Chromium Speciation (Cr)
Chromium (Cr) is a polyvalent element and can exist in several distinct oxidation states, but only trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)] occur with any frequency in the natural environment. The mobility, bioavailability, and toxicity of chromium largely depend on which of these two chemical species is prevalent. The speciation of chromium is determined by the processes that control reduction/oxidation reactions in the environment. As can be seen by the adjacent simplified Pourbaix diagram of chromium species in water species conversion can occur with only fairly minor changes in pH and Eh.
Chromium is a naturally occurring metal found in small quantities associated with other metals, particularly iron. It is commonly used for making steel and other alloys, bricks in furnaces, dyes and pigments, chrome plating, leather tanning, and wood preserving. Due to its extensive use in industrial processes, large quantities of chromium compounds are discharged into the environment.
For special applications that can benefit from the analysis of both Cr(III) and Cr(VI), Brooks Applied Labs offers a custom method to determine and quantify the concentrations of both species in aqueous samples. Our method couples ion chromatography (IC) with inductively coupled plasma – mass spectrometry (ICP-MS), and employs optimized interference removal technologies (DRC, CRC, and QQQ) parameters. This IC-ICP- MS configuration allows for multi-isotopic detection, high sensitivity, a wide linear dynamic range, and minimal polyatomic interferences. This allows us to separate and quantify chromium species in even the most complex matrices while maintaining ultra-low detection limits.
Brooks Applied Labs offers an array of chromium speciation methods including EPA Methods 7196A and 7199 and our proprietary methods to meet nearly any project quality objective. Accurate hexavalent chromium testing to determine ng/L levels is a major challenge because the existing methods are neither not selective nor not sensitive enough. For instance, the colorimetric determination of hexavalent chromium (EPA Method 7196A) is prone to interferences from molybdenum, vanadium, iron, suspended solids, humic compounds, and other organics that absorb light. Anion chromatography is used in EPA Method 7199 to separate hexavalent chromium from the matrix. In that method, hexavalent chromium is determined spectrophotometrically after a post column reaction with diphenylcarbazide. Even though most of the problems mentioned above are avoided with this technique, there are still problems when permanganate is present in the samples; thus, Brooks Applied Labs favors ICP-MS for detection instead of spectrophotometry.
To learn more about our innovative analytical methods and how they can benefit your projects, contact us today.