Title

MEASUREMNT OF POLYCYCLIC AROMATIC HYDROCARBONS COLLECTED FROM AMBIENT STOCKTON AIR

Introduction

PAHs are byproducts of combustion, which include automobile emissions, barbeques, cigarette smoking, and other processes such as roofing, oil refining, and coal gasification. Quantification of PAHs in the air is important because PAHs are known to be mutagenic/carcinogenic through examination of workers exposed to PAHs through their job environment as well as experimentation on animals.1 Using Gas Chromatography/Mass Spectrometry (GC/MS), 16 common PAHs are quantified in aerosols collected in Stockton air.

Purpose

To quantify the concentration of 16 common PAHs in Stockton air

Method

Using a known standard containing 16 of the most common Polycyclic Aromatic Hydrocarbons (PAHs) with the concentration of 100μg/mL, multiple serial dilutions were used to obtain concentrations between 0.5 to 5 μg/mL. These standards were then analyzed using GC/MS in order to identify the retention times of the PAHs from GC, and to characterize the mass spectral response. Each standard was analyzed twice on the GC/MS. The first run detected all possible ions at a given retention time while the second run, based on the results of the first run, narrowed in only on the specific ion with the highest peak at a given retention time in order to isolate the desired peak and to lower the detection limit. These peaks based on MS were produced by the known PAH as confirmed by a library search. With the GCMS response known for the PAH standards, the same parameters and methods for the standards were used for PAHs collected from ambient air. Parameters used included using a 30m 0.32mm ID capillary column coated with 0.25μL film thickness cross-linked 5% diphenyl/95% dimethylpolysiloxane, and employing Electron Impact ionization. GC temperature was held at 70ºC for 1 minute, raised to 120ºC at the rate of 25ºC/min and held for 5 min, raised to 150ºC at the rate of 25ºC/min and held for 4.2min, raised to 250ºC at rate of 10ºC/min and held for 20min, and finally raised to 300ºC at rate of 25ºC/min and held for 12 min. Aerosol samples were collected from the air using a micro-orifice impactor (MOUDI). PAHs, if present in the sample, should produce a peak at the same retention time as the standards through GC, and a similar ion fragmentation spectrum through MS. Also, through the standard calibration, the amount of PAHs in the aerosol sample was quantified. The amount of a particular PAH was then divided by the amount of air filtered using the MOUDI, to obtain an approximate concentration of that PAH in the air.

Results

Through running each different concentration of the known standard, an approximate retention time for each of the 16 PAHs was obtained with the set parameters ran on the GC/MS. Each of the PAHs produced a different retention time as a result of varying boiling points and intermolecular interactions. For the fragmentation ion spectrum, most of the PAHs stayed intact as aromatic rings are quite stable and can accommodate a loss of an electron. For each of the 16 different PAHs, the concentration of each of the PAHs was graphed against the peak area obtained through the chromatogram produced by GC/MS. The R2 value obtained from this graph was at least 0.99 for all PAHs. These graphs were then used to quantify the unknown samples collected through the MOUDI, by using the equation obtained from the line and plugging in the peak area obtained from GC/MS. This data as of currently is still being obtained. Several blank samples were also run in order to determine the detection limit. An extremely low detection limit could complicate sample collection and require a large volume of air to be sampled, or a spike recovery method to detect small amounts of sample.

Significance

PAHs are known carcinogens produced in abundance as byproducts of combustion. By quantifying the concentration of PAHs in the air, this data can be used to determine if levels of PAH in the atmosphere is high enough to be toxic to humans as well as other living creatures.

Location

DeRosa University Center, Stockton campus, University of the Pacific

Format

Poster Presentation

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Mar 25th, 10:00 AM Mar 25th, 3:00 PM

MEASUREMNT OF POLYCYCLIC AROMATIC HYDROCARBONS COLLECTED FROM AMBIENT STOCKTON AIR

DeRosa University Center, Stockton campus, University of the Pacific

PAHs are byproducts of combustion, which include automobile emissions, barbeques, cigarette smoking, and other processes such as roofing, oil refining, and coal gasification. Quantification of PAHs in the air is important because PAHs are known to be mutagenic/carcinogenic through examination of workers exposed to PAHs through their job environment as well as experimentation on animals.1 Using Gas Chromatography/Mass Spectrometry (GC/MS), 16 common PAHs are quantified in aerosols collected in Stockton air.