Development and food science applications of an automated short-path thermal desorption apparatus.

摘要

An automated, personal computer controlled Short Path thermal desorption apparatus with up to twelve sample capacity has been designed, built and tested. The novel apparatus is capable of introducing volatile organic compounds (VOC's) from solid, liquid, and vapor samples to an unmodified gas chromatograph (GC) for analysis. It operates unattended in either purge & trap mode or direct thermal desorption mode. It builds upon existing technology with unattended analysis features, but preserves a unique transfer path for each sample that minimizes cross contamination, and uses existing sample preparation equipment. Software has been developed to operate the unit from a personal computer. Data has been obtained on baseline blanks, mechanical ruggedness, and precision. Mechanical performance was faultless and an acceptable baseline was obtained under high sensitivity GC-MS conditions. The system affords relative standard deviation (RSD) values of 2.8% and 3.2% with the unattended analyses of replicate n-dodecane and n-tetradecane paraffin standards, respectively. Linearity data from BHT/d-20 BHT surrogate standard experiments gave an R2 value of 0.998 and y-intercept of .0081 indicating an acceptable efficiency of sample transfer over three decades of BHT concentration. The apparatus has been used to obtain never before published data on the volatile organic compounds that occur in trace levels from electron beam (EB) cured coatings. Mass spectral analysis of the samples indicates that residual short chain monomers, hydrocarbons, plasticizers, and polymerization accelerators can outgas from the coating matrix. The automated features have been exploited to run several samples of EB cured coatings in purge and trap mode to develop a VOC profile of trace level components in these coatings. The method has been used to assess efficiency of cure in ink only and varnish only coated paperboard samples. Finally the instrument has been used in direct thermal desorption mode to develop an accurate, precise method to assay key essential oil components useful for varietal characterization of hops. Validation data was acquired for Galena, Willamette, and Cluster hop varieties. Examination of the data gives approximately 60 compounds per cultivar, including terpenes, sequiterpenes, carbonyls, and hydrocarbons. The system reproducibility is between 0.4 and 1.5, and relative standard deviation between 7.0%--10%.