Reparoducibilityof Mounting of Solid Samples of Chlorine-36 Compounds for Radioactivity Measurements POUL SORENSEN Central Laboratory, Sadolin
& Holmblad, Ltd., Copenhagen, Denmark counts and the whole counting procedure was performed twiceLe., a relative activity was determined with a statistical counting error of 0.617,.
A series of measurements with four different organic chlorine-36 compounds is described. Three different persons have prepared samples.
CALCULATION
S
ET'ERAL years' experience has shown that radioactivity of solid samples of chlorine-36 compounds can be determined
The relative activity of a sample is calculated from:
accurately.
counts per minute of sample
a, = counts per minute of standard
EXPERIMENTAL
Equipment. Geiger-Muller counter. An ordinary end-window counter was used [Madsen-tube ( I ) ] ; window thickness, 3 mg. per sq. cm.,; window diameter, 30 mm.; background, about 12 counts per minute. Scaler. Bliiel and Kjer electronic counter 6501. Aluminum dishes. The samples were mounted in aluminum dishes, 14 mm. in diameter, 2 mm. high. A dish was used for only one determination. Mounting of Samples. An amount of 50 f 5 mg. of the crystalline compound is placed in an aluminum dish, a few drops of methanol or acetone are added, and the slurry is smoothed with a nickel spatula during evaporation of the suspending agent. Finally the sample is dried under an infrared lamp.
Corrected activity is calculated from: ajo =
50 a,
+ ( 5 - 50) X 0.0060
where a, = relative activity of s-dl mg. sample aaa = relative activity of the sample corrected to correspond
to a weight of 50 mg.
The last term in the expression is the self-absorption correction and has been determined from the measurements here described.
Table I. Activity Measurements of Different Compounds Operator
Weight, mg.
Compound I Relative Activity hleasured Corrected
Very skilled
45.78 50.16 51.10 53.87 57.55
0,942 1.001 1.001 1.044 1.108
hledium skilled
44,62 47,25 50.15 51.14 54.25
0.922 0.965 1.002 1.020 1.059
Unskilled
46.44 49.25 52.75 54.50 55.80
1.001 0.999 0.986 0.992 1.008 A r . 0 . 997 S 0.008 1.000
1.004 1.000 1.005 1.000 Av. 1.002 s 0.002 0,920 0.970 0.993 1.003 1 ,040 1.002 1.057 0.997 1.076 1.000 .4v. 0.994 9 0,014
Weight, mg.
Compound I1 Relative Activity Measured Corrected
46.70 48.15 49.25 53.26 54.65
0,957 0,975 0.997 1.054 1.048
45.69 47.78 50.84 53.33 55.93
0.958 0.989 1.010 1.051
47.32 49.01 50.82 51.90 54.49
1.060
0.980 0.972 1.018 1.032 1,042
1.004 1.001 1.007 1.009 0.987 1.001 0.009 1.021 1.022 0.999 1.005 0.983 1.006 0.016 1.018 0.985 1.006 1.006 0.984 1,000 0.015
Materials. The compounds were pre ared for other purposes (2, 3), and were chosen because t f e y differ appreciably in solubility and crystal structure. melting Compound I. 4-Chloro-2-methvl~henoxyacetanilide, point 130' C. Compound 11. 2,4-Dichlorophenoxyacetanilide, melting point 111' c. Compound 111. Methyl-3-chloroanisate, melting point 94' C. Compound IV. Pyrocatechol-di-(3-chloroanisate), melting point 175'C. Compound I1 has a cottonlike structure and had to be mounted in the dish with acetone. Methanol was used for the other cornpounds. The activity of the compounds m-as 1000 to 2000 counts per minute per 50 mg.
Weight, mg.
Compound I11 Relative Activity Measured Corrected
47.95 50.20 51.00 53.32 57.22
0.972 1.006 1.014 1.046 1.087
46.35 48.62 49.86 51.60 53.80
0.941 0.971 0.990 0.997 1.038
45.40 48.90 51.86 53.27 54 90
0.929 0.972 1.017 1.035 1.043
1.001 1 002 1.000 1.000 0.992 0.999 0,004 0.993 0.990 0.992
0.976 0.987 0.988 0.007 0.994 0.987 0.991
0.992 0.979 0.989
Weight, mg.
Compound IF' Relative Activity Measured Corrected
48.00 50.15 51.00 52.95 56.70
0.976 1.008 1.016 1.036 1.091
47.75 49.10 50.17 51.05 55.64
0.991 0.983 1.000 1.014 1.082
47.00 48.40 48.84 53.90 56.32
1,022 0.986 0.971 1.050 1.084
0.006
1.003 1.005 1.002 0.99fi 1.002 1.002 0.003 1.023 0.995 0.997 0,999 1.006
1.004 0.011 1.069 1,008 0.987 0.997 1.000 1.012 0.033
DISCUS SIOK
The results' (given in Table I ) show that errors introduced by preparing the samples usually are small in comparison with the
counting error* In the author's laboratory a chlorine-36 dilution analysis is
Table 11. Duplicate Determinations in Routine Analyses KO,of Duplicate Deviation between Detns. 24 14
11
Counting. The samples from one compound were all counted against a standard sample of the same compound having a weight of 50.0 mg. Each sample was counted-to about 20,000
a 6
391
Duplicate Detns., % 0 -0.5 0.5-1.0 1 .O-1.5 1.5-2.0 2.0-2.5
ANALYTICAL CHEMISTRY
392 used as routine analysis ( 2 ) . Counting is carried out with 4chloro-2-methylphenoxyacetanilide as described in this note. ..I series of duplicate determinations has been performed, and Table I1 gives the deviations between these. Calculation of these results shows that a single determination is performed nith a standard deviation of 0.79%. The small difference from the statistical counting error (0.61%) shows that no other factors have a serious influence.
ACKNOWLEDGhIEYT
The assistance of Jytle J@rn-Jensenand Yi.vian Larsson is gmtefully acknowledged. LITER4TURE CITED ( 1 ) dmbrosen, J., Madsen. B., Ottesen, J.,
and Zerahn, Ii.,Acta
Physiol. Scand., 10, 195 (1945). (2) Sorensen, Poul, -4b.i~. CHEY.,26, 1581 (1954). (3) Ib& 27, 388 (1955). .
R E C E I V EforD r e v i e r July 19, 1954. Accepted S o v e m b e r 23, 1954
Reduction of Nitroguanidine by Titanium(ll1) Chloride WARREN W. BRANDT’, JOHN E. DEVRIES, and E. ST. CLAIR GANTZ Analytical Chemistry Branch,
U. S. N a v a l
Ordnance Test Station, Inyokern, China Lake, Calif.
The reduction of nitroguanidine by titanium(II1) chloride in 1 to 1 hydrochloric acid w-as studied with the addition of iron(II), in a 20 to 1 ratio to nitroguanidine. The redox reaction is 98% complete for consumption of 8 equivalents of titanium(II1). The route and mechanism of the iron “catalyzed” reaction was also studied. The end products of the reaction are guanidine and ammonia. It is proposed that the function of the iron(I1) is to stabilize, by complexation, hydroxylaminoguanidine and to make this intermediate susceptible to further reaction with titanium(II1). The reduction of nitroguanidine using a 20 to 20 to 1 ratio of titanium(III), iron(II), and nitroguanidine is quantitative and could be used for assay of nitroguanidine.
T
HE reduction of nitro groups with titanium( 111) has be-
come a standard analytical method for their quantitative determination. The usual procedure involves adding an excess of titaniuni(III), boiling for a short period, and back-titrating with iron(II1) ( 3 ) . Nitro groups in compounds such as nitrobenzene require 6 equivalents of titanium per mole. I n general, the reduction is carried out in strongly acidic solution. The extension of this method to the nitramine group revealed that in these cases the nitro group required only 4 equivalents of titanium(II1). Kouba and coworkers ( 2 ) determined nitroguanidine quantitatively by this method. However, when they attempted to determine RDX (hexahydro-1,3,5-trinitro-s-triazine) by the same procedure the 4-equivalent reduction per nitro group was only 60% complete. They found that by introducing iron(I1) to the reaction mixture the reduction was within lyOof theory for 4 equivalents. Zimmerman and Lieber ( 7 ) extended the investigation of titanium( 111) reductions to include several nitroammonocarbonic acids. When iron(I1) was introduced into thi! reduction of nitroguanidine and nitroaminoguanidine, they found that the reaction then approached a total of 8 equivalents per mole instead of the usual 4. A new path of reduction was proposed to ekplain this phenomenon. Their proposal involved reductive cleavage of the nitroguanidine as the first step, and subsequent reduction of the nitramino group to a hydrazine. NHSO?
/
PiHN02
/
1 Present address, Chemistry Department, Purdue University, Lafayette. Ind.
iVHNO* +
C=SH H‘
6(H) -+ C=SH
+ 2H2O
(2)
H‘
Recently, Sternglantz ( 5 ) has ahon-n that under weakly acidic conditions, using citrate buffer, nitroguanidine consumes 6 equivalents of titanium(II1) per mole. The current investigation was undertaken in order to study in more detail the iron(I1)-catalyzed reduction of nitroguanidine by titanium(II1) and to attempt to demonstrate the mechanism of the function of the iron(I1). APPARA‘TU S
Because of the instability of titanium(II1) in air, all reagent, solutions were kept under an atmosphere of carbon dioxide both in storage and in the burets. The reaction flasks were all connected to reflux condensers by ground-glass joints. The former were also equipped with a small inlet side arm for introducing a stream of carbon dioxide over the surface of the solution. This flow of carbon dioxide over t,he surface was started following the initial degassing of the acid to be used and continued through the final t,itration with iron( 111) without interruption. All carbon dioxide passing into the react,ion flasks was passed through bubblers, so that the rate of flow was readily visible at all times. RE4GE\TS
; i0 . 4 s titanium(II1) solution n a s prepared in 1 to 1 hvdrochloric acid. It is convenient to use titanium hydride (SIetal Hydrides, Inc., Beverly, Mass.) as recommended by Wagner et al. ( 6 ) . A 1 . O N iron(I1) solution was prepared in 1 to 1 hydrochloric acid from reagent grade iron(I1) sulfate. Reagent grade iron(II1) alum [Fe(XH4)(S04):.12H*0]x a s used to prepare a 0.3A\r iron(II1) solution in 1 t o 1 hydrochloric acid. All hydrochloric acid was Baker and idamson C.P. reagent, 3T to 38%. Nitroguanidine was prepared by recrystallization of a commercial sample from water. Potassium nitrate was Baker and .idamson reagent grade. Sitrosoguanidine (melting point 165’ C.) was prepared by the procedure described by Davis ( 1). Aminoguanidine hydrochloride was prepared from Eastman’s white label aminoguanidine bicarbonate. The titanium( 111) and iron( 11) solutions were standardized against rational Bureau of Standards potassium dichromate using sodium diphenylbenzidine sulfonate indicator. The iron(111)was standardized against the titanium( 111). REDUCTIO? PROCEDURE
The weighed sample u a s dissolved in 50 ml. of 1 to 1 hydrochloric acid and the solution degassed with carbon dioxide for 5 to T minutes. The titanium(II1) and iron(I1) were then added and the solution was refluxed. The mixture was then cooled in a water bath and titrated with iron(II1) to a thiocyanate end point. The time of reflux !vas measured from the start of vigorous bubbling. In the reactions of potassium nitrate and nitrosoguanidine the
