Spectroscopy - May 2008 - (Page 14)

14 SPECTROSCOPY GLOBAL EDITION MAY 2008 have to be quite as careful with the blank as we would for a semiconductor-grade water application, for example. If we can manage matrix effects (drinking waters can have quite high total dissolved solids) simply and effectively as well as common polyatomic interferences, we can achieve the necessary reporting limits easily (~0.1 ppb). More-complex samples such as soil digests or geological samples require more careful management of matrix effects, which can vary significantly from sample to sample. While dilution is used commonly, other techniques that can minimize matrix effects without diluting the sample are preferred because they eliminate the dilution factor as well as the potential for contamination and error associated with dilution. A newly developed technique called aerosol dilution (2) addresses the need to minimize matrix effects without the need for conventional dilution. With matrix effects under control, the accuracy of internal standard correction also is enhanced significantly. Managing polyatomics is also more critical in variable and complex matrices in which the interferences might be unknown and differ significantly from sample to sample. Because of this, neither mathematical correction nor the use of reactive collision cell gases is ideal, because neither is universal. Fortunately, the use of helium collision mode coupled with kinetic energy discrimination can reduce polyatomic interferences universally in complex, variable, and unknown samples to low parts-pertrillion levels with good reliability. References (1) E. McCurdy and G. Woods, J. Anal. At. Spectrom. 19, 607–615 (2004). (2) “Direct Analysis of Undiluted Soil Digests Using the Agilent High Matrix Introduction Accessory with the 7500cx ICP-MS,” Agilent Technologies application note 5989-7929EN 2008. Steve Wilbur is a senior applications scientist in the ICP-MS group at Agilent Technologies. He is part of a small, but ardent group of fanatics worldwide who believe we will ultimately build the “perfect” mass spectrometer. In the meantime, he spends his time thinking about both living with and eliminating the current “imperfections.” The views expressed in this column are his and do not represent those of Agilent Technologies. For more information on this topic, please visit our homepage at www.spectroscopyonline.com http://www.spectroscopyonline.com

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Spectroscopy - May 2008 Contents A Pragmatic Approach to Managing Interferences in ICP-MS Pittcon 2008: Back to New Orleans and Coffee and Beignets for Breakfast News Market Profile Calendar

Spectroscopy - May 2008

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