On the Elimination of Interference of Calcium in the ICP-MS Determination of Iron with Low Concentration in Water

It was found that the ICP-MS determination of cFe<0.06 mg·L-1 in water was interfered seriously by the presence of 40 mg·L-1 Ca2+. It was proved that the interference of Ca2+ could be eliminated by either of the following ways: ① by using the collision cell, no interference by Ca2+ is observed, and either of the isotopes 56Fe or 57Fe can be used; ② in case of without using collision cell, the interfernce of Ca2+ is varied according to the mass concentrations of Fe(Ⅲ) and the co-existing Ca2+, i.e., (a) in case of cFe<0.10 mg·L-1 and cCa<1 mg·L-1, the interference can be neglected by using the isotope 57Fe; (b) when cFe<0.10 mg·L-1 and cCa>1 mg·L-1, the interference is significant by using either of the 2 istopes; (c) when cFe>0.10 mg·L-1 and cCa<5 mg·L-1, the interference can be neglected and either of the 2 isotopes can be used, and when cCa>5 mg·L-1, the interference can be eliminated only by using the isotope 56Fe.