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Higher-order electric field affect the performance of ion trap mass analyzers.In this study,the effect of positive and negative octopole fields on the performance of a linear quadrupole ion trap mass spectrometer was carefully investigated using both theoretical simulations and experiments.The linear ion trap with added octopole components was built by using one pair of larger semi-circular rods and one pair of smaller semi-circular rods.The results showed that a certain amount of positive octopole component enhances ion trap mass resolving power and ion signal intensity,and also increases the collision induced dissociation efficiency.Furthermore,the low mass cutoff can be significantly recovered by including a positive octopole component.More specifically,a certain amount of positive octopole component benefits the mass resolution,but including any amount of negative octopole component greatly distorts the mass resolution; Mass resolution increased with increasing the amplitude of the positive octopole components,and reached its highest value of 1700 at m/z=609(~1000 Dalton/s)when 2.56%octopole component was added.With further intensity increases in the octopole component,the mass resolution decreased.The larger the negative octopole component,the worse the mass resolution.The experimental collision induced dissociation efficiency increased when octopole components were added,and the ion signal intensity increased by at least two times when the octopole components increased from 0%to 2.56%.The low mass cutoff was obviously reduced when some octopole was added,and more low mass fragments were observed when more octopole component was added.