Chapter III: Results & Discussion

Results


The result of the SIM mode should be something like this.

Discussion


Detection limit


The World Health Organization Air Quality Guidelines for Europe, the unit risk is 9 X 10(-5) per ng/m(3) of B[a]P as indicator of the total PAH content, namely, lifetime exposure to 0.1 ng/m(3) would theoretically lead to one extra cancer case in 100,000 exposed individuals. This concentration of 0.1 ng/m(3) of B[a]P is suggested as a health-based guideline.



This method is actually sensitive enough to be able to detect concentration of PAHs at such a low limit.

A plot to show the change in sensitivity with the change in initial PTV inlet temperature.


A plot to show the linearity with a given change in volume injected.



Reference
http://www.ncbi.nlm.nih.gov/pubmed/12060843
http://pubs.awma.org/gsearch/journal/2002/1/Norlock.pdf

Chapter II: Method Overview

1.      Method Overview

·         [A] Sample Preparation

·         [B[ Soxhlet extraction

·         [C] Silica gel cleanup

·         [D] Kudema-Danish (K-D) volume reduction

·         [E] GC-MS SIM (Selective Ion Monitoring) mode analysis

2.      Materials & Apparatus

[A] Air sampling cartridge with AIRCON pump

       Internal Standard (naphthalene-d8, acenaphthene-d10, phenanthrene-d10,     

      chrysene-d12, and perylene-d12)  

      

[B] 10% ethyl ether in hexane (GC grade)

       Methylene chloride (GC grade)

       Soxhlet extractor

[C] Silica gel (100-200 mesh, Davisil Grade 644)

      Chromatographic column (11 x 300 mm)

[D] Kudema-Danish (K-D) concentrator

       Nitrogen supply

[E] GC-MS instrument coupled with PTV injection system and SVE-COC column

     

3.      Procedure

[A] Sample Preparation

Place 3 air sampling cartridge inside the gent’s toilet close together, each of the sampling cartridges contains 3 cm polyurethane foam (PUF) that holds XAD-2 resin trap in place. (XAD-2 resin serves to trap the sample analyte PAHs in the atmosphere) An AIRCON pump is coupled with the cartridge as it is used to draw air through the cartridge at a flow rate of 10 L/min for 48 hr. Spike the cartridge with exactly 2ul of the internal standard (24ug/mL of each component) after starting the pump.

{Explanation: Large volume (28,800L) of air is driven through the cartridge as the concentration of individual PAHs in air is usually very low (and it can be as low as a few pg/m3). The efficiency of the resin trap also has to be taken into account, since it is not 100% effective; using a larger volume of air would ensure that any error due to its inefficiency can be minimized}

           
 [B] Sample extraction (Soxhlet extraction)

The sample collected on the cartridge is extracted by refluxing on Soxhlet extractors using 10% ethyl ether in hexane for 24 hr followed by two subsequent 24-hr extractions using methylene chloride. After the extraction, combine the extract.

{Explanation: Typically, Soxhlet extraction is used when the desired compound has a limited solubility in a solvent, and the impurity is insoluble in that solvent. In the first cycle of Soxhlet extraction, the solvent is introduced through the condenser where it will fill a thimble that holds the sample containing the slightly soluble analyte and insoluble impurities. The solvent is added till before it overflows, then a siphon side arm would drain the solvent containing the analyte into a distillation flask. Meanwhile the distillation flask is heated to vaporize the solvent; the vaporized solvent is condensed as it reaches the condenser and drips back into the thimble.

After many cycle, the desired analyte is concentrated in the distillation flask, which is prudent as aforementioned the concentration of individual PAHs found in air is extremely low thus it’s necessary to concentrate the analyte.}

[C] Sample cleanup (Silica Gel Fractionation Chromatography)

Using the chromatographic column (11 x 300 mm) with 100% activated silica gel, run the column with the Soxhlet extract together with the eluting solvent (hexane), highly polar sample components are irreversibly retained in the column.  The aliphatic fraction is first eluted with hexane, and then the aromatic fraction is eluted with 50% DCM in hexane later.

{Explanation: Silica Gel Fractionation Chromatography is used to physically separate the sample components based on their polarity. Its use separates PAHs and polychlorinated biphenyls (PCBs) into two groups, while simultaneously eliminating most interfering substances for subsequent instrumental analysis.}

[D] Concentration (Kudema-Danish volume reduction)

The volume of the sample eluted from the clean-up column was reduced by K-D to ~4 mL and then further reduced by nitrogen to 2 mL for instrumental analysis. Fill up the sample vial with the concentrate.

{Explanation: Before injecting the sample into the GC system, it first has to be concentrated so that trace amounts of the PAHs can be detected.}

[E] GC-MS analysis

For GC-MS analysis, we are using large volume injection by PTV (Programmed Temperature Vaporization) and SVE-COC column (Solvent Vaporization Exit - Cool on-column). Adjust the automated injection system to take up 100 μL of the sample concentrate and run it through the GC-MS SIM mode.

{Explanation: By increasing the injection volume from 1 or 2 μL by traditional split/splitless inlet to 100 μL or higher with PTV inlet, analytical sensitivity is greatly enhanced for analytes with low concentrations. In addition, tedious sample pretreatment procedures may be simplified by

eliminating or shortening the solvent evaporation step, which is not only time-consuming but also subject to chemical loss due to high temperatures or a vacuum. Alternatively, a lesser amount of sample can be collected for predetermined detection limits.

In the SIM mode, the instrument is set to look for only masses of interest in a specified time range, thus it can be specific for a particular analyte of interest.}

References

http://pubs.awma.org/gsearch/journal/2002/1/Norlock.pdf

http://en.wikipedia.org/wiki/Soxhlet_extractor

http://cp.literature.agilent.com/litweb/pdf/5990-4883EN.pdf

http://www.ncbi.nlm.nih.gov/pubmed/11513123

http://www.env.gov.bc.ca/epd/remediation/analytical_methods/pdf/analytical_method_7.pdf

http://www.thomassci.com/Equipment/Evaporators/_/KUDERNA-DANISH-CONCENTRATOR/

Chapter I: Introduction to GC-MS analysis

GC/MS is an instrumental analytical technique comprised of a gas chromatograph and a mass spectrometer. In general, the GC is used to separate complex chemical mixtures into individual components. Once separated, the chemicals can be identified and quantified by the mass spectrometer.

GC: Separation
Before analysis can occur a sample must be prepared, usually by extracting the analytes of interest into a liquid solvent phase. This extract is then injected into the GC where it is swept onto a separation column by an inert carrier gas such as hydrogen or helium. The analytes in the mixture are carried through the column by the carrier gas where they are separated from one another by their interaction between the coating (stationary phase) on the inside wall of the column and the carrier gas. Each analyte interacts with the stationary phase at different rates. Those that react very little move through the column quickly and will exit into the mass spectrometer before those analytes having longer interaction and retention times.

MS: Identification & Quantitation
When the individual analytes exit the GC column they enter the ionization area (ion source) of the MS. Here they are bombarded with electrons which form ionized fragments of the analyte. These ionized fragments are then accelerated into the quadrapole via a series of lenses and separated based on their mass to charge ratio. This separation is accomplished by applying alternating RF frequency and DC voltage to diagonally opposite ends of the quadrapole, which in turn allows a specific mass fragment to pass through the quadrapole filter. From here the fragments enter the mass detector (electron multiplier) and are recorded. The MS computer graphs a mass spectrum scan showing the abundance of each ionized mass fragment.

Full-Scan: Identification
The GC-MS full-scan mode will monitor a range of masses know as mass to charge ratio (m/z). A typical mass scan range will cover from 35-500 m/z four times per second and will detect compound fragments within that range over a set time period. Laboratories have extensive computer libraries containing mass-spectra of many different compounds to compare to the unknown analyte spectrum.

SIM mode: Quantitation
Operation of a GC/MS in SIM mode allows for detection of specific analytes with increased sensitivity. In SIM mode the MS gathers data for masses of interest rather than looking for all masses over a wide range. Because the instrument is set to look for only masses of interest it can be specific for a particular analyte of interest. Typically two to four ions are monitored per compound and the ratios of those ions will be unique to the analyte of interest. In order to increase sensitivity, the mass scan rate and dwell times (the time spent looking at each mass) are adjusted.



References
http://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=121&tid=25
http://www.caslab.com/News/gcms-full-scan-vs-cgms-sim.html

Preface: Tar Sands in Alberta

Description -- Tar Sands in Alberta is Canada's worst environmental disaster. It covers an area the size of england (As of April 2011, the total area has increased to 140,200 km squared, or 54,132 square miles) Currently, this is actually larger than the size of England (it's about the size of England and Wales combined).
Oil from the tar sands is one of the world's most carbon-intensive fuels
Two tonnes of tar sand produces a single barrel of oil.
The tar sands generate 40 million tonnes of carbon dioxide per year, more than every car in Canada combined.
The oil itself is bitumen which contains cancer-causing polycyclic aromatic hydrocarbons.
To reach the bitumen, the Boreal Forest is destroyed.
Because of the tar sands, Canada's greenhouse gas emissions have grown more since 1990 than those of any other G8 nation.
Important waterways like the Athabasca River are being contaminated by 11 million litres of toxic waste every day.
Because of the Canada oil sands, the air is polluted with dangerous toxins, poisoning communities with rare cancers and autoimmune diseases.
It destroys critical animal habitats and some of Canada's most pristine landscapes.
Unfortunately, the Alberta government has approved every proposed project.
Take action and spread the word!

Preface: Article on Pre-natal exposure to PAHs

http://ehp03.niehs.nih.gov/article/info%3Adoi%2F10.1289%2Fehp.1104315
Abstract -- Airborne polycyclic aromatic hydrocarbons (PAH) are widespread urban air pollutants from fossil fuel burning and other combustion sources. It is reported that a broad spectrum of combustion-related DNA adducts in cord blood was associated with attention problems at 6–7 years of age in the Columbia Center for Children’s Environmental Health (CCCEH) longitudinal cohort study.

Preface: Case Study

Description -- Real estate buildings constructed on land polluted with high levels of PAHs

Preface: Formation of PAHs