Enhanced sensitivity in the analysis of trace organochlorine compounds by negative-ion mass spectrometry with ammonia as reagent gas

A comparison of the performances of ammonia and methane as reagent gases for the analysis of trace organochlorine compounds by gas chromatography coupled to negative-ion chemical ionization mass spectrometry is performed in the present study. Examples of standard mixtures and human blood samples analyzed with both reagents in scan and selected-ion monitoring mode are shown. Important advantages are observed as a consequence of the use of ammonia. These concern detection and quantitation limits and the lower dependence of sensitivity on the degree of chlorine substitution of the compounds.