fundamental studies on retention and band broadening; pharmaceutical analysis.
In one of his early studies, Fekete was the first to evaluate the impact of operating pressure on protein retention and selectivity in reversed-phase LC. A huge pressure effect was observed even in gradient mode, which was not expected. It was found that pressure can be an important parameter in method development to adjust protein retention. Fekete has also published valuable work on the retention modeling of large proteins (monoclonal antibodies) using computer simulation, suggesting a generic method development approach and platform methods, which are very important for pharmaceutical industrial laboratories. He has also carried out fundamental studies in which the effect of longitudinal temperature gradient on retention, caused by frictional heating, was experimentally dissociated from the combined effect of pressure and frictional heating. Through this work, the specific contributions of these effects to the overall retention were determined for both small and large solutes.
Fekete has published 104 papers, with more than 1528 citations. He has also given more than 50 oral and 30 poster presentations at scientific conferences and has won five “best poster” awards at international conferences. He also received the György Oláh award from the University of Technology of Budapest in 2011.
Most Important Recent Research
In one of his first important research studies, Fekete and co-workers explored the detailed effects of pressure and mobile-phase velocity on the retention properties of small molecules, peptides, and proteins (such as monoclonal antibodies) in ultrahigh-pressure liquid chromatography (UHPLC) (17). They learned that the effect of pressure and mobile-phase velocity on retention varies in proportion with the size of the molecule and that the conformational properties of large biomolecules play important role in their retention properties.
In another study that same year, Fekete and coworkers evaluated a generic method development approach for reversed-phase LC for the analysis of monoclonal antibodies (mAbs) (18). This method development strategy considered optimization of analytical conditions based on the selectivity, efficiency, recovery, and thermal degradation potential of selected analytes. They discovered that the gradient steepness and temperature cannot be optimized using either the traditional van ’t Hoff linear model or the common linear solvent strength model, but that by applying quadratic models, the prediction accuracy of retention times was found to be excellent with a relative error between 0.5 and 1%. The quadratic approach was verified using two separations of mAb fragments.
Further work by Fekete evaluated changes in retention times as influenced by frictional heating, pressure, and temperature for UHPLC conditions (19). This work involved four model proteins, namely, lysozyme, myoglobin, fligrastim, and interferon alpha-2A, with molecular weights over the range of 14 to 20 kDa. Fekete discovered that retention times of tested protein molecules cannot be explained solely by frictional heating and pressure effects, and that maximum retention factor values on computed van ’t Hoff plots indicate a probable change of secondary protein structure or conformation with changes in pressure and temperature. Based on this study, it appears that a combination of pressure and temperature causes protein denaturation and a folding–unfolding process, which is clearly protein molecule dependent.
Fekete coauthored the first review on the application of superficially porous particles used in modern HPLC (20), and this work has received nearly 250 citations to date and is his most highly cited paper. The goal of this review paper was to describe recent developments in the application of short and narrow-bore columns packed with modern core–shell and very fine fully porous particles, in fast or “ultrafast” HPLC. Efficiency data obtained with modern commercialized columns were compared in terms of separation time and efficiency. It was found that the expected theoretical efficiency versus the measured efficiency varied and was most pronounced for narrow-bore columns; furthermore, it is thought not yet possible to realize the full efficiency of these small columns.
Fekete was the senior author on a “Fundamentals and Applied Reviews” paper for the journal Analytical Chemistry (21), which has been cited over 135 times. This review covers the analysis of protein-based biopharmaceutical molecules with HPLC, UHPLC, IEC, SEC, HIC, HILIC, and reversed-phase LC. The detailed review describes the characterization of multiple protein types and molecular sizes along with sample preparation modes for each type. As one example, mAbs characterization is typically completed by analysis of the protein, peptide, glycan, and amino acid levels. During sample preparation, partial enzymatic digestions or reduction of disulfide bonds are frequently used to assist in the production of smaller protein fragments. This predigestion step is required because of the limited resolving power of different separation modes on intact proteins. The digestion process produces smaller protein fragments, which are easier to characterize. There are a number of details regarding sample preparation that are addressed in this review.
Work Most Highly Cited
Fekete’s most cited work on fast LC has been mentioned previously in this article (20). His second most cited work involves a comparative study of mass-transfer resistance for stationary phase materials, comparing SPPs, sub-2-μm fully porous particles, and monolithic (22). This paper, cited over 170 times (according to Google Scholar), describes the dependence of mass-transfer resistance on stationary phase particle size with an understanding of the practical limits versus the theoretical expectations for plate height and mass-transfer resistance. An approach was taken to study particles with shortened diffusion paths to enhance the efficiency of separations. Selected commercially available columns were compared using van Deemter and Knox plots, and theoretical Poppe plots were used to compare kinetic performance. This work used polar neutral analytes and compared low molecular weight compounds (from 270 to 430 Da) and one higher molecular weight compound (~ 900 Da). This work defined relationships between high flow rates, very fast separations, and column efficiency.
Another highly cited work from Fekete (over 150 citations) involves a study of the theory and application of SEC for quantitative and qualitative analysis of therapeutic protein aggregates (23). The main advantage to using SEC for this application is the mild mobile phase chemistry that has minimal impact on the conformational structure and local environment of protein aggregates. A series of method strategies and generic rules is explained to address peak shape and chromatographic parameters for SEC method development. Other topics discussed include smaller columns with reduced particle size stationary phase for improved resolution and throughput; and the factors involved in combining SEC with refractive index (RI), ultraviolet (UV), multi-angle laser light scattering (MALLS), viscometer (IV), and mass spectrometry (MS) detectors.
Since its commercial launch in 2004, UHPLC has revolutionized the throughput rate of HPLC methods. Fekete and coauthors reviewed this subject in a highly cited paper in 2014, with over 135 citations (24). This review discussed the many advantages of UHPLC, in addition to its power to perform fast separations with good resolution. Some of the additional benefits described include high-resolution analysis of complex samples; the ability to perform hyphenated chromatographic modes, including chiral LC, SEC, IEC, HILIC, and SFC; and the ability to handle dynamic pressure changes, higher temperature runs, smaller particle sizes, and adaptable stationary phases; and the overall improved kinetic performance. The application of UHPLC greatly improves the characterization of biopharmaceuticals and provides for hyphenation to mass spectrometry (UHPLC–MS) as an analytical tool for multi-protein-residue screening, and metabolomics.
Fekete and coworkers produced a substantial review for the journal Analytical Chemistry, which provided his next most highly cited paper (21). As previously described, this review explored the use of separation science, electrophoresis, and mass spectrometry for analysis of protein biopharmaceuticals.
Pharmaceutical analysis laboratories use chromatographic methods on a regular basis and understanding instrumentation is essential for optimizing analytical method development. In another highly cited review paper (over 120 citations), Fekete describes the importance of understanding instrumentation for fast LC applications in pharmaceutical analysis (25). Improvements in separation speed, sensitivity, and ease of operation are some of the most notable changes for modern chromatographic instrumentation. This review describes the issues associated with maximum system pressure, dwell volume, extracolumn variance, injection cycle time, and detector data acquisition rate. Details of column packing and types of particles useful on a conventional LC instrument are explained in detail. In addition, the compatibility of different instrument types with a variety of column configurations is discussed.
Reversed-phase LC has become a workhorse technique for the analysis of therapeutic peptides and proteins in the pharmaceutical industry. Fekete addressed the subject of reversed-phase separations for both LC and LC–MS in another review article (26). The authors discuss the issues associated with using reversed-phase methods for biomolecules, specifically for characterization of peptides and proteins. Advances in reversed-phase columns and particle types are described in detail, along with the effects of elevated temperature, and performance based upon both kinetic efficiency and selectivity. Multiple methods and applications are described along with the compatibility of reversed-phase separations with MS in terms of matrix-assisted laser desorption–ionization (MALDI) and electrospray ionization (ESI) techniques. This paper has 114 citations.
Praise for Fekete
A number of separation scientists have been impressed by Fekete and his work. Jean-Luc Veuthey, a full professor at the University of Geneva (Switzerland), was Fekete’s post-doctorate advisor in 2011 and supervised Fekete’s research work on the analysis of biopharmaceuticals. “He possesses a great knowledge in fundamental chromatography and therefore he has developed many elegant and innovative methods for analyzing complex compounds such as biopharmaceuticals in their intact form as well as in middle-up/middle down approaches,” he said. “He has an impressive knowledge of software-assisted liquid chromatography-based method development tools and has published relevant papers in this area with Dr. Imre Molnár and others.”
Sándor Görög was a professor and the director of analytical research at Gedeon Richter Plc. in Budapest in 2000 when he first met Fekete, who worked in the firm’s analytical R&D group while completing his masters and PhD studies. Görög found Fekete to be inquisitive and talented. “Szabolcs often came to me to discuss his new ideas and asking for my help mainly in the preparation of his first scientific publications,” he said. “I was pleased to help him since I soon realized that he was a very talented and ambitious young man.”
Görög also appreciated Fekete’s balance of theory and practice. “He is strong in the fundamentals of chromatography but always keeps in mind the practical aspects which is important since chromatography at the end is an applied science,” he said. “His findings can help the everyday-work of many practicing chromatographers.”
Katalin Ganzler is the department head at the Chemical Works of Gedeon Richter, where she supervised and worked closely with Fekete for eight years. She appreciated not only his excellent science-citing his publications on chromatographic stationary phases and protein separations as his best work-but also his personal qualities-mentioning his open-mindedness, curiosity and enthusiasm.
Davy Guillarme, who is a senior lecturer and research associate at the University of Geneva, in Switzerland, has worked with Fekete since the summer of 2011, when Fekete came to the University of Geneva as a post-doctoral researcher. “I was really looking forward to working with Szabolcs, since he had good expertise in the field of biopharmaceuticals analysis, something in which we did not have any expertise in at this time,” he said. “Szabolcs has made a huge number of significant contributions in the field of chromatography since then and published 117 publications in peer-reviewed journals between 2009 and 2019.”
In particular, Guillarme notes that Fekete’s highly cited papers-including the 11 he published during his PhD, from 2009 to 2011-have contributed to the popularization of core–shell column technology. But even more so, Guillarme is impressed with Fekete’s work on the analysis of protein biopharmaceuticals. “He has published more than 100 papers on this topic and can be considered today as one of the most renowned or knowledgeable persons in therapeutic proteins analysis,” Guillarme said.
Imre Molnár, the President of the Molnár-Institute in Berlin, Germany, was teaching a short course in 2008 when he met Fekete, who demonstrated his talent by suggesting a solution to a difficult problem. “Suddenly a young man jumped up and rushed to the screen and pointed out precisely how it should be done,“ he said. “After the session was closed, I asked him about his plans for obtaining a PhD.” At the time, Fekete had not such plans. “I spoke with Prof. Jenö Fekete, suggesting that he give Szabolcs a chance-advice he soon followed.” Fekete began his PhD studies the next year.
Matthew Lauber is a consulting scientist in the Chemistry R&D section of Waters Corporation and has been collaborating with Fekete for over four years, following an initial meeting at an HPLC conference. “Our first area of overlapping interest was in using widepore polyamide bonded stationary phases to venture into HILIC of intact proteins-a topic that most chromatographers had up until then shied away from and assumed was impossible,” he said. Fekete and Lauber have co-authored a number of research papers and have established a vibrant collaboration, including visits to each other’s laboratories. Lauber is very impressed with Fekete’s research. “Easily, Szabolcs’s greatest contributions would be his insights into protein chromatography, whether they are those related to size-based separations, milder reversed phase chromatography, or exploring new limits with HILIC,” he says. “Unlike most scientists in this field of work, Szabolcs has a unique ability to turn empirical observations into new formulae and models for describing the chromatographic behavior of large molecules.”
An Emerging Leader
Fekete has many hallmarks of an emerging leader in separation science: a strong focus on both fundamentals and applied science, a strong drive, and excellent output. “He is really a great scientist, passionate about the fundamental aspects of chromatography and its application to solve real-life problems,” said Guillarme. “He is very creative and productive, and I sincerely hope that Szabolcs will be able to obtain a fixed position at the University of Geneva.”
Molnár agrees. “Szabolcs is an extraordinarily productive young scientist,” he said. “His energy is astonishing, and his skill in running HPLC analysis is of an expert.”
Lauber echoes those views. “Szabolcs has a drive and enthusiasm for separation science that stands out among his peers,” he said. “In some ways, he is a fundamentalist and he is better for it. I can see him having a long, successful career in either academia or industry.” Molnár hopes it will be the latter. “For the last five years, he has been in Switzerland, but I hope he will change his employer to the Molnár-Institute in Berlin,” he quipped.
Jerome Workman, Jr. is the Senior Technical Editor of LCGC and Spectroscopy. Direct correspondence to: firstname.lastname@example.org