Anal. Chem. 1981, 53, 299-304
299
Complexation of Some Transition Metals, Rare Earth Elements, and Thorium with a Poly(dithi0carbamate) Chelating Resin Akira Miyarakl' and Ramon M. Barnes* Department of Chemistry, GRC Towers, University of Massachusetts, Amherst, Massachusetts 0 1003
Compiexatlon properties of a poly(dithiocarbamate) resin for Fe(III), Fe(II), Cr(VI), Cr(III), V(V), V(IV), Ti(IV), Mo(VI), W(VI), Th(IV), 14 rare earth elements, and Os are examined by ICP-AES. Fe(II1) and Cr(V1) complex with the resin, whereas Fe(I1) and Cr( 111) do not. Considerable differences in uptake also exist between V(V) and V(IV) and Ce(II1) and Ce(1V). The digestion of the resin with nitric acid followed by dilution with (3 1) nitrlc acid-water Is suitable for Inductively coupled plasma-atomic emission spectrometry except for W.
+
Demands for trace element determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES) are rapidly increasing as its many advantages are demonstrated. However, trace elements determination of complex matrices, such as seawater (1) or biological samples (2), are still sometimes troublesome even with ICP-AES, although dynamic background correction methods and some new nebulizing systems have been developed (3). Rare earth and thorium are important elements not only in industrial applications but also in energy and environmental problems. Several methods have been used, such as neutron activation analysis, radioactivity measurements, mass spectrometry, and emission spectrometry for the determination of rare earth elements and thorium (4). Among these analytical techniques, ICP-AES has advantages in that it offers both good detection limits for rare earth elements and thorium and simultaneous multielement analysis capability. Fassel e t al. (5) compared the capabilities of flame and ICP spectroscopy for the determination of rare earth elements, and Nikdel et al. (6) and Broekaert et al. (7) examined the properties and applications of ICP-AES for the determination of rare earth elements. However, in trace element determinations using ICP-AES, large amounts of calcium and magnesium, which exist universally, interfere with the analysis because of instrumental stray light effects and background shifts (8-10). Preconcentration is often required for the determination of trace elements in samples such as seawater or biological samples because the abundance of these elements is too low to be determined directly by ICP-AES (11-13). Several procedures such as solvent extraction, coprecipitation and flotation (14),and resin chelation (1,15) have been used with ICP-AES to improve sensitivity and reduce interferences. Heavy metals, trivalent rare earth elements, and thorium are chelated by resins such as Chelex-100 (16),but this chelating resin also has affinity for alkali and alkaline earth elements, which limits the concentration factor achievable and necessitates additional separation steps (I, 15). Recently, Barnes and Genna (13) demonstrated that a poly(dithi0carbamate) chelating resin developed by Hackett and Siggia (17) alleviated these problems in the determination of trace elements in urine by ICP-AES. Because alkali and 'On leave from National Research Institute for Pollution and Resources,,Yatabe, Ibaraki, 305, Japan. 0003-2700~81/0353-0299$01.OO/O
Table I. ICP-AES Instruments and Operating Conditioiy Plasma-Therm Model HFS- 5 OOOD,40.6 8 ICP source MHz operating power 1.0 kW 3-turn copper tubing, in. 0.d. load coil cross flow (tip orifice diameters 100 pm) nebulizer plasma, 1 5 L/min; auxiliary, none; argon flow rates aerosol, 1.3 L/min at 20 psig. sample uptake 2.2 mL/min (av) rate monochromator Minuteman 310-SMP, l - m Czernyturner; grating, 1200 lines/mm; slit widths, 50 pm; slit height, 5 mm quartz lens, 2411. diameter, 200 mm optics focal length (Oriel No, A-11-661-37) recorder Heath EU-BOB observn height 18 mm above coil alkaline earth elements do not complex with this resin, complete separation of many metals from calcium, magnesium, sodium, and other electrolytes was possible. Subsequent study in our laboratory has shown that more than 50 elements complex with the poly(dithiocarbamate) resin. A poly(acrylamidoxime) resin described by Colella et al. (18, 19) also possesses similar metal selectively, but the total number of elements has not been established nor has it been applied in ICP-AES. Bray et al. (20) also examined the complexation properties of the poly(dithi0carbamate) resin for 16 elements including Cr, Fe, and V. However, no data for uptake between the different oxidation states of the elements was reported. On surveying the complexation properties of the resin, we have found that Cr(V1) and Fe(II1) complex with the resin, whereas Cr(II1) and Fe(I1) do not. Considerable uptake differences also exist between V(V) and V(1V) and Ce(1V) and Ce(II1). The purpose of this report is to demonstrate the complexation properties of 7 transition metals, 14 rare earth elements, and thorium with the poly(dithiocarbamate) resin and discuss the applicability of this resin in ICP-AES. EXPERIMENTAL SECTION Apparatus. The ICP-AES instruments and their operating conditions are given in Table I. The analysis wavelengths used in ICP-AES are listed in Table 11. Reagents. Standard solution of the rare earth elements were prepared by dissolving the metals (99.9% purity, Cerac, Milwaukee, WI, and Alfa, Ventron, Danven, MA) in dilute nitric acid. For Pr and Eu the oil in the containers used to prevent oxidation of these elements was washed off with toluene, and metals were dried with argon before they were weighed and dissolved in dilute nitric acid in an atmosphere of argon. The lanthanium standard solution was prepared by dissolving La(N03)3.6Hz0in dilute nitric acid. Ce(1V) standard solution was prepared by dissolving Ce(S04)z.2(NH4)z~S04~2Hz0 in dilute nitric acid. Ce(II1) standard solution was prepared by reducing ceric ammonium sulfate solution with hydrochloric acid and hydroxylamine hydrochloride. Thorium standard solution was prepared by dissolving thorium nitrate Th(N03)z.4Hz0in dilute nitric acid. Other standard solutions were obtained as follows: Fe(III), Fe(NH4)(S04)z.12Hz0; Fe(II), Fe(NH4)2(S04)z.6Hz0;Cr(VI), NH4Cr04; Cr(III), CrC13.6HzO; V(V), NH4V03; V(IV), VOSO,.xH,O; Mo(VI), (NOS, H4),Mo7Oz4.4HZO; Ti(IV), Ti metal; W(VI), (NH4)10W12041; 0 1981 American Chemical Society
300
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
Table 11. ICP-AES Wavelengths and Detection Limits detection limit,a ng/mL acid acid wavelength, 0.1 N matrix matrix 2c 1it.d nm element HNO, l b La I1 Ce I1 Pr I1 Nd I1 Sm I1 Eu I1 Gd I1 Tb I1 Dy I1 Ho I1 Er I1 Tm I1 Yb I1 Lu I1 Th I1 Cr I1 Fe I1 Ti I1 v I1 Mo I1 w I1 os I1
408.67 413.77 390.84 401.23 359.26 381.97 342.25 350.92 353.17 345.60 337.27 346.22 289.14 261.54 401.91 267.72 238.20 334.94 292.40 281.62 248.92 225.59
67 84 180 43 47 13 32 41 20 14 29 21 45 15 100 12 6 4
8
880 90 52
8
30 130 5
10 48 37 50 43 27 14 23 10 5.7 10
640 590 970 3 00 280 150 390 3 50 170 190 2 50 250 380 130
260 1160 53
36 14 7 20 85
8.6 1 83 7 4 4 7.5 14 73 0.4
a Detection limit is the concentration equivalent to three times the standard deviation of the background In signal. In 90% (v/v) 1:1nitric acid-sulfuric acid. 3 : l nitric acid-water matrix. Reference 21.
OsC1,. Concentrations of Cr and V in Cr(II1) and V(1V) solutions were calibrated with Cr(V1) and V(V) standard solutions using ICP-AES, because the Cr(II1) reagent was slightly wet and the V(1V) reagent contained an ambiguous amount of crystalline water. In order to prevent the oxidation of Fe(I1) to Fe(III), ascorbic acid solution was added to give a final ascorbic acid concentration of 0.3%. Distilled, deionized water was used throughout. All reagents and acids were ACS reagent grade. Resin Synthesis. During the synthesis of new batches of resin, the sulfur content of the resin was monitored as a function of reaction time between carbon disulfide and the 8/1 PEI-18-PAP1 resin. Prior to analysis, the resin was dried for 48 h in open air. After 12-h of reaction the sulfur content was 18.32%,after 24 h, 18.56 and 18.85%,after 60 h, 18.08%,and after 672 h, 17.65%. These data indicate that an overnight reaction is sufficient, in contrast to the 4-week reaction employed by Hackett and Siggia (17). Batch Test. The uptake of all elements with the resin were studied by use of a batch test (17). Single-element solutions and binary mixtures (Nd-Sm, Gd-Tb, Dy-Ho, Er-Tm) at different pH values (20 mL for Eu and Lu, 10 mL and 25 mL for Mo, 10 mL for others) which contained 5 mg (10 mg for Mo) of metals were shaken in 60-mL polyethylene containers with 50 mg of the resin (60-80 mesh). pH of solutions, except for Ce(III), Fe(II), Cr(III), and V(IV), was adjusted with HN03 and "SOH. For these species, HC1 and NHIOH were used. Ammonium citrate solution (5 mL of 5% for La, Yb, Th, and 5 mL of 10%for others) was added to all the rare earth elements, Fe(III), Ti(IV), and Mo(V1) samples and blanks to prevent precipitation of metal hydroxides in the high range. In Fe(I1)and Cr(II1) experiments, each 60-mL polyethylene bottle was purged with argon, and the opening between the bottle and its cap was sealed with vinyl tape to prevent the oxidation of Fe(I1) and Cr(II1) by air during shaking. After 24-h of equilibration on a mgchanical shaker, each solution was filtered with suction and the resin was collected on filter paper (Whatman, Quantitative No. 1). The solution was diluted to 50 mL with 0.1 N HN03 (0.1 N HCl for Ce(II1)). The concentrations of metals in the filtrate were measured by means of the method of additions by ICP-AES. Duplicate samples and blanks were prepared and analyzed at each pH value. Metal Recovery. The concentrations of metals chelated by the resin were also determined to establish quantitatively the recovery for each metal from the resin. Previously, Barnes and
Genna (13) used a one-to-one (v/v) nitric acid-sulfuric acid mixture digestion followed by dilution with water to 60% (v/v) or 50% (v/v) acid mixture. Further investigations showed that a white precipitate, which seemed to be due to hydrolysis of the incompletely digested resin in the 60% (v/v) one-to-one nitric acid-sulfuric acid mixtures, was sometimes formed after a day. The precipitation is explained as follows: the poly(dithi0carbamate) resin is synthesized by cross-linking between polyethylenimine and polymethylene polyphenyl isocyanate followed by the sulfonation reaction with carbon disulfide. In acid, some parts of the resin can be attacked, but a considerable part remains. The resin contains a large number of amino groups, which are principally basic. They are not soluble in water or dilute acid but are soluble in concentrated acid. In fact, determination by ICP-AES of carbon content in the acid-digested resin samples indicated that only 58.6% and 74.3%of the resin was decomposed when 3 and 5 mL, respectively, of 1:l nitric acid-sulfuric acid mixture were used for digestion of 100 mg of resin. In these experiments, a 90% (v/v) 1:l nitric acid-sulfuric acid mixture was applied to all elements except Ti and V. No precipitation was observed in this matrix in solutions stored for 2 weeks. The resin on the filter paper was washed with a small volume of water into a 25-mL glass beaker, and the mixture was evaporated gently on a hot plate. Fifteen milliliters of 1:l (v/v) nitric acid-sulfuric acid mixture was added to the resin, and the beaker with a watch glass was heated gently on a hot plate until a clear solution was obtained (usually 10-15 min). After cooling, the solution was made up to 25 mL with 1:l nitric acid-sulfuric acid mixture and water, so that final acid concentration was 90% (v/v) 1:l nitric acid-sulfuric acid mixture. To prevent the loss of Os by volatilization as Os04 (bp 130 "C), the digestion was carried out in a 25-mL distillation flask with a water condenser using a 125 OC oil bath. The concentration of each metal in these solutions was determined by ICP-AES from a calibration function prepared for the specific element in the same acid matrix. The signals from blank solutions in ICP-AES were not distinguishable from the background which verified low metal reagent blanks. The disadvantage of this digestion method is that detection limits for the metals in ICP-AES are poorer than obtained with water or dilute acid because of increased viscosity of acid. A perchloric acid and nitric acid mixture and nitric acid alone were investigated to improve the digestion of the resin. In the perchloric and nitric acid mixture test, the residue was soluble in dilute HC1 or "OS, and no precipitation was observed for at least a week, but the approach was time consuming. Finally, digestion with concentrated HN03 followed by dilution with a 3:l nitric acidwater mixture was found to prevent any precipitation in the digested solutions for at least up to 2 months. When HNOa-H20 mixtures less than a 2:l dilution were used, slight precipitation was observed in 2 days. Dilution with (3 + 1) HN03-H20 was adopted for the tests performed with Ti, V, and Mo. After the filtration of the transition-metal solution previously shaken with the resin, the resin on the filter paper was washed with a small volume of water into a 25-mL glass beaker, and the mixture was evaporated gently on a hot plate. After 15 mL of nitric acid was added to the resin, the beaker with a watch glass was heated gently until a clear solution was obtained (usually 15-20 min). Upon cooling, the solution was transferred to a 25-mL volumetric flask and made up to volume with (3 + 1) nitric acid-water mixture. The concentration of metals was determined by ICP-AES from calibration functions prepared with standard solutions in the same acid concentration matrix.
RESULTS AND DISCUSSION Detection Limits. The ICP-AES detection limits for elements studied were determined in standard solutions prepared with 0.1 N HN03 matrix, 90% (v/v) 1:l nitric acidsulfuric acid mixture, and 3:l nitric acid-water matrix. The results are given in Table 11. The detection limits in the (3 1)nitric acid matrix were 2 to 3 times poorer than those for 0.1 N "OB matrix. This factor was almost the same as the factor for 60% (v/v) 1:l nitric acid-sulfuric acid mixture described by Barnes and Genna (13). With 90% (v/v) 1:l nitric acid-sulfuric acid mixture in water, results are 9 times
+
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
301
Table 111. Resin Properties capacity, mg metal/g resin Aa B b Cc
optielement mum (oxidation state) pH
b P 3
4
6
5
La(111) Ce(II1) Ce(1V) Pr( 111) Nd(II1) Sm(II1) Eu( 111) Gd( 111) Tb(111) DY(W Ho( 111) Er( 111) Tm(II1) Yb(II1) Lu( 111) Th(1V) Fe(II1) Fe( 11) Cr(V1) cr(IIIj V(V) VIV) Ti( IV) W(VI 1 Mo(VI)
\a1
i
8
9
10
Figure 1. pH dependences of uptake for (a) Lu (upper) and (b) Pr
(lower) in solutions containing one element: (M) calculated from the filtrate and (0)calculated from the digested resin. The uptake is the ratio of element concentration found to the initial concentration expressed in percent.
,
I
I
I
I
I
5.98 5.09 5.06 4.01 4.12 3.97 3.94 4.04 3.95 3.95 4.00 3.97 4.01 5.94 4.02 4.89 3.04
28.7 25.3 9.5 38.6 39.4 32.8 43.1 37.5 27.5 39.6 31.1 20.5 30.0 33.7 28.5 74.2 20.4 0 95.8 0 62.9 30.8 29.8 77.6 31.0 84.3
2.01 3.09 3.01 2.01 2.90 4.98 4.09
os
19.5 19.1 25.1 23.9 29.1 29.2 24.8 26.2
46e 14e 45f 45f 50f
recovery? %
93.4 87.8 95.2 100.0 91.4 90.5 90.4 97.4 101.2 100.7 89.4 100.0 98.4 84.4 92.7 16.3 80.4 104 91.4 99.0 89.2 98.0 104 97.8
Poly( dithiocarbamate) resin at optimum pH. Poly(dithiocarbamate) resin with two elements in solution toPoly(acry1amidoxime) resin. From ref 18. rther. Concentration from digested resin/concentration from filtrate in %. e At pH 2. At pH 5. a
PH
20
cc /
L I
\
// \
Figure 2. pH dependences of uptake for Gd and Tb in solutions containing the two elements together: ( 0 )Gd calculated from filtrate, (0)Gd calculated from digested resin, (M) Tb calculated from filtrate, (0) Tb calculated from digested resin.
poorer than those for 0.1 N HN03 matrix because of acid mixture viscosity. Compared with the values reported for pneumatic nebulization (21),the results for 0.1 N H N 0 3 are slightly poorer. More precise optimization of ICP-AES operating conditions might improve the detection limit; however, the values were suitable for the experiment undertaken here. pH Dependence of Metal uptake. Rare Earth Elements and Thorium. The pH dependences of uptake for Lu(II1) and Pr(II1) by the resin are shown in Figure 1. The two curves correspond to determinations performed with the filtrate and the dissolved resin solution. Although the uptake at each pH is slightly different for each solution, pH dependences of uptake are almost the same. The results in Figure 1are typical of most of the rare earth elements in the single-element samples. Of the 14 rare earth elements studied here, 11 elements (except for La, Ce, and Yb) showed the maximum uptake ratio a t pH 4 (Table 111). The pH-dependent uptake of Gd(II1) and Tb(II1) for the solutions containing both 4.79 mg of Gd(II1) and 5.20 mg of Tb(II1) is illustrated in Figure 2. The pH maximum uptake was still p H 4, although a second peak was observed a t pH 8. The features shown in Figure 2 were common to all of the solutions containing two elements, such as Nd-Sm, Gd-Tb, Dy-Ho, and Er-Tm, tested in the present experiment. These results suggest that when several rare earth elements exist
1i
\
/ A
/
/
/
/
/
'\
\
I
/ \
//
PH
Flgure 3. pH dependences of uptake ratlo for Ce(1V) and Ce(II1): (M) Ce(1V) calculated from filtrate, (0) Ce(1V)calculated from digested resin ( 0 )Ce(II1) calculated from filtrate, (0)Ce(II1) calculatsd from digested
resin.
together in the solution, which is usually the case, they can be concentrated with the poly(dithi0carbamate) resin at the same maximum uptake pH obtained from the solutions containing one element. Compromise pH for the preconcentration of all the rare earth elements is in the range of 4-5. The pH dependences of uptake for Ce(1V) and Ce(II1) are given in Figure 3. The uptake for Ce(II1) was similar to those for another trivalent rare earth elements, whereas Ce(1V) showed a low uptake. This fact indicates that the reduction of Ce(1V) to Ce(II1) is effective to increase the uptake ratio of Ce in the preconcentration of rare earth elements with this resin. Although the uptake calculated from the resin-digested solutions was systematically lower than those calculated from the filtrates, the ratio indicates the total recovery expected
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
302
5 0
1
2
3
4
5
6
7
8
9
1
02 0
PH
Flgure 4. pH dependence of uptake for Th(1V): (B)calculated from calculated from digested resin. filtrate, (0) I
I
I
I
I
I
I
I
I
I
1
2
I
L A
0
1
2
3
4
5
701
i
\\ 6
7
8
9
1
0
PH
Figure 5. pH dependences of uptake for Fe(II1) and Fe(I1): (B) Fe(II1) Fe(II1) calculated from the digested resin, calculated from filtrate, (0) (0)Fe(II1) calculated from filtrate, (0)Fe(I1) calculated from digested resin.
a t the measured concentration level from batch or column analysis of practical samples. The recoveries based upon the difference between these two solutions at the optimum pH are listed in Table 111. These values were within 90% for most of the rare earth elements. Prior to practical application the uptake and recovery are measured as a function of element concentration to verify quantitation especially at trace levels (17). The pH dependence for Th(1V) is documented in Figure 4. The pH of maximum uptake was from pH 2 to 5. This property is different from that of uranium without a masking reagent as described by Barnes and Genna (13). The low thorium recovery calculated from the filtrate and the resin digest is due to the precipitation of thorium sulfate in the digested samples. The content of thorium in the digested samples was determined by ICP-AES after centrifuging the solution. The nitric acid digestion method has to be used when large amounts of thorium exist in the samples. The maximum uptake pH, capacity of the resin, and recovery for rare earth elements and thorium are summarized in Table 111. The uptake and capacities of the elements in a solution containing one element are generally higher than those in the solution containing two elements together. This reflects the competition between the two elements for complexation with the resin. The resin displays very similar capacities for all the trivalent rare earth elements. The average of capacity for 14 trivalent rare earth elements is 32.6 f 6.3 mg of metal/g of resin. The capacity for thorium is considerably higher than those for the rare earth elements. Transition Metals. The pH dependences of uptake ratio for Fe(II1)-Fe(II), Cr(V1)-Cr(III), V(V)-V(IV), Ti(IV), Mo(VI), W(VI), and Os are shown in Figures 5-11. All of the transition metals investigated complex with the resin when the appropriate oxidation state is selected. Hackett and Siggia (17)reported that iron did not complex with the resin, although the oxidation state used was not defined. The results presented in Figure 5 indicate that Fe(II1) complexes with the
4
5
6 PH
7
8
9
1
0
Figure 6. pH dependences of uptake for Cr(V1) and Cr(II1): (W) Cr(V1) Cr(V1) calculated from the digested resin, calculated from filtrate, (0) (0)Cr(II1) calculated from filtrate, (0)Cr(II1) calculated from the dlgested resin. .
1 I 4
\\
3
,
I
I
I
I
I
60: 50
$40
LOl 3
20
‘“t 0
PH
Figure 7. pH dependeces of uptake for V(V) and V(1V): (W) V(V) V(V) calculated from the digested resin, calculated from filtrate, (0) (0)V(IV) calculated from the filtrate, (0)V(IV) calculated from the digested resin.
PH
Flgure 8. pH dependence of uptake for Ti(IV): (B)Ti(1V) calculated Ti(1V) calculated from the digested resin. from filtrate, (0)
0
i u 1
2
3
4
5
6
7
8
9
1
0
PH
Flgure 9. pH dependence of uptake for Mo(V1): (W) Mo(V1) calculated from filtrate, (0)Mo(V1) calculated from the digested resin.
ANALYTICAL CHEMISTRY, V M . 53, NO. 2, FEBRUARY 1981
0
1
2
3
4
5
6
7
8
PH
Np Pu Am Cm Bk Cf
Figure 10. pH dependence of uptake for W(V1): (DW(V1) calculated
from fikrate and (0) W(V1) calculated from the digested resin.
1
2
3
4
5
PH Flgure 11. pH dependence of uplake for Os: (.)Os Os calculated from the digested resin. fiiirate. (0)
calculated from
resin, hut Fe(I1) does not. This suggests that reduction of Fe(II1) to Fe(I1) is essential to exclude iron from chelating with the resin. As illustrated in Figure 6, Cr(V1) complexes strongly with the resin, whereas Cr(II1) does not. The uptake ratio for Cr(V1) was almost 100% at pH 2.0 and was still very high to pH 6. Uptake for Cr(II1) was almost zero to pH 5. Above pH 5, the precipitation of hydroxide was observed. This suggests that differential analysis of trace amounts of Cr(V1) and Cr(II1) may he possible with the resin if pH below 5 is maintained. Recently, a differential determination of Cr(VI) and Cr(II1) with the resin combined with the conventional KMnO, oxidation method was developed (22). Considerable differences also existed between V(V) and V(IV) uptake (Figure 7). V(V) showed high uptake in the wide pH range (pH 3 to 71, and uptake for V(1V) was maximum at pH 3 and decreased to near zero at pH 8 (Figure 8). Mo(VI) showed almost constant uptake up to pH 6, and it decreased above pH 7 (Figure 9). The uptake for W(V1) was maximum at pH 3, but it was high over a wide pH range (pH 1-8) (Figure 10). Although exact oxidation state was not defined, Os showed the increasing uptake which became constant above pH 3 (Figure 11). The precipitation of hydroxide occurred above pH 4. The values reported in Figures 1-11 are averages for two samples, and the relative standard deviation was less than 5%. Compared with the data of Bray et al. (ZO),although they have not described the oxidation state of metals, the pH dependences of uptake for Mo(V1) and V(V) in this experiment are similar. The lower uptake for Mo(V1) in this experiment was probably due to the difference between the amount of metal used in the two experiments. We used exMo(V1) (10 mg) to investigate the optimum pH of uptake and the resin capacity, whereas they used trace amounts of Mo. The pH dependence of the uptake for Ti(1V) in our experi-
EE Fm Md NO Lw
' Y
Figure 12. Elements whch m p l e x wiih the resin represented by dark shading. Nonmplexing elemem are given by I* shadng and o h m
have
0
303
not
oeen anempled
ment is somewhat different from that for Ti in their experiment, but the reason lor this difference is not clear. Using AAS, Colella et al. (18, 19) found that a pdy(acry. lamidoxime) resin complexed with CrrVIJ but did not complex with Cr(III). They also demonstrated that V(V), Fe(lll), Fe(II), Ti(IV), and nine other elements romplexed with the poly(arrylamidoxime) resin. However, the pH dependence of metals uptake with the polyrarrylamidoximeJ resin are somewhat different from those of poly(dithiwarhamate)rwin. This results from the different funrtional chelating groups in the two resins. The pH of maximum uptake, rapacities. and recoveries for the trnnsition metals with the poly(dithiocarbamateJ resin are given in Table 111. The capacities of poly(acry1amidoximeJ resin described hy Colella et al. (1.8)are also included in the table. The capacities of poly(dithiorarliamateJ resin are larger for Cr(VIj and V(V1, but smaller fur Fe(Ill1, Fe(llJ.and TiW) than those of poly(acry1amidoxime) resin. No data are presently availahle for the rare e a n h elements with the poly(acry1amidoxime) resin. The results of this investigation demonstrate that the poly(dithiocarbamate) resin romplexes with rare earth elements, thorium, and specific oxidation states of light transition metals. For individual element determination, the optimum pH can he selerted. and for simultaneous multielement determinations as provided hy ICP-AES, one or more compromise pH values are required. The compromise pH for rare earth elements corresponds to the optimum, whereas the compromise pH of 3 should he used for simultaneous multielement chelation of the transition elements studied here. Prior tn application, however. the recovery should be measured ior each metal at concentration levels corresponding to the actual sample as illustrated in previous applications to sea. water and urine (13, 17). Hesin Digestion. The data for Ti,V, and Mo indicate that the results calculated from the filtrate are very similar tn t h w frnm nitric arid digestion of the rmin. The recoveries for mnat of these elements given in Table 111 are within 90% at the optimum pH. This suggests that the nitric acid in place of the nitrir acidliulfuric acid digestion method can he used for most of the elementn inrluding thorium. However, this method cnnnot he applied when large amounts of tungsten exist in the samples, hecause tungsten acid precipitates. In this case, 90% ( v / v ) I:1 nitric arid and sulfuric acid should be selerted. S u m m a r y of Metal Complexation. Elements which romplrx u,ith the poly(dithi0rarhamate) resin studied thus far in our lahoracnry are indicated by shading in Figure 12. More than SO elements are complexed. whereas the alkali and alkaline earth elements, manganese. Cr(1lli. and Fe(lll are not. Bray et al. (20) also reported low uptake for boron and
304
Anal. Chem. 1981, 53, 304-308
increasing uptake for manganese in base. The complexing characteristics of the remaining nonradioactive elements (Li, Be, Rb, Cs, Zr, Nb, Hf, and Ta) are now being determined. The properties of the poly(dithi0carbamate) resin for the metals of this investigation remain to be tested at trace concentration levels and in column rather than batch modes. However, previous experience with other elements (13, 17) suggests that once the optimum pH for chelation is determined in batch studies, collection of trace concentration levels by column techniques provides quantitative recovery. The results of this study and those reported previously for water, milk, and urine samples (13, 17) indicate that the poly(dithi0carbamate) resin possesses unique potential for many applications in environmental, pollution, geochemical, and biological problems for which the determination of trace amounts of metals by ICP-AES and other spectrochemical methods is presently limited by the high concentrations of iron or alkali and alkaline earth elements. The development of some typical applications is presently under way.
ACKNOWLEDGMENT The assistance of G. Dabkowski in preparing the resin samples and contributing the synthesis test data and the discussions with M. B. Colella concerning the resin digestion are greatly appreciated.
LITERATURE CITED Berman, S. S.; McLaren, J. W.; Willie, S. N. Anal. Cbem. 1980, 52, 488-492. Haas, W. J.; Fassel, V. A. "Elemental Analysis of Biological Materials, Technical Report Series, No. 197"; Internatlonal Atomic Energy Agency: Vienna, Austria, 1979; Chapter 9, pp 167-199. Fassel, V. A. Anal. Cbem. 1979, 57,1290A. Baudin, G. Prog. Anal. At. Spectrosc. 1980, 3 , 1-63. Fassel, V. A.; Knlseley, R. N.; Butler, C. C. "Analysis and Application of the Rare Earth Materials"; Mlchelsen, 0. B., Ed., Universitetsfor-
logqet: Osio, Norway, 1973; pp 71-86.
(6) Nikdei, S.; Massoumi, A.; Winefordner, J. D. Mlcrochem. J . 1979, 24,
1-7. (7) Broekaert, J. A. C.; Leis, F.; Laqua. K. Spectrocblm. Acta, Part 6 1979, 348, 73-84. (8) Larson, G. F.; Fassei V. A.; Winge, R. K; Kniseley, R. N. Appl. SpectrOSC. 1978, 30, 384-391. (9) Fassel, V. A.; Katzenberger, J. M.; Winge, R. K. Appl. Spectrosc. 1979, 33, 1-5. (10) Larson, G. F.; Fassel, V. A. Appl. Spectrosc. 1979, 33, 592-599. (11) Subramanian, K. S.; Chakrabart, C. L. Prog. Anal. At. Spectrosc. 1979, 2, 287-306. (12) Slavin, W. At. Spectrosc. 1980, 7 , 66-71. (13) Barnes, R. M.; Genna, J. S. Anal. Chem. 1979, 57, 1065-1070. (14) Hlralde, M.; Ito, M; Baba, M.; Kawaguchi, H.; Mizuike. A. Anal. Chem. 1980, 52,804-807. (15) Sturgeon, R. E.; Berman, S. S.; Desaulniers, J. A. H.; Mykytiuk, A. P.; McLaren, J. W.; Russell, D. S. Anal. Chem. 1980, 52, 1585. (16) Bulletin 2020, Bio-Rad Laboratories Product Information, 1978. (17) Hackett, D. S.; Siggia, S. I n "Environmental Analysis"; Ewlng, G. W., Ed., Academic Press: New York, 1977; p 253. (18) Colella, M. B.; Siggia, S.; Barnes, R. M. Anal. Chem. 1980, 52, 967-972. (19) Colella, M. 8.; Sggia, S.; Barnes, R. M. Anal. Chem. 1980, 52, 2347. (20) Bray, J. T.; Reiily, F. T., Jr.; Bates, J. M.; van Rij, A. M.; Porles, W. J. Presented In part at the 14th Annual Conference on Trace Substances In Environmental Health, Columbia, MO, June 1980. (21) Winge, R. K.; Peterson, V. J.; Fassei, V. A. Appl. Spectrosc. 1979, 33, 206-219. (22) Miyazakl, A.; Barnes, R. M. Anal. Chem., companion paper In this issue.
RECEIVED for review August 6,1980. Accepted November 21, 1980. This work was supported by Department of Energy (Office of Health and Environmental Research) Contract DE-AC02-77EV-04320. Results were presented in part at the Sixth Annual Meeting of the Federation of Analytical Chemistry and Spectroscopy Societies, the 29th Annual Meeting of the Japan Society for Analytical Chemistry, and the 27th Canadian Spectroscopy Symposium. A.M. acknowledges the Science and Technology Agency of Japan for his travel support.
Electron Ionization-Flash Desorption in Mass Spectrometry of Tetraalkylammonium Halide Salts Terry D. Lee, William R. Anderson, Jr., and G. Doyle Daves, Jr." Depattment of Chemistry and Biochemical Sciences, Oregon Graduate Center, Beavetton, Oregon 97006
Electron lonlzatlon (EI)m a s spectra of tetraalkylammonium halide salts have been recorded by use of the technlque of electron ionization-flash desorption. These spectra exhlblt R4N+Ions and fragment Ions which characterize the structure of the quaternary ammonium cation. Ion productlon requires both rapid sample heatlng (flash desorption) and electron bombardment and occurs in the gas phase from volatile precursors. The volatile precursors to R4N+ Ions may be Intact R4NX molecules or (R4NX), clusters. Alternatlvely, It Is possible that thermal reductlon of the solld (or molten) saH occurs to yleld neutral R4Nwhich Is volatlle and undergoes electron Impact induced ionlzatlon to R4N+.
In connection with our ongoing research on mass spectrometry of nonvolatile and thermally unstable molecules (I-i'), we report the first electron ionization (EI) mass spectra of tetraalkylammonium salts which exhibit ions characteristic 0003-2700/8 1/0353-0304$01 .OO/O
of the quaternary amine moiety (1, 8). Recent studies of quaternary ammonium salts by field desorption (9-15), electrohydrodynamic (16),secondary ion (ion bombardment) (In,in beam chemical ionization (18, 19),laser desorption (20, 21), and 252Cfplasma (fission fragment induced) desorption (21) mass spectrometries, which (presumably) are surface ionization techniques ( l ) have , been justified largely on the basis of the assumed inaccessability of R4N+ions by E1 mass spectrometry. Prior to the present investigation, E1 mass spectrometry of tetraalkylammonium salts has invariably involved initial thermal dealkylation to achieve volatilization of one or more tertiary amines followed by electron ionization of the pyrolysis products (22). The spectra we have obtained by electron impact-flash desorption mass spectrometry exhibit even electron R4N+ ions and characteristic E1 fragment ions. Electron ionization-flash desorption mass spectrometry involves heating a sample absorbed on a metal surface, positioned within the ion source of a conventional E1 mass 0 1981 American Chemical Society
