CORRESPONDENCE Separation of Calcium--Strontium Investigated by the Use of Tracers SIR: The separation of calcium from strontium using nitric acid is a very useful step in radiochemical analysis of strontium-89 and -90. It is used in procedures for the determination of strontium-89 and -90 in milk, food, water, and other media (1-5). This technique or procedure will lead to poor recoveries of strontium or excessive weight of precipitate (poor separation from calcium) if not performed correctly. A previous study (6) many years ago established 79 to 81% as 2n optimum concentration range of ”01 which allows the highest recovery of strontium. This investigation utilizing calcium-47 and strontium45 tracers was performed to verify this study. In this experiment, the normality of the nitric acid solutions used was adjusted by adding varying amounts of fuming nitric acid. The solution to which the acid was added was in 0-;’ / I , I all cases 5 ml of H 2 0 containing Ca2+,Sr2+,”Sr, and “Ca. 65 ’ m’ 75 80 z This simulated the dissolved SrCO3-CaCO7 precipitate 14.1 14.9 16,O 16.9 l7,6 18,4 M found in r? :iostrontium analysis. The acid concentrations NlRlc ACID CWZNTMTICCI of solutioii; ‘yere checked by titrating an aliquot of 5 ml of Figure 1. Strontium-calcium separation H20 required volume 21N H N 0 3 against a standardized solution of NaOH. The actual normality of the fuming -0- Strontium, 1 ext. HN03 was greater than 21N. The label on the fuming - Strontium, 2 ext. -0Calcium, 1 ext. nitric acid stock bottle usually reads a “Minimum 90 Z.’’ -ACalcium, 2 ext. The concentration of the nitric acid should always be checked before performing Ca-Sr separation. The amounts of stable strontium and calcium used in all samples such as milk and food. These are: Sr2+ = 20 mg, analyses simulated the concentrations found in environmental CaZ+= 1000 mg. The strontium is usually added to a sample as a carrier. The separations (one and two) were studied a t six nitric acid concentrations. (1) G. K. Murthy, L. P. Jarnagin, and A. S. Goldin, J. Duiry Sci., 42, 1276-1287 (1959). Data and results using one separation for the six normalities (2) G. K. Murthy, J. E. Gaetjin, J . L. Kulp, and W. R. Eckelman, are shown on Table I. The results employing two separaibid., 43, 151-154 (1960). tions are listed on Table 11. In order to make comparisons (3) C. R. Porter and B. Kahn, ANAL.CHEM., 36, 676--678 (1964). on a percentage basis, this is also listed. The samples were (4) C. R. Porter, R . J. Augustine, J. M. Matusek, Jr., and M. W. Carter, Public Health Service Pub. No 999-RH-10. Environcounted on a shielded 4-in. X 4-311. NaI(T1) crystal coupled mental Health Series (1965). to a multichannel analyzer for a sufficient period of time ( 5 ) A. S. Goldin, R . J. Velton, and G. W. Frishkorn. ANAL.CHEM.. to lower the error due to counting to less than 2 %. 31, 1490-1492 (1959). Figure 1 which shows a visual representation, indicates (6) H. H. Willard and E. W. Goodspeed, l i i d Eirg. Chew!.,8, 414that approximately 15N (67 %) is the best nitric acid concen418 (1936).
,
+
- -+-
Table I. Sr/Ca-One Separation (47Ca and *5Sr in dpm/sx)
Acid, 64 67 71 74.3 77 80
Acid, 64 67 71 74.3 77 80
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Z
Normality
85Sr
14.1 14.9 16.0 16.9 17.6 18.4
95 1 lo00 lo00 1000
1MX) 1000
Normality
85Sr
14.1 14.9 16.0 16.9 17.6 18.4
939 986 98 1 lo00 970 1000
47Ca 36.7 95 495 769 859 918
=Sr std 1000 lo00 lo00 lo00 lo00 lo00
“Ca std 1000 1000 lo00 lo00 lo00 lo00
Table 11. Sr/Ca-Two Separations %r std “Ca 4Ta std 0
7 406 686 819 912
1000 lo00 loo0
1000 1000 lo00
ANALYTICAL CHEMISTRY, VOL. 43, NO. 8, JULY 1971
lo00 lo00 loo0 lo00 lo00 lo00
Sr,
z
95.1 100 100 100 100 100
z
Sr, 93.9 98.6 98.1 100 97.0 100
Ca,
z
Ca, mg
3.7 9.5 49.5
37 95 495
77.0 85.9 91.8
770 859 918
Ca, Z
Ca, mg
0 0.7 40.6 68.6 81.9 91.2
0
7 406 686 819 912
tration to assure maximum removal of calcium without excessive loss of strontium when using 2 separations. Since fuming or regular concentrated nitric acid is not supplied with an accurate concentration value, i t is rccommended that the concentration be determined before separations ~f this type are made This concentration does not agree with that used by Willard and Goodsreed (6); however, Sunderman and rownley (71 found that in usinc: Willard’s coricentration the prxipitate was contaminated with calcium. They recommended using 60 IIN03. Hcwever this redvcrs the yield of the strontium recovery. “Radioassay for Era ironmental Sxnple:” (8) recommends 70 FINO3.
The latest proposal standard method for the “Determination of Strontium-89 and -90 in Milk by Ion Exchange” (9) recornmeiids the use of 115-16N (68-71 %) HNOa as optimum concentratim. T h e later works appear to be confirmed b> cur findings. EDMONDJ. EARATTA FORREST E. KNOWLES, JR. Northeastern R adjo1ogical Hmlth Laboratory Environmental Frotectron Agency Analytical Quality Control Service Winchester, Msss. 01899
RECFIVED for review March 19, 1971. Accepted April 30, (7) D. N Suiderman 8nd C . W . I‘ownley, N P . S - N S ? 0 ? 0 f p p 4 1 2 ) (1970). (8) “Radioassay for Frivironmentel Samples,” Enviro::meiital Ilealtl: Series, PHS Piiblicatioi, No. PFY-RH-27 (1357)
OBTAWINGA DIGITAL RECORD of the output of an infrared Spectrophotometer can be 21: expensive undertaking, depending upon the construction of the instrument. ‘The Hilger-Watts M-1200 is an inexpensive grating infrared spectrophotometer (marketed by Wilks Scientific Corp., Norwaik, Conn., for about $3500), and commercially available digital data reduction systems for such an instrument would requjre more capital investment than the spectrophotometer. The interface designed by Gulf General Atomic for this instrument can be built at a cost of about $450 in components and about 70 hours of labor for construction, installation, and checkout. We have employed the system to record digital spectra using a cassette magnetic tape recorder. Fhe interface can also he used to transmit data directly to the computer memory. Data are reco~dedand stored os &bit binary characters representing the ordinate every 2.5 cm-’ from 4000 to 2000 cm-I, and every 0.5 cm-1 from 2000 to 650 cm-l (because of scale change at 2000 cm-l). The precision of the recorded spectra is thus better than the manufactwer’s specifications for the instrument (10 cm-1 from QOOO to 2000 cm-I; 2 cm-’ from 2000 to 650 cml; 1 transmittance photometric precision). The interface can be modified to expand or compress the presentation to as many as 33,000 points per spectrum, or as few as desired. OUI spectra have 3300 points from 4000 to 650 cm-I. There are zero and gain controls for scale expansion of the ordinate up to IOX. An analog output is provided for a separatt: recorder, INTERF K E DESCRIPTION
The electronic circuitry for the interface between the HilgerWatts H-1?00 and a Mohaik 305 cassette tape recorder is Present address, Quar.iiita Indu:!ries, Monroe, La. 71201
Inc., P.O. Box 6010,
1.971. (’3) “APHA-Standard Methods for the Examination of Dairy
Products,” 12th ed., (in press),
shown in Figure 1. Th: value of the ordinate of the HilgerWatts H-1200 (the pen position on a transmittance scale) is determined from the eervopot which is already connected to the pen servomotor. 1Jsing this servopot, a 0 to -10 V analog signal is presented to an %bit analog-to-digital converter (Burr-Brown No. ADC30-08N-USB, no buffer a n plifier). The strobe pulse to the ADC is obtained in a unique but reliable fashion. There is a small D C motor on the Hilger-Watts H-1200 which rotates the grating and drives the chart recorder. This motor operates at a maximum of about 2000 rprn, and is geared down 488:l at the working end. The rear end of the motor shaft is flush with the rear bearing surfax, and this end of the shaft rotates at from 0 to 2001) rpin. One ha!f ofthe rear end of the motor shaft was painted black, and a small light is directed onto the end of the shaft, with the reflected light directed into a small PIN photodiode. The light bulb and photodiode are held in an aluminum block, which is machined to fit on the end of the motor casing. A sine wme output is obtained from the PIN photodiode as the shafi rotates, and the positive-going signal is used to obtain a 5-V pulse from a Schmidt trigger. In the present arrangement. a divide-by-ten digital logic circuit is used to present this 5-V strobe pulse to the ADC once every 10 revolutions of “re chart drive motor. The strobe signal is used to initiate the digitizing step of the ADC, and a dataready pulse from the ADC is used to strobe the tape recorder for data acquisition. The ADC has a maximum 20-psec conversion time, yet the interface/spectrophotometer arrangenient we employ has a maximum data rate of only 3 points per second. Of course:, by bypassing the divide-byten circuit, this rate can bc expanded to 30 points per second. The cassette tape recorder presently being uszd has a maximum incremental speed of 120 &bit characters per second. (The tape units are made 19) hlohark Instruments, Sunnyvale, A N A L Y L ? A L CHEMISTRY, VOL. 43, NO. 8 , JULY 1971
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