The reproducibility of plasma protein quantitation between laboratories and between instrument types was examined in a large-scale international study involving 16 laboratories and 19 LC-MS/MS platforms, using two kits designed to evaluate instrument performance and one kit designed to evaluate the entire bottom-up workflow. There was little effect of instrument type on the quality of the results, demonstrating the robustness of LC/MRM-MS with isotopically labeled standards. Technician skill was a factor, as errors in sample preparation and sub-optimal LC-MS performance were evident. This highlights the importance of proper training and routine quality control before quantitation is done on patient samples.
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