analysis of ppb_levels_of__nitrous_oxide_by_gas_chromatography
DESCRIPTION
A PID Analyzers portable GC Model 312 was used to detect ppb levels of N2O in the atmosphere.TRANSCRIPT
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Analysis of ppb Levels ofAnalysis of ppb Levels ofAnalysis of ppb Levels of Analysis of ppb Levels of Nitrous Oxide by Gas Nitrous Oxide by Gas
Ch t hCh t hChromatography Chromatography
Pittcon Paper # 460Paper # 460--77ppDr. John N. DriscollDr. John N. DriscollPID PID Analyzers, LLCAnalyzers, LLCPID PID Analyzers, LLCAnalyzers, LLC
Sandwich, MA www hnu comwww hnu comwww.hnu.comwww.hnu.com
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INTRODUCTIONINTRODUCTIONNitrous oxide (NNitrous oxide (N22O) is produced in the soil by the decomposition O) is produced in the soil by the decomposition of nitrogen compounds. This results in an average atmospheric of nitrogen compounds. This results in an average atmospheric concentration of approximately 0.25 ppm. It is also used in concentration of approximately 0.25 ppm. It is also used in dental offices and in hospital operating rooms during surgerydental offices and in hospital operating rooms during surgerydental offices and in hospital operating rooms during surgery. dental offices and in hospital operating rooms during surgery. MethodsMethods usedused forfor determinationdetermination ofof NN22OO includeinclude infraredinfrared (IR)(IR)spectroscopyspectroscopy andand gasgas chromatographychromatography.. TheThe formerformer methodmethod isisusefuluseful toto justjust belowbelow 11 ppmppm althoughalthough photoacousticphotoacoustic IRIR hashas aausefuluseful toto justjust belowbelow 11 ppmppm althoughalthough photoacousticphotoacoustic IRIR hashas aadetectiondetection limitlimit ofof 3030 ppbppb.. TheThe GCGC detectorsdetectors usedused forfor NN22OOincludeinclude thethe thermalthermal conductivityconductivity detectordetector (TCD)(TCD) forfor highhigh levelslevels (>(>100100 ppm)ppm) andand thethe electronelectron capturecapture detectordetector (ECD)(ECD) ((100100 ppmppm toto
00 11 ))appapp.. 00..11 ppm)ppm)..WeWe willwill bebe evaluatingevaluating aa FarFar UVUV absorbanceabsorbance detectordetector coupledcoupled totoaa concentratorconcentrator toto detectdetect lowlow ppbppb levelslevels ofof NN22OO
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FUV DetectorFUV Detector
Consists of a uv lamp (120 nm), a 1 cm pathlength cell (50 uL) and a UV photodiode that measures lamp intensityAs a sample enters the cell, the signal will decrease in proportion to the absorption coefficient of the speciesResponse- organic HC, fixed gases & inorganic gases as shown in next slide
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Chromatogram of HC with FUV DetectorChromatogram of HC with FUV Detector
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Far UV Far UV DetectorDetector
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Photo of Model 301Photo of Model 301--BBPhoto of Model 301Photo of Model 301 BB
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Equipment usedEquipment usedEquipment usedEquipment used
PA Model 301-B GCPA Model 301 B GCModified by adding a 6 port manual valve with sample loops from 0 1 to 50 ccwith sample loops from 0.1 to 50 ccLow ppm concentrations prepared by dil ti f t d d (1000 N O) idilution of gas standard (1000 ppm N2O) in zero air10 M x 0.53mm PLOT MolesieveFar UV detector (50 uL dead volume)
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Actual vs Measured N2O by GC-FUV (ppm)
y = 1 0162x - 0 5833120
on y = 1.0162x - 0.5833R2 = 0.9987
80
100
ncen
trat
io
40
60
ed N
2O c
o
0
20
Mea
sure
00 20 40 60 80 100 120
Actual N2O concentration
Detection limit- 500 ppb
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Concentrator for NConcentrator for N22OO
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Concentrator ParametersConcentrator Parameters
Material : molecular sieve- 80/100 meshDesorb volume- 10-50 ccDesorb volume 10 50 ccDesorb temperature: 150°CTi T 4 dTime to max.T – 4 secondsCan vary Tmax from 1 second to 4 min.Cycled between runs to clean columnAll parameters are under PC controlAll parameters are under PC control
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Chromatogram of 50 ppm Chromatogram of 50 ppm NN22O with FUV DetectorO with FUV Detector
10 M x 0.53 mm PLOT10 M x 0.53 mm PLOTMolesieve, 15 cc/min. 80C; 50 ppm N2O in
bi t iambient air
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NN22O 10 foldO 10 fold
concentrationconcentration
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100 ppb N2O25 fold25 fold
concentration
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Calibration Curve Calibration Curve for Concentratorfor Concentratorfor Concentratorfor Concentrator
ppb Levels of N2Oppb Levels of N2O
y = 1.0257x - 0.4667120140
yR2 = 0.9913
6080
100120
Mea
sure
d
0204060
ppb
M
00 20 40 60 80 100 120 140
ppb Actual
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SUMMARYSUMMARYSUMMARYSUMMARYBy coupling a FUV detector to a PLOT column, wey p ghave been able to detect from 500 ppm down to 250ppb of N2O.This covers approximately the same range as theThis covers approximately the same range as theECDWe have evaluated a concentrator/ thermal desorberTh t i th d t ti f N O t 5 bThat improves the detection of N2O to 5 ppb.The FUV (without a concentrator) is will provide arange that would be adequate for workplacegmonitoring of N2O.The FUV with a concentrator is ideal for monitoringN2O in ambient airN2O in ambient air