Platinum- FIux Technique for Determining Oxygen in Titanium W. R. HANSEN, M. W. MALLETT, and M. J. TRZECIAK Battelle Memorial Institute, 505 King Ave., Columbus I , Ohio
b An investigation was made of the reproducibility of the platinum bath technique for determining oxygen in titanium and its alloys. Although several variations of the platinum-bath technique were tried, the results were not satisfactorily reproducible. However, a modified technique, platinum flux, was developed. The accuracy of the dry-crucible and the platinum-flux techniques as applied to unalloyed titanium, and one alloy, Ti-6AI-4Vl was determined b y using standard samples. Both techniques appeared capable of recovering at least 9270 of the oxygen in unalloyed titanium standards. In most cases the recovery was much better. Average oxygen recovery from Ti-6AI-4V alloy standards was 93% b y both the platinum-flux and the dry-crucible techniques. Studies on the reproducibility of analytical values made on three other alloys, Ti-8Mn, Ti-2Fe2Cr-2M0, and Ti-5AI-2.5Snl indicated that satisfactory results could be obtained b y both techniques.
0
THE, methods for determining oxygen in metals, the, one most widely accepted and extensively used has been the vacuum-fusion method. Attrnipts to apply established modifications of the method to titanium re\-c~alrtlthat it, reacted differently and offrrrd more complications than many mct:ils.. The first techniques developed \vhich :ippeared to yield accurate and prrrisc, results were those of JYalter (10) (dry crucible) and Derge ( 3 ) (iron bath). l’hc rwults are comparable ( 1 ) but the tlr>.-crilcihle technique is more widely ncceptcd and is now used for umpire :inalyws. Hon-ever, t’hc determination is r:+thcr SIOK and costlj.. Hence, when Air Force specifications (H) as to the masin-iuni t’olerable oxygen content of tit:iniiini :ind its alloys were established, titanium producers and users were faced with :in increase in the cost, of their product. Therefore, t h r w n-as a real n e d for 3 faster, c1ieapc.r method of mnlysis. The platinum bath technique looked most promising in filling this need. This technique was first used by Gregory and Mapper (4)for the vacuum-fusion :inalysis of microsamples of hery!!ium.
F
They also suggested its applicability to zirconium. I n the same year, 1055, Sniiley (8) used a platinum bath t o flux iron, steel, aluminum, and thorium samples analyzed by his capillary trap (nonvacuum) method. His experiments with titanium n ere less successful and he suggested that addition of platinum to the sample might iinprove results. Later Wilkins (11) used a vacuum-fusion platinum bath technique for several metals, including titmiuni. At the beginning of the present investigation, representatives of several laboratories had informally indicated that they were having difficulty in obtaining consistent results by the platinum bath techniques. However. the technique appeared worthy of furtlier evaluation. Therefore, a n investigation ( 5 ) of the reproducibility and the accuracy of results obtainable by the platinum bath technique \Tas initiated. to compare results a i t h those obtained I n the dry-crucible technique. EXPERIMENTAL
APPARATVS. The vacuum-fusion apparatus has been described ( 7 ) . hfaTERIALS. Commercially pure unalloyed A-70 titanium used for checking the reproducibility of methods was obtained from the Rem-Cru Titanium Corp. in the form of a 1-inch-diameter rod. Reproducibility checks made on alloys were carried out using materials obtained from the Task Force on Oxygen by Vacuum-Fusion Analysis, Panel on Methods of Analysis, of the Watertown Arsenal JIetallurgical Advisory Committee on Titanium. Unalloyed standard samples were prepared from low oxygen electrorefined titanium obtained from the Bureau of Mines and from iodide titanium. Ti-6A1-4V alloy standards were prepared from the electrorefined titanium and from high purity aluminum and vanadium. Oxygen for preparation of standard samples came from t m sources; the thermal decomposition of potassium permanganate and dry ACS reagent grade titanium dioxide. Standards Preparation. Oxygen standards of unalloyed titanium were prepared by three techniques. Those of the Ti-6A1-4V alloy were prepared using only t h e first of t h e folloning techniques. INDIVIDUAL SAhlPLES. Electrorefined titanium was con9olidated into button
ingots by arc melting three tinies in a water-cooled copper crucible in a n argon atmosphere using a tungsten electrode. The Ti-6A1-4V alloy was prepared similarly, The homogeneity and base oxygen levels of the ingots were established by analyzing (dry-crucible technique) 0.25-gram samples taken from several different positions in the button ingots. The standard samples were prepared by placing 0.25-gra1n abraded specimens from the buttons in sniall individual Vycor reaction tubes, which rvere then attached to a calibrated vacuum system containing a McLeod gage. One specimen a t a time was then hrated by induction to a dull red heat to remove a n y hydrogen contained in the material. This usually required about 15 minutes. .4measured quantity of oxygen was then introduced into the reaction system. Heating \\a5 continued until the oxygen had entirely reacted. The reactcd sample was then cooled and the cycle started for the next sample. Because, these standards n ere to be analyzed in their entirety and as prepared, no attempt was made to diffuse oxygen into the sample to make it homogeneous. IXQOTS WITH GASEOUS OXYGEN ADDITIONS. Thirty-gram samples of electrorefined titanium n-ere placed in a Vycor reaction tube attached to a vacuum system containing a 50-ml. gas buret. The material n a s degassed at 700’ C. for 1 hour. Oxygen n-as then added to the reaction tube and the material Fvab heated until all the gas \yas absorbed. The material was subsequently arc-melted three times in a water-cooled copper crucible in an argon atmosphere using a tungsten electrode. INGOTS WITH OXIDE POWDER ADUITIONS. Standards were prepared by placing weighed additions of dry titanium dioxide in drilled holes in “asdeposited” iodide titanium rods. The holes viere plugged with iodide titanium and the rods were arc-melted ah dcscribed a b o w . ANALYTICAL PROCEDURES A N D RESULTS
Dry-Crucible Technique. The drycrucible technique used as a reference standard was essentially that described by Walter (10). REPRODUCIBILITY AND ACCURACY. The reproducibility of results obtained for unalloyed titanium by the drycrucible technique was determined in two ways. I n one, commercially pure A-70 titanium rod was analyzed. Seven VOL. 31, NO.
7,JULY 1959
1237
Table I. Analyses of Watertown Arsenal Cooperative Titanium Samples b y Vacuum Fusion Using Platinum-Flux and Dry-Crucible Techniques
Oxygen, 11%. %, Results and Deviation Average Dry crucible Platinum flus 0.152 0.135 0.145 0.132 0.146 0.143 0.127 0.109 Av. 0.142 f 0.008 0.130 f 0.010 0.114 0.108 0.121 0.118
Painple
Code WA-10-DA -TB -GC -DD
Alloy Unalloyed
\VA-58-&1 -F2
Ti-8Mn
-A3
0.108
-H4 Av. WA-62-GE -AF -SG
Ti-2Fe-2Cr-2Mo
WA-69-PP
Ti-5A1-2.5Sn
-“ Av.
-nQ -RR -1)s
Av. WA-70-DJ
.
Ti-6A1-4V
Av. pie shaped samples were cut at equal intervals along a &inch length of the rod. Four of the samples were taken from the “top” and three from the “bottom” of the rod. Results of seven analyses made in two runs ranged from 0.155 t o 0.170 weight %. The average value was 0.162 weight yo with a mean deviation of zt0.005, showing that reproducibilitv is good and that the rod was homogeneous. The reproducibility of results was also studied with an unalloyed titanium sample WA-10 (see Table I) of the Watertown Arsenal cooperative study. The results of four analyses which ’ showed good average 0.130 weight % reproducibility with a n average deviation of iO.010 weight %. This result compares favorably with the 0.143 weight yo obtained by the 17 laboratories participating in the Watertown study. ,4nalyses of four alloys used in the same study appear in Table I. The results are in good agreement n-ith the best values obtained by the 17 laboratories cooperating in the Watertown Arsenal program.
Battelle Results, Oxygen,
wt . 7%
Alloy Ti-8hln Ti-2Fe-2Cr-2LTo Ti-5A41-2.5Sn Ti-6A1-4V 1238
Best Results, Cooperative Program Oxygen, wt .
0 115 f 0 010 0,198 f 0 002 0.155 zt 0 010 0 111 i
0.007
ANALYTICAL CHEMISTRY
%
0 103 0 195
0 166 0 112
0.098 0.110 f 0.008 0.199 0.188 0.102 0.213 0.198 ==! 0.008 0.179 0.185 0.184 0.180 0.184 i 0.003 0.126 0.122 0.122 0.122 0.123 f 0.001
0.132 0.102
0.115 & 0.010 0.196 0.196 0.199 0.201 0.198 f 0.002 0.174 0.154
0.157 0.136 0.155 f 0.010
0.101 0.109
0.109 0.126 0.111
&
0.007
The reproducibility of the Battelle results, based on four analyses of each allov, is within 10 relative %. The reproducibility of the drycrucible technique having been established, the accuracy of the technique was then studied. Results obtained on four unalloyed titanium standards (0.3 weight % oxygen) prepared individually by gaseous additions showed a n average oxygen recovery of 94%. Three Ti6A1-4V standards prepared in the same manner as the unaIloyed standards gave oxygen recoveries from 92 to 95%. Platinum-Bath Technique. The investigation of platinum-bath techniques Kas begun with a 25-gram platinum bath containing a 2-gram addition of iron. Oxygen recovery from t h e A-70 titanium rod previously described was 92 t o 94% of t h a t extracted by t h e dry-crucible technique. These results were considered reasonably satisfactory. Another run was made under t h e same conditions, except that no iron was added. Erratic results were obtained for five samples. The oxygen recovery ranged from 80 to 100% with most of the results showing less than 90% recovery. Hence it seemed that iron was a necessary addition for obtaining satisfactory results. However, five more samples analyzed in t n o runs made with iron additions also gave inconsistent results. This is in contrast to the results of Rennett and Covington ( 2 ) , who report “no erratic results” when analyzing titanium alloys in a platinum bath.
However, the)- also state, “At tiinw, the bath does not properly condition and low results are obtained.” Khen it was recognized that results were running 1011, they rectified the condition of the bath to permit its continued use. I n an attcnipt to eliminate the erratic behavior of the bath technique, sevcral runs were made in which bath temperatures from 1950” to 2100” C. mere uscd. Runs were made both with and without a crucible lid. I n all cases, inconsistent results n cre obtained. This suggested that the melting procedure should be reviened in some detail. Therefore, a platinum bath was prepared in a graphite crucible and degassed for 6 hours at 1950” C. hletallographic CYamination of the resultant ingot shown in Figure 1 revealed that a heavy concentration of large graphite flakes had formed in the melt. Similar platinum melts made for shorter times contained fewer and smaller flakes. Other melts were made of platinum ’ titanium. containing 2 to 7 weight % ’I’heii inqots sho\\etl a similar layer of graphitc flakcx S o precipitate of titanium carbide n as observed. Recause of the grcat density difference betn w n titanium and platinum, it seemed that titanium, dropped into the platinum bath, iriirht in some instances merely float on graphite flakes. Such samples rould then fuse to the graphit(, crucible, forming a titanium cinder wch as that indicated by the findings of Kroll and Schlechton ( 6 ) . To eliminate this possibility, a mwns W R S sought to assure that the sample came in contact with platinum only. This n.as accomplished by nrapping the sample in platinum before introducing it into the bath. It was hypothesized that such an aggregate nould fvse. forming a fluid mass from n hich the gas content could be readily eutractrd. This would happen whether the sample and wrapping lodged on top of a melt or was submerged. Twelve samples of the -4-70 unalloyed titanium rod neie wrapped in about five to nine times their weight of platinum and dropped into B 25-gram platinum bath a t 1850” C. The results were consistent, giving a n average recovery of 0.161 =k 0.005 weight % oxygen. If the average oxygen recovery described above for the drycrucible technique. 0.162 weight yo is taken as a standard, the results in Table I1 show that betwecn 93 and 107% oxygen was recovered. The average oxygen recovery \vas 100%. It seemed desirable for economic reasons to keep the size of the initial platinum bath at a minimum. Therefore, experiments using different bath sizes were started. Two runs composing a total of 14 samples nere made with no initial bath. Results of analyses were considerably more erratic than
.
Figure 2. Cross section of p l a t i n u m flux ingot melted in grophite for 8 hours a t 1850" C.
Figurz 1 . Cross section of platinum melted in grophite crucible for 6 hours at 1950" C.
Fiye times mognifled
Seven timer magnifled
those obtained using a bath. The per cent oxygen recovery ranged from 51 to 121. Without the two extreme values, the range is from 82 to 110% with a n average of 9SY0. It seems possible that hotb extremes may have resulted from errom in tcchnique. Disregarding the two extremes, the values are not as consistent as those obtained using a n initial bath, but were sufficiently promising to warrant further investigation of this technique. I n the early runs the ratio of platinum t o titanium was not held constant. It seemed likely that there is a minimum ratio of platinum to titanium which must be exceeded t o secure reliable results. Another set of analyses in which the ratio of the platinum flux wrapper t o the titanium sample was kept at 8 t o 1 by weight was made on A-70 unalloyed titanium. Results on 14 samples were consistent, showing a n average oxygen value of 0.156 0.008 weight %. Again, if the drycrucible results are taken as standard, the oxygen recovery ranged from 83 t o 105%. Furthermore, only one value fell below 90%. Because the initial presence of a bath was found unnecessary when enough flux was added with the sample, further runs were made without a bath. For convenience, this modified technique was termed platinum flux. This is consistent with prior usage of "flux" by vacuum-fusion analysts to designate any metal added t o the crucible simultaneously with a sample to promote fusion. A flux preestablished in the crucible is, of course, II bath. Whenever a titanium sample wrapped in platinum was melted, a brilliant flash occurred and the newly fused material momentarily became much hotter than the cmcihle. This phenomenon was construed to be the result of a n ex+ thermic reaction. A flash was not observed in experiments with hare samples dropped into a platinum bath. However, Smiley (5') reports a flash
*
occurring with the first sample dropped into a platinum bath. The consistent results obtained u?th the platinum flux may be related to the occurrence of the exothermic flash. A residue ingot from a platinum flux melt was examined metallographically. Figure 2, a photomicrograph of this ingot, shows a uniform structure in which there is no concentration of graphite flakes. The good fluidity of the melt is evidenced by creepage of metal u p the crucible walls. Platinum-Flux Technique. Samples weighing approximately 0.25 gram are cut with a hacksaw from t h e material t o be analyzed, abraded with a clean degreased file, and weighed. After weighing, samples are wrapped in at least eight times their weight of platinum and placed in t h e loading a r m of the vkcuum-fusion :I"1111**-. >> *"
The crucible assembly, which consists
of a eraohite meltine rmcihle. R u a n h i t r
heater .crucible, 200-mesh graphite powder (for insulation), and a quarts thimble suspended by platinum wires, is ~
degassed at about 2350" C . for 1 to 1.5 hours. A 30-minute furnace blank at the operating temperature, 1850" C . is collected and annlyzed. Analysis is then started. This consists of dropping the samples wrapped in platinum into the crucible and collecting the evolved gas. The extraction is carried out for 30 minutes. However, blank rate, indicating complete extraction, is often obtained within 20 minutes. The 30-minute blank for the apparatus used in this study is 0,020 to 0.030 ml. (STP). The blank composition is usually about 65% carbon monoxide, 20% hydrogen, and 15% nitrogen. Based on a 0.25-gram sample and a 0.030 ml. total blank, the blank correction for oxygen is equivalent to 40 p.p.m. by weight. An additional correction for the oxygen contained in the platinum (2 grams) amounts t o only 1.2 p.p.m. .. R~~~~~~~~~~~~~~ and Accuracy of Technique. Obtained t h e above technique for a continuous series of analyses made under conditions comparable t o a two-shift operation are given in
Table 11.
Oxygen Results Obtained on A-70 Titanium Using Platinum-Flux Technique and a 25-Gram Bath" Recovery, Sample Oxygen, w. % 7' Based on Weight, Deviation Dry-Crucible, from aversee( A"eraee Sampleb Gram Analysis " 0.252 0.173 +0.012 107 0.257 0.163 101 +0.002 0.255 0.157 -0.004 97 0.229 0.157 -0.004 07 0.223 0.167 +0.000 103 0.271 0.159 -0.002 98 7 0.246 0.164 +0.003 101 8 0.174 0.168 +0.007 104 0.176 10 9 0.162 +0.001 100 0.150 0.261 -0.011 93 11 0.284 0.159 -0.002 98 12 0.264 0.158 -0.OOR OR .. Av. 0.161 =t0.005 100 Analytical specimens wrapped in 1.5 grams of platinum. Samples listed in order analyzed. First six samples were analyzed one day and the next six, another day. Based on average value obtained for analyses listed. ~~
VOL. 31, NO. 7, JULY 1959
1239
Extensive Series of Consecutive Analyses of A - 7 0 Titanium b y the Platinum-Flux Technique
Table 111.
Sample I >
-
3 4 5
-
6
b
9 10 11 12 13 14 15
16 17 18 19 20 21 22 23 24 25
Sample Weight, Gram 0.266 0.288 0.263 0.274 0.216 0.235 0.280 0,294 0.290 0.286 0.223 0.280 0,287 0.254 0.278 0.242 0.172 0.184 0.163
0.271 0,202 0.153 0.216 0.193 0.287
Oxygen, R't.
-
Analysis Hours 0 to l i b 0.165 0.162 0.162 0.160 0.169 0.169 0.166 0.165 0.170
Recovery,
yoBased on
70
Deviation from averagea
Dry-Crucible Average
$0.002
-0.001
102 100 100 99 104 104 102 102 105 98 101 96 99 100
$0.006
95 104
+0.005
104 104
-0.001
-0.002 -0.003
$0.006 $ 0 . 006
+$0.003 0,002 $0.008
-0.004 0.000 -0.008
0.159
0.163 0.155 0.160 0.162 0.153 0.169 0.178
-0.003
-0.010
$0.015
Hours 24 to 32b 0.168 0.168 0.159 0.153 0.172 0.163 0.164 0.160
$0.005 -0.004 +0.010 +0.009
0.000
$0.001 -0.003
110
98 95 106 101 101 99
Hours 48 to 53 -0.006 97 0.157 -0.008 96 0.155 -0.004 99 0.160 -0.004 98 0.159 102 $0.003 0.166 101 Av. 0.163 =to.005 a Deviation based on average value obtained for analysis. * At this point the crucible was cooled to room temperature for several hours, then reheated to resume analysis. 26 27 28 29 30
0.293 0.264 0.332 0.264 0,252
Table 111. Also listed are values obtained for t h e continuation of this qeries with intermittent cooling of the crucible t o room temperature \\-ithout breaking t h e vacuum. Again t h e results were consistent. The xverage analytical value for oxygen \\as 0.163 =t 0.005 neight % based on determinations. Oxygen recovery 1 based on dry-crucible results as stand:ird) ranged from 95 to 110%. These analytical values reflect the result of cqerience rvith the method and are :{bout 4% higher and somewhat more c-onsistent than the earlier results of 0.156 =t0.008 weight % found for 14 .amplee. During the initial part of the iun, 17 samples r e r e analyzed in 17 hours. After cooling for 8 hours, the i.rucible was reheated and eight more zamples n'ere analyzed. The crucible \vas then cooled for 16 hours and the last of the samples nhich had been loaded nere analyzed. It is significant that no trend in results over the duration of the run is apparent. The last sample, the 30th in the crucible, gave a n oxygen recovery of 10270. It seems likely that several more samples could have bern analyzed in this same series.
1240
ANALYTICAL CHEMISTRY
Results by the platinum-flux technique on other unalloyed titanium specimens, Tl'aterton-n -irsenal cooperative material ITA-IO, shoiv an average oxygen content of 0.142 + 0.008 weight %. Because the platinum-flux technique looked satisfactory for unalloyed titanium, it was next, tried for some of its alloys. The reproducibility obtained for Ti-8lln, Ti-2Fe-2Cr-2AI0, Ti-5Al2.5Sn, and Ti-6.U-41' is shown in Table I. The average oxygen values were 0.110 i 0.008, 0.198 + 0.008, 0.184 i 0.003, and 0.123 i 0.001 weight %, respectively. As in the case of the drycrucible results, the values obtained by platinum flux agreed with the best value obtained by the cooperating laboratories within 10 relative Yo. It is perhaps significant that in this series of analyses platinum-flux results were considerably higher than dry-crucible values for alloys of Ti-5A1-2.5Sn and Ti-6A1-41'. The method was reproducible for both unalloyed and alloyed titanium; hence attention was next turned to the analysis of standard samples prepared by three different techniques. I n Table IV
results are listed for standards priyimd by making gaseous additions to individual analytical speciniens. T h r first eight standards were prepared to contain approximately 0.17 weight % ' of oxygen. The last 10, contain about 0.30 weight % of oxygen. The oxygrn recovery ranged from 87 to 112% with a n average of 97%. Other analyses were made of standards prepared by making gaseous additions of oxvgen to 30-gram lots of titanium and with subsequent arc melting of the material. Again. two levels of oxygen are represented. One level mas approximately 0.08 weight %. The analysis of two samples a t this level yieldrd oxygen recoveries of 102 and 105%. At the other level. about 0.50 weight %. oxygen recoveries of 96 and 97% were obtained. Also, ox) gen standards prepared by adding titanium dioxide to iodidc titanium and then arc melting the coniposite specimens r e r e analyzed. Standards were prepared a t tlvo levels, about 0.12 and 0.19 weight %. For t n o samples a t the 0.12 weight % oxygen level, the oxygen recovery TI as 98Y0 in both cases. At the 0.19 M eight 06 oxygen level, two analyses yielded recoveries of 106 and 107%. Next, the accuracy of the platinumflux technique for one alloy, Ti-6.41-4Y was checked. Standard samples were prepared by making gaseous additions of oxygen to individual specimens. The oxygen levels were about 0.10 and 0.20 weight At the 0.10% oxygen level, t n o analyses yielded oxygen recoveries of 89 and 97%. ilt the 0.20% oxygen level, three standards yielded recoveries of 85, 94, and 99%. The over-all average oxygen recovery was 93%
x.
DISCUSSION O F PLATINUM-FLUX TECHNIQUE
The platinum-flux technique iiiggested by Smiley ( 8 ) and developed in this work offers a number of advantages over techniqucs using the dry-crucible, iron bath, arid platinum bath. Among these arc the tlimination ot the followiny, Pome of which are ritwssary for analysis by each of these other methods: use of graphite chiys, use of crucible lid, preconditioning of a metal bath, preconditioning of crucible and graphite chips with tin, and loss of time changing furnace temperature and making supplementary addition- to the crucible Slightly less than one hour per analysis is required with the platinuniflux technique, including a proportionate amount of the degassing time. The crucible may be cooled, reheated, and the analysis resumed without breaking the vacuiini. The reproducibility of values obtained by this technique appears to be exceptionally good. The results agree much better than the 10
relative yo usually obtained by the vacuum-fusion techniques. Also, the technique has been shown t o be accurate. Another factor of importance in evaluating the technique is the decreased cost of analysis. The cost per analysis (in this laboratory) by the platinum-flus technique is about 40% of that by the other vacuum-fusion tcrhniques.
Table IV.
Platinum-Flux Analysis of Unalloyed Titanium Standard Samples
Sample“ 1 2
3 4 5 6 7
8 9
LITERATURE CITED
( I ) Albrecht, TI7. M., Mallett, M. W., ANAL.CHEM. 26, 401 (1954).
(2) Bennett, S. J., Covington, L. C., Zbzd., 30, 363 (1958). (3) Derge, G., J . Metals 1, No. 10, 31 (1949). (4) Gregory, J. N., Mapper, D., Analyst 80. 230 (1955\. -~ (5) Hansen, W. R., Mallett, hl. W., Trzeciak, M. J., TML Rept. 89, Titanium Metallurgical Labbratory, Battelle Memorial Institute, Columbus, Ohio, Dee. 6, 1957. 161 Kroll. W. .J.. Schlerhton. A . W.. J . Electroihem. Sic. 93, 247 (1948). ( 7 ) Mallett, M. IT.,Griffith, C. B., Trans. A m . Sac. Metals 46, 375 (1954). (8) Smiley, W. G., ANAL. CmM. 27, 1098 (1955). (9) U. S. rlir Force Soecification Bull. 108A (May 6, 1955) ?superseding KO.
10
11 12 13 14 15 16
\
a
Sample Weight, Gram 0.245 0.238 0,187 0.257 0.268 0.212 0.214 0,278 0 234
0,228 0.219 0.197 0.231
Gaseous addition 0.143 0.143 0 145 0 139 0 141 0.142 0.140 0.156 0 297 0 294 0 280 0 303 0 290 0.29% 0 303 0 277 0.307
Oxygen, K t . % Estimated total ;inalysis 0 171 0 152 0 191 0 171 0 176 0 173 0 167 0 161 0.169 0 166 0 170 0 179 0 168 0 165 0 184 0 li,? 0 31J 0 324 0 321 0 278 0.30; 0 307 0 330 0 316 0 294 0.321
Oxygen Recovery,
%
89 112 102 97
98
105 98 95 97 87 100
96
93 99 0 330 0 309 93 0 324 0.296 $1I 0.189 17 0 334 0.196 0.315 91 18 0.250 0.283 0 310 0.301 97 Av. 97 Base material analyzed 0.028 weight 9c oxygen for samples 1 through 8, 0.027 for
0 . 177 0 196
samples 9 through 18.
108, Aug. 9, 1954), “Quality Requirements for Wrought Titanium and Titanium Alloys.” (10) Walter, D. I., ANAL. CHEw 22, 297 (1950).
!11) Wilkins, D. H., Fleischer, J. F., -4nal. Chim. Acta 15, 334 (1956).
RECEIVEDfor review July Accepted February 5, 1959.
14, 1958.
Rapid Colorimetric Method for Determining Glyoxal C. S. WISE, C. L. MEHLTRETTER, and J. W. VAN CLEVE Northern Utilization Research and Development Division, Agricultural Research Service,
F A rapid and selective spectrophotometric method for determining glyoxal in the presence of reducing sugars has been developed for use in studies on the production of glyoxal b y the hydrolysis of periodate-oxdized starch. The method i s an extension of the work of Wanzlick and Lochel, who showed that 1 , I ’-3,3’-tetraphenyl-2,2’biimidazolidine, formed by reaction of glyoxal with dianilinoethane, produces a blue color upon heating with hydrochloric acid. A small aliquot containing about 1.2 mg. of glyoxal i s heated for 30 minutes with an alcoholic acid solution of dianilinoethane. After dilution to 100 ml. the absorbance is measured at 550 mp and is constant for at least 2 days. Formaldehyde, acetaldehyde, glucose, and erythrose d o not interfere.
I
of the acid hydrolysis of periodate-oxidized starch, it was necessary to determine the amount of glyoxal produced as the reaction neared completion. A more facile colorimetric procedure was desired than the method of Dechary, Kun, and Pitot (Z), which utilizes 2,3-diaminophenazine and N A STUDY
requires several subsequent reactions to eliminate the effect of excps? reagent. Other methods for the quantitative estimation of glyoxal were either too time-consuming or not suited for use in an aqueous system containing reducing sugars (1, 3-5, 7 ) . *4 comparatively selective color reaction between glyoxal and 1,2-dianilinoethane in acid solution was described by Kanzlick and Lochel (8). The rolor produced by reaction with mineral acid of the intermediate l.l’-3,3’-tetrapheny1-2,2’-biimidazolidineformed by condensation of the above reagents was extremely sensitive to glyoxal concentration. The niethod was unaffected by reducing sugars and appearcd adequate for the quantitative detcrmination of glyoxal in solutions of highly hydrolyzed periodate ouystarch. The presence of a considtmlile quantity of unhydrolyzed ouystzrch interfered, through production of glyoxal during color formation n ith the acid rcagcnt. The method appears. lion-rwr. to be generally applicable for the a n a l ~ s i sof glyoxal in aqueous solutions. Thc reaction conditions of Wanzlick and Lochel were modified t o achieve optimum color development by increasing
U. S. Department o f Agriculture,
Peoria, Ill.
the ratio of dianilinoethane t o glJ-osal and conducting the reaction of 77” C. in an ethyl alcohol solution, under controlled acidity for a limited time. Absorbance was measured a t 550 mp and found to be constant for a t least 2 days. Formaldehyde, acetaldehyde, glucose, and erythrose did not interfere with the color reaction. APPARATUS AND REAGENTS
SPECTROPHOTOMETER, Colenian Junior Model 6ii, or similar anparatus. BOROSILICATE GLASSTUBES,18 X 150 mm., selected for uniformity in spectrophotometric meusurements. 1,2-DIANILINOETHANE DIHYDRCCHLO RIDE reagent (8). A stock solution was prepared by dissolving 1.3333 grams in 100 ml. of 9570 ethyl alcohol. ST.4NDARD SoLCTION O F GLYOXAL. A stock solution x i s made by weighing 0.1895 gram of the pure, crystalline monohydrate of glyoxal-sodium bisulfite (6) and diluting to 100 ml. with water. A 3-ml. aliiuot contains 1.161 mg. of glyoxal (0.02 mmole). PROCEDURE
Place in a test tube a 3-ml. aliquot of the unknonn gl\-oxal solution con. taining approximately 1.2 mg. of glyoxal. VOL. 31, NO. 7, JULY 1959
1241
