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HRMS and APGC-MS measurement of TCDD Douglas G. Hayward Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.5b02689 • Publication Date (Web): 21 Sep 2015 Downloaded from http://pubs.acs.org on September 26, 2015
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Analytical Chemistry
Comment on APGC-MS and HRMS measurement of TCDD Douglas G. Hayward US Food and Drug Administration 5100 Paint Branch Parkway College Park, MD 20740
[email protected] I read with great interest a just accepted article by Organtini et al. Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.5b01705, describing a new and promising mass spectrometry technique that could replace the “traditional” HRMS magnetic sector instrument used to measure 2,3,7,8-tetrachloro-dibenzo-p-dioxin in food and environmental matrices. The authors state that the new technique (APGC-QQQ) would provide 2-18 times better sensitivity when compared to HRMS. The difference in sensitivity mentioned in the abstract is demonstrated in the article through a comparison of MDLs (method detection limits) listed in Table 2 for the two matrices studied, sediment and fish. The MDL for TCDD in fish by APGC is listed in Table 2 as 0.23 pg/g (APGC-MS) and 4.3 pg/g by HRMS or 18.7 times lower by APGC-MS. We assume, but have no indication of it in Table 2, that the MDLs were estimated on a dry weight basis for one reference fish reported in Table S4. On a wet weight basis the MDLs might be about 4 times lower or 0.06 for APGC and 1.1 pg/g fresh weight for HRMS for TCDD. While such MDLs may seem very low for fish, an MDL for TCDD of 0.23 or 0.06 pg/g has been reached or surpassed for a long time by both HRMS and MS/MS1. Current EU guidelines on dioxin concentrations in fish for human consumption require the total TEQ to be less than 3.5 pg/g fresh weight and that methods used as confirmatory techniques be capable of measuring 1/5 that amount or less2 . Confirmatory mass spectrometry techniques are evaluated based on their upper bound TEQ MDL that can be generated routinely. The upper bound TEQ MDL is the sum of the full value for the MDLs for all dioxin/furan congeners weighted for their TEF2. The upper bound TEQ MDLs reported by Organtini et al. for fish would be 1.35 pg/g for APGC and 9.3 pg/g for HRMS magnetic sector or about 0.34 and 2.3 pg/g fresh weight respectively assuming 75% moisture. This suggests that the traditional HRMS technique might not be able assess whether a fish sample was over the current EU maximum limit of 3.5 pg/g, which is not consistent with current reports. Indeed, the authors own measurements for a low contaminated reference fish using APGCMS/MS estimate the TEQ for the reference dried fish much lower than the 1.35 pg/g TEQ MDL stated in Table 2. The authors report a TEQ of 0.44 pg/g measuring 16 of 17 analytes. HRMS reported an upper bound TEQ of 0.43 pg/g with only 2 congeners reported above the MDLs (Table S4). If the non-detects are set to zero the TEQ would be 0.16 pg/g by HRMS nearly 200% inaccurate. Very large differences in the TEQ estimate such is the case here between the upper and lower bound TEQ indicates trouble for the HRMS analysis2. The article uses reference fish and sediment to compare the accuracy and sensitivity of the two techniques. While this approach is the commonly accepted mode for determining accuracy of methods, dioxin measuring laboratories more often use naturally contaminated matrices of widely differing foods which are distributed to as many as 85 laboratories most recently in 2015. Consensus
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values are established. Then, a laboratory’s individual results and the TEQ can be evaluated accordingly. Table 1 gives the consensus values for two studies of fish measured in the 2000 and 2015 rounds of the “Inter-laboratory comparison study of POPs in food”, Norwegian Institute of Public Health, Olso, Norway with FDA’s reported values for each congener using MS/MS (2000) and HRMS (2015). Note in both years the estimate of the upper bound TEQ by FDA is within 15% of the consensus regardless of the concentration as are most individual congeners. Table 1 Fish test materials 2000 and 2015
Weight wet pg/g 2,3,7,8-TCDF 2,3,7,8-TCDD 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF 1,2,3,4,6,7,8-HpCDD OCDF OCDD Upper bound TEQ FDA (WHO 2005 TEFs)
2015
2000
HRMS FDA pg/g 6.20 0.4000 0.830 4.80 0.610 0.1200 0.1700 0.1400
