The quantification of quaternary ammonium compounds in environmental and biological samples is problematic using conventional chromatography techniques because the compounds are highly soluble in water. While analyzing them by liquid chromatography coupled tandem mass spectrometry it has been found that they follow an exception rule. Under standard electrospray ionization (ESI) conditions, mono- and di-quaternary ammonium compounds form molecular ions with the formula of m q / z q rather than m + z / z . [ clarification needed ] Formation of m q / 2 is observed for di-quaternary ammonium compounds (like diquat ) as precursor ion and m q / 1 as product ion due to the loss of one of the quaternary charge during CID. In di-quaternary ammonium compounds, this process can also result in the formation of fragment ions with higher mass as compared to their precursor ion. Hydrophilic interaction liquid chromatographic separation has been reported to demonstrate a successful separation of quaternary ammonium compounds for their quantification in ESI-MS/MS with higher precision. 
The scene is meant to be funny, but in many ways, it's not too far off the mark. Plague is a real disease, and for much of human history, outbreaks have sparked desperate attempts to stop its spread. During past plague pandemics, some communities persecuted and executed minorities believed to be responsible for the illness. Officials also sealed infected people and their families inside their homes. People under such quarantines had no way of working or buying food, and starvation was a real possibility. Death tolls were so high that bodies had to be carted away and buried together in mass graves. Because of the sheer number of deaths England, there is less genetic diversity there today than there was in the 11th century [source: New Scientist ].