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CORNELL CEE 453 - Lecture Slides

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PowerPoint PresentationOverviewGas ChromatographGas Chromatograph CalibrationExample Calibration: OctaneVOC Contaminated Site MapSyringe TechniqueSyringe Technique: solutionOctane Exposure LimitsSite AssessmentHazardous Waste Site SurveysSoil Gas SurveySoil Gas Survey: MethodsSoil Gas SamplingField AnalysisPortable Gas ChromatographPhotoionization Air MonitorFlame Ionization DetectorPotential SitesUnderground Storage Tankshttp://www.nwk.usace.army.mil/Geology/htrw.htmlOverviewOverviewGas Chromatograph calibrationSyringe TechniqueVOC exposure limitSite AssessmentPotential sitesSoil Gas SurveysField AnalysisGas Chromatograph calibrationSyringe TechniqueVOC exposure limitSite AssessmentPotential sitesSoil Gas SurveysField AnalysisGas Chromatographinjection volumeinjection volumeOutputchromatogramconverted to peak areas and peak timesConvert peak area to mass using injection of known mass (standard)peak area is proportional to mass injectedmass injected can be converted to concentration given _________ _________Alternately use peak area (PA) as surrogate for mass(If a calibrated mass isn’t required)Gas Chromatograph CalibrationWe can use the headspace sample from source vials to calibrate the GC.We will use the ideal gas law and the vapor pressure of the VOCs.liquidliquidgasgasOctaneOctaneAcetoneAcetoneTolueneToluenevapor pressureat 25 °Cvapor pressureat 25 °C1.88 kPa1.88 kPa24 kPa24 kPa3.8 kPa3.8 kPaMWMW114.23 g114.23 g58.08 g58.08 g92.14 g92.14 gdensitydensity0.71 g/mL0.71 g/mL0.79 g/mL0.79 g/mL0.87 g/mL0.87 g/mLExample Calibration: OctanePVnRT=PVnRT=   K298 KmolkPaL8.31L10 x 100 kPa 1.88n6-   K298 KmolkPaL8.31L10 x 100 kPa 1.88n6-nmol 75.9 =mol 10 x 9.57n9nmol 75.9 =mol 10 x 9.57n9Calculate moles, mass, and equivalent liquid volume of 100 µL headspace sample at 25 °C.Calculate moles, mass, and equivalent liquid volume of 100 µL headspace sample at 25 °C.g 8.67g 10 x 8.67mol114.23gmol 10 x 75.969g 8.67g 10 x 8.67mol114.23gmol 10 x 75.969nL 12.2 = L 10 x .221g 0.71L 10g 10 x 8.67936 nL 12.2 = L 10 x .221g 0.71L 10g 10 x 8.67936 liquidoctanegasKmolkPaL8.31RKmolkPaL8.31RmolesmassvolumeTableVOC Contaminated Site MapReport gas concentrations in mg/m3.Example: Given a peak area of 1 x 104 from an injection volume of 100 µL, calculate the concentration in mg/m3. Assume the peak area from the source vial injections was 2 x 108.384mg/m 4.3g/L 4.3PA10 x 2g 8.67L 100PA 1x10sample PAsample PAcalibration PAcalibration PAsample volumesample volumemass injected for calibrationmass injected for calibrationSyringe TechniqueThe Problem:VOC vapors sorb to glass barrel, Teflon plunger, and stainless steel needleThe Solution:Remove GC needle.Purge syringe 10 times with room air to remove any residual VOCs.Put on sample needle. (continued)Syringe Technique: solutionSyringe Technique: solutionInsert into sample bottle (with syringe at zero volume).Fill syringe fully with gas and purge syringe contents back into the source bottle (repeat 3 times).Fill syringe and adjust to 100 µL.Close syringe valve and remove syringe from sample vial and remove sample needle.Put on GC needle.Instruct GC to measure sample.Insert needle in injection port, open syringe valve, inject sample, hit enter button all as quickly as possible.Remove syringe from the GC injection port.Insert into sample bottle (with syringe at zero volume).Fill syringe fully with gas and purge syringe contents back into the source bottle (repeat 3 times).Fill syringe and adjust to 100 µL.Close syringe valve and remove syringe from sample vial and remove sample needle.Put on GC needle.Instruct GC to measure sample.Insert needle in injection port, open syringe valve, inject sample, hit enter button all as quickly as possible.Remove syringe from the GC injection port.Equilibrate with headspaceEliminate needle carryoverOctane Exposure LimitsOSHA PEL (Permissible exposure level) 500 ppm TWA (approximately ____ mg/m3)LC50CAS# 111-65-9: Inhalation, rat: LC50 =118 g/m3/4H.336-6g/m 86.5mL 1000L 10 x 100g 10 x 8.67concentration in octane source vialconcentration in octane source vial500(1 m3 of air is approximately 1 kg)Site AssessmentContaminated soil, a global problemDifficult to assess subsurface contaminationcan’t see it3-d problemeven with lots of monitoring wells can miss important subsurface features.Expensive to decontaminate sitescompeting national prioritieshighest priority needs to be preventionHazardous Waste Site Surveysloading zoneshydraulically operated liftsaccidental spillsstorage tanksvegetative distressherbicide applicationhazardous materialsstained soilfill materialused to hide evidence of spillmay contain hazardous substanceswater and sewer linesprovide pathways for migration of subsurface contaminantsSoil Gas SurveyEffective screening technique for mapping the extent of VOCsIndicates location of contaminant sourcesAdvantagesrapidlow costminimal disturbance to siteno waste generatedadaptable to site conditionsAdvantagesrapidlow costminimal disturbance to siteno waste generatedadaptable to site conditionsDisadvantagesdetection limits may be too highsome compounds may not be detectedfield results are semi-quantitativeDisadvantagesdetection limits may be too highsome compounds may not be detectedfield results are semi-quantitativeSampling MatrixSoil Gas SurveySoil Gas Survey: MethodsPlace hollow, small diameter probe in soilApply vacuum to probeExtract soil pore gasTake a sample of soil pore gas using:syringe - on-site gas chromatograph analysisTedlar bag - on-site or off-site analysisunaffected by most compoundsimpermeable to gas exchangestainless steel adsorption tube - quantitative laboratory analysisSoil Gas SamplingSoil Gas SamplingStatic sampling can be done two ways: An in-situ adsorbent (usually an activated charcoal rod) is buried in the soil for a period of days to weeks. The adsorbent is retrieved and analyzed at a laboratory for VOCs. Samples are collected from containers placed in the surface soil and analyzed using portable


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