Mark Dietz

 (414) 229-1748
 Chemistry Building 643


Ph.D., University of Arizona

Research Areas

Few analytical methods are truly specific for a single species. As a result, problems in chemical analysis frequently involve a preliminary separation step to isolate the species of interest from matrix constituents and from potential interferents. Chemical separations play an equally important role in many preparative and process-scale applications, the preparation of high-purity radiopharmaceuticals and the reprocessing of spent nuclear fuel representing just two of many possible examples.

In general terms, the goal of our research is to devise improved reagents, media, and processes for the separation and preconcentration of metal ions and organic molecules, and to explore the fundamental chemistry underlying their use. Of particular interest is the development of environmentally benign approaches to chemical separations. Within this broad framework lie two specific areas of study: room-temperature ionic liquids (RTILs) and supercritical fluids (SCFs). Supercritical fluids comprise a unique class of solvents with properties intermediate between those of a liquid and a gas.

Fig. 1. Phase diagram for carbon dioxide.

Ionic liquids, unlike SCFs or conventional molecular solvents, consist entirely of ions, and as a result, exhibit a wide variety of interesting and useful properties.

Fig. 2. A representative room-temperature ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate

Both classes of solvents show enormous potential as replacements for the toxic and volatile organic solvents employed in many separation processes, in part a result of their extraordinary tunabililty. In the case of SCFs, simply changing the temperature or pressure can significantly alter the solvent properties of the fluid. Similarly, for RTILs, minor changes in the nature of the cation or anion comprising the solvent can lead to dramatic changes in its behavior. It is this tunability that we seek to exploit in developing improved methods of separation.

Our recent work in this area has focused on three topics:

    • Preparation and characterization of “inorganic liquids”, a novel sub-class of ionic liquids incorporating at least one inorganic component (e.g., a polyoxometalate anion), and evaluation of their potential utility in separations.
Fig. 3. The 1-ethyl-3-methylimidazolium salt of the Lindqvist anion.
    • Elucidation of the factors (e.g., RTIL cation and anion structure) determining the mode of metal ion transfer from aqueous solution into an ionic liquid in the presence of various types of ligands (e.g., crown ethers).
Fig. 4. Possible partitioning modes for metal ions in biphasic aqueous-RTIL systems in the presence of a macrocyclic polyether.
    • Development of alternatives to fluorination as a means of improving the compatibility of organic extractants with supercritical carbon dioxide.
Fig. 5. A trimethylsilylpropyl esterified diphosphonic acid.

Progress in these areas is expected to provide the basis of efficient and selective “green” approaches to the separation of metal ions and organic molecules from a variety of complex matrices.

Selected Publications

Wankowski, James L., and Dietz, Mark L. “Ionic Liquid (IL) Cation and Anion Structural Effects on Metal Ion Extraction into Quaternary Ammonium-based ILs.” Solvent Extraction and Ion Exchange 34.1 (2016): 48-59.
Momen, M. A., and Dietz, Mark L. “Sol-Gel Glass-Encapsulated Crown Ethers for the Separation andPreconcentration of Strontium from Acidic Media.” Separation Science and Technology 50.18, SI (2015): 2873-2880.
Hawkins, Cory A., Rud, Anna, Guthrie, Margaret L., and Dietz, Mark L. “Rapid quantification of imidazolium-based ionic liquids by hydrophilicinteraction liquid chromatography: Methodology and an investigation ofthe retention mechanisms.” Journal of Chromatography A 1400. (2015): 54-64.
Hawkins, Cory A., Momen, M. A., Garvey, Sarah L., Kestell, John, and Dietz, Mark L. “Evaluation of solid-supported room-temperature ionic liquids containingcrown ethers as media for metal ion separation and preconcentration.” Talanta 135. (2014): 115-123.
Pawlak, Alan J., and Dietz, Mark L. “Thermal Properties of Macrocyclic Polyethers: Implications for theDesign of Crown Ether-Based Ionic Liquids.” Separation Science and Technology 49.18 (2014): 2847-2855.
Garvey, Sarah L., Shahmohammadi, Golbon, McLain, Derek R., and Dietz, Mark L. “Determination of Calcium in Dietary Supplements: Statistical Comparisonof Methods in the Analytical Laboratory.” Journal of Chemical Education 92.1 (2014): 167-169.
Garvey, Sarah L., and Dietz, Mark L. “Ionic liquid anion effects in the extraction of metal ions bymacrocyclic polyethers.” SEPARATION AND PURIFICATION TECHNOLOGY 123. (2013): 145-152.
Hawkins, Cory A., and Dietz, Mark L. “Novel tandem column method for the rapid isolation of radiostrontiumfrom human urine.” Analytica Chimica Acta 746. (2012): 114-122.
Hawkins, Cory A., Garvey, Sarah L., and Dietz, Mark L. “Structural variations in room-temperature ionic liquids: Influence onmetal ion partitioning modes and extraction selectivity.” Separation and Purification Technology 89. (2011): 31-38.
Beyhaghi, Saman, Pillai, Krishna M., Qadah, Diab T., and Dietz, Mark L. “Evaporation and transport of non-dilute, multi-component liquid mixturesin porous wicks: Simulation and experimental validation.” International Journal of Heat and Mass Transfer 54.25-26 (2011): 5216-5230.
Dietz, Mark L. “On the radiation stability of crown ethers in ionic liquids.” Journal of Physical Chemistry-B 115.14 (2011): 3903-11.
Dietz, Mark L. “Extraction and reductive stripping of pertechnetate from spent nuclear fuel waste streams.” Separation Science and Technology 46. (2011): 357-368.
Dietz, Mark L., Qadah, Diab T., and Garvey, Sarah L. “Extraction of tetra-oxo anions into a hydrophobic, ionic liquid-based solvent without concomitant ion exchange.” Industrial and Engineering Chemistry Research 49. (2010): 5863-5868.
Dietz, Mark L. “Neoteric solvents as the basis of alternative approaches to the separation of actinides and fission products.” Ion Exchange and Solvent Extraction: A Series of Advances 19. Ed. Moyer, Bruce A. CRC Press, (2009): 617-639.
Dietz, Mark L. “Tetraalkylphosphonium Polyoxometalates as Novel Ionic Liquids.” Solvent Extraction: Fundamentals to Industrial Applications. Ed. Moyer, Bruce A. Canadian Institute of Mining, Metallurgy and Petroleum, (2008): 799-804.
Dietz, Mark L. “Fundamental Aspects of Metal Ion Transfer into Ionic Liquids: Implications for the Design of Ionic Liquid-Based Solvent Extraction Systems.” Proceedings of the DAE-BRNS Biennial Symposium on Emerging Trends in Separation Science and Technology. Ed. Pathak, P N. Board of Research in Nuclear Sciences, (2008): 5-11.