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Lithium aluminum tritide in active hydrogen analysis
InternationalJournal&Applied Radiationand Isotopes,1964,Vol. 15, pp. 565-567. PergamonPressLtd. Printedin NorthernIreland
Lithium
Aluminum
Tritide
Hydrogen
Analysis
in Active
(Received 15 Januay 1964) CHLECK et uZ.(l) have reported a method for determining active hydrogen by counting the tritium evolved by reaction with lithium aluminum tritide (LAT). Working with aniline, benzoic acid, nbutanol and water, they obtained in each case a linear relationship between weight of sample and tritium count. Each individual compound had, however, been analyzed with an LAT solution of a different specific activity. They stated that “since the stoichiometry of the reaction of LAH [lithium aluminum hydride] and active hydrogen compounds has been studied by KRYNITSKY et al., no attempt here was made to correlate data between compounds” and reached the conclusion that “any of the four calibration curves, using the same specific activity of LAT, could be used to determine the active hydrogen content of an unknown”. This conclusion seemed plausible, but when we attempted to apply the method to the determination of active hydroxyl hydrogen in an ethylene glycol adipate polyester, we found that a curve based on n-butanol was not applicable to that substance. Further investigation disclosed the fact that although values for benzoic acid agreed with those for nbutanol, values for aniline did not. It would, accordingly, appear that the LAT method for active hydrogen is not an absolute one whereby unknown substances may be analyzed for active hydrogen by reference to a curve prepared with any other substance of known active hydrogen content. The method actually requires standards based on samples of the specific substance being analyzed. In this respect it differs from the manometric or volumetric method.
Experimental
and
of a three-necked, IOO-ml, round-bottom flask containing a Teflon (polytetrafluoroethylene)-covered magnetic stirring bar, since vigorous agitation was required for proper disintegration of, and complete liberation of active hydrogen from, the insoluble products of reduction of the polyester sample. The counting gas was introduced by means of a 4-mm. i.d. glass tube placed with its end above the surface of the 0.4M LAT solution, since immersion beneath the reagent of a narrow capillary led to an accumulation of solid products which clogged the capillary. The counting gas was dried by passage over (Drierite) calcium sulfate (use of an LAH scrubbing solution led to mechanical difficulties due to clogging of sintered glass diffusers). Finally, instead of a buret for introducing the sample, one neck of the reaction flask was stoppered with a rubber septum and samples were introduced by means of syringes. Samples were made up in diethylcarbitol rather than tetrahydrofuran and a count was accumulated for twenty minutes. Figure 1 shows the straight lines obtained with n-butanol and a polyester sample with the same The active hydrogen values batch of reagent. plotted were corrected for a trace of moisture and, in the case of polyester, for a small amount of acid present. The hydroxyl values of the polyester sample had been determined by acetylation in pyridine.* Fifty microliter samples of various dilutions were used for the determinations for polyester and n-butanol. Benzoic acid values agreed satisfactorily with those for n-butanol. Figure 1 also gives some points determined for n-butanol and aniline with a different batch of reagent having a different specific activity. Although there are too few points to warrant drawing a curve, it may be concluded that active hydrogen values for aniline would also not fall on the corresponding n-butanol curve.
Discussion In addition to the data just presented, which illustrate the effect of sample composition on the degree of liberation of tritium, we also observed a certain behavior of aniline which reinforces this
results
The results reported here were obtained with the equipment and method described by CHLECK et al.(l), with a few modifications. The reaction cell consisted
* We polyester 565
are indebted analyses.
to
Dr.
John
Cl. Ryan
for
566
Lettersto the editon
240
. -
240
Left
-
220
_
200
Right
-
180
t
c-
160
scale Reagent
I - 0 polyester
Reagent
I- o
200 180
n-butonol
160
; ?I N x E
220
.
;’
scale Reagent
2 -
Reagent
2-
140
aniline
l
; *
A n-butanol
120 5
2
140
4.E’
120
cd
A
100 .I
f z
,x,
-
80 60 40 20
:, 0
2
4
6
8
IO
12
Milliequivalents
FIG. I. Net count
14
active
vs. active
16
I8
8
80
.;
60
g
40
E
20 0
22
20
hydrogen
100
x IO3
hydrogen
content.
i
. / . /. l Aniline
b n- Butanol
0
5
:c’
15
/
,
20
25
Milliequlvalents
FIG. 2. Net count
/ 30
active
vs. active
,
,
35
40
hydrogen
hydrogen
,
,
]
45
50
55
xI03
content.
Letters to the editors point. Aniline, n-butanol and benzoic acid were analyzed with the same reagent solution. The aniline analyses were interspersed among the n-butanol and benzoic acid analyses. For 21.4 mmoles of active hydrogen, the replicate counts for 20 min for aniline were 80-, 118-, 196- and 128 x 256 in that order; and for 10.7 mmoles of active hydrogen, 20 x 256 It was necessary to repeat the aniline and zero. analyses with previously unused reagent in order to get the duplicate aniline values shown in Fig. 1. The corresponding butanol values were obtained later with the same reagent. In other words, for aniline, the active hydrogen values found and their reproducibility were influenced by the presence of previously formed reaction by-products, whereas values for butanol were not so influenced. The explanation for this dependence of the extent of tritium liberation on the nature of the sample, and as with aniline, on the amount and nature of byproducts present, must involve the existence of a variable degree of exchange between either LAT or liberated tritium with the hydrogen of the reduction by-products or of the lithium aluminum compounds left as a result of active hydrogen liberation. This would result in variations in the amount of tritium entering the counter, even though the total volume of hydrogen (protium plus tritium) might be what would be expected from the stoichiometry of the reaction. By sweeping with methane-free argon, which was subsequently mixed with a mixture of argon and methane before going through the detector, it could be demonstrated that methane underwent no appreciable exchange with LAT under the conditions of the analysis. The extent of the interfering exchange could depend partly on the nature of the compounds involved, and partly on the existence or absence, in a cage, of tritium in a reactive form. Such reactive tritium might conceivably consist of free atoms with a suitable lifetime, in close proximity to exchangeable hydrogen. Additional
data
Some questions were raised concerning the validity of the data in this letter when related to the published method of CHLECK et al.(l), since many of the experimental conditions had been changed. In order to settle this point, the determinations with aniline and butanol were repeated with apparatus and conditions as described in that paper. (The only difference was the introduction of the sample by a syringe through a rubber septum in the reaction vessel rather than by an attached buret.) Figure 2 gives the results obtained with aniline and n-butanol with the same LAT reagent. As was shown by the results in Fig. 1, here too it is obvious that a calibration curve based on one compound is
567
not necessarily applicable to another. The fact that the relationship between the aniline and butanol curves in Fig. 2 is different from what is suggested for those two compounds by the points in Fig. 1 would seem to emphasize the importance of changes in conditions such as concentration and time, in determining the amount of liberated tritium for a given total volume of hydrogen liberated. American Cyanamid Company Bound Brook, N. J.
W. SEAMAN D. STEWART, JR.
Reference 1. CHLECK D.J., BROUSAIDESF.J.,SULLIVAN W. and ZEIGLER C. A. Int. 3. appl. Rad. Isotopes 7, 182 (1960).
International Journal of Applied Radiation and Isotopes, 1964, Vol. 15, pp. 567-568. Pergamon Press Ltd. Printed in Northern Ireland
Calibration Factors for the Type 1383A P-y Ionization Chamber (Received 27 January 1964) IN 1961, in a paper”’ describing the uses and calibration of the 1383A ionization chamber a table was included (Table 3) giving the instrument response for chamber serial number 14 in terms of current per millicurie or current per mcjml as appropriate for all the radionuclides calibrated up to the date of publication. Since then, other radionuclides have been measured for which calibration data is now available. In addition, the methods of measuring the disintegration rate of certain radionuclides have changed and some nuclides which were calibrated by %rp proportional counting or by ionization chamber measurements, are now standardized by the 4+y coincidence or tracer techniques. Accordingly a new table is given below for the calibration factors of chamber 14. The errors quoted in this table include both the error in the absolute measurement and the error in the measurement of the ionization current, but do not take into account the errors due to the difference in response between chamber 14 and any other chamber. This means that the errors quoted should be increased by & 1 per cent for y-emitters and +3 per cent for B-emitters except for chambers which have been calibrated directly against chamber 14 at NPL, in which case the overall errors will not be significantly different from those given in Table 1. It should be emphasized that these calibration factors apply to an unshielded
Lithium
Aluminum
Tritide
Hydrogen
Analysis
in Active
(Received 15 Januay 1964) CHLECK et uZ.(l) have reported a method for determining active hydrogen by counting the tritium evolved by reaction with lithium aluminum tritide (LAT). Working with aniline, benzoic acid, nbutanol and water, they obtained in each case a linear relationship between weight of sample and tritium count. Each individual compound had, however, been analyzed with an LAT solution of a different specific activity. They stated that “since the stoichiometry of the reaction of LAH [lithium aluminum hydride] and active hydrogen compounds has been studied by KRYNITSKY et al., no attempt here was made to correlate data between compounds” and reached the conclusion that “any of the four calibration curves, using the same specific activity of LAT, could be used to determine the active hydrogen content of an unknown”. This conclusion seemed plausible, but when we attempted to apply the method to the determination of active hydroxyl hydrogen in an ethylene glycol adipate polyester, we found that a curve based on n-butanol was not applicable to that substance. Further investigation disclosed the fact that although values for benzoic acid agreed with those for nbutanol, values for aniline did not. It would, accordingly, appear that the LAT method for active hydrogen is not an absolute one whereby unknown substances may be analyzed for active hydrogen by reference to a curve prepared with any other substance of known active hydrogen content. The method actually requires standards based on samples of the specific substance being analyzed. In this respect it differs from the manometric or volumetric method.
Experimental
and
of a three-necked, IOO-ml, round-bottom flask containing a Teflon (polytetrafluoroethylene)-covered magnetic stirring bar, since vigorous agitation was required for proper disintegration of, and complete liberation of active hydrogen from, the insoluble products of reduction of the polyester sample. The counting gas was introduced by means of a 4-mm. i.d. glass tube placed with its end above the surface of the 0.4M LAT solution, since immersion beneath the reagent of a narrow capillary led to an accumulation of solid products which clogged the capillary. The counting gas was dried by passage over (Drierite) calcium sulfate (use of an LAH scrubbing solution led to mechanical difficulties due to clogging of sintered glass diffusers). Finally, instead of a buret for introducing the sample, one neck of the reaction flask was stoppered with a rubber septum and samples were introduced by means of syringes. Samples were made up in diethylcarbitol rather than tetrahydrofuran and a count was accumulated for twenty minutes. Figure 1 shows the straight lines obtained with n-butanol and a polyester sample with the same The active hydrogen values batch of reagent. plotted were corrected for a trace of moisture and, in the case of polyester, for a small amount of acid present. The hydroxyl values of the polyester sample had been determined by acetylation in pyridine.* Fifty microliter samples of various dilutions were used for the determinations for polyester and n-butanol. Benzoic acid values agreed satisfactorily with those for n-butanol. Figure 1 also gives some points determined for n-butanol and aniline with a different batch of reagent having a different specific activity. Although there are too few points to warrant drawing a curve, it may be concluded that active hydrogen values for aniline would also not fall on the corresponding n-butanol curve.
Discussion In addition to the data just presented, which illustrate the effect of sample composition on the degree of liberation of tritium, we also observed a certain behavior of aniline which reinforces this
results
The results reported here were obtained with the equipment and method described by CHLECK et al.(l), with a few modifications. The reaction cell consisted
* We polyester 565
are indebted analyses.
to
Dr.
John
Cl. Ryan
for
566
Lettersto the editon
240
. -
240
Left
-
220
_
200
Right
-
180
t
c-
160
scale Reagent
I - 0 polyester
Reagent
I- o
200 180
n-butonol
160
; ?I N x E
220
.
;’
scale Reagent
2 -
Reagent
2-
140
aniline
l
; *
A n-butanol
120 5
2
140
4.E’
120
cd
A
100 .I
f z
,x,
-
80 60 40 20
:, 0
2
4
6
8
IO
12
Milliequivalents
FIG. I. Net count
14
active
vs. active
16
I8
8
80
.;
60
g
40
E
20 0
22
20
hydrogen
100
x IO3
hydrogen
content.
i
. / . /. l Aniline
b n- Butanol
0
5
:c’
15
/
,
20
25
Milliequlvalents
FIG. 2. Net count
/ 30
active
vs. active
,
,
35
40
hydrogen
hydrogen
,
,
]
45
50
55
xI03
content.
Letters to the editors point. Aniline, n-butanol and benzoic acid were analyzed with the same reagent solution. The aniline analyses were interspersed among the n-butanol and benzoic acid analyses. For 21.4 mmoles of active hydrogen, the replicate counts for 20 min for aniline were 80-, 118-, 196- and 128 x 256 in that order; and for 10.7 mmoles of active hydrogen, 20 x 256 It was necessary to repeat the aniline and zero. analyses with previously unused reagent in order to get the duplicate aniline values shown in Fig. 1. The corresponding butanol values were obtained later with the same reagent. In other words, for aniline, the active hydrogen values found and their reproducibility were influenced by the presence of previously formed reaction by-products, whereas values for butanol were not so influenced. The explanation for this dependence of the extent of tritium liberation on the nature of the sample, and as with aniline, on the amount and nature of byproducts present, must involve the existence of a variable degree of exchange between either LAT or liberated tritium with the hydrogen of the reduction by-products or of the lithium aluminum compounds left as a result of active hydrogen liberation. This would result in variations in the amount of tritium entering the counter, even though the total volume of hydrogen (protium plus tritium) might be what would be expected from the stoichiometry of the reaction. By sweeping with methane-free argon, which was subsequently mixed with a mixture of argon and methane before going through the detector, it could be demonstrated that methane underwent no appreciable exchange with LAT under the conditions of the analysis. The extent of the interfering exchange could depend partly on the nature of the compounds involved, and partly on the existence or absence, in a cage, of tritium in a reactive form. Such reactive tritium might conceivably consist of free atoms with a suitable lifetime, in close proximity to exchangeable hydrogen. Additional
data
Some questions were raised concerning the validity of the data in this letter when related to the published method of CHLECK et al.(l), since many of the experimental conditions had been changed. In order to settle this point, the determinations with aniline and butanol were repeated with apparatus and conditions as described in that paper. (The only difference was the introduction of the sample by a syringe through a rubber septum in the reaction vessel rather than by an attached buret.) Figure 2 gives the results obtained with aniline and n-butanol with the same LAT reagent. As was shown by the results in Fig. 1, here too it is obvious that a calibration curve based on one compound is
567
not necessarily applicable to another. The fact that the relationship between the aniline and butanol curves in Fig. 2 is different from what is suggested for those two compounds by the points in Fig. 1 would seem to emphasize the importance of changes in conditions such as concentration and time, in determining the amount of liberated tritium for a given total volume of hydrogen liberated. American Cyanamid Company Bound Brook, N. J.
W. SEAMAN D. STEWART, JR.
Reference 1. CHLECK D.J., BROUSAIDESF.J.,SULLIVAN W. and ZEIGLER C. A. Int. 3. appl. Rad. Isotopes 7, 182 (1960).
International Journal of Applied Radiation and Isotopes, 1964, Vol. 15, pp. 567-568. Pergamon Press Ltd. Printed in Northern Ireland
Calibration Factors for the Type 1383A P-y Ionization Chamber (Received 27 January 1964) IN 1961, in a paper”’ describing the uses and calibration of the 1383A ionization chamber a table was included (Table 3) giving the instrument response for chamber serial number 14 in terms of current per millicurie or current per mcjml as appropriate for all the radionuclides calibrated up to the date of publication. Since then, other radionuclides have been measured for which calibration data is now available. In addition, the methods of measuring the disintegration rate of certain radionuclides have changed and some nuclides which were calibrated by %rp proportional counting or by ionization chamber measurements, are now standardized by the 4+y coincidence or tracer techniques. Accordingly a new table is given below for the calibration factors of chamber 14. The errors quoted in this table include both the error in the absolute measurement and the error in the measurement of the ionization current, but do not take into account the errors due to the difference in response between chamber 14 and any other chamber. This means that the errors quoted should be increased by & 1 per cent for y-emitters and +3 per cent for B-emitters except for chambers which have been calibrated directly against chamber 14 at NPL, in which case the overall errors will not be significantly different from those given in Table 1. It should be emphasized that these calibration factors apply to an unshielded