Multichannel Atomic Fluorescence and Flame Photometric Determination of Calcium, Copper, Magnesium, Manganese, Potassium, and Zinc in Soil Extracts R . M. Dagnall, G . F. Kirkbright, T. S. West, and Roger Wood Department of Chemistry, Imperial College of Science and Technology, London, S . W.7., England Exchangeable calcium, copper, magnesium, manganese, potassium, and zinc in soils have been determined in ammonium acetate, acetic acid, and EDTA extracts using a six-channel atomic fluorescence spectrophotometer. Determination of all six elements in a single extract at two dilutions is possible using this technique. The results obtained compare favorably with the results of single channel atomic absorption analyses for the same extracts. The method is shown to permit rapid, sensitive, and accurate analysis for these samples.
THEANALYSIS of soil extracts for trace metals which are essential for the healthy growth of flora and fauna, or which are toxic, is essentially a task which demands large numbers of determinations of a fairly wide range of elements. The large numbers of analyses which are demanded make it important that the analytical procedure should be rapid, reasonably precise a n d unequivocal, a n d easy t o operate. This set of requirements precludes methods based o n molecular absorption or fluorescence techniques in solution and to a lesser extent, electrochemical methods such as polarography. Methods based o n atomic spectrometry are particularly advantageous because they d o not demand much sample pretreatment following preparation of the soil extract, a n d are a t the same time reasonably precise, rapid, a n d unequivocal. Atomic spectrometry methods with flames are well suited t o this type of analysis because the test sample is a n aqueous solution of reasonably moderate and near constant electrolyte concentration. The choice of flame photometry, atomic absorption, or atomic fluorescence spectrometry as the analytical technique, therefore, depends o n the nature of the problem. It is generally recognized that for elements with low excitation energies, such as potassium, flame photometry shows low detection limits and a reasonable degree of freedom from spectral interference even with a filter instrument, although this cannot be said for elements such as C u , Mg, M n , and Z n . I n addition, line sources for potassium absorption or fluorescence measurements are not very satisfactory. The choice of atomic absorption or fluorescence for Cu, Mg, M n , and Z n is such that given a reasonably intense line source, low detection limits would be expected for all these elements-and certainly for Mg, M n , and Z n a higher sensitivity than in flame photometry. Ca c a n also be determined very easily by any of the three techniques though fluorescence or absorption might be preferred because of consideration of sensitivity and freedom from band emission interferences. Additionally, it is easier physically to arrange for multiple analysis in fluorescence than in absorption because a single detector c a n be used in conjunction with high transmission cut-off filters when individual line sources are being used. In absorption instrumentation, a multichannel approach requires multiple detectors to be used in conjunction with resonance monochromators or a polychromator technique must be employed.
It is also possible t o arrange in fluorescence that the line sources should effectively be only allowed t o irradiate the flame one a t a time, in sequence, so that spectral interference is virtually eliminated except in a few rare instances of spectral line overlap. A multichannel atomic fluorescence approach is particularly well suited t o this type of problem because the instrumentation (filters and only one detector) is compact, because the channels c a n easily be changed (lamp a n d possibly filter), and because it is easier to arrange a blend of two emission techniques efficiently than to mix absorption and emission capabilities. For these reasons the Technicon AFS6 multichannel atomic fluorescence-emission system was investigated for this problem. The determination of exchangeable cations in soil extracts by flame atomic emission or atomic absorption spectrophotometry has been reported by many workers (1-10). A number of solutions have been employed t o obtain the soil extracts-1M ammonium chloride (1) or acetate (5, 6, 8, 11), 2 . 5 z acetic acid (IZ), and 0.05M E D T A (9, IO). The use of lanthanum (13, 14) and strontium (15) solutions have been recommmended t o overcome chemical interferences in the determination of these elements (and of calcium in particular) by flame spectrophotometric techniques. David (1) has compared the two releasing agents and recommends the use of strontium as releasing agent t o suppress the interferences from aluminum, phosphate, silicate, and sulfate. This communication reports the rapid sequential (essentially simultaneous) determination of the exchangeable cations calcium, copper, magnesium, manganese, potassium, and zinc in soils extracted with 1M ammonium acetate, 2.5% acetic acid, or 0.05M E D T A using a commercially available multichannel atomic fluorescence spectrophotometer; the results obtained are compared with those obtained by atomic absorption spectrophotometry with a single channel atomic D. J. David, Atictlyst, 85, 495 (1960). G. F. Griffin, Soil Sci. SOC.Amer. Proc., 32, 803 (1968). A. T. Temperli and H. Mistel, A t i d . Bioclirm., 27, 361 (1969). T. R . Williams, B. Wilkinson, G. A. Wadsworth, D. H. Barter, and W. J. Beer, J . Sei. Food Agr., 17, 344 (1966). (5) S. Pawluk, At. Absorptiori Newslett., 6 , 53 (1967). (6) L. R . Hossner and L. W. Ferrera, ihid., p 71. (7) W. S. G. Macphee and D. F. Ball, J. Sci. Food .4,yr., 18, 376 (I) (2) (3) (4)
( 1967).
(8) J. Lacy, Aiialyst, 90, 65 (1965). (9) J. E. Allan, ihid., 86, 530 (1961). (10) A. M. Ure and M . L. Berrow, Aim/. Cliim. Acta, 52, 247 (1970). (1 1) Association
of Official Agricultural Chemists, “Official Methods of Analyses of the Association of Official Agricultural Chemists,” 7th ed., Washington 4, D.C., 1950. (12) A. M. Ure, Macaulay Institute for Soil Research, Aberdeen, U.K., private communication, 1971. ( I 3) J. Yofe and R. Finkelstein, Aiial. Cliim. Acta, 19, 166 (1958). (14) C. H . Williams, ibid., 22, 163 (1960). (15) R. L. Mitchell, “The Spectrographic Analysis of Soils, Plants, and Related Materials,” Tech. Comm. No. 44, Commonwealth Bureau of Soil Science, 1948.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
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Table I. Detection and Upper Concentration Limit of the Atomic Fluorescence and Atomic Emission Spectrophotometric Determinations
Element Wavelength, nm Calcium 422.7 Copper 324.8 Magnesium 285.2 Manganese 279.5 Potassiuma 766.5 Zinc 213.9 a Flame atomic emission.
Detection limits, pg ml-1 0.007 0.01 0.004 0.01
0.007 0.007
Upper concentration limit, gg ml-1 5
4 4 4 2 5
Table 11. Precision of Atomic Fluorescence Signals Relative standard deviation,____ Concentration. 5 1 0.5 0.25 dml Element Calcium 0.6 1.9 3.2 4.3 Copper 0.9 6.5 6.8 3.4 Magnesium 0.2 1 .o 1.4 2.1 Manganese 0.7 4.0 8.8 11 .o Potassium" 0.3 0.9 1.7 4.3 Zinc 0.5 4.5 3.2 3.1 Flame atomic emission.
absorption instrument. The instrumental sensitivity and the precision obtained in the determination of each element by atomic fluorescence spectrophotometry has also been examined. EXPERIMENTAL
Apparatus. A six-channel atomic fluorescence spectrophotometer (Technicon Corp., Tarrytown, N.Y., Model AFS6) was employed. This instrument is based o n the system originally described by Mitchell and Johansson (16) and employs pulse modulated hollow-cathode lamp sources to sequentially excite atomic fluorescence radiation from atoms produced by sample nebulization into a premixed air-acetylene flame. Fluorescence radiation is collected from the flame with a wide aperture mirror system and passed through appropriate interference filters to a single multiplier phototube detector. The characteristics of the filters employed have been described previously (17). The resulting fluorescence signals are processed using a multiplexed signal processing system and digital read-out (17). F o r soil extract analyses, five channels (Ca, C u , Mg, Mn, and Zn) were employed in the atomic fluorescence mode, while one charnel was employed for the determination of potassium by flame atomic emission spectrophotometry. Single channel atomic absorption analyses were made for five elements using a Perkin-Elmer spectrophotometer (Model 403, Perkin-Elmer, Norwalk, Conn.), and by flame emission for potassium. Nebulizer and Flame Assembly. The multichannel spectrophotometer employs a n indirect nebulizer a n d premix chamber similar t o the Technicon Flame IV system. This is used with a circular carbon burner head which has nineteen holes, 0.036-in. in diameter, arranged concentrically t o produce a flame of approximately 1 cm in diameter. With
__
(16) D. G. Mitchell and A. Johansson, Spectrochim. Acta, 25B,
175 (1970). (17) D. R. Demers and D. G . Mitchell, paper presented at the Technicon International Congress, New York, N.Y., 1970. 1766
the argon shielded air-acetylene flame employed, the nebulizer uptake rate was 3.8 ml/minute a n d the nebulizer efficiency was ca. 3.5 %. Reagents. Solutions, 1000 pg ml+, of calcium, copper, magnesium, manganese(II), potassium, and zinc, and 10,000 p g ml-' solution of strontium and sodium were prepared from analytical reagent grade salts of the elements. These were diluted to prepare solutions containing all six analyte elements for use as calibration standards; each of these solutions was made to contain 1500 pg ml-l strontium and 250 p g ml-1 sodium. Ammonium acetate solution was prepared from 57 ml of glacial acetic acid, which was diluted to 800 ml with distilled water and neutralized with concentrated ammonia (S.G. 0.88) solution to p H 7.0; the solution was then diluted to 1 1. Acetic acid ( 2 S x vjv water) and E D T A (0.05M at p H 7.0) were also prepared from analytical reagent grade chemicals. Preparation of Samples. Ten grams of each of thirteen air-dried soils were shaken with 100 ml of 1 M ammonium acetate solution, 2.5 % acetic acid, o r 0.05M E D T A solution a t room temperature (ca. 15 "C) for two hours o n a n automatic shaker. The solution was then filtered a n d the extract diluted as required. Although ammonium acetate is the most commonly employed extracting agent ( I I ) , acetic acid and EDTA were also used as they are often employed when copper, manganese, and zinc (10) are to be determined in soil extracts. The soil extracts were diluted both 10- and 100-fold with distilled water and the extracts a t both dilutions were made to contain 1500 pg ml-1 strontium and 250 pg ml-1 sodium in a similar fashion to the standards to ensure that interferences and ionization effects were negligible. All six elements were determined in each of the three dilutions of the extract (concentrated extract, IO-, and 100-fold dilutions) in order to ensure that measurement for each element could be made a t a concentration o n the linear portion o f the calibration graph for that element. Because of the widely differing concentrations of the six elements in the soil extracts, it was not possible to use a single dilution at which all the elements could be simultaneously determined accurately. In practice, when large numbers of samples are to be analyzed, it would be possible to automate sequential analyses a t two different dilutions cia an AutoAnalyzer system and t o program the spectrophotometer to measure each element in the appropriately diluted aliquot. RESULTS
Instrumental Sensitivity, Linear Range, and Precision. I n order to determine the optimum dilution factor for the soil extracts, the detection limit a n d linear range obtainable for each element were established with the prototype instrumental arrangement employed. The flow-rate of air a n d acetylene and the nebulizer uptake rate were optimized to produce the best overall detection limits for the six elements. The fluorescence radiation was viewed between 5 and 8 m m above the primary reaction zones, and variation of the height of observation between 3 and 12 m m above these zones had little effect o n the signal intensities. With digital signal presentation, the detection limit for each element was obtained by selecting the point o n its calibration curve a t which the relative standard deviation of ten successive measurements was 50z. The detection limits obtained in this way a t the resonance lines for each element are shown in Table I. The upper concentration limit for each element in aqueous solution for which a linear calibration graph was obtained is also shown in Table I. Table I1 shows the precision data obtained a t different concentrations for each element investigated; the relative standard deviation obtained from ten successive measurements is presented
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
Table 111. Effect of Diverse Ions on the Determination of the Six Analyte Elements Elements concentration, 1 pg/ml Concentration, K Mg Mn Ca cu crg/ml
Diverse ion A1
100 10 100 100 10 100 100 100 100 100 100 10 100 100 10 100 100 100 100 100 10 100 100 100 100 100 100 100
Ba Bi Ca Cd co Cr cu Fe Hg K
Mg Mn Na Ni Pb
Th
10
100 100 10 100 100 10 100 100 100 100 100 100 100 100
Ti V
Zn c1F-
NOaPO^ 3so42-
+ Sr + Sr + Sr + Sr
+ Sr + Sr
-4797, -72%
...
+9z
...
... ... ... ... +22% ... ... ... ... ... ... ...
...
... ... ... ... ...
...
... ...
*..
*.. ..*
+47%
..
...
+ Sr
+ Sr
...
+8%
...
...
... ...
...
...
...
...
... ...
... ...
+ii97,
+50%
...
...
.. ...
... ...
... ,.
...
... -84% -2797,
...
-23%
...
+5597,
... ... ... ... ... ... ... ...
... ...
..,
...
+ Sr
+iix
-25%
...
...
.*.
...
...
...
+ll%
...
-42%
...
...
e . .
...
+ Sr
...
...
..
... ...
*.. ... ...
... ...
* . *
+1297,
...
... ...
Zn
... ... ...
...
...
... ... ...
~
Interference Studies. The effect of the presence of 100-fold weight excesses of some diverse ions o n the simultaneous determination of each of the six elements was measured a t the 1 pg ml-I level. An ion was considered t o interfere when it produced a variation in signal intensity of greater than twice t h e relative standard deviation for this concentration of the
...
...
*..
... *..
...
... ...
...
... - 12%
...
... ... ... ... ...
... ...
..,
... ...
...
Table IV. Determination of Elements in TechElements, concentration in soil, ppm Soil niquea Ca Cu Kb Mg Mn Zn 1 AA 320 0.6 180 86 12.9 2.39 AF 316 0.5 180 2.42 82 12.2 0.3 2 AA 1380 167 52 5.1 0.72 AF 1510 0.5 160 46 4.3 0.8 0.2 187 6.0 1.14 3 AA 1100 81 AF 1081 180 75 5.6 1.4 0.3 100 7.7 980 0.4 167 1.7 4 AA AF 990 0.5 150 102 7.0 1.7 1190 0.2 97 6.4 5 AA 134 0.43 0.3 130 AF 1199 90 5.5 0.32 0.6 167 314 6 AA 2200 1.0 0.89 0.7 160 AF 2380 311 1.05 1 . 0 7 AA 1500 0.3 243 85 6.4 1.31 AF 1520 0.4 230 78 5.6 1.30 AA atomic absorption; AF atomic fluorescence. Flame atomic emission.
...
... ...
-i2z
-i?x
... ... ...
*..
... ... ...
... - 1497,
...
Ammonium Acetate Soil Extracts TechElements, concentration in Soil niquea Ca Cu Kb Mg 96 0.3 165 8 AA 1460 89 170 1450 0.3 AF 85 250 1500 0.3 9 AA 78 250 1520 0.4 AF 168 117 1420 0.3 10 AA 160 115 0.5 AF 1478 24 0.5 153 900 11 AA 23.3 150 908 0.5 AF 193 112 1630 0.6 12 AA 190 111 0.5 1840 AF 75 1940 168 0.1 13 AA 160 68 0.4 AF 1950
...
soil, ppm Mn Zn 12.8 1.97 2.07 11.3 1.31 6.4 5.6 1.3 28.8 0.9 28.6 1.1 1.92 0.75 1.85 0.73 10.2 1.14 9.5 1.25 0.76 17.5 16.3 1.0
analyte element. The effect of each element is summarized in Table 111. Under the conditions employed, n o interference was observed due t o scatter of source radiation by particulate material in the flame, although severe chemical interferences were observed t o depress the analytical signal in many instances. When the solutions were prepared to
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
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Table V. Determination of Elements in 2.5 % Acetic Acid Soil Extracts TechSoil niquea 1 AA
Elements, concn in soil, ppm -Cu Kb Mg Mn Zn 0.2 158 84 36.3 11.3 AF 0.4 160 81 40.1 12.0 2 AA 0.2 191 60 33.9 3.29 AF 0.4 180 50 36.8 3.42 3 AA 0.1 172 81 30.6 8.38 AF 0.1 170 74 34.2 9.00 4 AA 0.1 146 108 34.0 15.5 AF 1080 0.2 140 107 37.4 15.8 5 AA 1420 0.0 143 117 44.0 17.16 AF 1330 0.0 150 111 49.6 18.0 6 AA 2950 0.8 179 664 34.0 40.4 AF 3030 1.1 180 681 37.6 44.0 7 AA 2960 0.0 280 664 45.1 6.0 AF 3040 0.0 280 681 50.6 6.0 a AA atomic absorption; A F atomic fluorescence. Flame atomic emission. ~
Ca 395 403 1700 1690 1270 1180 1140
Soil 1
A
2
C A
3
C A
B B
B
c 4
A
B C 5
A
B 6
C A
B C 7
A
8
C A
B Table VI. Determination of Elements in 0.05M EDTA Soil Extracts Elements, concn in soil, ppm Ca Cu Kb Mg Mn 556 8.05 53.5 39 90 AF 547 8.2 56 38 86 2 AA 2220 3.2 75 47.7 169 2300 2.7 77 48 AF 167 3 AA 1500 3.8 75 50 135 AF 1450 3.1 78 52 140 4 AA 1330 3.6 59 81 154 AF 1380 3.6 64 78 151 5 AA 1650 3.9 43 124 109 AF 1620 3.9 39 129 109 6 AA 3560 26 67 114 58 AF 3650 27 65 111 57 7 AA 4.9 122 4060 266 69 AF 3870 5.0 126 273 73 8 AA 1945 2.6 29 66 81 AF 1955 2.4 33 64 78 9 AA 2055 147 1.3 57 40 1995 1.6 149 AF 59 43 1885 28 61 181 10 AA 4.5 AF 1850 32 62 178 6.8 11 AA 1220 8.4 47 165 154 AF 1190 48 170 158 8.2 12 AA 2160 12.2 73 68 40 AF 2080 12.0 81 68 40 13 AA 3.9 37 59 177 2665 40 AF 2550 4.0 56 183 a AA atomic absorption; A F atomic fluorescence. Flame atomic emission.
TechSoil nique" 1 AA
B C Zn 19.3 18.1
13 12.6 12.8 11.2 4.5 4.7 8.2 8.8 46 50 11.5
11.6 2.8 2.9 1.8 2.3 3.6 4.0 9.0 8.8 5.2 5.3 3.6 3.9
contain 1500 pg ml-l strontium as releasing agent in each case, all chemical interferences were removed. The concentrations of these foreign ions which are commonly found in soil extracts are considerably lower than those investigated, and with the exception of Cr and Na, n o interference effects are observed at these levels (Table 111). The apparent sodium interference is almost certainly due to suppression of ionization of the potassium in the air-acetylene flame, a n effect which is corrected in sample analysis by the addition of sodium to act as a n ionization buffer. The enhancement observed in the presence of chromium may be due t o molecular band emission from C r O or CrH species a t the potassium wavelength (766.5 nm). 1768
9
A
B
Table VJI. Recovery Experiments on Ammonium Acetate Soil Extracts _ _ _ _ . _ _Element _ _ ~ Caa Cub Ka Mg" Mnb 0.34 0.02 0.14 0.06 0.46 1.37 1.01 1.20 1.09 1.41 103% 99% 106% 103% 95% 1.49 0.01 0.12 0.02 0.08 2.54 1.00 1.13 1.03 1.07 l06Z 99% 101% 101% 99% 1.12 0.03 0.14 0.05 0.10 2.12 1.00 1.16 1.05 1.04 100% 97% 102z 100% 99% 0.98 0.03 0.13 0.07 0.13 2.06 1.08 1.16 1.12 1.12 108% 105% 103% 105% 99% 1.25 0.03 0.08 0.07 0.23 2.33 1.01 1.08 1.06 1.19 108% 98% 100% 99% 96% 2.44 0.02 0.13 0.30 0.05 3.42 1.05 1.13 1.30 1.01 98% 103% 100% 100% 96% 2.27 0.01 0.21 0.41 0.05 3.34 0.97 1.20 1.42 1.08 107% 96% 99% 101% 103% 1.53 0.02 0.13 0.07 0.50 2.53 1 .07 1.07 1.07 1.55 100% 105% 94% 100% 105% 1.59 0.02 0.23 0.06 0.03 2.56 1 .OO 1.22 1.06 1.01 97% 98% 99% 100% 98% 1.49 0.03 0.12 0.09 1.17 2.54 1.05 1.13 1.09 2.12 105% 102% 101% 100% 95% 0.96 0.03 0.10 0.00 0.72 2.02 1.03 1 . 1 1 1.01 1.73
Znh 0.10 1.07 97% 0.03 1.03 100%
0.06 1.07 101% 0.06 1.07 101%
0.09 1.04 95% 0.08 1.07 99% 0.04 1.06 102% 0.08 1.04 96% 0.02 1.01
99% 10 0.04 B 1.07 C 103% 11 A 0.03 B 1.02 C 106% 100% 101% 101% 101% 99% 12 A 1.79 0.02 0.15 0.09 0.44 0.04 B 2.87 0.99 1.17 1.10 1.36 1.00 C 108% 97% 102% 101% 92% 96% 13 A 2.09 0.02 0.12 0.06 0.70 0.07 B 3.06 1.04 1.10 1.04 1.77 1.03 C 97% 102% 98% 98% 107% 96% A. Initial concentration (figirnl) found in suitably diluted extract. B. Concentration ( p g i r n l ) found in suitably diluted extract after addition of 1 pg/ml of each analyte element. C. Percentage recovery of the added element. Using extract diluted 100-fold. Using extract diluted 2-fold. C A
Standard Analyses. Each element was determined in the extracts under optimum conditions by the multielement atomic fluorescence spectrophotometer, and the results were compared with the equivalent atomic absorption analyses performed under the single channel spectrophotometer. The results are shown in Tables IV-VI. Recovery Experiments. Pairs of aliquots of each ammonium acetate and acetic acid extract were taken; one aliquot was diluted with strontium and sodium solutions while the other was diluted with sodium, strontium, and with each of the six elements to be determined, so that the final concentration of strontium in each solution was 1500 pg ml-I and the final concentration of sodium was 250 p g m1-I. The extracts were diluted 2- and 100-fold so that the concentration of the exchanged element would be of the same order as the added element. Calcium, magnesium, and potassium were determined in the extract diluted 100-fold, and copper, manganese, and zinc in the extract diluted two-fold. The results for the recovery of each element, expressed as a percentage of the added concentration, are shown in Table V1I and VIII.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBE.R 1 9 7 1
Table VIII. Recovery Experiments on Acetic Acid Soil Extracts Element __~__ __.____K" Mg" Mnh Znb Soil Ca5 Cub 1 A 0.34 0.02 0.12 0.06 1.59 0.61 B 1.34 1.05 1.11 1.06 2.61 1.66 C 100% 103% 99% 100% 102% 105% 2 A 1.74 0.01 0.14 0.03 1.50 0.13 B 2.72 1.00 1.14 1.04 2.51 1.17 C 98% 99% 100% 101% 101% 104% 3 A 1.22 0.00 0.13 0.05 1.35 0.40 I3 2.26 1.02 1.14 1.06 2.33 1.45 C 1047< 102% 101% 101% 98% 105% 4 A 1.10 0.01 0.10 0.09 1.52 0.80 B 2.08 0.98 1.10 1.10 2.50 1.87 C 98% 97% 100% 101% 98% 107% 5 A 1.31 0.02 0.11 0.09 1.40 0.92 B 2.32 1.02 1.08 1.10 2.85 1.97 C 101% 100% 97% 101% 95% 105% 6 A 3.13 0.05 0.16 0.50 1.48 2.34 B 4.13 1.10 1 . 1 1 1.48 2.52 2.30 C 100% 105% 95% 98% 104z 96% 7 A 3.10 0.00 0.26 0.75 1.99 0.27 B 4.08 0.98 1.18 1.63 3.03 1.27 C 98% 98% 92% 98% 104% 100x A. Initial concentration (pg/ml) found in suitably diluted extract. B. Concentration (pg/ml) found in suitably diluted extract after addition of 1 pgjml of each analyte element. C. Percentage recovery of the added element. Using extract diluted 100-fold. * Using extract diluted 2-fold. CONCLUSION
The analytical results show that the atomic fluorescence and atomic absorption determinations o n each soil extract were identical within experimental error. The former, however, may be obtained virtually simultaneously, resulting in considerable saving of time when many samples are t o be analyzed. Although the sample preparation time is identical for both techniques, the determination of the six analyte
elements in large numbers of samples with the multichannel atomic fluorescence spectrometer takes only one eighth of the time required using the single channel atomic absorption spectrophotometer when the latter is used with the longest integration time (10 seconds). This must be compared with the 16-second measuring cycle in which the atomic fluorescence spectrophotometer yields a result for each of the six channels. Additionally, time is saved a n d less operating skill is required because of the use of interference filters in the atomic fluorescence instrument. It is not necessary to change sources repetitively and to set the required wavelength accurately for a particular analyte element, and n o possibility of monochromator drift arises during the course of analysis of a large number of samples. The attained sensitivity and precision of the atomic fluorescence determinations is sufficient to permit the determination of the six elements examined in all common soil samples. With some samples, however, preconcentration of copper before analysis might be necessary. The results of the recovery experiments conducted indicate that atomic fluorescence measurements made for the analyte elements o n the ammonium acetate and acetic acid extracts are free from interference effects from extraneous ions. The multielement analysis of soil extracts in a single extract a t two dilutions by atomic fluorescence spectrophotometry is accurate and precise, and offers the potential of considerable time saving in routine determinations. ACKNOWLEDGMENT
We are grateful to Technicon Instrument Corp. for the loan of the atomic fluorescence spectrophotometer used in this work. We would like to thank also the Macaulay Institute for Soil Research, Aberdeen, Scotland, for the provision of soil samples. RECEIVED for review May 24, 1971. Accepted August 16, 1971. Financial support was provided t o one of US (R. W.) by the Technicon Instrument Corp.
Atomic Fluorescence Spectrometry with Continuous Nebulization into a Platinum Furnace M. S. Black, T. H. Glenn, M. P. Bratzel,' a n d J. D. W i n e f o r d n e P Department of' Chemistrj., Unicersit)*o f Florida, Gainescille, Fla. 32601 Atomic vapor of several metals (Cd, Zn, Cu, Hg, and Fe) was produced by continuous nebulization of an aqueous sample through a simple platinum tube furnace, and atomic fluorescence was excited by means of line radiation from electrodeless discharge lamps. Two furnace designs were evaluated and compared with respect to limits of detection, ranges of linearity of analytical curves, and interferences.
MOST ATOMIC FLUORESCENCE spectrometric studies have employed flames produced by nebulizer-burners t o generate a n atcmic vapor of the analyte. Flames are rather inefficient
Present address. Department of Chemistry, Carleton University, Ottawa. Canada. Author to whom reprint requests should be sent.
atomizers for many elements and also contain significant concentrations of efficient quenchers of excited atoms, such as CO?, CO, Nz, etc. ( I ) . Therefore, nonflame cells have been utilized in analytical atomic fluorescence spectrometry. Nonflame cells were first used by King ( 2 ) for fundamental studies and by L'vov (3) for analytical atomic absorption spectrometry. However, the first nonflame cell used in atomic fluorescence spectrometry, a graphite tube furnace, was described in 1968 by Massmann ( 4 ) . Since then, West (1) J. Winefordner, V. Svoboda, and L. Cline, CRC. Crit. Reu. A t i d . Clieni., 1, 233 (1970). (2) A. King, Astroplzys. J . , 28, 300 (1908). (3) B. L'vov, Spectrochim. Acta, 17, 761 (1961). (4) H.Massmann, ibid., 23B, 215 (1968).
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