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An Evaluation of Unit and ½ Mass Correction Approaches as a Means of Minimizing the False Positives Produced by M+2 species in US EPA Method 200.8 using ICP-MS (webinar presentation)
Citation:
Creed, J., S. Smith, P. Creed, J. Landero-Figueroa, K. Kubachka, AND R. Wilson. An Evaluation of Unit and ½ Mass Correction Approaches as a Means of Minimizing the False Positives Produced by M+2 species in US EPA Method 200.8 using ICP-MS (webinar presentation). 2017 Laboratory and Technical Information Group Conference, NA, May 01 - 04, 2017.
Impact/Purpose:
Oral Presentation via webinar for EPA Laboratory Technical Information Group (LTIG) annual conference. Presenting data on the update of Method 200.8
Description:
Rare earth elements (REE) and certain alkaline earths can produce M+2 interferences in ICP-MS because they have sufficiently low second ionization energies. Four REEs (150Sm, 150Nd, 156Gd and 156Dy) produce false positives on 75As and 78Se and 132Ba can produce a false positive on 66Zn. Currently, US EPA Method 200.8 does not address these as sources of false positives. Additionally, these M+2 false positives are typically enhanced if collision cell technology is utilized to reduce polyatomic interferences associated with ICP-MS detection. A preliminary evaluation indicates that instrumental tuning conditions can impact the observed M+2/M+1 ratio and in turn the false positives generated on Zn, As and Se. Both unit and ½ mass approaches will be evaluated to correct for these false positives relative to the benchmark concentrations estimates from a triple quadrupole ICP-MS using standard solutions. The impact of matrix on these M+2 corrections will be evaluated over multiple analysis days with a focus on evaluating internal standards that mirror the matrix induced shifts in the M+2 ion transmission. The goal of this evaluation is to move away from fixed M+2 corrective approaches and move towards sample specific approaches that mimic the sample matrix induced variability while attempting to address intra-day variability of the M+2 correction factors through the use of internal standards.