Determination of PAHs: A Practical Example of Validation and Uncertainty Assessment Evelyn de F. Guimara˜ es 1,2 *, Janaı´na M. Rodrigues 1 , Marcus H. C. de la Cruz 1 ,Andre´ V. Sartori 1 , Vanderle´a de Souza 1 and Jose´ Daniel Figueroa-Villar 2 1 Chemical Metrology Division, Scientific and Industrial Metrology Directorate, National Institute of Metrology, Quality and Technology – INMETRO, Duque de Caxias, RJ, Brazil, and 2 Chemistry Department, Military Institute of Engineering – IME, Rio de Janeiro, RJ, Brazil *Author to whom correspondence should be addressed. Email: efguimaraes@inmetro.gov.br Received 18 October 2011; revised 24 October 2012 The objective of this study was to present a reliable and practical example of method validation and uncertainty assessment with an analytical method for the determination of polycyclic aromatic hydrocarbons (PAHs) in urban dust. The method was gas chroma- tography –mass spectrometry in combination with isotope dilution principle to achieve better accuracy for the results. The method performance parameters for five PAHs were determined (phenan- threne, fluoranthene, benzo[a]anthracene, benzo[a]pyrene and ben- zo[ ghi]perylene); this method was used in the key comparison of CCQM-K50b for PAHs in particulate matter. The limits of detection and quantification were lower than 0.075 and 0.250 mg/g, respect- ively. The linear correlation coefficients were greater than 0.99. The major uncertainty contributions resulted from the accuracy of each analyzed PAH and the repeatability of the process. Certified reference material (National Institute of Standards and Technology SRM 1649a, urban dust) was used to determine the accuracy and precision of the method. The obtained results were satisfactory and agreed with all evaluated performance parameters. Introduction Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous envir- onmental contaminants originating from anthropogenic natural sources, primarily pyrogenic and petrogenic sources. Emissions from automotive vehicles are considered to be important contri- butors to the high concentrations of PAHs in atmospheric par- ticulate materials and the gas phase of urban areas (1). Due to their persistency in the environment and their toxic potential (mutagenic and carcinogenic properties), several PAHs are on the list of priority pollutants of the U.S. Environmental Protection Agency and are considered to be of interest for public health by regulatory organizations in many countries (2). Several methods for the determination of PAHs in particulate material are described in the literature including methods for urban dust. The classic procedures generally involve the extrac- tion of the analytes by Soxhlet techniques, followed by cleanup using solid-phase extraction (SPE) and analysis by gas chroma- tography–mass spectrometry (GC–MS) (3). The accurate determination of these compounds in atmos- pheric particulate materials is important for several purposes, including exposure studies, risk assessment and regulation (4). Accordingly, these analytical results should be obtained through an integral process, in which the validation of the ana- lytical methods is presented as an essential stage. The application of certified reference materials (CRMs) in environmental analyses has great importance in the validation of analytical methodologies. CRMs are used to evaluate and val- idate the accuracy of analytical methods. Therefore, they must possess similar characteristics to the matrix of the sample in analysis, participating in all stages of the analytical procedure, in addition to establishing traceability for the measurements (3). Many authors have successfully applied CRMs to the valid- ation of analytical methodologies for the analysis of PAHs in en- vironmental matrices (5 – 9). Isotope dilution mass spectrometry (IDMS) has been applied to the determination of environmental contaminants by metrol- ogy institutes and research laboratories, with the objective to provide greater accuracy for measurements (10). IDMS is classi- fied as a primary ratio measurement method by the Comite´ Consultatif pour la Quantite´ de Matie`re (CCQM), because it is traceable to the International System of Units (SI) (11, 12). IDMS is based on the principle that isotopes (internal stan- dards) behave in the same manner throughout the whole ana- lytical processes as the corresponding native compounds (10). Thus, error factors resulting from instrumental and operational alterations; for example, low extraction recovery, which affects the quantification of losses during sampling clean-up and injec- tion in the GC, can be minimized or eliminated, improving the performance of the analytical method (4). Deuterium-labeled (PAH-d) and 13 C-labeled PAHs have been used as stable internal standards for the determination of PAHs by GC–IDMS. In this study, a method based on GC–IDMS was implemen- ted and validated for the analysis of five PAHs in urban dust, using PAH-d as internal standards. The CRM SRM 1649a (urban dust) of the U.S. National Institute of Standards and Technology (NIST) was used to validate the analytical method. The International Organization for Standardization (ISO) stand- ard ISO/IEC 17025, which defines general requirements for the competence of laboratories, reports the need for estimated meas- urement uncertainty and the validation of analytical methods (13). Method validation procedures have been described by Scientific and Industrial Metrology directorate, National Institute of Metrology, Quality and Technology (Inmetro) in a validation guidance document, which involves steps such as the evaluation of the estimated uncertainty and the repeatabil- ity and reproducibility. The concept of estimating measure- ment uncertainty was initially developed for physical processes, but it has recently been widely employed for chem- ical determinations (14). However, estimating the measurement uncertainty for the results of chemical analysis is much more # The Author [2012]. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com Journal of Chromatographic Science 2013;51:845– 855 doi:10.1093/chromsci/bms185 Advance Access publication November 27, 2012 Article