Measurement of Trace metals in Ambient air case study

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Trace metals are found at low concentration in the ambient environment and are associated with adverse health effects. The gold standard metal measurement is Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES); however, sample preparation is laborious and expensive.

The Xact 625 metals monitor uses non-destructive X-ray fluorescence technology. A built-in sample collection system enables near-real-time trace metal measurements in ambient air. Modifying the Xact monitor to also characterise metal concentrations on externally collected filters would greatly expedite the analysis process and reduce costs.

Research Objectives

  1. Extend the measurement capabilities of the Xact monitor to include filter based metal measurements.
  2. Examine Xact monitor’s precision and accuracy of external filter analysis.

METHODOLOGY

Metal concentrations were measured using both the Xact Monitor and ICP-AES for three general sets of filter samples: (1) ambient air, (2) a standard reference material (SRM) and (3) blanks. SRM is standardised dust with certificate composition available from NIST. Coal Fly Ash SRM was used in this study.

SUMMARY

Comparison between Xact Metals Monitor and ICP-AES

  1. Linear regression models showed that the results from the Xact metals monitor has a better correlation with the NIST certificated composition than ICP-AES
  2. Significant differences have been identified between the results from the Xact monitor and ICP-AES. The Xact metals monitor generally overestimates sample metals concentration whereas ICP-AES underestimates. Follow-up analysis is needed to further investigate the reasons
  3. Metals analysis of filter samples using the Xact metals monitor takes significantly less time (~20 minutes) than using ICP-AES (90 minutes hot water bath for sample acid digestion, ~5 minutes per sample when analyzing)
  4. Near-real-time analysis of metals with the Xact monitor allows for potentially improved identification of pollution sources; however, further validation studies are needed

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