称取过0.074 mm筛孔样筛的钛铁矿样品0.10~0.50 g置于预先铺垫了粉状焦硫酸钾2 g的瓷坩埚中，再加入焦硫酸钾3 g，混匀，加盖，置于马弗炉中，温度升至350℃时，摇动坩埚使样品与熔剂均匀接触，继续升温至600℃，熔融1 h，除去坩埚盖，继续保持30 min。取出坩埚，稍冷却后，加水将熔块溶解并定容至100.0 mL。按规定方法对D201型阴离子交换树脂进行预处理后装入交换柱中。经试验，在硫酸浓度为0.01 mol·L^-1，K₂SO₄浓度为0.5 mol·L^-1的硫酸盐溶液中，铀及钍的硫酸盐阴离子在交换树脂上的交换吸附率均超过98%。据此，在交换柱的储液杯中加入上述硫酸盐溶液20 mL后，定量加入样品溶液5.0 mL，使溶液逐滴通过交换柱。当溶液滴尽时，用0.01 mol·L^-1硫酸溶液淋洗树脂2次（每次用5 mL），随即用0.5 mol·L^-1盐酸溶液14 mL及水6 mL洗脱吸附于树脂上的铀和钍。收集淋洗液并加水定容至50.0 mL，此溶液在仪器工作条件下进行电感耦合等离子体质谱分析，并利用三通活塞在线加入10 μg·L^-1的铑标准溶液作为内标，在标准模式下选择原子丰度较高的同位素²³⁸U、²³²Th、¹⁰³Rh进行测定。铀、钍的标准曲线的线性范围均在100 μg·L^-1以内，检出限（3s）依次为0.029，0.036 μg·L^-1。对两种元素的测定进行精密度试验，测得相对标准偏差（n=5）值均小于10%。应用本方法测定了4件国家一级标准物质的铀、钍的含量，测定值与认定值基本相符。

Ilmenite was crushed to pass through sample sieve with boring of 0.074 mm. 0.10 to 0.50 g of the ilmenite sample was taken and placed into a porcelain crucible in which 2 g of powdered K₂S₂O₇ had been bedded at the bottom of the crucible. Another portion of 3 g of K₂S₂O₇ was added to the crucible and well mixed with the sample. After putting on the crucible cover, the crucible was placed into a muffle furnace and the temperature was elevated. At 350℃, the crucible was shaken carefully by swirling to make the sample dispersed homogeneously in the melted flux. Then the temperature was raised to 600℃, and the sample with the flux in the crucible was fused for 1 h, and after removing the crucible cover, the sample was fused for 30 min in addition to have the residual SO₃ volatized. The crucible was then taken out from the muffle furnace, and after cooling, water was added to dissolved the melt and the volume of the sample solution was made up to 100.0 mL. On the other hand, a definite amount of D201 anion exchange resin was taken and pretreated as prescribed. And the resin was packed into an exchange column. It was found that sulfate anions of uranium and thorium can be satisfactorily separated from the matrix of ilmenite by exchange adsorption on the D201 anion exchange resin in a acidic sulfate solution with H₂SO₄ of 0.01 mol·L^-1 and K₂SO₄ of 0.5 mol·L^-1, giving rates of exchange adsorption over 98%. Based on this finding, 5.0 mL of the sample solution together with 20 mL of the acidic sulfate solution were added into the reservoir at the top of the exchange column, and the sulfate solution containing the sample was then passed through the column by dropping, after which the column was rinsed twice with 0.01 mol·L^-1 surfuric acid solution (5 mL for each rinse), and finally U and Th were eluted from the exchange column with 14 mL of 0.5 mol·L^-1 HCl solution and 6 mL of water successively. The eluates were collected and diluted to 50.0 mL, which was used for the ICP-MS analysis under the working conditions of the instrument. 10 μg·L^-1 rhodium standard solution was added as internal standard online through the tee of the instrument. Isotopes of ²³⁸U, ²³²Th and ¹⁰³Rh with relatively higher atomic abundance were selected in the determination. Linearity ranges of the standard curves of U and Th were found same within 100 μg·L^-1, and values of detection limits (3s) found were 0.029 μg·L^-1 and 0.036 μg·L^-1 respectively. Values of RSDs (n=5) found for the 2 elements were less than 10%. The proposed method was used in analyzing 4 national standards for the contents of U and Th, giving results consistent with the certified values.