Detection of Calcium-45 in Bone Solutions Donald E. Pickering, Helen L. Reed, and Robert L. Morris, Departments of Biochemistry and Pediatrics, University of Oregon Medical School, Portland, Ore.
A
SYSTEM for counting calcium-45 in inorganic solutions of bone is described. The critical element of the system is a spiral capillary phosphor into which solubilized bone samples are injected. The aliquots may be recovered from the capillary following the determination of Ca45 for analysis of chemical components. Contrasted with solid counting systems, this method of detection has increased efficiency, eliminated self-absorption phenomena, and reduced sample preparation time. Also, multiple chemical and radiochemical analyses can bc performed on tissue a1iqi;ots of limitcd sizc,.
phosphor as a new composition of scintillation chemicals in polyvinyltoluene. T h e plastic is soluble in aromatic solvent, but unaffected by water. I n this laboratory t h e plastic lVasfound to be unaffected by I'' nitric acid. Salts of and strontium are easily removed by Versene and water rinsing; however, compounds containing iodine-131 have been difficult to remove from the spiral. The wall of the capillary phosphor
provides the high voltage, discriminator, and scaler. A sample of approximately 0.5 ml. Of ashed bone (dissolved in 1N nitric acid) is adequate to fill the spiral capillary and connecting tubes. The sample activity is then calculated from the sample and standard count values. The detector is shown in Figure 1. DISCUSSION
Spiral Capillary Phosphor. T h e manufacturers describe t h e plastic 3000
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APPARATUS A N D PROCEDURE
The system includes a spiral capillary plastic phosphor assembly (Model NE 501, Kuclear Enterprises, Winnipeg, Canada) of approximately 1&mm. outside diameter, encased in plastic, and mounted n i t h silicone fluid to a multiplier phototube (DuMont Type 6292). The phosphor, multiplier phototube, and cathode follower (LIodel SC-2, National Radiac, Newark, K. J.) are housed in a stand utilizing 2-inch thick lead shielding (Model ShI-2, National Radiac) , A single-channel analvzer (Tracerlab, Waltham, Rlass.)
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ANALYTICAL CHEMISTRY
Figure 3. spectra
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Spiral flow counter Ca45 and background 1 -volt window width
System Efficiency. T h e efficiency of t h e over-all system (spiral and detection instruments) has been determined t o be 10.9%. I n actual operation, t h e windon n i d t h and gain settings were adjusted t o give an optimum sample count t o background count ratio. This v, orking efficiency m x s 7.15% u i t h a background count of 10 t o 12 counts per minute. T h e efficiency of this system exceeded that of our pievious method of Ca45detection (Comar, C. L., "Radioisotopes in Biology arid Agriculture," pp. 170-1, LlcGraw-Hill, S e n York, 1955) (with a n anthracene c r p t a l ) from a calcium oxalate platc by a factor of 1.51. The evcellrrit resolution of the system and the portion of the spectruni used in
Ca" det'ection are shown in Figurc. 3. This system would appear to be statistically similar to more expensive liquid scintillation counting methods; the efficiency is lovier, but the background is proportionately reduced [Lutwak, L.. AKAL. CHEM. 31, :340-3 (1959)]. From the aspects of ease of operatioii, elimination of self-absorption errors, antl recovery of sample, this system provides an excellent method for radioisotope assay in clear inorganic liquid samples.
Volumetric Technique Utilizing Molecular Sieves for Determination of n-Paraffin Content of Olefin-Free Petroleum Distillates
tative froin niisturcs in which the nparaffin content approached tht, capacity of the sieve.
Lewis P. Larson and Harry C. Becker, Texaco Research Center, Beacon, N. Y.
Volumetric Technique. A measured volume ( 5 t o 10 nil.) of t h e hydrocarbon sample, containing not, more than 1 .O nil. of n-parnffirI, is pipettctl into n 25-mI. volunietric flask containing 10.00 grams of 5 .i. sieve. l/,,-incli pellets. Because air is evolved from t h e sieve as the nparaffins arc adsorbed, the flask is stoppered n.ith a cork fitted n.ith a capillary (0.5 n m . , 6.0 mm. in outside diameter, 6.0 em. long). This permits escape of the air and minimizes evaporation of tmhesample. ilfter a given timc ( 15 to 24 hours), the volume required to fill the flask to t,he mark is measured b \ ~ adding cyclohexane from a 10-ml. h r e t . It may be necessary first to agitate the flask slightly t o remove'air t m t r a p p d by the 1;ellets. The volunie :idsorbed is determined by comparison \\it11 a blank on cyclohexane. The loliexane should be pretreated with e LA. adsorbent t o remove adsorbable impurities, particularly if the c,yclo1iex:ine is used in making sample dilutions. A satisfactory procedure is to allow the cyclohexane to stand over one third of its volume of the selective adsorbent! with occasional agitation, for several days.
is of adequate thickness to give good sensitivity for beta particles with a maximum energy from 0.01 to 0.3 m.e.v.; however. the ielatively low stopping power of the capillary makes i t insensitix to gamma radiation as well as to beta particles with an energy greater than 0.7 m.e.v. Increased ion concentration has been found to have no effect on the counting rate; selfabsorption is reduced to a minimum hecause of the provimity of the solution to the phosphoi. The volume of the spiral has been determined b y plotting activity us. the volume of Ca4s solutions injected. The effective volume thus determined 0.002 has been found to lie 0.234 ml. (Figure 2 ) .
rr
IIL syntlictic zeolitcl which has an effectirc . channel nidth of 5 A. i. highly sclective in the adsorption of .traight-chain hydrocarbons from mixtures i+ith branched-chain and cyclic cwmpounds. ;Lleasuremr,nts on known mixtures of liquids have shown that as this adsorption proceeds there is a caorrcsponding dccrcase in thf volume of the samplc,. This changt. in volume may 1)o used to deterinin(> thc amount of rt-paraffins in an olcfin-frw distillate. Preferential nourxchange adsorption or occlusion of n-paraffins by natural zcwlitcs was reported by Barrer and lklchetz [ J . SOC.Chem. Ind. 64, 131-3 (1945)l. I n more recent work a synthetic zeolite, or 1Iolccular Sieve, has beeii used for the sclective adsorption of ti-paraffins. Schwartz antl Ih-asseaus [ANAL. Cmar. 29, 1022-6 (1957)] reported a method for thc tlctermination of n-paraffins in olefinfree petroleum distillates, in \\ hich the -ample is first distilled t o yield fractions containing only one n-paraffin, and the distillates are fractionated on a Molecular Siew column. The nparaffin content is determined by comparison of the refractive indices of thc original sample and the. pure n-paraffin assumed present. I n a considerably different method Nelson, Grimes, and Heinrich [ANAL. CHEW 29, 1026-9 [ 1957)] brought a weighed quantity of .ample in contact with the tared Molecular Sieve, and removed the unadsorbed material by vacuum evaporation a t 100' C. The neight of n-hytlrocarbon was then determined b y re\\ eighing the sieve. In thi. work, a liquid volumetric
tecliiiique ha5 l ~ c c ~used i with a 5 A. Molecular Sicvc.. /16-inch pellets, to determine the volume per cent of n-paraffins. The technique possesscs several inherent advantages: simpk apparatus, applicability to a uiclt, hoiiing range sainplc, and no intrrfuence due to surface adsorption. A study was niadc of the rate of adsorption for n-paraffins in the Ci t o CISrange at room teniperaturc (25' C.). Searly 15 hours n c w required for coniplete adsorption as mcasurcd by thc decrease in liquid volume. The shorter chain n-paraffins cwter the s i w e mor? rapidly than the longer chain n-paraffins-for cxample. ?i-hcptanr n as conipletcly adiorbcd in less than 2 hours, compared with nearly 15 hours for n-tetradecanc. Capacitj nicasureiiients undw the same conditions havt. shonn that thc sieve is capablc of holding approximately 1.5 nil. of n-paraffin per I O grams of sieve. However, the adsorption of n-paraffinq v ab not quanti-
T\'ORK supported by grants from the Collins 3Iedical Trust Fund, Medical Research Foundation of Oregon, Inc., and t,he United States Public Hcdth Swvice, Grant .1-2597.
Table I.
Volume Decrease as Known n-Paraffins Are Adsorbed from Cyclohexane Solutions x-l'arafin Added, ('YClO1)ecrcase i l l ml. Cornpourid hexane, 311. voi., m. 1 .OO u-Decane 9 . 00 1 . 0 2 , 1.00 1 .OO n-Dodecane 9.00 1.01, 0 . 9 9 , L O 2 0.10 n-Dodecane 9 . 00 0.11, 0.13 0.50 n-Dodecane 9.50 0.49, 0.50 0.50 n-Dodecane .I. 50 0.50 1 .OO Ti-Tetradecane 9 , 00 0.97, 0 99, 1 . 0 0 1.00 1/3 ml. each of n-decane, n-dodecane, and ntrtraderane 9.00 1 00
VOL. 32, NO. 9, AUGUST 1960
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