*2.9. Identification and Quantification of Branched NPs*

NPs were identified by their retention times, and the quantifier and qualifier ions by standard chemicals. Branched NP concentrations were obtained by summing the isomers. For NP quantification in 1185 food samples, the calibration curve obtained using 4-n-NP and relative detected responses of linear and branched compounds was used. The relative response factor was calculated with respect to the area of corresponding analytes with equivalent amounts, in order to convert the concentration obtained using linear 4-n-NP into the total concentration of branched NP isomers. The recovery rates for conversion from 4-n-NP to NPs, which are both composed of isomers, were assumed to be identical, and only detected response values were considered [17].
