Chrome has long been used in industries like electroplating, stainless steel production, leather tanning, textile manufacturing, and wood preservation. Generally, the active compound is the +6, or hexavalent, oxidation state. These chromate compounds are effective anti-corrosion agents for metals and pigments in dyes and paints.
Although a useful material, hexavalent chromium is a carcinogenic water contaminant. Even though the trivalent form has long been considered a necessary micronutrient, the Cr(VI) oxidation state is harmful. Current drinking water regulations target the total chromium level, with an EPA limit at 100-ppb in water, even though the trivalent form is far less of a concern than the hexavalent form. This disconnect will be corrected as new regulations take effect.
More and more, hex chrome is being banned. California regulators are in the rule-making process for a proposed 10-ppb level in water. These changes will add new requirements to measure, monitor, and analyze Cr(VI) in water, soil, and air.
There are three primary methods for Cr(VI) analysis. EPA method 200.8 relies upon ICP/MS, the gold standard for metal analysis and speciation. The equipment for ICP/MS is expensive and complex, requiring well-trained operators and specialized laboratories. Alternatively, Method 218.6 uses ion chromatography for hex chrome, an approach that is a bit less expensive, but not simple. If you cannot afford your own IC or ICP, then you can send a sample to a third-party laboratory for analysis, a process that takes days to weeks and costs hundreds per sample once packaging, handling, and transport are included.
The third alternative for hex chrome analysis is colorimetry. Recent improvements in colorimetric kits suggest 5-ppb detection limit; however, in real world samples, it is nearly impossible to achieve anything below 10-ppb. Complex ground or wastewater samples greatly constrain the performance limits of colorimetry.
Raman spectroscopy for hex chrome analysis
If you need to monitor Cr(VI), you are stuck between high-performance tests costing hundreds of dollars per sample to poorly-performing, low-quality tests costing a few dollars. And this limitation is why we have developed the OndaVia OPAL-106 Hexavalent Chromium Analyzer. This system relies upon Quantitative Raman Spectroscopy to achieve low-ppb detection limits in complex field samples with only a few pipette steps.
Our hex chrome analysis method is simple: preserve your sample using the standard buffer solution, add OndaVia-supplied reagents, and analyze in the spectrometer. A couple pipettes and two minutes with low-ppb detection limits. The analytical performance far surpasses colorimetry at a fraction of the cost and time of Method 200.8. Below, we present results in spiked tap water using our PPB range test kit designed for 0-100-ppb analysis. The limit of detection is 3.9-ppb.