Quantitative Analysis of Deuterium Using Laser-Induced Plasma at

Anal. Chem. 2006, 78, 5768-5773

Quantitative Analysis of Deuterium Using Laser-Induced Plasma at Low Pressure of Helium Koo Hendrik Kurniawan,* Tjung Jie Lie, Maria Margaretha Suliyanti, Rinda Hedwig, Marincan Pardede, and Davy Putra Kurniawan

Research Center of Maju Makmur Mandiri Foundation, 40 Srengseng Raya, Kembangan, Jakarta Barat 11630, Indonesia Yoshihumi Kusumoto

Department of Chemistry and Bio-Science, Faculty of Science, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan Kiichiro Kagawa

Department of Physics, Faculty of Education and Regional Studies, 9-1 bunkyo 3-chome, Fukui 910, Japan

It was proved that the analysis of deuterium can be conducted using laser-induced plasma spectroscopy. By selecting the appropriate surrounding gas, its pressure, and gating time of the detection system, it was shown that the emission lines of both hydrogen (Hr) and deuterium (Dr), separated by only 0.179 nm, can be fully resolved. A linear calibration curve was also obtained, indicating that this technique has the potential for quantitative analysis of deuterium. The minimum detection limit achieved in this stage of research was estimated to be 50 ppm. We have also shown that this technique can be used as a simple and rapid method for D and H analysis in solid samples. Recently, laser-induced plasma spectroscopy,1 in particular, laser-induced breakdown spectroscopy (LIBS),2,3 has become a popular analytical tool. For LIBS at atmospheric pressure, a pulsed Nd:YAG laser with a typical energy of several tens of milliJoules is focused onto the surface of the sample, resulting in a plasma with high temperature and electron density. A gated optical multichannel analyzer (OMA) is used to remove the strong background emission emitted from the plasma. The use of LIBS in rapid quantitative analyses has been demonstrated on many elements in various fields such as the following: soil analysis,4-6 * To whom correspondence should be addressed. Tel: 62-21-5867663, 62-215867660. Fax: 62-21-5867670 or 62-21-5809144. E-mail: [email protected], Homepage: http://www.mmm.or.id. (1) Brech, F.; Cross, L. Appl. Spectrosc. 1962, 16, 59. (2) Loree, T. R.; Radziemski, L. J. Plasma Chem. Plasma Process. 1981, 1, 271279. (3) Radziemski, L. J.; Loree, T. R. Plasma Chem. Plasma Process. 1981, 1, 281293. (4) Capitelli, F.; Coloa, F.; Provenzano, M. R.; Fantoni, R.; Brunetti, G.; Senesi, N. Geoderma 2002, 106, 45-62. (5) Bustamante, M. F.; Rinaldi, C. A.; Ferrero, J. C. Spectrochim. Acta 2002, 57B, 303-309. (6) Barbini, R.; Colao, F.; Fantoni, R.; Palucci, A.; Capitelli, F. Appl. Phys. A 1999, 69, S175.

5768 Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

liquid analysis,7-9 art conservation,10 ceramic analysis,11 environmental and industrial applications,12-17 and pharmaceutical products.18-20 Despite this reputation, its application to hydrogen analysis has yet been reported. Due to the use of surrounding gas at atmospheric pressure, the hydrogen emission line obtained invariably suffers from severe pressure broadening21 and strong Stark broadening effects.22,23 We have also previously reported that the diminution of the hydrogen emission intensity is due to a mismatching effect: the lack of synchronization between the (7) Yaroshchyk, P.; Morrison, R. J. S.; Body, D.; Chadwick, B. L. Spectrochim. Acta 2005, 60B, 986-992. (8) Janzen, C.; Fleige, R.; Noll, R.; Schwenke, H.; Lahmann, W.; Knoth, J.; Beaven, P.; Jantzen, E, Oest, A.; Koke, P. Spectrochim. Acta 2005, 60B, 983-1001. (9) Lazic, V.; Colao, F.; Fantoni, R.; Spizzicchino, V. Spectrochim. Acta 2005, 60B, 1002-1013. (10) Anglos, D.; Couris, S.; Fotakis, C. Appl. Spectrosc. 2001, 55, 186A. (11) Kuzuya, M.; Murakami, M.; Maruyama, N. Spectrochim. Acta 2003, 58B, 957-965. (12) Noll, R.; Monch, I.; Klein, O.; Lamott, A. Spectrochim. Acta 2005, 60B, 10701075. (13) Freedman, A.; Iannarilli, F. J.; Wormhoudt, J. C. Spectrochim. Acta 2005, 60B, 1076-1082. (14) Stavropoulos, P.; Michalakon, A.; Skevis, G.; Couris, S. Spectrochim. Acta 2005, 60B, 1092-1097. (15) Caneve, L.; Colao, F.; Sarto, F.; Spizzichino, V.; Vadrucci, M. Spectrochim. Acta 2005, 60B, 1098-1102. (16) Lopez, A. J.; Nicolas, G.; Mateo, M. P.; Pinon, V.; Tobar, M. J.; Ramil, A. Spectrochim. Acta 2005, 60B, 1149-1154. (17) Carmona, M.; Oujja, M.; Rebollar, E.; Romich, H.; Castilejo, M. Spectrochim. Acta 2005, 60B, 1155-1162. (18) St-Onge, L.; Kwong, E.; Sabsabi, M.; Vadas, E. B. Spectrochim. Acta 2002, 57B, 1131-1140. (19) Mowery, M. D.; Sing, R.; Kirsch, J.; Razaghi, A.; Bechard, S.; Reed, R. A. J. Pharm. Biomed. Anal. 2002, 28, 935-943. (20) Boyain-Goitia, A. R.; Beddows, D. C. S.; Griffiths, G. C.; Telle, H. H. Appl. Opt. 2003, 42, 6119-6132. (21) Idris, N.; Kurniawan, K. H.; Lie, T. J.; Pardede, M.; Suyanto, H.; Hedwig, R.; Kobayashi, T.; Kagawa, K.; Maruyama, T. Jpn. J. Appl. Phys. 2004, 43, 7A, 4221-4228. (22) Konjevic, N. Phys. Rep. 1999, 316, 339-401. (23) Zikic, R.; Gigosos, M. A.; Ivkovic, M.; Gonzales, M. A.; Konjevic, N. Spectrochim. Acta 2002, 57B, 987. 10.1021/ac060633h CCC: $33.50

© 2006 American Chemical Society Published on Web 07/12/2006

shock wave generation and the fast movement of hydrogen atoms from the target.24-26 On the other hand, by applying our unique low-pressure plasma, commonly referred to as laser-induced shock wave plasma spectroscopy (LISPS),27,28 we have demonstrated the unequivocal detection of a sharp H (I) 656.2-nm (HR) emission line from metal samples.24,29 This was made possible due to the typical LISPS detection conditionsslow-pressure surrounding gas, which is crucial in overcoming the undesirable broadening effect and the resulting diminution in the intensity of the hydrogen emission. The resulting calibration curve clearly indicates the potential of this technique for quantitative analysis.29 Apart from technical advancement, we feel strongly that the quantitative analysis of hydrogen and deuterium needs to be explored. Deuterium is an isotope of hydrogen, and its peaks of emission spectra shift from the Balmer series of HR, Hβ, and Hγ are only 0.179, 0.133, and 0.119 nm, respectively.30 However, the detection of the deuterium emission spectrum, DR, is substantially more difficult to achieve due to the fact that the hydrogen emission, HR, experiences significant spectral broadening compared to other emission lines of heavy atoms, because of the Stark broadening effect. In this light, once the spectral broadening effect is suppressed, it is expected that the deuterium emission, DR, can also be detected along with the HR emission. In our previous study,31 we have shown that the deuterium emission can be detected along with hydrogen emission using low-pressure plasma in a helium surrounding gas. However, due to the low-resolution OMA system employed in that work, the complete separation of HR and DR was not achieved and a calibration curve could not be obtained. We present in this report further results obtained by extending our previous studies.21,24-26,29,31 The findings herein show that the deuterium and hydrogen emission is strongly dependent on several factors, namely, type of surrounding gas and the gas pressure and gating time of the detection system as well as the type of the sample itself. Finally, the application of our LISPS technique for the detection of deuterium can be considered as a new type of time-integrated dosemeter for neutron irradiation because hydrogen in materials, such as stone and fossil, slowly changes to deuterium by capturing a neutron with a large cross section32 and this remains in the material forever. EXPERIMENTAL PROCEDURE The basic experimental setup used in this study was similar to that used in our previous work.24,26 In this experiment, the (24) Kurniawan, K. H.; Lie, T. J.; Idris, N.; Kobayashi, T.; Maruyama, T.; Suyanto, H.; Kagawa, K.; Tjia, M. O. J. Appl. Phys, 2004, 96, 1301-1309. (25) Idris, N.; Terai, S.; Lie, T. J.; Kurniawan, K. H.; Kobayashi, T.; Maruyama, T.; Kagawa, K. Appl. Spectrosc, 2005, 59, 115-120. (26) Kurniawan, K. H.; Kagawa, K. Appl. Spectrosc. Rev, 2006, 41, 99-130. (27) Kagawa, K.; Ohtani, M.; Yokoi, S.; Nakajima, S. Spectrochim. Acta 1984, 39B, 525-536. (28) Kurniawan, K. H.; Lahna, K.; Lie, T. J.; Kagawa, K.; Tjia, M. O. Appl. Spectrosc. 2001, 55, 92-97. (29) Kurniawan, K. H.; Lie, T. J.; Idris, N.; Kobayashi, T.; Maruyama, T.; Kagawa, K.; Tjia, M. O.; Chumakov, A. N. J. Appl. Phys. 2004, 96, 6859-6861. (30) Herzberg, G. Atomic Spectra and Atomic Structure; Prentice Hall, Inc.: New York, 1937. (31) Idris, N.; Kobayashi, T.; Kurniawan, K. H.; Lie, T. J.; Maruyama, T.; Kagawa, K. Jpn. J. Appl. Phys. 2004, 43, 11A, 7531-7535. (32) Littler, D. J.; Raffle, J. F. An Introduction to Reactor Physics; Pergamon Press: London, 1957.

lasers, a 1064-nm Nd:YAG (Quanta Ray, Lab Series, 450 mJ, 8 ns) was operated in the Q-sw mode at a 10-Hz repetition rate with the laser output energy fixed at 75 mJ by means of a set of filters. The laser beam was focused to a spot size of 120 µm by a lens (f ) 100 mm) through a quartz window onto the sample surface. The shot-to-shot fluctuation of the laser was monitored to be ∼3%. The samples employed in these experiments consisted of a glass slide (the actual hydrogen concentration in the glass slide was not known; however, according to OH- analysis using infrared spectroscopy, the glass slide contained at least 1000 ppm hydrogen), pure copper plate (Rare Metallic, 4N, thickness of 0.4 mm), pure aluminum plate (Rare Metallic, 4N, thickness of 0.5 mm), shell fossil (Macrocephalitidae, Eucycloceras sp., 106 mm, Middle Jurassic (coll. FL) found in Waimena, Papua, Indonesia), a porous alumina usually used in a chemical laboratory (C.C., thickness of 10 mm, 4N), heavy water (Wako, 3N), and distilled water (Wako, 3N). When shell fossil was used as a sample, the fossil was struck into smaller pieces of irregular shape using a hammer. For the purpose of producing the calibration curve, a mixture of heavy water and distilled water was prepared with the ratios of D2O/H2O of 1:20, 2:20, 4:20, 8:20, and 16:20. These five mixtures were poured into different Petri dishes (diameter of 30 mm and height of ∼5 mm). Five porous alumina blocks of 20 mm × 20 mm were prepared. These alumina blocks were submerged in the prepared mixtures for 1 min prior to laser irradiation. In each experiment, the sample was placed in a small, vacuumtight metal chamber measuring 11 cm × 11 cm × 12.5 cm, which could be evacuated with a vacuum pump and filled with a surrounding gas at the desired pressure. The gas used in this experiment was helium gas (purity of 99.999%) and nitrogen gas (purity of 99.999%). The gas flow through the chamber was regulated by a needle valve in the air line and a second valve in the pumping line. The chamber pressure was monitored by means of a digital Pirani meter. Plasma radiation was detected by an OMA system. In this experiment, two OMA systems were used. One OMA system was used for a low-resolution spectrum with wide-wavelength window, and another OMA system was used for a high-resolution spectrum with narrow-wavelength window. The low-resolution OMA system (Princeton Instrument IRY-700) was attached to a monochromator with a focal length of 150 mm and connected to an optical fiber with its entrance placed in front of the observation window of the vacuum chamber. The detector used in this system was a gateable intensified photodiode array with a gating width ranging from 40 ns to 80 ms. The spectral window, covered by the detector, had a width of 80 nm at 500 nm. The detected signals were monitored on a screen. The spectral resolution of the OMA system was 0.4 nm at 500 nm. In the high-resolution OMA system, McPherson model 2061 with 1000-mm focal length, f /8.6 CzernyTurner high-resolution, high-throughput spectrometer, and scanning monochromator with Andor I*Star intensified CCD 1024 × 256 pixels, 26-µm-square (960 × 256 active pixels) fiber was coupled to high-resolution, 25-mm grade 1 Gen 2 intensifier with built-in digital delay generator. The spectral window, covered by the detector had a width of 20 nm at 500 nm. The detected signals were monitored on a screen. The spectral resolution of the OMA system is 0.01 nm at 500 nm, accuracy of 0.05 nm and reproducibility of 0.005 nm for grating of 1200 grooves/mm. Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

5769

Figure 1. Hydrogen spectrum taken from glass slide under helium gas pressure of 5 Torr. The laser energy was kept constant at 75 mJ. This spectrum was taken by using low-resolution OMA system. The gate delay and gate width was set at 200 ns and 50 µs, respectively.

EXPERIMENTAL RESULTS As reported in our previous work,33 the use of helium as the surrounding gas yielded a low background spectrum with high S/B ratio. This indicates that, for helium plasma, the density of electrons and ions is much lower than air. To simultaneously detect HR and DR, it is crucial that the spectral width of hydrogen, which is normally widened due to the Stark broadening effect, is made as narrow as possible.22,23 It was naturally assumed that, by reducing the number of electrons and ions in the plasma, the Stark broadening could be significantly suppressed. Therefore, in this study, helium gas was used as a surrounding gas. Figure 1 showed a hydrogen spectrum taken from a glass slide under helium gas pressure of 5 Torr. The laser energy was kept constant at 75 mJ. It is seen that strong emission of hydrogen with narrow spectral width could be easily obtained. This spectrum was taken using a low-resolution OMA system using a gating time of 200 ns. A similar spectrum was observed when we used a porous fossil in place of the glass slide because the fossil also contains a considerable amount of hydrogen, which is trapped in the form of water during the sedimentation process. The optimal conditions for the detection of hydrogen were explored using a glass slide sample. Figure 2 shows the emission intensity (a) and full width of half-maximum (fwhm) (b) of H I 656.2 nm as a function of gating time in helium gas of 5, 25, and 760 Torr. The result obtained in helium of lower pressure (1 Torr) is not included in the figure as the emission intensity was greatly reduced due to ineffective formation of shock wave plasma. It can be seen that the emission intensity of H I 656.2 nm at a helium pressure of 5 Torr decreases with increasing gating time (until 10 µs), and it was barely detected at 15 µs. A similar pattern of hydrogen emission intensity was also observed in helium at 25 Torr. However, the emission intensity was slightly lower than that observed in helium at 5 Torr. Meanwhile, the fwhm of H I 656.2 nm in helium of 5 Torr slowly decreases with increasing gating time and remains constant after 10 µs, a pattern shared also by that observed in helium at 25 Torr, only with slightly higher fwhm values. This work also demonstrates that an increase in the (33) Kurniawan, K. H.; Suyanto, H.; Kagawa, K, Maruyama, T.; Tjia, M. O. Jpn. J. Appl. Phys. 2001, 40, 188-194.

5770 Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

Figure 2. Emission intensity (a) and fwhm (b) of H I 656.2 nm emission as a function of gating time at helium gas pressures of 5, 25, and 760 Torr in a glass slide sample. High-resolution OMA system was used in this experiment, and the gate width was fixed at 50 µs.

surrounding gas pressure causes a decrease in the hydrogen peak emission intensity and a broadening of the fwhm. Furthermore, the data plotted in Figure 2a and b for helium at 1 atm (760 Torr) showed that the hydrogen emission intensity was extremely low and the spectral width was wider than 1.5 Å. This means that the simultaneous detection of HR and DR, which are separated by only 1.8 Å, cannot be carried out using standard LIBS techniques. Similar experiments were carried out using nitrogen as a surrounding gas to reconfirm the preference of helium, and the results are presented in Figure 3a for the hydrogen peak emission intensity and in (b) for the fwhm of H I 656.2 nm emission. The data were taken at the surrounding nitrogen pressures of 1, 5, and 760 Torr, which show lower intensities than those obtained in helium gas pressures of 5, 25, and 760 Torr. This was done in consideration of the influence of different gas densities as shown in Sedov’s equation35 and is incidentally similar to that used in our laser-induced shock wave plasma experiment.36 As shown in Figure 3a, the peak emission intensity of H I 656.2 nm is slightly lower than for helium in Figure 2a. It can also be seen that the hydrogen emission intensity in 5 Torr nitrogen generally shares a pattern similar to that observed in 25 Torr helium. Meanwhile, for nitrogen at 1 Torr, the peak emission intensity of hydrogen (34) Suliyanti, M. M.; Sardy, S.; Kusnowo, A.; Pardede, M.; Hedwig, R.; Kurniawan, K. H.; Lie, T. J.; Kurniawan, D. P.; Kagawa, K. J. Appl. Phys. 2005, 98, 093307 1-8. (35) Sedov, L. I. Similarity and Dimensional Methods in Mechanics; Academic Press: New York, 1959; p 213. (36) Kurniawan, K. H.; Kobayashi, T.; Kagawa, K. Appl. Spectrosc. 1992, 46, 581-586.

Figure 4. Fully resolved HR and DR spectrum. Pure heavy water was painted on the surface of the fossil sample. This spectrum was taken under helium gas at 5 Torr. High-resolution OMA system was used, and the gate delay and gate width of the OMA system was set at 15 and 50 µs, respectively.

Figure 3. Emission intensity (a) and fwhm (b) of H I 656.2 nm emission as a function of gating time at nitrogen gas pressures of 1, 5, and 760 Torr in a glass slide sample. High-resolution OMA system was used in this experiment, and the gate width was fixed at 50 µs.

drastically decreases with increasing gating time, which does not show commonality with the results obtained in helium at 5 Torr as given in Figure 2a. Although the fwhm of hydrogen emission in nitrogen is only slightly wider as compared to that observed in helium, the surrounding gas which results in the smallest fwhm is highly preferred due to the minute wavelength separation between HR and DR. It must also be noted that, for nitrogen at 1 atm (760 Torr), which is the standard condition for LIBS, the hydrogen emission is extremely weak with an fwhm of ∼4 Å, even at gating time of 5 µs. This further reinforces our earlier point, that LIBS cannot be used for the simultaneous detection of HR and DR. Based on the results presented in Figure 2 and Figure 3, the optimal condition for the simultaneous detection of HR and DR is achieved in helium gas at 5 Torr with gating time of 5 µs. Under this condition, a narrow and sharp emission of HR (low fwhm) can be obtained with sufficient peak emission intensity. We believe that the simultaneous detection of HR and DR in metals is a pressing concern, especially in nuclear power plants. Therefore, it is also important to prove whether the optimal condition for detection of HR and DR in a glass slide can be applied to metal samples. For this purpose, the same experiment was carried out using pure copper and pure aluminum samples. It is understood that metallic surfaces are covered by water molecules under ordinary conditions. In fact, we have previously demonstrated that the behavior of the hydrogen emission from surface water in metal was similar to that of hydrogen trapped as an impurity in the metal.24 The H emission characteristics of surface water in pure copper and aluminum were also examined in terms of its peak emission intensity and fwhm as functions of gating time. The results show that both profiles for the peak intensity

and fwhm of hydrogen emission in metallic samples are similar to those obtained in the glass slide (Figure 2). Therefore, we conclude that the optimal condition for the simultaneous detection of HR and DR in metallic samples is similar to that found for the glass slide (Figure 2), namely, in helium gas at 5 Torr with a gating time of 5 µs. The possibility of quantitative analysis was explored by the use of samples containing varying concentrations of H and D. Unfortunately, finding a reliable, standard commercial sample containing known concentrations of H and D was not feasible. To solve this problem, we used a rather interesting technique in which the liquid sample was adsorbed by porous solid samples such as porous alumina and porous fossil. As a control, we carried out experiments on alumina and fossil using conditions adopted for the results displayed in Figures 2 and 3. Again, we observe that the general pattern of the emission intensity of H I 656.2 nm in porous alumina and porous fossil is similar to that obtained in the glass slide presented in Figure 2a. Meanwhile, the fwhm of H I 656.2 nm emission from fossils is slightly narrower than those detected from the alumina and the glass slide. Therefore, it should be technically possible to obtain a fully resolved spectrum of HR and DR using a fossil sample. To demonstrate this, pure heavy water was painted on the surface of the fossil. Figure 4 shows the spectrum of fully resolved HR and DR emission lines. This spectrum was taken in helium gas at 5 Torr. In this experiment, the gate delay and gate width of the OMA system were set at 15 µs in order to obtain the narrower spectral width of the H and D emission lines, which remain clearly observable in this case. Unfortunately, we could not use this fossil to produce a calibration curve because of the uneven sample surface. Therefore, porous alumina was used and the alumina was submerged for ∼1 min in the liquid containing different proportions of water and heavy water prior to laser irradiation. Figure 5 shows the HR and DR emission spectrum obtained in helium gas at 5 Torr with D2O/ H2O ratios of (a) 0.2, (b) 0.4, and (c) 0.8. The gate delay and gate Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

5771

Figure 6. Resulting calibration curve for deuterium. Each data point on the curve for any specific concentration was the mean result of three consecutive measurements.

Figure 5. HR and DR spectra using a mixture of heavy water and water painted on the surface of porous alumina sample with ratios of (a) D2O/H2O at 0.2, (b) D2O/H2O at 0.4, and (c) D2O/H2O at 0.8. The gate delay and gate width of the high-resolution OMA system was set at 5 and 50 µs, respectively. The helium gas pressure was kept constant at 5 Torr.

width of the OMA system were set at 5 and 50 µs, respectively. It should be noted that the intrinsic amount of hydrogen in the alumina was ignored, as it is insignificant compared to that in the mixed liquid used for this experiment. Figure 6 shows the 5772 Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

resulting calibration curve. Each data point on the curve for any specific concentration was the mean result of three consecutive measurements. The fluctuation of the observed value is less than 5%. The curve displays a consistent monotonic and linear relationship between deuterium emission intensity and deuterium concentration with a zero y-axis intercept, although the number of data are insufficient for statistical treatment. It should be stressed that simultaneous detection of HR and DR presented in this study is rather rudimentary in nature. Nevertheless, the result is quite significant, as the experiment was carried out using a single laser source. This is an improvement over our previous work37 in which we reported the complete spectral separation of H and D as gaseous sample utilizing helium plasma, where the helium metastable state plays a vital role in the excitation process of deuterium and hydrogen. However, its extension to solid sample analysis required the use of a two-laser system: one for the ablation process, another for producing the helium metastable state.38 This configuration is both complicated and costly. The detection limit at this stage of research was estimated to be ∼50 ppm. Figure 7 displays the spectrum obtained from a D2O/ H2O mixture with a ratio of 1:100, where the DR peak can be clearly distinguished. On the other hand, spectra obtained using high-purity water only did not register this peak, implying that the DR peak in this figure is not due to elemental impurities in the sample. One may further add that this DRemission was detected at very low intensity, perhaps close to the system detection limit, and hence vulnerable to instrumental or other disturbances including the nearby HR emission. It is indeed not unlikely that the DR line gets a bit pushed aside by the tail of the strong superposing HR line. The amount of liquid mixture was estimated to be ∼5% in weight against the total sample, according to the amount and the volume of the water absorption region in the porous alumina. It can hence be concluded that the detected DR emission in Figure 7 corresponds to a concentration of (1/100) × 5%, or 500 ppm. By enlarging the spectrum obtained in Figure 7 and by assuming that the minimum detectable signal should be at least three times the noise level, it can be further (37) Kurniawan, K. H.; Lie, T. J.; Suliyanti, M. M.; Hedwig, R.; Abdulmajid, S. N.; Pardede, M.; Idris, N.; Kobayashi, T.; Kusumoto, Y.; Kagawa, K.; Tjia, M. O. J. Appl. Phys. 2005, 98, 093302 1-3. (38) Pardede, M.; Kurniawan, K. H.; Lie, T. J.; Hedwig, R.; Idris, N.; Kobayashi, T.; Maruyama, T.; Lee, Y. I.; Kagawa, K.; Tjia, M. O. J. Appl. Phys. 2005, 98, 043105 1-5.

CONCLUSION

Figure 7. HR and DR spectrum using a mixture of heavy water and water painted on the surface of porous alumina sample with the ratio of D2O/H2O at 0.01. The gate delay and gate width of the highresolution OMA system was set at 15 and 50 µs, respectively. The helium gas pressure was kept constant at 5 Torr.

concluded that the minimum detectable DR concentration is ∼50 ppm. It is believed that further improvement of this technique will lead to the possible detection of deuterium in natural water, which has the ratio of 1:6700.

It is demonstrated that simultaneous detection of deuterium and hydrogen in solid samples using a laser-induced plasma method can be carried out by using ambient helium gas at low pressure. By selecting the proper gating time of ∼5 µs, a fully resolved HR and DR spectrum can be obtained. The resulting linear calibration curve with a zero intercept indicates the possibility for quantitative analysis of deuterium. An interesting spin-off of this new technique is its possible application in the field of archaeology for detecting the age of a fossil as hydrogen in fossils is slowly converted into deuterium by capturing weak natural neutron irradiation with a large cross section, and this remains in the fossil forever. Therefore, by measuring the D/H ratio, the age of the fossil can be estimated with some degree of certainty.

Received for review April 6, 2006. Accepted June 15, 2006. AC060633H

Analytical Chemistry, Vol. 78, No. 16, August 15, 2006

5773