ISO 11083 Water Quality - Determination of Chromium - Spectrometric Measurement Method Using 1,5-Diphenylcarbazide

The ISO 11083 standard developed by the International Standards Organization (ISO), this International Standard spectrometer method for the determination of chromium(VI) in water. The method is applicable for the determination of dissolved chromium (VI) in waters in the concentration range of 0,05 mg/l to 3 mg/l. The application range can be extended by diluting the sample.

Alter sample pretreatment (aims to stabilize the valence states of chromium (VI) and chromium(III) if present) 1,5-diphenylcarbazone complex from red-violet chromium with chromium (VI) 1,5-diphenylcarbazide. The absorbance of this complex is then measured at a wavelength between 540 nm and 550 nm, the full wavelength is given in the test report.

Only accepted analytical grade reagents and only distilled water or water of equivalent purity should be used. Commercially available reagents at guaranteed concentrations may also be used.

In the presence of lead, barium, and silver ions (salts), low-solubility chromates may form and their chromium (VI) content cannot be determined.

Hexavalent salts of molybdenum and mercury, also yellow or blue, respectively, with the reagent, but the concentrations are much lower than for chromium (VI). At concentrations above 1 mg/l, iron (III) turns yellow and vanadium forms a pale yellow color.

Chromium(III) and other interfering metal ions are precipitated in a phosphate buffered solution using aluminum sulfate as a precipitation aid and removed by filtration. Valence changes of chromium due to the presence of oxidizing or reducing agents can be prevented using the following pretreatment steps.

By adding sulfite to the neutralized sample, oxidizing agents are reduced; chromium(VI) does not react under these conditions. Excess sulfide and other reducing agents are then oxidized with hypochlorite. Excess hypochlorite and formed chloroamines are destroyed in acid solution by adding sodium chloride and the formed chlorine is cleaned with air.

Despite this pretreatment of the sample, slow reduction of chromium (VI) may occur in some waters. Leachate from landfills, raw domestic wastewater and some wastewater from chemical plants will show chromium(VI) losses after a few hours. Therefore, it is important that these samples are analyzed as soon as possible after collection.

Ammonia nitrogen is immiscible at concentrations below 500 mg/l, amine compounds can be converted by hypochlorite to chloroamines, which are not always decomposed by the addition of chloride. This interference is indicated by the appearance of a yellow or boxy color when 1,5-diphenylcarbazide is added.

Nitrite nitrogen interferes with the formation of the red purple chromium (VI)-20-diphenylcarbanzone complex at concentrations exceeding 1,5 mg/l. More than 4 mg/l vanadium and more than 200 mg/l molybdenum and mercury may interfere.

ISO 11083 Test Procedure

Transfer 50 ml (volume V) of the filtrate into a 100 ml measuring flask. Add 2 ml of phosphoric acid solution B and 2 ml of diphenylcarbazide solution and dilute to 100 ml with water.

Using water in the reference cell at a wavelength of 540 nm to 550 nm and available across the optical path of 0,5 mg/l or 40 mm for movements and 0,5 mm for the 3 mg/l and 10 ml/l groups.

If the concentration is higher than 3 mg/l, it is recommended to use a smaller aliquot (volume V) of the filtrate. Use a blind test to determine using water instead of sample for the blank value. If the measured measurement does not match the unit of measurement in calibration, take a second.

If the filtrate is the colored vehicle, take another aliquot and process as described in this item, bypassing the 1,5-diphenylcarbazide packet. Measured absorbance is used as color correction.

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