2O-fold, the detection limits given for the elements in Table I decreased by about 20-fold. Of course, if the nebulization chamber were reduced too greatly, then desolvation would be incomplete resulting in poorer rather than better detection limits. Further studies involving chamber size as well
as studies involving emission of atomic species from the hot gases above the vitreous-carbon tube are being carried out. RECEIVEDfor review March 11, 1974. Accepted June 3, 1974. This work was supported by AF-AFOSR-74-2574.
Flame Atomic Fluorescence and Emission Spectrometry with a Microsampling Cup Technique J. K. Grime and T. J. Vickers Deparfment of Chemistry, Florida State University, Tallahassee, Fla .32306
For many applications, and especially with biological materials, trace element determinations must be carried out with limited amounts of sample material. Recognition of this need has led to extensive development of microsampling techniques for atomic absorption spectrophotometry. Furnace, rod, strip, and several other types of electrothermal atomization devices have received considerable attention ( I , 2) and, for several of these devices, very high absolute sensitivities have been demonstrated for a range of elements. There are, however, disadvantages to the nonflame atomization devices: The initial equipment cost is in most cases large; and rapid conversion between nonflame and flame atomization is not possible because the nonflame atomization device must be critically aligned for optimum performance. This is a severe handicap since, when adequate amounts of sample are available, flame atomizers are usable for a larger number of elements, are often more convenient, and provide better precision than the nonflame atomizers. Probably the best method so far reported for microsample analysis with a flame atomizer is that of Delves ( 3 ) .In this technique, solution residues are vaporized from nickel crucibles into an absorption tube placed in a long path flame. This method appears to have achieved wide acceptance for the determination of lead in blood ( 4 ) , and preliminary results have been reported (5-8) for its application to other elements: Ag, As, Bi, Cd, Hg, Se, Te, Ti, Zn. To achieve adequate sensitivity and precision with the Delves cup technique, great care must be exercised in obtaining correct alignment of the cup with respect to the absorption tube (9, I O ) . Because of the consequent long setup time, frequent conversion between normal spraying and Delves cup sample introduction is discouraged. Sychra et al. ( 1 1 ) have recently described the use of two atomization techniques, a sampling cup and a hot wire loop atomizer in conjunction with atomic fluorescence spectros(1) (2) (3) (4)
J. D. Winefordner and T. J. J. D. Winefordner and T. J.
Vickers, Anal. Chem., 42, 206R (1970). Vickers, Anal. Chem., 44, 150R (1972). H. T. Delves, Analyst(London),95, 431 (1970). J. M. Hicks, A . N. Gutierrez, and B. E. Worthy, Clln. Chem., 19, 322
(1973). (5) J. D. Kerber and F. J. Fernandez, At. Absorption Newslett, 10, 78 (1971). (6) M. M. Joselow and J. D. Bogden, At. Absorption Newsleft., 11, 127 (1972). (7) D. Clark, R . M. Dagnall, and T. S. Wes:, Anal. Cbim. Acta, 58, 339 (1972). (8) R. D. Ediger and R. L. Coleman, At. Absorption Newslett., 12, 3 (1973). (9) F. J . Fernandez, At. Absorption Newslett., 12, 70 (1973). (10) E. D. Olsen and P. i. Jatlow, Clin. Chem., 18, 1312 (1972). (11) V. Sychra and D. Kolihova, lnt. Congr. At. Absorption, At. Fluorescence Spectrom. Pap., 3rd, 7977, Vol. 1 , Wiley, New York, N.Y., 1973, p 265.
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copy. This apparatus has been used to determine cadmium and zinc in serum with good sensitivity, precision, and reproducibility. The geometry of atomic fluorescence and emission flame spectrometry systems is such that the use of a flame atomizer with a configuration similar to the sampling cup, but without an absorption tube, can be considered. Accordingly, cup alignment becomes less critical and the ready interchange between the microsampling and spraying modes is facilitated. In this report, we describe the results of an evaluation of such a system for the determination of thallium, using a relatively inexpensive adaptation of the Delves technique. With the Delves cup atomic absorption technique, the detection limit for thallium was reported by Kerber and Fernandez ( 5 )to be 1ng, and Shkolnik and Bevi11 (12) reported sensitivities of 0.6 ng and 0.7 ng for thallium in urine and plasma, respectively. Thallium in microsamples has also been determined by atomic absorption spectrophotometry with a carbon rod atomizer ( 1 3 ) and with the tantalum sampling boat technique ( 5 ) . With conventional sprayed samples, the detection limit for thallium by atomic fluorescence has been reported by Zacha e t al. (14) to be 0.008 pg/ml.
EXPERIMENTAL Apparatus. Instrument specifications and operating parameters are listed in Table I. For atomic fluorescence measurements, t h e source was placed a t approximately 90° t o t h e flame-monochromator axis. No lenses or mirrors were employed to focus the radiation, b u t t h e source was placed as close as possible to t h e flame (approximately 7 cm) and the flame was placed as close as possible to the entrance slit of the monochromator (approximately 6 cm). T h e sampling cup was identical to t h a t employed in t h e Delves technique. T h e cup holder was fabricated locally from 0.25-mm thick nickel sheet. A 6-mm wide band of the nickel sheet was formed into a loop with a double thickness handle approximately 20 m m long. T h e handle was firmly attached t o a 6-mm diameter nickel rod, which was in turn mounted on a rotatable post, as shown in Figure 1. T h e height of the cup with respect t o t h e monochromator was readily varied by moving t h e rod holder on t h e mounting post. T h e post could be rotated through 90" between fixed stops to provide movement of t h e cup in the horizontal plane and reproducible placement of the cup in t h e flame. A brief study indicated t h a t best results were obtained by placing the cup just lower than the bottom of the entrance slit of the monochromator and approximately 5 m m above t h e burner top. Optimum operating conditions for t h e T1 electrodeless discharge lamp were briefly investigated. T h e lamp was operated in a cylin(12) G. Shkolnik and R . F. Bevill, At. Absorption Newslett., 12, 112 (1973). (13) N. P. Kubasik and M. T. Volosin, Clin. Chem., 19, 954 (1973). (14) K . E. Zacha, M. P. Bratzel, J. M. Mansfield, and J. D. Winefordner, Anal. Chem., 40, 1733 (1968).
1974
Table I. Instrument Specifications and O p e r a t i n g Parameters
Monochromator Photomultiplier Electrodeless discharge lamp
Burner
Sampling cup
Ileath/’McPherson EU-700 with 1.8mm slit width, set for 377.6 nm. RCA lP28 with Heath ‘McPherson power supply and dc amplifier. ‘rl lamp (Opthos Instruments) operated in cylindrical cavity with heater 21s described by Bail (15).Scintillonics HV15A microwave generator. Lamp operated at 60 watts indicated power with cavity at 410 O K . Alkemade type burner (16) with circular array of 0.8-mm diameter holes. Array consists of a central hole and 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, and 66 holes on concentric circles of respective diameters of 3.2, 6.4, 9.6, 12.8, 16.0, 19.2, 22.4, 25.6, 28.8, 32.0, and 35.2 mni. The 5 outermost circles of holes are used for the N? sheath gas. Flame conditions for microsamples: Air-----l4.51./min, H2-4.7 l.Jmin, N,8.7 1,:min. Flame conditions for sprayed samples: Air--11.0 l.,’min, H2---3.7 l./’min, N2-6.2 1. Imin. Perkin-Elmer 303-0813.
drical cavity with provision for convective heating as described by Ball (15).Figure 2 shows the effect on the fluorescence intensity at 377.6 nm of heating the cavity. It would appear that the chief advantage of heating for the thallium lamp is that peak output can be obtained at a much lower power setting. Our findings seem in general agreement with those of Browner and Winefordner ( 1 7 ) . The gas flow rates were optimized with respect to peak shape. It was observed that flow rates less than those listed in Table I produced “tailing” of the peaks. Reagents. A stock solution of approximately 1000 fig/ml T1 was prepared by dissolving the appropriate weight of T12SOJ in distilled water. Lower concentration standards were prepared by successive dilutions. Procedure. A cup is placed in the holder and heated in the flame to remove impurities. After cooling, a 10-fil sample is added with a 50.~1glass syringe with Chaney adapter. The holder is rotated to position the cup over the hot plate (at 140 “C), and the cup is heated for 90 sec. The cup is then rotated into the flame, and the atomic fluorescence peak recorded. After removal from the flame, the cup is allowed to cool for at least 60 sec prior to addition of the next sample.
HOT
MONOCHROMATOR ENTRANCE SLIT
PLATE
-
STOP
Figure 1. Top view showing arrangement of components for microsampling
INDICATED MICROWAVE POWER (WATTS)+
Figure 2. Plots of fluorescence intensity at 377.6 nm for 10 pg/ml TI a s a function of indicated microwave power for the cavity heated to 410 O K ( A ) and the cavity with no auxiliary heating ( B )
RESULTS AND DISCUSSION Analytical Curves. In Figure 3, results obtained with the microsampling atomic fluorescence technique are compared with those for normal sprayed samples. Both analytical curves are substantially linear at low concentration. T h e flattening of the microsampling curve at high concentration is expected for atomic fluorescence measurements. Note that the sensitivity of the microsampling method is approximately 15 times that of the normal sprayed sample method. At concentrations at which the fluorescence curve is nonlinear, the T1 in 10-p1 samples is readily determined by thermal emission. Curve C in Figure 3 is t h e analytical curve for emission. Figure 4 illustrates the appearance of the T1 fluorescence peaks at various concentrations. T1 is clearly detectable a t the 0.05 pg/ml level with a 10-pl sample (0.5 ng Tl). A t this
$1 E
l
4
l 0 01
o
0
THAL
(15) J. J. Ball, Rev. Sci. /nstrurn.,44, 1141 (1973). (16) P. J. Slevin, V. I. Muscat, and T. J. Vickers. Appl. Specfrosc., 26, 296 (1972). (17) R . F. Browner and J. D. Winefordner, Specfrochim. Acta. Part B, 28, 263 (1973).
u
UM C3NCEh’QAT
3N
A 103 io00
uq/ml
Figure 3. Analytical curves obtained for thallium A Atomic fluorescence with the microsampling technique (10-fil sample) B, Atomic fluorescence with sprayed samples C, Atomic emission with the microsampling technique (10-fil sample)
ANALYTICAL CHEMISTRY, VOL. 4 6 , NO. 12, OCTOBER 1 9 7 4
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?_
15 SEC
H INTRODUCED c"pvu
ELAM 0 02
005
05
0 02
C.05
I 01
T a b l e 11. Relative Standard Deviation for Ten Determinations
IO I
CWCENTRATKX@g/rrI) SEMlTlVlTY FACTORS
Figure 4. Recorder tracings for blank and fluorescence peaks for
various TI concentrations X marks the TI measurement peak. The sensitivity factor is the factor by which the intensity value should be multiplied to place it on the same relative intensity scale as the peak for the most concentrated TI solution
T I concn, d m l
Re1 std dev, %
10.0 1 .oo
2.3 3.4
0.50
3.4
mersed in what appears to be a largely homogeneous thermal and chemical environment and, a t least in part, this seems to be the origin of the improvement in precision and cup life compared to previously reported atomic absorption studies with slot burners.
CONCLUSIONS level, the change in the background signal resulting from introduction of the cup, its heating, and removal is clearly evident. The increase in background signal during cup heating (shown in the blank trace) is due a t least in part to incandescent emission from the cup. Precision. Table I1 lists the within-run precision of the method expressed as the relative standard deviation a t three concentration levels. Standard deviations were computed from 10 determinations a t each concentration. The relative standard deviation is approximately t h a t expected due to uncertainty in the micropipetting, and it is clear that adequate reproducibility in cup placement is readily achieved. No sensitivity variations were noted with cup aging, and no deterioration of the cup was apparent even after several hundred determinations. With the burner employed in the present study, the cup is completely im-
The results obtained demonstrate that thallium can be determined by a microsampling cup flame atomic fluorescence technique with a sensitivity a t least as good as t h a t achieved with the Delves cup procedure. The precision obtained is somewhat better than that normally obtained with the Delves procedure. With the addition of the flame emission technique, the procedure described can be used to determine T1 to concentrations a t least as high as 1000 Hg/ ml. Cup alignment for the fluorescence procedure is readily and rapidly obtained, and the microsampling device does not interfere with use of the burner in the normal sprayedsample mode.
RECEIVEDfor review March 22, 1974. Accepted June 12, 1974. Work supported in part by funds from PHS Grant R01-GM15996.
Separation of Trace Metal Impurities from Nuclear.Grade Uranium by Long-chain Amine Extraction and Direct Determination by Atomic Absorption Spectrophotometry Sergio de Moraes and Alcidio Abrao Chemical Engineering Department, lnstituto de Energia Atbmica, Caixa Postal 11.049 e C.E.P. 05.508, Sao Paulo, Brazil
The purification and conversion of uranium concentrates to nuclear grade products require the identification and determination of a series of trace metal impurities, some of which have deleteriously high thermal neutron capture cross-sections. The majority of the published literature in this area has approached the problem by an initial separation of the matrix uranium using, for instance, solvent extraction, and determining the trace impurities in the raffinate. Any procedure that could primarily separate the impurities by solvent extraction, or otherwise, from the major constituent, uranium, would be advantageous and attractive. This paper deals with such a n approach for the separation, concentration, and determination of microgram quantities of a series of metals present as impurities in high grade uranium. Long-chain amines have been utilized extensively as extracting agents for various elements, including uranium. 1812
The literature on the subject is extensive (1-9). Such procedures have also been investigated in this laboratory for isolating trace metal concentrations from hydrochloric acid media ( 1 0 ) . Of pertinent interest is the use of tri-n-octyl (1) F. L. Moore, Rept. NAS-NS-3101 (1960). (2) M. Y. Mirza, M. Ejaz, A. R. Sarni, S.Ullah, M. Raschid, and G. Samdani. Anal. Chim. Acta, 37, 402 (1967). (3) A. D. Nelson, J. L. Fasching, and R. L. MacDonald, J. horg. Nucl. Chem., 27,439 (1965). ( 4 ) W . J. Maeck, G. L. Booman, M. C. Elliott, and J. E. Rein, Anal. Chern., 30, 1902 (1958). (5) W . J. Maeck, G. L. Booman. M. C. Elliott, and J. E. Rein, Anal. Chern., 32,605 (1960). (6) W . J. Maeck, G. L. Booman, M. E. Kussy and J. E. Rein, Anal. Chern., 33, 1775 (1961). (7) F. L. Moore, Rept. ORNL-1314 (1952). (8) F. L. Moore, Anal. Chem., 29, 1660 (1957). (9) W. D. Arnold and D. J. Crouse, Rept. ORNL-3030 (1961). (10) A. Abrgo, Ph.D. Thesis, lnstituto de Ouimica, Universidade de Sgo Pauio, Brazil, 197 1.
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 12. OCTOBER 1974
