Quadrupole ICPMS Determination of Iron in Drosophila melanogaster S2 Cell Cultures using Collision Cell and Desolvation Strategies

Abstract

Inductively coupled plasma mass spectrometry (ICPMS) has become the preferred technique for trace and ultra‐trace determination of elemental concentrations in a wide variety of sample matrices. In our studies of iron uptake and metabolism in insect cells, we evaluated different ICPMS procedures to measure picogram to microgram quantities of iron in whole insects and Drosophila melanogaster S2 cells. While a well‐known spectrophotometric iron assay with ferrozine suffices for microgram amounts of the elements, ICPMS is imperative for lower level work.The determination of iron by ICPMS faces several significant challenges: samples must be decomposed to mineralize organic matter; the separation of iron from the matrix may be required in some circumstances; all sample preparation and analytical processes must be conducted under sufficiently “clean”, low‐blank conditions; and the interference of polyatomic ions (ArN+, ArO+, ArOH+) upon iron ions must be addressed. To address these challenges, samples were digested and mineralized by heating with nitric acid at 90°C in fluoropolymer containers. “Trace metal” grades of HNO3 were found to be satisfactory for minimizing reagent contributions to the overall blank. As quadrupole mass analyzers cannot distinguish between ions of the same nominal mass (e.g., 40Ar16O+ vs. 56Fe+), alternative strategies must be used to suppress the formation of polyatomic ions so that Fe+ ions can be observed above background signal. We used two different approaches. The first is de‐solvation of the sample aerosol, where water vapor is removed by a membrane dryer with countercurrent Ar gas flow. The second is passage of the extracted ions through a “collision cell” prior to mass analysis, which selectively attenuates the polyatomic ions via ion kinetic energy discrimination. A combination of both approaches lowered solution detection limits for Fe from ~ 50 – 100 micrograms/liter to << 1 microgram/liter. We present optimized procedures for the routine determination of Fe in digested cell and insect tissue samples.Support or Funding InformationNSF IOS‐1656407This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.