practically no information on the distribution in depth of the production of the continuum. The calculation of the integral in Equation 21 is cumbersome, particularly when several absorption edges of elements present in the specimen are located between X, and Xt, the wavelengths which correspond to the initial electron energy and the critical excitation potential of the line of element A , respectively. HCnoc (27) proposed a method of formal integration for this expression. This procedure, however, is based upon the assumption that the mass absorption coefficients vary as the cube of wavelength. COR uses a numerical integration method which renders this approximation unnecessary. Owing to the complexity of this correction, it is frequently omitted. Preliminary investigations in our laboratory indicate that this omission entails no significant error unless the measured radiation is of short wavelength. However,
if hard radiation is measured, the effect of the continuum may be significant, particularly if a large fIaction of the specimen is composed of elements of low atomic number. We have not yet fully evaluated the importance of this correction; it is suggested, however, that L lines rather than K lines of elements of atomic number above 30 should be used in analysis, particularly in the presence of large amounts of elements of low atomic number.
(27) J. Hhoc, Nat. Bur. Stand. (U.S.) Spec. Publ., 298, 197 (1968).
RECEIVED for review May 5,1971. Accepted August 16,1971.
CONCLUSION
With careful consideration of the factors we have discussed, the errors in the analysis for each element of atomic number above ten should not exceed a fraction of total weight equal to j=O.Ol. It is hoped that further progress in the study of potential sources of error will reduce the margin of error, bringing it close to the limits imposed by the precision of the experimental procedure.
Automated Method for Determination of Nitrilotriacet ic Acid in Natural Water, Detergents, and Sewage Samples Badar K . Afghan, Peter D. Goulden, and James F. Ryan Department of the Environment, Inland Waters Branch, Water Quality Division, 45 Spencer Street, Ottawa, Ontario An automated method for the determination of total nitrilotriacetic acid (NTA) in natural waters, detergents, and sewage samples is described. The method is based on the formation of bismuth-NTA complex at pH 2 using Twin Cell Oscillographic DC Polarography. All the manual operations of sample preparation and polarographic determination are automated. The analysis may be performed at a rate of 15 samples per hour. The method can be used to detect levels of NTA as low as 10 pg/liter, without any preconcentration of the sample. The above method has been used to determine NTA in natural waters, detergents, and sewage effluents in the Water Quality Division laboratory for over 18 months. The coefficient of variation at 100 pg/liter was found to be 1.3%.
INCREASING CONCERN for the effects of phosphorus in the eutrophication of water bodies has resulted in the intensification of the search for a substitute for the sodium tripolyphosphate in laundry detergents. The substitute that had appeared to be the most suitable is nitrilotriacetic acid (NTA) ( I ) , but recent animal studies (2) have shown that NTA may enhance the teratogenic effect of such heavy metals as cadmium and mercury. The use of NTA in detergents has been suspended pending a conclusive determination of its safety. When it appeared likely that a large amount of NTA would be used in detergents and released to the sewage systems and receiving waters, a need was seen in the Water Quality Division laboratories for an analytical technique that would enable the waters in the National Water Quality Network to be monitored for trace amounts of NTA. Studies that were undertaken of the behavior of NTA and its metal chelates in (1) R. R. Pollard, Petrochem. Dewlop., 45, 197 (1966). (2) W. D. Ruckelshaus and J. L. Steinfeld, Joint Statement on NTA on behalf of Environmental Protection Agency, Washington, D.C., December 18, 1970. 354
rn
activated sludge system and studies of the mechanism of possible transport of heavy metals in natural waters also required a technology that would permit the analysis of a large number of samples for traces of NTA. There are many spectrophotometric (3, 4 ) , ion-selective electrode (5, 6 ) , and polarographic methods (7-9) available in the literature. All these methods have been evaluated (IO) in our laboratory and it was found that the use of a bismuthNTA complex at pH 2.0, using twin cell Oscillographic DC Polarography, proved the most useful method for the determination of NTA down to 10 pg/liter (9). The above procedure does not involve any preconcentration or separation of the samples. Therefore, this method was automated. Furthermore, automation of the manual method improved the precision by eliminating any errors during preparation of the sample prior to polarography. All the manual operations of sample preparation such as dilution, addition of the reagents, addition of the supporting electrolyte, adjustment of pH, filling and emptying of cells, and oxygen removal are automated. The resultant polarograms are either recorded or photographed using the Oscillo(3) G. G. Clinckemaille, Anal. Chim. Acta, 43, 520 (1968). (4) J. E. Thompson and J. R. Duthie, J . WaferPollut. Contr. Fed., 40, 306 (1968). ( 5 ) G. H. Rechnitz and N. C. Kenne, Paper presented at Fourteenth Conference on Great Lakes Research, April 19-21,1971, Toronto, Canada. (6) B. K. Afghan and I. Sekerka, unpublished data, 1971. (7) R. B. LeBlanc, ANAL.CHEM.,31, 1840 (1959). (8) J. P. Haberman, ibid., 43, 63 (1971). (9) B. K. Afghan and P. D. Goulden, Enciron. Sci. Tecknol., 5, 601 (1971). (10) B. K. Afghan, Proceedings of International Symposium on Identification and Measurement of Environmental Pollutants, Ottawa, Canada, June 1971.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2, FEBRUARY 1972
Figure 2. Modified electrode stand containing twin cells
Z-J-1
Q
Figure 1. Details of construction of new polarographic cell for the automation scope camera. The method may he operated at the rate of 15 samples per hour without any manual chemical manipulations. T o our knowledge, it is the first attempt to automate twin cell Oscillographic DC Polarography described in the literature and it is hoped that this automation will make the above technique practical in laboratories where large numbers of samples are assessed daily. Although the procedure described is for the analysis of NT'A, the technique is readily applicable to other polarographic analyses. In our laboratory, the application of automated twin cell Oscillographic DC Polarography has been extended to analyze different heavy metals in natural waters at microgram/liter levels and the details of individual procedures will be published later. APPARATUS AND REAGENTS
The twin cell Oscillographic DC Polarograph used was manufactured by Southern Analytical Ltd., England, under the name "Davis differential cathode ray polarograph type A-1660". The capillaries used in each of the two cells were matched so that when mercury drop rates were adjusted to 10 + 0.2 seconds, the signals from two cells containing the same solutions were effectivelyidentical. Two new cells, using an external reference electrode, were constructed for the automation so that they could fit in the water bath of the existing polarographic stand. The polarographic cell normally supplied with the polarograph was unsuitable for automation. Furthermore, only a mercury pool anode could be employed with this cell, which in some cases gave a drift in polarograms due t o a change in standard potential of the mercury pool. Therefore, a new cell had to be designed which could he used with an external reference electrode and which was capable of being emptied and filled without lifting the dropping mercury electrodes. Furthermore, the cell should also possess some leveling device so that each time it contained the same amount of solution for equal deoxygenation when nitrogen was bubbled at a fixed rate. This precaution was necessary to obtain reproducible results. Figure 1 gives the details of such a cell. The dropping mercury electrode is placed in central compartment (A). The cell contains small diameter side arms ( B and C') as inlets for sample and nitrogen, reference electrode compartment (D), and a large diameter sample outlet (E) at the bottom of the
cell. T o maintain a constant volume in the cell, a small overflow tube (F), enclosed by a large diameter tube, was also incorporated. The overRow waste outlet and the sample outlet of the cell were fitted with '/,-inch o.d., 3/lsinch i.d. tygon tubing. Polarographic cells were made t o contain approximately 5 ml of the solution and the central compartment was made as small as possible without interfering with the drop knock mechanism of the dropping mercury electrode. In manual operation, the glass skirts are normally raised to wash the cell and transfer the new sample. In the automated system, the cells were emptied and filled automatically without raising the skirts. The automated emptying of the cells resulted in a pressure drop in the central compartment of the cell which in turn contaminated the cell with water from the water bath. This was prevented by modifying the glass skirt to incorporate a 1-inch side arm of 'is-inch i.d. to the exterior of the skirt walls near the center of the glass skirt which was bent t o stay above the surface of the water. The electrode stand supplied with the polarograph was modified t o accept the new cells for the automation. These cells contained two outlets each, one t o drain the cell and one the drain from the overflow device. Connections were made t o these drain outlets by '14-inch 0.d. tygon tubing and holes were drilled through the side of the water bath and fitted with unions to accommodate this tubing. The cells were aligned in the bath of the stand so that the drop knocking mechanism worked freely and were then suspended in the bath by c l a m p ing the overflow section of the cells t o external ring stands situated on each side of the stand. This arraneement is shown in detail in Figure 2. A Mallorv Industrial Seauence Timer ftvoe 15T) was used to control ail the operation; in the automated procedure. In most of the work described here, a six-minute drive motor (M6M) was used to analyze samples at the rate of 10 samples per hour. l a t e r it was found that the cycle could he w m pressed t o four minutes to give an analysis rate of 15 per hour, an M4M motor was then used on the sequence timer. The sequence timer consists of a series of double throw snap action switches, each of which is actuated by a separate adjustable cam. The cams are mounted on a common drive shaft which is rotated at a speed dependent on the drive motor selected. Each function is set by adjusting a high and low cam position for each switch. The sequence is set by adjusting each switch in relation t o that of others resulting in synchronization of the various functions during the analysis of the sample. Each switch interrupts the power only once during the cycle. Therefore, if the operation of one of the components is repeated more than once, as in case of solenoid valve I, it is necessary that such a component he operated by connecting a suitable number of switches in series. I
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2, FEBRUARY 1972
355
NITROGEN&
CELL N C l l
TUBE SIZE NOMINAL ID (INCHES1
Figure 3. Manifold for the determination of N T A
1 o - J ~D ,
I
CELL NP2
I
I
I .
WASTE I N IM HCI 1M KCI
1M HCI
1M KCI
PROPORTIONING PUMP N01
7-
WASTE
I PROPORTlONlN G PUMP NQ2
Three Fisher electro-hosecocks were used to control the flow of nitrogen and the transfer of solution into the polarographic cells. All other components used in the manifold were standard Technicon AutoAnalyzer components. An Industrial Sampler was modified by controlling the desired “total” cycle time externally, through the Mallory Sequence Timer switch. This ensured complete synchronization of sampling sequence with all other manipulations in the automated procedure. The advance of the tray was accomplished by connecting a switch in the sequence timer so that 110 volts power is momentarily applied across the turntable position limit switch. This initiates the turntable progression and sampling cycle. The switch in the sequence timer is in series with the limit switch on the sampler arm. This prevents the rotation of the turntable while the sampler arm is in a sample, since the sample arm limit switch is energized only when the sample is free. The ratio of sample to wash time is still controlled by the sample timer on the sampler. The sample probe supplied with the sampler was replaced with an 8l/?-inch length of 1-mm i.d. and 3-mm 0.d. Teflon (Du Pont) tubing to eliminate any sample/wash cross contamination and also to avoid any inconsistency in the volumes delivered to the polarographic cells. The wash receptacle on the side of the sampler was filled with deionized water from a large reservoir using a piston metering pump, set for a water flow slightly greater than that at which the liquid was pumped into the system. Stock solution, 0.2M, of nitrilotriacetic acid was prepared and neutralized with potassium hydroxide to pH 7.0. The stock solution was standardized with zinc using bromothymol blue as indicator. All other stock solutions used in this work were prepared from reagent grade chemicals. EXPERIMENTAL
General Operating Procedures. The details of the manifold are shown diagrammatically in Figure 3. Two separate proportioning pumps are used to pump the reagents and the sample. The manifold is designed so that the length of time required for both aliquots of the sample and the reagents to travel to their respective cells is equal and as short as possible. This is accomplished by adjusting the length of the corresponding transmission lines. 356
The sample is aspirated at the rate of 32 ml/minute for a period of 64 seconds, and the probe is then returned to deionized water. This volume is sufficient to wash the cells and then fill them with the respective solutions for anaiysis. The sample, after aspiration, is mixed with 2 hydroxylamine hydrochloride to reduce any iron(II1) in the sample. It is then separated into two streams, a “blank” stream and a “sample” stream. The blank is mixed with a supporting electrolyte which is the mixture of 1M potassium chloride and 1M hydrochloric acid aspirated at the rates of 1.6 ml/minute and 0.16 ml/minute, respectively. The supporting electrolyte also acts as a buffer to maintain the pH of the solution 2.0 & 0.05. The sample stream is treated identically except that a bismuth stock solution is substituted for hydrochloric acid. The treated streams are then mixed in separate single mixing coils and pumped to their respective polarographic cells. The cells are washed once with water, rinsed with blank or sample stream, and filled for deoxygenation. All these functions are controlled by connecting the outlets of the cells to a cell drain solenoid I. During washing, rinsing, and filling of the cells, the solenoid valve closes twice for 20 seconds to fill the cells and opens twice for a period of 6 seconds to drain the solutions from both cells. At the end of the cycle, it is opened and closed to drain the cells and accept the incoming solution from the manifold to wash the cells for the next sample. The above three functions of solenoid I are controlled by three switches, in the sequence timer, wired in series. After the cells are filled with the solutions, the incoming solution is directed to waste through a T-junction which is controlled by solenoid 11. After the cells are filled, solenoid I1 opens to let the solution go to waste through the T-junction which is placed in the transmission tubing between the mixing coil and cell. At the end of the cycle, solenoid I1 closes to let the incoming solution enter the cells. Nitrogen is used to deoxygenate the solutions. The nitrogen line is run directly from the cylinder to the polarograph cells with a pressure reducing valve placed in the line between solenoid I11 and the cylinder. A T-junction is placed in the line to divide the flow of nitrogen equally between both cells. Nitrogen flow, during deoxygenation and washing, is controlled by solenoid 111. It remains open for the first 255 seconds of the cycle to facilitate the washing and deoxygenation of the solution prior to polarographic measurements. After deoxygenation, the flow of nitrogen is stopped by closing
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2, FEBRUARY 1972
MALLORY INDUSTRIPIL SEQUENCE TIMER 1 5 1 EMPLOYING M-6-M DRIVE MOTOR
OPEN
C'RCUIT
20-280 50-66'
r
2c
I II
4
-NTA
.D
I
e-*.
In-NTA
P
'\
I-
t
4,
E IO
364-360*
I
3 U
'\\
0
b
I
I
I
I
I
2
4
6
8
10
I_ 12
PH
-
Figure 5. Effect of pH on peak height of bismuth-NTA complex, lead-NTA complex, and indium-NTA complex
LEGEND -LINE COMMON
Figure 4. Details of wiring of various switches in the Mallory Industrial Sequence Timer solenoid I11 for the remaining period until the sample is analyzed and results are recorded. A period of 105 seconds is provided, in each cycle, to record the trace between 0.0 t o -0.5 V us. the Ag/AgCl reference electrode. If more time is required to record or photograph the polarogram, a manual switch wired in parallel with the drive motor sequence switch can be opened to stop the drive motor of the sequence timer. This will stop the sample probe aspirating the next sample in the system. Fifty seconds prior to the end of the cycle, the probe of the sampler is activated to commence the aspiration of another sample for the next cycle. This is done so that by the time the first cycle is finished, the second sample has reached such a point in the manifold that it contains just enough water to enable the cells to be washed with deionized water once prior to the entry of the second sample. Details of the wiring of various switches of the Mallory Industrial Sequence Timer to obtain the desired sequence of operations during analysis are given in Figure 4. RESULTS AND DISCUSSION
Choice of Suitable Metal Ion. Various polyvalent metal ions known to form metal-nitrilotriacetates were investigated as possible reagents for the analysis of NTA. Of 15 metal ions investigated, only bismuth, cadmium, copper, indium, lead, and zinc gave polarographic waves using twin cell Oscillographic DC Polarography, with a scan rate 0.25 Vjsecond. The changes in peak potentials ( E p ) and peak currents (i,) of the cathodic waves of these complexes with changes in pH, were the same as those of the classical polarography. For each metal complex, E, values of the complex moved to increasingly negative potentials with increases in pH until they reached a certain plateau, as the pH is increased beyond this point the E, values become less negative. For divalent metals, the plateau lies in the neutral region while trivalent metals attain a plateau on the more acidic side. The i, vs. p H curve for each complex has the same shape as the E, OS. pH curve with the maximum iP value occurring at the
same p H as the maximum E, value. The decrease in the Ep value above a certain pH indicates that the metal complex is being converted to a less stable species or that the metal complex is being rendered less stable by the occurrence of competing reactions-e.g., metal hydroxide precipitation. As discussed in previous work (9), all the results are consistent with the complexed metal being reduced to M ', the free NTA acid produced does not show any polarographic activity. Typical results of the variation of i, values of lead, bismuth, and indium complexes with pH are given in Figure 5 . In our laboratory, all these metal ions are evaluated in detail for the analysis of NTA (10). Of all the metal complexes, bismuth-NTA complex was found to be the most sensitive and selective for the determination of NTA in natural waters, detergents, and sewage samples. Therefore, this complex was chosen for automation. Deoxygenation and Washing. Before automating the above polarographic method, it was necessary to establish the minimum volume required to accomplish the analysis, the minimum time required for deoxygenation, plus the number of washes required to eliminate the possible cross contamination of the sample during analysis. Preliminary studies indicated that at least 2 minutes were required to deoxygenate 5 ml of sample. Attempts to minimize the time of deoxygenation by use of chemical deoxygenating agents either interfered with the determination or were not effective a t p H 2.0, which is the optimum p H for the analysis of NTA using bismuth-NTA method. In order to eliminate any cross contamination from samples in the automated method, two washings were necessary to prevent any cross contamination of consecutive samples in the cells. For these studies, a number of samples ranging from 1 mg/liter to 50 pg/liter were analyzed in an alternating pattern-Le., a high concentration followed by a low concentration. Samples did not indicate any cross contamination effect after flushing the cell twice with the incoming sample, prior to analysis. Effect of Interfering Ions. The proposed method has been tested in the presence of a number of substances commonly found in natural waters, detergents, and synthetic sewage components. A 100-fold molar excess of individual metal ion was added to a solution containing 0.1 mg/liter of NTA, and the NTA was determined by the proposed method. The
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2, FEBRUARY 1972
357
Table I. Recovery of NTA from Metal-Nitrilotriacetate Complexes
Solution composition NasNTA Aluminum-NTA complex Calcium-NTA complex Copper-NTA complex Iron(II1)-NTA complex Magnesium-NTA complex Zinc-NTA complex
Table 11. Analysis of NTA in Different Samples Using the Above Procedure
Recovery Recovery from from synthetic sewage lake water, effluents, x 10-5~ % %
Amt of complex added 0.5 1.o 2.0 0.5 1.o 2.0 0.5 1.0 2.0 0.5 1.o 2.0 0.5 1.o 2.0 0.5 1.0 2.0 0.5 1.o 2.0
100 100 100 100 100 102 98 102 97 108 96 102 100 104 98 100 100 98 100 98 100
103 105 96 105 97 101 101 100 106 100 100 105 102 100 96 90 96 98 100 103 98
metal ions investigated included antimony, arsenic, cadmium, chromium(III), chromium(VI), cobalt, copper, iron(II), iron (111), indium, nickel, vanadium, and zinc. None of the above metal ions interfered except iron(II1). Iron(II1) forms NTA complex a t pH 2.0 resulting in a prewave which is close to that of bismuth-NTA complex. The addition of hydroxylamine hydrochloride to reduce iron(II1) to iron(I1) eliminates this prewave. Therefore, if the presence of iron is suspected in a sample, it is necessary to reduce with hydroxylamine hydrochloride prior to the determination of NTA. None of the anions such as chloride, sulfate, nitrate, bicarbonate, and perchlorate interfered using 200 mg/liter of individual anions. Furthermore, the method was applicable to the determination of NTA spiked into sea water samples. Interference of other compounds which might be present in waters and synthetic sewage was also studied. The compounds included amino acids, dipotassium hydrogen phosphate, glucose, nutrient broth, peptone, beef extract, sodium chloride, and urea. Recovery of NTA from Different Metal-Nitrilotriacetate Complexes. NTA is a powerful complexing agent and is capable of forming strong complexes with heavy metals. Therefore, it was necessary to establish if the above method would be capable of displacing NTA from heavy metals normally found in natural waters. Table I shows the recovery of NTA from different metal-nitrilotriacetates using bismuth-NTA complex at p H 2.0. The recovery of complexed NTA was also verified in synthetic lake water and in the presence of other synthetic sewage components. Results from the above experiments indicated quantitative recovery of NTA from different metal complexes. In our laboratory, this method has been used to determine total NTA during the studies of biodegradability of different metal-nitrilotriacetate complexes. Calibration Curve. A calibration curve was prepared by taking a series of solutions through the automated procedure as given under “General Operating Procedure.” Figure 6 358
0
Type of sample
NTA found
Lake water sample I
...
Amount added, mgiliter
Amount found,a mg/liter
0.05 0.10 0.20
0.045 0. 100 0.205
0.05 0.10 0.20
0.050 0.095 0.200
0.05 0.10 0.20
0.040 0.096 0.205
...
... ...
0.05 0.10 0.20
0.050 0.095 0.200
Sewage effluent I
... ... ...
1.00 2.50 5.00
1,000 2.520 5.010
Sewage effluent I1
... ... ...
1.00 2.50 5.00
1.020 2.500 5.050
Detergent I
0.1%
1.00 5.00 10.00
1.005 5.010 10.020
Detergent I1
12.7%
1.oo 5.00 10.00
1,000 5.050 10.010
Detergent 111
5.6Z
1 .00 5.00 10.00
0.995 5.000 10.050
Lake water sample I1
... ... ... ... ...
...
Sea water I
...
... Sea water I1
a The above results are the averages of five determinations using different samples.
mg/LITRE NTA
Figure 6. Calibration curve for NTA shows the calibration curve obtained for NTA from 0.05-0.25 mg/liter. Identical curves were obtained in synthetic lake water and in the presence of all components normally used in synthetic sewage. The coefficient of variation of the method was determined at 100 pg/liter NTA level from 20 replicate analyses of synthetic lake water samples and detergents solutions spiked with NTA a t the rate of 10 samples/hour. Under these conditions the coefficient of variation was found to 1.3 %. Analysis of Actual Samples. The method has been used in our laboratory for over 18 months to analyze various
ANALYTICAL CHEMISTRY, VOL. 44, NO. 2, FEBRUARY 1972
natural water samples, detergents, and sewage samples. The only type of sample which required pretreatment before the polarographic work was that obtained from an anaerobic digestor. This digestor was fed with glucose and beef extract. This sample on analysis gave a prewave which was found to be due to some sulfur-containing compounds. This interference was eliminated by oxidizing the sulfur-containing compounds with hydrogen peroxide. The normal procedure used to analyze sewage samples was as follows: The suspended material in the sample was first removed by centrifuging the sample at 15000 rpm. The clear portion of the sample was filtered through 0.45-millimicron filter paper. The pH of the sample was adjusted to pH 2.0 i 0.05 with
hydrochloric acid and oxygen was bubbled through the sample for half an hour to remove hydrogen peroxide at pH 2.0 and were boiled for 15 minutes, cooled, and analyzed as above. Table I1 shows some typical results obtained for the analyses of NTA in lake waters, detergents, and sewage effluents using the proposed method.
RECEIVED for review July 23, 1971. Accepted September 16, 1971. This paper was presented by B. K. Afghan at the Pittsburgh Conference of Analytical Chemistry and Applied Spectroscopy, February 1971. Permission to publish the paper was given by the Director of Inland Waters Branch.
Effect of Carbon-Loading upon Product Distribution of Laser-Induced Degradations W. T. Ristau and N. E. Vanderborgh Department of Chemistry, University of New Mexico, Albuquerque, N.M. 87106 Products found from the quenching of laser-induced plasmas were separated and analyzed using a gas chromatograph. Product distributions were correlated with free energy calculations of the possible degradation products. Carbon additives do significantly alter degradation products distributions of inorganic systems. The effect upon organic systems is less pronounced.
CONSIDERABLE INTEREST currently exists in the use of pulsed laser radiation as a pyrolysis technique. Typically, pulsed, high intensity laser radiation is deposited into material, a laser plasma is formed and, then, with removal of the pulse, degradation products form from the thermal quenching of that plasma. Studies on this technique illustrate that complex, characteristic product distributions can be determined (1-4).
Mild conditions of radiation, 0.1 to 1 joule/pulse, do not always effectively couple with the material under study. This can be thought as arising from low absorptivity of the laser wavelength with the particular sample. T o circumvent this problem, “fillers” are often added to the sample to increase the extent of absorption. Typically, one mixes carbon (5% powdered graphite by weight) with materials of low absorptivity. The use of such additives is generally thought not to effect the resulting product distribution, and it is concluded that there are no or negligible effects of the carbon filler and degradation product distribution ( I , 2). This has been contrary to preliminary experiments we undertook on carbon loaded organic systems. We decided to investigate this phenomenon more fully by selecting degradation systems, such as inorganic ones, which should show a more pronounced effect than found with hydrocarbon molecules. Free energy calculations were also carried out in
an attempt to determine the feasibility of predicting the product distribution of these systems using thermodynamic data. A number of kinetic investigations have been performed on the quenching of high temperature carbon-hydrogen plasmas with a fair degree of success (5, 6) and we model the approach after those studies. Free Energy Predictions. A survey of the temperatures reached in a laser-induced plasma was presented in a previous communication (7). Data showed temperatures in the 10,000-90,000 “K region were not unusual. Chemical bonds cannot be expected to survive such an environment ; degradation products form on the cooling side of the thermal pulse, i.e., by thermally quenching the plasma. The product distribution is quite complicated with organic systems. As has been shown previously, larger molecular weight fragments do occur as products of degradations of organic molecules ( I , 2, 5 , 8). These most probably result from milder pyrolysis of the solid surface in the region surrounding the laser crater. Inorganic systems should not show the same degree of complexity since only a limited number of volatile degradation fragments can occur. The prediction of products formed from such a process is not entirely straight forward. For instance, taking silver nitrate as a specific example, when AgN03 is irradiated, a portion of the sample is vaporized and a plasma is formed. As the plasma is thermally quenched, chemical reactions can occur resulting in a number of different possible products and product distributions. The problem of predicting the most likely distribution is simplified by the experimental observation that a silver mirror is left (within the degradation chamber) from the event and that no evidence of silver oxide is found. ( 5 ) J. D. Rogers and A. Sesonske, “Graphite-Hydrogen-Methane
(1) B. T. Guran, R. J. O’Brien, and D. H. Anderson, ANAL. CHEM., 42, 115 (1970). ( 2 ) 0. F. Folmer and L. U. Azarraga, “Advances in Chromatography-1969,’’ A. Zlatkis, Ed., Preston Technical Abstracts. (3) R. H. Wiley and P. Veeraga, J. Phys. Chem., 72, 2417 (1968). (4) W. ‘1. Ristau and N. E. Vanderborgh, ANAL.CHEM., 42, 1848 (1970).
Kinetics Above 1600”K,” Los Alamos Scientific Report LAMS2896, 1963. (6) R. E. Duff and S. H. Bauer, “The Equilibrium Composition of the C/H System at Elevated Temperature,” Los Alamos Scientific Report, LA-2556, 1961. (7) W. T. Ristau and N. E. Vanderborgh, ANAL.CHEM., 43,(1971). (8) F. P. Miknis and J. P. Biscar, J. Phys. Chem., 75,727 (1971).
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