Preparation of mixed standards of non-threshold analytes at MRPL/MRL

Code: 23A21VA

The non-threshold substances in the WADA Prohibited List that are analysed by mass spectrometric methods have a minimum required performance level (MRPL) associated with them. These levels are set in Technical Document TD22MRPL. Some of these substances also have a method reporting limit (MRL). The MRL is either larger or equal to the MRPL. As specified in the document – “The MRPL is intended to harmonize, to the extent possible, the analytical performance of chromatographic-mass spectrometric Analytical Methods applied to the detection of Non-Threshold Substances.” To achieve such harmonisation is not a simple task. In an ideal world, all WADA laboratories would have access to a common standard material, preferably an incurred urine sample, whose concentration had been established by one or more reference laboratories using isotope dilution mass spectrometry. This approach of preparing certified reference materials has been adopted and funded by WADA for a few threshold substances but it is a very expensive process costing in excess of $50,000 for each analyte. Even if such funding were available for the almost one hundred non-threshold substances, the isotope dilution method can only be applied to compounds that are relatively stable in urine. Some of the substances degrade significantly within days. A different lower cost approach is needed to enhance harmonisation of the MRPLs and MRLs between the thirty WADA laboratories. The problem of having certified reference standards for aqueous samples is a problem that has faced environmental laboratories for many years. It is impractical to prepare and ship large volumes (1-5 litres) of spiked water samples to laboratories around the world so that their performance can be assessed in proficiency studies. There is also the problem of the stability of some analytes in water. The approach that is most used is to provide the laboratories with a small volume of a concentrated spiking solution (normally in methanol) in a sealed glass ampoule which is then diluted to a known volume with water. The spiking solution is prepared by weighing standards of known purity. It is proposed to adopt a similar approach in this project. The objective is to improve harmonisation by providing all the WADA laboratories with one to three spiked samples covering most of the non-threshold substances and including all those substances with a MRL. Each sample would contain approximately thirty analytes at concentrations close to the MRPL for each. A third sample would contain the four substances that have a MRL higher than the MRPL. Stock solutions of each of the substances would be made by weighing reference standards to prepare the spiking solutions. The samples would be distributed to and analysed by the WADA laboratories, and the results coordinated to provide a consensus mean. Analysis of the results should provide estimates of precision, accuracy and reproducibility. This laboratory has begun a pilot study by preparing two spiking solutions each containing some thirty substances at or near their MRPL. These will be distributed to the WADA laboratories and results collated.