Iron testing – which method to use?

Palintest offers three iron tests: a low range (0–1 mg/L), medium range (0–5 mg/L) and high range (0–10 mg/L). These three iron tests rely on different chemical methods. Iron is present in water samples in several different forms, and the methods detect different fractions of the dissolved iron. The application of these methods varies based on the fractions of dissolved iron and range they measure.

Why is it Important to Monitor Iron in Water?

Iron occurs widely in nature and is found in many natural and treated waters. It is present in both domestic and industrial water supplies. Iron presence in water is undesired as it affects the taste of beverages and causes unsightly staining of laundered clothes, plumbing fittings and swimming pool surfaces. The formation of insoluble iron deposits causes issues in many industrial and agricultural water applications, such as drip feed irrigation. In industry, iron salts occur through corrosion of plant and equipment, and from industrial processes.

Iron is therefore an important test for monitoring natural and drinking waters, for corrosion control in industry and for checking of effluents and wastewaters. To find out more about where iron needs to be monitored and recommended guidelines visit our iron parameter page.

What Form does Iron Take in Water?

Iron may be present in solution in both ferrous (Fe2+) and ferric (Fe3+) forms, as free iron and as weakly or strongly complexed iron. Chemicals such as EDTA (used in pool winterising treatment) and Calgon (a water softener) rapidly react with iron forming strong complexes. Iron may also be present in colloidal and particulate form.

What is the Difference Between the Palintest Iron Testing Methods?

The table below shows the differences between the three Palintest Iron tests:

Test Method Range Chemistry
Palintest Iron LR 0 to 1 mg/L Fe A decomplexing/ reducing agent breaks down weakly complexed forms of iron and converts ferric iron to ferrous iron. The ferrous iron reacts with PPST to form a pink colour.
Palintest Iron MR 0 to 5 mg/L Fe A strong decomplexing/ reducing agent, dithionite, breaks down complexed iron and reduced it to the ferrous iron form. This reacts with 1,10-phenanthroline to from an orange-coloured species.
Palintest Iron HR 0 to 10 mg/L Fe Thioglycollate breaks down weakly complexed forms of iron and reduced ferric iron to ferrous iron. This, together with any ferrous iron present in the sample, reacts with excess thioglycolate to produce a pink colour.

 

Palintest Iron MR Test

The Palintest Iron MR test uses a powerful decomplexing agent, and this test can release iron from EDTA and other water treatment chemicals such as Calgon. It will also dissolve and quantify fine particulate iron. The test result may be treated as total iron. The chemistry of the Palintest Iron MR test has good specificity with few interferences. All these considerations make it a particularly useful test for industrial water applications and corrosion monitoring.

Palintest Iron LR and HR Tests

The Palintest Iron LR and HR tests determine free iron and weakly complexed iron. The tests are normally complete within one minute, and therefore provide useful instant information on free soluble iron, for example in swimming pools.

Complexing agents such as Calgon will delay the response of the test. Continuing colour development after one minute indicates the presence of strongly bound iron complexes in the water. If the tests are allowed to stand for longer, until the colour development is complete, more strongly bound complexed iron will be included in the measurement. This could take up to 20 minutes. A second reading after a 20-minute standing period can offer useful information on the presence of strongly bound iron species in the sample.

 

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