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Anal. Chem. 1981, 53, 1138-1 139
LITERATURE CITED (1) Fuwa, K.; Notsu, K.; Tsunoda, K.; Yamamoto, Y.; Okamoto, K.; Doklya, y.; Toda, S. Bull. Chem. SOC. Jpn. 1978, 51, 1078-1082. (2) Dokiya, Y.; Taguchi, M.;Toda, S.;Fuwa, K. Anal. Chem. 1978, 50, 533-536. (3) Okamoto, K.; Yamamoto, Y.; Fuwa, K. Anal. Chem. 1878, 50, 1950-1951. (4) Okamoto, K., Ed. "Preparation, Analysis and Certification of Pepperbush Standard Reference Material"; Research Report No. 18 from the National Institute for Environmental Studies: Ibarakl, Japan, 1980. (5) Certificate of Analysis, River Sediment, SRM 1645, US. Department
of Commerce, National Bureau of Standards, Washington DC, 1978. (6) Ishikawa, K.; Fujlmori, T.; Kume, H. "Jikken Kelkaku-ho"; Tokyo Kagaku Dojln: Tokyo, 1967; p 202. (7) Bowen, H. J. M. "Environmental Chemistry of the Elements"; Academic Press: London, 1979; pp 36, 60. (8) Goldberg, E. D.; Hodge, V.; Koide, M.;Griffin, J. J. Geochem. J . 1876, 10, 165-174.
for review December 8, lggo* Accepted February
26, 1981.
Modification of the Dow-Beckman Carbonaceous Analyzer for Wet Oxidation Kenneth M. Johnson" and John McN. Sleburth Graduate School of Oceanography, University of Rhode Island, Kingston, Rhode Island 0288 1
Older Dow-Beckman carbonaceous analyzers (Beckman Instruments, Fullerton, CA) which analyze microliter volumes of water samples by dry combustion and detect the resultant COZ by infrared photometry are unsuitable for determining low concentrations of dissolved organic carbon (DOC) in fresh and marine waters. For this purpose the wet oxidation method ( I ) using milliliter sample volumes and infrared detection is recommended (2). However, for laboratories equipped with the Dow-Beckman instrument and unable to purchase newer equipment, we can suggest a way to adapt these carbon analyzers to wet oxidation without sacrificing their direct injection capability. The front panel of the ampule analyzing unit (Model 0524B) manufactured by Oceanography International Corp. (College Station, TX) can be frame mounted to the Dow-Beckman carbonaceous analyzer console and the ampule analyzer output interfaced with the Beckman IR-315 or IR-215 as shown in Figure 1. In this way the unit is quickly adapted to the standard persulfate oxidation method for DOC in natural waters (I). The Dow-Beckman instrument used had already been upgraded by replacing the glass combustion tube with a ceramic tube and all other glass components in the combustion train with stainless steel. The original gas connections on the carbonaceous analyzer were removed and the oxygen carrier gas was reconnected to the ampule analyzer and the Dow-Beckman unit with l/s or 1/4 in. hard white Impolene thermoplastic tubing (Imperial Eastman Corp., Chicago, IL) according to the instruction manuals furnished by the manufacturers. The two units were interfaced by installing two three-way brass ball valves (Whitney Co., Oakland, CA). One at the inlet of the IR analyzer allowed us to select either the output of the ampule analyzer or the oxidation furnace. The second valve on the ampule analyzer unit formed an IR bypass line and rerouted the carrier gas through the combustion furnace or alternatively to an ampule sparging unit when the ampule analyzer was not in use. Thus a single tank of oxygen (purified by a heated catalyst, ascarite and silica gel to remove COz,water vapor, and volatile organics as COz)was regulated by the flow meter on the ampule analyzer panel and sufficed for all phases of carbon analysis. The output of the IR-315 was integrated by a CRS-208 Infotronics digital integrator (Columbia Scientific, Houston, TX) and the output displayed on a Bristol Recor4%;@ristol Co., Waterbury, CT). For routine deterl;n'Inhtions,the ampule method requires 10 mL of sample while the direct injection method usually requires only 20 wL. This discrepancy is easily handled. To avoid saturating the IR detector, the unit may be adapted to
Table I. Dissolved Organic Carbon Analysis with the Dow-Beckman Carbonaceous Analyzer Modified for the Menzel-Vaccaro Method (I )" sample replino. cates mg L-l std dev % CV 1 2 3 4 5 6
3 3 3 3 3 3
1.53 1.95 2.10 2.21 2.26 1.89 1.99
+0.047
1-0.028 50.140 rtO.180
1-0.130 k0.060
3.1 1.4 6.7 8.1 5.7 3.2 5.2
means 1-0.11 a All samples were collected in lower Narragansett Bay, RI.
the ampule method where DOC levels of 0.5-5.0 mg L-l (5-50 pg C 10 mL-l) are to be expected by injecting into the furnace 20-pL portions of a 3000 mg L-' DOC standard (60 pg C 20 pL-l) and adjusting the amplifier gain for a meter deflection 95% of full scale. However, the wet and high-temperature oxidations should be standardized independently. A calibration gas mixture of 1000 ppm COz in Nz passed through the cells at the same flow rate as the zero gas (200 mL min-l) was used to monitor and correct amplifier drift. Standards utilizing potassium hydrogen phthalate as a carbon source were made up in both filtered distilled water and artificial seawater. The system was tested on seawater samples obtained from lower Narragansett Bay, RI. The samples were gravity filtered through precombusted Gelman glass fiber filters (Type A/E) and analyzed by persulfate oxidation ( I ) with minor modifications and precautions (3). For the initial six analyses shown in Table I, the average standard deviation was 50.11 mg L-l, which is identical with the precision usually cited for the method, and better by a factor of 10 than the kl.0 mg L-l given by Beckman for the direct injection method. Subsequently, 48 additional DOC analyses have been made on samples from the lower bay. For these data the mean was 1.60 mg L-l, but the average standard deviation decreased to *0.061 mg L-l for a %CV of 3.8%. The latter results compare well with even the newest carbon analyzers. The modification described extends the analytical capability of the Beckman and possibly other high-temperature combustion instruments heretofore considered unsatisfactory for marine samples ( 4 ) . In addition to the required level of precision and sensitivity for determining dissolved organic
0003-2700/61/0353-1138$01.25/00 1981 American Chemical Society
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Anal. Chem. 1981, 53, 1139-1140
is about 10-15% of the purchase price for a new instrument of the same capability without an integrator and somewhat more if an integrator were purchased.
ri
ACKNOWLEDGMENT We wish to thank Alan Fredericks, formerly of Oceanography International Corp., and Edward Milukas of Beckman Instruments for their cooperation and technical advice and Richard Kerr for critically reading the manuscript.
SUPPLY
3- WAY VALVE AT ANALYZER
LITERATURE CITED (1) Menzel, D. W.: Vaccaro, R. F. Limnol. Oceanogr. 1964, 9 , 138-142. (2) van Steenderen, R. A.; Basson, W. D.; van Duuren, F. A. Water Res. 1979, 13, 539-543. (3) Kerr, R. A.; Quinn, J. G. Deep-sea Res. 1975, 22, 107-116. (4) Sharp, J. H. Mar. Chem. 1973, I , 211-229.
I L
Figure 1. Schematic representation showing how the Dow-Beckman carbonaceous analyzer Is interfaced with an ampule analyzing unit and an improved read-out system.
carbon, the determination of particulate organic carbon, sediment carbon, inorganic carbon, and even microbial biomass is also possible. The cost of the modification including the calibration gas arid catalytic furnace for O2 purification
RECEIVED for review February 26, 1981. Accepted April 6, 1981. This work was supported by National Science Foundation Grant No. OCE-74-01537-A02.
Dissolution of Elulk Specimens of Silicon Nitride Warren F. Davis" and Emery J. Merkle Natlonal Aeronautics anid Space Administration, Lewis Research Center, Cleveland, Ohio 44 135
Efforts currently being made to incorporate silicon nitride components into advanced heat engines have emphasized the need for accurate chemical characterization of this ceramic material. Recently research on this material has progressed to fabrication of turbline components. Chemical analysis of bulk specimens is made difficult or impossible because there are no suitable methods for dissolving solid silicon nitride. Grinding procedures result in serious contamination which cannot be compensated by a blank. This contamination is in addition to that contributed by reagents used to effect dissolution. Silicon nitride powder can be dissolved by fusion with 10-15 parts of various alkaline fluxes or by acid mixtures in a Teflon-lined pressure vessel at 150 "C. Parker and Healy (I) used a (1 1)mixture of concentrated hydrofluoric and hydrochloric acids. Feirraro and Strauss (2) used mixtures of hydrofluoric and nitric acid to decompose silicon nitride powder. Particle sizes were minus 44-mesh and minus 160mesh, respectively. Reference 2 mentions that a magnet was passed through the pulverized samples several times to remove iron contaminant picked up from the mortar and pestle. However, none of the above procedures is applicable to bulk silicon nitride. Furthermore, grinding media of steel, tungsten carbide, silicon carbide, or boron nitride are quickly scratched or destroyed due to the diamondlike hardness of silicon nitride. Our results show that up to at least 0.6 g solid pieces of various samples of hot pressed and reaction bonded silicon nitride can be decomposed in a mixture of 3 mL hydrofluoric acid and 1mL nitric acid overnight at 150 "C in a Model 4745 Parr bomb (Parr Instrument Co., Moline, IL). This result is advantageous for determinations of trace elements but seems contrary to what has lbeen reported in the literature. For this reason we further evduated this dissolution procedure using solid materials obtained by a variety of processing methods. Table I lists the types and size of samples which were successfully dissolved or decomposed in the Parr vessel.
+
Table I. Dissolution of Solid Silicon Nitride and Sialon Materials" sample wt , source/description mg Norton NC-132 (Norton Co., Worcester, MA) 147 Norton hot pressed Si,N, 269 Wesgo sintered ball (Western Gold and 462 Platinum Div. GTE, Belmont, CA) A M E Reaction Bonded Si,N, (Advanced 214 Materials Engineering, Ltd., Durham, England ) Reaction bonded Si,N,, vibratory milled 437 Polished Si,N,, wet milled 657 Avco billet 1016, hot pressed Si,N, 145 (Avco Corp., Wilmington, MA) Plessey hot pressed Si,N, 169 (Plessey, Inc., Frenchtown, NJ) Norton NCX-34, Lewis billet 27 217 Norton NCX-34, Lewis billet 28 178 Sialon 8F* 193 Sialon 8SL 192 a All of the Si,N, samples and the two sialon samples were decomposed by using 3 mL of hydrofluoric acid and 1mL of nitric acid in the Parr bomb overnight at 150 'C. Sialon is a generic name for ceramic containing silicon nitride, aluminum nitride, and aluminum oxide,
*
-
High-purity silicon nitride is completely soluble in nitric acid after treatment in the bomb. However, materials of silicon nitride usually contain sintering additives, such as oxides of calcium, magnesium, and yttrium, in addition to impurities introduced by grinding with steel or tungsten carbide prior to consolidation. For these materials, additional sample preparation is necessary. Following decomposition, silicon and hydrofluoric acid are volatilized and insoluble fluorides are converted to a soluble form. Tungsten is kept
This article not subject to US. Copyright. Published 1981 by the American Chemical Soclety
