F i u o i ~ o ~ ~ a80 l ; (20- to SOrt'. 9 1J.s.i.; hydrogen ; air prcssurc, 26 p.s.1.; f l o ~rate, 3.3 flonmeter (40 nil. y r minutc) : c d u m n teiiipc~ature, 200" C.; injcctiori port tcmpcrature, maximum; power. 100 volts; attenuation, DEG 4> data obtained oil thrw samples of high purity TEG :tnalyzed for DEG by three different c*heniical coriipanies, using a mutually dcvcloped gas chromatographic method.' The method in use ut,ilizes an instrument containing a thermist'or det&or in conjunction with a %-foot 5% Chrbowax 2011 on Fluoropak column. Hcliuin is the carrier gas. Separations
(1) Clifford, J., ;lnalyst 85, KO.7, 475-8
Flame Ionization Method Peak ht . Area n t .
(1960).
14 cm./O.lc&DEG, at 4>< 58 mg./O.l('i DEG, attenuation 1 sq. cm. = 14 mg. Conventional Method 0.9 cm./O.l% IIEG, a t 1 X 2.4 mg./O.l X DEG, attenuation
Peak ht. 4rea w t .
( 2 ) Ginsberg.
Leonard,
CHEM.
SAL.
31. 1822-4 11959).
(8) kadeau, H. 6 , Oaks, I). M., Ibzd., 32, 176WL (1960). ( 4 ) Kisnien-T-ski, D. F., Stalker, G. C., Prtrol. Rejner 40, S o E, 117-20 (1961).
S.inruEL SPENCER HERBERT G. NADEAU Olin Alathieson Chemical Corp. Xew Haven, Conn.
- .. -. r . .. n . -. Activation Analysis ot Iantalum in a Niobium Matrix I
.
SIR: This method was developed an independent check on the results ohtaincd for the determination of small :mounts of Ta in Kb by x-ray fluoresw n c r and emission spectroscopy. The intthod utilizes beta counting of a w n p l e prcpared by evaporating a solution in ;I counting cup. This technique improvcs t h r sensitivity over other activation methods dependent upon counting the gamma activity of solids :I*
(1 3 ) . PROCEDURE
Sample Preparation. Twenty-one samples of Xb205 containing various amounts of Taa05 and one sample of pure T a 2 0 j \\ere carefully packed in individual aluminum containers and iriadiated a t t h e -1rgonne Yational Laboratories. T h e neutron flux 17 as identical for all t h e samples. Previous experiments in t h e pile had indicated t h a t , within experimental error, there was no difference in activity due t o position of the individual sami-les in the pile. After about I0 days, a t a total flux dfnsity of 1.2 X IO1* neutronel w. sq. em., they w r e removed and nlloaed to stand for 4 weeks before work was started, to allow any shortlived activities to decay to a negligible Ievrl. The samplcs aere made up as follows: 1. Six samples of c~~mmercially pure of Nb205 prepared from the same lot of PlTb205 with known amounts of pure Ta2O5added to five of these samples. 2. One sample of pure Tan05used to make the five above samples establiqhed as a standard of 100% Ta205. 3. Four different lots of commercially pure KbL05.
.
I
L .
4. Three samples of one lot of Sbz05 \\ith added Ta2O5,SO,, TiO,, and Fe.
steel sample counting cups. Equal aliquots of the solutions, usually 0.100 nil., were deposited onto the filter paper. The sample was immediately absorbed by filter paper, uniformly dispersing the sample over the entire area. In this manner any corrections due to self-
Since the six samples of SblOs described in (1) were prepared from the same lot of Sb&, each contains the same amount of Ta205 as an initial impurity. Therefore, the intercept obtained by plotting the per cent of added Ta206as a function of activity is a measure of the original TanOB Table 1. Determination of Original To present. Present in Nb206 Counting Sample Preparation. T h e piocedure used for preparation of Sample yo TaaOj Counts/ the counting samples was based upon so. Added ?vIin./Mg. a method described by Ruben (4, 1 0 000 17.3 \\hereby total solids and counting ge2 0 195 45 4 ometry are constant for both known 3 0.292 58.5 4 0 683 114 (standard) and unknon n samples. -5 0.975 141 6 1 .XI0 266 Filter paper disks were cemented t o the bottom of I-inch diameter stainless
Sample so. 0
1 2
3
Table II. Comparison of Methods 1 and 2 Ta&
Sample Description Pure Ta20s Nb206, lot 1 with known amounts of Tal06
added
4
5 6 7 8
9 10 11 12 13
14
High purity Nb205, lot 2 ?;b,O,. lot 3 with added impurities (Ti, Si, Fe, and Ta205) Lots of Nb20schosen a t random
Counts/ lIin./AIg, 13,000 17.3 45.4 58.5
114 141 266 4.8 276 626 1215 95 3 26 8 32 1 277
from Fig. 1 ...
0.140 0.335 0.432 0.823 1.12 2.09 0.038 2.17 4 94 9 0 0 0
61
770 200 294 2 17
9'0 TanOs
Based on Sample 0 100 0.132 0.346 0.445 0.854 1.07 2.12 0.037 2.10
70Dev. from AV.
... 2.94 1.32 1.49 1.85
2.27 1.39 1.33 1.65 1.64 1.86 2.94 0.99 2.32 1.40
4 78
9 26
0 726 0 204 0 308
2 12
VOL. 33, NO. 1 1 , OCTOBER 1961
0
1627
absorption and counting geometry could be neglected. PROCEDURE. The samples weighing from 15 to 45 mg. were dissolved by a bisulfate fusion in porcelain crucibles and leached out with a 4y0 ammonium omlate solution. Additional solids n ere added to the diluted solution to total 0.8 gram per 100 ml. in every case. The samples were diluted in such a manner that counting rates in the range 300 to 10,000 counts per minute i\ere obtained. The counting was accomplished with an end-window Geiger counter.
Table 111.
8 9
10
RESULTS
The results obtained from the six samples of the one lot of commercially pure Nb206containing known amounts of Ta206 are given in Table I. The intercept obtained by the leastsquares method when the per cent of Ti1205 added was plotted against the counts per minute per milligram was 0.14. This value is the per cent Ta2O5 originally present in this lot of Kb20s as a n impurity. Adding this value (0.14%) to the known per cent T a 2 0 5added, another curve may be plotted of the true amount of TazOs as a function of activity. Using this new curve, all the other samples could be analyzed for the amount of Ta205. Figure 1 is a plot of these values and
0
I00
200
300
400
500
600
700
COUNTS/ MINUTE/ MILLIGRAM
Figure 1.
Impurities added to Samples 8, 9,and 10
0 20 0 50 1 00
0 50
5 00 10 00
0 25 0 50 1 00
dicate that the added elements do not interfere in the analysis. The good agreement between the tvio values obtained by independent methods leads to the conclusion that the results are fairly valid. The precision of values for the two or three samples made for each lot was also good, with a deviation from the average around 2%.
Tantalum found by Method 1
LITERATURE CITED
(1) Eicholz, C. G., Nucleonics
10, 58
(1952).
was used as one method of obtaining the amount of Taz06 present in the other samples analyzed. The second method employed was more direct. It consisted of measuring the activity of the pure Ta20j, assuming it to be 100% Ta205,and then comparing it to the activities of all the NblOj samples. A comparison of these two methods is found in Table TI. The results reported in Table I1 in-
12) . , Kohn. Andre, C o m p t . r a d . 236, 1419
(1953). ' (3) Long, J. V. P., Snalyst 76, 644 (1951). (4) Ruben, S., Hussid, U. Z., Kanen, AI. D., J . Am. Chem. Soc. 61, 661 (1939). GILBERT HALVERSOS' A L B E R T SHTASEL
Research Division Fansteel Metallurgical Corp. North Chicago, Ill. 1 Present address, Radiation Research Corp., West Palm Beach, Fla.
P-2-Thienyl-DL-alanine, Internal Standard for Automatic Determination of Amino Acids Frank
L.
Siege1 and M a r y K. Roach, Clayton Foundation Biochemical Institute, University of Texas, Austin, Tex.
automatic determination of amino T acids as described by Spackman, HE
Stein, and Moore (1) employs ninhydrin as the color-developing reagent. Ninhydrin reagent is stored in a dark bottle, under nitrogen, since this material is .susceptible t o osidation. A small leak in the system can markedly decrease the color yield of the ninhydrin reaction, with commensurate loss of analytical accuracy. Small losses in color yield may go undetected while valuable machine time is lost. The use of a n internal standard seemed indicated, and several compounds were screened for this purpose. Ideally, the standard should not be naturally occurring, should occupy a unique position on the amino acid elution pattern, should be recovered quantitatively from the column, and 1628
ANALYTICAL CHEMISTRY
should be of use on both the 150-cm. and 50-cm. columns of the instrument. -4 compound which is almost ideal by these criteria is P-%thienyl-~~alanine (Nutritional Biochemicals Corp., Cleveland, Ohio) ; this compound is now used routinely as an internal rtandFor both ard i n this laboratory. 30"-50" and 50" analyses on the 15O-cm. column p-%thienyl-~~-alanine emerges between leucine and tyrosine. On the 50-em. column analysis it emerges before the combined tyrosinephenylalanine peak. T o date the only compound we have found to overlap this standard is 3,4-dihydro~yphenylalanine (DOPA4); p-alanine and norleucine do not interfere. I n urine and in liver extracts there is a compound which emerges with P-2-thieriyl-u~-alanine and prei ents it
