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At the end of 1991 the interface part of the VG Plasma Quad 2 plus ICP-MS was modified. This report describes the performance and the level of molecular interferences of the modified ICP-MS apparatus. The apparatus was optimized for maximal sensitivity, maximal stability and minimal contribution of molucular interferences. Detection limits were four to ten times better than with the standard ICP-MS apparatus and ranged from 6 ng/l for Cd to 1,3 mug/l for B. Using indium as an internal standard, the short term stability was <2% RSD and the long term stability was <4% RSD for elements in the mass range m/z = 51-208. Li, Be, B, Bi and Th had higher RSD values due to unsuitability of the internal standard and to memory effects. The precision ranged from 33% RSD at the detection limit to 0.2-0.7% RSD at 1000x higher concentrations (m/z=51-208). Calibration curves were linear up to at least 200 mug/l. Spectral interferences due to compounds of Na, Cl, S, Ca or Mg prevented the analysis of V, Cr, Ni, Cu, Zn, As and Se at low concentration levels (<20 mug/l.)