Determination of Fe and Ca in alumina-based nickel-molybdenum hydrodesulphurization catalysts using inductively coupled plasma optical emission spectrometry and inductively coupled plasma dynamic reaction cell mass spectrometry

Abstract

The analytical performance of inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry GCP-MS) for the determination of Fe and Ca in alumina-based nickelmolybdenum hydrodesulphurization catalysts was evaluated. Although the typical concentration of both elements is quite high (0.02-0.4% for Fe and 0.02-0.2% for Ca), the complex matrix of the catalysts strongly influences the results. Before measurements, effective digestion using HClO4+HF, H 3BO3, and HCl was executed. The accuracy of the results was evaluated by spiking a raw catalyst sample before digestion and measuring the recoveries. In the case of ICP-OES, a 10-fold dilution of the sample digest solution yielded recoveries of 95% for Fe and 102% for Ca. In the case of ICP-MS, the use of dynamic reaction cell (DRC) with ammonia as a reaction gas along with the low mass bandpass was crucial. The optimized ICP-DRC-MS conditions were as follows: 56Fe and 42Ca as monitored isotopes, ammonia flow rate of 0.45 mL min-1, RPa of 0.00 and RPq of 0.65 mL min-1. Applying these conditions, the recovery was 97% for Fe and 89% for Ca, and the results of ICP-OES and ICPMS were in satisfactory agreement. As no appropriate reference materials are available, cross-validation of both methods turned out to be a crucial tool for confirmation of the accuracy of the results. This work also shows that the use of DRC is an effective way for spectral interference elimination in a complex matrix.