are matched thermistors, 8000-ohm nominal, maintained at 10 volts in connection with a conventional 0 to 1 mv. stripchart recorder. The helium carrier gas is adjusted to inlet pressures near 15 p.s.i. t,o give a flow rate of 35 ml. er minute as measured by a bureb-soap ubble meter. Test temperatures are: injection block, 310’ c.;column, 240’ c. Other conditions, such as sample handling and blending, are as previously described (9,4).
(2) Ibid., Appendix I, p. 1076,1958.
ACKNOWLEDGMENT
The authors express appreciation to K. E. Thompson for help in develop ment of the method.
E
LITERATURE CITED
(3) Porter, R. S., Johnson, J. F., ANAL. CHEM, J1, 866 (1959). (4) Porter, R. S., Johnson, J. F., Petrol. Refiner 39, No.6,193(19130).
ROGERS. PORTER JULIAN F. JOHNSON California Research Corp. Richmond, Calif.
sot. Testing ~ ~ b ~pmec i ~ h ,
(1)
delphia, Pa., “ASTM Standards on Petroleum Produc&,” P. 170, Method D 322-58T, 1959.
A Spectrophotometric Determination of Rhenium SIR: In studies concerning rhenium in this laboratory, it was necessary to determine rhenium concentrations in standard solutions. Many of the known methods for the colorimetric determination of ihenium require special procedures such as solvent extraction to stabilize the color (1,6,7,9), A quick and reliable method was sought which would not involve any of these special procedures. The basis of the colorimetric procedure described below was the qualitative scheme involving 1henium and several chemically similar elements recently reported by Fadhil, Magee, and Wilson (4). Rhenium was identified by the orange color produced on treating perrhenate ion with dimethylglyoxime(DMG) and stannous chloridehydrochloric acid solutions.
adjusted to 10 ml. The absorbance of the deep orange-colored solution was measured immediately, and then at time intervals of 25 minutes, 2 houm, and 49.5 hours after preparation. The results shown in Figure 1 demonstrate that the color is stable for at least 2 hours after preparation, which precludes the use of solvent extraction for stabilization. To several solutions, each c o n t a e g
153 p.p.m. of Re per ml., v a r q g
amounts of concentrated hydroch 0110 acid were added, a n d , the color WBB developed as described previously. Absorbance meaaurements were made at 620mp after 30 minutes had elapsed. The p H dependence of the color is illustrated by the results given in Table
APPARATUS A N D REAGENTS
-
21
A Leite-Photrometer (No. 21942) waa used for the absorbance measurements and l-cm. square quartz cells were employed to contain the solution. The solutions used were: aqueous solution of potassium perrhenate, ethyl alcohol saturated with DMG, and a 2 M solution of stannous chloride in 10M hydrochloric acid.
20-
EXPERIMENTAL
13-
Stability of the orange color was investigated in the following manner: One milliliter of DMG solution was added to a perrhenate solution (766.5 p.p.m. of Re) in a 10-ml. volumetric ftask, followed by 0.5 ml. of stannous chloride solution, and the volume waa
19-
2 min. allar preparation 25 min. ofler prenaration
18-
2 hr. after preparation 49 S hr. alter preparation
16-
1 5 1 4 -
2:1 1 -
1 2 -
I O -
09-
06-
Table 1.
pH Dependence
Absorbance Color PH 0.302 1.620 Orange -0.230 1.409 Orange with green hue -0.462 0.883 Orange with green -0.612 -0.724
-0.886 -1.004 1130
tint
0.568 0.310 0.154 0.102
Orange-green Green with orange
0 5 04-
030201
0
I
400
tint
Yellow-green Light green
ANALYTICAL CHEMISTRY
460
I
520
I
580
I
I
640
mP
Figure 1. with time
Several standard solutions of rhenium were prepared and the orange color was develo ed by adding 1 ml. of DMG and 0.5 of stannous chloride solutions, and adjusting the volume to 10 ml. After standing for 30 minutes, the absorption waa measured at 520 mp. To test the validity and reproducibility of this method, two sets of standard samples of varying rhenium concentrations were prepared and the absorbance waa measured after the orange color had been developed in each one.
mf
The results are summarized in Table
1 7 -
2
I. The pH of the first sample, which had no exceea acid, is on an approximate plateau and thus is at what would be considered an optimum pH. An even higher p H would be desirable, but solutions of stannous chloride must have 5 certain acid concentration to prevent hydrolysis.
Variation of absorbance
I1 and Figure 2. The average error was 5%. Above 260 pap.m.of rhenium, because of the extremely dark orange coloration, i t waa very difficult to read the Photrometer absorbance scale accurately. Below 1 p.p.m. of rhenium, a white precipitate formed and anomalous results occurred. Decreasing the DMG or stannous chloride concentrations did not alleviate this trouble. Although interfering ions were not present in the solutions meaaured, some work was performed in this area with the idea that this method could be developed into a general procedure in the future. Copper does not interfere even
Table II. Percentage Error P.P.M. Re Added % Error 1.012 8.4 6.11 13.7 20.44 7.0 30.44 1.8 51.1 2.0 3.5 75.65 1.2 102 2 127.75 6.5 204.4 4.6 204.4 2.1 I
in concentrations of 100 p.p.m., while platinum, molybdcnurn, and ruthenium interfere if present in excess of about 2 p.p.m. However, the interference by molybdenum may be removed by heating slightly, whereas the rhenium color is stable to heat. Rimshaw (IO) has pointed out that a number of heavy metals such as iron form highly colored complexes with DMG (6),but that these heavy metals can be readily separated from rhenium by precipitation as hydroxides. It is also possible to separate rhenium from many elements by using ion exchange techniques (2) or distillation methods (3).
0 -Triol
I
A
n m
-Triol
0 -TmI
- Pomlr
used I o draw slondwd
CV~YI
17-
161514-
13-
g'
2pi1 -
210. 090 8 -
0 7 .
DISCUSSION
The fact that Beer's law is not strictly obeyed does not invalidate this method of determining rhenium. Ample evidence of this is provided by Figure 2 and Table 11. The nonlinearity of the curve does raise the question of the nature of the color-producing species. Competition between chloro complexes and DMG complexes of rhenium could possibly be the answer. Magee (8) has suggested that complexes may be formed between DMG and lower valent states of rhenium. Mole ratio plots between DMG and rhenium and chloride and rhenium yielded very high results. This suggests that the manner in which the colored species is produced may be rather complex. Nothing more may be said beyond this because of the lack of experimental evidence. Further work in this area should afford a general method for the determination of rhenium. However, since this procedure provided the
04 0 3 0 2 0
IO
20 30 40 50
too
70 P
Figure 2.
I20
150
255
200
P R~e
Standard absorbance vs. concentration curve
means for determining rhenium in standard solutions and thereby satisfied the purpose of this investigation, no further work in this area is being considered at the present time. LITERATURE CITED
(1) Andrew, T., Gentry, C., Analyst 82, 372 (1957'1. (2)-Boyd, G., Larson, Q., J. Phys. Chem. 60,707 (1960). (3) Broda, E., "Advances in R a d b chemistry," p 94-6, Cambridge Universit Press, g e w York, 1950 (4) FadGI, J., Magee, R., Whon, C., Tulunta.4, 17 (1960). \ - - - - , -
( 5 ) Gurvitch, A,, Zhur. ObshcheZ Khim. 27, 40, 316 (1957); C.A. 51, 13635d, 144635 (1957). (6) Hurd, L., Babler, B., IND. ENQ. CHEM.,ANAL.ED.8, 112 (1936). 17) Lazarev. A.. Zhur. Anal. Khim. 14.' . 362 (1959j; C:A. 54,8459b (1960).' (8) Magee, R., private communication, Feb. 15, 1961. (9) Meloche V., Martin, R., ANAL.CHEM. 28,1671 (1956). (10) Rimshaw. 5.. Drivate communication. . Feb. 21, 190i. I
.
Department of Chemistry University of Arkansae B. T. KENNA Fayetteville, Ark. RESEARCH performed under the auspices of the U. S. Atomic Energy Commission.
p-Anisidine-Phosphoric Acid as a Color Reagent for Sialic Acid Compounds on Paper Chromatograms SIR:Many reagents have been used for the detection of sugars on paper chromatograms (I). A preferred reagent is one which gives different color reactions with different classes of sugars, and p-anisidine meets this desideratum (2)* I n recent years the necessity has arisen to distinguish sialic acid and sialic acid-containing compounds from other sugars on paper chromatograms. Benzidine-trichloroacetic acid in aqueous ethyl alcohol has been recommended for that purpose ( 4 ) . However, panisidine-phosphoric acid (2) has been found to be a more satisfactory reagent
for differentiation of several classes of sugars and polyols, and, in the present research, for distinguishing sialic acidcontaining compounds from other sugars. The paper chromatogram is dipped in a solution of p-anisidine (0.5 gram) and phosphoric acid (3 ml. of 85 to 88%) in methanol (100 ml. of 80% aqueous) (2). The paper is blotted to remove excess reagent and heated for approximately 10 minutes a t 105' to 110' C. Sialic acid and sialic acidcontaining compounds appear slowly, giving purplish-gray spots in about 10 minutes. The color of the spots distinguishes sialic compounds from d l
other sugars tested. The background with this reagent is colored pale yellow. Neutral sugars appear after 1 minute a t 105" to 110" C., aldoses as brown spots and ketoses as yellow spots; polyols appear as white spots in 5 to 10 minutes (S). Amino hexoses give brown spots. I n parallel tests the panisidine reagent has proved to be more sensitive than the benzidine reagent for sialic acid-containing compounds because the background is much lighter and the spots are seen more readily. Sialidolactose and sialic acid prepared from bovine colostrum (4, and 6-a-D-sialyl-N-acetylgalactosamine, NVOL. 33, NO. 8, JULY 1961
o
1131
