采用电感耦合等离子体质谱法测定水中小于0.06 mg·L-1铁量时受到共存的钙(40 mg·L-1)的严重干扰。经验证,钙的干扰可借以下途径消除:① 采用碰撞池和56Fe、57Fe两同位素中的任一种,钙的干扰均可忽略不计。② 如采用非碰撞池,则钙的干扰将因铁与其共存钙的质量浓度的不同而变化:(a) 当cFe<0.10 mg·L-1,cCa<1 mg·L-1,并采用57Fe同位素时,钙的干扰可以忽略;(b) 当cFe<0.10 mg·L-1,cCa>1 mg·L-1时,采用两同位素中的任一种都无法克服钙的严重干扰;(c) 当cFe>0.10 mg·L-1,cCa<5 mg·L-1,无论采用同位素56Fe或57Fe,钙的干扰都不明显,而如cCa>5 mg·L-1时,则只能用同位素56Fe才可避免钙的干扰。

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.