Iron Test Kits

Phenanthroline Method (Total & Soluble; Total & Ferrous)

With the Phenanthroline method, ferrous iron reacts with 1,10-phenanthroline to form an orange-coloured chelate. To determine total iron, thioglycolic acid solution is added to reduce ferric iron to the ferrous state. The reagent formulation minimises interferences from various metals. Results are expressed as ppm (mg/l) Fe.

References:
APHA Standard Methods, 22^nd Ed., Method 3500-Fe B - 1997.
ASTM D 1068-77, Iron in Water, Test Method A.
J.A. Tetlow and A.L. Wilson, "The Absorptiometric Determination of Iron in Boiler Feed-water," Analyst. Vol. 89, p. 442 (1964).

Technical Data Sheet

Ferric Thiocyanate Method (Iron in Brine)

The Iron in Brine test employs the ferric thiocyanate chemistry. In an acidic solution, hydrogen peroxide oxidises ferrous iron. The resulting ferric iron reacts with ammonium thiocyanate forming a red-orange coloured thiocyanate complex, in direct proportion to the iron concentration.

Results, expressed in mg/l, can be converted to mg/kg by dividing by the density of the brine.

References:
D. F. Boltz and J. A. Howell, eds., Colorimetric Determination of Nonmetals, 2^nd ed., Vol. 8, p. 304 (1978).
Carpenter, J.F. "A New Field Method for Determining the Levels of Iron Contamination in Oilfield Completion Brine", SPE International Symposium (2004).

Applications

The drinking water industry measures iron to maintain water quality. Iron is not hazardous to health, but it is an aesthetic contaminant in drinking water. Ferrous iron gives water a metallic taste and when used in drinks it turns an inky black colour and cause discolouration to food. Iron can also leave ugly reddish-brown stains on fixtures and fabrics that it encounters. Iron can also build up inside pipes causing damage or reduced flow rate. Elevated levels in drinking water supplies are most commonly the result of corrosion of old cast iron water pipes. Elevated iron levels in well water may occur due to neighbouring geology. The drinking water standards for iron are generally set more for aesthetic reasons and taste than health concerns. Higher iron concentrations can result in discoloured water with an undesirable brown or orange colour. Laundrettes ensure that their mains water is iron-free to prevent staining. The US National Secondary Drinking Water Standard for iron is 0.3 mg/l, as iron concentrations in excess of this level impart a foul taste and cause staining. The National Prescribed Concentration or Value (PCV) for Iron in drinking water supplies in the UK is 200µg/l or ppb (0.2 mg/l). The Specified Concentration or Value (SCV) for Iron in drinking water in Ireland is the same.

Boilers and power plants monitor iron concentration to prevent corrosion and maintain efficient heat exchange. High iron concentrations in surface waters can indicate the presence of industrial effluents or runoff.

Iron is a key parameter for the oil and gas industry. Iron contamination in oil field brines are typically the result of corrosion processes of iron-containing metallic components and equipment. Accumulation of insoluble iron salts in a brine completion fluid can result in substantial formation damage and significantly affect an oil well’s productivity. Quantifying total iron in brine is critical to prevent costly shutdowns and maintenance.

What is Iron?

Iron is a metal in the transitional group 8 of the periodic table and is able to form variable oxidation states. Iron is mainly present in two forms, the soluble ferrous iron (Fe²⁺) or the insoluble ferric iron (Fe³⁺). Water that contains ferrous iron is clear and colourless as the iron is totally dissolved. When the iron is oxidised it turns into ferric iron. Water containing ferric iron has a reddish-brown colour and possibly an insoluble sediment. Iron can also be found in the +6 oxidation state, for instance, as ferrate (FeO₄^2-), a powerful oxidising agent.

Metallic iron is rarely found in nature, as it readily oxidises, and is primarily present as oxides (iron ore) and to a lesser degree, silicate (fayalite) or sulphide. In natural environments iron dissolves when water runs over rocks or soil containing iron. The soluble iron content of surface waters rarely exceeds 1 mg/l, while groundwaters often contain higher concentrations.