About the Author
Jamal Miah has a Bachelor's degree in Computer Science from Brunel University. He works at the Marketing & Web Communications department of GMI Inc.
Polycyclic Aromatic Hydrocarbons (PAHs) are pervasive by products of combustion. PAHs are a group of over 100 chemicals formed during incomplete combustion of products such as coal, diesel-fueled engines, cigarettes and tobacco, grilled or charbroiled meat and coke burners. Some of these hydrocarbons are also manufactured and can be found in coal, crude oil, roofing tar, dyes, pesticides and creosotes. Manufactured PAHs can be colorless, white or pale yellow-green solids.
PAHs enter the air mostly through releases from burning coal, forest fires and automobile exhaust. Some readily evaporate into the air while some break down upon reaction to sunlight. PAHs enter water through discharges from treatment plants. Because PAHs don’t easily dissolve in water, they settle at the bottom of a body of water for weeks or months.
PAHs can cause damage to the body in several ways. Polycyclic aromatic hydrocarbons (PAHs) are stored in the fat tissue of the breast and increase the risk of breast cancer. When PAHs are associated with aryl hydrocarbon receptor (AhR), a protein, a series of cell changes is initiated leading to altered cell signals that increase DNA mutation. PAHs can be genotoxic, meaning chemicals themselves interact with the genes directly causing DNA damages.
Due to the health risks that exposures to PAHs bring, the Environmental Protection Agency (EPA) has regulated the maximum allowable levels in drinking water and releases to the environment. In this regulation, reliable and sensitive analytical methods are essential in the determination of PAHs presence and levels. The two common methods for determining PAHs presence and level are through high performance liquid chromatography (HPLC) and gas chromatography (GC).
The EPA method 8270 uses a gas chromatography/mass spectrometry (GC/MS) in full scan mode. This provides absolute identification through the spectral libraries for the confirmation of compounds. However, the main limitation in this process is the inability to achieve low detection limits for some applications. To overcome this, the GC is programed to use selected Ion monitoring process to collect data at masses of interest. This means that the mass spectrometer will only respond to compounds with the selected ions.
A GC Capillary Column with a length of 15 meters and a diameter of 0.10 mm was used in the analysis. This column accommodates a 0.10 µm film. A 0.5µL of sample was injected to a PAHs standard mixture.
Other parameters used:
|Oven||140°C, 0.5 min, 30°C/min, 220°C, 15°C/min, 300°C|
|Inj||PTV 80°C, 0 min, 999°C/min, 400°C|
|Carrier||H2 0.5 mL/min|
|Split Flow||50 mL/min, split ratio 1:100|
Recent developments in GC systems have also overcome problems in low temperature that lead to decreasing responses and sensitivity. A GC with inert ion sources is needed for such operations. These ions allow for higher operating temperatures.
Figure 2. Chromatogram output using a DANI Master GC Base Unit.
The DANI Master GC is equipped with a Universal Injector System, an FID 86/C Detection System and a Master GC-AC 1 instrument. In the analysis, a GC 15 meter capillary column with a 0.25mm diameter and a 0.25µm- thick film was used. A 0.5 µL of sample of polyaromatic hydrocarbons standard mixture was injected into a sample. This chromatogram was done for the separation of PAHs by a specifically designed column.
|Oven||140°C, 1 min, 10°C/min, 350°C, 1 min|
|Injector||PTV, temperature: 40°C, 0 min, 999°C/min, 400°C, 5 min|
|Carrier gas||Hydrogen, 1mL/min, constant flow|
|Split Flow||50 mL/min, split ratio 1:50|
Polycyclic Aromatic Hydrocarbons (PAHs) have a great impact to human health. While exposure is difficult to prevent and completely eliminate, the levels they are found and the analysis of their presence in particular substances and environments is essential in preventing diseases such as breast cancer. This makes a gas chromatography system capable of analyzing such substances, indispensable in any laboratory.