The limits of detection for the xenobiotics and human estrogens ranged from 0.01 to 5.7 ng/mL with a median of 0.08 ng/mL in solvent (Table , Figure ). In matrix the median LOD increased to 0.7 (urine, Figure ) and 0.5 (plasma, Figure ) most likely due to matrix effects and matrix interferences. Phytoestrogens like daidzein and genistein and personal care product ingredients, e.g., parabens, exhibited the lowest LODs. The LODs were, for most xenobiotics and human estrogens, sufficient to detect them in averagely contaminated samples considering concentration levels from published human biomonitoring studies (Table ). Six analytes for which certified reference values are available in SRM3672 (Organic Contaminants in 'Smoker's Urine) were detected and quantified (Table ). As the values stated in the certificate were total analyte concentrations after hydrolysis, βglucuronidase/arylsulfatase-treated reference urine was analyzed. The relative error compared to the reference value was < 20% for all of these (Figure ). 1-OH-pyrene and MEHP were not detected, although they are present in the smokers' urine, due to their low concentration below the method's quantification limits. Besides several amino acids, PFOA and PFOS were quantified in SRM1950 (Metabolites in Frozen Human Plasma) and compared to the certificate (Figure , Table ). Threonine was not evaluated as it coeluted with homoserine; therefore, only a combined value for both amino acids was available. Isoleucine and leucine were not baseline separated as well, but for both molecules, reference values were given. Therefore the sum of both concentrations was compared. The relative error was < 26% for all amino acids, whereby the recoveries were in general lower for the high abundance amino acids (glycine (75%), alanine (82%), isoleucine/leucine (74%)), possibly due to saturation effects as the values were outside of the calibration range (Figure ). The samples were injected undiluted to ensure a high detectability of low-concentrated xenobiotics despite possible saturation issues for the endogenous metabolites at higher concentrations. The relative errors of PFOA and PFOS were even < 5% and < 20%, respectively.