Retention of radioactive tracers in dry ashing of blood

307

Technzcal notes

Retention

of

Radioactive

Ashing (Recwed

0

1”

^^

Z”

30

I 10

Tracers

in

Dry

of Blood 24 A@1

1962)

A RECENT report m this Journal(l) presented data on the loss of trace quantities of radloactlve metals from blood durmg ashmg Techmques employing dry ashmg m a muffle furnace and wet ashmg usmg The wet ashmg oxldlzmg acids were considered procedure emplo\mg a reflux condenser was found to be superior Dry ashmg at elevated temperaturer was rejected as slgmficant loss of many elements occurred due to absorption mto the crucible and to volatlhzatlon An alternate method of decomposmg orgamc material, which has recelvrcl scant attention, utlllzcs a stream of oxygen cxclted by an electrical discharge

hr 1 La varlatlon de I’mdex de peroxyde et de I’mdex d’acldltk dans lep-xylkne lrradle en presence d’oxygene T = 13O”C, Jo = 760 torr, D = 6 lh-I, n = 1 ,25 1013 eV 9-l set-I, d, = lO$ crne2 set-l FIG

modlficatlon des condltlons de reactIon Le fait que le rendement radlochlmlque des products acldes est de l’ordre de cent et qu’ll est mdtpendant de la temperature (dam l’mtervalle 60-130°C) nous a permls de consldtrer que la rtactlon d’oxydatlon radlolytlque serait determmte par un mCchamsme en chaine et nous avons utlhst des actlvateurs En consequence, nous avons p&park une solution de j-xylene qul contenant 1 pour cent de naphtCnate de cobalt La r& action d’oxydatlon en absence des rayonnements n’a pas eu lieu, les autres condltlons de reaction restant ldentlques Sous l’actlon des rayonnements, 11 en rCsulte un rendement chlmlque pour l’acldep-tolulque de 13-15 pour cent aprPs 8 hr d’lrradlatlon (Le temp d’lrradlatlon n’a pas ttC augment6 A cause du blocage de l’mstallatlon, prodmt par le prCclplti: abondant d’aclde p-tolulque). I1 est mtCrcssant de remarquer qu’aprb avolr filtri. la solution n-radlke, 11se forme un dCpBt crystallm d’aclde p-tolulque (5-7 pour cent) dans le hqulde r&duel Amsl le rendement total en aclde p-tohque rapport6 g la quantltt nutlale du pxyltne est de 18-22 pour cent T COSTEA Laboratorje de Rndzochzrme C. MANTESCO Instntut de Pfgmqzce Atomque I NE00E~20 Bucarest, Roumanze Reference 1

I.UAMURA J

et OHTA N Tokyo KOPJO Shzkensho Hokoku 55, 346 (1960)) Nucl. Scz Abstr 15, 6031 (1961)

FIG

1

Apparatus

for electromc

dry

ashmg

Figure 1 lllustratcs schcmatlcally the apparatus employed m this techmque Oxygen 1s admitted through a needle valve (A) and passed mto a 3 m. diameter Vycor reaction chamber (B) which contams the material to be clccomposed Inside the chamber the molecularoxygen 1s converted bymeansofa radlofrequency discharge mto a highly reactive dlssoclated gas, which reacts rapldly with organic media The exhaust vapours, prmclpally CO,, H,O and O,, pass through a dry ice-acetone trap (Cj The CO, and 0, are removed by a mechamcal vacuum pump located at D. Power 1s supplied by a 15OW, 27 megacycle radlofrequcncy oscillator (E) coupled mductlvely to the reactlon vessel by means of a copper co11 1Y variable capacitor provides a convenient means of tunmg the plate tank-clrcult for optimum power transfer To compare the electrical discharge techmque with convcntlonal dry ashmg, the experlmental condltlons employed m the earher studle&?) were essentially duphcated. Human blood (-1 ml) contammg cltrlc acid as an anticoagulant was plpetted Into a Pyrex combustion boat, radloactlve tracer added, the sample dried m a drslccator contammg CaCl, at room temperature, and the combustion boat placed mslde the reactlon chamber Oxygen gas at a pressure of 400 /c of Hg was admitted to the reaction

308

Techma1

chamber at a rate of 4 cm”/mm Sample temperature remained below 90°C After 1 5 hr the ashmg process was termmated and the sample and combustlon boat counted m a Tracellab SC-57 NaI(T1) well-countci The sample was then weighed and dlssolvrd m a small amount of mmeral acid for additional counting The weight of the ash was that expected from complete mmerahzatlon, 6-8 per cent and the sample was cntlrely soluble m the acid, demonstratmg that decomposition was complete. TABLE 1 Retention (Percentage

Element Sb .\S Cr CO ,iu Fe cu Hz

Pb Mn MO As

Ztl

of radioactive traces m dry ashmg of blood letamed m original vessel)

r f discharge 1 5 hr at -: 9O’C 99 100 100 101 70 102 102 66 07 99 100 77 99

Muffle furnace(l) 24 hr 3 hr 400°C 900% 67 23 99 98 19 86 100 =: 1 103 99 100 65 100

9 0 56 30 0 27 58 0 13 79 83 21 30

Table 1 presents the results of these experiments As countmg statlstlcs allow a 3 per cent standard devlatlon, these experiments mdlcate that Sb, As, Cr, Co, Fe, Pb, Mn, MO and Zn are quantltatlvely retained m the combustion boat The elements 11~1, Kg and Ag were partially volatlhzed However, these species were redeposited wlthm the glass reactlon system and could be easily recovered by rmsmg the mslde of the glassware with mmeral acids For example, the gold tracer not retained m the combustion boat was quantitatively recovered by treating the reactlon chamber and cold trap with warm aqua regla for 15 mm Preliminary experiments mdlcate that this technique 1s apphcable to a wide variety of biological substances Exploratory experiments have shown that fat and muscle tissue and vegetable matter as well as whole small mammals can be quantltatlvely mmerallzed by this techmque wlthout loss of most trace metalhc constituents C E GLEIT Tracerlab Inc , a Dmszon of W D HOLLAND Laboratory for Electromcs Rzchmond, Calzforma

notes

References 1 2

PIJCK J , GILLIS J and H~STL J Int J qf@l Rtrd Irotofies 10, 149 (1961) PIJCK J , HOSTE J and GILLIS J P~oceedzrz~sof the Internakonal Sym$oslum 012l121xrochemzst~, Uzrrmnghnrn. 1958 p 48 Pergamon Press, London (1958 1.

External

Standard

mination

Method

for the Deter-

of the Efficiency

Scintillation

(Fzrst received 30 January 3 A&l

in Liquid

Counting 1962 and zn final &)~ll 1962)

ALTHOUCFI liquid scmtlllatlon counting 1s widely used for the assay of low energy /?-emitters, It has some disadvantages for practical measurement One of the most important 1s the quenching of the scmtdlatlon process resulting m a reduction of the counting tfliciency This 1s due to the presence of lmpulltles, mcludmg the sample Itself, m the scmtlllator The degrer of quenchmg becomes quite large for low-energy iiemitters and it 1s often necessary to dctermme the efficiency for each sample which IS counted To do this the internal standard method(l) 1s widely used Though it 1s the most rigorous m prmclple, it does have the followmg mam disadvantages (1) the time involved can be considerable, especlall\ if the counter operates at a reduced temperature (2) no knowledge of the efficiency IS avaIlable until after the sample has been counted, and (3) after the addition of the internal standard, the sample 1s no longer m its orlgmal form for any rccountmg that ma\ be necessary Recently BAILLIE published a new method(z) which uses the variation of pulse-height dlstributlon caused by quenching l’hla method overcomes the above-mentioned disadvantages of the internal standard method, but 1s not suitable for samples glvmg very low count rates To overcome these dlfficultles the use of an external y-source was investigated to see if the detectlon of the y-rays m the scmtlllatlon counter could be corrclattd usefully with the efficiency The hquld scmtlllatlon counter used by the authors 1s a low-level comcldence type employed for study mg the dlstrtbutlon of Cl4 m nature It 1s operated at a reduced temperature mslde an iron shield 10 cm thick and takes samples of 120 cm3 of scmtlllator made up from toluene contammg 4 g/l of PPO and 0 4 g/l of xNP0 The y-source 1s accurately located m a lead housing 25 cm above the iron shield It can be brought mto use by removing a shutter from Its housing and openmg up part of the non shield