I’ve started to wonder if some analysts are taking the language in EPA Methods 1613 and 8290a for high resolution GC – high resolution mass spectrometry of chlorinated dioxins and furans too literally when it comes to confirmatory analysis for 2,3,7,8-tetrachlorodibenzofuran (2378 TCDF), which cannot be done on the DB-5 (5% diphenyl – 95% dimethyl polysiloxane) column suggested for primary analysis. I’ve copied the language for the methods below, but in summary they recommend either 50% cyanopropyl methyl – 50% phenyl methyl or 90% biscyanopropyl – 10% phenyl cyanopropyl stationary phases that have very low maximum operating temperatures (240-275°C), not good for chlorinated dioxin/furan analysis, especially if you want to keep them in the same GC oven as the 5% phenyl primary column that has a maximum operating temperature of 350°C.
By “too literally”, I’m specifically talking about the “or equivalent” language. I can easily provide isomer specificity for 2378 TCDF on our Rtx-Dioxin2, as well as 2,3,4,7,8-pentachlorodibenzofuran specificity, but as regards being totally “equivalent”, well, the Rtx-Dioxin2 with its 340°C maximum operating temperature is way better than some old high-bleed, thermally unstable cyano column.
Check out the chromatograms below where both 2,3,7,8- tetrachlorodibenzodioxin (2378 TCDD) and 2378 TCDF are easily separated from potentially interfering congeners on Rtx-Dioxin2. Compare this to the (very confusing) chromatogram taken from EPA Method 1613 where I believe they are trying to show 2378 TCDF on a DB-225 column, not a DB-5 column as labeled in the chromatogram. Also take note of the fact that the chromatogram was generated in 1988! Can we please get some recent technology for these methods?!
EPA Method 1613, 16.5
Confirmatory Analysis—Isomer specificity for 2,3,7,8-TCDF cannot be achieved on the DB-5 column. Therefore, any sample in which 2,3,7,8-TCDF is identified by analysis on a DB-5 column must have a confirmatory analysis performed on a DB-225, SP-2330, or equivalent GC column. The operating conditions in Section 10.1.1 may be adjusted to optimize the analysis on the second GC column, but the GC/MS must meet the mass resolution and calibration specifications in Section 10.
EPA Method 8290a, 3.4
A high-resolution capillary column (60-m DB-5, J&W Scientific, or equivalent) is used in this method. However, no single column is known to resolve all isomers. The 60-m DB-5 GC column is capable of 2,3,7,8-TCDD isomer specificity (Sec. 8.1.1). In order to determine the concentration of the 2,3,7,8-TCDF (if detected on the DB-5 column), the sample extract must be reanalyzed on a column capable of 2,3,7,8-TCDF isomer specificity (e.g., DB-225, SP-2330, SP-2331, or equivalent).