Detecting Polycylic Aromatic Hydrocarbons in Food

Drying, smoking, grilling, roasting, and frying are major PAH-generating food processes and can contribute to alarming PAH levels. Smoked fish and barbequed meat may contain up to 200 µg/kg of PAHs. Charcoal-grilled duck breast steaks were reported to contain up to 300 µg/kg PAH. Smoke-processed duck breast steak contained up to 53 µg/kg of carcinogenic PAHs.

Vegetable oils used for seasoning and cooking, as well as those incorporated into biscuits and cakes, are significant dietary sources of PAHs. Their occurrence and level varies widely depending on drying processes and refining.

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Figure 1. Elution of critical PAH peak pairs on standard 5ms and 17ms-type GC columns.

In 2002, the former EU Scientific Committee on Food identified 15 PAHs as potentially carcinogenic and suggested benzo[a]pyrene as an indicator of the occurrence and effect of carcinogenic PAHs in food. In 2005, the Joint FAO/WHO Expert Committee on Food Additives confirmed these findings and proposed adding benzo[c]fluorine. This group of PAHs has become known as 15+1 EU priority PAHs (see Table 1, above).

Recent scientific opinion of the EFSA Scientific Panel on Contaminants in the Food Chain led to the adoption of an alternative and more limited list of PAHs for food risk characterization. Oral carcinogenicity data are only available for benzo[a]pyrene, benz[a]anthracene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[g,h,i]perylene, chrysene, dibenzo[a,h]anthracene, and indeno[1,2,3-cd]pyrene.

For some time, benzo[a]pyrene was thought to be a suitable marker for the occurrence and effects of carcinogenic PAHs in food and was, therefore, the only regulated one. The EFSA panel concluded, however, that these eight PAHs (PAH8), either individually or in combination, were the best indicators of PAH toxicity in food. More recently, benzo[a]pyrene, chrysene, benz[a]anthracene, and benzo[b]fluoranthene (PAH4) have been suggested by the EFSA panel as suitable PAH indicators. The PAH4 EU regulation will come into effect in 2010-2011.

Accurate quantification of individual PAHs and PAH sets, either as 16 EPA, PAH(15+1), or the subset PAH4, requires separation of individual PAHs from interferences either by mass ion and/or by chromatographic separation.

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Figure 2. Critical PAH Peak-Pair Separations on the Varian Select PAH GC column, 30 m x 0.25 x 0.15 µm, Programmed GC/MS Analysis in SIM Mode.

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Figure 3. GC/MS analysis (total ion chromatogram [TIC]) of PAHs in salmon using a Select PAH column, 15 m x 0.15 mm x 0.10 µm.

GC/MS Analysis for PAH Monitoring

PAH analysis in food is typically performed using gas chromatography-mass spectrometry (GC/MS) operated in the selective ion-monitoring (SIM) mode. The SIM mode improves selectivity while increasing sensitivity. Given the rising number of PAH analytes targeted for routine monitoring, along with regulation changes and the fact that many PAH congeners exhibit identical MS ion fragmentation, the chromatographic separation and selectivity of the GC column used for PAH analysis has gained importance. Often, general-purpose GC columns do not deliver the degree of selectivity required by the new regulations for more detailed PAH analyses. The chromatographic separation of PAH congeners that have very similar chemical structures and molecular mass is challenging (see Table 2, left).

GC columns for PAH analysis should be able to distinguish the small structural differences that exist between PAHs with virtually similar physicochemical properties. The high-boiling nature of the 5/6-ring congeners requires high GC column elution temperatures, in excess of 325°C. Obviously, GC columns and liquid phases for the analysis of these 5/6-ring PAHs should therefore be highly temperature resistant.

Recently introduced columns based on ionic liquids lack the thermal robustness for elution of the 5/6 -ing PAHs and, hence, have a limited durability. The majority of liquid phases are based on polysiloxane backbone chemistry, which is generally more thermally resistant. In recent years, functional groups (i.e., phenyl) have been incorporated into the polysiloxane chain as arylene inclusions, increasing the thermal and oxidative resistance of the liquid phase. Columns coated with such phases can operate at higher temperatures. This increased thermal resistance is apparent at temperatures above about 300°C. These arylene low bleed columns support the elution temperatures necessary for high-boiling dibenzopyrenes.