ANALYTICAL CHEMISTRY, VOL. 04, NO. 7, APRIL 1, 1992 35 7 1.
C0,-
HzO
NASA Tap
0
100
200
300
400
Time in Minutes Flgure 2. Varlatlon wlth tlme of the 6l80 composltlon of CO, equllibrated wlth our laboratory working standard (NASA tap water). Oxygen Isotope exchange equlllbratbn Is complete In about 1.5 h (broken line).
Table I. b * 8 0 Results for Three International Water Standards and Three Laboratory Standards
sample name V-SMOW GISP SLAP
no. of prepa- std dev measd" P O normalizedb P O rations lu, L SMOW, k SMOW, L 5 6
5
International Standards f0.05 +0.04 k0.02 f0.03
0.00
-24.85
-24.83
-55.59
-55.50
Laboratory Standards k0.05 +0.36
GOMS 24 NASAtap 33 k0.02 -6.63 20 f0.05 -41.34 ADAM These data were calculated using the COz-HzO fractionation factor of 1.041 20 recommended by Friedman and @Neil (1977).1° bThesedata were normalized to A(V-SMOW - SLAP) = -55.50%.
831
water sample and facilitates more rapid oxygen isotope exchange. Accuracy and Precision. Data for the oxygen isotope composition of six different water standards using the technique described in this paper are reported in Table I. Our three laboratory s t a n h d s consist of an isotopically light water (ADAM, acronym for average depleted Antarctic meltwater) prepared by filtering a block of Antarctic ice, a water of intermediate isotopic composition (NASA tap, distilled Houston tap water), and a water relatively enriched in P O (GOMS, acronym for Gulf of Mexico sea water, distilled sea water taken from the south shore of Galveston Island, TX). International standards provided by the IAEA, Vienna, that were analyzed include V-SMOW, SLAP, and GISP. On the basis of the number of analyses, reproducibility of all six standards using our technique is generally better than f0.05Lat the 1u level of confidence. Furthermore, the oxygen isotope composition of the international standards V-SMOW, SLAP, and GISP are well within the mean of reported values."
CONCLUSIONS The method described in this paper satisfies the need for a rapid and inexpensive l80/l6O water extraction technique. Since the preevacuated vials are discarded after use, the potential for memory effects during extraction is eliminated. Furthermore, good sample reproducibility makes our method acceptable for routine l80/l6O water extractions. ACKNOWLEDGMENT We thank Dale Schoeller for drawing our attention to the use of preevacuated vials. This research was supported by the NASA Planetary Biology Program. Use of trade names and manufacturers/suppliers in this publication is for de. scriptive purposes only and does not constitute endorsement by Lockheed Engineering and Sciences Co. or NASA. Registry No. lSO, 14797-71-8; water, 7732-18-5.
isotopic ratio results are reported relative to SMOW.S
REFERENCES
RESULTS AND DISCUSSION Equilibration Time. Figure 2 is a plot of P O of our laboratory working standard water (NASA tap) versus time and indicates the time needed to reach isotopic equilibrium between COz and HzO. Seven vials were filled with 1.5 cm3 of NASA tap and 150 pmol of COP These were shaken in a 25 "C water bath for up to 380 min. The P O value at time = 0 is the initial oxygen isotope composition of the injected COz. With increasing time, the P O composition of the C02 approaches an equilibrium value with that of the water in the vial. Data indicate that equilibration is completed in at least 90 min if the vials are placed sideways and shaken. The process of shaking the vials sideways breaks the surface of the
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
Schoeiler, D. J . Nufr. 1988, 778, 1278. Epstein, S.; Mayeda, T. Geochim. C o s m h i m . Acta 1953, 4 , 213. YoshMa, N.; Mizutani, Y. Anal. Chem. 1986, 58, 1273. Roether, W. I n t . J . Appl. Radlet. Isot. 1970, 72, 379. Majzoub, M.; Nief, G. A&. Mass Specfrom. 1968, 4 . 511. Hagemann, R.; Lohez, P. A&. Mass Spectrom. 1978, 7 A , 504. Schoeiier, D. A.; Klein, P. D. Bbmed. Mass Specfrom. 1978, 5 , 29. Ajami, A. M.; Watkins, J. B. Clin. Chem. 1983, 29, 725. Craig, H. Geochlm. Cosmochlm. Acta 1957, 12, 133-149. Friedman, I.; O'Neii, J. R. U.S. Geol. Surv. Prof. Pap. 1977, No. 440-KK. (1 1) Hut, G. R e p H to the Director General, Consultant's Group Meeting on Stable Isotope Reference Standards, Vienna, Sep 16-18, 1985; IAEA: Vienna, 1987; 42 pp.
RECEIVED for review September 30,1991. Accepted January 8,1992.
CORRECTION Enzymatic Flow Injection Analysis in Nonaqueous Media Lorenzo Braco, Josd A. Darbs, Miguel de la Guardia (Anal. Chem. 1992,64, 129-133). On page 129, on the first line under the Experimental Section, the word spiralis should be species.
