Test Method Technical Information


Tests For: Zinc in Natural and Treated Waters
Tests Range: 0–4.0 mg/L
Reagent Chemistry Used: Zincon
Basis of Test Method: Standard Method 3500-Zn-B
Method Detection Limit*: 0.030 mg/L
Limit of Quantification**: 0.096 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 Zinc

Zinc compounds are used as corrosion inhibitors in industrial cooling water systems and similar applications. Control of the zinc level is an important aspect of corrosion control in such systems. Zinc and zinc containing alloys are widely used in industry and zinc salts are commonly found in industrial effluents.

The Palintest Zinc test provides a simple means of testing zinc levels over the range 0–4 mg/L and is suitable for testing cooling waters and industrial effluents, and for the monitoring of natural and drinking waters.

Reagent Chemistry

Zinc reacts with 5-(o-carboxyphenyl)-1-(2-hydroxy-5-sulphophenyl)-3-phenyl-formazan (Zincon) in alkaline solution to give an intense blue colour. The reagent itself is orange in solution. At different zinc levels a distinctive colour range from orange through purple to blue is produced. In the Palintest Zinc test a tablet reagent containing both Zincon and an alkaline buffer is used for maximum convenience. The test is simply carried out by adding a tablet to a sample of the water.

The colour produced in the test is indicative of the zinc concentration and is measured using a Palintest Photometer.


Samples containing high chlorine residuals are pre-treated with a special dechlorinating tablet to prevent bleaching of the test colours.

Copper reacts in a similar manner to zinc and a correction procedure using EDTA is applied to those samples which contain both zinc and copper. EDTA destroys the colour complex formed with zinc

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”).