Background
Polyaromatic hydrocarbons (PAHs) are ubiquitous in the environment, resulting from both natural and manmade sources of combustion. Farm animals, such as cows, can become exposed to them through both consumption of contaminated feed and water, and inhalation of contaminated atmosphere.¹ Consequently, these compounds can be present in dairy products produced from cow’s milk such as cheese and butter. Analysis of these compounds in butter can pose a special challenge due to the high fat content and the lipophilic nature of PAHs. Recovery of the PAHs often results in coextraction of the fatty matrix. In this application, Supelclean™ EZ-POP NP SPE was used as part of an extraction and cleanup procedure for the analysis of PAHs in butter by GC/MS in selected ion mode (SIM). After EZ-POP NP extraction, a secondary cleanup was done using silica gel. This produced an extract with low GC/MS background that could be analyzed on a single quadrupole instrument. The method was compared with an alternative sample preparation approach using a large silica gel SPE cartridge, and was found to produce better recoveries and lower background.
Experimental
Butter was spiked at 20 ng/g with 28 different PAHs, containing 2-6 rings in their structures. The butter was melted and 1 g was diluted to 1 mL in cyclohexane. After mixing, sediment was allowed to settle and the resulting supernatant was drawn off for extraction. Replicate samples were extracted in two separate sets using the procedures outlined in Tables 1 and 2. Analysis was performed by GC/MS-SIM using the conditions listed in Table 3. GC/MS conditions were optimized for response and peak shape of the PAHs, especially those with 5 and 6 rings. Quantitation was performed using 5-point calibration curves prepared in unspiked butter extract. Separate curves were prepared for each set of samples and internal standard correction was used in calculating response.
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