THE CONTINUOUS ONLINE MONITORING OF THE TRACE ELEMENTAL COMPOSITION OF INDUSTRIAL ETHENE GAS BY MEANS OF INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

An instrumental set-up based on an inductively coupled plasma mass spe ctrometer (ICP-MS) was developed with the objective to monitor the tra ce elemental composition of industrial ethene gas. For this, a dual-sa mple introduction system was built enabling the use of aqueous solutio ns as reference. Since both short-and long-term concentration variatio ns had to be addressed, the ICP-MS instrument was installed as a conti nuous on-line instrument. Consequently, the complete set-up was placed in an unmanned plant laboratory were it was operative for a year. The immense amount of data obtained was processed off-line by means of pa rtially in-house developed software. Herewith, averages and accompanyi ng standard deviations at three different timing levels were obtained with which concentration variations could be detected and examined. Th is study revealed that in the polymer-grade ethene produced (extreme) low levels of inorganic impurities were found. The only significant co ncentration variations detected were caused by nitrogen showing up as polyatomic species at different masses. The performance of the ICP-MS instrument under these very demanding conditions showed that this type of instrumentation can be used effectively as a continuous on-line mo nitor. (C) 1997 Elsevier Science B.V.