This document specifies a test method for the determination of iron-55 (⁵⁵Fe) activity concentration in samples of all types of water using liquid scintillation counting (LSC). Using currently available liquid scintillation counters, this test method can measure the ⁵⁵Fe activity concentrations in the range from the limit of detection up to 120°°mBq°°l^-1. These values can be achieved with a counting time between°°7°°200°°s and°°10°°800°°s for a sample volume from°°0,5°°l to°°1,5°°l. Higher activity concentrations can be measured by either diluting the sample or using smaller sample aliquots or both.

NOTE°°°°°°°°°° These performance indicators are wholly dependent on the measurement regimes in individual laboratories; in particular, the detection limits are influenced by amount of stable iron present.

The range of application depends on the amount of dissolved material in the water and on the performance characteristics of the measurement equipment (background count rate and counting efficiency).

It is the laboratory°°°s responsibility to ensure the suitability of this test method for the water samples tested.