benzonitrile, correlate with the order of the dielectric character of the solvents [water (D20) (dielectric constant, 78) >> acetonitrile (dielectric constant, 37.5) > benzonitrile (dielectric constant, 25.2)]. The dipole moments of the three solvents are 1.86, 3.44, and 4.02 D for water (DzO), acetonitrile, and benzonitrile, respectively, and as a set do not appear to be directly accountable for the variation in the distribution of diprotonated 2,2'-dipicolylamine in the three different media. However, to understand fully the detailed aspects of the nature of this solvent effect, particularly that of hydrogen bond interactions in protic solvents and other specific interactions contributing to the mediation of the charges in the diprotonated species, studies in additional solvent systems will be necessary.
ACKNOWLEDGMENT We wish to thank the Reilly Tar and Chemical Company for the generous gift of 2,2'-dipicolylamine.
LITERATURE CITED E. Grunwald, A. Lowenstein, and S. J. Meiboom, J. Chem. Phys., 27, 641 (1957). A. Lowenstein and J. D. Roberts, J. Am. Chem. SOC.,82,2705 (1960). J. N. Shoolery, Varian Tech. hform. Bull., 2, No. 3 (1959). G. A. Focier and J. W. Olver, Anal. Chem., 37, 1447 (1965). R. C. Larson and R. T. Iwamoto, J. Am. Chem. Soc., 82,3239 (1960). I. Suzuki, Pharm. Bull., (Tokyo),4, 211-16 (1956). J. L. Sudmeier and C. N. Reilley, Anal. Chem., 36, 1698 (1964). R. B. Fischer and D. G. Peters, "Quantitative Chemical Analysis", W. B. Saunders Co., Philadelphia, Pa., 1968, p 277. B. P. Dailey and J. N. Shoolery, J. Am. Chem. SOC.,77, 3977 (1955). H. Sigel, P. R. Huber, and R. F. Pasternack, lnorg. Chem., I O , 945 (197 1). E. Gonick, W. C. Fernelius, and B. E. Douglas, J. Am. Chem. SOC..76, 5253 (1954). H. Buhler and G. Anderegg, Chimia. 24, 433 (1970). R. J. Bruehlman and F. H. Verhock, J. Am. Chem. SOC., 70, 1401 (1948).
RECEIVEDfor review July 21, 1975. Accepted September 12, 1975. The authors gratefully acknowledge the support of the National Science Foundation (Grants GP-11313 and GP-28332).
Rapid Radiochemical Separation of Selected Toxic Elements in Environmental Samples Prior to Gamma Ray Spectrometry Frank W. Wilshire, Joseph
P. Lambert,
and Frank E. Butler
Analytical Chemistry Branch, Quality Assurance and Environmental Monitoring Laboratory, U S . Environmental Protection Agency, Research Triangle Park, N.C . 277 1 1
Toxic elements in a variety of environmental samples are activated by neutron bombardment for subsequent analysis by y-ray spectrometry. The radioactive isotopes of arsenic, cadmium, mercury, Selenium, iodine, and zinc are chemically separated by using the liquid anion exchanger, triisooctyiamine, following sample combustion. Significant improvements over currently used procedures are: a radiochemical separation that is quantitative in that all of the products trapped during combustion are contained in one of three sample fractions; an isolation of elements of interest from those elements with interfering y energies; a procedure that has few chemical manipulations, thus minimizing related errors; a separation that is simple and requires less than 5 minutes to complete foilowing combustion. in addition, the elements contained in liquid samples can be separated directly by liquid anion exchange, eliminating the combustion procedure. The methodology was tested by radiotracer experiments and by analyzing independently tested and certified coal and fly-ash samples.
Increased emphasis has been placed on the measurement of toxic elements in emission sources and ambient air following the formation of the U.S. Environmental Protection Agency (EPA) and the passage of the Clean Air Act of 1970 (1). Recently, von Lehmden, Jungers, and Lee investigated toxic elements of interest and compared results from six analytical techniques (2, 3 ) . One of these techniques, neutron activation analysis (NAA), is the method discussed here. A need exists to remove interferences from many samples that are to be sensitively analyzed by y-ray spectrometry. Pollutants of interest to this laboratory (As, Cd, Hg,
Se, U, and Zn) are usually a mixture of volatile compounds in a variety of matrices. The detection of these pollutants is often difficult because of interferences or masking effects. Bromine, present in many environmental samples, was the major interference limiting our NAA capabilities because of the 36-hour half-life and multiple y rays of the 82Br isotope. A series of radiochemical separation procedures developed by the National Bureau of Standards (NBS) ( 4 ) was used to separate these elements of interest. These procedures involve the combustion and subsequent reduction of irradiated samples to remove the more volatile elements from less volatile interferences. Distillates are trapped in a liquid nitrogen-cooled condenser, dissolved in a mixed acid, and precipitated twice as sulfides to remove the bromine interference. In an effort to minimize time requirements and to ensure against any losses of the desired elements by incomplete sulfide precipitation, the postcombustion radiochemical separation procedure was modified. Space and equipment were other parameters considered, while still maintaining a high level of bromine decontamination. Experiments were conducted to develop a liquid anion exchange procedure for the separation of the desired radionuclides collected during sample combustion by the NBS procedure. Triisooctylamine (TIOA) diluted to 10% in xylene had been used previously in the rapid radiochemical separation of several of these elements (5) and was therefore chosen for this work. The goal then was to develop a rapid separation of the radioactive isotopes of arsenic, cadmium, mercury, selenium, iodine (as an indicator of naturally occurring uranium), and zinc into several fractions containing no appreciable interferences from isotopes emitting unwanted y energies.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
2399
0 . l 2 0 0 ~c
A
isl
VYCOR COMBUSTION TUBE
OUARTZ WOOL PLUG
COMBUSTION
EXTRACTION
ANOIOR OXIDATION
LlOUlO NITROGEN COLOTRAP
1 1
GASINLET
IRRADIATED
3
J VVCOR CONDENSER TUBE
SAMPLE
WOOL PLUG
I
Figure 1. Sample combustion train
I 104 HNO3 FRACTION Hg, Cd, Zn. Br
Figure 3. Flow chart for handling irradiated samples tion technique
E L 80
I
1
60
I "1 :
1
i NORMALITY
OF H N O j
Figure 2. Determination of optimum partition coefficient using
"03
in contact with TIOA
EXPERIMENTAL Apparatus. Combustion Train. The first stage of the radiochemical separation occurs in the sample combustion train (Figure 11, consisting basically of three parts: the furnace, combustion tube, and condenser. Both the combustion tube and the condenser are made of Vycor, with an inside diameter of 18 mm and lengths of 50 and 25 cm, respectively. (Mention of commercial products or company names does not constitute endorsement by EPA.) Connection between the combustion tube and the condenser is accomplished with a 3 19/38 Vycor joint. The distillates are trapped in the condenser by a liquid nitrogen cold trap. The furnace must be capable of maintaining and monitoring temperatures up to 1200 OC. Ion Exchange Glassware. The final stage of the radiochemical separation is accomplished by a simple liquid ion exchange procedure, using standard laboratory glassware. Reactor. The PULSTAR Reactor a t North Carolina State University, Raleigh, N.C., was used. Counting Equipment. A Ge(Li) (lithium drifted germanium) detector with 17% relative efficiency and a 4000-channel pulse height analyzer with 4000 channels of storage were used. Reagents. All reagents are American Chemical Society grade or equivalent. The following reagents are used: 1) 203Hg (35 kg/ml). Tracer solution prepared by dissolving a weighed quantity of irradiated HgO in concentrated high-purity nitric acid and diluting to volume with distilled water. 2) Acids. 2 N HCl, 10 N "03, and 2 N mixed acid (1.8 N NC1 0.2 N "03). 3) Anion Exchange Liquid. Triisooctylamine (TIOA) diluted to 10% in xylene. (Stored in a dark bottle away from light.) TIOA is available from Bram Metallurgical Chemical Co., Philadelphia, Pa. 4) Mixed Carrier. Mixture containing 1.00 g each of As, Cd, Hg, Se, and Zn. Procedure. Determination of Partition Coefficient. To determine the partition coefficient for the liquid anion exchange procedure, varying concentrations of "03 were tried for the removal of z03Hgfrom the TIOA. The 203Hgwas concentrated into 100 ml
+
2400
by the combus-
of TIOA from which several 10-ml portions were removed and counted using a Ge(Li) detector and a 4000-channel pulse height analyzer. Similar 10-ml aliquots of the *03Hg-TIOA concentrate were counted and stripped with 2, 4,6, 8, 10, and 1 2 N solutions of "03. The TIOA fractions were then recounted. The percent ?-03Hg removed from the TIOA to the 10 N "03 fraction was computed to be greater than 91% (see Figure 2). Additionally, a 65Zn tracer was subjected to a similar procedure and the percent @Zn found in aqueous, 10 N "03, and TIOA fractions was computed. Greater than 91% of the 65Zn was found in the 10 N "03 fraction. Sample Analysis. Solids. During the irradiation and analysis of environmental samples, NBS standard reference materials of coal, fly ash, bovine liver, and orchard leaves were used as calibration standards. Samples, standards, and flux monitors were placed in appropriate vials, sealed, and irradiated for 4 hr a t a thermal flux of 1.5 X loi3 n cm-' sec-' in the PULSTAR reactor. The irradiated samples and standards were then allowed to decay 3 days to minimize personnel radiation exposures and to remove any short-lived interferences present. Sample and standard vials were rinsed with 1:1 HN03 and dried. Immediately prior to combustion, the samples or standards were weighed into a tared ceramic combustion boat containing -10 mg mixed carrier. Samples were then combusted according to the NBS procedure described by Orvini et al. ( 4 ) . After combustion, the condenser containing the collected distillates was placed in a 3 19/38 30-ml round-bottomed flask. Time was allowed for the frozen distillates to melt a t room temperature into the round-bottomed flask before continuing the separation procedure. Any distillates remaining in the condenser were dissolved and washed into the round-bottomed flask with 0.2 ml of concentrated HN03 and 2.3 ml of concentrated HCl. Dissolution of the sample was completed by partially inverting the condenser-flask assembly and swirling the solution. Following dissolution, the sample was quantitatively transferred to a 60-ml separatory funnel, using -12.5 ml distilled water. A 9-ml portion of the 10% TIOA-xylene solution was added to the separatory funnel and shaken vigorously for 5 sec. The aqueous (bottom) layer was drained into a 60-ml polyethylene bottle and the TIOA solution was rinsed with 1 ml of 2 N HCl, which was then added to the aqueous sample. A 5-ml portion of 10 N "03 was added to the separatory funnel, vigorously shaken for 5 seconds, and drained into a second polyethylene bottle. A second 5-ml portion of 10 N "03 was added to the separatory funnel, shaken, and drained into the polyethylene bottle containing the first 5 ml of 10 N "03. The TIOA solution was then poured from the top of the separatory funnel into a third polyethylene bottle. The separatory funnel was rinsed with an additional 1 ml of the TIOA solution, and this rinse was added to the polyethylene bottle containing the 9 ml of TIOA. Each sample fraction was then counted separately for the radionuclides of interest (aqueous-As and Se; 10 N HNOZ-Hg, Cd, and Zn; TIOA-Br, Sb, and I). Figure 3 is a flow chart of the complete NAA radiochemical procedure. Sample Analysis. Liquids. Analyses for mercury were performed on several iodine monochloride solutions, which were supplied to this laboratory as part of an EPA-sponsored round-robin analysis involving six laboratories. Iodine monochloride solutions are used to absorb mercury from industrial gaseous effluents (6). After irradiation, these solutions were diluted with deionized water to the 15-ml mark on a separatory funnel, resulting in an approximately 2 N solution. The solutions were then separated directly (without the NBS combustion step) by the TIOA technique, with the 10 N HN03 fraction containing the mercury. The 10 N "03 fraction was then counted for an appropriate length of time and
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
FLYASH Zn
CHEM - N I T R I C
I
DECAY - 1 WEEK FULL SPECTRUM
I
I 777
I I 1 336 438 527
78
I
II 15
FLYASH
Sb
I
CHEM - O R G A N I C D E C A Y . 1 WEEK F U L L SPECTRUM
I
I
I
364
564
777
I
I
1318
1691
FLYASH CHEM - A Q U E O U S
Se Se
Se
DECAY - 2 WEEKS FULL SPECTRUM
Sb Zn
40
K
Sb EKG
I
136
l
264
l
559 657
400
I
777
1115
I
1213
I
1691
ENERGY (keV) Figure 4. Gamma spectra of an irradiated fly-ash sample following chemical separation
Table I. Precision a n d Accuracy of NAA and F A A Methods Hg, p p m
NAAQ Sample
No. o f detns
Mean a n d std dev
FAA
N o . of detns
Mean a n d s t d dev
Field 5 25.4 i 2.3 11 25.3 i 2.6 Replicate field 2 34.7 i 0.1 9 35.0 t 2.1 Nominal std. 2 1 3 . 0 i 0.0 4 1 2 . 8 i 1.4 (12.0 p p m ) Nominal s t d . 1 50.1 (N.A.) 8 47.9 t. 1 . 0 (48.2 p p m ) a NAA using t h e liquid anion exchange technique w i t h o u t the NBS combustion procedure.
the mercury content calculated. Table I lists the results of this laboratory and one other, showing the consistent precision and accuracy of two different methods [flameless atomic absorption (FAA) and NAA]. Laboratory Z, an independent laboratory, was chosen for this comparison because of its familiarity and expertise with flameless atomic absorption techniques.
DISCUSSION T h e objective of these experiments was t o develop a procedure whereby the desired radionuclides (As, Cd, Hg, s e , I, a n d Zn) could b e s e p a r a t e d from those isotopes with i n terfering y energies a n d b e quantitatively recovered. T h i s procedure could t h e n b e applied t o a large n u m b e r of environmental samples i n a variety of matrices. The primary advantage t o be gained b y separating t h e volatilized elem e n t s i n t o fractions is that of improved sensitivity.
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
2401
Table 11. Comparison of Precipitation and Liquid Ion Exchange Results for Multiple Analyses of a Coal Samplea 65Zn
Ig7Hg
llsmIn
"Se
Pptn
TIOA
Pptn
TIOA
Pptn
TIOA
26.4 22.1 26.0 27.1 27.0 20.7 21.9
14.8 17.1 14.3 16.2 14.7 15.4 16.7 15.8 15.6
159.6 172.4 185.9 102.2 188.7 158.5 175.0
125.0 120.7 136.1 135.8 122.1 134.6 130.1
166.0 171.3 158.2 158.1 139.1 138.7 N.D.C
95.5 87.4 118.5 115.5 177.3 111.8 90.9 93.4 103.8
l3l1b
-
Pptn
TIOA
4.9 2.5 6.1 6.3 6.8 2.4 2.7
3.4 3.4 4.0 4.9 4.8 4.1 4.2
TIOA
5.3 4.9 5.5 5.5 4.9 5.2 4.9 ... ... ... ... ... ... 5.1 Mean 24.5 129.2 155.2 4.5 4.1 5.2 163.2 Std dev 2.8 6.6 13.6 13.2 1.0 1.9 0.6 0.2 29.3 Re1 std dev, 7% 11 6 13 18 5 9 43 14 5 a Thousands of counts per minute normalized to 1 g of coal at completion of irradiation. b Not evident by precipitation procedure. C Not determined.
Table 111. Comparison of Uranium Analyses on Coal Samples from Various U.S. Mines Uranium. Dum T I O A separation and LEPD,a triplicate Ge(Li) detector system, analyses, mean value single analyses
Sample
DRB-A DRB-B DRB-C DRB-D DRB-E
1.6 0.1 1.0 f 0.1 1.3 i 0.1 1.1i 0.1 1.3 i 0.0 G-1 3.4 i 0.2 2.4 I 0.1 P-1 1.6 i 0.0 P-2 P-3 7.6 t 0.3 1.9 i 0.1 P-4 0.7 i 0.0 P-5 a Low-energy photon detection system (8). _+
1.0
0.2 1.0
2.0 1.0
3.0 3.0 1.0
8.0 2.0 0.9
Using the physical parameters unique to NAA (irradiation time, cross-section, flux, etc.), the theoretical sensitivity of the method for various elements can be calculated. In practice, however, this calculated value is seldom achieved because of interfering y energies in the spectrum. By removing the bulk of the bromine interference from the environmental samples, As, Cd, Hg, Se, and Zn can be easily quantitated. This liquid ion exchange procedure partitions approximately 75% of the bromine into the TIOA fraction, 15% into the aqueous fraction, and 10% into the 10 N "03 fraction. Figure 4 presents y spectra for a fly ash sample after separation. The chemical separation step and the period of decay are noted on the spectra. Intensity (log scale) is plotted vs. energy (keV) on the abscissa. It is evident from the y plots that one major interference has been eliminated and another significantly reduced. Any possible sodium interference has been eliminated by the combustion procedure and consequently does not appear in the spectra. As previously mentioned, the bulk of the bromine interference has been isolated in the organic (TIOA) fraction. Only a small percentage of bromine interference remains in the 10 N H N 0 3 and aqueous fractions. Although the remaining bromine can be removed from the aqueous and 10 N H N 0 3 fractions by additional washings with fresh TIOA, this step was unnecessary for rapid and accurate determinations. The removal and/or reduction of these interferences thus enhances the peak prominence of the isotopes of interest and negates long delays associated with the decay of these interferences. 2402
Other advantages of this liquid anion exchange procedure are those of speed (approximately 5 min to complete after combustion) and efficiency (all the products trapped in the condenser are counted in one of the three fractionsaqueous, 10 N HN03, or TIOA). Therefore, the accuracy of the results is not limited by factors associated with the chemical separation. Hg and Zn were shown to exchange from 2 N HCl to an anion exchange resin by Kraus and Nelson (7). Since As and Se are more soluble in H N 0 3 than in HC1, the distillates were dissolved in a 2 N acid solution containing HC1 and HN03. During the liquid anion exchange procedure, Hg and Zn exchanged to the TIOA while As and Se remained in the aqueous fraction. Since many environmental samples contain bromine, which also exchanges to the TIOA, experiments were conducted to determine the amount of bromine that could be bound to the TIOA while stripping out the Hg and Zn. After trying various concentrations of acid, it was found that 10 N H N 0 3 stripped greater than 91% of the Hg and Zn from the TIOA while leaving approximately 90% of the bromine bound to the TIOA. Table I1 shows the comparative precisions of the sulfide precipitation procedure and the TIOA technique after repeated analyses of the same coal sample. Following combustion, seven samples were precipitated and a minimum of seven samples were separated by the TIOA technique. All results are normalized to counts per minute per gram of coal at the end of irradiation. Although the mean counts for lg7Hg,65Zn, 115mIn,and 75Se were lower by the TIOA technique, this was compensated for by comparison with standards, using the same geometry. Note also that the sample contained 1311, not detected in the precipitate, which is used to calculate natural uranium content. Thirty hours after separation, the cadmium content of a sample can be calculated by using the peak area of the daughter isotope 115m1~.
The 528-keV peak, originally thought to be l15Cd, remained in the TIOA fraction after 10 N H N 0 3 extraction of several freshly irradiated environmental samples. This was confusing since the cadmium should have exchanged to the 10 N fraction. Half-life studies showed the 528-keV peak to be 1331.The 1311(364.5 keV) isotope was also identified by half-life study. These isotopes, which are the fission products of natural uranium in coal and other environmental samples, had not been evident by the precipitation method. After liquid separation, the 1331isotope can then be used to calculate the uranium content in the sample. This becomes an advantage when consideration is given to a recent article by Gladney et al. ( 8 ) which references the
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
tellurium interference in 1311determinations. Coal samples from various US.mines were analyzed for uranium in our laboratory by the TIOA technique and counted on a Ge(Li) detector using a pulse height analyzer. These values were then compared to the results obtained by Weaver (9) using a low-energy photon detection system on similar coals (Table 111). As previously mentioned, liquid IC1 round-robin samples were separated by the TIOA technique prior to analysis. Table I shows the excellent agreement between the two methods used (NAA and FAA). Without compromising accuracy or precision, it was possible to separate the element of interest (Hg) from other elements having interfering y energies while eliminating the NBS combustion step. In addition to isolating the element to be analyzed, another advantage is that of time reduction in the separation process. Without the NBS combustion step, the liquid anion exchange process takes approximately 5 min for completion. Similar analyses have been performed on scrubber water samples from the phosphate fertilizer industry with comparable results. As a result of the change in sample geometry, some efficiency was lost by counting the y emitters in liquid solution rather than in a precipitate form. This is demonstrated in Figure 5 . A 1-ml sample containing mixed radionuclides was counted. After the addition of water and mixing, the sample was repeatedly counted a t different volumes. Note that there is a 20% drop in counts from 1 to 10 ml and a further drop of 21% from 10 to 25 ml. These data demonstrated the need for minimizing all volumes.
CONCLUSION This technique of liquid anion exchange is applicable in performing rapid and accurate radiochemical separations in a wide variety of samples prior to y-ray spectrometry. The versatility of the technique is demonstrated by its applicability to both solid and liquid samples. Future studies in this laboratory may include the analysis of trace elements in total suspended particulate matter from environmental high-volume filter samples. Also being considered is the rapid separation and analysis of irradiated petroleum samples without using the NBS combustion procedure.
* o o l 90
80
a U
60
50 *..
40
0
5
10
15
20
25
4 30
VOLUME 0FSOLUTION.ml
Figure 5. Effect of sample geometry (volume) on counting accuracy
ACKNOWLEDGMENT The authors express their gratitude for the assistance given them by William Mitchell of EPA, Tom Gills of NBS, and Jack Weaver, James McGaughey, and Mark Jensen of North Carolina State University.
LITERATURE CITED (1) U.S. Congress, "Clean Air Amendments of 1970." Public Law 91-604, 91st Congress, H.R. 17255,Dec. 31, 1970. (2)D. von Lehmden, R. Jungers. and R. E. Lee, Anal. Chem., 46, 239-245 (1974). (3)R. E. Lee and D. von Lehmden J. Air Pollut. Control Assoc.. 23, 853-857 (1973). (4)E. Orvini, Thomas E. Gills, and Philip D. LaFleur, Anal. Chem., 46, 12941297,(1974). (5) F. E. Butler, A. R. Boulogne, and E. A. Whitley, Health Phys., 12, 927933 (1966). (6)Fed. Reg., "National Emission Standards for Hazardous Air Pollutants: Asbestos, Beryllium, and Mercury", Volume 38, No. 66,Pari II, 88318840 (April 6,1973). (7)K. A. Kraus and F. Nelson, Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, Geneva, 1955,Paper No. 837. (8) E. S.Gladney and H. L. Rook, Anal. Chem., 47,1554-1557 (1975). (9)J. Weaver, Anal. Chem., 46, 1292-1294 (1974).
RECEIVEDfor review May 19, 1975. Accepted September 15, 1975.
Determination of Lithium, Boron, and Carbon by Quasi-Prompt Charged Particle Activation Analysis John R. McGlnley and Emile A. Schwelkert Center for Trace Characterization, Department of Chemistry, Texas A&M University, College Station, Texas 77843
A novel approach for rapid nondestructive trace anaiysls is presented, based on the detection of short-lived high energy 0 emitters (10 msec I t j I 2 I 1 sec) produced by charged particle bombardment. Lithium, borQn, and carbon are determined via 'LI(d,p)'LI, "B(d,p)I2B and I2C(p,n)l2N, respectively. These elements have been measured at the l-to 350-ppm level with a relative precision of 5 to 30% In glasses, semiconductor materials, botanical specimens, and metals. Experimental detection limits are 0.50 ppm for lithium, boron, and 50 ppm for carbon.
Most of the work so far in charged particle activation analysis has been based on the detection of radioisotopes having half-lives greater than 1 min. Only a few recent studies have been concerned with the analytical exploitation of short-lived nuclides ( t l l z < 1 min) (1-4). An interesting aspect of this approach is that several light elements yield very short-lived species (tllz < 1 sec) under charged particle bombardment. The objective of the present study was to examine these possibilities from the analyst's standpoint, focusing on those cases where the product nuclides
ANALYTICAL CHEMISTRY, VOL. 47, NO. 14, DECEMBER 1975
2403
