Mutual interference between 3,6-dichlorinated carbazole and p,p'-dichlorodiphenyltrichloroethane in gas...

The widespread contamination of the environment by polyhalogenated carbazoles (PHCZs) has been increasingly observed during the past decade. Among numerous PHCZ congeners, 3,6-dichlorocarbazole (36-CCZ) is often among the most frequently detected at higher concentrations. Although the environmental level of the legacy pesticide p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) has been declining, it continues to be ubiquitously detected. These two compounds were found to interfere with each other during analyses using gas chromatography (GC) coupled with single- or triple-quadrupole low-resolution mass spectrometry (MS or MS/MS). The base peak in the mass spectra was that of m/z 235 for both compounds. In MS/MS with multiple reaction monitoring (MRM), the same transitions (235 → 200 and 235 → 165) were often used. Under the same GC operating conditions, the SH-I-5MS capillary column used in this work did not resolve the two compounds at baseline. Pre-treatment using cleanup column chromatography can fractionate the sample extract, with the two compounds separated in different fractions before instrumental analyses. Reversed-phase HPLC columns also work for resolving 36-CCZ and p,p'-DDT. Possible overlaps in GC retention and similarity in MS spectra might have caused data inaccuracy for 36-CCZ as well as p,p'-DDT in some studies published to date, and steps to avoid the interference should be taken into quality control protocols in future research and environmental monitoring.