Dioxin Detection Prevents Contamination of Meat Supply

FC43 was used as a reference compound to provide the inherent lock and calibration masses. These reference masses are monitored scan to scan to ensure the highest mass precision, stability, and ruggedness necessary for routine target compound analysis on an HRMS. For all native dioxin congeners, as well as for their specific 13C labeled internal standards, one quantification mass and one ratio mass were implemented in the MID setup.

The effective resolution is constantly monitored on the reference masses and documented in the data files for each MID window. Modifications of the MID descriptor used in this application might be necessary for different applications. For example, the EPA method 1613 standards typically do not contain the octa-furan 13C labeled internal standard. To set the boundaries of the MID retention time windows for each individual congener group, a window defining standard such as a fly ash must be used to properly set the MID time windows.

Selecting the dioxin confirmation masses requires special attention and may vary according to different analysis methods. In this setup, the ratio mass at m/z 371.82300 (52%) was used for the native hexa-furan instead of the normal furan ratio mass trace at m/z 375.81723 (81%). This was done because the FC43 reference mass at m/z 375.980170 is too close in mass to the analyte and may interfere in the signal of the analyte ion. This alternate ion selection decreases the background noise and increases the signal-to-noise value of the analyte mass trace. A similar situation can be seen for the hepta-dioxin ratio mass at m/z 425.77317. Here, the FC43 mass m/z at 425.976977 is close and could cause interferences.

In spite of these effects, FC43 offers practical advantages over perfluorokerosin (PFK) as an alternative reference compound. For dioxin analysis, FC43 provides reference masses with good intensity for all MID windows, even at reduced reference gas flows into the ion source. In addition to having a lower boiling point, FC43 contaminates the ion source less than PFK. The optimization of the electron energy on the instrument is critical in obtaining the best results. On the DFS instrument used for the demonstrated measurements, an electron energy of 48eV provided optimum sensitivity.

This parameter should be determined once for a given instrument; typical optimum values are generally found between 40 and 50eV. During the optimized procedure, the best instrument performance was achieved by autotuning the ion source on the FC43 reference mass m/z 414 with a resolution setting of 10,000.

Sample Measurements

Two types of experiments were conducted to prove instrument sensitivity, stability, and robustness. First, a sequence of 72 repeated injections measuring 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) masses of a 17fg/mL 2,3,7,8-TCDD standard (diluted from a 100fg/mL TCDD standard; Wellington Laboratories Inc., Guelph, Ontario, Canada) was performed. Next, a real-life sample series was analyzed by measuring the full set of dioxin/furan masses of a blood pool sample that contained low concentrations of dioxins/furans quantified for 2,3,7,8-TCDD at 20fg/mL.

Repeat injections were made of several analytical sequences. A method 1613 CS1 calibration standard (1:10 diluted = 50fg/mL tetras; 250fg/mL pentas to heptas; 500fg/mL octas; Cambridge Isotope Laboratories Inc., Andover, Mass.) was used to check the chromatographic separation performance of the system.

A typical separation using the GC parameters of an EPA 1613 CS1 dioxin standard at 50fg/mL of TCDD and 2,3,7,8- tetrachlorodibzofuran (TCDF). These GC parameters were also employed for the blood sample. Instrument sensitivity is demonstrated by the injection of a 20fg/mL TCDD standard. To demonstrate how well the system performs using low dioxin concentrations in dirty matrices, repeated injections were made of a challenging real-life sample, a pooled blood sample extract.