chromium and arsenic speciation using IC-ICP-MSAfter my last two posts on dealing with the challenges of interference in trace elemental analysis (link to post) and an overview on the analysis of fracking wastewater (link to post), I thought I would turn my attention to discussing elemental speciation in this post.

Elemental speciation, or speciation, is an analysis technique to separate and then quantify different chemical species (forms) of a particular element. Speciation is very important for environmental monitoring (link to our community site) because studies have shown that different oxidation states and chemical forms of an element contribute different levels of toxicity. The concept of speciation was first used in 1954 to improve the understanding of biogeochemical cycling of trace elements in sea water. However, the lack of more sensitive analytical technologies was the bottleneck for speciation. With multiple speciation techniques developed and improved in recent years, advanced instrumentation today allows accurate and precise measurement of elemental species. Today elemental speciation has become a routine analytical approach in many laboratories.

Why Speciation is Necessary?

Multiple metal poisoning stories indicate measurement of the total element concentration may not be sufficient to assess overall toxicity and provide solutions. Speciation is thus necessary to separate the good guys (species) from the bad to provide correct information for ensuring good human health.

In the 1940s, accumulated toxic methylmercury in fish killed 900 people and affected 2 million people in the Minamata incident in Japan (link to story). In the 1990s, the land and groundwater for residents in Hinkley, California, was contaminated with carcinogen chromium (VI) and caused severe health problems but P&E told the local residents that it was a safe form of chromium (depicted in the movie Erin Brockovich). Also in the 1990s, arsenic contamination (link to the bulletin of World Health Organization 2000, 78 (9)), in drinking well-water, affected 20-million people in Bangladesh and caused skin diseases and different types of cancers. Powerful speciation analysis tools can provide scientific evidence for regulations to prevent water poisoning.

Speciation Challenges

Analytical technologies for speciation face strong challenges. First, only trace amounts of the toxic species (not all species) of a particular element pose a threat to human health. Sensitive detection technologies with good sensitivity, accuracy, and precision are needed for trace detection. Second, due to changes in pH, temperature, light, and collection and storage, a toxic species can transform to a nontoxic species, and vice versa. Third, extraction methods may not remove all metal species equally and can also contribute to interspecies transformation.

A recent webinar, now available on-demand, by my colleagues, Mr. Kristan Bahten and Dr. Shona McSheehy, Complete Inorganic Speciation Solutions for Environmental Applications (link to the webinar; you will need to fill out a short registration page before playing the webinar), demonstrates how IC-ICP-MS (ion chromatography-inductively coupled plasma-mass spectrometry) hyphenated technologies provide a good solution for elemental speciation. The webinar explains speciation of chromium and arsenic in drinking water and natural water, respectively.

Chromium Speciation

Chromium (VI) is highly toxic and can cause liver, kidney, lung, and gastrointestinal cancers, whereas chromium (III) is essential for the human body’s glucose metabolism. Determination of chromium VI can be achieved by ion chromatography alone, or coupled with ICP-MS. The hyphenated method is a powerful tool for speciation of multiple elements, as described in this White Paper, Benefits of Coupling IC with ICP-MS, (downloadable PDF).

Arsenic Speciation

Arsenic speciation in natural water or other environments is another important application described in the webinar. Inorganic arsenic (III) and arsenic (V) are much more toxic than organoarsenic species. Long-term exposure to inorganic arsenic, even at low concentrations, can lead to different types of cancers such as skin, kidney, and bladder cancers.

In our featured webinar, Shona has shown that all the different species of arsenic can be effectively separated by IC with gradient elution; each species is quantitated by ICP-MS using the Q cell to remove polyatomic interferences. Since the intent of arsenic speciation is to distinguish the inorganic and organoarsenic forms, a recent webinar, on available on-demand after filling out a short registration form and titled, ICP-MS for Arsenic Speciation, by Professor Andy Meharg illustrates a method to first convert arsenic (III) to arsenic (V), then separate the inorganic species from the organoarsenic species by IC followed by ICP-MS quantitation. You can also learn more in a recent post, on this blog, on arsenic speciation in rice by Paul Dewsbury (link to post). Different arsenic speciation methods (link to an EPA presentation on arsenic speciation) can also be used.

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Besides chromium and arsenic speciation, mercury speciation is also a popular topic and you can learn more about detailed speciation methods for these elements in thid downloadable speciation summary notebook: Speciation Applications Summary: Ion Chromatography.

The Benefits of Using IC-ICP-MS

The greatest benefit of using ion chromatography (rather than HPLC) coupled with ICP-MS is that the ion chromatography instrument is metal-free, whereas the HPLC system is not; the metal-free feature eliminates possible trace metal contamination from system components, such as pumps or tubing.

The ICP-MS technique offers the following advantages for speciation:

  • Great sensitivity (benefit: low detection limit)
  • Wide dynamic range (benefit: no dilution necessary regardless of the analyte concentration)
  • High matrix tolerance (benefit: works even in more complex matrix, not just for water)
  • Powerful interference removal (benefit: getting reliable and accurate results)

Last, but not least, the interface connection between ion chromatography and ICP-MS is easy and straightforward with integrated software to control both ion chromatography and ICP-MS for simple operation. An operator can make the quick connection without any help from a field engineer.

If you have questions on speciation analysis, do enter them in the Comments box below. I look forward to hearing from you.

 

 

Wei Liu is a Senior Market Development Manager with a focus on trace elemental analysis applications in environmental and industrial markets in the Chromatography and Mass Spectrometry Division at Thermo Fisher Scientific Inc. Formerly a scientist, Wei worked in the field of industrial enzymes and drug discovery. After obtaining his MBA from the Haas School of Business, UC Berkeley, he held a wide range of roles including regional marketing manager, marketing consultant, product manager, and market research manager. Wei earned a Ph.D. in Molecular Microbiology from the University of Illinois at Chicago and completed postdoctoral training at Stanford University. He has 13 international scientific publications and 4 patents to his credit.