Sentence:  Furthermore , the exchange would not be expected to be sensitive to trace <WSD>amounts</WSD> of impurities because it would not be apt to be a chain reaction since the activation energy for abstraction of chlorine by a chlorine atom would be expected to be too high ; also it would be expected that * * f would compete very effectively with any impurities as a scavenger for * * f radicals . 
Meaning of the word marked with <WSD> tags:  how much there is or how many there are of something that you can quantify