FPRW 2011

Persistent organic pollutants (POPs) are a group of chemicals that includes halogenated pesticides, brominated diphenyl ethers (BDEs) and polychlorinated biphenyls (PCBs). Due to the lipophilic nature of these components, they accumulate in the fatty tissue of animals and bioaccumulate up the food chain. According to the World Health Organization human breast milk is an ideal matrix to monitor the levels of POPs in not only the mother and infant, but also as a key indicator of the levels of these chemicals in the local environment. Current methodology for the analysis of halogenated pesticides, PCBs, and BDEs can be expensive, solvent intensive, and time-consuming. The QuEChERS extraction approach coupled with a silica cartridge SPE cleanup may be an attractive sample preparation alternative for biomonitoring efforts for halogenated POPs in milk. Comprehensive two-dimensional gas chromatography (GCxGC) with an electron capture detector (ECD) may also offer a more cost-effective alternative. Method development was done using whole cow milk and later compared to a NIST Standard Reference Material of Human Breast Milk.

Although many halogenated pesticides and flame retardants are currently banned and have been phased out of production, they continue to be monitored due to their persistence in the environment and bioaccumulation in humans and animals. The United States Environmental Protection Agency has developed Method 527 for the determination of selected pesticides and brominated flame retardants in drinking water. This method recommends a splitless injection but allows for the use of alternative injection techniques such as large volume injections which typically require a special injection port. However, a relatively new technique describes the use of a typical splitless injection port for large volume splitless injections (LVSI) (patent# US 6,995,709 B2). This technique utilizes a fast autosampler injection onto a liner containing glass wool, a pre-column (e.g. 5 m x 0.53 mm) press-fitted to the analytical column, and a starting oven temperature below the boiling point of the solvent.

Polycyclic aromatic hydrocarbons (PAHs) were determined in various sugarcane products using QuEChERS sample preparation, GC/MS with selected ion monitoring (SIM), and comprehensive two-dimensional GC with time-of-flight MS (GCxGC-TOFMS). In sugarcane production, it is common to set fields on fire to make harvesting easier by burning the leaves while leaving the sugarcane stalks intact. Unfortunately, sugarcane burning can produce toxic PAHs. Although a variety of sugarcane products (e.g. juice, liquors) have been tested for the presence of PAHs, often the number of PAHs investigated has been limited.

We tested sugarcane products, including cachaça, other sugarcane liquors, and sugarcane for the presence of PAHs. QuEChERS-based sample preparation and separations on an Rxi®-17Sil MS column were investigated with attention to extraction recoveries and chromatographic resolution of isobaric PAH compounds from EPA and EU lists, as well as others.

Currently, the United States Department of Agriculture (USDA) regulates only infestation and disease on imported cut flowers, representing approximately 70% of the rose market. This regulatory situation unintentionally encourages heavy use of pesticides, which are not regulated by USDA for cut flowers. Heavy pesticide use can have serious consequences for the health of workers in the flower industry, and their local environment. To address those issues, an organic flower industry exists that advertises agricultural sustainability practices that include limited pesticide use.

In this contribution, the Quick – Easy – Cheap – Effective – Rugged – Safe (QuEChERS) sample preparation method was used with GC-TOFMS and GCxGC-TOFMS to analyze pesticides on cut roses. Pesticide classes selected for investigation include organochlorine, organophosphorus, carbamate, pyrethroid, and triazole compounds that are routinely used by the flower industry. Development and optimization of sample preparation, including extraction and cleanup, will be highlighted. Baseline residue levels for organic certified roses and non-certified roses will be estimated in hopes of determining whether “a rose is a rose is a rose”.

The QuEChERS sample preparation approach is by now well used and several commercial vendors provide pre-packaged extraction salts and dispersive solid phase extraction sorbents. Unfortunately, in some cases the extraction salts (magnesium sulfate, etc.) come in the 50 mL centrifuge tube used for extraction, which is inconvenient because the method specifies addition of homogenized sample and acetonitrile extraction solvent to that tube prior to salt addition. This necessitates a transfer of salts, from one tube to another, increasing the risk of leakage due to salts in cap threads, and possibly increasing plastic waste.

We have been exploring the use of tablets for QuEChERS extraction salts to make the delivery of these salts even easier. A tablet allows an easy delivery of extraction salts to sample/acetonitrile in a centrifuge tube, and decreases the risk of spillage and leakage. This presentation will focus on initial results achieved for QuEChERS extractions with tablets, discussing features, benefits, and manufacturing difficulties.

Food pesticide residue monitoring has traditionally been performed using gas chromatography (GC), but there is increasing use of liquid chromatography (LC) with tandem mass spectrometry (MS/MS). LC is favored for polar, less thermally-stable, less volatile, compounds. GC-MS is preferred for volatile, thermally-stable species, and pesticides that do not ionize well in electrospray or atmospheric pressure chemical ionization LC sources. With MS, complete chromatographic resolution of compounds is not essential, as selected ions or selected reaction monitoring (SRM) transitions are used for pesticide identification and quantification. However, data quality can be improved through better retention and separation of components, especially for structurally similar pesticides. In GC, this better separation can come from comprehensive two-dimensional GC (GCxGC), an approach involving two separations on an orthogonal column set in one analytical run. A fast time-of-flight (TOF) MS records data from the 100 ms wide peaks produced from GCxGC.

In this work, the QuEChERS extraction approach was used for red bell pepper, cucumber, lemon, raisins, spinach, hazelnuts, and red grapes with subsequent pesticide determinations by LC/MS/MS and GCxGC-TOFMS. Samples spiked with carbamate, organophosphorus, aniline, conazole, macrocyclic lactone, phenylurea, benzoylphenylurea, and strobilurin pesticides at 10 ppb and then QuEChERS-extracted showed good recoveries. While GCxGC-TOFMS was limited in the number of pesticides determined due to the compound classes involved, versus LC/MS/MS, selectivity and sensitivity were enhanced by GCxGC. The full mass range capability of TOFMS allowed non-target compound identification (e.g. in the pepper: endosulfans, endosulfan sulfate, nicotine, and permethrins). LC-MS/MS was extremely sensitive and selective for the targeted compounds. Dilution of QuEChERS extracts prior to LC/MS/MS may allow analysts to avoid extract cleanups.