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13- lab13- Gc-FID detn VOC - Chem 223 Experiment 13 GC/FID...

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Chem 223: Experiment 13 GC/FID Determination of Toluene in Air References: 1. Harris. Chap. 24 2. Kealey. Pp. 137-154 3. Harvey. 12D 4. http://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/gaschrm.htm. This experimental procedure is based on the experiment on website: http://web.pdx.edu/~atkinsdb/teach/427/Expt-GCTolAir.pdf I. Purpose of the experiment In this experiment you will measure the volume fraction concentration (in parts per billion by volume, ppbv) of toluene in air samples that you will collect. The samples will be collected and stored in Teflon bags which will be returned to the laboratory for analysis. The method of analysis is gas chromatography with cryogenic preconcentration and flame ionization detection (GC/FID). The quantitation method will be based on an internal standard using m-xylene and a standard addition of toluene. Several air samples will be analyzed. Your group will first go out into the “real world” and draw a few (three to four) air samples, and bring them back to the laboratory for analysis. You should try to collect samples that will show a variation in hydrocarbon pollution content. Take notes on where you took the samples and the relevant atmospheric conditions. You’ll run two gas chromatograms per sample (raw and spiked, both with the internal standard) except for the first sample, where you will also run an experiment without cryogenic preconcentration. The non-preconcentrated run can be compared to the same sample with preconcentration to determine the extent of the preconcentration. The time per analysis (each chromatographic analysis will be referred to as a “run”) is over 20 minutes, so you need to be on the ball to get three or more air samples done during the lab period. You will be pumping the air samples through a small (~ 100 μL) metal sample loop that is immersed in liquid nitrogen (the cryogen) for a pre-planned length of time, usually about 5 minutes. The N 2 doesn’t affect the majority components of air (nitrogen and oxygen) under our conditions, so they flow on through to the air pump. The hydrocarbons (and water and carbon dioxide) are trapped in the sampling loop during the passage. Theoretically, the longer you run the air through the cryogenically cooled loop, the more hydrocarbon you will end up with in the loop; but in the interest of time, we won’t test that idea. After the preconcentration (or shortly after the flow is established in the non-preconcentrated sample) a sample valve similar to those used in liquid chromatography is used to inject the volatile contents of the sample loop onto the column for separation and eventual detection and measurement by a flame ionization detector (FID). II.Introduction:
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Gas chromatography - specifically gas-liquid chromatography - involves a sample being vapourised and injected onto the head of the chromatographic column. The sample is transported through the column by the flow of inert, gaseous mobile phase. The column itself contains a liquid stationary phase which is adsorbed onto the surface of an inert solid.
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