Anal. Chem. 1981, 53, 1719-1721
solution, which wm followed by an unspiked solution. The amount of PCB in the aqueous phases and on the test tubes was determined by liquid scintillation counting.
RESULTS AND DISCUSSION Between 2.2% and 49.9% of the organic solutes were lost from the spiked solutions (Table I). Only 0.078 (*0.009) mL or 0.8% of the originall 10 mL of water remained in the test tube; therefore, both phthalates and PCB were adsorbed onto the glass test tubes. The adsorbed compounds were only partially recovered by subsequent water rinses. A solvent rinse of the containers recovered the remainder of the compounds adsorbed to the surface. The amount of phthalate bound to the glass test tubes appears to be a function of the aqueous solubility of the phthalate. The solubilities of the phthalates have been reported to be 3.2 mg of DBP and 1.2 mg of BEHP/L of artificial seawater (8). Table I shows that the more soluble DBP is absorbed far less than BEHP. The amount of solute also appears to be altered by the presence of other material already on the surface. Between 70% and 80% of the total PCB stayed in the aqueous phase when BEHP was not present. When approximately 400 ng of BEHP was adsorbed to each test tube, only 55% of the total PCB stayed in the aqueous phase. The increased lipophilicity due to the presence of' BEHP apparently increased the adsorption of PCB by thle glass test tubes. The significant percentages of these organic pollutants in the unspiked water rinses indicates that their adsorption is reversible. Once the compounds are adsorbed to the glass, they can desorb into thle next solution that is placed into the
1719
container, which is a concern during the repeated use of the same storage or sampling container. The cross contamination of samples and the loss of the analyte can be reduced by rinsing the container with clean water or solvent which is then proceised with the sample or by extracting the sample in the container.
LITERATURE CITED (1) Dogan, S.;Haerdi, W. Anal. Chim. Acta 1978, 101, 433-436. (2) Hoyle, W. C.; Atkinson, A. Appl. Spectrosc. 1979, 33, 37-40. (3) Plcer, M.; Picer, N.; Strohal, P. Scl. TotelEnviron. 1977, 8 , 159-164. (4) Pepe, M. G.; Byrne, J. J. Bull. Environ. Contam. Toxicol. 1980, 25, 936-940. (5) Glam, C. S.; Chan, H. S.; Neff, 0. S. "Marlne Pollutant Transfer"; Windom, H. L., Duce, R. A., Eds.; D. C. Heath & Co.: New York, 1976; pp 375-386. (6) Glam, C. S.; Chan, H. S.;Neff, G. S.;Atlas, E. L. Science 1978, 199, 419-421, (7) Sullivan, K. F. M.S. Thesis, Texas A&M Unlverslty, Aug 1980. (8) Kakreka, J. P. M.S. Thesis, Texas A&M University, Dec 1974.
Kevin F. Sullivan Elliot L. Atlas Choo-Seng Giam* College of Science University of Texas at El Paso El Paso, Texas 79968
RECEIVED for review April 13, 1981. Accepted June 23, 1981. This work was supported by the National Science Foundation, Grant Nos. OCE76-14148 and 0CE77-12482, and by the Robert A. Welch Foundation.
Element Distribution Coefficients for Hydrofluoric Acid/Nitric Acid Solutions and the Anion Exchange Resin Dowex 1x8
Sir: Anion exchange resins have proved to be extremely useful for performing rapid quantitative separations in trace element analysis. Mixtures of hydrofluoric acid and nitric acid are best suited for the decomposition of a number of matrices such as refractory metals, glasses, geological samples, and others. In such cases, it would be advantageous if the separation could be carried out in the presence of both acids. However, because of the lack of knowledge of the distribution coefficients for this medium, the removal of nitric acid prior to the separation has been the common practice. The removal can be carried out either by evaporation or by addition of formic acid. The former procedure is time-consuming and, in addition, losses of slome elements may occur by volatilization. In the latter procedure, ions of some elements such as Ag, Re, Pt, Au, and others are reduced and this makes their processing difficult. For this reason, we have investigated the distribution of elements directly from the mixture of HF and HNOBby anion exchange and the results are given below. The adsorption of the elements by anion exchange from hydrofluoric acid ( I ) and from nitric acid (2) was studied by Faris under dynamic conditions. On the basis of his results obtained for HF solutions, we investigated the distribution of the ions of more than 30 elements between the anion exchanger and the solutions of HF and of the HF/HN03 mix-
tures under static conditions. For alkali and alkaline earth metals only representative elements Na, K, Mg, and Ca were investigated. The distribution data were obtained by determining the portion of the elements remaining in the aqueous phase after the establishment of the equilibrium by using the radioactive tracer technique. For the multivalent elements the following oxidation states were tested Fe(III),As(V), Se(IV),Tc(VII), Pd(II), Re(VII), Ir(IV), Pt(IV), and Au(II1). The distribution coefficient D is defined as the ratio of the total (analytical) amount of solute per gram of dry ion exchanger to the concentration of solute (total amount per milliliter) in the external solution. D was determined by the batch equilibration technique at 20 1"C. For this purpose, 2.4 mL of the respective solution, containing the labeled element investigated, was mixed with 50 mg of air-dried Dowex 1 x 8 (100-200 mesh) for 2 h. The adsorbabilities of the elements on Dowex 1 x 8 for different media are shown in Figures 1-4: in Figure 1 from hydrofluoric acid solutions for concentrations from 4 M to 24 M in Figure 2 from the mixture of hydrofluoric acid and nitric acid 9:l for concentrations from 3.6 M HF/0.25 M HN03 to 21.6 M HF/1.5 M "0,; in Figure 3 from the mixture of hydrofluoric acid and nitric acid 3:l in the concentration
0003-2700/81/0353-1719$01.25/00 1981 American Chemical Society
*
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ANALYTICAL CHEMISTRY, VOL.
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3
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53, NO. 11, SEPTEMBER 1981
3
ITa
Mo
2
2
log D
-
iog D
1
Hf
1
Fe
Ta Pt
-
Sn
OV
Se 0 Se
0 0 Fe
-
0
' I 1
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I
= Ig
4
- E a , C r , Mn, C 8
4 1 , C u , Zn, Ga, C d , In
12
16
20
24
M-HF
Flgure 1. Distribution coefficients for Dowex 1x8 resin and HF sobtlons. D = distribution coefficient [mL g-']. The D value of the elements shown as a row in the bottom of the figure is lower than 0.1.
0.625
6 1.25
9 1.875
12 2.5
I 18 M - H 3.75 M-HN03
15 3.125
Figure 3. Distribution coefficients for Dowex 1x8 resin and solutions of the mixture HF (40%)/HN03(65%), 3:l. Notation cf. Figure 1.
3
3
2
2
log D
4u
log D
Au r
ir Pt Pd
1
P
1
Ta Nb
w
AS
AS
rc
TC
m W
0
H
0
0.25
a5
r.n
1.0
1.2s
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Flgure 2. Distribution coefficients for Dowex 1x8 resin and solutions (65%), 9:l. Notation cf. Figure 1.
of the mixture HF (40%)/"03
2 1.25
4 2.5
0 3.75
8 5
10 6.25
12 M-HF 7.5 M - W
Flgure 4. Distribution coefficients for Dowex 1x8 resin and solutions of the mixture HF (40%)/HN03(65%), 1:l. Notation cf. Figure I.
1721
Anal. Chem. 1981, 53, 1721-1723
interval from 3 M HF/0.625 M HNOBto 21.6 M HF/1.5 M HNO,; and in Figure 4 from the mixture of hydrofloric acid and nitric acid 1:l between 2 M HF/1.25 M HNOB and 12 M HF/7.5 M "0,. The quoted values are the average of a minimum of two determinations. For an adsorption of 50% (log D F= 1.7) the relative standard deviation is *3%. The results in Figure 1 are in accordance with the data published by Faris for dynamic conditions (1). Only for palladium, platinum, gold, and mercury differing D values have been obtained, presumably due to dzferent experimental conditions. Rather unreproducible results were obtained for the adsorption of silver ,and antimony. These results are not given in detail. For niobium, the observed increase in D with increasing acid concentration can be attributed to the disappearance of oxyfluoro complexes. The comparison of results given in Figures 1-4 indicates that with increasing fraction of nitric acid there is a continous decrease of the D value of all elements tested. This can be explained by the formation of less charged and less adsorbable anionic species in the presence of nitric acid. These distribution data enable one to work out useful separation procedures. For instance, on their basis a rapid
separation procedure has been developed for the radiochemical neutron activation analysis of high-purity niobium involving short-lived indicator radionuclides (3).
LITERATURE CITED (1) Faris, J. P. Anal. Chem. 1960, 32, 520-522. (2) Faris, J. P. Anal. Chem. 1064, 36, 1157-1158. (3) Faix, W. G.; Caietka, R.; Krivan, V. Anal. Chem. 1981, 53, 1594- 1598.
Werner G. Faix Rostislav Calet ka Viliam Krivan* Sektion Analytik und Hochstreinigung Universitat Ulm Oberer Eselsberg N26, D-7900 Ulm Federal Republic of Germany RECEIVED for review March 24,1981. Accepted May 26,1981. This project was financially supported by Bundesministerium fur Forschung und Technologie, Bonn. Irradiation facilities for the production of radionuclides were provided by Kernforschungszentrum Karlsruhe.
Comments on Noise and Digital Resolution in a Microprocessor-Controlled Spectrophotometer Sir; We would like to a.dd to the paper by Kaye and Barber ( I ) . They made the remark that surprisingly they found the temperature coefficient of the photomultipliers was somewhat less than the figure given by the manufacturer, Hamamatsu Corp. This is not especially surprising to us. The main reason being that all of our data are taken from large samplings and in general indicate a worse case situation. That is true not only for temperature coefficientsbut also for spectral response curves. In actuality, there is a resonable variance tube to tube, since the cathodes of photomultiplier tubes tend to be both interference filters and plhoto emissive devices. Each layer of the film tends to be quite thin and not precisely controlled in thickness. In recent years we have found a tendency for the detectors to become more and more uniform. This is probably the result of better control over the materials used in making the tube, plus a better environment within our factory situation. But, the user and especially the design engineer should take note
of the fact that the data shown in detector manufacturer's catalogs is statistical in nature and does not represent any particular tube. For this reason, for many years Hamamatsu has taken a very strong negative stand utilizing photomultiplier tubes as standards over a long period of time. Applications such as the one described by Kaye, which rely on relatively short term stability are within the state of the art.
LITERATURE CITED (I) Kaye, Wibur; Barber, Duane Anal. Chem. 1981, 53, 366-369.
R. Eno Hamamatsu Corporation 420 South A~~~~~ Middlesex, N~~ jersey 08846 RECEIVED for review March 4,1981. Accepted April 10,1981.
AIDS FOR ANALYTICAL CHEMISTS Colorimetric Measurements in a Liquid Scintillation Counter Martin W. Heitzmann" sind Leonard A. Ford Division of Drug Chemistty, Food and Drug Administration, Washington, D.C. 20204
The concept of making high-precision photometric measurements by using a radiosotopic light source was first reported by Ross ( I ) . The instrument used in his experiments was a hybrid constructed from portions of a liquid scintillation counter (LSC), a multichannel pulse height analyzer, and a
custom-made sample chamber containing standard 1-cm cuvettes for the light source and sample holder. In an earlier paper (21, Ross described the use of an isolated internal standard cell to distinguish between the contributions of chemical and color quenching to total quenching. By se-
This article not subject to U S . Copyright. Published 1981 by the American Chemical Society
