Using the Agilent 6890N GC/MS for Sampling Volatile Organic Compounds by Bob Castro, B.S. Chemical Eng., M.S. Environmental Eng. Edited by Don Marek, Lab Manager 1
Table of Contents GC/MS Concepts... 3 Figure 1-1: Stainless Steel Silonite Coated Canister... 4 Figure 1-2: GC/MS Conceptual Diagram...5 Figure 1-3: GC-MS Schematic Diagram... 6 GC/MS Standard Operations Procedure... 8 Figure 2-1. - Tuning with the PTFBA spectra... 8 Figure 2-2. Peak widths... 10 Figure 2-3 Relationship between peak width and AMU gain and AMU offset... 10 Figure 2-4: Sample Log Table... 12 Figure 2-5. Start sequence options...13 BFB Tuning Validation...13 Microscale Purge and Trap/ Pre-concentration...14 Figure: Schematic Diagram of the Pre-concentrator... 14 Quantification Standard Operation Procedures... 17 Figure 3-1: Butane Calibration Curve...19 Using the Chemstation Data Analysis Software to Qauntitate the Data...20 Figure 3-3: Manual Integration of the Isoprene Peak... 21 Figure 3-4: Peak Overlap...22 Standard Operation Procedure for Canister Cleaning...23 Standard Operation Procedure for Standards Preparation... 24 Purging the Regulator... 24 Standard Preparation by Static Dilution... 25 Internal Standard Preparation... 27 Standard Operation Procedure For VOC Sample Collection... 28 Figure: Schematic Diagram of Sample Collection System...28 References...30 2
GC/MS Concepts Introduction The Analytical tools of Gas Chromatography with Mass Spectrometry Detection (GC/MS) will be used to identify the Volatile Organic Carbons (VOC). The USEPA Compendium method TO- 15 will be followed in the sample collection and analysis of the ambient air samples. Compendium Method TO 15 The analytical strategy of Compendium Method TO -15 involves using a high resolution GC coupled to a mass spectrometer. Mass spectra for the individual peaks in the total ion chromatogram are examined with respect to fragmentation pattern of ions corresponding to various VOCs including the intensity of primary and secondary ions. The fragmentation pattern is compared with stored spectra taken under similar condition in order to identify the component. For any given compound, the intensity of the primary fragment is compared with the system response to the primary fragment for known amounts of the compound. This establishes the compound concentration that exists in the sample. Canisters The canisters used to collect the ambient air samples are made of stainless steel and coated with silonite. The canisters are 6 Liters in volume and are evacuated to a vacuum of 50 militorr. A picture of the canister is shown in Figure 1-1. below. When the valve to the can is opened, the air passes through a flow restrictor which is an orifice that restricts the flow rate into the can. A diaphragm below the flow restrictor, regulates the flow into the can so that the flow of air at a fixed rate. 3
Figure 1-1: Stainless Steel Silonite Coated Canister Preconcentration The air sample from the canister is directed to a pre-concentrator which traps the VOCs and remove much of the excess air in the sample. Additionally the pre-concentrator has a purge and trap to remove water vapor from the sample. The sample is desorbed off the trap and carried off with Helium into the GC column for separation. GC/MS GC/MS is the combination of two powerful analytical techniques. Gas chromatography is the physical separation of two or more compounds based on their volatility from the liquid phase to the gas phase. The gas chromatograph employs a carrier gas (mobile phase) to move a sample in the vapor phase through a column coated with a stationary phase where separation takes place. A detector converts the column eluent to an electrical signal that is measured and recorded. The out put of the GC is a plot of detector signal abundance versus time. The abundance remains at a low baseline level except when a separated sample component elutes from the column and produces a peak in the chromatogram plots. Chromatographic peaks can be identified from their 4
corresponding retention times measured from the time of sample injection to the time of the peak maximum. The retention time of any component peak is unaffected by the presence of other sample components. The height of the area of a peak may be used to measure the concentration of a component in the sample mixture. Mass Analysis A mass spectrometer is one kind of GC detector. As the separated sample component molecules elute from the column to the inside of the MS, they are bombarded with energy. This is to remove an electron from them and converts them into unipositive ions. Some chemical bonds may also break up in this process and the resulting fragments may rearrange or break up again to form more stable fragments. A mass spectrum is a recording of the masses of each of the ionized fragments, representing a unique fingerprint of a molecule that can be used in identification. How GC/MS works: Figure 1-2: GC/MS Conceptual Diagram As shown in Figure 1-2 above, the sample is separated into its components by the gas chromatograph. The components are then ionized and identified by their characteristic spectra produced by the mass spectrometer. What are Mass Spectra? ( Molecular Fingerprints ) A mass spectrum is a plot showing the mass/charge ratio (in a.m.u) versus abundance data for ions from the sample molecule and its fragments. The charge of ions formed in the GC/MC is +1 5
and the mass / charge ratio of any fragment is therefore normally equal to the mass for that fragment. The largest peak in the spectrum is called the BASE PEAK. Certain fragments are more prone to form from the parent molecule than others, due to the presence of functional groups in the molecule and their interconnection. The masses of these fragments are used to deduce the structure of the parent compound. The ionized parent molecule, when seen as part of the mass spectrum, is referred to as MOLECULAR ION. ABCD - e - ABCD +. ABCD +. A + + BCD. A. + BCD + BC + + D. ABCD. + D. + ABC + A + BC + The mass spectra of certain compounds exhibit cluster of mass peaks. These clusters represent naturally occurring impurities or isotopes that are present for carbon, nitrogen, sulfur, chlorine, bromine, and a few other elements. The relative percentage of these cluster ions provides more clues useful in identifying a parent molecule from its molecular fingerprints. GS/MS Flow Chart Figure 1-3: GC-MS Schematic Diagram GC Column: The column separates the mixture into its components. 6
Interface: The interface between the GC and MS must transfer the sample / carrier gas matrix from positive pressure inside the MS. It must reliably transmit the entire sample without compromising the performance of the GC or the MS GC Oven: The temperature of the GC oven can be programmed to optimize separation and resolution of the components of a given sample. Precise temperature control of the oven allows the chromatography to be reproducible. Ion Source: In the electron impact (EI) ion source, a filament wire emits electrons that strike the sample molecule as they elute from the column. Ions are produced from the electron/molecule collisions and a series of lenses propels and focuses them toward the quadrupole. Quadrapole: The quadrapole consists of four conductive rods, separates ionized fragments according to their mass/charge ratio. Voltage on the rods can be set to allow ions of a particular mass to pass through and ions of the wrong mass will be pumped away by the vacuum system. Vacuum System: The MS operates under a vacuum of about 10-5 torr. The reduced pressure increases the distance between the molecules, minimizing the number of intermolecular collisions inside the ion source. Detector: The detector counts the ions that pass through the quadrapole. This signal is small and must be amplified. An electron multiplier detector measures the abundance of each component ion, and the presence of an ion is ultimately recorded as a mass peak in a mass spectrum. Data System: The data system is responsible for the total control of the GC/MS system. This includes GC temperatures, tuning the MS system, controlling the voltages on the quadruple during the data acquisition, detecting the abundance of each ion, and processing the acquired data. 7
GC/MS Standard Operations Procedure Before samples can be analyzed using the GC/MS, the mass spectrometer must be tuned. The MS is tuned by adjusting several parameters while the Per-fluoro tributylamine (PFTBA)is injected to the MS chamber Below is the procedure for tuning the GC/MS 1) Click on the Instrument #1 icon to start the Chemstation software. 2) From the View menu select Manual Tune. 3) When prompted be sure changes are saved. Switch View Now?, select Yes 4) In the Manual Tune view select the AdjParam menu to adjust the tune parameters. 5) From The AdjParam menu select Edit MS Params menu 6) From the edit MS Params menu select Scan and you should see a similar PTFBA spectra a s shown in Figure 2-1. Wait 30 seconds for the PFTBA levels to stabilize before changing any tune parameters. Figure 2-1. - Tuning with the PTFBA spectra The scan from 10-700 amu should have less than 200 peaks. If there are more than 200 peaks then some sort of contamination is entering the MS chamber and further trouble shooting should be done. 8
The mass spectrum of PFTBA has a base peak of 69 amu. The relative abundance of the mass peak of 219 to the base peak in the PTFBA spectra should be between 40 and 85%. The relative abundance of the mass peak of 502 to the base peak in the PTFBA spectra should be between 2.5 and 5%. In the mass column in Figure 2-1, if the masses of 69, 219, and 502 are off by more than 0.2amu then the mass axis should be adjusted. This is done by selecting Mass Axis from the calibrate menu. By doing this the mass axis is automatically adjusted by the software. The Rel Abund column shows the relative abundance of the 69, 219, and 502 masses. To adjust the relative abundance, the EN lens and the EntLens offset parameters should be adjusted. The Entrance lens parameters are inversely proportional to the relative abundance, which means that if you wish to increase the relative abundance you should lower the entrance lens setting and vise versa. The abundance of mass 69 should be between 200,000 and 400,000. To adjust the abundance the EM volts parameter should be adjusted. The EM volts are directly proportional to the abundance. An increase in the EM volts parameter will increase the abundance. Click on the Prof button to get a profile of the 69, 219, and 502 peaks. The profiles are shown in Figure 2-2. The peak with at 50% of the peak height (Pw50) should be between 0.57-0.63 9
Figure 2-2. Peak widths To adjust the peak widths the amu gain and the amu off set parameters should be adjusted. The relationship between the peak widths and the amu gain and the AMU off set are shown in Figure 2-3. In order to increase the peak width the amu gain and the amu off set parameters should be decreased, and vice versa to decrease the peak width. Figure 2-3 Relationship between peak width and AMU gain and AMU offset 7) After changing the tune parameters print the parameter settings by selecting print from the file menu. 8) Click on OK to leave the edit Parameters view. 9) Save the tune values by selecting save tune values from the file menu. Save the file as ATUNE.U. 10) Select Top from the view menu, to switch to the top view. When Prompted be sure changes are saved. Switch View Now?, select Yes Note, if changes have not been saved go ahead and do so now other wise the changes will be lost once the view has been switched. After the mass spectrometer has been tuned then a sequence table will be prepared to run the samples using the AAVOC1 method. The instrument parameters for the GC/MS-FID system are shown in the table below: 10
Columns Flow Rate Injector Temperature MS transfer interface FID settings MS settings Temperature Program DB-1. 60m long, 0.32mm OD, 1 micron coating Gas Pro, 30m long, 0.32mmOD He; 1.3 ml/min Mode: Splitless 150 C 280 C Temperature: 250 C Hydrogen flow: 40 ml/min Air flow: 450 ml/min Make up gas flow: 45 ml/min Scan range: 35 200 atomic mass units Scan Rate: 4.3 scans per second Solvent delay: 4.17 min MS Source: 230 C MS Quad: 150 C Initial oven temperature:20 C Initial hold time:2.7 First ramp:2.76 C/min Next temp: 90 C Hold: 0 min Second ramp: 10.90 C/min Next temp: 130 C Hold: 0 min Third ramp: 6.18 C/min Next temp: 220 C Hold: 18 min Total Run Time: 64.3 11) From the top view select edit sample log table from the sequence table. A sample sequence table is shown in Figure 2-4: 11
Figure 2-4: Sample Log Table The vial number will always be 1 The data file name is limited to eight characters The method for GC/MS analysis that the class will use is AAVOC1 The sample name can be more descriptive and can be longer than eight characters. More information about the sample can be entered in the Miscellaneous Information Box. Normally such information and the sample volume and internal standard volume injected and perhaps the canister size are entered here. The Expected Barcode Box is left blank. At the end of each sequence, there should be a data file called end 2 which is ran with method end2. The end2 method turns off the liquid nitrogen at the end of the sequence.. 12) Click on OK to close the sample log table. 13) Select Run from the Sequence menu to run the sequence. Figure 2-5 shows the start sequence options 14) Select Full Method, select Inject anyway on Barcode Mismatch. Do not select Overwrite existing data files. 15) Entering a sequence comment is optional. 16) Enter your name under the operator name. 17) Enter C:\msdchem\1\DATA\Measurements Class\ for the data file directory 18) Click on the Run Sequence button to run the sequence. 12
Figure 2-5. Start sequence options BFB Tuning Validation For quality control and quality assurance, to verify that the MS has been properly tuned, BFB tuning validation must be performed. A sample volume of 20 ml of 103 ppb Bromofluorobenzene (BFB) is used for this validation process. After the BFB sample run is complete, the BFB data file is analyzed using the Chemstation Data Analysis software. 1) Click on the Instrument #1 Data analysis icon. 2) Open the BFB data file from the data file directory chosen, by selecting Load Data File from the file menu. 3) Load method voc0316.m, by selecting load method from the file menu 4) Zoom in on the BFB peak which has a retention time of 33.3 minutes. Zooming is performed by dragging a square around the peak, while pressing the left mouse button. 5) Obtain an average spectrum of the BFB peak by dragging a square inside the peak while pressing the right mouse button. 6) Select Evaluate BFB from the Tuner menu 7) Evaluate the BFB to the screen 8) If any of the ions in the BFB tuning evaluation fail, then trouble shooting must be done to determine why it failed. 13
Microscale Purge and Trap/ Pre-concentration. In order to avoid interferences of the MS results, the air, carbon dioxide and water must be removed from the sample. These components are removed with the Entech 7100a preconcentrator. In Module 1 (M1) of the pre-concentrator the VOC s are trapped onto glass beads while all gases more volatile than methane, which include carbon dioxide and air, are allowed to pass through. Module 2 (M2) of the pre-concentrator contains a sorbent material called Tenax which absorbs the water from the sample. In Module 3 (M3), the focusing module, the VOC s in the sample are liquefied and then quickly vaporized, and injected into the GC transfer line. A schematic diagram of the pre-concentrator is shown in the figure below. The settings for the pre-concentrator are shown in the tables below: Figure: Schematic Diagram of the Pre-concentrator. 14
M1 M1 bulk head M2 M2 bulk head M3 Event ( C) ( C) ( C) ( C) ( C) Concentration -155 10-60 30-180 Preheat 10 -- No -- Desorption 10 10 180 60 100 Bake out 180 150 180 150 Module Event Temperatures Zone ( C) Rotary Valve 100 GC Transfer Line 100 Manifold Transfer Line 100 Auto sampler Rotary Valve 100 Sample ambient Zone Temperatures Flows and Volumes Pre-flush Flow rate Volume Medium (sec) (cc/min) (cc) Internal Standard 5 75 20 Analytical Standard 5 -- -- Sample 10 75 400 Final sweep/purge flush 15 75 50 M1-M2 Transfer -- 12 30 Flows and Volumes Event (Min) Transfer to Focuser 2.5 Injection 2 Bakeout (M1 and M2) 5 Focuser Bake out 3 Wait Time 64 Event durations 1) Connect the canisters to the sample ports. Make the connections finger tight first, then tighten with a wrench. 2) Click on the NT 7000.exe icon to open the Entec Pre-concentrator Software. 3) Enter the sample names in the same order as the sample log table for the GC/MS 4) The internal standard volume for all samples, will be set at 20 ml 5) After entering the sample name click on the sample port that the can is connected to. 6) Enter the sample volume of 400 ml 7) Enter C:\Smart\tceq4.mpt as the method 8) Click on the add icon to add the sample to the sequence table 15
9) After all the samples have been added to the sequence table, click on the leak icon to leak check the connections to the canisters. It is important that there are no leaks otherwise air from the lab can dilute the sample drawn into the pre-concentrator. Make sure that all the canister valves are closed before leak checking. 10) Click Go to start the leak check. The leak check fails if the initial pressure is not the same as the final pressure. If a sample port fails, undo the connection, reconnect, retighten, and leak check again. 11) After all sample ports pass the leak check, click on the green Go Icon. Make sure that all canister valves are open before pressing Go. 16
Quantification Standard Operation Procedures Calibration curves have been developed to quantitate 59 different VOC components. A list of the components is given below in table 3-1. The first five components ethane through propylene, are measured using a flame ionization detector (FID). All the other components are measured using the mass spectrometer as the detector. The components are listed in the order of their retention time. The target ion used to quantitate the component and the qualifying ions used to identify the component are also listed in Table 3-1. An asterisk * is placed before compounds which are internal standards. In each sample run the same amount of internal standard is added. For each sample run, 5.15 ppb internal standard is added. Each VOC component is measured relative to the internal standard component listed above it in table 3-1. Table 3-1: VOC Component List Retention Time Target Qualifying Qualifying Qualifying Compound Name (min) Ion Ion (1) Ion (2) Ion (3) ethane 5.41 FID ethylene 6.09 FID Acetylene 10.2 FID propane 11.94 FID propylene 18.06 FID *bromochloro methane 12.8 49 isobutane 4.6 39 1-butene 4.93 56 41 butane 4.99 43 58 trans-2-butene 5.16 56 55 41 cis-2-butene 5.41 56 55 41 isopentane 6.44 56 57 72 1-pentene 7.17 55 70 42 n-pentane 6.9 57 72 isoprene 7.52 67 53 68 trans-2-pentene 7.47 55 70 cis-2-pentene 7.74 55 70 2,2-dimethylbutane 8.49 71 57 43 2,3-dimethylbutane 9.82 71 55 2-methylpentane 9.93 71 43 3-methylpentane 10.68 57 56 41 1-hexene 11.1 56 41 69 84 n-hexane 11.55 57 56 41 86 2,4-dimethylpentane 13.24 57 43 85 methylcyclopentane 13.34 56 41 69 *1,4 difluoro benzene 16.8 114 benzene 15.38 78 cyclohexane 15.54 84 56 69 2-methylhexane 15.64 85 56 43 2,3-dimethylpentane 15.88 56 43 71 3-methylhexane 16.25 70 57 43 17
2,2,4-trimethylpentane 17.12 57 56 n-heptane 17.89 71 57 43 methylcyclohexane 19.83 55 83 98 2,3,4-trimethylpentane 21.48 43 71 2-methylheptane 22.5 57 43 99 toluene 22.76 91 92 3-methylheptane 23.03 85 57 43 n-octane 24.94 43 57 85 *chlrorbenzene-d5 28.34 117 ethyl benzene 29.33 91 106 para-xylene 29.8 91 106 meta-xylene 29.88 91 106 styrene 30.88 104 78 51 ortho-xylene 30.94 91 106 n-nonane 31.04 57 43 85 isopropylbenzene 32.2 105 120 propylbenzene 33.32 91 120 m-ethyl toluene 33.56 105 120 p-ethyl toluene 33.68 105 120 1,3,5-trimethylbenzene 33.84 105 120 o-ethyl toluene 34.17 105 120 1,2,4-trimethylbenzene 34.73 105 120 decane 35.32 43 57 71 85 1.2,3 trimethylbenzene 35.65 105 120 m-diethyl benzene 36.86 105 119 134 p-diethyl benzene 37.12 119 105 134 Undecane 38.24 43 57 71 85 Dodecane 42.01 43 57 71 85 18
Figure 3-1: Butane Calibration Curve The Calibration curve for butane is shown in Figure 3-1. The response ratio on the Y-axis is calculated by the following equation. Response Ratio = A c /A i Where A c is the peak response area of the component, and A i is the peak response area of the internal standard. The internal standard for the component butane, is, bromochloro methane. The amount ratio on the X-axis is calculated by the following equation. Amont ratio = C c /C i Where C c is the concentration of the component and C i is the concentration of the internal standard. C i is always the same, it is 5.15 ppb. The calibration curve is a 6 point curve made by measuring the VOC Standard concentrations of 24.3, 9.72, 2.43, 0.972, 0.413, and 0.194 ppb. 19
Using the Chemstation Data Analysis Software to Qauntitate the Data 1) Click on the Instrument #1 Data Analysis icon to start the software. 2) We will be using a method called VOC0316W.M to quantitate the data. Load the method by selecting load method from the File menu. Select VOC0316W.M from the methods folder. 3) Load your data file by selecting Load Data File from the File menu. 4) We will initially quantitiate the data by generating a report. Select Generate a Report from the Quant menu. The report generated shows the estimated concentrations in the sample. The estimated concentrations are estimated based on the peak areas measured in the chromatogram based on an algorithm in the software. Unfortunately this algorithm is not perfect and occasionally makes mistakes, so the peak areas need to be measured or integrated manually. 5) You can integrate the peaks manually by selecting Qedit Quant Result from the Quant menu. For the most part peaks the Chemstation algorithm for integrating peaks works fine for smooth peaks. If the peak is jagged as shown in Figure 3-2. below, the peak will need to be manually integrated. The peak should be located within the retention time window. The peak should be located on the retention time marker. The retention time marker is the cyan dashed vertical line. The area of integration is marked by the dark blue line. Since the isoprene peak is jagged the algorithm incorrectly started measuring the peak late and ended early. This can be corrected by the following steps: Figure 3-2: Qedit, Peak Integration of Isoprene 20
6) Zoom into the peak by dragging a square over the peak while holding down the left mouse button. Double clicking the left mouse button zooms out. 7) Manually integrate the peak by clicking the right mouse button on the beginning of the peak and dragging to the end point of the peak. Note, if the end of the peak peak tails like the last peak on the right in Figure 3-2, the end point of the peak is where the peak signal begins to become horizontal. After this step is completed the dark blue peak integration area line should look as it is in Figure 3-3 below. Note, that the response has increased but the estimated concentration is still 1.0 ppb. This indicates that the integrated peak area response is below the lowest level in the calibration curve. Figure 3-3: Manual Integration of the Isoprene Peak 21
Figure 3-4: Peak Overlap When peaks over lap as shown in Figure 3-4 the end point of the peak is where the next peak starts to rise. In Figure 3-4, the 2,3 dimethyl butane peak which has a retention time of 9.8 minutes is overlapping with the 2-methylpentane peak which has a retention time of 9.9 minutes. 8) After each peak has been examined or manually integrated click on the Exit Icon in the Quick Edit activated window. When prompted select Yes to save your changes made to the quantitation results. 9) Select View Quant Results from the Quant menu. This generates a text file with the quantitation results. Save the text file. 10) The last and final step is to get the text data into a more usable format. Cut the header information from the text and save the resultant text file under a different name. The resultant text file can be imported into an excel spreadsheet using fixed width separation to put the text into columns. 22
Standard Operation Procedure for Canister Cleaning After the sample has been analyzed by the GC/MS the 6L canisters are cleaned for reuse. The canisters are cleaned by flushing the canisters with humidified zero grade air, evacuating the canister to 0.2 psia with a rough pump, and further evacuating the canister to 100 militorr. The flushing and evacuations are repeated for four cycles. In the final evacuation the canisters are evacuated to 50 militorr. During the flushing/evacuation cycles heating bands heat the canisters to vaporize any condensation along the canister walls. 1) Make sure the cylinder pressure of the zero grade air is above 500 psig. If the Pressure is below 500 psig, replace the zero grade air cylinder with a new one. Make sure the line pressure is at 50 psig. 2) Make sure that the water level of canister cleaner is between 80-20%. If the water level is below 20% then HPLC grade water needs to be added. Before removing the humidifying vessel from the canister cleaner be sure to close the valve to the zero grade air cylinder. Fill the humidifying vessel with HPLC grade water till the level is 80% full. Re connect the humidifying vessel to the can cleaner. Open the valve to the zero grade air cylinder. Check for an air leak on the nut of the humidifying vessel. Spray the nut with a 50/50 mixture of methanol and water. If bubbles form at the nut. Then tighten the nut till the leak stops. 3) Wrap the heating bands around the can. Turn on the power strip which the heating bands are plugged into. 4) Connect can to Canister Cleaner. Tighten the nuts by hand first. Then tighten them with a 9/16 wrench. Make sure the valves to the canisters are closed. 5) Open the software to control the canister cleaner by clicking on the canister cleaner icon. 6) Click on Open and select canclean.m30 to load the set points for the method. 7) Click on Run to get to the run control screen. 8) Before the can cleaning process is started, the connection of the canisters to the canister cleaner must be leak checked. Click on the rough pump button wait till the pressure of the system is approximately 0.1 psia 9) Click on the all off button. The system should be able to maintain a vacuum for 1 minute. If the pressure increases by 0.1 psi during this time then there is a leak in the system. If there is a leak in the system, trouble shooting will need to be done to identify the leak If the pressure of the system does not increase during the 1 minute, then the leak check has passed. 10) Open the valves to the cans. 11) Click on the Go Icon to start the can cleaning process. 12) After the cans have gone through 4 cleaning cycles and final evacuation. Close the valves to the can. Hit the all off button. Turn off the power to the heating bans. 23
Standard Operation Procedure for Standards Preparation Purging the Regulator There are three standards, which are the Internal Standard, the 4-Bromofluro-Benzene (BFB) and the Ozone Precursor Mix. Each standard cylinder has a regulator. When a new standard cylinder is received the regulator must be flushed with the new standard to remove pockets of lab air in the regulator. 1. The cylinder valve on the cylinder should be open the regulator valve should be closed. The needle valve to the cylinder should be closed. 2. Connect the cylinder to the canister cleaner. 3. Perform a manual leak check of the system. Click on the rough pump button wait till the pressure of the system is approximately 0.1 psia 4. Click on the all off button. The system should be able to maintain a vacuum for 1 minute. If the pressure increases by 0.1 psi during this time then there is a leak in the system. If there is a leak in the system, trouble shooting will need to be done to identify the leak If the pressure of the system does not increase during the 1 minute, then the leak check has passed. 5. Close the regulator valve on the regulator. 6. Open the needle valve to the cylinder. 7. Click on the rough pump button and evacuate the system to about 0.1 psia. 8. Click on the all off button 9. Open the regulator valve on the regulator slowly till the gauge on the regulator reads about -5 psig. 10. Close the needle valve to the cylinder. 11. Click in the rough pump button and evacuate the system to about 0.1 psia. 12. Click on the all off button 13. Open the needle valve to the cylinder to allow some gas to flow through. The gauge on the regulator should increase to -5 psig. 14. Repeat steps 9-12 six times to flush the regulator. 24
Standard Preparation by Static Dilution A VWR Traceable Pressure Meter will be used in preparing a static dilution. This pressure meter should be re-calibrated every year. The pressure meter reads gauge pressure so add barometric pressure in the room (usually 14.7psi) to the meter reading to convert the pressure into absolute terms. A diagram of the connections of the pressure meter, canister and the cylinder should be connected to the canister cleaner is shown in the figure below. 1) The cylinder valve on the cylinder should be open the regulator valve should be closed. The needle valve to the cylinder should be closed. 2) Connect the cylinder, a clean evacuated canister, and the pressure meter to the canister cleaner. Note: it important that the canister is at room temperature. If the canister has just been cleaned allow the canister 1 hour to cool to room temperature before using in the preparation of a static dilution. 3) Perform a manual leak check of the system. Click on the rough pump button wait till the pressure of the system is approximately 0.1 psia. (Use reading from canister cleaner system) 4) Click on the all off button. The system should be able to maintain a vacuum for 1 minute. If the pressure increases by 0.1 psi during this time then there is a leak in the system. If there is a leak in the system, trouble shooting will need to be done to identify the leak If the pressure of the system does not increase during the 1 minute, then the leak check has passed. 5) Click on the High Vacuum button. Wait till the system is evacuated to 25 militorr. 6) Click on the all off button 25
7) Open the needle valve to the cylinder 8) Slowly open the regulator valve till the pressure on the VWR Traceable pressure meter is about -10.7 psi 9) Open the valve to the clean evacuated cylinder. 10) Close the needle valve to the cylinder when the pressure on the VWR Traceable pressure meter is about -10.7 psi. 11) Record the pressure reading on the VWR Traceable pressure meter. This is the initial pressure reading. 12) Click on the diluent button till the pressure on the VWR Traceable pressure meter is about 25.3. 13) Click on the all off button. (Tip: Click on the all off button when the VWR Traceable pressure meter is at 20 psi. The pressure will increase a few psi after the all off button has been clicked.) 14) Record the pressure reading on the VWR Traceable pressure meter. This is the final pressure reading 15) Allow the system 15 minutes to equilibrate before closing the valve to the canister. 16) Close the valve to the canister. 17) Convert the pressure readings from the VWR Traceable pressure meter to absolute pressure. 18) The concentration in the Canister can be calculated by the following equation. Initial Pr essure Re ading( psia) Concentrat ion = * OriginalCylinderConcentration Final Pr essure Re ading( psia) 26
Internal Standard Preparation The Internal standard does not need any dilution, however the standard must transferred from the cylinder into a six liter canister. A diagram of how the cylinder, canister and canister cleaner should be connected is shown in the figure below: 1) The cylinder valve on the cylinder should be open the regulator valve should be closed. The needle valve to the cylinder should be closed. 2) Connect the cylinder, and the canister to the tee as show in figure 1. Connect the tee to the canister cleaner system. 3) Perform a manual leak check of the system. Click on the rough pump button wait till the pressure of the system is approximately 0.1 psia. 4) Click on the all off button. The system should be able to maintain a vacuum for 1 minute. If the pressure increases by 0.1 psi during this time then there is a leak in the system. If there is a leak in the system, trouble shooting will need to be done to identify the leak If the pressure of the system does not increase during the 1 minute, then the leak check has passed. 5) Click on the High Vacuum button. Wait till the system is evacuated to 25 militorr. 6) Click on the all off button 7) Close the needle valve to the canister cleaner. 8) Open the needle valve to the cylinder. 9) Open the regulator valve slowly till the line pressure is 35 psig 10) Open the valve to the evacuated canister. Wait till the line pressure returns to 35 psig. 11) Close the valve to the canister. 12) Close the needle to the cylinder. 13) Close the regulator valve. 27
Standard Operation Procedure For VOC Sample Collection The VOC sample collection system is designed to collect four three hour samples. The four samples consist of a morning, noon, afternoon, and night time sample. The sampling times are 5:00 8:00, 11:00 14:00, 17:00 0 20:00 and 23:00 2:00. A schematic diagram of the VOC sample collection system is shown in the figure below. The housing for the sample collection system is ventilated so that the temperature inside the housing remains cool. A small pump pumps air from outside the housing into the sample system tubing. The canisters are evacuated to 50 militorr. When the solenoid valve is opened the air passes through a flow restrictor which is an orifice that restricts the flow rate into the can. The flow controller which is a diaphragm below the flow restrictor, regulates the flow into the can so that the flow of air is at a constant rate. Without the flow controller the flow rate into the can would decrease as the pressure in the can approaches ambient pressure and majority of the volume collected in the can would be over representative of the 1 st hour of collection. The canister timers control the opening and closing of the solenoid valve. The main timer is used to set the day of which the samples are to be collected. Figure: Schematic Diagram of Sample Collection System. Below are the steps for the operation of the VOC sample collection system: 1. Press the On/Off button of the main timer to turn on power to the canister timers. 2. Turn on the canister timer knob (counter clockwise one click) and record the pressure gauge reading on the back of the tag of the canister. Mark as Pf for final pressure in the can 28
3. Turn off the canister timer knob (counter clockwise one click). and record the pressure gauge reading on the back of the tag of the canister. Mark as Pg for gauge pressure when the solenoid valve is closed. 4. If 0 < (Pf Pg ) <5 then the timer setting is good. If (Pf Pg ) = 0 then decrease the sample time on the canister timer by 15minutes. Note: each notch on the timer is about 15 minutes. If (Pf-Pg) >5 then increase the sample time on the canister timer by 15 minutes. Repeat steps 3-6 for each canister. 5. Press the On/Off button of the main timer to turn off power to the canister timers 6. Make sure all canister timers are set at 10pm. 7. Close the canister valves on all the canisters. 8. Disconnect the cans from the sampling let the samplers rest on top of the can before moving the cans out of the housing. This is to prevent the sample system tubing from snapping off. Remove the cans from the housing 9. Now that the housing is empty it is a good time to stick your head in and change the time on the main timer. a) Check the time on the main timer and maker sure that it is displaying the current time and day. b) press the Program button to see program 1 on screen make sure that the program on time for program 1 is 10pm. Change the Day to today s date by pressing the day button. c) Press the on/off button to see the off time for program 1. Make sure the that the program on time for program 1 is 10pm. Change the day to tomorrow s date by pressing the day button. d) Press the time select button when finished changing program 1. e) Make sure that the main timer is in the auto mode. If the words Automode are not shown on the display then press the mode button. 10. Place the new cans in the housing and put samplers on top of the canisters before connecting them (again to avoid the sample line tubing from snapping off). 11. Connect the cans to the sampling system. Make sure the connections are tight. It is recommend tightening the nut with your fingers first to avoid striping the threads of the nut. Then tighten with the wrench. 12. Put the labels on the cans. 13. Open the valves on the cans. 29
References Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air Second Edition Compendium Method TO-15 Determination Of Volatile Organic Compounds (VOCs) In Air Collected In Specially-Prepared Canisters And Analyzed By Gas Chromatography/Mass Spectrometry (GC/MS) Center for Environmental Research Information Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH 45268, January 1999 http://www.epa.gov/ttnamti1/files/ambient/airtox/to-15r.pdf Methods of Air Sampling and Analysis, Third Edition, James P. Lodge Jr., c1989, Catalog# TD, 890, M488, 1989 30