1814
Anal. Chem. 1993, 65, 1814-1818
Ozone Gas-Phase Chemiluminescence for Silane and Its Application to the Determination of Silicate in Natural Waters Kitao Fujiwara,' Masayuki Uchida,?Min-min Chen, Yu-ichiro Kumamoto, and Takahiro Kumamarut Faculty of Integrated Arts and Sciences, Hiroshima University, Hiroshima 730, Japan
Chemiluminescence emission generated by mixing silane with ozone was investigated for the determination of silicate in natural water. This chemiluminescence spectra extends 400-850 nm providing a maximum at 600 nm. Chemiluminescence spectra obtained by mixing diborane and ozone were also shown. For the purpose of generating silane from the aqueous solution of silicate, the following procedure was adopted: The sample solution was dried and mixed homogeneously with powdered lithium aluminum hydride in a Teflon tube or a molybdenum boat. When this mixture was heated at 200 OC, 97 f 3% of silicate in the sample was reduced to silane. After the generated silane was collected in the trap, the silane was mixed with ozone, and chemiluminescence was detected directly by a photomultiplier. The calibration curve was linear from l to 500 pg Si, and the detection limit was 0.5 pg of Si for this method. Phosphorus and arsenic give the positive interference, which is, however, negligible for the practical analysis of natural waters. The analytical results for river waters and seawaters (the Tokyo Bay and the North Pacific Ocean) are in good agreement with those confirmed by molybdenum yellow colorimetry. Gas-phase chemiluminescence using ozone as the oxidant gas is one of the most popular methods in environmental analysis.'-3 This method has been first proposed for the measurement of NO, in the a t m ~ s p h e r ewhere , ~ the reaction between ozone and nitrogen monoxide was used. Hills and Zimmerman proposed the application of ozone chemiluminescence technique to determine atmospheric isoprene generated from leaves of the white oak as the byproduct of photosynthesis.5 Simplicity of the method, inexpensive equipment, and capacity of real-time measurement are the merits of using the ozone gas-phase chemiluminescence. Previously,the ozone gas-phasechemiluminescencetechnique was proposed to measure metalloid elements (As, Sb, Sn, and Se).6,7 In this method, these elements in the sample are converted to gas hydrides and mixed with ozone. Generation of gaseous hydride is a well-known technique in atomic t Faculty of Science, Hiroshima University, Higashi-Hiroshima 724, Japan. (1) Chisaka, F.; Yanagihara, S. Anal. Chem. 1982,54, 1015-1017. (2) Takeuchi, K.; Ibusuki, T. Anal. Chem. 1989, 61, 619-623. (3) Kanda, Y.; Taira, Y. Anal. Chem. 1990, 62, 2084-2087. (4) Fontijn, A.; Sabadell, A. J.; Ronco, R. J. Anal. Chem. 1970, 42, 575-579. (5) Hills, A. J.; Zimmerman, P. R. Anal. Chem. 1990,62, 1055-1060. (6) Fujiwara, K.; Watanabe, Y.; Fuwa, K.; Winefordner, J. D. Anal. Chem. 1982, 54, 125-128. (7) Fujiwara, K.; Kuramochi, A.; Tsubota, H. Anal. Sci. 1990,6, 425430.
0003-2700/93/0365-1814$04.00/0
spectrometry for the elements such as As, Ge, Pb, Sb, Se, Sn, and Te where tetrahydroborate is used as the reducing agent. Hydride generation for phosphorus is also possible, but in this case, drying a mixture of the sample and tetrahydroborate is required because the redox potential in the reduction of phosphate to phosphine is lower than that of water to hydr~gen.~,~ Silane (SiH4) itself is poisonous to human health, Le., the American Conference of Governmental Industrial Hygienists has prescribed the safety guide for the concentration of silane in the atmosphere as 5 ppmv. With an increase in the use of silane, accidents have also happened: two students recently died in a silane explosion during an experiment to produce silicon wafers. These facts denote the necessity of an urgent development of a simple and sensitive spectrometric method to detect silane. One possibility is the spectrometric detection of silane by ozone gas-phase chemiluminescence. It has been pointed out that silane gives chemiluminescence on mixing with oz0ne1O-l3 and active nitrogen.14 Besides the importance of the silane detection in the atmosphere, the measurement of silicate ion through the method to generate silane is also important, especially for aqueous samples. The silicate ion is an important chemical species to limit the biomass in natural waters such as seawater and is enumerated as a nutrient along with phosphate and nitrate (+ nitrite). In spite of the importance of measurement, there are very few methods available to measure the silicate ion quantitatively in water samples. As shown in Table I, most of the methods for silicate measurement includingliquidphase chemiluminescence are based on the formation of molybdenum heteropolysilicic acid, which was facilitated by reacting silicate with ammonium molybdate under highly acidic conditions. However, this technique involves several drawbacks such as a large number of interfering species including phosphate and arsenate, a complex chemical procedure, and specific sensitivity, i.e., only sensitive to the orthosilicate ion. AlthoughICP atomic emission spectrometry is effective for measuring all the silicate species in the sample, atomic absorption spectrometry requires the chemical modification of silicate. Otherwise,it cannot be employed because of low sensitivity to silicon. In this paper, a method to determine silicate in natural water by ozone gas-phase chemiluminescence in which (8) Hashimoto, S.; Fujiwara, K.; Fuwa, K. Anal. Chem. 1985,57,13051309. (9) Fujiwara, K.; Kanchi, T.; Tsumura, S.;Kumamaru, T. Anal. Chem. 1989, 61, 2699-2703. (10) Glinski, R. J.; Gole, J. L.; Dixon, D. A. J. Am. Chem. SOC. 1986, -107. - . , 5891-5894. ----
(11) Inoue, K.; Suzuki, M.; Kawabayashi, 0. Ger. Offen. DE1525700 (Cl. GOlN21176) 1986; Chem. Abstr. 1986,104, 155074s. (12) Shirata, K.; Mukai, S.; Miki, S. Jpn. Kokai Tokkyo A [oho JP 61 90044 [8690044] (Cl. G01N21/76) 1986; Chem. Abstr. 1986,106,95:203n. (13) Kugo, T.; Hiromoto, M.; Ueki, H. Jpn. Kokai Tokk,yo Koho JP 01 53137 [89 531371 (CI.GOlN21/76) 1989; Chem. Abstr.. 1989, 111, 2244745. (14) Horie, 0.;Potzinger, P.; Reimann, B. Chem. Phys. Lett. 1986, 129, 231-236. 0 1993 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 65,
Table I. Methods of Silicate Measurement method fluorometry colorimetry
chemiluminescence polarography voltammetry AAS ICP-AES a
reaction
oxidation of thiamine by MHAa formation of MHA blue formation of MHA yellow complexation of MHA and crystal violet complexation of reduced MHA and chromopyrazoleI1 complexation of vanado-MHA and rhodamine B complexation of MHA and malachite green complexation of MHA and ethylrhodamineB oxidation of luminol by MHA formation of MHA sorption of MHA on galssy carbon electrode graphite furnace
NO. 14, JULY 15, 1993 1815
detection range
literature ref
30-600 pg/L 05-10 mg/L 3-100 pg/L 0.1-10 mg/L DL,b 120 pg/L 0.4-10 pg/L DL, 28 rg/L 0.3 pg/L+ DL, 52 pg/L 2.5 pg/L
