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Comparative measurements of standards for carbon isotopes
Geochimica et Cosmochimica Acta, 1953, Vol. 3, pp. 253 to 256.
Pergamon Press Ltd., London
Comparativemeasurements of standardsfor carbon isotopes WILLI Universitetets
DANSGAARD
biofysiske laboratorium,
Copenhagen
{Received 8 November, 1952) ABSTRACT ~~e~u~ments on two American, one Swedish and one Danish standard for carbon isotopes are reported. These measurements are intended to provide 8, direct comparison between American and Scandinavian measurements on oarbon isotopes. CO, samples are used in the mess-spectrometry and it is shown that differences in 0”-abundance may cause measurable errors.
Lately much work has been done in determining the abundance of the heavy carbon isotope Cl3 in nature. The great accuracy with which such measurements can be made has made it desirable to consider carefully the basis on which they depend. The abundance of carbon isotopes in a given sample is often stated by the numerical ratio of Cl2 to C13-atoms, characterized in this paper by 02/CY3. Massspectrographic determination of this ratio is very difficult, but differences in Ci2/U3 can be found with great accuracy. A standard is chosen, and results are normally reported either simply as the difference from the standard or as the C12/C13-value obtained from attaching some value to the standar*d and adding the difference measured. Neither of these procedures, however, permits of comparison with other results, unless the differences are known between the particular standards that were used. Professors A. 0. NIER and H. C. UREP have each kindly suppiied samples of their standards (CaCO,; in this paper called N and U respectively). A comparison has t’herefore been made of each of these with a Swedish standard (BaCO,; called X) from Naturhistoriska Riksmuseum in Stockholm and a Danish one (bomb-CO,; called D). The measurements were made with a Consolidated-Nier Isotope-Ratio Mass Spectrometer, model 21-201. In this instrument it is necessary to admit each sample of carbon in t’he form of CO,. The combustion of the solid standards can be achieved in different ways. Some investigators use H,PO,, others HCl and, in Sweden BaCO, is heated together with NaH,PO,. These procedures are indicated in t,his paper by H3P0,, HCl and NaH,PO, respectively. After ionization of the CO,-molecules in the mass spectrometer an electromagnetic deflection of their paths takes place, so that all singly charged ions with the same mass are focused and measured together. The instrument primarily gives a value for 46144, i.e. the ratio of quantities between ions with mass 45 (C130~16and C1zOl~017) and ions with mass 44 {C1zO~16). The values of 45144 for the Swedish and the American standards were found to be higher than the Danish, and the differences from the Danish 45144, have been recorded in Table 1. In the main part of this table the figure after “&” indicates the reproducibility of the last figure on the particulir day. In the last line, however, it means the standard deviation of the mean. 253
WILLI DANSGAARD
Table 1. Differences above the Danish value Preparation
1951, Aug. Dec. ,, ,, 9, it ,, 1952, lkr. Jun. Aug. >, Moan
21 10 11 12 13 14 15 15 9 16 10 11
100) of 45144
u
N
W’O,
0.0262, 0.0261, 0.0262
(x
HP& 5 (NaH&‘O,) 2 (NaH,PO,) 3 (NaH2P0,) 3 (NaH,PO,) 3 (H3P0,) 3 (~~H~PO*)
0.0144 0.0142 0.0132 0.0133 0.0138 0.0141
& + + f & i
0.0136
ri: Z(HC1)
0.0138
_i 2
rtr.2 & 2 & 2
0.0264h -.&2
0.0281 0.0289
f t
0.02625
0.0285
jz 4
i. 7
6 4
It is seen that the combustion method does not affect the result. If NIER’S measurement of the standard “Jurassic Limestone, Solenhofen, Bavaria” (NIER, 1950) is used as basis with the C13~C1z-~~lueof 1.124% jO-003 (here -&O-O03 refers to 1.124 as an absolute value), and if it is presupposed that the 017-abundance is the same in all the standards (so that no corrections for W016017 are necessary, since they disappear in forming the differences) the values given in Table 2 are now found.
However, the presupposition does not hold, as can be seen by measuring the O’s-abundance. This is feasible by measuring 46/(44 + 45), i.e. the ratio between ions of mass 46 (C1W601s mainly) and ions of the masses 45 (C?30,16 and CF201”01’) and 44 (~lzO~16). Against 46144 in Table 3 the results are corrected for differences It is clear that the standards have not the same in Cf3- as well as in 01’-abundance. Ols-abundance. In order to ascertain the consequence of any differences in 017-abundance, CO, from each standard was shaken with excess of distilled water. An exchange of oxygen atoms then takes place between CO, and H,O, for example CO26 + H,Ol’
+ C01601’ + HZ016,
and if an excess of water exists, the CO, will after some time have an 017-abundance 254
imperative
rne~rerne~~
of stcmdards for carbon isotopes Table 3
u
N
% 46j(44 -j- 45) 46144 Difference from D
i
N, U, S and’D after exchange
D
s
%
04242 o-4293
0.4316
O-0070
0.0093
0.4219
0.4223
.0.4271
-0~0004
which corresponds to that of the water. COHN and UREY (1938) mention 3 hours In my first experiment 64 hours and in the others -as the shaking time required. not below 8 hours were used. That oxygen exchange was complete was checked by measuring 46144 which gave the same value for the four samples. Table 4
!
.____-__-L.---
I
N
u
I
~-
.---
s
.-..-
1
1952, Aug. 11 Aug. 13 Aug. 15
0.0235
Mean
* 4
0.0137 -L_3
0.0251 + 1
The differences in 45144 (now identical with differences in CY3/P) between N, U and X with I) after dessication with liquid air are recorded in Table 4. As ant.icipated from the very small difference in 46/44 between X and _D, the difference in 45/44 between these two was not changed, whereas 11’ and U were changed considerably. From the values in Table 4, and taking as basis 1.124% for Cr3/P2 in N, Table 5 was obtained. Table 5
I / (y3/@
c12/c13
N
I
I
/
1.124% 1 88.9,
/
1
l2
/
s
,
1.114,% 89.7,
/
n
I
1,125,% 88$
/
I-loo,y~ 90.8,
If in conformity with what is done in defining some physical magnitudes we put the Ci3/CY2-value of NTER’S standard at I*12400/,, corresponding to 88.9’7 for Ci2/C13, the other standards will acquire t#he values in Table 6. The error of these relative values of CY2/CY3scarcely exceeds O-06. 255
WILLI DANSOAARD:Compwative
of standards for carbon isotopes
rne~~rn~~ Table 6
Table 7
1 -.-
u
N
i
S
% Difference from D (before exchange) Difference from unexchanged (after exchange) Change in 45144
II
I
0’
76
./a
0‘0285
* 4
O-0138 ri-_2
o*oooo
4
0.0268
3 3
0.0165
5 3
0.0028
-f 3
-0~0005
* 4
--0~0017
& 5
0.0027
& 4
0.0028
+ 3
-0.0022
+ 4
-0.0035
*
0.0052
0.0257
Change in 46144
i
D
f
4
I +: 4 / 0.0048 i_ 4
L-
If we look at the changes in 45/M and 46144 caused by the oxygen exchange we get the values in Table 7, the last line of which is taken from Table 3. It is evident that differences in 017-abundance between sample and standard may cause measurable deviations if they are not taken into consideration. To secure the same 017-abundance in standard and sample, the most rational way is to allow both of them to exchange with water. Failure to do so may involve an error of at least 0.36 in C12jCf3 or O.OO45o/oin CY3/02. This is evident in Table 7 from t,he 017-difference before the exchange between U and -I), giving (0.0028 & 3) + (0.0017 f
5) = 0.0045%
&- 6
when C1s/C12 = 1.1 y0 app roximately. This means that the absolute error of C?3/82 may a,mount to O*OO45o/oor even more, merely as a consequence of difference in 017-abundance. REFERENCES COHN, M. and UREY, H. C. NIER, A. 0.
1938 1950
J. Amer. Chem. 60, 679 Phys. Rev. 77, 789
256
Pergamon Press Ltd., London
Comparativemeasurements of standardsfor carbon isotopes WILLI Universitetets
DANSGAARD
biofysiske laboratorium,
Copenhagen
{Received 8 November, 1952) ABSTRACT ~~e~u~ments on two American, one Swedish and one Danish standard for carbon isotopes are reported. These measurements are intended to provide 8, direct comparison between American and Scandinavian measurements on oarbon isotopes. CO, samples are used in the mess-spectrometry and it is shown that differences in 0”-abundance may cause measurable errors.
Lately much work has been done in determining the abundance of the heavy carbon isotope Cl3 in nature. The great accuracy with which such measurements can be made has made it desirable to consider carefully the basis on which they depend. The abundance of carbon isotopes in a given sample is often stated by the numerical ratio of Cl2 to C13-atoms, characterized in this paper by 02/CY3. Massspectrographic determination of this ratio is very difficult, but differences in Ci2/U3 can be found with great accuracy. A standard is chosen, and results are normally reported either simply as the difference from the standard or as the C12/C13-value obtained from attaching some value to the standar*d and adding the difference measured. Neither of these procedures, however, permits of comparison with other results, unless the differences are known between the particular standards that were used. Professors A. 0. NIER and H. C. UREP have each kindly suppiied samples of their standards (CaCO,; in this paper called N and U respectively). A comparison has t’herefore been made of each of these with a Swedish standard (BaCO,; called X) from Naturhistoriska Riksmuseum in Stockholm and a Danish one (bomb-CO,; called D). The measurements were made with a Consolidated-Nier Isotope-Ratio Mass Spectrometer, model 21-201. In this instrument it is necessary to admit each sample of carbon in t’he form of CO,. The combustion of the solid standards can be achieved in different ways. Some investigators use H,PO,, others HCl and, in Sweden BaCO, is heated together with NaH,PO,. These procedures are indicated in t,his paper by H3P0,, HCl and NaH,PO, respectively. After ionization of the CO,-molecules in the mass spectrometer an electromagnetic deflection of their paths takes place, so that all singly charged ions with the same mass are focused and measured together. The instrument primarily gives a value for 46144, i.e. the ratio of quantities between ions with mass 45 (C130~16and C1zOl~017) and ions with mass 44 {C1zO~16). The values of 45144 for the Swedish and the American standards were found to be higher than the Danish, and the differences from the Danish 45144, have been recorded in Table 1. In the main part of this table the figure after “&” indicates the reproducibility of the last figure on the particulir day. In the last line, however, it means the standard deviation of the mean. 253
WILLI DANSGAARD
Table 1. Differences above the Danish value Preparation
1951, Aug. Dec. ,, ,, 9, it ,, 1952, lkr. Jun. Aug. >, Moan
21 10 11 12 13 14 15 15 9 16 10 11
100) of 45144
u
N
W’O,
0.0262, 0.0261, 0.0262
(x
HP& 5 (NaH&‘O,) 2 (NaH,PO,) 3 (NaH2P0,) 3 (NaH,PO,) 3 (H3P0,) 3 (~~H~PO*)
0.0144 0.0142 0.0132 0.0133 0.0138 0.0141
& + + f & i
0.0136
ri: Z(HC1)
0.0138
_i 2
rtr.2 & 2 & 2
0.0264h -.&2
0.0281 0.0289
f t
0.02625
0.0285
jz 4
i. 7
6 4
It is seen that the combustion method does not affect the result. If NIER’S measurement of the standard “Jurassic Limestone, Solenhofen, Bavaria” (NIER, 1950) is used as basis with the C13~C1z-~~lueof 1.124% jO-003 (here -&O-O03 refers to 1.124 as an absolute value), and if it is presupposed that the 017-abundance is the same in all the standards (so that no corrections for W016017 are necessary, since they disappear in forming the differences) the values given in Table 2 are now found.
However, the presupposition does not hold, as can be seen by measuring the O’s-abundance. This is feasible by measuring 46/(44 + 45), i.e. the ratio between ions of mass 46 (C1W601s mainly) and ions of the masses 45 (C?30,16 and CF201”01’) and 44 (~lzO~16). Against 46144 in Table 3 the results are corrected for differences It is clear that the standards have not the same in Cf3- as well as in 01’-abundance. Ols-abundance. In order to ascertain the consequence of any differences in 017-abundance, CO, from each standard was shaken with excess of distilled water. An exchange of oxygen atoms then takes place between CO, and H,O, for example CO26 + H,Ol’
+ C01601’ + HZ016,
and if an excess of water exists, the CO, will after some time have an 017-abundance 254
imperative
rne~rerne~~
of stcmdards for carbon isotopes Table 3
u
N
% 46j(44 -j- 45) 46144 Difference from D
i
N, U, S and’D after exchange
D
s
%
04242 o-4293
0.4316
O-0070
0.0093
0.4219
0.4223
.0.4271
-0~0004
which corresponds to that of the water. COHN and UREY (1938) mention 3 hours In my first experiment 64 hours and in the others -as the shaking time required. not below 8 hours were used. That oxygen exchange was complete was checked by measuring 46144 which gave the same value for the four samples. Table 4
!
.____-__-L.---
I
N
u
I
~-
.---
s
.-..-
1
1952, Aug. 11 Aug. 13 Aug. 15
0.0235
Mean
* 4
0.0137 -L_3
0.0251 + 1
The differences in 45144 (now identical with differences in CY3/P) between N, U and X with I) after dessication with liquid air are recorded in Table 4. As ant.icipated from the very small difference in 46/44 between X and _D, the difference in 45/44 between these two was not changed, whereas 11’ and U were changed considerably. From the values in Table 4, and taking as basis 1.124% for Cr3/P2 in N, Table 5 was obtained. Table 5
I / (y3/@
c12/c13
N
I
I
/
1.124% 1 88.9,
/
1
l2
/
s
,
1.114,% 89.7,
/
n
I
1,125,% 88$
/
I-loo,y~ 90.8,
If in conformity with what is done in defining some physical magnitudes we put the Ci3/CY2-value of NTER’S standard at I*12400/,, corresponding to 88.9’7 for Ci2/C13, the other standards will acquire t#he values in Table 6. The error of these relative values of CY2/CY3scarcely exceeds O-06. 255
WILLI DANSOAARD:Compwative
of standards for carbon isotopes
rne~~rn~~ Table 6
Table 7
1 -.-
u
N
i
S
% Difference from D (before exchange) Difference from unexchanged (after exchange) Change in 45144
II
I
0’
76
./a
0‘0285
* 4
O-0138 ri-_2
o*oooo
4
0.0268
3 3
0.0165
5 3
0.0028
-f 3
-0~0005
* 4
--0~0017
& 5
0.0027
& 4
0.0028
+ 3
-0.0022
+ 4
-0.0035
*
0.0052
0.0257
Change in 46144
i
D
f
4
I +: 4 / 0.0048 i_ 4
L-
If we look at the changes in 45/M and 46144 caused by the oxygen exchange we get the values in Table 7, the last line of which is taken from Table 3. It is evident that differences in 017-abundance between sample and standard may cause measurable deviations if they are not taken into consideration. To secure the same 017-abundance in standard and sample, the most rational way is to allow both of them to exchange with water. Failure to do so may involve an error of at least 0.36 in C12jCf3 or O.OO45o/oin CY3/02. This is evident in Table 7 from t,he 017-difference before the exchange between U and -I), giving (0.0028 & 3) + (0.0017 f
5) = 0.0045%
&- 6
when C1s/C12 = 1.1 y0 app roximately. This means that the absolute error of C?3/82 may a,mount to O*OO45o/oor even more, merely as a consequence of difference in 017-abundance. REFERENCES COHN, M. and UREY, H. C. NIER, A. 0.
1938 1950
J. Amer. Chem. 60, 679 Phys. Rev. 77, 789
256