Supplementary comparison study - fipronil-sulfone in chicken egg powder (APMP.QM-S16)
Authors: Guo Zhen , Li Xianjiang , Li Xiuqin , Zhang Qinghe , Li Hongmei , Ho Clare , Lam Tony CH , Teo Tang Lin , Cheow Pui Sze , Gui Ee Mei , Wang Juan , Dabrio Marta , Shegunova Penka , Shearman Kittiya , Chaiphet Thitiphan , Fortune Thippaya Junvee , Tangtrirat Pradthana , Bilsel Mine , Binici Burcu 
Published: July 2022

Main text
The APMP.QM-S16 comparison was coordinated by the National Institute of Metrology, China (NIM) on behalf of the Technical Committee on Amount of Substance (TCQM) of the Asia Pacific Metrology Programme (APMP) and the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) for National Measurement Institutes (NMIs) and Designated Institutes (DIs) which provide measurement services in organic analysis under the 'Comité International des Poids et Mesures' Mutual Recognition Arrangement (CIPM MRA).
Fipronil is a broad-spectrum insecticide attributed to the phenylpyrazole family. Due to its high toxicity to invertebrates and long persistence, it has been one of the most widely used insecticides to control household and agricultural pests since its appearance in the market. Fipronil has also shown genotoxicity and cytotoxicity to many vertebrate animals, like mammals, birds, fish, reptiles and so on. Moreover, fipronil could have negative effects on the liver, kidneys and thyroid glands of humans. Its oxidation metabolite is fipronil-sulfone that could induce even higher toxicity than fipronil. In 2017, a fipronil-in-egg scandal occurred in the European Union (EU) that involved more than 15 states. The detected concentration of the sum of fipronil and fipronil-sulfone was many times higher than the EU maximum residue limit in bird egg (5 μg/kg). Besides European countries, fipronil-contaminated eggs were also found in Asian areas like China, Hong Kong and South Korea. Systematic monitoring and control of pesticide residues are necessary to safeguard public health.
Fipronil-sulfone was selected to be representative of pesticide residues in this comparison. This study provides the means for assessing measurement capabilities for determination of low-polarity measurands in a procedure that requires extraction, clean-up, analytical separation, and selective detection in a food matrix. Generally, it provides a demonstration of a laboratory's capabilities in determining the medium molecular weight analytes (mass range 300-500) with low polarity (pKow < -2) at mass fraction levels of 4 to 400 μg/kg in a high fat, high protein and low carbohydrate food matrix that falls within Sector 4 of the AOAC Food-matrix Triangle.
Seven NMIs/DIs participated in the APMP.QM-S16 comparison. Different methods such as liquid-liquid extraction, QuEChERS and SPE were applied in the sample pre-treatment and HPLC-MS/MS, HPLC-HRMS, and GC-MS/MS were applied for detection by the participants. Most participating laboratories applied isotope dilution mass spectrometry (IDMS) techniques with fipronil-sulfone-13C4,15N2 as internal standard, except EC-JRC-Geel which used matrix matched external calibration method. In the aspect of the traceability for the measurement results, most participants either used their own CRMs, other NMIs' CRMs or the pure materials assessed in-house to guarantee traceability to SI unit. One lab was excluded from the SCRV evaluation, as they did not meet the CIPM metrological traceability requirements. As a result, six sets of valid results were used for the estimation of the SCRV. Finally Hierarchical Bayes was considered to be the appropriate estimator to calculate SCRV, which was determined as 121.82 μg/kg with a standard uncertainty of 1.77 μg/kg. Inspection of the degree of equivalence plots for the fipronil-sulfone mass fraction assignments in APMP.QM-S16 indicated that there was excellent agreement of results.
To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.
The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).