Molybdate LR

Test Method Technical Information

TECHNICAL SPECIFICATION

Tests For: Low Levels of Molybdate in Industrial Waters and Effluents
Tests Range: 0–20 mg/L
Reagent Chemistry Used: Dihydroxybenzene disulfonic acid
Method Detection Limit*: 0.13 mg/L
Limit of Quantification**: 0.41 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. Low level molybdate treatment finds application in cooling systems. Molybdate based formulations have replaced older forms of corrosion inhibitors.
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 LR test provides a simple means of measuring low levels of molybdate in industrial waters and effluents and covers the range 0–20 mg/L MoO4 (0–12 mg/L Mo).

Reagent Chemistry

Molybdates react with a dihydroxybenzene disulphonic acid salt under slightly acid conditions to give a yellow-coloured complex. 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.

Interferences

Copper 20 mg/L, zinc 20 mg/L, phosphate 100 mg/L and calcium 200 mg/L do not interfere in this test.

Iron 10 mg/L and chlorine 10 mg/L cause slightly high blank readings equivalent to 0.6 mg/L Mo. However, they do not cause any interference in samples which contain molybdate.


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”).
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