Tandem calibration methodology: dual nebulizer sample introduction for ICP-MS

The application to inductively coupled plasma mass spectrometry (ICP-MS) of a calibration method called the TCM (tandem calibration method) is described. The TCM involves simultaneous introduction of sample and standard into the plasma by two nebulizers operated in parallel. Figures of merit were determined by comparing the results obtained with those produced using the method of standard additions and external standard calibration was used as a probe of the severity of the matrix effect induced. The test solutions in this study contained Cu, Y, Pt and Pb as analytes and 10 mM Ba and 35 mM Na as matrix effect generators. Classical standard addition verified the validity of the TCM and the two methods were shown to be statistically equivalent. The precision of the results obtained was limited by the noise of the sample introduction device (about 4% RSD on difficult samples versus roughly 1% on clean standards), while the accuracy was only slightly limited by the short and long term stability of the arrangement, typically around 2% relative error. The method was easy to implement on existing equipment, inexpensive and potentially suited to automation.