Table I. Separation Factors for Various Metal Ions with Respect to Zirconium(1V) in 0.1 M NPyOx/Xylene and TOAO/Xylene Systems Using 10 M Nitric Acid and 0.1 M Sulfuric Acid, Respectively Separator factor Ion
Concentration, M
QQmTc( VIII) 233u(v1)
C.F." 10-3
1 8 7 w (VI)
10-7
95Nb(V) lslTa(V) 234Th(IV) 144Ce(IV) 55~~(111) 9 0 (111) ~ 144ce(111)
C.F. 10-9 C.F. 10-8 10-5 C.F. 10-8 C.F. 10-9 10-9 10-8 10-9 10-4
140~~(111)
90sr(11) 140~~(11)
65zn(11) ~OCO(I1) 54~n(11) 137cs 10-8 a C.F = Carrier-free.
NPyOx 103 6 X lo2 102 25 1.5 x 104 3.9 15 4 x 10-2 1.2 x 104 1.28 x 104 105 1.04 x 103 7 x 104 104 2.1 x 104 1.5 x 105 3 x 103
TOAO
... 9 0.33 102 2.5 10 -103 -103 -103 -103 -103 -103
...
-104 -105 -105 -105
from uranium, and rare earth nuclides and other fission products by 0.1 M NPyOx/xylene. The selectivity of the extraction of zirconium was checked from 10 M nitric acid by carrying out the separation of 95Zr from a test solution (10 ml) with known concentrations of the test components (99Tc, 144Ce, 137Cs, 140Ba, 140La indicator amounts, milligram amounts of U, 15 mg/ml) byO.l M 4-(5-nonyl)pyridine oxide in xylene. The organic phase was washed twice with 10 M nitric acid and zirconium was back-extracted by 0.5 M sulfuric acid. Gamma spectra showed the clean separation of zirconium. In the commonly used phosphorus bonded oxygen donor extractant, T B P , uranium and rare earth elements are co-
extracted from this acidity. Although the separation of zirconium from uranium can be effected in dilute acid solutions by TBP, the separation factor is not high in the case of uranium and, secondly, the simultaneous separation of rare earth elements is not possible.
ACKNOWLEDGMENT The author thanks D. J. Carswell for his kind suggestions during this work and V. Djohadze for translating a number of Russian papers. The assistance of the microanalytical laboratory in the School of Chemistry, University of New South Wales, Australia, for carrying out the analyses of the amine oxides used is also gratefully acknowledged. LITERATURE CITED (1) V. G. Torgov, V. A. Mikhailov, I. L.,Kotylarevskii, and A. V. Mikolaev, Dokl. Akad. Nauk. SSSR.,150., 156 (3),616 (1964). (2)V. G. Torgov, V. A. Mikhailov, E. A. Startseva,and A. V. Nikolaev, Zh. Neorg. Khim., 10, 2780 (1965). (3)V. G. Torgov, V. A. Mikhailov, E. A. Startseva, and A. V. Nikolaev, Dokl. Akad. Nauk. SSSR., 168 (4).836 (1966). (4)V. G. Torgov, V. A. Mikhailov, P. I. Artyukhim, E. N. Gilbert, and A. V. Nikolaev, Dokl. Akad. Nauk. SSSR.. 174, 1329 (1967). (5) 2. B. Maksirnovic and R. G. Puzic, J. lnorg. Nucl. Chem., 34, 1031 (1972). (6)M. Ejaz, Anal. Chim. Acta, 71, 383 (1974). (7) M. Ejaz and D. J. Carswell, J. lnorg. Nucl. Chem., 37, 233 (1975). (8) M. Ejaz, Sep. Sci., 10 (4),425 (1975). (9)M. Ejaz, Talanta, 23, 193 (1976). (10) N. M. Adarnskii, S.M. Karpacheva, I. N. Melhikov, and A. M. Rozen, Radiokhimiya, 2 , 400 (1960). (11) K. Alcock, F.G. Bedford,W. H. Hardwick,and H. A. C. Mckay, J. horg. Nucl. Chem., 4, 100 (1957). (12)B. 2. lofaand A. S.Yushchenko, Zh. Neorg. Khim, I O , 558 (1965). (13)0.A. Mostovaya, T. V. Momot, and G. A. Yogodin, Zh. Neorg. Khim., 9,1280 (1964). (14)E. H. Hesford and H. A. C. Mckay, Trans. Faraday Soc., 54, 573 (1958). (15)A. E. Levitt and H. J. Freund, J. Am. Chem. Soc., 76, 1545 (1956). (16)C. F. Coleman, C. A. Blake, and K. B. Brown, Talanta, 9,297 (1962). (17) A. J. Lister and L. A. McDonald, J. Chem. Soc., 43151 (1952). (18)K. Kraus and J. Johnson, J. Am. Chem. SOC.,78, 26,(1956). (19) A. S.Solovkin and S. V. Isretkova, Russ. Chem. Rev., 31 (1I),655 (1962). (20)S.V. Gerovorkyan and N. A. Gurovich, lav. Akad. Nauk. Armyan., SSSR, Ser. Khim. Nauk., 6, 389 (1957). (21)K. lsslib and H. Reinhold, Z.Anorg. Allg. Chem., 314, 113 (1962). (22) A. M. Rozen, Yu. I. Murinov, and Yu. Nikitin, Radiokhimiya, 12, 516 (1970). (23)C.J. Hardy and D. Scargill, J. lnorg. Nucl. Chem., 17, 347 (1961).
RECEIVEDfor review May 9,1975. Accepted March 15,1976.
Comparison of lnterelement Effects in a Microwave Single Electrode Plasma and in a Radiofrequency Inductively Coupled Plasma George F. Larson and Velmer A. Fassel* Ames Laboratory-ERDA
and Department of Chemistry, Iowa State University, Ames, Iowa 500 11
The results of a comparative study on the extent to which various interelement or interference effects are observed in a microwave-excited, single-electrode plasma (SEP) and a radiofrequency-excited,inductively coupled plasma (ICP) are presented. These studies confirmed earlier reports that easlly ionizable elements generally produce severe changes on the line emission of analyte elements In the SEP, whereas only negligible or small effects are observed in the ICP. It is also shown that several concomitantswith differing ionization potentials produce significant changes in the emission Intensity of Mo in the SEP although only small effects are observed in the ICP and that P043- or AI3+ concomitantsproduce slgnificant interference on calcium atomic and ionic line emission in the SEP while negligible effects are observed in the ICP.
Flame-like, electrically-generated plasmas possess several distinctive advantages over combustion flames for generating free atoms from trace metals in solution and for exciting the optical emission spectra of the released atoms (1-6).Among the various plasmas that have been proposed for these purposes, two versions have emerged as particularly promising atomization and excitation sources for the optical atomic emission determination of trace elements in solution. One of these plasmas is sustained by capacitive coupling of the plasma to the high frequency field concentrated a t the tip of a single electrode. A radiofrequency (43 MHz) version of such a plasma was first employed for the determination of elements in solution by BBdHrBu et al. ( 7 ) ,and a microwave-excited version, in which the plasma was formed on the central conductor of a coaxial waveguide, was first employed by MavroANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
I161
dineanu and Hughes (8)for the same purpose. We will call this version a single-electrode plasma (SEP) in accordance with Reference 9, although such terms as “electronic torch”, “high frequency brush discharge”, and “ultra high frequency plasma torch” have been employed. The other version, which derives its sustaining power primarily by induction from the radiofrequency magnetic fields, i.e., an inductively coupled plasma (ICP),was first applied to the determination of trace elements in solution by Greenfield and associates (10)and by Wendt and Fassel (11). Although the promise of these plasmas as atomization and excitation sources for optical emission spectroscopy resides primarily in their excellent powers of detection ( I , 3, 6, 12), their freedom from interelement or matrix effects will be an important factor in determining their eventual scope of application for the determination of trace metals in samples of widely varying composition. Even though the interelement effects reported in this paper should be considered as a unique set of observations dependent not only on the exciting frequency and nature of the support gas but also on such experimental parameters as the method of coupling the high frequency power supply to the plasma, the characteristics of the power generator, the power dissipated in the plasma, the torch configuration and gas flow rates, the viewing field of the optical transfer system, and the method of sample transport and injection, it is of interest to make direct comparisons of the relative magnitude of the effects in plasmas operated under the experimental conditions either recommended or commonly used for the analysis of samples. In this communication, we report on a comparative study of the interelement effects observed in S E P and ICP plasmas (similar to those which are commercially available) produced by: (a) an easily ionizable element (Na) on the emission intensities of neutral atom and ion lines of Ca, Cr, Mo, and Zn; (b) concomitants of different ionization potential on Mo neutral atom and ion line emission; and (c) the well-known phosphate on calcium and aluminum on calcium solute vaporization interferences. After this paper was submitted for publication and while a revision was being prepared, another comparative study in which greater freedom from interference effects was found in an ICP than in a S E P sustained in NP (rather than Ar as employed in the present study) was published ( 1 3 ) . EXPERIMENTAL SEP Facility. The Hitachi UHF Torch Generator employed was similar to the version described in References 14 and 15. T h e magnetron (H3032L, 2.45 GHz) was operated a t an anode current of 260 mA a t 2 kV. The Ar sheath or coolant gas flow between two quartz tubes concentric with the electrode was 5.6 l./min. The aerosol carrier gas flow rate between the electrode and the inner quartz tube was set a t 2.6 l./min; the interference effects reported in this paper were not strongly dependent on the aerosol carrier gas flow rate between 2 and 3 l./min. The nebulizer (161, dual tube aerosol chamber (17), and desolvation facility (18) have been previously described. The aerosol transport rate into the plasma was equivalent t o -0.06 ml/min with a solution uptake rate of 1.7 ml/min. These conditions correspond to those recommended by the manufacturer. The spectrometric instrumentation has been previously described (191, except that the following modifications were made: (a) 2 0 - ~ m entrance and exit slits masked to a height of 3 mm were employed; (b) the external optics consisted of a 15 cm X 5 cm diameter planoconvex fused quartz lens positioned a t 28.3 cm (twice the focal length a t 303.4 nm) from the slit and 28.3 cm from the plasma; and (c) a Keithley Model 417 picoammeter and a Texas Instruments Model FWD recorder were employed. ICP Facility. The ICP facility has been previously described ( 17, 20). The forward power was 1025 W and the reflected power was approximately 10 W. The aerosol carrier gas flow rate was 1.0 l./min. No external desolvation apparatus was employed. Procedure. The preparation of solutions and data collection procedures have been previously described (20), except that relative 1162
ANALYTICAL CHEMISTRY, VOL. 48, NO. 8, JULY 1976
intensity measurements for the SEP were obtained from strip chart recordings.
RESULTS AND DISCUSSION I n t e r f e r e n c e Effects Produced by Easily Ionizable Elements. There have been numerous reports of rather severe interference effects caused by changing concentrations of easily ionizable elements in various versions of the SEP. BhdhrEiu (7) reported depressions of P b I 405.7-nm emission with increasing concentrations of alkali and alkaline earth elements in a radiofrequency-excited (43 MHz) SEP sustained in air. Tappe and van Calker (21,22) observed severe interferences on Mn 1403.0-nm emission with increasing concentrations of the alkali elements in a radiofrequency-excited (27 MHz) SEP sustained in air. Jantsch (23) has described interferences produced by increasing concentrations of Na on Fe I 371.99-nm and A1 1396.1-nm emission intensity in a microwave-excited (2.45 GHz) SEP supported by N2. At the observation height where maximum intensity for Fe I 371.99 nm was observed (18 mm above electrode tip), the addition of 1840 pg/ml Na produced enhancements of -20% in the Fe I intensity and -300% in the A1 I intensity. In a more extensive study with a very similar S E P sustained by N2, Sermin (24) found that the interference effects produced by Na were quite dependent on the analyte. For example, Ni neutral atom emission was only slightly affected (
