For trace analysis of organic compounds in environmental samples, liquid injection has been the traditional sample introduction technique for their quantification by gas chromatography-mass spectrometry (GC/MS) methods. This approach has the inherent disadvantages of being labor-intensive and consumption of a large amount of solvents. In this dissertation work, I have explored and established in-injection port thermal desorption (TD) to be used as a sample introduction technique for GC/MS analysis of two types of airborne organic compounds....[ Read more ]

For trace analysis of organic compounds in environmental samples, liquid injection has been the traditional sample introduction technique for their quantification by gas chromatography-mass spectrometry (GC/MS) methods. This approach has the inherent disadvantages of being labor-intensive and consumption of a large amount of solvents. In this dissertation work, I have explored and established in-injection port thermal desorption (TD) to be used as a sample introduction technique for GC/MS analysis of two types of airborne organic compounds.

The first type of airborne organic compounds is gaseous carbonyl species. Carbonyl compounds in air are collected onto a solid sorbent tube packed with a derivatization agent that reacts with carbonyls to form thermostable derivatives suitable for subsequent analysis by GC/MS. The solid sorbent tube is designed to have the same dimensions as those of the GC injector liner. This design allows TD to take place inside the GC injector by exchanging the GC injector liner with the sorbent tube. Two derivatizing agents, O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) and 2,3,4,5,6-pentafluorophenyl hydrazine (PFPH), are identified to be suitable for collection and TD-GC/MS analysis of the carbonyl compounds. Among the two derivatization agents, PFPH is found to be superior to PFBHA. PFPH offers more efficient collection of carbonyls and it is 10 times cheaper than PFBHA. The PFPH-TD-GC/MS method is shown to have method detection limits of sub-nanomoles of carbonyls per sampling tube, corresponding to air concentrations of < 0.3 ppbv for a sampled volume of 24 L. These limits are 2 - 12 times lower than those that can be obtained with a standard method for airborne carbonyls that employs liquid injection and HPLC/UV analysis. The newly-developed TD-GC/MS method has been successfully applied to determine carbonyl concentrations in ambient air and in environments impacted by emission sources (e.g., incense burning and cooking).

The second type of airborne organic compounds is non-polar organic compounds (e.g., n-alkanes and polycyclic aromatic hydrocarbons (PAHs)) that reside in aerosol phase. Their analysis is traditionally accomplished by solvent extraction of filter samples followed by volume reduction of the solvent and liquid injection of the concentrate for GC/MS determination. In my thesis work, I have demonstrated the feasibility of applying the in-injection port TD approach for their introduction to a GC/MS for analysis. A small fraction of the filter sample is directly inserted in the GC injector liner. Alkanes and PAHs are then thermally desorbed in the injector port and transferred to and focused on the head of the GC column before their separation and detection by the GC/MS. The in-injection port TD approach has been compared with the solvent extraction approach and the two are shown to generate comparable results.

Through this work, thermal desorption is demonstrated to be a viable and better alternative to liquid injection for analysis of certain trace level organic compounds in air. The most prominent advantages of the TD approach are dramatic reduction of time and labour in sample pre-treatment and improved method detection limits.