Analysis of 19 PCB congeners in catfish tissue using a modified QuEChERS method with GC–MS/MS

Highlights

• A simple and reliable procedure for monitoring 19 toxic polychlorinated biphenyl in catfish was validated.

• The method increase sample throughput by using quick extraction and sample cleanup approach of QuEChERS method.

• The method reduces cost of using toxic solvent, labor, and lab supplies.

• GC–MS/MS provide excellent selectivity and sensitivity with an LOQ below 1 ng/g.

Abstract

A simple approach to determine 19 PCB congeners in catfish tissue was presented. A modified QuEChERS method employing high solvent to sample ratio 10:1 was used to improve the extraction recovery of 19 PCB congeners. After salting out by shaking with anhydrous magnesium sulfate and sodium chloride, 1 mL of acetonitrile extract was pipetted into a 2-mL centrifuge tube containing anhydrous magnesium sulfate, primary secondary amine sorbent, and C-18 sorbent. The tube was then shaken and centrifuged to absorb fat and fatty acid residue present in the acetonitrile extract. The acetonitrile extract was analyzed by GC–MS/MS. The excellent sensitivity of GC–MS/MS allows for the direct injection of the samples to detect the low level of the PCB congeners. The method therefore is high throughput, uses fewer consumable lab supplies, and provides excellent sensitivity with an LOQ below 1 ng/g.

Introduction

Polychlorinated biphenyls (PCB) are synthetic organic chlorinated compounds that are widely used as fluids in transformers and capacitors. The lipophilic nature and persistence of these compounds contribute to their high potential for bioaccumulation in the food chain. The main producer of PCBs was Monsanto Corporation with more than 90% of the world production sold under the trade name Aroclor (Ivanov & Sandell, 1992). Aroclor is a complex mixture of individual PCB congeners (209 possible congeners). In 1980, a numbering system (BZ, named after Ballschmiter and Zell) was developed that assigned a sequential number to each of the 209 PCB congeners (Ballschmiter & Zell, 1980).

There are many different lists of PCB congeners, including those from the whole health organization (WHO) and national oceanic and atmospheric organization (NOAA), that laboratories consider in developing their analytical methods. For example WHO has designated 12 of the 209 congeners that are the most toxic to human health and the environment (WHO, 1997), while NOAA suggested up to 18 PCB congeners that are toxically significant in the environment (NOAA, 1089). Numerous methods have been published over the past 30 years related to specific analytical techniques for the determination of PCB and organochlorine pesticides in food and environmental matrices. Different extraction techniques have been used such as Soxhlet extractor, high speed blending with solvent, matrix solid phase dispersion, sonication-assisted extraction, microwave-assisted extraction and pressurized liquid extraction (Lopez-Avila, 1999).

Currently, the FDA Southern Regional Laboratory uses the Pesticide Analytical Manual volume I (PAM) method to determine PCB in fish tissue (US FDA, 1994). This method is time consuming, labor intensive, uses a large quantity of toxic solvent (petroleum ether), and requires a Florisil column cleanup to eliminate fat and polar coextractives. After a long evaporation step, the final extract is then injected into a gas chromatograph with electron capture detector (GC/ECD) to determine the total PCB content in the sample.

In order to minimize solvent usage and time for sample cleanup while maintaining acceptable recovery of pesticides in food matrix, Anastassiades, Lehotay, Stajnbaher, and Schenck (2003) developed an approach that they named as quick, easy, cheap, effective, rugged, and safe (QuEChERS). This method involves extraction with acetonitrile partitioned from the aqueous matrix using anhydrous magnesium sulfate (MgSO₄) and sodium chloride (NaCl) followed by a dispersive solid-phase extraction clean up with MgSO₄ and primary secondary amine (PSA). The method has already received worldwide acceptance and, with minor modifications, has become an Official Method of the Association of Official Agricultural Chemists (AOAC) International and the Committee of European Normalization (CEN) (CENT/TC, 2006, Lehotay, 2007).

The QuEChERS approach with acetonitrile extraction has already shown to be effective in minimizing coextraction of lipids from fatty foods due to low solubility of the lipids in acetonitrile, while maintaining high recoveries of non-polar pesticides (Chamkasem, Ollis, Harmon, Lee, & Mercer, 2013). The dispersive SPE with MgSO₄-PSA-C18 sample cleanup technique has been used with QuEChERS extraction in flaxseed and avocado for pesticide analysis (Chamkasem et al., 2013, Koesukwiwat et al., 2010). The role of MgSO₄ is to absorb the trace amount of water in the acetonitrile extract. PSA retains fatty acids from the acetonitrile extract with a weak anion exchange mechanism. The non-polar sorbent C-18 retains trace amounts of lipophilic interference and/or fat residue from the extract. The QuEChERS extraction and dispersive cleanup along with GC/ECD have been used to determine 19 PCB congeners in fish (Agilent, 2012). This method requires two different GC columns (DB-35ms and DB-XLB) on one instrument to allow simultaneous identification and confirmation of the presence of the PCBs. In spite of exhausted cleanup procedure, co-elution of PCB congeners and chlorinated pesticides was still a problem in the analysis. High resolution mass spectrometry (HRMS) has previously been used to resolve the coelution problem (US EPA, 1999). GC/MS/MS has also been used to determine PCB in foodstuffs and animal feed using exhaustive extraction with silica and Florisil column cleanup (Agilent, 2011).

The purpose of this study is to develop an analytical method that combines the simplicity of the QuEChERS extraction and cleanup approach with great sensitivity and selectivity of the GC–MS/MS for the determination of toxic 19 PCB congeners in catfish tissue.