The proficiency testing (PT) RVEP 0970 showed that the IFU7a can be operated under routine conditions within the limits of R. Nevertheless, it may be questioned whether the reproducibility R isstilluptodate.WithinthePTRVEP0970,theHPLC–IMERshowed promising results. But in order to compare the proficiency of both methods, the HPLC–IMER needs to be validated and precision data has to be determined. The HPLC–IMER showed high potential to surpass the IFU 7a as a future reference method for the determina-tion of SO2.