Effects of temperature and sample amount on the electron capture negative ion mass spectra of polychloro-n-alkanes

Ion source temperature, sample amount and the positions of the chlorine atoms attached to the neutral molecule all had profound effects on the appearance of the ECNI mass spectra of a number of synthesized polychloro-n-alkanes (PCAs). Increases in the ion source temperature resulted in a decrease in the abundances of both the [M + Cl]− and [M − Cl]− ions, while the abundances of the structurally non-characteristic ions, HCl2− and Cl2−•, increased. An increase in the amount of the injected PCA resulted in an increase in the abundance of the [M + Cl]− ion, most notably for congeners containing chlorine atoms only 1,2-substituted at both ends of the alkane chain. The abundance of the [M − Cl]− ion increases with decreasing ion source temperature down to 120°C, the lowest temperature easily maintained with our instrument. For analytical purposes we recommend that this source temperature be used.