It's expensive to buy a GC/MS machine. The tubes you use for each sample are expensive. You need a trained operator. If you don't have your own machine you'll have to send the specimen off to be...
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This should be broken down into two separate questions. The two are very different methods with really almost nothing in common.
first vaporize, and then ionize
analytical tool in which molecules are bombarded with high energy electron and converted topositively charged ion which can break into fragment ions