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The “Dioxin Prep System”: A Multi-Layer Silica Gel Column Connected to a Dual-Layer Reversible Carbon Column for Rapid Determinations of PCDD/FS*

Reporter EU Volume 11

Introduction

Reference methods (Methods US EPA 23 or 1613 B; European method EN-1948) for the quantitative analysis of the seventeen toxic 2 ,3 ,7 , 8-PCDD/Fs involve successive clean-up steps on various chromatographic adsorbents (multi-layer silica, Florisil, alumina, activated carbon) which considerably increase the time needed for analysis. Recently, Supelco launched a new preparation kit for rapid clean-up of dioxin samples, called the “Dioxin Prep System” and composed of a multi-layer silica gel column and a dual-layer carbon cartridge connected in series. This system aims at shortening considerably sample preparation time while maintaining high accuracy for performing PCDD/Fs analysis. To date, it has mainly been applied in Japan for a range of environmental samples such as stack emissions, fly ashes and waste waters 1, 2, 3. Before the Dioxin Prep System became commercially available in the UK, Corus UK and Hall Analytical Laboratories were invited to evaluate it alongside their existing dioxin analytical procedure that is derived from US EPA method 23 and is UKAS accredited (ISO 17025). Results from this evaluation are summarised in this paper.

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The dioxin Prep System

As shown in Fig.1, the Supelco multi-layer silica gel column contained 7 layers of treated silica, which met the requirements of Japanese Industrial Standard Methods K-0311 and K-0312. The dual-layer carbon column was composed of two 100mg carbon layers, Carboxen 1016 (surface area 75 m2/g) and Carboxen 1000 (surface area 1200m2/g). Prior to clean-up, multi-layer silica gel and dual-layer carbon columns were pre-conditioned separately using 200ml of n-hexane, and 50ml toluene followed by 100 ml n-hexane, respectively. Extracts were applied to the Supelco combination columns and eluted with 200ml n-hexane. Multi-layer silica columns were disconnected and replaced by empty silica columns. Dual-layer carbon cartridges were then back-eluted using 80ml toluene to obtain PCDD/F fractions. Elution steps were all performed under vacuum (100-400mmHg; 3ml/min) using a vacuum manifold (Fig. 2: picture of Dioxin Prep System).

Figure 1 Schematic of the Supelco’s Dioxin Prep System for rapid clean-up of PCDD/F extracts

Figure 2 Picture of the Dioxin Prep System

Blanks and quality control (QC) materials were analysed both by Corus UK and Hall Analytical Laboratories to evaluate the efficiency of the clean-up using Supelco’s Dioxin Prep System. Quantitation of 2, 3, 7, 8 substituted PCDD/Fs congeners was by isotope dilution using US EPA method 23 standard solutions. Samples were extracted by accelerated solvent extraction (Dionex ASE 200) using toluene. Analysis of cleaned-up extracts for PCDD/Fs was conducted by HRGC/HRMS using a 60m DB5-MS column and a Micromass Autospec Ultima high resolution mass spectrometer.

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Results

The first step in the evaluation of the Dioxin Prep System consisted of analysing blank samples spiked with 13C12- labeled PCDD/Fs. After extraction and clean-up using the Dioxin Prep System, mean recoveries of 13C12-labeled internal standards ranged from 66 to 90% (Fig. 3), well within the acceptance criteria of the method US EPA 23. Relative standard deviation (RSD %; N=3) ranged from 10 to 20 %.

Figure 3 Recoveries of 13C12-PCDD/Fs internal standards after analysis of blank samples cleaned-up using Supelco Dioxin Prep System

A QC material (waste dust from an iron making process) was analysed. Figure 4 shows the results obtained by Corus UK and Hall Analytical Laboratories using the Dioxin Prep System and compares it to the mean values of the QC data obtained using their current UKAS accredited procedure (N = 59 replicate analysis; RSD % ranged from 8 to 25%). Both laboratories obtained results well in agreement with the QC data showing the efficiency of the clean-up which enables accurate analysis of PCDD/Fs.

Figure 4 Analysis of a QC material by Corus UK and Hall Analytical Laboratories using the Supelco Dioxin Prep System. Dioxin results are compared with QC data from the replicate analysis of N = 59 samples using the existing Corus analytical procedure

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Conclusion

The Supelco Dioxin Prep System enabled determination of toxic PCDD/Fs for a complex environmental sample (waste dust from an iron-making process) with acceptable internal standards recoveries. The Dioxin Prep System provides the opportunity to perform a rapid clean-up step of environmental samples when compared with reference standard procedures.

*Eric Aries1, David R. Anderson1, Nicholas Ordsmith2, Lisa Fitzpatrick3 and Fiona Barclay3 1 - Chorus UK, Rotherham 2 - Hall Analytical, Manchester 3 - Supelco UK

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References

  1. Maeoka et al., 2001. Study on saving time for dioxin analysis based on JIS Method, 10th Symposium on Environmental Chemistry, p. 314-315.
  2. Matsumoto et al., 2000. Study on sample preparation for dioxins, 9th Symposium on Environmental Chemistry, p. 238-239.
  3. Matsumura et al., 2000. Simplifying sample preparation for dioxins, 8th Symposium on Environmental Chemistry, p.202-203.

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