Technique for thermal desorption analyses of thermo labile volatile compounds
Inventors
Alborn, Hans T. • Willms, Steven D.
Assignees
US Department of Agriculture USDA
Publication Number
US-10078071-B2
Publication Date
2018-09-18
Expiration Date
2035-09-29
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Abstract
Herein is described an apparatus for adaptation to existing GC/MS systems, utilizing a splitless injector as the desorption oven with a liquid CO2 cooled low thermal mass cryo trap that eliminates the need for flash heating of volatile compounds.
Core Innovation
The invention is an apparatus for analyzing volatile organic compounds in a gas chromatogram thermal desorption system that adapts to existing GC/MS systems by using a splitless injector as the desorption oven. It includes a low thermal mass cryo trap cooled by liquid CO2, which eliminates the need for flash heating of volatile compounds. This design produces a temperature gradient for more efficient trapping and focusing, and the low thermal mass allows the cryo trap to follow temperature changes between 5° C. per min to 10° C. per min without additional heating.
The problem solved by the invention arises from existing thermal desorption systems which use cryo traps that are evenly cooled, causing aerosol formation due to abrupt temperature changes when warm desorption gas rapidly cools to about −78° C. This necessitates flash heating of the entire trap to 200° C. or higher to prevent chromatographic peak broadening, which degrades labile compounds. Furthermore, prior systems are complex, expensive, require dedicated GC/MS systems, use transfer lines causing losses and degradation, and often cause sample degradation due to active trap sites and repeated heating.
The invention addresses these issues by integrating the cryo trap directly onto a standard split/splitless GC injector used as the desorption oven, which can also function as a normal injector without physical changes. The cryo trap design creates a temperature gradient from a warm entrance near the desorption oven gradually cooled along its length to minimize aerosol formation and obviate the need for flash heating. Its low thermal mass allows it to remain in the GC oven when not in use without affecting chromatography or requiring oven changes. Additional features include a control box for regulating liquid CO2 flow to the cryo trap synchronized with the GC operation.
Claims Coverage
The patent includes one independent claim covering the core invention with several main inventive features related to the apparatus configuration and functional characteristics.
Direct attachment of cryo trap to split/splitless injector
The apparatus includes a cryo trap directly attached to a split/splitless injector which serves as the desorption oven.
Low thermal mass cryo trap design
The cryo trap has a low thermal mass allowing it to follow temperature changes at rates between 5° C. per minute and 10° C. per minute, enabling it to remain in the GC oven without additional heating or affecting chromatography.
Restrictor portion creating a pressure drop and localized cooling
A restrictor portion in the liquid cooled delivery segment of the cryo trap causes a pressure drop and cooling concentrated at the end of the restrictor portion located at the bottom of the cryo trap, establishing a temperature gradient along the trap.
Split/splitless injector dual configuration
The split/splitless injector is configured for dual use as either a desorption oven in thermal desorption or a normal injector as needed, with easy switching and no physical alteration.
Means for transferring desorbed compounds to chromatographic column
The apparatus includes a means for transferring desorbed compounds from the injector to the top part of a chromatographic column located inside the cryo trap, facilitating efficient trapping and focusing of volatiles.
Together, these inventive features define an improved thermal desorption apparatus integrated with existing GC/MS systems, addressing prior issues of aerosol formation, sample degradation, complexity, and loss of labile compounds by a novel cryo trap design coupled with the splitless injector and efficient temperature management.
Stated Advantages
Eliminates the need for flash heating injection step due to low thermal mass and temperature gradient cryo trap design.
Reduces aerosol formation by avoiding abrupt temperature changes, improving trapping efficiency.
Enables use of existing GC/MS splitless injectors as desorption ovens without modification, allowing easy switching between thermal desorption and normal injection.
Allows the cryo trap to remain in the GC oven when not in use without affecting chromatography or requiring oven changes.
Less degradation of labile compounds due to reduced heating and improved temperature control.
Minimizes CO2 consumption by limiting ultra-cold temperature to a small section of the cryo trap.
Documented Applications
Collection and analysis of volatile organic compounds released by plants or insects for natural product chemistry and behavioral studies.
Collection of trace volatiles in soil or confined environments such as bee hives or glands of individual insects where short and specific sampling times are needed.
Analysis of highly labile compounds like sesquiterpenes and 12 carbon terpenoids that degrade under high-temperature thermal desorption conditions.
Sampling of volatiles using adsorption filters such as Tenax for direct thermal desorption onto GC/MS without solvent extraction.
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