14C analysis via intracavity optogalvanic spectroscopy

Abstract

A new ultra sensitive laser-based analytical technique, intracavity optogalvanic spectroscopy (ICOGS), allowing extremely high sensitivity for detection of 14 C-labeled carbon dioxide has recently been demonstrated. Capable of replacing accelerator mass spectrometers (AMS) for many applications, the technique quantifies zeptomoles of 14 C in sub micromole CO 2 samples. Based on the specificity of narrow laser resonances coupled with the sensitivity provided by standing waves in an optical cavity, and detection via impedance variations, limits of detection near 10 −15 14 C/ 12 C ratios have been obtained with theoretical limits much lower. Using a 15 W 14 CO 2 laser, a linear calibration with samples from 5 × 10 −15 to >1.5 × 10 −12 in 14 C/ 12 C ratios, as determined by AMS, was demonstrated. Calibration becomes non linear over larger concentration ranges due to interactions between CO 2 and buffer gas, laser saturation effects and changes in equilibration time constants. The instrument is small (table top), low maintenance and can be coupled to GC or LC input. The method can also be applied to detection of other trace entities. Possible applications include microdosing studies in drug development, individualized sub therapeutic tests of drug metabolism, carbon dating and real time monitoring of atmospheric radiocarbon.

Intracavity optogalvanic spectroscopy: Is there any evidence of a radiocarbon signal?

“…Still, a clear correlation between the peak amplitude and the concentration of 14 C in the sample could not be found in any of these measurement conditions. (see table 2), and the particular parameters P20 and 100 Pa were presented mostly for comparison with earlier studies [1,2,5,6]. In a previous study [5], chemical reactions in the plasma causing dissociation of CO 2 , were identified as one possible cause of instabilities in the measurements.…”

“…Since the start of the project in 2010, we have not been able to reproduce the results of Murnick et al [1,2]. Despite more than one year of additional experiments since our last report [6], and several iterations of the setup, including replacing the plasma excitation source, and the OG detection scheme with a custom-made SSRR sample cell, we have found no indications that ICOGS is capable of unambiguous No other research group has, to our knowledge, been able to demonstrate ICOGS as a radiocarbon measurement method for the isotopic ratio span routinely accessible to AMS.…”

“…The output of the laser was investigated in a reference cell, based on the same technology as used in the original ICOGS reports [1,2,6,8], together with two power meters -one thermopile for average power measurements and one pyroelectric for fast time resolved detection of laser pulses [6]. The wavelength of the laser was also measured in an IR spectrum analyzer.…”

“…Six years ago, the first reports of a new, ultrasensitive radiocarbon detection method, utilizing ro-vibrational spectroscopy, were published by Murnick et al [1,2]. The method was called intracavity optogalvanic spectroscopy (ICOGS), and claimed a limit-of-detection (LOD) in Apart from being less complicated and expensive than competing technologies, ICOGS could supposedly facilitate analysis of smaller samples [1].…”

“…This "intracavity" approach has been claimed to increase the sensitivity by almost 7 orders of magnitude, compared to extracavity optogalvanic (OG) spectroscopy [1,2]. However, despite the methodical and thorough efforts of at least five research groups worldwide -one of them being the Division of Ion Physics at Uppsala University -the exceptional claims regarding the sensitivity and LOD of ICOGS have not been possible to confirm.…”