Developing an Improved Strategy for the Analysis of Polychlorinated Dibenzo-p-Dioxins/Furans and Dioxin-like Polychlorinated Biphenyls in Contaminated Soils Using a Combination of a One-Step Cleanup Method and Gas Chromatography with Triple Quadrupole Mass Spectrometry

Abstract

Soils contaminated with polychlorodibenzo-p-dioxins (PCDDs), polychlorodibenzofurans (PCDFs), and dioxin-like (dl) polychlorinated biphenyls (PCBs), known as persistent organic pollutants (POPs), have garnered global attention because of their toxicity and persistence in the environment. The standard method for target analytes has been used; however, it is an obstacle in large-scale sample analysis due to the comprehensive sample preparation and high-cost instrumental analysis. Thus, analytical development of inexpensive methods with lower barriers to determine PCDDs/Fs and dl-PCBs in soil is needed. In this study, a one-step cleanup method was developed and validated by combining a multilayer silica gel column and Florisil micro-column followed by gas chromatography with triple quadrupole mass spectrometry (GC-QqQ-MS/MS). To optimize the separation and quantification of 17 PCDDs/Fs and 12 dl-PCBs in soils, the sample cleanup and instrumental conditions were investigated. For quantification method validation, spiking experiments were conducted to determine the linearity of the calibration, recovery, and method detection limit of PCDDs/Fs and dl-PCBs using isotopic dilution GC-QqQ-MS/MS. The applicability of the simultaneous determination of PCDDs/Fs and dl-PCBs was confirmed by the recovery of native target congeners and labeled surrogate congeners spiked into the quality-control and actual soil samples. The results were in good agreement with the requirements imposed by standard methods. The findings in this work demonstrated the high accessibility of the sample cleanup and analysis methods for the efficient determination of PCDDs/Fs and dl-PCBs in contaminated soils.

Keywords: dioxin-like polychlorinated biphenyls (dl-PCBs); gas chromatography with triple quadrupole mass spectrometry (GC-QqQ-MS/MS); one-step cleanup; persistent organic pollutants (POPs); polychlorodibenzo-p-dioxins (PCDDs); polychlorodibenzofurans (PCDFs); soils.

Figure 1

Elution profiles of (a) dl-PCBs and (b) PCDDs/Fs using the combined columns (multilayer silica gel and Florisil micro-column). The shaded part of the graph represents the elution volumes for dl-PCB fraction eluted by 175 mL of n-hexane and 25 mL of 2% dichloromethane (DCM) in n-hexane and PCDD/F fraction eluted by 75 mL of DCM.

Figure 2

Precision and accuracy of native (a) dl-PCBs and (b) PCDDs/Fs under the optimum conditions of sample preparation obtained by the recovery assays. The bars represent the mean recoveries of the native congeners spiked into the control samples (n = 9). The error bars indicate the relative standard deviation (RSD). The red dots represent the upper and lower QC limits imposed by EPA 1668C and EPA 1613B methods.

Figure 3

Overlay signals of the MRM chromatograms obtained by a blank, experimental MDL, and positive soil sample; (A) dl-PCB Chromatogram (a) 1.59 pg/g 2,3′,4,4′,5-pentachlorobiphenyl (PCB 118) and its ¹³C labeled standard, and (b) 0.50 pg/g 2,3,4,4′,5-pentachlorobiphenyl (PCB 114) and its ¹³C labeled standard, (B) PCDD/F Chromatogram (a) 2.88 pg/g 2,3,4,6,7,8-hexachlorodibenzofuran (HxCDF) and its ¹³C labeled standard, and (b) 0.65 pg/g 1,2,3,7,8,9-HxCDF and its ¹³C labeled standard.

Figure 4

Average recoveries of ¹³C labeled (a) dl-PCBs and (b) PCDDs/Fs congeners.

Figure 5

QC results obtained during sample analysis for each homologue group (tetra-, penta-, hexa-, hepta-, and octa-) of (a) dl-PCBs and (b) PCDDs/Fs. The total recoveries of each homologue group for dl-PCBs and PCDDs/Fs were calculated using the sum of individual congeners of the same degree of chlorination. The dotted lines represent 95% and 99% confidence intervals (±2SD and ±3SD, respectively).