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ANALYTICAL CHEMISTRY, VOL. 50, NO. 8, JULY 1978
Parametric Study of Exploding Wire Continuum Radiation Peter Thomas and Richard D. Sacks" Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48 109
Spectral radlant lntenslty of the contlnuum radlatlon produced by wires exploded by capacitive dlscharge was measured In the wavelength range from 250 to 340 nm. For all condltlons tested, lntenslty increases wlth decreasing wavelength.. Spectra were obtained from Cu, Ag, Au, W, and chrome1 wlres wlth 0.051-mm dlameter, Au wires produclng the greatest contlnuum lntenslty. Exploslons were conducted under water and In Ar, He, and air at atmospherlc pressure wlth Ar produclng the greatest lntenslty. The continuum lntenslty Increases rapldly wlth Increasing Ar pressure from 500 to I 0 0 0 Torr and wlth Increasing energy from 46 to 184 J. The peak Intensity under these condltlons of about 2200 W/sr-nm at 250 nm compares very favorably with flashlamps. Explosion reproduclblllty Is best In Ar wlth relatlve standard devlations typlcally less than f5 %. Hlgh continuum lntenslty appears to result from lnertlal confinement of the discharge current channel. Current density and peak brightness temperature are greater than values reported In most flashlamp studles.
A number of techniques of analytical interest including atomic fluorescence, flash photolysis, and laser pumping require intense radiation sources for their implementation. Continuum sources are attractive because of their wide wavelength coverage. In many cases, CW continuum sources are not sufficiently intense. Pulsed sources, such as tunable lasers and flashlamps often have adequate intensity in the visible region but are inadequate in the ultraviolet region. This is quite significant in atomic fluorescence, since many elements have resonance lines at wavelengths less than 300 nm. Since preliminary studies ( I ) indicate that the ultraviolet continuum intensity from exploding wires may be considerably greater than that obtained from flashlamps operated at comparable energy, a number of analytically significant applications is suggested. Oster and Marcus (2,3) used exploding Nichrome wires for flash photolysis. They suggest that the absence of an envelope may make exploding wires more useful than flashlamps in the far ultraviolet region. Marcus ( 4 ) notes that exploding wires may be more useful than flashlamps in photochemical applications because of higher spectral output in the vacuum ultraviolet as well as greater stability and reproducibility. Brinkman and Sacks ( I ) used the intense continuum radiation from exploding Chrome1 A wires to excite atomic fluorescence of Co, Cd, and Mn in an Ar-sheathed, nitrous oxide-acetylene flame. They claim that continuum intensity is reproducible to within k5% and that the intensity is three to five orders of magnitude greater than a 1600-W CW Xe arc lamp in the wavelength region between 220 and 400 nm. Stevenson et al. (5) used exploding wire continuum radiation as a pump source for high-power, pulsed lasers. They reported continuum intensity in the ultraviolet and visible region that was typically an order of magnitude greater than that obtained from Xe flashlamps operated at the same energy. Peak laser power from ruby and CaF2:U3+was at least a factor of two greater with an exploding wire pump source relative to flashlamp pumping. Church et al. (6) described experiments using Cu, W, and Nichrome wires as a pump source for a ruby
laser. Jones and Ali (7) discussed using exploding wires for pumping Na vapor for lasing a t 372 A. Ali (8) suggests that exploding wires should be useful for laser pumping a t wavelengths below 1000 A. While Brinkman and Sacks ( I ) have shown that the continuum intensity in the ultraviolet region increases nearly linearly with increasing explosion energy and, in addition, increases with increasing pressure for explosions conducted in Ar atmosphere, no detailed parametric study of the continuum radiation from wire explosions could be found in the literature. The present study attempts to delineate the effects of wire material and diameter, explosion energy and surrounding gas pressure and composition on continuum intensity, spectral distribution in the ultraviolet region, and explosion reproducibility.
EXPERIMENTAL Apparatus. The capacitive discharge circuit and its associated triggering electronics have been discussed in detail (9). The discharge tank circuit used 7.5 pF of capacitance and 2.8 pH inductance for all experiments. This resulted in an underdamped circuit with a ringing frequency of 33.3 kHz. Explosions were conducted in a 14.5-cm long by 12.5-cm i.d. cast acrylic chamber. A 1.0-cm thick chamber wall was necessary to withstand the intense hydrodynamic shock wave generated from high-energy,underwater explosions. The chamber was sealed with an O-ring to a 1.7-cm thick acrylic plastic top plate and glued to a similar bottom plate. A vacuum line connection and water drain is provided in the bottom plate. Cylindrical brass electrodes (12-mm diameter) were sealed in the chamber wall about 7 cm from the bottom plate. The wire is mounted in a cassette made of two conical, brass electrodes, which are held 6.8 cm apart by a U-shaped piece of polycarbonate plastic. The cassette rests on the cylindrical electrodes, which provide electrical connection to the discharge circuit. The 6.8-cm long wire segment is oriented perpendicular to both the chamber axis and the optical axis. Radiation is viewed through a 6.4-cm diameter, 6-mm thick quartz window mounted on the side of the chamber. Optical Monitoring. All spectra were recorded on Kodak SA1 plates using a 1.0-m Czerny-Turner spectrograph (Jarrell-Ash Model 78-460) with a 100-pm entrance slit and a first-order linear reciprocal dispersion of 0.8 nm/mm. The wire segment was located 28 cm from the spectrograph entrance slit. No focusing optics were employed, and the spectrograph viewed the entire plasma volume. The computerized emulsion calibration and optical density-to-intensity conversion procedures are discussed in Reference 10. The emulsion was calibrated at 10-nm intervals using an exploding wire as a calibration source. Optical densities were measured on a Joyce-Loebl Mark IIIB recording microdensitometer. Absolute Intensity Measurement. This was accomplished by comparing the intensity of a standard lamp with known intensity and spectral distribution with the intensity obtained from wire explosions under similar measurement conditions. A spectrum of a quartz tungsten-iodine lamp (General Electric, 6.6A/TAlCL) operated at 6.5 A as in Stair et al. (11) was recorded on an SA1 plate over the wavelength region of interest (250-340 nm). The standard lamp intensity was too low to obtain reliable measurements at wavelengths less than about 250 nm. In addition, 90 nm was about the maximum coverage which could be obtained with a single exposure. The lamp was positioned on the optical axis at the point normally occupied by the wire. Independent measurements of exploding-wire plasmas indicated that the
0003-2700/78/0350-1084$01.00/00 1978 Amerlcan Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 8, JULY 1978
Table I. Physical Properties of Wire Materials Boiling Diameter, Mass, Energy to mm Metal point, K mg vaporize, J 0.130 6.91 21 -0 2485 Ag 0.080 2.74 8.3 2485 Ag 0.051 2.03 4.1 Au 2933 0.51 0.025 1.0 2933 Au 5.93 0.130 36.8 2868 cu 2.35 14.6 0.080 2868 cu 5.04 0.080 25.8 6273 W 2.19 Chrome1 0.080 2800 17.5 plasma diameter at the time of peak intensity is very similar to the diameter of the standard lamp. Thus, direct intensity comparisons could be made without a solid angle correction. However, since some variation in plasma diameter is expected with changing experimental conditions, absolute intensity measurements reported here should be regarded as only semiquantitative. The measured intensity of the standard lamp was obtained from the spectrum at 10-nm intervals. From the known intensity distribution of the lamp, relative correction factors were obtained at these wavelengths, which take into account the wavelength dependence of the emulsion sensitivity as well as the spectrograph efficiency. These relative correction factors were converted to absolute values by a single measurement at 340 nm of the lamp intensity and the peak intensity from a wire explosion. These intensities were measured with a 1P28 photomultiplier tube biased at -900 V and using a l-kR load resistor. The peak exploding wire intensity was obtained from an oscilloscope display of the photomultiplier output. Since the exploding-wire continuum intensity at 340 nm is nearly five orders of magnitude greater than the standard lamp intensity, the linearity of the photomultiplier tube was evaluated independently over this intensity range. The tube was found to be linear to within &5%. Photographically obtained exploding-wireintensities represent values integrated over the duration of the explosion. However, photoelectric time-resolved spectra obtained under a variety of experimental conditions showed that the ratio of peak intensity to integrated intensity was constant to within h3%. Thus, peak intensities could be computed reliably from the photographic spectra. Since the range of observed intensity values exceeded the emulsion latitude, all spectra were recorded through a two-step neutral density filter, which has an absorbing step optical density of 0.63. Wire Materials and Properties. Exploding-wirespectra were obtained for the wire materials and diameters listed in Table I. Tungsten was included to determine the effect of a highly refractory wire material. Two sizes each of Ag, Au, and Cu were used so that the effect of wire mass and vaporization energy would be ascertained. Vaporization energies were computed assuming thermodynamically reversible vaporization processes. This may not be valid for fast wire explosions (12).
RESULTS AND DISCUSSION Two distinct explosion mechanisms have been described (13). If the voltage remaining on the capacitor bank following vaporization of the wire is sufficient to obtain dielectric breakdown of the surrounding gas, a plasma sheath develops in the gas surrounding the cylinder of metal vapor. The discharge current then transfers, uninterrupted, from the wire material to the surrounding plasma sheath. This type of explosion, with plasma current conduction along the periphery of the metal vapor cloud, results in strong line emission from the wire material with relatively low intensity continuum background, Peripheral explosions are favored by high residual capacitor voltage following vaporization as well as a low dielectric strength medium surrounding the wire. If the residual capacitor voltage following vaporization is insufficient to obtain dielectric breakdown of the surrounding medium, t h e discharge can continue only by dielectric breakdown of the metal vapor. This type of explosion with
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Flgure 1. Microdensitometer trace of the spectrum from a 0.051-mm diameter Au wire exploded under water uslng a 5-kV, 94-J capacitive discharge
0 Wovolenqth, nm
Flgure 2. Spectral radiant intensity vs. wavelength plots for several wire materlals and sizes exploded in Ar at 730 Torr with a 5-kV, 94-J capacitive discharge. (A) 0.051-mm dlameter Au; (B) 0.080-mm diameter Chromel-A; (C) 0.080-mm diameter W; (D) 0.080-mm dlameter Ag; (E) 0.025-mm diameter Au; (F) 0.13-mm dlameter Ag
current conduction following vaporization along the axis of the metal vapor cylinder, is characterized by lower intensity line emission and much greater continuum intensity. Axial explosions are favored by low capacitor voltage and a high dielectric strength surrounding medium. Experiments were designed to emphasize axial explosions. Because of its high dielectric strength as well as high density, deionized water should be an excellent explosion medium. Figure 1shows a microdensitometer trace of the spectrum of a 0.051-mm diameter Au wire exploded under water using a 5-kV, 94-5 capacitive discharge. The spectrum is dominated by intense continuum radiation over the entire measured wavelength range as well as a number of relatively intense and very broad emission lines. The strongly self reversed Au(1) neutral-atom resonance line a t 267.6 nm is characteristic of axial-type explosions of most wire materials. Wire Material and Size. Figure 2 shows plots of spectral radiant intensity as functions of wavelength for six different wire material and size combinations. All explosions were conducted in dry Ar at 730 Torr (atmospheric pressure) using a 5-kV, 94-5 discharge. Each point in Figure 2 and in all subsequent figures represents the average intensity from five explosions conducted under the same conditions. While spectra were obtained for 0.13- and 0.080-mm diameter Cu wires, presentation clarity favored their omission from Figure 2. In all cases, spectral radiant intensity increases slowly with decreasing wavelength in the range from 340 to 280 nm. Below 280 nm, the intensity increases quite rapidly with decreasing wavelength. In general, the effect of wire size for a given material confirms the results reported by Sacks and Holcombe (13) and Brinkman and Sacks ( I ) . That is, decreasing wire size results in increasing intensity over the entire measured
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Figure 3. Spectral radiant intensity vs. wavelength plots for 0.051-mm
diameter Au wires exploded in Ar, air, He, and under water using a 7-kV, 184-J discharge
wavelength range. This trend, however, is reversed when very thin wires are exploded. For example, 0.051-mm diameter Au wires produced considerably greater continuum intensity than 0.025-mm Au wires. An explanation for these trends is not straightforward since changing the wire diameter changes a number of explosion properties, which may affect continuum intensity. These include the available energy per atom following vaporization, the strength of the shock wave caused by the rapid expansion of the metal vapor, and the efficiency of the electrical coupling of the wire and the discharge tank circuit. However, it does appear that once the wire mass falls below a certain value, the decrease in the total number of radiating particles becomes the dominant factor in reducing the spectral radiant intensity. It is interesting to note that the shape of the plots in Figure 2 shows relatively little dependence on the wire size or material. While the wire material has a significant effect on continuum intensity, attempts a t correlating the intensity with the bulk wire properties such as heat of vaporization, ionization potential, and atomic weight were unsuccessful. However, all further parametric studies utilized 0.051-mm diameter Au wires, since they produced the most intense radiation. Medium Composition and Pressure. The density and dielectric strength of the medium surrounding the wire profoundly affect the continuum intensity in two ways. First, the dielectric strength of the medium together with the voltage remaining on the capacitor bank following vaporization of the wire determines whether the plasma restrike occurs through the surrounding medium or through the metal vapor. Second, the density of the medium controls the rate of metal vapor expansion, and this, in turn, controls the current density when plasma restrike occurs through the metal vapor. Figure 3 shows spectral radiant intensity plots for 0.051-mm diameter Au wires exploded in Ar, He, air, and under water. All explosions were conducted using a 7-kV, 184-5 discharge. The underwater explosions were all conducted at a depth of 5.0 cm to maintain a constant hydrostatic pressure. All gases were employed a t 730 Torr. The continuum intensity is considerably greater in Ar than in the other gases. Initially, it was expected that water would provide an ideal explosion medium because of its high dielectric strength and high density. The reasons for the relatively poor performance of water are not completely clear. However, considerable turbulence caused by the strong shock wave generated by the initial wire vaporization may result in refraction and scattering of the radiation. In addition, a 100to 200-ws delay period between vaporization and axial restrike was observed with underwater explosions. During this period, considerable cooling of the vapor will occur, and, in addition, an inward moving secondary shock wave (14) may sweep the contents of the vapor cylinder into a thin, very high density
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Figure 4. Spectral radiant intensity vs. pressure plots for 0.051-mm diameter Au wires exploded in Ar and He using a 7-kV, 1844 discharge
and optically thick hollow shell (snowplow effect). Either of these effects could result in considerable diminution of continuum intensity. In the three gases, the radiation intensity is ordered in the same way as gas density. This strongly suggests that inertial confinement and its attendant effect on plasma volume and current density is the dominant influence of the surrounding gas with axial restrike plasmas. Figure 4 shows plots of spectral radiant intensity as functions of pressure a t three selected wavelengths for explosions conducted in Ar and He. All explosions were obtained at 7 kV and 184 J. In Ar, intensity increases considerably with increasing pressure up to about 1000 Torr and shows relatively little change at higher pressures. In He, the increase in intensity with increasing pressure is nearly linear over the entire pressure range. This difference in behavior of Ar and He is consistent with the much lower density of He, again assuming an inertial confinement model for axial restrike plasmas. I t is interesting to note that the relative increase in intensity with increasing pressure is quite independent of wavelength. Since the increase in intensity in Ar at pressures greater than 730 Torr was not considered significant relative to the increased experimental difficulties, all further studies were conducted in Ar a t atmospheric pressure. Explosion Energy. A series of 0.051-mm diameter Au wires was exploded in Ar at 730 Torr using five capacitor energies ranging from 46 to 184 J. I t should be noted that the 4.1 J required to vaporize these wires represents nearly 10% of the 46 J of total available energy used in the lowest energy explosions. The explosion energy was varied by changing the tank circuit voltage rather than its capacitance in order to maintain a constant ringing frequency. This was necessary to ensure a constant ratio of peak to integrated radiation intensity. Figure 5 shows plots of intensity as functions of explosion energy a t three selected wavelengths. While the intensity
ANALYTICAL CHEMISTRY, VOL. 50, NO. 8, JULY 1978
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Figure 5. Spectral radiant intensity vs. energy plots for 0.051-mm diameter Au wires exploded in Ar at 730 Torr
Table 11. Percent Relative Standard Deviations for Exploding-Wire Continuum Intensity % Rel. std. dev. Energy, 250-290 300-340 Atmosphere J nm nm Underwater 46 6.5 15.0 60 21.8 15.5 94 17.7 26.2 135 11.9 15.5 184 38.1 23.9 He, 730 Torr 46 7.5 3.9 60 6.5 7.6 14.3 10.3 94 135 8.7 12.3 184 3.8 12.8 Air, 730 Torr 46 4.0 4.5 60 5.2 11.6 94 6.1 7.2 135 5.0 6.4 184 8.0 8.0 Ar, 730 Torr 46 2.9 4.3 60 3.6 3.9 94 3.7 3.7 135 2.4 6.2 184 2.2 2.9 increases rapidly with increasing energy a t all three wavelengths, there is indication of a leveling off at high energies a t 260 and 320 nm. Somewhat higher intensities, however, should be attainable at energies greater than the 184 J employed here. The peak intensity of 2200 W/sr-nm at 250 nm for the 184-5 explosion (not shown in Figure 5) is quite remarkable and compares favorably with flashlamps operated a t considerably greater energy ( 1 5 ) . Explosion Reproducibility. In many potential analytical applications, intensity reproducibility may be of greater concern than extremely high intensity. Reproducibility studies based on the relative standard deviations from five explosions were conducted using 0.051-mm diameter Au wires exploded a t atmospheric pressure in Ar, air, and He and under water using five values of explosion energy. The results are summarized in Table 11. While measurements were made at 10-nm intervals from 250 to 340 nm, relative standard deviations were pooled for the 250- to 290-nm region and for the 300- to 340-nm region. Underwater explosions were by far the least reproducible. Again, this suggests that shock-wave induced turbulence may be a dominant factor. While the reproducibility of He explosions was considerably better than the underwater explosions, Ar, in general, was far superior. In fact, the relative standard deviations obtained in Ar, which usually are less than &5%, approach the limits imposed by photometric measurements on photographic emulsions. It is fortuitous that Ar explosions produce both the most intense continuum radiation and the lowest relative standard deviations. The
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Figure 6. Peak brightness temperature vs. wavelength plots for 0.051-mm diameter Au wires exploded in Ar at 730 Torr using various discharge energies
values for Ar in Table I1 are somewhat better than typical values reported for flashlamps. COMPARISON WITH FLASHLAMPS High intensity flashlamps generally operate in a wallstabilized mode. That is, the lamp is designed so that the current channel fills the lamp, and thus the discharge current together with the cross sectional area of the lamp determines the current density. Current density appears to be the most significant parameter in controlling peak intensity. Filler gas, pressure, and lamp current are relatively less important (15). Emmett and Schawlow (16) have shown that in the wavelength range from 300 to 550 nm, continuum intensity increases linearly with current density in the range from 0.8 X lo4 to 3 X lo4 A/cm2 for a commercial Xe flashlamp. Maximum current density and rise time in flashlamps are limited by the destructive action of the shock wave formed by the discharge. If the shock wave is too strong, catastrophic lamp failure will occur. In addition, ablation of wall material and the formation of color centers result in a gradual deterioration of the lamp with an attendant change in peak intensity. The radiative properties of exploding wires are similar to those of flashlamps and appear to be governed by the same processes and mechanisms. In an axial restrike explosion, the periphery of the expanding metal-vapor cylinder confines the current channel and determines the current density. However, there is no fragile wall present to limit either peak current density or rise time. In addition, there is no long term stability problem. Time resolved streaking photographs of axial explosions have shown that the vapor cylinder diameter at the time of the first current maximum is typically a few mm. The peak current in a 7-kV, 184-5 explosion has been measured a t 11 kA. If the vapor cylinder diameter is 5 mm a t peak current, the resulting current density has a lower limit of about 59 kA/cm2. This value, which is probably a conservative estimate, is considerably greater than the peak current densities used with commercial flashlamps and provides a reasonable explanation for the very high continuum intensities reported here. Attempts at fitting the exploding-wire spectra to the free-free and free-bound transition model of Unsold (17)and Maecker and Peters (18) were unsuccessful as were attempts at fitting the spectra to a blackbody model. However, by direct comparison with the standard lamp spectrum, it is possible to describe the exploding-wire continuum intensity in terms of a wavelength-dependent brightness of effective temperature. Peak brightness temperature for flashlamps often is greater than 3 X lo4,and values greater than 5 X lo4 K are reported occasionally. Figure 6 shows plots of peak brightness temperature as functions of wavelength for 0.051-mm diameter Au wires exploded at various energies in Ar a t atmospheric pressure. The peak value of over 9 X lo4 K observed at 250
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ANALYTICAL CHEMISTRY, VOL. 50, NO. 8, JULY 1978
nm for the 184-5 explosion is noteworthy. The values shown in Figure 6 compare favorably with values reported for flashlamps operated a t comparable energies. In summary, the extremely high ultraviolet intensity, excellent reproducibility, good long-term stability, and low operating cost should make axial wire explosions an excellent continuum source in a number of analytically significant applications. Additional studies extending into the vacuum-ultraviolet region would be most useful. Studies in Kr, Xe, or mixed heavy gases, while much less cost effective, would be worthwhile.
C. H. Church, R. D. Hawn, Jr., T. A. Oslal, and E. V. Somers, Westlnghouse Research Lab., Sci. Paper 62-1 12-259-PI (July, 1962). W. W. Jones and A. W. Ali, Phys. Lett. A , 5 0 , 101 (1974). A. W. Ali, N.R.L. Memo Report 2792 (1974). J. A. Holcombe and R. D. Sacks, Spectrochlm. Acta, Part B , 28, 451 (1973). J. A. Holcombe, D. W. Brinkman, and R. D. Sacks, Anal. Chem., 47, 441 (1975). R. Stair, W. E. Schneider, and J. K. Jackson, Appl. Opt., 2, 1151 (1963). W. G Chace, Phys. fluids, 2, 230 (1959). R. D. Sacks and J. A. Holcombe, Appl. Spectrosc., 28, 518 (1974). W. Tieman, 2. Naturforsch. A , 23, 1952 (1968). R. D. Sacks, "Shock Tubes, Exploding Conductors and Flashlamps", in "Analytical Uses of Pbsmas", R. M. Barnes, Ed., Wiley-Interscience, New York. N Y , in Dress --J.-L,'Emmett and A. L. Schawlow, Appl. Phys. Lett., 2 , 204 (1963). A. Unsold. Ann. Phvs. Leiozia. 33. 607 (1938). H. Maecker and T. Peters,' Zrbhys., 139, 448 (1954).
LITERATURE CITED D. W. Brinkman and R. D. Sacks, Anal. Chem., 47, 1279 (1975). G. K. Oster and R. A. Marcus, J. Chem. Phys., 27, 189 (1957). G. K. Oster and R. A. Marcus, J. Chem. Phys., 27, 472 (1957). R. A. Marcus, In "Exploding Wires", W. G. Chace and H. K. Moore, Ed., Plenum Press, New York, N.Y., 1959, Voi. 1, p 307. (5) M. J. Stevenson, W. Reuter, N. Braslau, P. P. Sorokin, and A. I. Landon, J. Appl. Phys., 34, 500 (1963).
(1) (2) (3) (4)
RECEIVED for review December 21,1977. Accepted April 19, 1978. The authors acknowledge support of this study by the Science Foundation through grant number MP72-05099 A02.
Atomic Emission Spectrometric Determination of Antimony, Germanium, and Methylgermanium Compounds in the Environment Robert S. Braman" and Michael A. Tompkins' Department of Chemistry, University of
South Florida,
Tampa, Florida 33620
Methods have been developed for the determination of Inorganic antimony and germanium and methylgermanium compounds In the environment. Compounds of these elements In aqueous solutlon at pH 1.5 are converted to the corresponding volatile hydrides by reduction with NaBH,. A dc discharge atomlc emlsslon type detector gave detectlon limits near 0.4 ng for antimony and germanium. Application was made to the analysis of natural waters and air particulate. Low concentrations of inorganic antimony and germanium were detected. No organometallic compounds of either element were detected in any environmental samples analyzed.
Antimony, found primarily in mineral ores, is derived principally from stibite, Sb&. Germanium is generally found as the +4 oxidation state oxide or in solution as germanic acid. Common valence states for S b are +3 and +5, while Ge forms divalent and tetravalent compounds of which only the latter are stable under environmental conditions. The number of known organogermanium compounds is numerous, but none has achieved significant industrial importance. Stibonic, RSbO(OH)2,and stibenic, R2SbOOH, acids are known but are likewise of small commercial importance. Although there are no reports of methylated compounds of antimony or germanium in.the environment, the stability of their alkyl-metal compounds under environmental conditions was sufficient to warrent their study. No methods have been reported for the determination of methylantimony or Present address, Department of Chemistry, Colorado State University, Fort Collins, Colo. 80523. 0003-2700/78/0350-1088$01 .OO/O
methylgermanium compounds at trace concentrations. Prior work has usually involved determination of total antimony or germanium. Antimony and germanium in low concentrations have been largely determined by spectrophotometric methods. While useful for the determination of these elements in the submicrogram range, such methods are sometimes complicated by the need for extraction or distillation procedures to avoid interferences from other trace metals (1,2). The Rhodamine-B method has been used for antimony in the 2-20 pg range (3). The reaction of germanium with phenylflurone in acid solution is used for analyses in the microgram range ( 4 ) . The more sensitive atomic absorption methods for antimony have sensitivities (1% absorption) in the 0.3 to 1.5 mg L-l range ( 5 , 6 ) . Recently, the use of a graphite tube furnace with NaBH, reduction of antimony to SbH3 has achieved a detection limit of 0.5 pg L-l (7). Pollock and West (8) were the first to report the determination of germanium by hydride generation with NaBH4. Standard flame atomic absorption techniques were used and resulted in a detection limit near 0.5 pg. Thomerson and Thompson (9) used a silica tube within an air-acetylene flame to obtain a detection limit of 0.5 pg Ge while a detection limit of 0.3 ng has been obtained with a graphite tube atomizer (10). Neutron activation analysis has demonstrated sensitivities in the low nanogram range for the determination of antimony and germanium in a variety of materials (11, 12). Foreback has done a preliminary study on the development of an analytical method for antimony(II1) and antimony(V), based on generation of stibine, SbH3 by NaBH, reduction with subsequent analysis by atomic emission spectrometry (13). The detection limit found was near 0.1 ng. Preliminary work by Johnson and Braman (14) indicated that germanium could 0 1978 American
Chemical Society
