peak for CuzO is identical to Poling's transmission peak, and there doesn't seem to be any reason to question the band assignment as CuzO.
progress is being made in this laboratory on the use of this thin film-internal reflection technique in studies of marine corrosion, adsorption on modified carbon surfaces, and in other allied areas.
SUMMARY AND CONCLUSIONS It is apparent t h a t the large infrared energy losses which would have been predicted for metal or carbon films a t the surface of internal reflection elements do not exist. These films can be used advantageously to explore surface-bound reaction products and intermediates in the infrared region of the spectrum without the distortion found in specular reflection spectrometry or the matrix effect of pellets of infrared-transparent salts. Encouraging
Received for review November 14, 1972. Accepted January 12, 1973. Contribution No. 1620 from the Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Fla. The support of the U.S. Atomic Energy Commission (Contract AT [40-11-3944) is gratefully acknowledged, as well as the National Science Foundation (Sea Grant GH-58) support.
New Manual Method for Nitrogen Oxides Emission Measurement L. A. Dee,' H. H. Martens, C. I. Merrill, and J. T. Nakamura Air Force Rocket Propulsion Laboratory, DYCA, Edwards, Calif. 93523
F. C. Jaye Environmental Protecfion Agency. Research Triangle Park, N.C. 2771 1
A new time-integrated sampling method and a rapid analysis technique have been developed for NOx emission measurement. The sample gas is drawn through a heated bed of uniquely active, crystalline PbOe, and NOx is quantitatively absorbed. Lead nitrate is extracted with water and subsequently determined with the nitrate liquid ion exchange electrode. A simple selective precipitation eliminates interferences derived from PbO2 absorption of other combustion products such as HCI, HF, SiF4, Son, and CO.
Considerable attention has been focused on nitrogen oxide emissions, NO, (NO + XOz), as a result of Congressional mandate to set stationary and mobile source emission standards. Bartok, Crawford, and Skopp ( I ) reported that approximately 60% of the NO, emissions in the United States during 1968 were derived from fossil fueled stationary combustion sources. In a recent survey, Berger et al (2) showed t h a t NO, emission levels vary from 20 ppm with small gas-fired boilers to as much as 1400 ppm with some coal-fired power plants. They further stated that, in most cases, the NO, emissions from stationary sources are principally nitric oxide. The currently accepted NO, sampling and analysis technique ( 3 ) consists of rapid gas sample collection in a n evacuated glass vessel (grab sample) containing a small amount of acidic aqueous H202 followed by nitrate ion analysis using phenol disulfonic acid ( P D S ) . Use of this sampling and analysrs technique introduces several unAuthor t o whom correspondence s h o u l d b e addressed. (1) W Bartok. A. R . Crawford, and A. Skopp. Chem. Eng. Progr.. 67, 64 (1971). ( 2 ) "Improved Chemical Methods for Sampling and Analysis of Gaseous Pollutants from the Combustion of Fossil Fueis," Walden Research Corp., Environmental Protection Agency APTD 1291, February 1970, Research Triangle Park. N.C. (3) Fed. Register. 36 (247), 24891-24893, Method No. 7. (1971).
controllable variables. The S O , emission level from most combustion sources varies rapidly with time, and accurate mean emission levels can be obtained only by taking many grab samples and averaging the results. In addition, rapid analysis is hampered by the fact t h a t the collected gas sample must stand for sixteen hours in order to allow sufficient time for NO to be oxidized. to YO2 and diffuse into the aqueous absorbing solution for further oxidation to nitrate ion. Coulehan and Lang ( 4 ) decreased the reaction time to 1 hour for NO, levels above 500 ppm by continuous mixing of the sample gas and absorbing solution. However, Berger e t al. ( 2 ) reported that the precision of the grab sample/PDS method decreases rapidly below 200 ppm YO,. From the foregoing discussion, it is evident t h a t the NO, sampling problems could be minimized if a reagent were available which would rapidly and quantitatively absorb KO, in a gas stream. This would allow time-integrated sample collection and also provide a sample concentration technique which could result in precise analysis of any NO, emission level. Jacobs and Hochheiser ( 5 ) developed a time-integrated sampling technique using aqueous NaOH for SO2 collection, but the efficiency reportedly (6) varies from 30 to 90+% inversely with the NO2 level. Nash (7) demonstrated t h a t NO2 can be rapidly and quantitatively absorbed in aqueous, alkaline o-methoxyphenol. However, quantitative gas phase oxidation of NO to NO2 in a mixture containing many other reactive species may be difficult. A much more promising timeintegrated sampling technique was suggested by Mishmash and Meloan ( 8 ) , who presented evidence for the quantitative reaction of both NO and NO2 with PbOz to (4) B. A. Coulehan and H . W . Lang. Environ. Sci. Techno/.. 5. 163 ( 1971) . ( 5 ) M .B.Jacobs and S . Hochheiser, Anal. Chem.. 30, 426 (1958). (6) T. R . Houser and C. M. Shy. Environ. Sci. Techno/..6, 890 (1972). (7) T. Nash, J , Chem. SOC. ( A ) , 1970, 3032. (8) H . E. Mishmash and C. E. Meloan, Microchem. J . , 1 4 , 181 (1969).
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
1477
A
Table I. NO Recovery YS. Sampling Rate (211 pprn NO/Nz) NO recovered. Dom Sampling rate, ml/min SI€ PDS 41 21 2 ... 68 199 214 135 204 196 253 21 6 204 256 223 202 51 3 21 2 190 513 203 196
W
1
Figure 1:
Sampling apparatus
Legend: 1 . Gas mixer, 2. Check valve ('/B-in. H,O), 3. Tube furnace, 4. Absorption tube (containing P b O l ) , 5 . Connecting tube (1/16-in.0 . d . s/s). 6. Toggle valve, 7 . Fine metering valve, 8. Differential pressure gauge, 9. Ballast vessel (5- or 34-liter).10. Vacuum valve, 1 1 . Vacuum-pump
form P b ( N 0 3 ) ~a t reaction temperatures from 40 to 190°C. Also, Pregl (9) observed t h a t PbOz does not react with COz, HzO, or Nz, which are the major gaseous products of air/fossil fuel combustion processes. TLe literature (1012) reveals that considerable controversy has existed concerning the reactivity and capacity of PbOz for NO and NOz. The source of this controversy has been traced by the authors to the existence of three crystal forms plus an amorphous form of PbOz. Reported herein is a reliable, time-integrated sampling method for NO, using PbOz as the solid sorbent and an accurate analysis method for nitrate ion using a nitrate liquid ion exchange electrode (SIE).
EXPERIMENTAL Apparatus. Characterization of the various PbOz samples and PbOZ/NO, reaction products was performed with both a Phillips Norelco (Type 12045) X-ray diffraction unit equipped with a wide range goniometer, and a Beckman (Model IR-5A) infrared spectrophotometer. For gas standards which were prepared by partial pressure, a Wallace and Tiernan (Model FA-145) differential pressure gauge was used for the NO pressure measurements. Analysis of the NO/He mixture was performed with a Beckman (Model GC-4) gas chromatograph equipped with a Carle (Model 2015) gas sampling valve, a 12-ft X Yg-in. 0.d. stainless steel column packed with 60/80 mesh Porapak Q, and a thermal conductivity detector. The gas chromatograph was calibrated for NO using a glass/polytetrafluoroethylene exponential dilution flask and a procedure similar t o that reported by Williams and Winefordner (13).The 1% NO in Nz standards was verified with a Bell and Howell/CEC (Model 21-490) mass spectrometer. Analyses for nitrate ion in aqueous solution were performed using either an Orion (Model 801) Digital pH/mV meter equipped with an Orion (Cat. No. 920700) nitrate liquid ion exchange electrode and a Ag/ AgCl reference electrode, or a Cary (Model 14) spectrophotometer operated a t 405 nm with 1-cm pathlength cells when the PDS method for nitrate ion was used. Reagents. The NO, NOz, HCl, HF, SOz, CO, and COZ (Matheson Gas Products) were used without further purification. All other reagents were ACS Reagent grade except where noted, and all aqueous solutions were stored in polyethylene containers. PbOz. The PbOz from commercial sources (Fisher Scientific Co., Cat. No. L-100 and Matheson Coleman and Bell, MCB Cat. No. LX-149) was used without further purification except where noted. The major source of PbOz for this work was prepared from the anode plates of several used lead/acid storage batteries. The crude product was digested in concentrated " 0 3 at 100 "C for several hours, followed by repeated extraction with distilled water ( 9 ) F. Pregl, "Quantitative Organic Microanalysis,"tran. by E. Fylernan, 2nd ed., 1924, Blakison's and Sons, Philadelphia, Pa. (10) M . Dennstedt and F. Hassler. Fresenius' Z. Anal. Chem., 42, 417 (1903). ( 1 1 ) F. R. Cropper, Mikrochim. Acta, 1954, 25. (12) W. R . Kirner. Ind. Eng. Chem., Anal. E d . , i o , 342 (1938). (13) H. P. Williams and J, D. Winefordner, J. G a s Chromatogr., 4, 271
(1966),
1478
A N A L Y T I C A L C H E M I S T R Y , VOL. 45, NO.
a, J U L Y
1973
x
210
200
s
8.4
8.3
until the extract contained less than 1 mg/l. of nitrate ion. The product was then dried a t 130 "C and 20 mm Hg for several hours, crushed, and sieved. The 30/50 mesh granules were retained for subsequent use. The Pb304 (Fisher Scientific Co.) and Pb(OOCCH3)4 (Alfa) were used without further purification. PbF2. The PbFz (K and K Laboratories, Inc.) contained a high level of some inorganic nitrate salt which was removed by repeated extraction with distilled water. The purified material was dried at 130 "C and 20 mm Hg. Phosphate Buffer Solutions. Five per cent, 2000 ppm, and 1000 ppm phosphate buffer solutions were prepared from Na3P04. 12Hz0 (J.T. Baker) and distilled water. Nitrate Standards. A 10,000 ppm NOS- standard was prepared from dried P b ( N 0 3 ) ~(J. T. Baker) and distilled water. Phosphate buffered 1000 and 500 ppm nitrate standards were prepared by appropriate dilution of equivolume mixtures of 10,000 ppm N o s - standard and 2000 ppm Po43- buffer with the 1000 ppm - buffer solution. Less concentrated standards were prepared by further dilution of the buffered standards with the 1000 ppm Po43- buffer solution. Phenoldisulfonic Acid. The phenoldisulfonic acid and other reagents necessary for the PDS method were prepared in accordance with published directions ( 3 ) except that neutral 3% H202 was used as the absorbing reagent. Gas Mixtures. Gas mixtures of NO with nitrogen (99.99% min) or helium (99.995% min) were prepared by partial pressure measurement. Mixtures containing approximately 1% nitric oxide were verified with the mass spectrometer, and more dilute mixtures were prepared by dynamic flow dilution of the concentrated standard. All flow measurements were performed with a gas buret. The 256 ppm NO/helium mixture was prepared in a large cylinder (size 1A) by partial pressure and was verified using the gas chromatograph. A helium matrix was necessary because nitrogen or argon could not be sufficiently resolved from NO to allow the gas chromatographic analysis. Since the calculated (256 ppm) and determined (252 f 'i ppm) values for NO agreed quite well, a second gas mixture containing 211 ppm NO in nitrogen was prepared in a similar manner. The appropriate compressihility factor (PV) for nitrogen was used in this calculated NO concentration. The gas mixtures used for the interference tests were prepared by metering the appropriate amount of pure contaminant ( S O z , HC1, etc.) into a glass dynamic flow dilution manifold through which the 211 ppm NO/Nz standard was flowing at a measured rate. Procedure. Sampling. Sampling tubes were constructed of 6-mm 0.d. borosilicate glass tubing that had been cut into 25-cm lengths. Each was fitted with a glass wool plug and loosely filled with 2-4 grams of the prepared PbOz. A second glass wool plug was used to hold the PbOz in place. The tube was inserted in the sampling apparatus as shown in Figure 1, heated to 190 "C, and the system was evacuated up to the toggle valve. With the vacuum valve closed, the initial pressure was recorded and then the toggle valve was opened so that the gas mixture was drawn through the sample tube. After the desired volume was collected, the toggle valve was closed and the final pressure was recorded. Grab samples of the gas mixtures also were taken in calibrated 2-liter flasks constructed and used in accordance with published directions ( 3 ) . Analysis. The entire contents of the sample tube (including the glass wool plugs) were transferred to a 12-ml screw-capped centrifuge tube followed by the addition of approximately 0.1 gram of
PbFz. Then 8.00 ml of distilled water were added to the mixture. The resulting slurry was mixed and then heated to 100 "C for 30 minutes, with occasional shaking, in boiling water. The centrifuge tube containing the hot slurry was then cooled to 0 "C in an ice bath for 15 minutes and centrifuged for 10 minutes at approximately 2500 rpm to separate the excess PbOz and PbFz. The resultant clear extract was decanted and combined with 0.15 ml of the 5% Po43- buffer solution. The nitrate ion concentration of this solution was determined using the nitrate liquid ion exchange electrode which had been calibrated with Po43- buffered nitrate ion standards. A cloudy precipitate of insoluble Pbs(P04)~was present in both the sample solutions and calibration standards but this caused no noticeable interference with the electrodes. However, it was necessary to separate the Pb3(P04)2 from the aqueous extract (by centrifuging the mixture) prior to nitrate ion determination using phenol disulfonic acid. If the gas sample contained none of the interfering combustion products ( e . g . , HCI, SOz, etc.), then the procedure was simplified merely to extraction of the PbOz with a measured amount of 1000 ppm Po43- buffer followed by separation of the insoluble material from the extract prior to nitrate ion determination. The PDS analysis procedure (3) was modified slightly in that only a 5-ml aliquot of the absorbing solution was evaporated t o dryness and the evaporation was performed in a platinum cruci-
~~~
Table II. NO Recovery
(14) "Ion Selective Electrodes," R. A . D u r s t , E d . . NBS Spec. Pub/. 314, Nov 1969, Washington D.C.
NO Concentration p p m NO, found
ppm NO, calcd
51 60 61 102 105 104 203 21 0 228 426 446 428 633 624 609 880 863 836
lola
21 1 21 1 21 la 420 420 420a 664 664 664O 900 900 900a Correlation coefficient ( r 2 ) Slope Intercept, ppm a
PDS 55 65 65 101 116 96 228 220 247 421 427 409 656 673 624 897 891 855
SIE
64 64 64a 101 101
ble.
RESULTS AND DISCUSSION NO Sampling and Analysis Criteria. An investigation of t h e nitrate SIE sensitivity t o pH changes revealed t h a t over the p H range of 3-6, the response for a given nitrate ion concentration would vary approximately 5 mV/pH unit with considerable drift. Therefore, all standards and samples were adjusted to p H 11.5 by preparing them in a 1000 p p m Po43- buffer solution prior to measuring the nitrate ion concentration with the SIE. A typical SIE calibration curve, prepared with buffered standards as described, was quite usable between 10 and 1000 ppm NO3with a slope of -9.6 ppm/mV between 50 and 500 ppm NOa-. Since the residence time of a N O molecule in the PbOz packed portion of the sample tube is relatively small ( - 1 second), there may be a n upper limit to the gas sampling rate beyond which quantitative recovery is not achieved. The 211-ppm NO/Nz standard was sampled a t various rates through PbOz tubes which were maintained a t 190 "C. Table I shows both the SIE and P D S analysis results of t h e aqueous buffered PbOz extracts. The Table I data show t h a t quantitative recovery of N O at the 211-ppm level can be achieved a t sampling rates of 50 t o 500 ml/ min. Since no trend is apparent in the data, even higher sampling rates may be possible if the configuration of the sample device is modified. T h e collection efficiency of the PbOz sampling tube was determined by sampling known mixtures of N O and nitrogen prepared by appropriate dynamic flow dilution of either the 211-ppm or the 1% NO/Nz standards. Both SIE and P D S analysis results of the aqueous buffered PbOz extracts are shown in Table 11. Acceptable correlation is shown for either analysis method when compared t o the calculated NO concentrations. The reactivity of electrolytically derived PbOz is further emphasized by the data which demonstrate quantitative N O collection a t 27 "C. In addition t o nitrogen oxides many other gases which may react with PbOz, may be present in the effluent of combustion processes. Such compounds as SOz, CO, HCl, and HF may react with PbOz t o form Pb(I1) salts ( i e . , PbS04, PbC03, PbC12, PbFz). Durst (14) has shown that the corresponding anions interfere with nitrate ion concentration measurements using the SIE. If these combus-
YS.
0.996 1.05 -8.9
0.997 1.03 -9.4
Sampled at 27 instead of 190 " C .
tion products indeed react with PbOz, they also may impair the quantitative collection of NOx. T o determine their effect on the NO collection efficiency and subsequent nitrate ion analyses, approximately a tenfold excess of each was individually combined with the 211-ppm NO/Nz standard using the pure gases and dynamic flow dilution with the KO standard. Extraction of the reacted PbOz with 1000 p p m Po43- buffer solution yielded unacceptably high results due t o exchange precipitation reactions such as the following which release large amounts of the interfering anions into solution: 3 PbSO,
+
2 PO,3--
3 PbC03
+
2
3 PbCl,
+
2 PO,3-
Pb3(P0,)21
-
+
3 SO,2- (1)
Pb3(P04), 1 + 3 C03'- (2) Pb3(P04),1+ 6 C1-
(3)
Reactions such as these occurred because of the extremely low solubility of P b s ( P 0 4 ) ~relative to other Pb(I1) salts. Extraction of the reacted PbOz with cold water and separation of the extract prior t o adding Po43- buffer generally yielded low results, apparently because the soluble p b ( N 0 ~formed )~ was occluded in the crystal structure of the less soluble Pb(I1) salts. This problem did not occur with the PbOz t h a t was used to sample the HC1 contaminated NO standard. T h e high solubility of PbC12 not only allowed the release of the Pb(NO3)z but also provided sufficient chloride ion t o give high results with the SIE (and low results with PDS). This problem was eliminated by addition of excess PbFz to the PbOz prior t o aqueous extraction. Thus, the presence of PbClz results in the formation of the much less soluble PbClF as shown in Equation 4. PbF,
+
PbCl, -2PbClF
3
(4)
This selective precipitation technique when combined with extraction of the PbOz with hot water, described in the Experimental section, yielded acceptable analysis reANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973 * 1479
Table I V . Thermochemical Calculations
-
Proposed reaction
+
NO 4-PbOz NO? PbO 2 NOz -I-PbOz+Pb(N03)2 CO2 PbOz PbCO3 '/2 02 SO2 f PbOz PbS04 2 "03 * H20 PbOz+ Pb(N03)z f 3Hz0 f '12 02
+
+
+
+
L
1
52
Figure 2.
'
1
'
48
$ 36 '
I '
3;
12
,
:2
28
'
X-Ray diffractionspectra of PbOz
Legend: 1. Fisher Scientific, 2. Matheson Coleman and Bell
Table Ill. NO Recovery in the Presence of Other Combustion Products ppm NO recovered, 21 1 ppm theor
SIE
Combustion product (ppm)
S02-(2200) S02-(2200) soz- (2200) SOz-(1080) s02-(1080) SOz-(1080) CO-(3000) CO-(3000) CO-(3000) HCI-(2400) HCI- (2400) HCI- (2400) HCI-(1500) HCI-(1500) HCI-(1500) HF/SiF4-(1700) HF/SiF4--(1700) HF/SiF4-(1700) H F/Si F4-( 1700) COz-( 14,000) COS- (14,000) CO2-(14,000)
x s
227 223 227 21 1 21 1 222 21 0 218 222 192 209 207 21 8 216 21 1 201 203 197 199 219 21 5 214 212 9.6
PDS
187 193 191 21 1 21 7 21 7 222 224 220 182 21 2 199 190 196 187 232 234 224 244 222 21 8 201 21 0 17.5
sults for all of the interfering combustion products tested. Table I11 shows both the SIE and PDS analysis results using this sample preparation technique when the 211ppm NO standard contained large quantities of each contaminant. The HF concentration shown in Table I11 may be conservative because, a t one atmosphere, pure H F vapor can exist in molecular multiples (H2F2, H3F3, etc.). SiF4 may have been present since the gas mixture was prepared in a glass dynamic flow dilution apparatus and passed over the hot (190 "C) glass wool plug in the inlet side of the glass reactor tube containing the PbO2. The PbOz exposed t o C02 was extracted with 1000 ppm Po43buffer, instead of hot water saturated with PbF2, in order to demonstrate that COz does not react with PbO2. The SIE results show that NO can be quantitatively collected in the presence of tenfold excesses of the compounds tested and t h a t accurate analysis results can be obtained through selective precipitation of interfering anions. 1480
ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
+
Reaction observed
Yes
4H20-
4F20"
(kcall mole)
(kcal/ mole)
Yes No Yes
-1.5 -58.2 -16.7 -84.0
No
12
-2.8
- 42 -4.7 -71.4 -24.2
PbOz Characterization. Two lots of Fisher PbO2 (Cat. No. L-100) were evaluated with the NO standards and both displayed a low NO recovery (90-9270). The more recent lot (NO.763934) was found to contain a large quanti. ty of C a ( N 0 3 ) ~which was extracted prior to the above tests. Subsequent communication with the vendor revealed that a small amount of zeolite is added to the PbOz to improve the integrity of the granules. Nitrate absorption by the zeolite may explain the negative bias in the results. A similar bias was indicated with flask/PDS data; however, both Berger et al. ( 2 ) and Margolis and Driscoll (15) also reported low results using this technique. The MCB PbO2 was also evaluated but the recovery was surprisingly low (15%). Cropper (11) reported that the NOz capacity is proportional to PbO2 surface area; therefore a second sample of MCB material was ball-milled for 72 hours prior to evaluation. However, the NO recovery was not sufficiently increased (30%). Since surface area is apparently not the most significant factor, other characteristics of the PbOz sample were investigated. X-ray diffraction spectra, shown in Figure 2, of the two P b 0 2 samples revealed major differences in their crystal structure. The Fisher PbO2 was primarily the cy and fl (orthorhombic and tetragonal) forms and the MCB product was largely a third unnamed crystal form (16). Baker (17) and Bode (18) demonstrated that the cy and fl forms of PbO2 are derived from the anodic oxidation of Pb(II), and a limited amount of experimental work by the authors indicated dithat the third crystal form can be derived from "03 gestion of Pb304. In addition, hydrolysis of P b ( OOCCH3)4 yielded primarily an amorphous form of PbOz (indicated by X-ray spectrum). The above chemically derived Pb02 was totally unreactive to NO while electrolytically derived PbO2 (from a lead/acid battery) absorbed greater than 75% of the theoretical capacity. The X-ray diffraction spectrum of the NO/Pb02 reaction product showed that no new crystalline material was formed (thus an amorphous product is indicated). In contrast, the X-ray diffraction spectrum of PbO2 from the same source similarly saturated with NO2 definitely showed the presence of crystalline P b ( N 0 3 ) ~(27% of the theoretical capacity). In addition, the infrared spectrum (5000 cm-I to 625 c m - l ) of the NO/PbOZ product exhibited a band at 1340 cm-1 which was much broader than the principal P b ( N 0 3 ) ~absorption at 1360 cm-1, and none of the minor absorptions due t o P b ( N 0 3 ) z were evident. However, the infrared spectrum of the NOZ/Pb02 product was identical to that of a n authentic Pb(N03)2 sample and, upon water extraction, nitrate was the only anion found from either PbOz (15) G. Margolis and J. N . Driscoll, Environ. Sci. Techno/.. 6, 727 (1972). (16) "inorganic index to the Powder Diffraction File," J. V . Smith, Ed., 1968, ASTM Pub/.. PDIS-l8i, American Society for Testing and Materials, Philadelphia, Pa. (17) R. A. Baker, J . Eiectrochem. SOC.,109, 337 (1962) (18) H. Bode.Angew. Chem.. 7 3 , 5 5 3 (1961).
reaction product. These observations indicate t h a t the reaction of NO with PbOz may be more complicated than t h a t proposed by Mishmash and Meloan. Additional support for this is shown by the thermochemical calculations (19) in Table IV. The anomalous behavior of NO with PbOz is clearly evident if one considers t h a t the net free energies and enthalpies of the reaction of COz and aqueous H N 0 3 with PbOz are somewhat more negative than t h a t of NO. Yet NO readily reacts with electrolytically derived PbOz whereas COz and aqueous H N 0 3 do not. ( 1 9 ) "JANAF 1.hermochemical Tables," D. R . Stull, Proj. Dlr., 1960. Dow Chemical Go., Midland, Mich.
Because of its unique reactivity with NO, only electrolyticrystal forms), obtained cally derived PbOz (a and/or from the anode plates of several used lead/acid batteries and purified as described, was used for the development of sampling and analysis criteria. Further work is in progress to apply this sampling device to the measurement of HCl, C12, SO,, HF, SiF4, and CO in combustion effluents. Received for review November 13, 1972. Accepted February 20, 1973. This work was partially funded by the Environmental Protection Agency under an interagency agreement with the Air Force Rocket Propulsion Laboratory.
Instrumental Photon Activation Analysis of Atmospheric Particulate Material N. K. Aras,l W. H. Zoller, and G . E. Gordon Department of Chemistry, University of Maryland, College Park, Md. 20742
G . J. Lutz Analyticai Chemistry Division. National Bureau of Standards. Washington. D.C. 20234
Concentrations of fourteen elements in atmospheric particulate matter have been measured by irradiation of the samples with bremsstrahlung from electrons of 35 MeV from the NBS electron linac and observation of y rays from the reaction products with Ge(Li) detectors. The elements routinely observed by this nondestructive method are: Na, CI, Ca, Ti, Cr, Ni, Zn, As, Br, Zr, Sb, I , Ce, and Pb. Several other elements such as Fe, Se, Rb, and Y are marginally observable. Although, in general, instrumental photon activation analysis (IPAA) is less sensitive than instrumental neutron activation analysis (INAA), with IPAA one can measure concentrations of several elements that are difficult or impossible to measure in urban particulates with INAA, especially Ti, Ni, As, I , and Pb. Measurements of Ni, As, and Pb are quite important because of their known toxicities.
Since the development of lithium-drifted germanium [Ge(Li)] y-ray detectors, nuclear methods have been successfully applied to the measurement of concentrations of many elements in complex environmental samples, often with much greater sensitivity than had been possible with older methods ( I ) . A total of 42 elements, for example, has been observed uia instrumental neutron activation analyses (INAA) in atmospheric particulate materials collected in various areas ( 2 ) . However, because of interferP e r m a n e n t address, D e p a r t m e n t of C h e m i s t r y , M i d d l e E a s t T e c h n i c a l U n i v e r s i t v . A n k a r a . Turkev. "Nuclear Methods in Environmental Research," J . R. Vogt, T, F, Parkinson, and R . L. Carter, Ed., University of Missouri Press, GOlumbia, Mo., 1971. G. E. Gordon, in "Proceedings of the International Symposium on Identification and Measurement of Environmental Pollutants," E. Westiey, Ed., ~ a t i o n a Research i Council of Canada, Ottawa, 1971, pp 138-143.
ences among elements, no more than about 30 elements have been measured in any one sample. Despite this success, INAA is not capable of analysis for all of the elements in atmospheric aerosols t h a t are of considerable environmental concern. For those important elements t h a t are apparently beyond the scope of INAA in environmental samples, alternate instrumental nuclear methods of analysis are needed. Samples of this sort generally have very complex, poorly characterized matrices. If one tries to dissolve them, great care must be exercised to prevent contamination, loss of volatile species, or loss of trace species by coprecipitation on insoluble residues or container walls. Thus, it is desirable to analyze these samples by nondestructive, instrumental methods if possible. Furthermore, to eliminate matrix effects, it is important that projectiles and radiations involved in the analysis have long ranges in the sample material. One nuclear method t h a t meets the above criteria is instrumental photon activation analysis (1PAA)-i. e . , the irradiation of samples with bremsstrahlung produced by deceleration of high-energy electrons (215 MeV) in a stopping medium. The incoming y rays t h a t induce nuclear reactions such as ( r , n ) , (y,p), etc. must have energies of about 7 MeV or greater, and thus have extremely long ranges in the sample material. Instrumental photon activation analysis has not been used extensively in the past, in part because sources of high-energy electrons are not widely available. Also, far less activity per unit irradiation time is produced with bremsstrahlung than with moderate-flux reactors. However, IPAA offers several advantages as a complement to INAA: (a) The reactions (y,n), (y,p), etc. of the target nuclides often lead to products other than those resulting from neutron irradiation, increasing the probability of forming products with half lives and 7-W' energies convenient for analysis. ( b ) As in the case of neutron reactions, ANALYTICAL CHEMISTRY, VOL. 45, NO. 8, JULY 1973
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