Intracavity Optogalvanic Spectroscopy Research Articles

Intracavity optogalvanic detection of 14C using a stabilized 14CO2 laser

Intracavity optogalvanic detection of 14C utilizes the narrow band specificity of 14CO2 laser resonances in the infrared spectrum, coupled with greatly enhanced sensitivity from amplified effective path lengths in optical cavities. Background (nonresonant) interactions are also enhanced in such cavities, making proper separation of signals from background imperative. Intracavity Optogalvanic Spectroscopy (ICOGS) is similar to cavity ring-down spectroscopy (CRDS) with certain crucial differences. An ICOGS model, based on a basic CO2 laser and optogalvanic effect physics, is presented. Experimental results using a laboratory instrument with a continuous flow of small CO2 samples in a buffer gas illustrate the model. It is shown that acquisition of optimized signal-to-background ratios for the quantitation of 14CO2 in samples of order 10 μg is achievable, considerably smaller than with CRDS.

Laser-based radiocarbon detection in the laboratory: How soon?

Research over the past 25 years and the use of accelerator mass spectrometry (AMS) have demonstrated benefits of single-atom counting of 14 C compared with scintillation monitoring of 14 C radioactive decay for a multitude of applications in drug development studies. These include pharmacokinetics and metabolism studies, microdosing studies, and quantification of DNA adducts. In the last decade, the possibility of single-atom counting using lasers has been demonstrated, providing the possibility of simplified laboratory-based systems, which can equal or excel AMS sensitivity and provide scintillation system convenience without high levels of radioactivity. To achieve the required sensitivity, optical storage cavities have been used to enhance the laser interaction of the low densities of radiocarbon present. Two types of laser technologies have been used-cavity ring-down spectroscopy (CRDS) and intracavity opto-galvanic spectroscopy (ICOGS). Problems to be overcome to achieve routine use have included separation of the 14 C signal from backgrounds, achievement of acceptable precision and accuracy, reduction of measurement times for small samples, and improvement in the ease of use for the operator. Both technologies have achieved impressive results to date using samples of order 1 mg with CRDS and 10 μg with ICOGS. Commercial development is the next step.

Reply to Comment Submitted by Murnick et al. on "Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection".

ADVERTISEMENT RETURN TO ISSUEPREVCommentNEXTReply to Comment Submitted by Murnick et al. on “Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection”Dipayan Paul and Harro A. J. Meijer*View Author Information Centre for Isotope Research (CIO), Energy and Sustainability Research Institute Groningen (ESRIG), University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands*E-mail: [email protected]Cite this: Anal. Chem. 2016, 88, 8, 4574–4577Publication Date (Web):March 25, 2016Publication History Published online5 April 2016Published inissue 19 April 2016https://doi.org/10.1021/acs.analchem.6b00473Copyright © 2016 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views528Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (904 KB) Get e-AlertsSUBJECTS:Analytical chemistry,Calibration,Carbon-14,Gases,Lasers Get e-Alerts

Comment on "Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection".

ADVERTISEMENT RETURN TO ISSUEPREVCommentNEXTComment on “Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection”Anders Persson† and Mehran Salehpour*‡View Author Information† Department of Engineering Sciences, Microsystems Technology, Uppsala University, Box 534, SE-751 21, Uppsala, Sweden‡ Department of Physics and Astronomy, Ion Physics, Uppsala University, Box 516, SE-751 20, Uppsala, Sweden*E-mail: [email protected]Cite this: Anal. Chem. 2016, 88, 8, 4578–4579Publication Date (Web):March 25, 2016Publication History Published online5 April 2016Published inissue 19 April 2016https://doi.org/10.1021/acs.analchem.6b00613Copyright © 2016 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views467Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (135 KB) Get e-AlertsSUBJECTS:Analytical chemistry,Carbon-14,Spectroscopy Get e-Alerts

Comment on "Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection".

ADVERTISEMENT RETURN TO ISSUEPREVCommentNEXTComment on “Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection”Daniel Murnick*, Junming Liu, and Mark DeGuzmanView Author Information Department of Physics, Rutgers University, Newark, New Jersey 07102, United States*E-mail: [email protected]Cite this: Anal. Chem. 2016, 88, 8, 4571–4573Publication Date (Web):March 25, 2016Publication History Published online5 April 2016Published inissue 19 April 2016https://doi.org/10.1021/acs.analchem.5b04943Copyright © 2016 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views491Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (901 KB) Get e-AlertsSUBJECTS:Carbon-14,Lasers,Quantum mechanics,Resonance structures,Stabilization Get e-Alerts

Invalidation of the Intracavity Optogalvanic Method for Radiocarbon Detection

AbstractThe 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 14CO2 laser cavity to detect changes in the discharge current under periodic modulation of the laser power to determine the 14CO2 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 12CO2 and data from the HITRAN database, we estimate that the limit of detection (3σx) is close to 1.5×104 Modern. By measuring a 1.5×104 Modern enriched CO2 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 1.5×104. The implications for previous ICOGS reports are discussed.

Response to “Comment on ‘Invalidation of the Intracavity Optogalvanic Method for Radiocarbon Detection’” by Daniel E Murnick

AbstractOur results, when taken alongside those of two other research groups, appear to invalidate the early positive results for intracavity optogalvanic spectroscopy (ICOGS) and its detection of radiocarbon. Daniel Murnick, whose lab published those early results, has directed a comment setting out the perceived shortcomings of our article and the reasons that the results do not constitute invalidation, as our article claims. Absent support from his own findings or published literature, his various counterclaims regarding our experimental procedure appear to constitute only his considered professional opinion and the largest confounder highlighted by our research is not even mentioned. The preponderance of documented evidence regarding ICOGS clearly supports the null hypothesis and in our opinion, nothing in Murnick’s comment indicates otherwise.

Comment on “Invalidation of the Intracavity Opto-galvanic Method for Radiocarbon Detection” by Cantwell G Carson, Martin Stute, Yinghuang Ji, Roseline Polle, Arthur Reboul, and Klaus S Lackner

AbstractCarson et al. (2016) have measured the optogalvanic response of an intracavity cell discharge containing carbon dioxide enriched in radiocarbon in a 14CO2 laser, and compared same to an unenriched sample. The measurement was carried out by modulating the laser wavelength while slowly tuning through the laser gain profile. The results of the measurements are claimed to “invalidate the optogalvanic method for radiocarbon detection.” A broadband linear absorption model is presented in support of this hypothesis. In fact, the experimental design was such as to minimize any possibility for 14C detection, and the model presented is not relevant to their experiment. Crucial control measurements were not carried out and the model used did not differentiate between broadband absorption spectroscopy and intracavity optogalvanic spectroscopy (ICOGS) with a narrow-band single-mode CO2 laser.

Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection

IntraCavity OptoGalvanic Spectroscopy as a radiocarbon detection technique was first reported by the Murnick group at Rutgers University, Newark, NJ, in 2008. This technique for radiocarbon detection was presented with tremendous potentials for applications in various fields of research. Significantly cheaper, this technique was portrayed as a possible complementary technique to the more expensive and complex accelerator mass spectrometry. Several groups around the world started developing this technique for various radiocarbon related applications. The IntraCavity OptoGalvanic Spectroscopy setup at the University of Groningen was constructed in 2012 in close collaboration with the Murnick group for exploring possible applications in the fields of radiocarbon dating and atmospheric monitoring. In this paper we describe a systematic evaluation of the IntraCavity OptoGalvanic Spectroscopy setup at Groningen for radiocarbon detection. Since the IntraCavity OptoGalvanic Spectroscopy setup was strictly planned for dating and atmospheric monitoring purposes, all the initial experiments were performed with CO2 samples containing contemporary levels and highly depleted levels of radiocarbon. Because of recurring failures in differentiating the two CO2 samples, with the radiocarbon concentration 3 orders of magnitude apart, CO2 samples containing elevated levels of radiocarbon were prepared in-house and experimented with. All results obtained thus far at Groningen are in sharp contrast to the results published by the Murnick group and rather support the results put forward by the Salehpour group at Uppsala University. From our extensive test work, we must conclude that the method is unsuited for ambient level radiocarbon measurements, and even highly enriched CO2 samples yield insignificant signal.

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

In 2008, the first report of an ultrasensitive method for ro-vibrational spectrometry of radiocarbon dioxide was published. The method, called intracavity optogalvanic spectroscopy (ICOGS), claimed a sensitivity and limit-of-detection comparable to accelerator mass spectroscopy. ICOGS was claimed to utilize the isotope-dependent ro-vibrational absorption lines of carbon dioxide in the infrared spectrum. In order to facilitate unambiguous detection of radiocarbon, the sample was placed inside the cavity of a radiocarbon dioxide laser. This intracavity approach was claimed to increase the sensitivity by seven orders of magnitude compared with traditional optogalvanic methods. However, despite the methodical and thorough efforts of several research groups worldwide, these claims have not been possible to reproduce. Instead, we have previously reported serious deviations from the original results, where we found that ICOGS suffers from considerable problems with the stability and reproducibility of the optogalvanic signal, and that misinterpretations of these uncertainties likely are the explanation for the claimed sensitivity in the first reports. Having identified the stability and reproducibility of the detection as major concerns, we decided to improve the setup by with state-of-the-art plasma source technology. Deploying a custom-made stripline split-ring resonator optogalvanic detector, we have now investigated the applicability of ICOGS to radiocarbon detection even further. Measurements have been made with a wide range of parameters including different gas mixtures at various pressures and wavelengths. We have also conducted measurements with gas flowing through the sample cell to investigate the effect of plasma induced decomposition of the sample. Still, we have seen no indications of a significant radiocarbon signal in a concentration range between 0.29 Modern and 9.7 Modern, i.e., the range of interest to the radiocarbon community. Hence, our conclusions after four years of working in this field, is that ICOGS is not a viable method for radiocarbon detection.

Stripline split-ring resonator with integrated optogalvanic sample cell

Intracavity optogalvanic spectroscopy (ICOGS) has been proposed as a method for unambiguous detection of rare isotopes. Of particular interest is 14C, where detection of extremely low concentrations in the 1:1015 range (14C: 12C), is of interest in, e.g., radiocarbon dating and pharmaceutical sciences. However, recent reports show that ICOGS suffers from substantial problems with reproducibility. To qualify ICOGS as an analytical method, more stable and reliable plasma generation and signal detection are needed. In our proposed setup, critical parameters have been improved. We have utilized a stripline split-ring resonator microwave-induced microplasma source to excite and sustain the plasma. Such a microplasma source offers several advantages over conventional ICOGS plasma sources. For example, the stripline split-ring resonator concept employs separated plasma generation and signal detection, which enables sensitive detection at stable plasma conditions. The concept also permits in situ observation of the discharge conditions, which was found to improve reproducibility. Unique to the stripline split-ring resonator microplasma source in this study, is that the optogalvanic sample cell has been embedded in the device itself. This integration enables improved temperature control and more stable and accurate signal detection. Significant improvements are demonstrated, including reproducibility, signal-to-noise ratio, and precision.

Evaluation of Intracavity Optogalvanic Spectroscopy for Radiocarbon Measurements

Ever since the first publication of intracavity optogalvanic spectroscopy (ICOGS) in 2008, this novel technique for measuring the (14)C/(12)C ratio in carbon dioxide has rendered considerable attention. As a result, there are currently at least five different research groups pursuing research on ICOGS. With a claimed limit of detection of 10(-15) ((14)C/(12)C), i.e., in the same order as accelerator mass spectroscopy, achieved with a relatively inexpensive and uncomplicated table-top system, ICOGS has major scientific and commercial implications. However, during the past 5 years, no research group has been able to reproduce these results or present additional proof for ICOGS's capability of unambiguous (14)C detection, including the authors of the original publication. Starting in 2010, our group has set up a state-of-the-art ICOGS laboratory and has investigated the basic methodology of ICOGS in general and tried to reproduce the reported experiments in particular. We have not been able to reproduce the reported results concerning the optogalvanic signals dependence on (14)C concentration and wavelength and, ultimately, not seen any evidence of the capability of ICOGS to unambiguously detect (14)C at all. Instead, we have found indications that the reported results can be products of measurement uncertainties and mistakes. Furthermore, our results strongly indicate that the reported limit of detection is likely to be overestimated by at least 2 orders of magnitude, based on the results presented in the original publication. Hence, we conclude that the original reports on ICOGS cannot be confirmed and therefore must be in error.

The Radiocarbon Intracavity Optogalvanic Spectroscopy Setup at Uppsala

Accelerator mass spectrometry (AMS) is by far the predominant technology deployed for radiocarbon tracer studies. Applications are widespread from archaeology to biological, environmental, and pharmaceutical sciences. In spite of its excellent performance, AMS is expensive and complicated to operate. Consequently, alternative detection techniques for 14C are of great interest, with the vision of a compact, user-friendly, and inexpensive analytical method. Here, we report on the use of intracavity optogalvanic spectroscopy (ICOGS) for measurements of the 14C/12C ratio. This new detection technique was developed by Murnick et al. (2008). In the infrared (IR) region, CO2 molecules have strong absorption coefficients. The IR-absorption lines are narrow in line width and shifted for different carbon isotopes. These properties can potentially be exploited to detect 14CO2, 13CO2, or 12CO2 molecules unambiguously. In ICOGS, the sample is in the form of CO2 gas, eliminating the graphitization step that h is required in most AMS labs. The status of the ICOGS setup in Uppsala is presented. The system is operational but not yet fully developed. Data are presented for initial results that illustrate the dependence of the optogalvanic signal on various parameters, such as background and plasma-induced changes in the sample gas composition.

The Radiocarbon Intracavity Optogalvanic Spectroscopy Setup at Uppsala

Accelerator mass spectrometry (AMS) is by far the predominant technology deployed for radiocarbon tracer studies. Applications are widespread from archaeology to biological, environmental, and pharmaceutical sciences. In spite of its excellent performance, AMS is expensive and complicated to operate. Consequently, alternative detection techniques for14C are of great interest, with the vision of a compact, user-friendly, and inexpensive analytical method. Here, we report on the use of intracavity optogalvanic spectroscopy (ICOGS) for measurements of the14C/12C ratio. This new detection technique was developed by Murnick et al. (2008). In the infrared (IR) region, CO2molecules have strong absorption coefficients. The IR-absorption lines are narrow in line width and shifted for different carbon isotopes. These properties can potentially be exploited to detect14CO2,13CO2, or12CO2molecules unambiguously. In ICOGS, the sample is in the form of CO2gas, eliminating the graphitization step that h is required in most AMS labs. The status of the ICOGS setup in Uppsala is presented. The system is operational but not yet fully developed. Data are presented for initial results that illustrate the dependence of the optogalvanic signal on various parameters, such as background and plasma-induced changes in the sample gas composition.

14C analysis via intracavity optogalvanic spectroscopy

A new ultra sensitive laser-based analytical technique, intracavity optogalvanic spectroscopy (ICOGS), allowing extremely high sensitivity for detection of 14C-labeled carbon dioxide has recently been demonstrated. Capable of replacing accelerator mass spectrometers (AMS) for many applications, the technique quantifies zeptomoles of 14C 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 14C/ 12C ratios have been obtained with theoretical limits much lower. Using a 15 W 14CO 2 laser, a linear calibration with samples from 5 × 10 −15 to >1.5 × 10 −12 in 14C/ 12C 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. An analytical technique for 14C analysis with subattomole sensitivity.

We show a new ultrasensitive laser-based analytical technique, intracavity optogalvanic spectroscopy, allowing extremely high sensitivity for detection of (14)C-labeled carbon dioxide. Capable of replacing large accelerator mass spectrometers, the technique quantifies attomoles of (14)C in submicrogram 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 are obtained. Using a 15-W (14)CO2 laser, a linear calibration with samples from 10(-15) to >1.5 x 10(-12) in (14)C/(12)C ratios, as determined by accelerator mass spectrometry, is demonstrated. Possible applications include microdosing studies in drug development, individualized subtherapeutic tests of drug metabolism, carbon dating and real time monitoring of atmospheric radiocarbon. The method can also be applied to detection of other trace entities.