Elimination of calcium and argon interferences in iron determination by ICP-MS using desferrioxamine chelating agent immobilized in sol–gel and cold plasma conditions

Abstract

The determination of iron by ICP-MS has not been convenient (at ultratrace level in complex matrices) due to polyatomic interferences of different isotopes produced by oxygen, argon and calcium on ⁵⁶Fe (⁴⁰Ar¹⁶O⁺ and ⁴⁰Ca¹⁶O⁺) and ⁵⁷Fe (⁴⁰Ca¹⁶O¹H⁺, ⁴⁰Ar¹⁶O¹H⁺).

The interferences produced by ⁴⁰Ar¹⁶O⁺ and ⁴⁰Ar ¹⁶O¹H⁺ on ⁵⁶Fe and ⁵⁷Fe, respectively, may be reduced using a shield torch (700 W rf power, 1.68 mL min⁻¹ nebulizer Ar gas and 14.6 mm sample depth), however it would increase the formation of ⁴⁰Ca¹⁶O⁺ and ⁴⁰Ca¹⁶O¹H⁺.

The interference of Ca on the Fe signal has been reduced by using an iron specific chelating agent, the mesylate salt of desferrioxamine B (Desferal) which is used currently as a drug for the clinical treatment of individuals suffering from acute iron toxicity (usually infant poisoning or chronic iron overload). A microcolumn (5.0 cm length and 3.0 mm of internal diameter) filled with the Desferal immobilized in sol–gel has been used online with an ICP-MS detector (Hewlett Packard 4500-plus). The parameters which affect Fe and Ca separations, have been optimized. A preconcentration factor ca. 92 and a LOD of 0.74 µg L⁻¹ were achieved using 10 min sampling and 200 µL of 1 mol L⁻¹ HNO₃ as eluent. The lifetime of the Desferal sol–gel was at least one month, which was equivalent to about 250 iron determinations.

The system is successfully applied to determine low levels of Fe in wastewater and mineral samples with a Ca level up to 40 mg L⁻¹. The proposed method not only eliminates the interferences of Ca on the determination of iron but also enhances the preconcentration factor considerably.