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Automatic spectrographic determination of gases in metals etc
SHORT
403
COMMUNICATIONS
Automatic
spectrographic
determination
of gases in metals etc.
The use of a high temperature hollow-cathode discharge for the determination of oxygen in steel has been reported 1. This method has now been extended to include the determination of other gaseous elements in a variety of materials, notably nitrogen and oxygen in steel and uranium carbide, oxygen in tungsten and copper, and hydrogen in zirconium and zircaloys. The simultaneous measurement of oxygen and nitrogen necessitated the incorporation of a second channel in the spectrometer but for the determination of hydrogen, since it is an independent analysis, only resetting of the monochromator is required. Experiments showed that the most sensitive atomic nitrogen lines at 4110.0 A and 4099.9 A were unsuitable because of spectral interference by vanadium and attention was turned to possible molecular bands; of these the Na 1st positive band head at 39x4.4 A was finally chosen, because of its sensitivity, freedom from interference and convenience from design considerations. The installation of a second channel for nitrogen was further complicated by the fact that the most intense emission was recorded when viewing directly into the cathode cavity, whereas the oxygen spectrum has to be viewed across the axis of the cathode to minimise the high background associated with the interior of the hot cavity. To meet these requirements and to obviate a cumbersome mirror system or the use of two monochromators. a standard
Fig. I. Schematic layout of the apparatus. C, cathode chamber; F, filters; M, concave mirrors: N, plane mirrors; G. plane grating; I, integrators; S, selectors; A, amplifiers; D.V., digital voltmctcr; D.C., high-voltage D.C. source unit.
&M Spex monochromator designed on a Czerny-Turner mounting was modified so that it is, in effect, a double monochromator as shown diagrammatically in Fig. I ; this arrangement is the subject of a patent application. One exit slit is aligned to measure the intensity of the OS 7772/s A multiplet and the adjacent background radiation, in the first-order spectrum, and the second exit slit is aligned to measure the Ns 1st positive band head at 39x4.4 A in the second-order spectrum. Adequate sensitivity is And.
Chrm. Acta, 36 (1966)
403-406
COMMUNICATIONS
SHORT
404
recorded for nitrogen (ancl incidentally for hydrogen) without monitoring the adjacent background. Suitable filters are mounted at the entrance slits to act as order sorters. With the exit slits accurately aligned relative to one another, minor drifts in the alignment of the monochromator are adjusted by rotating the grating in the usual way. To accommodate the longer emission time of nitrogen the integration period is extended to 2.5 min and during the next 30 set, while the source is switched off, the readings arc printed out and the integrators reset. At appropriate intervals, samples are fed into the cathodc during the reset period. Uranium carbide and tungsten are analysed under similar conditions except that they are dropped into the cathode encapsulated in nickel sheet which appears to form a homogeneous melt with the samples in the hot cathode, a correction being made for the small oxygen and nitrogen contents of the nickel. In the determination of oxygen in copper the samples are dropped into a cathode containing a bath of 0.5 g of nickel. The source controls are maintained at a fixed setting which corresponds to a current of 0.9 A with a clean cathode containing only the nickel bath. The current decreases as the proportion of copper in the bath increases but this does not appear to affect the evaluation of the oxygen contents. For the determination of hydrogen in zirconium the monochromator is realigned so that the “oxygen channel” measures the intensity of the hydrogen line at 6562.8 A. The discharge is run at 0.8 A and care must be taken to ensure that this value is not exceeded, otherwise the samples are liable to melt and give anomalous results. An integration time of go set is adequate to allow complete evolution of hydrogen from samples weighing up to IOO mg. As previously reported, standard steel samples or synthetic standards can be used to calibrate the apparatus for the determination of oxygen. This calibration has been found to apply equally well for the determination of oxygen in uranium carbide, tungsten and copper. No satisfactory synthetic standard has been found for the determination of nitrogen and standard samples of steel and uranium carbide are used to calibrate for the determination of nitrogen in steel and uranium carbide respectively. Different factors were obtained for these 2 matrix materials. TABLE
I
DETERMINATION
OF
NITROGEN
IN
STPRL
-----
___. -_-----.-.-._.-_
NBS
Ccrtificatc of analysis % Nu Hollow cathodo % Nab No. of dctcrnxinations Standard dcvifltion Cocfficicnt of varintion
-
stmzdard samples
BISR.4 vxstandard
8i
lOXB
343
r2ga
0.018
0.039
o-074
0.0175
0,034 ” 20%
1.1
15%
----___.__
B.C.S. No.
r49
China. Actn.
36 (x966) 403-406
Ns
pure iro>a
steel
0.0060
o.orz
0.005go
(0.0x(i)
0.0055
0.012
o.ooG3
14 7%’
-
13N”
CR
0.002
o.orG
0.07”-
0.005s
‘5 25%
15 0.0035 -
G
2
-
-----
” Used ns stnnderd, obscrvntions extcndcd Over R pcriocl of 4 weeks. b Sample weights of 4-G nq used for the N.B.S. standards and 20-50 mg for the others. 0 Vncuum fusion figure. Awl.
LoUl-
10
o.ooog5 -
SHORT COhIMUNICATIONS
405
The results of analyses by this technique carried out on independently analysed samples are summarised in the Tables I to IV. In general, there is reasonable agreement between the results obtained by the hollow-cathode technique and other methods. The apparent reproducibility is in many cases more a measure of the sample heterogeneity than the performance of the method; with the more homogeneous samples (e.g. the coppers), the coefficient of variation is an acceptable figure. Estimates of the limit of detection for the respective analyses are listed in TABLE
II
DBTBRMINATION
OF
Sample
OXYGEN
NITROGEN
A
- __... ------
’
Oxywa (%I
l3y vat. fusion By hallow cathodca No. of determinations Coefficient of variation Nilvogel,
AND
IN
URANIUM
B
-.--
0.20
0.07
0.02G
0.20
0.06
o.oz.#
12 25
-
-
0.037 0.048 g 23
0.037 0.035 6 -
0.018 6 -
20
(O/o)
chemical method o.ogr By hollow cathode” (0.051) No. of determinations 12 Cocfficicnt of variation (%) 20 .a Sample weights of 8-10 rn6 used for Samples 1)Sample A used for calibration.
6
5
0.022
A, B and C and x5-25
III
mg for D.
.
DRTRRMINATION
OF
OXYGRN
IN
TUNCSTRN
_-.-.-
AND
COPPRR
--_-_
-__
Copper
Sample -
_.
0 Sample weights of 30-50
- ._._. - .__,. --
Tztngslen
I
p.p.m. 02 (vat. fusion) 290 p,p. m. 02 (hollow cathode) n 295 No. of determinations 7 Standard deviation @p.m.) 32 Cocfficicnt of variation (%) rx
TABLE
D
0.12
By
TABLE
C
o.og I2
(%)
CARBIDE
a
I
a
3
150
5.5 7.3 II
35 25 ,5
22 2o 5
11.5 -
-
IGO
4 -
6.6
-
mg used.
IV
DETERMINATION
OF
HYDROGEN
IN
ZIRCONIUhI
AND
%r metal.
Sanrple _.-_.-
-.-_.--
.__-
p.p.m. Ha p.p.m. He (hollow cathodc)b No. of determinations Coefficient
of variation
46 (46) II 5.0
(%)
0 Used for calibration. b Sample weights of 20-50
--....--.----
ZIRCALOYS
Zircaloy A
B
140 I33 5 -_
r5o =43 4.6
mg used. Anal.
Chim. Ada,
36 (x966)
403-406
SHORT COMMUNICATIONS
406 Table V. These are based on the variations 3 o level of significance, The improvement
in the blank readings and are quoted at the in the limit of detection for oxygen in steel
TABLE V LIhfIT
OP DETI’.CTION
Mdcrial
a~zuly.wl
CJ/ delecliolz
(.in
03
N?,
Hz
Steel
0.35
Tungsten
Copper
0.65 0.75
0.55 2.5 -
-
Zirconium
-
-
0.0.5
_-
Litrail
--
.--
pg)
-
Urani~~n~carbitlc
1.5
--
.-
over that previously rcportecl has rcsultcd from the use of the new high-dispersion monochromator. The higher limits in the analysis of uranium carbide and tungsten are inevitable because of the increased variation due to oxygen and nitrogen in the nickel “cans” ; in the case of nitrogen the variation is also due to the less favourable calibration [actor. Grateful acknowlcdgcmcnt is made to: The British Iron Sr Steel Research Association (BISRA) for supplying the Standard Steel Samples, The British NonFerrous Metals I&search Association for the copper samples, J, A. CALDWELL of Murex Ltd. for a tungsten sample, and Mr. H. I. SHAI.GOSKY who arranged for the alternative mcthocls of analysis. U.K.A.E.A. Research Croufi, A~aJyticaL Sciences Division, C.37, Royal ArsenaZ, Wciolwicl~, London S.E.18 (Great Britain) I M. s. w. WEUU (Reccivcd
AND
R.
J.
Wnnu.
Annl.
M. S. W. WGI~R R. J. WEBB
Ciri*tl. rlclrc, 33 (1965) 138.
June 16th, 1966)
Annl. Chinr. Ada, $3 (x$X)
403-406
Gas chromatographic analysis of a mixture with a modified sampling device*
of
hydrogen
and
oxygen
Gas analysis of hydrogen has been extensively studied by various methods’. HILL AND GRIFFITH~ designed an instrument for direct determination of hydrogen in oxygen, but there is no convenient method of analysing directly and simultaneously both hydrogen and oxygen in a gaseous mixture in very small amounts. Gas chromatography may be used to analyse a gaseous mixture of hydrogen over and oxygen in amounts of ca. IO -8 mole. The advantages of gas chromatography Anal. Chim. Ada, 36 (x966) 406-408
403
COMMUNICATIONS
Automatic
spectrographic
determination
of gases in metals etc.
The use of a high temperature hollow-cathode discharge for the determination of oxygen in steel has been reported 1. This method has now been extended to include the determination of other gaseous elements in a variety of materials, notably nitrogen and oxygen in steel and uranium carbide, oxygen in tungsten and copper, and hydrogen in zirconium and zircaloys. The simultaneous measurement of oxygen and nitrogen necessitated the incorporation of a second channel in the spectrometer but for the determination of hydrogen, since it is an independent analysis, only resetting of the monochromator is required. Experiments showed that the most sensitive atomic nitrogen lines at 4110.0 A and 4099.9 A were unsuitable because of spectral interference by vanadium and attention was turned to possible molecular bands; of these the Na 1st positive band head at 39x4.4 A was finally chosen, because of its sensitivity, freedom from interference and convenience from design considerations. The installation of a second channel for nitrogen was further complicated by the fact that the most intense emission was recorded when viewing directly into the cathode cavity, whereas the oxygen spectrum has to be viewed across the axis of the cathode to minimise the high background associated with the interior of the hot cavity. To meet these requirements and to obviate a cumbersome mirror system or the use of two monochromators. a standard
Fig. I. Schematic layout of the apparatus. C, cathode chamber; F, filters; M, concave mirrors: N, plane mirrors; G. plane grating; I, integrators; S, selectors; A, amplifiers; D.V., digital voltmctcr; D.C., high-voltage D.C. source unit.
&M Spex monochromator designed on a Czerny-Turner mounting was modified so that it is, in effect, a double monochromator as shown diagrammatically in Fig. I ; this arrangement is the subject of a patent application. One exit slit is aligned to measure the intensity of the OS 7772/s A multiplet and the adjacent background radiation, in the first-order spectrum, and the second exit slit is aligned to measure the Ns 1st positive band head at 39x4.4 A in the second-order spectrum. Adequate sensitivity is And.
Chrm. Acta, 36 (1966)
403-406
COMMUNICATIONS
SHORT
404
recorded for nitrogen (ancl incidentally for hydrogen) without monitoring the adjacent background. Suitable filters are mounted at the entrance slits to act as order sorters. With the exit slits accurately aligned relative to one another, minor drifts in the alignment of the monochromator are adjusted by rotating the grating in the usual way. To accommodate the longer emission time of nitrogen the integration period is extended to 2.5 min and during the next 30 set, while the source is switched off, the readings arc printed out and the integrators reset. At appropriate intervals, samples are fed into the cathodc during the reset period. Uranium carbide and tungsten are analysed under similar conditions except that they are dropped into the cathode encapsulated in nickel sheet which appears to form a homogeneous melt with the samples in the hot cathode, a correction being made for the small oxygen and nitrogen contents of the nickel. In the determination of oxygen in copper the samples are dropped into a cathode containing a bath of 0.5 g of nickel. The source controls are maintained at a fixed setting which corresponds to a current of 0.9 A with a clean cathode containing only the nickel bath. The current decreases as the proportion of copper in the bath increases but this does not appear to affect the evaluation of the oxygen contents. For the determination of hydrogen in zirconium the monochromator is realigned so that the “oxygen channel” measures the intensity of the hydrogen line at 6562.8 A. The discharge is run at 0.8 A and care must be taken to ensure that this value is not exceeded, otherwise the samples are liable to melt and give anomalous results. An integration time of go set is adequate to allow complete evolution of hydrogen from samples weighing up to IOO mg. As previously reported, standard steel samples or synthetic standards can be used to calibrate the apparatus for the determination of oxygen. This calibration has been found to apply equally well for the determination of oxygen in uranium carbide, tungsten and copper. No satisfactory synthetic standard has been found for the determination of nitrogen and standard samples of steel and uranium carbide are used to calibrate for the determination of nitrogen in steel and uranium carbide respectively. Different factors were obtained for these 2 matrix materials. TABLE
I
DETERMINATION
OF
NITROGEN
IN
STPRL
-----
___. -_-----.-.-._.-_
NBS
Ccrtificatc of analysis % Nu Hollow cathodo % Nab No. of dctcrnxinations Standard dcvifltion Cocfficicnt of varintion
-
stmzdard samples
BISR.4 vxstandard
8i
lOXB
343
r2ga
0.018
0.039
o-074
0.0175
0,034 ” 20%
1.1
15%
----___.__
B.C.S. No.
r49
China. Actn.
36 (x966) 403-406
Ns
pure iro>a
steel
0.0060
o.orz
0.005go
(0.0x(i)
0.0055
0.012
o.ooG3
14 7%’
-
13N”
CR
0.002
o.orG
0.07”-
0.005s
‘5 25%
15 0.0035 -
G
2
-
-----
” Used ns stnnderd, obscrvntions extcndcd Over R pcriocl of 4 weeks. b Sample weights of 4-G nq used for the N.B.S. standards and 20-50 mg for the others. 0 Vncuum fusion figure. Awl.
LoUl-
10
o.ooog5 -
SHORT COhIMUNICATIONS
405
The results of analyses by this technique carried out on independently analysed samples are summarised in the Tables I to IV. In general, there is reasonable agreement between the results obtained by the hollow-cathode technique and other methods. The apparent reproducibility is in many cases more a measure of the sample heterogeneity than the performance of the method; with the more homogeneous samples (e.g. the coppers), the coefficient of variation is an acceptable figure. Estimates of the limit of detection for the respective analyses are listed in TABLE
II
DBTBRMINATION
OF
Sample
OXYGEN
NITROGEN
A
- __... ------
’
Oxywa (%I
l3y vat. fusion By hallow cathodca No. of determinations Coefficient of variation Nilvogel,
AND
IN
URANIUM
B
-.--
0.20
0.07
0.02G
0.20
0.06
o.oz.#
12 25
-
-
0.037 0.048 g 23
0.037 0.035 6 -
0.018 6 -
20
(O/o)
chemical method o.ogr By hollow cathode” (0.051) No. of determinations 12 Cocfficicnt of variation (%) 20 .a Sample weights of 8-10 rn6 used for Samples 1)Sample A used for calibration.
6
5
0.022
A, B and C and x5-25
III
mg for D.
.
DRTRRMINATION
OF
OXYGRN
IN
TUNCSTRN
_-.-.-
AND
COPPRR
--_-_
-__
Copper
Sample -
_.
0 Sample weights of 30-50
- ._._. - .__,. --
Tztngslen
I
p.p.m. 02 (vat. fusion) 290 p,p. m. 02 (hollow cathode) n 295 No. of determinations 7 Standard deviation @p.m.) 32 Cocfficicnt of variation (%) rx
TABLE
D
0.12
By
TABLE
C
o.og I2
(%)
CARBIDE
a
I
a
3
150
5.5 7.3 II
35 25 ,5
22 2o 5
11.5 -
-
IGO
4 -
6.6
-
mg used.
IV
DETERMINATION
OF
HYDROGEN
IN
ZIRCONIUhI
AND
%r metal.
Sanrple _.-_.-
-.-_.--
.__-
p.p.m. Ha p.p.m. He (hollow cathodc)b No. of determinations Coefficient
of variation
46 (46) II 5.0
(%)
0 Used for calibration. b Sample weights of 20-50
--....--.----
ZIRCALOYS
Zircaloy A
B
140 I33 5 -_
r5o =43 4.6
mg used. Anal.
Chim. Ada,
36 (x966)
403-406
SHORT COMMUNICATIONS
406 Table V. These are based on the variations 3 o level of significance, The improvement
in the blank readings and are quoted at the in the limit of detection for oxygen in steel
TABLE V LIhfIT
OP DETI’.CTION
Mdcrial
a~zuly.wl
CJ/ delecliolz
(.in
03
N?,
Hz
Steel
0.35
Tungsten
Copper
0.65 0.75
0.55 2.5 -
-
Zirconium
-
-
0.0.5
_-
Litrail
--
.--
pg)
-
Urani~~n~carbitlc
1.5
--
.-
over that previously rcportecl has rcsultcd from the use of the new high-dispersion monochromator. The higher limits in the analysis of uranium carbide and tungsten are inevitable because of the increased variation due to oxygen and nitrogen in the nickel “cans” ; in the case of nitrogen the variation is also due to the less favourable calibration [actor. Grateful acknowlcdgcmcnt is made to: The British Iron Sr Steel Research Association (BISRA) for supplying the Standard Steel Samples, The British NonFerrous Metals I&search Association for the copper samples, J, A. CALDWELL of Murex Ltd. for a tungsten sample, and Mr. H. I. SHAI.GOSKY who arranged for the alternative mcthocls of analysis. U.K.A.E.A. Research Croufi, A~aJyticaL Sciences Division, C.37, Royal ArsenaZ, Wciolwicl~, London S.E.18 (Great Britain) I M. s. w. WEUU (Reccivcd
AND
R.
J.
Wnnu.
Annl.
M. S. W. WGI~R R. J. WEBB
Ciri*tl. rlclrc, 33 (1965) 138.
June 16th, 1966)
Annl. Chinr. Ada, $3 (x$X)
403-406
Gas chromatographic analysis of a mixture with a modified sampling device*
of
hydrogen
and
oxygen
Gas analysis of hydrogen has been extensively studied by various methods’. HILL AND GRIFFITH~ designed an instrument for direct determination of hydrogen in oxygen, but there is no convenient method of analysing directly and simultaneously both hydrogen and oxygen in a gaseous mixture in very small amounts. Gas chromatography may be used to analyse a gaseous mixture of hydrogen over and oxygen in amounts of ca. IO -8 mole. The advantages of gas chromatography Anal. Chim. Ada, 36 (x966) 406-408