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United States Department of Agriculture

Agricultural Research Service

Title: Parallel Path Nebulizer: Critical Parameters for Use with Microseparation Techniques Combined with Inductively Coupled Plasma Mass Spectrometry

Authors
item Yanes Santos, Enrique
item Miller-Ihli, Nancy

Submitted to: Spectrochimica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2005
Publication Date: March 31, 2005
Citation: Yanes Santos, E.G., Miller-Ihli, N.J. 2005. Parallel path nebulizer: critical parameters for use with microseparation techniques combined with inductively coupled plasma mass spectrometry. Spectrochimica Acta. 60:555-561.

Interpretive Summary: Speciation measurements are most often accomplished by combining separation techniques with element specific detectors. In this work, Mira Mist CE nebulizers were evaluated for interfacing microseparation methods with ICP-MS. These parallel path nebulizers are unique because they are not self-aspirating and therefore do not deteriorate the separation. The orientation of the gas outlet at the end of the nebulizer was studied extensively to determine the position which provided the best angle to promote aerosol introduction into the ICP-MS. Use of organic solvents such as methanol are known to enhance analytical signals by ICP-MS and this study focused on elements with varying ionization potentials to better understand the rationale for signal enhancement. We found that with methanol we saw improved transport efficiency and we observed a carbon enhancement effect as well. This work is important to researchers interested in combining microseparation techniques with ICP-MS for speciation because it compares four different nebulizers of the same model, delineates how to best optimize the orientation of the gas outlet, and addresses the rationale for signal enhancement when using methanol.

Technical Abstract: Four different, low flow parallel path Mira Mist CE nebulizers were compared and evaluated in support of an ongoing project related to the use of microseparation techniques interfaced to inductively coupled plasma mass spectrometry (ICP-MS) for the quantification of cobalamin species (Vitamin B12). For the characterization of the different Mira Mist CE nebulizers, the nebulizer orientation as well as the effect of methanol on analytical response was the focus of the study. The position of the gas outlet on the nebulizer which consistently provided the greatest signal was when it was rotated to the 11 o'clock position when the nebulizer is viewed end-on. With this orientation the increased signal may be explained by the fact that the cone angle of the aerosol is such that the largest percentage of the aerosol is directed to the center of the spray chamber and consequently into the plasma. To characterize the nebulizer's performance, the signal response of a multi-element solution containing elements with a variety of ionization potentials was used. The selection of elements with varying ionization energies and degrees of ionization was essential for a better understanding of observed increases in signal enhancement when methanol was used. Two different phenomena contribute to signal enhancement when using methanol: the first is improved transport efficiency and the second is the 'carbon enhancement effect. The net result was that as much as a thirty-fold increase in signal was observed for As and Mg when using a make-up solution of 20% methanol at a 15 'L/min flow rate which is equivalent to a net volume of 3 uL/min of methanol

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