Grantee Research Project Results
Final Report: Field-Usable Compact Capillary Based Liquid/Ion Chromatographs - Real Time Gas/Aerosol Analyzers
EPA Grant Number: R825344Title: Field-Usable Compact Capillary Based Liquid/Ion Chromatographs - Real Time Gas/Aerosol Analyzers
Investigators: Dasgupta, Purnendu K.
Institution: Towson University
EPA Project Officer: Hahn, Intaek
Project Period: October 15, 1996 through October 14, 1999
Project Amount: $333,141
RFA: Analytical and Monitoring Methods (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Environmental Statistics , Water , Land and Waste Management , Air , Ecological Indicators/Assessment/Restoration
Objective:
Ion and liquid chromatography are two of the most widely used techniques in environmental analysis. Both remain relegated to the laboratory due to the lack of truly portable and robust equipment. The objective of the present project is to construct capillary liquid and ion chromatographs, containing appropriate detectors that will be easily portable and useable in the field. All operational control and data acquisition will be provided by a laptop personal computer. The chromatographic efficiencies will rival those of present day conventional size benchtop instruments.
Summary/Accomplishments (Outputs/Outcomes):
A completely portable capillary scale IC system was developed under this funding. This was coupled to a micro scale wet denuder and its viability as a trace gas analyzer was demonstrated. To further the technology a gradient capable pumping system was designed to enable reverse phase separations to be performed in the field. To reduce analysis time along with increasing system performance the upper pressure limit was increased to 14,000 psi. Column heating was also explored as a method to increase system performance. High-speed gradient separations were performed at 250°C. Studies were also conducted into using only water as a reverse phase eluent at temperatures as high as 400°C.
An inexpensive, compact parallel plate diffusion denuder coupled capillary IC system was demonstrated for the determination of soluble ionogenic atmospheric trace gases. The active sampling area (0.6 x 10 cm) of the denuder is formed in a novel manner by thermally bonding silica gel particles to the surface of Plexiglas plates. The effluent liquid from the parallel plate diffusion denuder is collected and preconcentrated on a capillary preconcentrator column before analysis using a capillary ion chromatograph. Using SO2 as the test gas, collection efficiency is essentially quantitative at air sampling rates up to 500 mL/min. The system provided a limit of detection (LOD) of 1.6 parts per trillion for SO2 for a 10 min sampling period.
The initial low pressure work in IC allowed the use of commercial glass syringes; however, the pressure requirements of a competitive reverse phase systems demands a pumping system that is capable of operating at much higher pressures. To solve this problem a stainless steel syringe was designed and constructed in-house. The syringes were developed using a displacement design allowing the Teflon seal to be placed at the end of the syringe. The addition of a high-pressure injection system allows this setup to operate at pressures up to 14,000 psi. The maximum peak efficiency during gradient operation was observed for toluene, which exhibited 168,500 theoretical plates. The average peak efficiency for the 10 components during the gradient run was 111,000 theoretical plates. This correlates to an average of 14,000 plates per minute.
To further increase system performance the effect of operating temperature was studied. The system is capable of operating at temperatures as high as 250°C and pressures up to 14,000 psi. Due to the reduction of the eluent viscosity and enhanced mass transport at elevated temperatures, the optimum flow rate is much higher than at ambient temperature. Further, performance limitations, due to poor mass transport at flow rates higher than the optimum, are greatly reduced. The high-pressure capability of the system then allows operation at unusually high flow rates, enabling high-speed gradient separations with excellent performance on temperature stable zirconia and titania based packings. This configuration allowed the separation of eight alkylbenzene derivatives in less than 2 minutes.
The use of varying organic modifiers in reverse phase liquid chromatography greatly complicates the use of more advanced detection methods such as flame ionization detection (FID) or mass spectrometers (MS). At elevated temperature the dielectric constant of water decreases to the point that organic modifiers are not needed. The system constructed uses water as the eluent while operating at temperatures from 100°C up to 400°C. Derivatives of alkylbenzenes up to butyl benzene have been separated.
We have successfully coupled the hot water based capillary unit to a flame ionization based detector. With such a detector, addition of extra restrictors between the column and the detector is problematic. As a result, an interesting question arises as to where in the column the eluent actually converts from the liquid to the gas phase. Steam tables and the Ergun equation were used in an iterative manner to investigate this. The experimental finding was that somewhere between 300°C and 400°C, the eluent goes to the gas phase early in the 12 cm column and no separation is achieved.
Conclusions:
In summary, we have described here a gradient capable pumping system for capillary RPLC. We have also explored the use of pure water as a non-polar eluent at elevated temperatures. The use of pure water as an eluent will enable the coupling of the capillary LC system to more powerful detection systems than previously possible.
Journal Articles on this Report : 7 Displayed | Download in RIS Format
Other project views: | All 15 publications | 7 publications in selected types | All 7 journal articles |
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Boring CB, Dasgupta PK, Sjogren A. Compact, field-portable capillary ion chromatograph. Journal of Chromatography A 1998;804(1-2):45-54. |
R825344 (1999) R825344 (Final) |
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Boring CB, Poruthoor SK, Dasgupta PK. Wet effluent parallel plate diffusion denuder coupled capillary ion chromatograph for the determination of atmospheric trace gases. Talanta 1999;48(3):675-684. |
R825344 (1999) R825344 (Final) |
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Dasgupta PK, Genfa Z, Poruthoor SK, Caldwell S, Dong S, Liu S-Y. High-sensitivity gas sensors based on gas-permeable liquid core waveguides and long-path absorbance detection. Analytical Chemistry 1998;70(22):4661-4669. |
R825344 (Final) |
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Kephart TS, Dasgupta PK, Alexander JN. An affordable high-performance pumping system for gradient capillary liquid chromatography. Journal of Microcolumn Separations 1999;11(4):299-304. |
R825344 (1999) R825344 (Final) |
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Kephart TS, Dasgupta PK. Hot eluent capillary liquid chromatography using zirconia and titania based stationary phases. Analytica Chimica Acta 2000;414(1-2):71-78. |
R825344 (1999) R825344 (2000) R825344 (Final) |
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Kephart TS, Dasgupta PK. Superheated water eluent capillary liquid chromatography. Talanta 2002;56(6):977-987. |
R825344 (2000) R825344 (Final) |
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Sjogren A, Boring CB, Dasgupta PK, Alexander IV JN. Capillary ion chromatography with on-line high-pressure electrodialytic NaOH eluent production and gradient generation. Analytical Chemistry 1997;69(7):1385-1391. |
R825344 (1999) R825344 (Final) |
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Supplemental Keywords:
ion chromatography, liquid chromatography, portable analyzers, environmental analysis, superheated water., RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Environmental Chemistry, Chemistry, Monitoring/Modeling, Engineering, environmental monitoring, ambient aerosol, ambient particle properties, environmental measurement, field portable monitoring, National Center for Atmospheric Research, optical detectors, analytical chemistry, aerosol analyzers, liquid chromatographs, real-time monitoringRelevant Websites:
http://www.ttu.edu/~chem/faculty/dasgupta/dasgupta.html ExitProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.