2.6. Quality assurance
The limit of detection (LOD) was calculated using an average of the lowest calibration point (n = 3) and 3*signal to noise (S/N). In the case of blank contamination the LOD was calculated using the average blank concentration (n = 6) plus three times the standard deviation. Details about method reproducibility and accuracy AZD3839 provided in the Supplementary Information and method validation parameters, recovery rates and blank concentrations are presented in Tables S3, S4 and S5, respectively.
2.7. Statistical analysis
An analysis of variance (ANOVA) was conducted using log10-transformed concentrations to examine factors implantation might influence blood serum levels of PFOS, PFHxS, and PFOA. Factors investigated included age, sex, serum protein levels, current smoking, blood donor (yes versus no), years of employment on jobs with foam contact, and indices of time-weighted intensity of foam contact before 2003 and after 2003 (see Supplementary Information).