Editor's Note: This article was prepared in cooperation with John M. Riviello, formerly of Dionex and Thermo Fisher, and a colleague of Christopher Pohl.
Scientist and inventor Christopher Pohl, no stranger to receiving awards, has been honored with the American Chemical Society Award 2023 in Chromatography. The award ceremony took place March 28 during the spring meeting of the American Chemical Society (ACS) in Indianapolis, Ind. A special symposium in honor of Pohl organized by Professor Purnendu K. (Sandy) Dasgupta, from University of Texas at Arlington, will be a part of ACS Fall 2023 in August, in San Francisco.
Most important inventions and accomplishments
Pohl was the technology innovator and driving force for the development of more than 50 unique polymeric stationary phases and IC columns for various applications. His inventions in stationary phase design remain the core separation technology for IC analysis of small ions. Additionally, those novel ion-exchange phases also have gained significant commercial success outside the traditional IC market for high-performance separations of proteins, nucleic acids and carbohydrates.
Pohl is an author or co-author of 105 US patents with numerous foreign equivalents in several areas including separation methods, stationary phase design, suppressor technology, solid-phase extraction, capillary electrophoresis techniques, methods of calibration, mixers, and accelerated solvent extraction (ASE). His knowledge and contributions to separation science are captured in 149 manuscripts in peer-reviewed journals, 14 book chapters on IC stationary phase design, mechanisms, consumables, and applications and in the most recent monograph on IC instrumentation and techniques. Pohl’s most significant accomplishments are listed below:
Mobile phase ion chromatography (MPIC)
Pohl’s first contribution to IC began soon after the commercial introduction of the method in 1975. As an analytical chemist at the Clorox Company, he was intrigued by this new technique of ion analysis. Clorox’s resistance to purchase a commercial IC resulted in Pohl developing a “suppressible” ion pair method using a polymeric reversed-phase column [1]. Pohl reduced this to practice, and it was this work that landed him his first R&D job at Dionex. Eventually, Dionex commercialized this new technique as mobile phase ion chromatography (MPIC).
High-performance anion-exchange separations of carbohydrates
In 1982, within collaboration of Dionex with Prof. Dennis Johnson, Pohl was working on the separation of carbohydrates in IC mode with electrochemical detection. He discovered that the best separation of carbohydrates could be achieved using high pH eluents instead of moderate pH borate eluents used at that time and realized that carbohydrate separation could proceed without borate based on completely different mechanism [2]. Pohl’s findings and mechanism interpretation for retention and separation of carbohydrates with anion-exchange chromatography at high pH led to the development of unique high-performance CarboPac column series belonging to the Dionex/Thermo Fisher Scientific portfolio.
Development of hydroxide-selective anion-exchange phases for IC
Since the inception of IC, hydroxide eluents were recognized as being ideal for use with conductivity detection. In coordination with Hamish Small and the development of electrolytic eluent generation, Pohl pioneered the development of hydroxide selective stationary phases [3]. His research on anion-exchange stationary phases behavior led to the observation that incorporation of one or more ethanol substituents in the quaternary ammonium site makes hydroxide a more effective eluent for the separation of anions.
This finding resulted in several advantages for ion analysis by IC: First, lower detection limits became achievable with hydroxide eluent as compared to carbonate eluent due to lower suppressed background conductivity of hydroxide. Second, hydroxide eluent provides a linear calibration curve, while carbonic acid formed after suppression of carbonate may affect linearity if operating in a wide range of concentrations. Third, development of numerous anion-exchangers suitable for gradient ion chromatography applications became possible, which allowed the analysis of mono- and polyvalent anions in one run and significantly broadened the range of suppressed IC applications. As a result, electrolytic hydroxide eluent generation and the range of hydroxide-selective stationary phases developed under Pohl’s guidance are the dominant form of gradient technology used in IC today.
Development of membrane suppressor technology
The development of hydroxide-selective IC columns was the driving force for the suppressors compatible with the higher eluent concentrations. Pohl led the development of the first commercial flat membrane suppressor at Dionex and was a co-inventor of the first Dionex patent covering the flat membrane suppressor [4]. This patent covered a critical component that helped Dionex dominate the IC market and remains the core suppression technology sold by Thermo Fisher Scientific with every ion chromatograph today.
Accelerated solvent extraction
In 1998, Dionex acquired Lee Scientific, a company commercializing supercritical chromatography (SFC) and supercritical fluid extraction (SFE). Pohl recognized the limitations of supercritical fluids and led the development of a new technique for extracting trace components from solid and semi-solid samples under elevated pressures and temperatures. The new technique, Accelerated Solvent Extraction (ASE) [4], was patented and commercialized by Dionex, and remains a successful sample preparation tool today.
Development of hyperbranched anion-exchange condensation polymer synthesis technology
Pohl’s development of hyperbranching technology based on forming step-growth polymer coatings [5] on the sulfonated substrate surface became a significant breakthrough in the anion-exchange stationary phase design for IC. The major advantages of hyperbranching process include ease of selectivity and capacity optimization, which makes this technology the most versatile stationary phase chemistry platform in IC. Nowadays, hyperbranched anion exchangers represent a significant part of Thermo Fisher Scientific IC column portfolio and are known for their exceptionally high performance.
As a prolific inventor and a mentor to many industrial chemists, Pohl has left an indelible mark in the field of IC and analytical chemistry. His dedication and passion to science made him a great role model and source of motivation and inspiration for his co-workers and other members of separation science community worldwide. Pohl’s inventions, from sample preparation to separation and detection, are responsible for making IC an essential technique in the analytical chemists’ toolbox and are supporting global laboratory workflows using Innovative ion chromatography systems every day for a variety of analytical applications.
Pohl’s contribution to IC was recognized by several prestigious awards, including: International Ion Chromatography Symposium Award (1990); Uwe Neue Award (2018); Eastern Analytical Symposium Separation Science Award (2018); and George N. Hatsopoulos Technical Innovation Award from Thermo Fisher Scientific (2020). Nominated by Prof. Dasgupta, Pohl became the second industrial chemist in over 60-years-long history of ACS National Awards to receive an award in Chromatography. The fact that the first industrial chemist acknowledged with such an award was “the father” of IC, Hamish Small himself (in 1991), makes this achievement even more significant.
Additional information
- Mobile phase ion chromatography
- CarboPac column series
- Electrolytic hydroxide eluent generation
- Hydroxide-selective stationary phases
- Hydroxide-selective IC columns
- Suppression technology
- Accelerated Solvent Extraction
- IC column portfolio
- Innovative ion chromatography systems
References
- Pohl, C. A. Chromatographic separation and quantitative analysis of ionic species. U. S. Patent 4,265,634, May 5, 1981.
- Rocklin, R.D., Pohl, C.A., Determination of carbohydrates by anion exchange chromatography with pulsed amperometric detection. J. Liq. Chromatogr. 1983; 6(9): p. 1577-90.
- Pohl, C.; Slingsby, R. W.; Stillian, J. R.; Gajek, R. Modified membrane suppressor and method for use. U. S. Patent 4,999,098, March 12, 1991.
- Richter, B.E., Jones, B.A., Ezzell, J.L., Porter, N.L., Avdalovic, N., Pohl, C., Accelerated solvent extraction: A technique for sample preparation. Anal. Chem. 1996; 68(6): p. 1033-1039.
- Pohl, C., Saini, C., New developments in the preparation of anion exchange media based on hyperbranched condensation polymers. J. Chrom. A. 2008; 1213(1): p. 37-44.
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