The method presented here overcomes analyte interference by separating the two chromium using a detection method specific for Cr(VI) that is capable of handling the high-ionic-strength sample matrices generated in many leaching, and digestion procedures. Cr(VI) is separated as the divalent anion on the IonPac AS7 column using ammonium sulfate, ammonium hydroxide eluent. After the separation, Cr(VI) reacts with the color reagent diphenylcarbohydrazide (DPC) and detected by UV absorbance at 520 nm. This method is consistent with U.S. EPA Method 218.6. Please refer to AU179 for an updated method.

Three methods are presented here for the determination of Chromium in various matrices. Method A utilizes a postcolumn reaction (PCR) with a color reagent. It is a very selective and sensitive method, allowing determination of Cr(III) & Cr(VI) at ppb levels. Method B also utilizes a PCR, but determines Cr (VI) only. It is used for industrial waste waters, analyzing samples that have undergone standard oxidation. Method C allows the determination of inorganic anions in addition to chromate by chemically suppressed conductivity. Please refer to AN1116, AU144, AU165 and AU179 for updated methods.

The work shown here describes modification of the conditions described in EPA Method 218.6, including use of the column in the 2 mm format and a smaller reaction coil to increase method sensitivity. The modified method uses Dionex IonPac AS7 column (2 × 250 mm), a 1000 μL injection volume, and post column reaction (using a 125 μL reaction coil) followed by visible absorbance detection at 530 nm. This method permits an MDL for chromate of 0.001 μg/L. This results in a quantitation limit of 0.003 μg/L, which is more than sufficient for analysis at the proposed California PHG level of 0.02 μg/L.

Hexavalent chromium, Cr(VI), is the most toxic form of chromium, a primary drinking water contaminant in the U.S. Cr(VI) can be determined as chromate by ion chromatography in drinking water, and wastewater.The California Department of Health Services recently issued a new Public Health Goal of 0.2 µg/L for Cr(VI). EPA Method 218.6 does not allow sufficient sensitivity for analysis at the California PHG level. This update describes modifications to Method 218.6 that significantly increase sensitivity over the existing method.Also refer to AU 179 for an updated method.

Speciation determinations of ionic compounds are important to determine the concentration of the more toxic form in the total elemental composition. Chromium is an industrial waste contaminant that can have serious health effects and therefore requires monitoring in municipal water systems. This method determines Chromium VI and Chromium III species in a municipal drinking water sample. The ions are separated by ion chromatography (IC) on an IonPac AG7 guard column and detected by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) at ng/g. This method is further optimized in AN43175.