MORE EFFICIENT ION-TRANSPORT FOR INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

A modification of the ion-lens system in an inductively coupled plasma mass spectrometer has been studied in an attempt to improve the ion t ransport efficiency. The modification consists of the placement of a m etal rod down the axis of the lens-stack. The rod is suspended in plac e via a ceramic insulator inserted through the photon stop. A negative potential is applied to the rod to help focus the positively charged ions into the quadrupole. Prior to the implementation of this modifica tion, a simple model was developed to determine if the voltages requir ed would be practical. The resulting simulated ion trajectories showed that focusing occurs with applied voltages on the order of -10 V, whi ch was approximately the optimal voltage found experimentally. The exp erimental data presented show that, with the modification, the limits of detection for 15 elements (m/z ranging from 24 through 238) improve d by factors ranging from two to ten times over those of the unmodifie d instrument.