2580
Anal. Chem. 1984, 56,2580-2585
Determination of Rare Earth Elements by Liquid Chromatography/Inductively Coupled Plasma Atomic Emission Spectrometry Kazuo Yoshida and Hiroki Haraguchi* Department of Chemistry, Faculty of Science, University of Tokyo, Bunkyo-ku, Tokyo 113, J a p a n
Inductively coupled plasma atomic emlsslon spectrometry (ICP-AES) Interfaced wlth hlgh-performance liquld chromatograhy (HPLC) has been applied to the determination of rare earth elements. ICP-AES was used as an element-selective detector for HPLC. The separatlon of rare earth elements wlth HPLC helped to avold erroneous analytlcal results due to spectral Interferences. Fiiteen rare earth elements (Y and 14 ianthanldes) were determlned selectively with the HPLCIICP-AES system using a concentratlon gradient method. The detectlon llmits wlth the present HPLCIICP-AES system were about 0.001-0.3 MgImL wlth a 1OO-hL sample Injectlon. The callbratlon curves obtalned by the peak helght measurements showed llnear reiatlonshlps In the concentratlon range below 500 pg/mL for all rare earth elements. A USGS rock standard sample, rare earth ores, and hlgh-purity ianthanlde reagents (>99.9 % ) were successfully analyzed wlthout spectral Interferences.
Recently rare earth elements have received much attention in the fields of geochemistry and industry (1-3). Rapid and accurate determinations of them are increasingly required as industrial demands expand. However, the determination of rare earth elements a t the trace level is still very difficult because of interelement interferences or lack of sensitivities, when instrumental analytical techniques are directly used for analysis without prior sample treatment. Serious interference problems are encountered when using direct determination instrumental techniques, especially when the samples contain large amounts of several rare earth elements at different concentration levels. Isotope dilution mass spectrometry (3,4) and neutron activation analysis (5-7) are commonly used for the determination of rare earth elements. Isotope dilution mass spectrometry provides fairly high sensitivities for rare earth elements. However, the selectivity of mass spectrometry is not sufficient to analyze the samples directly. Therefore some separation is required before measurement. Such techniques for separation are sequential precipitation, solvent extraction, and chromatographic methods. The isotope dilution mass spectrometric technique has another substantial problem, that is, Pr, Tb, Ho, and T m cannot be detected because these elements do not have plural stable isotopes. As for neutron activation analysis, several rare earth elementa can be determined with high sensitivities. The neutron activation technique, however, suffers from the following problems: high cost and cumbersome instrumentation, slow analysis time, poor precision, and interelement interferences. In the determination of rare earth elements by neutron activation analysis, separation techniques similar to those employed in isotope dilution mass spectrometry are also commonly performed because of the interferences with other coexisting elements in analysis. Recently inductively coupled plasma atomic emission spectrometry (ICP-AES) has been extensively applied to the
determination of metallic elements (8-10). As is well known, ICP-AES has advantages such as low detection limits, good precision and/or accuracy, wide dynamic ranges of calibration curves, and capability of simultaneous multielement analysis. In the determination of rare earth elements, ICP-AES provides extremely higher sensitivities (11-13) than atomic absorption spectrometry (14), flame emission spectrometry (8), and atomic fluorescence spectrometry (13). In the determination with ICP-AES, however, a number of emission lines are excited, compared to other chemical flames, and so spectral interferences due to rare earth elements themselves are prone to be serious problems (11, 12). Crock et al. (13) corrected the spectral interferences from other coexisting rare earth elements in addition to selecting the analytical wavelengths. They separated rare earth elements from other elements with ion exchange techniques using cation and anion exchange resins and determined them in geological materials which were contained at almost similar concentration levels. The applications of ICP-AES to the analysis of such samples that contain very different concentrations of rare earth elements are remarkably difficult even when the ion exchange method is used for separation. This is because the spectral interferences are too large to make exact experimental correction. Therefore, development of a combined system of ICP-AES with separation techniques for rare earth elements is desired for the rapid and accurate determination. In recent years, ICP-AES interfaced with liquid chromatogrpahy has been investigated because of the advantages of both instrumental techniques (16-24). However, the analytical applications to those samples which require relatively high salt concentration of mobile phase for column separation of chemical species are still limited. This is because the large content of salts in the mobile phase causes clogging of the ICP-AES torch, which prevents sample introduction into the plasma. In the present experiment, ICP-AES interfaced with high-performance liquid chromatography (HPLC) is applied to the determination of rare earth elements. The problem caused by direct and long-term introduction of the high salt solution for the concentration gradient separation of rare earth elements has been overcome by using the modified plasma torch and adjusting the suitable torch position. Consequently, rare earth elements in a USGS rock standard sample, rare earth ores, and high-purity lanthanide reagents (>99.9%) have been determined without spectral interferences by the HPLC/ICP-AES system. EXPERIMENTAL SECTION Apparatus. The HPLC system consisted of two solvent delivery pumps, an injection valve (Model 7125 from Rheodyne Co., Cotati, CA), and an associated column. The solvent flow rates from pump A and pump B were controlled with a gradient programmer (Model GRE-3A from Shimadzu Co., Japan). The separation was performed by using a 4 mm i d . X 250 mm long stainless steel column packed with a strong cation exchange resin (IEX-21OSC from Toyo Soda Co., Japan). The column temperature was maintained at 50 O C with a column oven (Model CTO-SA from Shimadzu Co., Japan). The sample volume injected
0003-2700/84/0356-2580$01.50/00 1984 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984
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Table I. Spectral Interferences" of Coexisting Rare Earth Elements at the Most Sensitive Emission Lines of Analyte Elements in ICP-AES with Direct Nebulization analyte element Y
La Ce Pr Nd Sm Eu Gd Tb DY Ho Er
Tm Yb Lu
wavelength, nm 371.03 379.48 413.77 390.84 401.23 359.26 381.97 342.25 350.92 353.17 345.60 337.27 313.13 328.94 261.54
interfering elements and interference factor Pr, 2.9; Nd, 1.8; Sm, 1.4; Eu, 1.5 Ce, 49; Pr, 36; Nd, 49; Sm, 33; Eu, 27; Ho, 48 Pr, 59; Nd, 85; Sm, 52; Eu, 63; Er, 330; Tm, 65; Yb, 81 Ce, 2200; Nd, 180; Sm, 140; Eu, 95; Gd, 66; Tb, 73; Dy, 81 Ce, 1050; Pr, 160; Tb, 59; Dy, 56 Y, 27; Pr, 35; Nd, 370; Gd, 1200; Tb, 50; Dy, 47; Ho, 47 Nd, 260; Er, 7.0 Ce, 59; Sm, 19; Tb, 67; Dy, 65; Ho, 76; Er, 29 La, 35; Ce, 31; Pr, 41; Sm, 190; Gd, 21; Dy, 46; Ho, 140 Nd, 35; Eu, 21; Tb, 45 Pr, 25; Nd, 12; Sm, 16; Tb, 36; Dy, 11 Tb, 160; Dy, 42; Ho, 23 Pr, 16; Sm, 10; Tb, 36; Er, 53 Pr, 1.6; Nd, 1.2; Tb, 1.3; Dy, 3.9; Ho, 4.4; Tm, 2.2
Values for spectral interferences are expressed in ng/mL of analyte element per 10 wg/mL of interfering element. into the column was 100 FL. The effluent outlet from the column was fed to a cross-flow nebulizer of the ICP spectrometer, which was interfaced with small diameter Teflon tubing (0.5 mm i.d. X 300 mm long). The ICP-AES instrument consisted of an ICP torch system with a rf generator (Model ICAP-BOA from Nippon Jarrell-Ash Co., Japan), a monochromator (Model HR 1000 from Jobin Yvon Co., France), a photomultiplier (R787 from Hamamatsu Photonics Co., Japan), and a recorder (Model R-10 from Rikadenki Co., Japan). The design and position of the sample tube of the ICP torch were modified and optimized in order to avoid salt clogging at the top of sample tube. The design of the sample tube was changed in this experiment to cyclindrical shape with wider inner diameter (2 mm). Moreover, the top of sample tube was positioned at the interval of 10 mm apart from the lowest load coil. The monochromator was of the Czerny-Turner type (focal length 1 m) with a holographic grating (2400 grooves/mm). The wavelength scanning of the monochromator, the photomultiplier voltage, and the recorder were controlled by a computer (Model IF 800 from Okidenki Co., Japan). Other instruments are similar to those described in the previous papers (22-24). Chemicals. All the chemicals used were of analytical reagent grade. High-purity lutetium oxide (>99.99%)was purchased from Aldrich Co., Milwaukee, WI. Lactic acid, liquid ammonia, and other high-purity rare earth reagents (>99.9%) were purchased from Wako Chemical Co., Japan. These reagents were used without further purification. RESULTS AND DISCUSSION Spectral Interferences i n ICP-AES Measurements with Direct Nebulization. When rare earth elements are detected by ICP-AES with direct nebulization, spectral interferences with other coexisting rare earth elements are often the cause of analytical errors. The interferences were evaluated by observing the profiles of emission intensity vs. wavelength for each analyte element. As an instance, Figure 1shows the emission profiles of Ce, Nd, and Er near Pr 390.84 nm. As can be seen from Figure 1,the emission lines from Ce, Nd, and Er are overlapped with P r 390.84 nm, which receives the spectral interferences from the former three elements. Table I shows spectral interferences with coexisting elements at the most sensitive spectral line of each rare earth element. The magnitude of interference from each coexisting element is indicated as the proportional value to the concentration for the analyte element (ng/mL of analyte element per 10 M g / m L of interfering element). The elements indicated as interfering elements in Table I are limited to those which provide interferences corresponding to more than three times of the detection limit for each analyte element. From the view point of the dispersion of the monochromator used in this experiment, these interfering emission lines exist within 0.02
I l
fi
_
L
0.04nm
I
Pr 390.844 nm Flgure 1. Emission profiles of Ce, Nd, and Er near emission llne at Pr 390.844 nm: Ce, . ; Nd, 0 ; Er, A.
Table 11. Operating Conditions of the HPLC/ICP-AES System for Determination of Rare Earth Elements HPLC column column packing mobile phase column oven sample volume ICP-AES monochromator rf power coolant argon gas auxiliary argon gas sample argon gas observation height
Shimadzu Model LC-3A stainless steel column (4 mm i.d. X 250 mm long) IEX-210 SC (Toyo Soda Co.) (cation exchange resin 10 pm) 0.4-1.0 M, ammonium lactate (pH 4.22) 50 OC 100 pL
Nippon Jarrell-Ash Model ICAP-50A Jobin Yvon Model HR 1000 1.2 kW 16 L/min 1.2 L/min 1.0 L/min 17 mm above load cell ~~
nm of that of the analyte element. Thus the determination of rare earth elements by ICP-AES is generally very difficult because of such interelement interferences. When ICP-AES is combined with HPLC, it is expected that the spectral interferences can be excluded, since rare earth elements can be separated with HPLC before their introduction into the plasma. Optimization of HPLC/ICP-AES System. The HPLC/ICP system was operated under the conditions specified in Table 11. These experimental conditions were optimized while aspirating 10 pg/mL standard solutions for each rare earth element. Rf power, carrier argon gas flow rate, and optical observation height showed slightly different optimized
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984
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I
I
2
Table 111. Retention Times and Half Peak Widths of Diverse Elements in the Chromatographic Measurements by the HPLC/ICP-AES System
element
Nilt Nat
100 100 100 100 100 10 10 10 1000
K’
lo00
Pb2+ Mn2+
10 100 1000 1000 10
V6+
Fe3+ Zr4+ Ti3+ ~1st
cu2+
Zn2+ 0
10
20 time
40
30
1
(rnin)
Figure 2. Chromatograms for rare earth elements obtained by the HPLCIICP-AES system: sample (10 pg of each rare earth element), (1) Lu, (2) Yb, (3) Tm, (4) Er, (5)Ho, (6)Y, (7) Dy, (8)Tb, (9) Gd,(10) ELI, (11) Sm, (12) Nd, (13) Pr, (14) Ce, (15) La: mobile phase (linear concentration gradient method), 0.4 M ammonium lactate, pH 4.22 (0-8 mln), 0.6 M ammonium lactate, pH 4.22 (18 mln), 1.0 M ammonium lactate, pH 4.22 (31-40 mln). +
concn, wg/mL
Mg2+
Ca2+ Cr3+
retention time,
half peak width, min
min 1.36 1.60 1.75 1.78 2.60 5.96 17.00 20.02 20.40 26.00 37.60 39.74 >40 >40 >40
0.22 0.22 0.24 0.24 0.30 0.58 0.56 0.62 0.94 1.40 0.90 0.71
+
conditions for each analyte element. However, a compromised set of conditions summarized in Table I1 was sufficient enough to perform the multielement determination. For the column separation of the rare earth elements, ammonium lactate was chosen as the buffer solution for the mobile phase. Generally, sodium or potassium salts of a-HIBA (a-hydroxyisobutylic acid), EDTA, and citric acid are used for the separation of these elements ( I , 2). The high contents of these elution reagents are not suitable for detection by ICP-AES, as these salts easily clog the ICP torch. Such salt solutions also influence the nebulization efficiency because of their high viscosity. In case of ammonium lactate, it was shown to be possible to introduce the solution a t the concentration below 1.5 M into the ICP, even when the long-term gradient elution was performed. Under these experimental conditions, stable measurement for a long period of time (more than 10 h) was also possible. The use of the ammonium ladate solution also resulted in efficient separation for rare earth elements. The flow rate of the mobile phase was an important variable for optimization in the HPLC/ICP-AES measurement. Considering the separation with HPLC, a low flow rate (below 1.0 mL/min) may be effective, because a lower flow rate generally provides better column efficiency. The strongest emission intensities, however, were obtained at the flow rate of 1.4-1.6 mL/min for sample introduction. Therefore, the flow rate of the mobile phase was set at 1.4 mL/min, which was the compromised flow rate for both HPLC and ICP-AES. Quantitative Determination by HPLC/ICP-AES System. Chromatograms for rare earth elements obtained by the HPLC/ICP system are schematically illustrated in Figure 2, where the separation of rare earth elements was performed by using a concentration gradient elution technique. The wavelengths of analyte rare earth elements used in this experiment were the same as those shown in Table I. As can be seen from Figure 2, the advantage of the present system is the capability of the determination without interferences. The HPLC separation of rare earth elements was efficient to reduce the interelement interferences as summarized in Table I. That is, in cases where adjacent elements in the elution order do not provide large spectral interferences such as Lu, Yb, Tm, Gd, Ho, and Sm, the chromatographic elution of these elements could be carried out quickly for rapid analysis. In the opposite case where adjacent elements provide the spectral interferences such as Sm, Nd, Pr, and Ce, the elution of these
Table IV. Analytical Figures of Merit for Rare Earth Elements Determined by HPLC/ICP-AES systemn
element
RT, min
HPW, min
Lu Yb Tm Er Ho
3.80 4.68 5.78 8.06 11.44 13.06 14.60 18.16 21.20 22.36 23.50 27.02 29.06 32.00 37.60
0.49 0.55 0.75 0.95 1.10 0.85 0.86 0.80 0.80 0.76 0.78 0.80 0.81 0.95 1.17
Y
DY Tb Gd Eu Sm Nd Pr Ce La
DL, wLg/mL HPLC/ ICPICPAES AES 0.0004 0.0001 0.004 0.003 0.003 0.0006 0.005 0.009 0.006 0.002 0.009 0.01 0.02 0.01 0.007
0.004 0.001 0.02 0.04 0.05 0.005 0.06 0.08 0.07 0.02 0.1 0.1 0.2 0.3 0.05
RSD, %
HPLC/ ICPAES 3.0 3.0 2.6 3.7 4.8 3.4 5.0 6.9 4.4 1.2 4.2 3.6 3.4 7.4 4.9
“RT, retention time; HPW, half peak width; DL, detection limit; RSD, relative standard deviation examined at 10 pg/mL. elements had to be performed slowly for efficient separation. In this system, when peak overlappings were observed near the wings of the peaks, the interferences of other rare earth elements were negligibly small, if the determination was made by peak height measurement at the peak maximum. Actually, spectral interferences were not observed when all diverse rare earth elements existed at the concentration below 100 pg/mL, as discussed below. In general, geological samples have complicated diverse matrices besides rare earth elements. Characteristics such as retention times and half peak widths for rare earth elements in the measurements with HPLC/ICP-AES are summarized in Table 111. According to the results in Table 111, vanadium, iron, zirconium, aluminum, and titanium did not show any interferences, as these elements eluted earlier than lutetium (retention time, 3.8 min) which was the first eluted element among the rare earth elements. Copper, zinc, nickel, sodium, potassium, and lead showed overlappings at the peak wings of some rare earth elements, but spectral interferences of these elements were not observed below the concentrations shown in Table 111. Furthermore, manganese, magnesium, calcium, and chromium did not cause spectral interference because of different retention times from those of rare earth elements.
.-
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984
Sam l e 0 . 2 5 g
-F Y
Na2C03
Table V. Recoveries of Rare Earth Elements in Acid Digestion and Sodium Carbonate Fusion with Coprecipitation
2g
a c i d d i g e s t i o n w i t h HN03 and H 2 0 2 d i s s o l v e w i t h 300 rnL w a t e r
I-
La Ce
10 %, c u p f e r r o n 50 nL
Pr
--r---a d j u s t pH a t 9 . 0 w i t h
t
Nd Sm NH40H
Eu Gd
Tb I
.t 7 t a k e residue e x t r a c t w i t h 100 mL C H C 1 ,
I
element
Y
s t a n d f o r 1 0 min
c
2583
1 4
DY Ho Er Tm Yb Lu
acid digestion added, found, recovrg/mL rLg/mL ery, % 9.97 9.82 10.1 10.1 9.98 10.2 9.93 10.2 11.5 9.84 10.1 10.4 9.97 12.8 10.1
9.73 9.58 9.78 9.63 9.67 10.1 9.52 10.2 11.1 9.48 9.80 10.0 9.69 12.5 10.2
98.6 97.6 96.8 95.3 97.8 99.0 95.9 100 96.5 96.3 97.0 96.1 97.2 97.7 103
alkali fusion added, found, recovPLgImL rLg/mL ery, % 3.95 3.93 4.04 4.04 3.96 4.08 3.97 4.08 4.60 3.94 4.04 4.16 3.99 5.12 4.04
3.81 3.71 3.81 3.81 3.72 3.87 3.81 3.81 4.45 3.81 3.93 4.03 3.82 4.99 3.82
iIi
96.5 94.5 94.3 96.0 94.0 94.8 96.0 93.3 96.8 96.8 97.3 96.8 95.8 97.5 94.5
c o l l e c t CHC13 p h a s e and h e a t t o d r y n e s s
a c i d d i g e s t i o n w i t h H N 0 3 and H 2 0 2
Table VI. Analytical Results for a USGS GSP-1Rock Sample Determined by the HPLC/ICP-AES System
GSP-1 ( U E / E )
USGS
f i l l up t o 50 mL
Figure 3. Experimental procedure of alkali fusion for dissolution of rare earth ores.
The detection limits and relative standard deviations for rare earth elements obtained with HPLC/ICP-AES are s u m marized in Table IV along with the detection limits obtained by direct measurements with ICP-AES. The detection limits are expressed as the concentration of each rare earth element which provided a chromatographic peak height corresponding to twice the base line noise level. The relative standard deviations were measured at the concentration of 10 bg/mL for each rare earth element. As can be seen from Table IV, the detection limits obtained with ICP-AES showed better results than those with the HPLC/ICP-AES system. From the comparison of the results obtained by ICP-AES and HPLC/ICP-AES, however, it can be concluded that the HPLC/ICP-AES detection is superior to the direct detection with ICP-AES in the determination of rare earth elements in terms of the following points. Firstly, the HPLC/ICP-AES system requires only 0.1 mL of the sample solution, while at least 1 mL of the sample solution is required in the determination by ICP-AES. Secondly, in the HPLC/ICP-AES system the separation with HPLC helps to avoid erroneous analytical results caused by spectral interferences, while ICP-AES suffers from spectral interferences which cause analytical errors in the direct detection. The calibration curves obtained by the peak height measurements showed linear relationships at the concentration range below 500 pg/mL for all rare earth elements. Determination of Rare Earth Elements in USGS Standard Rock Sample and Rare Earth Ores. The samples were dissolved by two methods. A low-temperature acid digestion using nitric acid, hydrogen peroxide, hydrofluoric acid, and perchloric acid was employed for digestion of a USGS standard rock sample. Sample treatments of alkali fusion followed by coprecipitation were performed for rare earth ores. The experimental procedure of alkali fusion is shown in Figure 3. Since rare earth elements in some minerals were suspected to be insoluble in the acid-digested solution, sodium carbonate fusion was required for rare earth ores. Coprecipitation using cupferron as a coprecipitation reagent, which formed the insoluble metal chelates quantitatively with rare earth elements, was carried out in order to remove sodium
element
Y La Ce
Pr Nd Sm Eu Gd Tb
DY Ho Er Tm Yb Lu
found
(certified value)
26 f 2 180 f 10 390 f 10 57 f 4 180 f 10 31 f 3 2.8 k 0.3 13 f 3
30.4 191 394 50 188 27.1 2.4 15 1.3 5.4 99.9%) are illustrated in Figure 6 which show the detections of praseodymium at different emission wavelengths. As has been
. ; Nd
Nd 401.23 nm
(C) Sm 359.26 nm
0
10
I\
20 30 retention time (min)
40
Flgure 4. Element-selective chromatograms for monazite sand detected at 390.84 nm (A), 401.23 nm (B), and 359.26 nm (C) by the HPLCIICP-AES system: sample, 0.2 mg of monazite sand; spectral interfering element, (a) Er (b) Sm (c) Nd (d) Ce (e) Gd.
mentioned previously, praseodymium could not be detected at 390.84 nm because of the peak overlapping (see Figure 6(left). On the other hand, at 422.29 nm the elution peak of praseodymium could be separated from that of cerium more clearly, as can be seen in Figure 6(center), although the interfering emission of cerium still provided small overlapping at the wing of the peak for praseodymium. It should be noted here that at 422.54 nm praseodymium could be spectrochemically separated from cerium. This is shown in Figure G(right). Therefore, the emission line of 422.54 nm was used for the determination of praseodymium in high-purity cerium oxide. Analytical results for the determination of rare earth impurities in high-purity rare earth oxides and salts are summarized in Table VIII. These results were obtained by measuring the chromatogram for each rare earth element which was similar to those illustrated in Figure 5. In most cases the determinations were successfully carried out at the most sensitive emission lines listed in Table I, but similar experimental difficulties discussed above in the determination of praseodymium in high-purity cerium oxide were also encountered in the determinations of neodymium in praseody-
Table VIII. Analytical Results for Rare Earth Impurities in High-Purity (>99.9%) Rare Earth Reagents Determined by the HPLC/ICP-AES System rare earth reagent y2°3
La203 CeOz PrsO11 Nd203 Sm203
EuC13 GdCl, Tb407 DYC13 HOC13 Er203 Tm203
YbCl3 L'203
Wavelength, 422.53 nm.
impurity concentration, pg/mL Gd, 14; Dy, 6.6; Ho, 30; Lu, 0.6 Y, 10; Ce, 42; Pr, 50; Dy, 13 Y, 5; La, 12; Pr, 76;" Nd, 28; Sm, 16; Gd, 13; Dy, 13; Ho, 24; Yb, 15 Y, 7; La, 16; Ce, 38; Nd, 110;*Eu, 4; Gd, 15; Dy, 8; Yb, 1.7 Y, 23; La, 98; Ce, 39; Pr, 112; Sm, 25QCEu, 6; Gd, 20; Dy, 15; Ho, 37; Yb, 8.2 Y, 11; La, 21; Nd, 64; Eu, 170; Gd, 36; Yb, 1 Y, 70; Sm, 38; Gd, 32; Tb, 20; Dy, 14; Yb, 2; Lu, 0.3 Y, 39; La, 23; Ce, 42; Eu, 120; Tb, 40; Yb, 15; Lu, 2 Y, 13; Gd, 9; Tb, 12; Lu, 0.9 Y, 120; Ce, 31; Eu, 2; Tb, 9; Ho, 19; Tb, 2; Lu, 0.6 Y, 4; La, 12; Ce, 32; Er, 4; Lu, 1 Y, 8; Yb, 17; Lu, 2 Y, 9; Er, 33; Yb, 19; Lu, 2 Y, 14; Lu, 43 Y, 23; Er, 24; Tm, 3; Yb, 42 Wavelength, 445.12 nm.
Wavelength, 443.39 nm.
ANALYTICAL CHEMISTRY, VOL. 56, NO. 13, NOVEMBER 1984
(A)
Y b 328.94 nm
(>99.9%) lanthanide reagents has been demonstrated in the present experiment. It has been elucidated that fairly high selectivity can be obtained with the HPLC/ICP-AES system by combining the analytical feasibilities of each instrumentation, that is, the chromatographic separation of chemical species with the HPLC and the element-selective detection with the ICP-AES. The spectral inteferences from coexisting rare earth elements as well as other diverse elements can be avoided by taking the advantages of efficient separation and element-selectivity in the present experimental system. Therefore, rare earth elements in various samples are successfully determined with the HPLC/ICP-AES system without suffering from any spectral interferences.
n
Yb
Y 371.03 nm
(C)
Nd 401.23 nm
2585
ACKNOWLEDGMENT The authors thank Keiichiro Fuwa in the Department of Chemistry, Faculty of Science, University of Tokyo, for his kind encouragement and valuable discussions through the present experiment. Registry No. Pr, 7440-10-0;Lu, 7439-94-3;Yb, 7440-64-4;Tm, 7440-30-4;Er, 7440-52-0; Ho, 7440-60-0;Y, 7440-65-5;Dy, 742991-6;Tb, 7440-27-9;Gd, 7440-54-2;Eu, 7440-53-1;Sm, 7440-19-9; Nd, 7440-00-8; C1, 7440-45-1; La, 7439-91-0.
La 379.48 nm
LITERATURE CITED (1) Topp, N. E. "The Chemistry of Rare Earth Elements"; Elsevier: New York, 1965. (2) Kano, T.; Yanagida, H. "Rare Earths: Properties and Applications"; Gihodo: Tokyo, 1980. (3) Jolly, J. H. "Rare Earth Elements and Yttrium, Mineral Facts, and Pr 390.84 nrn
Pr 422.29 nrn
Pr 422.54 nrn
Problems"; Bureau of Mlnes, Unlted States Department of the Interlor: Washington, DC, 1975. (4) Masuda, A.; Nakamura, N.; Tanaka, T. Geochim Cosmochim. Acta
1913,37,239-248.
Jlj
d 25 30 35 !5
30
retention time
L
3!
9i425
30
3!
(rnin)
Figure 6, Element-selective chromatograms for determination of Pr in high-purity cerium oxide (>99.9 %) detected at various wavelengths: (a) emission signal of Ce.
.
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mium oxide and samarium in neodymium oxide. In these cases, neodymium and samarium could be determined by measuring the emission intensities at Nd 445.12 am and Sm 443.39 nm. Such selection of other analytical wavelengths, however, resulted in the poorer detection limits for both elements by about l order of magnitude. Even though, rare earth impurities in high-purity reagents of 15 rare earth elements could be successfully determined with the HPLC/ICP-AES system, as summarized in Table VIII.
RECEIVED for review April 10, 1984. Accepted July 5, 1984.
CONCLUSIONS The rapid determination of rare earth elements in a USGS rock standard sample, rare earth ores, and high-purity
The present research has been supported by the Grant-in-Aid in the Special Research Project for Environmental Science (Grant No. 58030029) from the ministry of Education, Culture, and Science, Japan.
