Re-visiting Spectral Correction in ICP-OES

Overcoming Interferences in Optical ICP Analyses
Oral Presentation

Prepared by R. Mealy
Wisconsin DNR - Lab Certification, 101 South Webster Street, PO Box 7921, Madison, WI, 53590, United States


Contact Information: Richard.Mealy@wisconsin.gov; 608-264-6006


ABSTRACT

Despite being a staple in environmental lab testing for over 30 years, ICP Optical Emission spectrometry (ICP-OES) remains one of the least understood environmental technologies in use today. While there are known and documented elements which cause spectral interference, many labs have become complacent and fail to consider the impact of non-target trace metals.

The methodologies available do not provide clear guidance on how to best evaluate for potential spectral interferences, including what elements should be evaluated. Consequently, most labs have adopted the archaic Contract Lab Program protocols for interference check standards. The ICS-A and ICS-AB approach not only does not provide for adequate assessment of spectral correction, but the approach is designed for data systems that are incapable of displaying negative values. Such systems became extinct many years ago.

Further exacerbating things is the reality that once "rare" trace elements are quickly becoming commonplace. Historically, many elements were not even considered for inclusion in spectral interference assessment due to their relative rarity in the environment. However, many formerly "rare" elements are encountered more routinely in environmental samples, and therefore resultant spectral interferences cannot be ignored. More recently, rare earth metals such as cerium and lanthanum have been used in wastewater treatment to remove phosphorus. These element have shown to cause high bias in arsenic and other priority pollutant metals using both ICP-OES and ICP/MS. In some cases, biosolids were rejected for land application due to results that were biased.

This paper discusses efforts in the state of Wisconsin to identify and then fortify weaknesses in the spectral interference correction protocol used in ICP-OES.