microFAST S4 - Accurate Determination of Si in Petrochemical Solvents by ICPMS

Abstract
The microFAST accurately determines low ppb concentrations of Si and other metals in undiluted, organic solvents by ICPMS. A dedicated syringe loads a sample or standard onto an injection valve where it is autodiluted or analyzed directly. A low flow rate carrier then injects the diluted sample and internal standard into a heated to the ICPMS. The combination of a low flow rate and heated spray chamber ensures that Si is accurately determined at low ppb levels (detection limit = 2.4 ppb, n=6, 3.4σ), regardless of the volatility of the Si species or solvent type.

Features:

  • Fully automated, syringe-driven autocalibration and autodilution
  • Direct analysis of undiluted organic solvents
  • Automatic addition of internal standard
  • Accurate Si results, regardless of species
  • Syringe loading of samples

Benefits:

  • Automatically calibrate from a single stock standard
  • Minimize offline sample preparation and dilution
  • Routine analysis of different organic solvents with the same configuration
  • Excellent washout
  • Low maintenance
  • High sensitivity

Introduction
Rapid multi-element capabilities and superb detection limits often make ICPMS the technique of choice for trace elemental determination. However, determination of Si by ICPMS is hindered by very high background, mostly from the presence of polyatomic interferences, such as CO and N2. In organic solvents, Si determination is further complicated by the increased abundance of carbon-based interferences from the solvent. In order to measure Si at low ppb levels, all of these polyatomic interferences must be dramatically reduced while maintaining adequate sensitivity for Si.

Together, the microFAST S4 and ICPMS accomplish the necessary reduction in polyatomic interferences required for this analysis. First, the microFAST S4 introduces sample at very precise, low flow rates, limiting the total amount of carbon that enters the plasma and reducing carbon-based polyatomic interferences. Next, plasma conditions are optimized to minimize the Si background while maximizing sensitivity for Si and other elements. Lastly, the DRC is optimized with simultaneous introduction of both NH3 and H2 which efficiently removes carbon-based interferences and stabilizes the Si background for excellent long-term results, regardless of solvent.

Traditional analysis of organic solvents by ICPMS is done by diluting samples in o-xylene and introducing the sample into a chilled spray chamber at flow rates between 100-300 μL/min. This approach produces inaccurate results for elements present in organometallic species that differ from those in the calibration standards. For example, with traditional sample flow rates and spray chamber temperatures, the different transport efficiencies of volatile organometallic Si species cause inaccurate results and long washout times. In addition, small changes in solvent composition may cause Si background shifts.

The low flow rate sample introduction and heated chamber of the microFAST S4 eliminate these common problems with Si determination in organic solvents. The heated chamber drives nearly 100% of Si into the plasma regardless of the volatility of any Si species. The low sample flow rate maintains plasma stability despite nearly 100% of the sample and solvent reaching the plasma. In addition, shifts in Si background due to changes in solvent composition and carryover from volatile species are eliminated. This “total consumption” sample introduction system ensures accurate results for Si regardless of species or solvent.

Conclusion:
The microFAST S4 achieves accurate Si determination by ICPMS at low ppb levels. The Si detection limit is 2.4 ppb (n=6, 3.4σ) in o-xylene at 20 μL/min. The combination of microFAST S4 and ICPMS provides the necessary polyatomic interference removal to achieve excellent detection limits and reproducible blanks required for low ppb Si detection in undiluted organic solvents by ICPMS.

microFAST S4 Application Note

microFAST S4 System Diagram

microFAST S4 System Diagram


Experimental Conditions

  • microFAST S4 sample introduction system
  • PC3x heated Peltier cyclonic chamber, 60 °C
  • Zero waste, drainless spray chamber
  • 1.8 mm sapphire injector
  • 20 μL/min sample flow rate
  • 10 μL/min internal standard flow rate
  • Wash time 35 s
  • ICPMS
  • Oxygen addition (20% O2/80% Ar) at 0.36 L/min to prevent carbon buildup on the cones
  • DRC mode, reaction gas, 0.4 mL/min NH3 and 2 mL/min H2

DRC Conditions
DRC mode with either NH3 or H2 gas significantly reduces the Si background. However, with only one of these gases, there are enough remaining polyatomic interferences that the Si background is still too high for good long-term results. However, simultaneously adding both NH3 and H2 to the chamber reduces the background substantially, improves long-term stability, and allows accurate Si determination in a wide variety of solvents.


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