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e
3 u,
2
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a
-20
5
a W a
8 a
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SECONDS
Figure 7. Separation of trace light gases Column and G. C.conditions same as Figure 6. Sample size: 5.7 X 0.035 in.; sample loop (90 pl) OSLL
=
8 X IO-%
(2)
A plot of OSLL us. effective plate number did not show a better data fit. From Table I, it can be seen that the columns used for the determination of Equation 2 consisted of various lengths, i.d.’s, and phases, both solid and liquid. Columns 4 and 6 were operated at twice their optimum flow rates as determined from their Van Deemter plots, while the others were operated at their optimum flow rates. The significance of OSLL can be readily observed by examining the effect of SLL on detector response (peak height)
and on column plate height. This is illustrated using Column 3. The OSLL for this column is approximately five inches (Figure 1). In Figure 4, it is shown that the peak height increases to a maximum with increasing SLL and that the maximum is slightly less than twice the peak height value at OSLL. The plate height, on the other hand, has more than doubled for the same increase in SLL (see Figure 5). At OSLL, the loss in column efficiency is only 15 to 20%. This behavior was typical of all the columns listed in Table I. Consequently, the OSLL represents a good compromise between the desirable increase in sensitivity and the undesirable degradation in column efficiency. The use of OSLL is illustrated for the rapid analysis of ethylene in a light gas mixture. The n required for the separation of ethylene and ethane on Porapak S was first determined. To this value, an additional 20% was added in order to offset the loss of column efficiency due to OSLL. The total plate number required was then found to be 710. By using Equation 2, OSSL is calculated to be 5.7 inches. In Figures 6 and 7 are compared an analysis using a 3-11 sample size and one using the OSLL, respectively. Comparison of the concentrations of the components shows that the sensitivity has increased by a factor of fifty while base-line separation between ethylene and ethane was still maintained. ACKNOWLEDGMENT The authors thank Ken Kee for the art work.
RECEIVED for review June 23, 1971. Accepted March 30, 1972. This paper was presented at the Seventh International Symposium on Advances in Chromatography, held in Las Vegas, Nevada, November 29-December 3,1971.
Neutron Activation Analysis of Copper by Substoichiometric Extraction with Neocuproine R. A. Nadkarni and B. C. Haldar Inorganic and Nuclear Chemistry Laboratory, Institute of Science. Bombay-32, India
COPPERIS ONE of the seven essential trace elements necessary for normal animal and plant metabolism. Copper deficiency in humans causes Wilson’s disease. Copper acts as an activator of lipid enzyme systems, particularly those concerned with phospholipid synthesis. At the same time copper is an important metal in various industries and technologies, and mineral prospecting for copper is important geochemically, Nondestructive activation analysis of copper is not feasible since 64Cubeing a positron emitt’er, any other activity in the irradiated material which decays by positron emission will interfere seriously in this determination. Hence, radiochemical separation of copper is necessary for its determination. By incorporating the substoichiometric principle in the radiochemical separation scheme, several purification steps can be eliminated, and the time of separation shortened, provided a suitable reagent is available. Dithizone ( I ) and diethyldithiocarbamate (2) are two reagents which have been (1) J. Ruzicka and J. Stary, “Substoichiometry in Radiochemical Analysis,” Pergamon Press, New York, N.Y., 1968, p 87. (2) M. Krivanek, F. Kukula, and J. Sluencko, Talanta, 12, 721 (1965). 1504
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
used for substoichiometric activation analysis of copper. As is well known, the former is a very unstable and sometimes unpredictable reagent, while in the case of the second reagent, there is interference from several elements which can be avoided only by employing a multichannel analyzer. Neocuproine has been known for long time as an almost specific spectrophotometric reagent for copper (3, 4 ) . We have developed a method for the determination of trace amounts of copper based on neutron activation and substoichiometric extraction of copper with neocuproine in chloroform. EXPERIMENTAL Copper standards were prepared by dissolving 99.999 pure copper metal in H N 0 3 and diluting by weight to the desired concentration. Aliquots of this solution were taken in quartz vials and dried. The samples were dried (except for blood serum which was freeze-dried) at 80 “C for several hours. About 50-200 mg of the sample and about 10 pg (3) C. L. Luke and M. E. Campbell, ANAL.CHEM., 25,1588 (1953). (4) A. R. Gahler, ibid., 26, 577 (1954).
Table I. Decontamination Studies in the Substoichiometric Extraction of Copper with Neocuproine in Chloroform Element
Decontamination factora 1.58 X 1.09 X 6.61 x 5.16 x
Element
Decontamination factora
106 lo6
105 105
x 105 2.83 X 1Oj 2.44 x 105 1.80 x 105 I .45 x 105b 1.36 x 105 9.81 X 10’ 4.51
-ML
OF 0sIM
64 C U S O 4 SOLUTION-
8.72
Figure 1. Substoichiometric extraction of Cu(I1) with neocuproine in chloroform
of the copper standard were sealed in quartz vials, and units of 2 samples and 1 standard were irradiated in the CIRUS reactor of Bhabha Atomic Research Centre, Trombay, for 24 hours in a thermal neutron flux of 1.5 X 10l2n ’ cm--2 set.-' After radiochemical separation the 64Cuactivity was measured either on a single channel analyzer connected to a well-type 1.5-in. X 1.541. NaI(T1) detector or on an endwindow type GM counter. Other reagents used were 0.1M CuS04 carrier solution, carrier free 64Cu isotopic tracer solution, 30% sodium citrate, 10 % hydroxylamine hydrochloride, and 0.05M neocuproine solution in ethanol. Substoichiometric Extraction of Cu(1) with Neocuproine. EFFECTOF VARIABLES.Extraction of copper with neocuproine takes place from pH 1 to 10.5; however, quantitative extraction occurs only at pH 1.5 to 4. Hydroxylamine hydrochloride was used as the reducing agent for converting Cu(I1) to Cu(1). Sodium citrate was used as a buffer as well as masking agent for any possible interference from other metals. REPRODUCIBILITY OF THE METHOD. T o a series of solutions containing increasing amounts of labeled 0.1M CuSO4 (“CU) were added 5 ml of hydroxylamine hydrochloride and 10 ml of citrate buffer. The pH of the solutions was adjusted to 2.5-3, and 6 ml of 0.05M neocuproine were added to each of them. The solutions were shaken for a minute with 10 ml of chloroform, and a 7-ml aliquot of the organic phase was taken for counting. The plot of amount of labeled 64Cutaken 6s. the activity in organic phase (Figure 1) shows linear increase till all of stoichiometric copper is extracted, after which the amount of copper extracted remains constant. The complex of Cu:neocuproineis seen to be 1 :1. Recommended Procedure. The irradiated and weighed samples are dissolved after addition of 1 ml of 0.1M &SO4 solution and about 5 mg each of other carriers. The geological samples are dissolved in H N 0 3 HzS04 HF mixture, while biological samples are dissolved in H N 0 3 HClO4 mixture. To this solution is added 10 ml of 10% hydroxylamine hydrochloride, and 10 ml of 30% sodium citrate. The pH of the solution is adjusted to 2.5-3, and 1 ml of 0.05M neocuproine solution is added t o it. The red color is extracted with 10 ml of chloroform. The organic phase is washed with 20 ml of water and a 7-ml aliquot of the organic phase is taken in a glass planchet, dried under a heat lamp, and the activity counted either on a gamma-ray spectrometer a t the channel corresponding to 0.51 MeV peak of 64Cu,or on an end window type G M counter. The irradiated copper standard is processed exactly the same way. The amount of copper in the sample is calculated in the usual fashion.
+
+
+
x
104
x
104
2.14 X
lo4
7.22
6.87 x 104 4.72 x 104 3.10 x 104
2.48 x 104~ 2.04 x 104 1.11 x 104d 6.07 x 103 4.51 x 103 2.36 x 103 2 . 2 2 x 103
Decontamination Factor = Activity taken/Activity in organic phase. b Oxalic acid used as the masking agent. c Phosphoric acid used as the masking agent. d Potassium iodide used as the masking agent.
RESULTS AND DISCUSSION
On thermal neutron irradiation 63Cu(69.2 % abundance) by (n, y ) reaction produces 64Cu. This reaction has a cross section of 4.7 barns, and 64Cuhas a half-life of 12.8 hours and emits gamma rays of 0.51 (by positron emission) and 1.35 MeV, and betas of 0.65 MeV energy. The same isotope can also be produced by the reaction 64Zn(n,~)6~Cu which has a cross section of 390 millibarns and 64Znhas 48.9% natural abundance. Since most geological or biological materials contain amounts of zinc comparable with those of copper, this reaction can pose some interference in the determination of copper. From calculations of amounts of copper activity that will be produced at a given flux by both (n,r) and (n,p) reactions, it is seen that 1 mg of zinc corresponds to 5.36 X mg of copper in terms of the activity produced (5). This correction is not appreciable unless the ratio of the amount of zinc to that of copper is very unfavorable in the material to be analyzed ; however, since zinc content of the materials analyzed was known t o a fair degree of certainty, this correction was applied to our copper results. Table I gives the decontamination factors obtained by using various isotopes in the substoichiometric extraction of copper with neocuproine in chloroform. The values obtained are satisfactory for most of the isotopes studied. When Hg(II), W(VI), and Sn(I1) are present, KI, H3P04, and oxalic acid have to be used as masking agents to suppress their interference. Table I1 gives the results of determination of copper in several geological and biological materials. The standard deviations given are from the replicate determinations calculated at 95% confidence limits. For the samples for which the data are available in literature, the agreement between our results and the reported or recommended values in literature is, for most part, excellent. Allende is a Cz carbonaceous chondrite and our value of 78.3 ppm is comparable with -100 ppm as the average value for copper in meteoritic
(5) J. T. Routti, ANAL.CHEM., 40, 593 (1968). ANALYTICAL CHEMISTRY, VOL. 44, NO. 8,JULY 1972
e
1505
Table 11. Determination of Copper by Substoichiometric Neutron Activation Analysis Cu reported: ppm Material Cu found,n ppm T-1 65.7 i 2.4 (3) 62(6) llO(7); 114 f 4(8) w-1 104 f 3 (2) 116 f 10 (9) Sye-1 29.3 i 2.9(2) 23 (IO); 25 (11) PCC- 1 9.23 i 0.09(2) 10.4(12); 8 f 2(9) G- 1 12.8 i 1.2(2) 13(7) GR 358 i 19 (2) 345 (13) Allende meteorite 78.3 f 2.9 (3) ... Bowen’s kale 5.20 f 0.06 (2) 4.81 f 0.74 (14) 1R1 tobacco 70.1 =t11.6(2) ... Human blood serum 1.65 i 0.05 (2) ... Artificial mixture 0.0083 pg 0.0077 pg Artificial mixture 0.0427 pg 0.0446 pg a Figures in parentheses indicate the number of replicate determinations carried out. Figures in parentheses indicate the reference numbers.
matter (15). 1R1tobacco is an international cigarette tobacco standard manufactured and distributed by the University of Kentucky, Lexington, Ky. Our value of 70.1 ppm may be
compared with the values 76.7 (16), 32.4 (19, 17-32 (18), and 15-21 (19) ppm in various commercial tobaccos reported in the literature. The wide variation in the values is a result of the tobacco crops grown on different soils. In freezedried human blood serum, we found 1.65 ppm of copper. Earlier values for copper in human blood serum were 1.54 (20) and 2 (21) ppm. To find out the experimental limits of copper determination by this method, two artificial mixtures containing 0.0077 pg and 0.045 pg of copper were analyzed and the values found were 0.0083 pg and 0.043 pg, respectively. Five samples containing the same amounts of copper were extracted by the procedure given, and the replicate results were found to agree within f1.84 relative per cent at 95% confidence limits. Two samples and a standard can be analyzed by this method in 45 minutes after receiving the irradiated material in our laboratory. The radiochemical purity of the isolated 64Cuactivity was checked by measuring its gamma-ray spectra, beta maximum energy, and half-life, and in all cases the samples were found to be highly pure. Thus, the proposed method can be used for the determination of trace amounts of copper in geological or biological materials with good degree of precision and in a very short time.
( 6 ) C. 0. Ingamells and N. H. Suhr, Geochirn. Cosmochinz. Acta,
27, 897 (1963). (7) M. Fleischer, ibid., 33,65 (1969). (8) 0. Johansen and E. Steinnes, Talanta, 17, 407 (1970). (9) R. A. Schmitt, T. A. Linn, Jr., and H. Wakita, Radiochim. Acta., 13, 200 (1970). (10) N. M. Sine, W. 0. Taylor, G. R. Webber, and C . L. Lewis, Geochim. Cosmochim. Acta, 33, 121 (1969). (11) G. R. Webber, ibid., 29, 229 (1965). (12) F. J. Flangan, ibid., 33, 81 (1969). (13) M. Roubault, H. de La Roche, and K. Govindraju, Sei. Terre, 13, 379 (1968). (14) H. J. M. Bowen, in “Advances in Activation Analysis,” J. M. A. Lenihan and S. J. Thompson, Ed., Academic Press, London, 1968, Vol. 1. (15) B. Mason, “Meteorites,” John Wiley, New York, N.Y., 1962.
RECEIVED for review July 12, 1971. Accepted January 28, 1972. The authors are grateful t o the Council of Scientific and Industrial Research, Government of India, New Delhi, for financial assistance to one of them (R.A.N.). (16) R. C. Voss and H. Nicol, Lancet, 2, 435 (1960). (17) A. G. Souliotis, Analyst, 94, 359 (1969). (18) E. C. Cogbill and M. E. Hobbs, Tobacco Sei., 1,68 (1957). (19) W. K. Collins, G. L. Jones, J. A. Weybrew, and D. F. Matzienger, Crop Sei., 1,407 (1961). (20) C. C . Thomas, G . P. Terecho, and J. A. Sondel, Nucl. Appl., 3, 53 (1967). (21) A. Jacobsen, J. Nucl. Med., 2,289 (1961).
Comparison of Neutron Activation Analysis and Other Analyses Procedures for Fish Samples N. D. Eckhoff,’ C. J. Pappas,2 and C. W. Deyoe2 Kansas State University, Manhattan, Kansas 66502 NEUTRON ACTIVATION ANALYSIS (NAA), well developed as a rapid, sensitive, and precise nondestructive methodology, is used routinely by many laboratories. Analysts employing the NAA technique with gamma-ray spectrometry use two analytical procedures principally : peak area, which is fast but imprecise, and least squares unfolding, which is precise but reasonably complex and time-consuming. In lieu of an ideal method-Le., fast and precise-to analyze large quantities of spectral data, we describe below a compromise method, used to process hundreds of fish samples for concentration estimates for K, Ca, Mn, C1, and Na. Department of Nuclear Engineering.
* Department of Grain Science and Industry. 1506
ANALYTICAL CHEMISTRY, VOL. 44, NO. 8, JULY 1972
Not all the gamma-ray spectral data are needed for a precise, nondestructive analysis of a sample ( I ) . Because large quantities of data need not be manipulated, this area of interest (AOI) least squares method, which saves computer time may be used : Each channel of the complex gamma-ray spectrum is assumed to be a linear combination of the elemental concentration estimate times the value of that channel in the elemental reference gamma-ray spectrum plus a deviation value Y=Ab+e
(1)
(1) N. D. Eckhoff and P. F. Ervin, Nucl. Instrum. Methods, 97, 263-6 (1971).
