zirconium K series lines from the hafnium LQ and Lg lines. Unfortunately, this also proved to be impractical for the low concentration levels of interest. Discrimination between two energies, one of which waa of much greater intensity than the other, was required. Because the pulse height distribution curve of the higher intensity has some pulses at all amplitudes, there are more counts due to zirconium at the hafnium energy peak than to hafnium itself. This problem of separating pulses of M e r e n t energies having greatly different intensities is discussed more fully by Miller (3.
Table V. Accuracy of Chemical and X-Ray Fluorescence Results“
yoSn yo Fe
Two relatively rapid and simple methods for determining tin, iron, chromium, and nickel, in Zircaloy-2 have been developed using fluorescent x-ray spectrometry. Method 1, the “oxide” method, requires the least amount of sample preparation but has a lower sensitivity. Method 2, the “extraction” method, while necessitating somewhat more sample preparation results in at least a twofold increase in sensitivity over Method 1 and could be of possible value in the analysis of other zirconium alloys. Both methods are advantageous, in
70Xi
1 . 4 4 0 138 0 102 0 054 u 0 03 0 002 0 0 0 2 0 0 0 1 Chemical 1.422 0 13‘: 0 102 0 019 u 0.002 0.OOi 00004 OOOO3 a Averages of six individual determina-
tions for each element made on aliquots from,the =me solution of sample 517’422.
Table VI. Hf LyI Intensity Measurements on Standard Samples
HI (Lyl),
Hafnium, CONCLUSION
yo Cr
X-ray
P.P.31. 50 __
250 415 885
1620
.4v.
CIS i58 .. 797 807 865 877
Background, AV.
.4v. Set
c/s
CIS
716 725 726 748 737
42 ~~
72 81 117 140
that the four individual element dekrminations can be carried out in rapid succession on a single sample. The four elements can be determined by Method 1 in about one quarter of the time required by webchemical methods, and by Method 2 in about one half the time. The precision and accuracy of the
results of both methods are comparable nith those of existing chemical methods and satisfactory fGr routine specificntion cheeks. The determination of hafnium does not appear to be feasible a t the low-level in which it occurs in reactor grade Zircaloy-2, at least Kith ellsting equipment. Because a rapid analysis by neutroi? activation i n s been developed at tliis project for hafnium analysis (e),ic \ w s not considered worthwhile to investignti. this determination b?. x-my nicthods exhaustively. LITERATURE CITED
( 1 ) Birks, L. S., Brooks, E. J., ASAL. CHEU.22, 1017 (1950). ( 2 ) Mackintosh. W. D.. Jervis. R. E.. Zbid.. 30, llsd (1958). ’ (3j-11iiier, D. C., Sorelco Reptr. 4, 37 (1957). (4) Iloak, W. D., “Determination of Hafnium in Zirconium by X-Rav Fluorescence S ctrometrv,”-S3mposiiim on ~
X-Ray DiKaction and S-Ray Emission Spectrometry Techniques, General Electric Co., Schenectady, N. T.,1957. ( 5 ) hloore, F. L., A N A L . CHE\I. 28,
997 (1956). (6) >fortimer, D. If.,Romans, D. -4.) J. O p t . SOC.Am. 42,673 (1952).
RECEIVED for review December 15, 195s. Accepted June 26, 1959. Second Conference on Analytical Chemistry in Kuclear Reactor Technology, Gatlinburg, Tenn., September 29 to October 1, 1958.
Sealed Tube Combustions for the Determination of Carbon-14 and Total Carbon DONALD
L
BUCHANAN and BHTY J. CORCORAN
Radioisotope Service, Veterans Administration Hospital, Wed Haven, Conn., and Department
of Biochemistry, Yale University, New Haven, Conn. ,Conventional wet or dry combustions are associated with the formation of nitrogen oxides which even in minute amounts cause undesirable effects in proportional counters. Simultaneous microdeterminations of total carbon and carbon-14 may be performed by oxidation with cupric oxide in sealed Vycor tubes at 850’ C. Manganese dioxide is added to provide free oxygen and cupric chloride displaces carbonate whenever basic metols are present. The carbon determination is as precise as it is in other types of oxidation used for carbon radioassay and the carbon dioxide is very pure as judged by its counting characteristics.
vfT
organiL compounds that c:mtam nitrogen are ozidized for counting by n e t (14) or ‘ c.;idstion. o d e ? of nitrogen ~ ~ and r n some wili co-con- adding n minganese tlioside trnp ( 7 ) or by filling t h e heated quartz tube \rit h en!cium ozidt’, but both procedures gave sniall nirrnory effects. Sealed static oxidations of organic compounds n-ere reported early (9) irith modifications later ( 2 ) . Grosac,
Hindin, and Krshenbaum (S) tniployed isotope dilution in conjunction with static Oxidation on a semimicro scale. Sealed tube oxidations h : i ~ e recently been used for the riltranlicrodetermination of curbon hy isotope dilution (S), and a dircct ninnoinc~tric ultramicroanalysis has been dcscriid (10).
IVilzbach and his coll(~ng1c.s have used scalctl tube combustions for r:itiioassay of carbon-14 (f5). They intlicati. that, t.his t:pc of Oxidation might be usoiiii ior the combined dctcrniinntioxi of carbon-14 :ind total cnr!mn. The prcwnt report givrs the tlrtnils oi i: mcthotl tle\.clopcd with thn: cznc! in vien-. EXPERIMENTA:
Vacuum Apparatus. The -,xcuuxi: system (Figure 1) is a simplification oi tiini previously described iar collectYOL. 31, NO. 10, OCTOBER 1959
@
1635
Figure 1. Apparatus for collection, measurement, and caunting of C 1 4 0 2 A.
Capsule breaker Water trap [dry iceCellosolve) COStrap (liquid nitrogen) D. Manometric system E. Counter filling system F. Combustion tube evacuation G. Mercury reservoir far manometer H. Inconel clamp for drawing out combustion tubes. A small piece of asbestos sepwater each half of the split tube from the end of the Vycor combustion tube 1. lnconel shield for heating combustion tubes in muffle furnace 6. C.
w
COUNTER
A
ing, measuring, and counting the carbon dioxide from wet oxidations (6). I t consists of a manifold used to evacuate the combustion tubes before they are sealed, F , and, after the samples have been oxidized, to break the capsules, A , purify and collect the carbon dioxide, B and C. measure it manometrically, D, and then to transfer it to a propcrtional gas counter via E. Tube A is of he3vy-;valled tubing, 24 mm. in outside diameter and about 50 cm. long n-ith a 24/40 T inner joint and outer cap a t one end. The glass a t the closed end of A is thickened to prevent breakage when sample tubes strike there. A short T-joint a t the balance point with a 14/30 T joint allo\vs the tube to pii.ot freely. A wad of aluminum foil protects the cap from breakage by the butt end of the combustion tube and a glass ~voolplug beyond the pivot joint filtcrs solid particles carried along when tlie capsule is broken. The connecting tubing and traps B and C are tubing of 12 mm. in outside diameter. Trap B is immersed in dry ice-Cellosolve. The small amount of water that collects is pumped off daily after rcniovul of the cooling mixture. The right limb of the manometer is of 8rani. outside diameter tubing, while the I: portion and the tubing extending up to the bulb are of 3-mm. inside diameter eapillar!~ tubing. Ball joints (12-mm.) allow this section of the manometer and the h u h to be removed for cleaning and for I diimetric calibration with mercury. Three bulbs in the U-section of the manoinetPr, each about 2 cm. in inside diameter, expedite the release of trapped air. The calibrated capacity of the manometer and the bulb is about 14 ml. The (winter is of metal and has the design described (6),but is smaller. The sensitive volume, 480 ml., is a cylinder 4 cm. in diameter and 48 cm. 1636
ANALYTICAL CHEMISTRY
lj
long. Glass tubes ( I ) have also been used with the apparatus. The electronic circuitry is essentially that previously used ( I , 6). The pumping system consists of a mechanical forepump and a two-stage oil diffusion pump so connected that the latter can be shunted out when air is present in the manifold. Combustion Apparatus. The combustion tubes are of Vycor (KO. 7900), 9 mm. in outside diameter and from 3 t o 9 ifiches long. Two new tubes are drawn from a n 18-inch length by sealing a t the constriction. After each use, the jagged open end of the tube is cut off with a glass cutting wheel and the tubes are emptied, rinsed n i t h water, and cleaned by immersing for about an hour in 1% hydrofluoric acid in a polyethylene beaker. Leakage of gas from the capsules a t the sealed tip will occur if the cleaning procedure is omitted. The clean tubes are heated to 850" C. in the furnace before use. A single tube may be re-used a dozen times if it is drawn out close t o the end each time. A clamp made by slitting an Inconel pipe longitudinally makes this easier (Figure 1, H). A shield of seven 9-inch lengths of Inconel tubing (14 mm. in outside diameter, 10 rim. in inside diameter) u ith an Inconri cnd plate held together with Niehrume \\ire (Figure 1. J ) holds the combustion tubes while they are in the muffle furnace. Weighings are carried out in smaller Vycor tubes (4 X 15 mm.) seaIed a t one end. Combustion Reagent. Cupric oxide powder is heated to 850" C., cooled, and mixed 5 : 1 : 1 Kith manganese dioxide and anhydrous cupric chloride, all reagent grade. The latter is prepared bj- drying CuCI2.2H20 a t 150" C. to constant weight and then pulverizing in a mortar. The mixture is kept in a screw cap bottle and measured
out with a scoop machined t o hold 1 gram. Procedure. T h e material t o be analyzed (5 t o 10 mg.) is weighed on a microbalance into a Vycor weighing tube, which is then gently pushed t o the bottom of t h e combustion tube with a glass rod. One gram of combustion reagent is added through a funnel to keep the powder from the wall of the tube in the region to be sealed. The combustion tube is then constricted at the end to about 1 mm., connected horizontally t o the manifold by rubber tubing (Figure 1, F), and evacuated by slowly opening the stopcock. I t is sealed and after it has cooled the contents are mixed, care being taken not to a l l o ~material to reach the d r a m - o u t tip. If this precaution is not taken, the tube is likely to explode when heated. Several tubes may be so prepared, placed in the shield, and then in a muffle furnace a t 850" C. for 30 minutes. Samples are individually analyzed by first placing in A and then evacuating the apparatus. A Dewar flmk with liquid nitrogen is placed around C, A is then gently tipped to allow the combustion tube to slide. If the impact is too hard, the combustion tube may shatter completely, but the sample is not lost. After thP collection of carbon dioxide in C (2 minutes) the C-D volume of the sJ-stem is isolated, the zero of the manometer is checked, and the carbon dioxide is transferred to D (3 minutes). The pressure is measured after bringing the temperature of the bulb t o that of the room with a water bath. The carbon dioxide is now transferred to E (3 minutes), allowed to expand into the counter, and flushed in with tank methane, the regulator being set t o deliver a t atmosphere pressure. A second sample can be hberated and measured while the first is counting. RESULTS AND DISCUSSION
A series of 12 determinations on recrystallized, uniformly labeled sucrose-C1d gave an average recovery of 100.0+0.3%. The weight of individual samples varied between 8.3 and 11.5 mg. The mean specific radioactivity was 109, 250 =k 700 counts per minute per millimole carbon. Thus the standard deviation of the specific radioactivity measurement is approximately double that of the carbon determination. When the sample weight rather than
the measured carbon dioxide was used
to calculate the specific radioactivity, the standard deviation was slightly less (650 counts per minute per millimole). This indicates that failure t o recover carbon from the sample is not a n important source of variation. Occasional aberrant values in specific radioactivity are usually brought into agreement with the results of duplicates when the computations are based on sample weight. I n Table I are given the results of analyses of a number of unlabeled compounds and Table I1 gives the results obtained with several substances isolated from a batch of yeast that had been grov-n on a medium with uniformly labeled sucrose-C14 as the sole carbon source. The difference in specific radioactivity between compounds does not necessarily indicate the variability of the method because differences of this degree could be the result of isotope effects or due to incomplete randomization of t,heisotope in the sucrose. The carbon dioxide obtained by this method of oxidation is always free of color, never corrodes the mercury, and when placed in a counter gives plateaus (counts us. voltage) of 600 to 800 volts, with slopes of less than 1% per hundred volts. In the authors' past experience and in the observations of others (4), these characteristics demonstrate virtual freedom from nitrogen oxides. The loss of counts due to resolving time is negligible below lo6 counts per minute and only 3 to 4y0 a t 4 X lo5counts per minute. Of the carbon methods that use sealed tube combustions, only two (10, 15) are direct; the third uses the isotope dilution principle (3). Kirsten (10) oxidized 0.1- to 0.3-mg. samples with oxygen and copper in a quartz tube (temperature not specified and no data given). The accuracy was "somewhat less good than that of the Pregl methods on a 5-mg. scale." Wilzbach and Sykes (15) cprried out combustions in tubes of Pyrex 1720 at 640" f 10' C. with a mixture of copper oxide and reduced copper. They do not claim that these conditions are useful for the analysis of carbon in all organic compounds. The authors' preliminary tests were not extensive but a i t h copper oxide alone or with combustion a t l o w r temperatures, recoveries were low and inconsistent with some compounds. Sucrose and the amino acids are incompletely oxidized at 700" C. Benzoic acid, on the other hand, gave good recovery at 600" C. but low and inconsistent yields at 700" t o 900" C. The values improved at 900" C. and when longer times were allowed. The explanation of this paradox now seems clear. Compounds such as sucrose which, on heating, decompose and form black carbon in
Table 1.
Carbon Analysis by Sealed Tube Combustion
Sample Compound Analyzed Potassium acid . phthalate 9 Adenylic acid 5 Betaine. HC1 5 Glutamic acid 5 Hi puric acid 4 2-&nino-5-chlorobenzoxazole 2 Cystine I Succinic acid 5 Taurine 5 Benzoic acid 5 0 With standard deviation.
Table II.
Yield. 100.3 & 0 . 4 100.0zk0.7 100.0f0.8 100.0=k0.3 9 9 . 2 f0 . 3 100.1 f O . 5 99.9 f 0 . 5 100 0 1 0 . 3 100OfO5 99.4 f 0 . 2
lent amount of oxFgen \rere added to the capsules before they w r c sealed, the results might be as gooti. If, in the case of compounds that coritain an alkali metal, such as potassiriin acid phthalate, a quantity of solid carbonate equivalent to the alkalai remained behind, the \kid of carbon dioxide would be niorc than 6% low. Actually, the recovery \vas less than I below the theoretical when onl!. cupric oxide and manganese diosidc were used. Cupric chloride \\-as added to prrvent any formation of carbonate and the recovery improved satisf:ictorily. For reasons not at all clear, the presence of cupric chloride also improved the re-
Analyses of Compounds" Isolated from Yeast Grown on SucroseCarbon- 1 4
Compound Sucrose*
Carbon Content, Mmole Calcd. Found 0.3235 0.3434 0.3128 0.3370 0.2575 0.3095 0.2621 0.2972 0.2763
Yield, ye
0.3257 0.3450 Lysine.HC1 0.3119 0.3362 Histidine.HC1.H20 0.2574 0.3091 Arginine.HC1 0.2634 Glutamic acid 0.29% Aspartic acid 0.2770 Glycogen' ... 0.2824 Glucanc ... 0.1322 a Amino acids are from an acid hydrolyzate of whole displacement chromatography ( 5 ) .
Specific Radioactivity. C ts lhIin./Mrnnle
100.7 100.5 99 7 99 8 100.0 99.9 100.5 100 4 loo 3 ... ...
26,750 26,946 2 5 , 9
