Measuring hexavalent chromium
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 anticorrosion 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. In California, the level for Cr(VI) is 10-ppb.
There are two 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 alternative for in-lab 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.
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.
The 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.
Need to measure hex chrome? Give us a call or drop us a note. OndaVia has the tool for you!