Molybdate HR

Test Method Technical Information


Tests For: High levels of Molybdate in Industrial Waters and Effluents
Tests Range: 0–100 mg/L
Reagent Chemistry Used: Thioglycollate
Method Detection Limit*: 0.26 mg/L
Limit of Quantification**: 0.62 mg/L

*The Method Detection Limit (MDL) is defined as the minimum measured concentration of a substance that can be reported with 99% confidence to be different from the method blank results.
**The Limit of Quantification (LOQ) is the smallest quantity that can be detected with reasonable certainty for a given analytical procedure.

Testing for Molybdate

Formulations containing molybdate are used as corrosion inhibitors in industrial water treatment. Molybdate finds application in closed recirculating systems such as hot water heating systems and chilled water systems. Molybdate-based formulations have replaced older forms of corrosion inhibitor such as chromate.

When using molybdate treatment it is necessary to control the molybdate concentration within specified levels depending on the application involved. Moreover, since molybdates are widely used in water treatment and in industrial processes, molybdate is an increasingly important test for effluents and industrial discharges.

The Palintest Molybdate HR test provides a simple means of measuring high levels of molybdate in industrial waters and effluents and covers the range 0–100 mg/L MoO4.

Reagent Chemistry

Molybdates react with thioglycollate under acid conditions to give a yellow-coloured complex. Slightly oxidising conditions are maintained during the acidification stage to keep the molybdate in a fully oxidised state. The reagents are provided in the form of two tablets for maximum convenience. The test is simply carried out by adding one of each tablet to a sample of water.

The intensity of the colour produced in the test is proportional to the molybdate concentration and is measured using a Palintest Photometer.


The presence of Fe2+ (ferrous) or Fe3+ (ferric) iron at 5 mg/l causes the rapid development of a red colour in the test. This may be prevented by the treatment of the 10 ml sample with one Palintest EDTA tablet prior to carrying out the test.

Best Practice Advice for Testing

  • Ensure each tablet is fully dissolved before proceeding to the next step for the most accurate results

EPA, Definition and Procedure for the Determination of the Method Detection Limit, Revision 2, Dec 2016.
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”).