A NEW ENHANCED SENSITIVITY QUADRUPOLE INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETER (ICP-MS)

A new quadrupole Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) has been developed which offers a very significant increase in sensitivity compared to other instruments. Importantly, the very high sensitivity is obtained while maintaining the low backgrounds which are characteristic of quadrupole ICP-MS instruments. This new enhanced sensitivity instrument has been characterized using a readily available sample introduction system, a Meinhard C type nebulizer with a Scott type spray chamber Signal enhancing techniques, which improve sample transport to the ICP (compared to a concentric nebulizer with a Scott type spray chamber), were not used, in order to allow the comparison of this new instrument with other ICP-MS instruments. The new ICP-MS, a PQII + ''S'', is manufactured by Fisons Instruments (UK). The most important modification from previous instruments is the lowering of the pressure in the region between the sampler and skimmer by a factor of 3 by the use of additional pumping on the interface volume. The sensitivity for monoisotopic elements with moderate ionization potentials is more than 500 million counts/second, normalized to a solution concentration of 1 ppm (mu g/g) of the analyte for elements in the mass region from La-139 to U-238. Background signals are typical of quadrupole instruments and are less than 10 counts/second for masses (most isotopes > 160 Daltons) where there are no measurable contributions fron analytes in the solution or from polyatomic ions of the plasma constituents. Limits of detection less than 10 ppq (10 fg/g) are achieved using 10 second data acquisition for high mass analytes when high purity reagents are used. As with other quadrupole based ICP-MS instruments, its response characteristics (sensitivity vs. mass) can be modified and optimized for specific analytical problems by judicious optimization of ion lens settings.