Determination of Trace Phosphorus in Copper-Containing Stainless Steel by High Resolution Inductively Coupled Plasma Magnetic Massspectrometry

Through testing, modifications were made and a method for determination of trace amount of phosphorus in copper containing stainless steel by high resolution inductively coupled plasma magneto-mass spectrometry (HR-ICP-MS) was proposed in this paper. By using resolution of 4 000, response peak of phosphorus was well-separated from the interfering peaks of several bi-atomic molecules or ion, thus to have the interferences eliminated. A mixed solution containing 1 μg·L^-1 of phosphorus and Fe(Ⅲ) as matrix was used in tuning of the instrument to optimize the parameters of gas flow and ionic lens, the signal of phosphorus was raised to 3×10⁵cps. And ⁴⁵Sc was added as internal standard to overcome the matrix effect and to improve stability of analytical results. Two different ways for preparation of standard curves, i.e. 1 adding standard solutions of phosphorus to a matrix of stainless steel sample, and 2 adding standard solutions of phosphorus to pure iron as matrix, were tested comparatively, and as shown by the results, good linearity was obtained for the standard curves prepared by both of the 2 ways, and the results of phosphorus together with the values of RSD found by either of the 2 curves in analyzing a sample were in satisfactory conformity. However, detection limits (3s) found rom the 2 curves were quite different, giving values of 1.0 μg·g^-1 for the former way, and of 0.18 μg·g^-1 for the latter. Procedure for pretreatment of sample was given as follows:0.10 g of the sample was reacted with 2 mL of hydrochloric acid and 1 mL of nitric acid in the digestion vessel and when the vigorous reaction subsides, the vessel was capped and placed into the microwave digestor, and the digestion of the sample was carried on for 10 min at 100℃ and for 20 min further at 200℃. After cooling, the solution was transferred to a 100 mL quartz volumetric flask, and after adding 1 mL of 0.2 μg·L^-1 scandium internal standard solution, water was added to the mark, and mix thoroughly. This was the sample solution used for HR-ICP-MS analysis under the working condition of the instrument. A Cu-containing stainless steel sample having its P-content of 15 μg·g^-1was analyzed by the propose method, giving value of RSDs (n=10) less than 4%. To test for its accuracy, 7 CRMs and known samples (including low alloy steel, copper-containing stainless steel, high temperature alloy and etc) were analyzed by the present method and by ICP-AES simultaneously. It was shown that the results of phosphorus found by the 2 methods were in consistency, but the results given by HR-ICP-MS method were more closer to the certified values of the CRMs; and that the HR-ICP-MS method was more effective in determination of phosphorus in trace amount (9 μg·g^-1).