Radiocarbon · 2016 · 11 citations · 23 references
Natural SciencesChemistryAnalytical ChemistrySpectroscopic AnalysisSpectroscopyDetector SystemsLaser SpectroscopyOptical SpectroscopyCarbon Dioxide DetectionDetection ThresholdsGas DetectionGas Detection InstrumentsGlow Discharge IonizationLower Limit Of QuantificationLower Limit Of QuantitationOptogalvanic Spectroscopy
Abstract The intracavity optogalvanic spectroscopy (ICOGS) method has been reported to quantify radiocarbon at subambient levels (<1 part per trillion). ICOGS uses a gas sample that is ionized in a low-pressure glow discharge located inside a 14 CO 2 laser cavity to detect changes in the discharge current under periodic modulation of the laser power to determine the 14 CO 2 concentration of the sample. When claims of detection thresholds below ambient levels were not verified by other researchers, we constructed a theoretical analysis to resolve differences between these conflicting reports and built and tested an ICOGS system to establish a lower limit of detection. Using a linear absorbance model of the background contribution of 12 CO 2 and data from the HITRAN database, we estimate that the limit of detection (3 σ x ) is close to 1.5×10 4 Modern. By measuring a 1.5×10 4 Modern enriched CO 2 sample in a cavity modulation ICOGS system without a clear signal, we conclude that for this system the limit of detection for ICOGS must be above 1.5×10 4 . The implications for previous ICOGS reports are discussed.
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