Analysis of inadvertent hydrolysis of BPA-G in spiked rat serum. A) Unspiked samples were analyzed for uBPA (blue) and BPA-G (green). uBPA was not detected by any laboratory; one of three laboratories reported BPA-G in this sample. B) Serum samples spiked with only BPA-G were analyzed for uBPA and BPA-G. uBPA was not measured above the LOQ by any laboratory. C) Sample spiked with uBPA concentrations at or near the LOD for the methods used by the participating laboratories (see Table 3), plus BPA-G. All three laboratories reported BPA-G, but only one measured uBPA at concentrations above the LOQ. For all panels, dotted lines indicate the concentrations spiked and graphs represent mean ± standard deviations reported from each laboratory with the exception of Laboratory 4, which could not perform replicate measures due to the volume of serum required for their assay and the limited amount of rodent serum available. UD indicates undetectable levels; <LOQ indicates detectable levels that were below the limit of quantification.