(Table I) show that strontium, niagnesium, cadmium, cerium(IV), silver, lead, bismuth, zirconium, neodymium, duminum, and thallium cause no interference even when the ratio of the foreign metal to tungsten is 30 to 1; ~iotassiumcauses no interference at a ratio of 500 t.o 1 . Molybdenum, titanium, iron, vanadium, and ruthenium iriterfere for weight ratios as low as 1 to I ; arsenic, cerium(III), nickel, and chromium(II1) and (VI) interfere a t ratios of 5 to 1 or greater; copper, t.in, :ind manganese(VI1) inkrfere for ratios of 10 to 1 or greater; and tantalum, nianganese(II), mercury, zinc, and c4obalt interfere when the ratio is 30 t o 1 or greater. The interference of wine of the metals was caused by the formation of precipitates and was erratic as shown in Table I. The most serious interference was caused by molybdenum. chromium, titanium, vanadium, and ruthenium. However, because the alloy samples analyzed by this method were of high purity. no attempt was made to eliminate the interference causcd by any foreign metal. Reliability. Because no standard samples of tungsten-tantalum-uranium alloys are awilable, the reliability of the method is based upon analyses of known solutions and upon a comparison of the analytical results for samples obtained by this color methodand by t h e gravimetric method ( 2 ) . An average for the tungsten found in 14 solutions of known concentration cmntaining 50 to 150 y of tungsten and wrious amounts of uranium and tantalum was 99.8%, with a standard c!vviation of 1.1% (Table 11). The results for eight unknown alloy simples analyzed by the two methods
are shown in Table 111. The average of the differences between the results obtained by the two methods was 0.02% absolute, or 4y0 relative. No bias between the methods is shown. Although several metals interfere with the direct colorimetric method for tungsten, the simplicity of the proTable 11.
Tungsten, Mg. 0.100 0,100 0.100 0.100 0 100 0.100 0 . 100 0.150 0.050 0.100 0.150 0.050 0.100 0.150
Effect of Foreign Metals on Color Reaction
Tantalum, Mg.
TungUranium, sten Mg. Found, Q/o 99.8 100.0 99.8 100.5 100.0
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
12.5
12 . .i
~~
25.0 25.0 25.0 50.0 50.0 50.0 Av . Av. dev. Std. dev.
99.8 59.8 100.0 56.0 100.4 100.4 100.0
100.4 100.1 99.8 0.5 1 1
Table ’”’ Analytical
for Uranium-Tantalum-Tungsten Alloys
Tungsten Found, % ColoriGraviSample metric metric 1 0.44 0.42 9 0 50 0.50 0.44 3 0 48 0.48 4 0.49 0.52 5 0.51 0.45 6 0.51 0.50 7 0.52 8 0.57 0 51
Diff., yo
0.02
-
0.00
0.04 0.01 0.01 0.02
0.02
0 06
Av. 0.02
cedure permits rapid analyses with highly reproducible results. A single sample may be dissolved and analyzed in about 2 hours, but 10 or 12 determinations may be performed simultaneously in 3 or 4 hours. The reproducibilit,y of this method is within 2% for multiplicate determinations of 20 y or more of tungsten. LITERATURE CITED
(1) Allen, S. H., Hamilton, M. B., Anal. Chim. Acta 7, 483 (1952). (2) Bagshawe, B., Elwell, W. T., J . Soc. Chem. Ind. (London) 66, 398 (1947). (3) Bogatski, G., Z . anal. Chem. 114, 170 (1938). (4) Defacgz, E., Compt. rend. 123, 308 (1896). (5) Fernjacic, S., 2. anal. Chem. 97, 332 (1934). (6) Goto, H., Ikeda, S., J . Chem. SOC. Japan, Pure Chem. Sect. 73, 654 (1952). (7) Gullstrom, D. K., hlellon, M. G., ANAL. CHEM. 25, 1809 (1953). (8) Heyne, G., 2. angew. Chem. 44, 237 (1931). (9) Hillebrand, W. F., Lundell, G. E. F., Bright, H. A,, Hoffman, J. I., “Applied Inorganic Analysis,” 2nd ed., p. 689, Wiley, New York, 1953. (10) Johnson, C. M., Iron Age 157, No. 14, 66 (1946). (11) Miller, C. C., Analysf 69, 109 (1944). (12) Nishida, H., Japan Analyst 3, 25 (1954). (13) Sandell, E. B., “Colorimetric Determination of Traces of h/Ietals,” 2nd ed., p. 587, Interscience, New York, 1950. (14) Travers, A,, Compt. rend. 165, 408 (1917). (15) Westwood, W., Mayer, A., Analyst 72, 464 (1947). (16) Wright, E. R., Mellon, M. G., IND. ENO. CHEM., ANAL. ED. 9, 251 (1937). RECEIVEDfor review December 26, 1956. Accepted March 7, 1957.
DifferentiaI Thermal Analysis of Some Polyglucosans HIROKAZU MORITA Chemis?ryDivision, Canada Department of Agriculture, Ottawa, Canada
b Alpha- and P-linked polyglucosans manifest distinct differential thermographic features. The results are offered as a contribution to organic differential thermal analysis.
T
of differential thermal analysis to natural polymers is under active investigation in this laboratory and some results extend and correlate earlier findings. Details pertaining t o the analytical procedure have been reported (11). HE APPLICATION
In the present work, 75-mg. vacuumdried samples were used to prepare the compressed ‘(sandwich” packing. A heating rate of 10” C. per minute was used throughout. Studies (9, IO) with the starch fractions and the dextrans have shown t h a t polysaccharides having predominantly the anhydroglucose linkages give thermograms featured by characteristic endotherms in the 100” t o 310” C. region which are due to dehydration and molecular rearrangements. It is
now shown that other polysaccharides possessing similar linkages give analogous thermograms. Reliable chemical evidence suggests that glycogens are closely related in their general macromolecular outline to starches. Similar conclusions can be inferred from differential thermal analysis. Rabbit liver glycogen (Figure 1, A ) shows endotherms a t 130” and 255’ C. Similar thermographic patterns have been observed with ox liver and northern pike liver glycogens. VOL. 29, NO. 7, JULY 1957
1095
Gumea pig liver glycogen ( B ) ,however, exhibits an exotherm a t 235" C., while hog roundworm glycogen (c)shows an endotherm a t 275" C . I n contrast to the afore-mentioned glycogens, that from Ascaris (D)exhibits an unusually extensive exotherni in the 265' to 625" C. region. The reason for this abnormality is not apparent. The differential thermal behavior of the glycogens is a t variance with methylation and periodate oxidation studiec which show #at all the glycogens used in this work have a repeating unit composed of approximately 12 anhydroglucose residues (2). Two tentative explanations may be offered: The observed differences may be due to the presence of impurities, or, alternatively despite chemical studies, the glycogens are not structurally identical. Of the two, the first seems unlikely, in view of the method used for the isolation of the glycogens (2, 6) and more particularly in view of previous work which showed that trace impurities rarely give pronounced thermographic changes ( I O ) . It seems more probable, therefore, that the differences in the thermograms are associated with structural variations in the glycogens-for example, in the degree of multiple branching or the presence of glycosidic linkages other than l,6 or 1,4 ( I ) . This latter possibility has been encountered with the dextrans (IO). Evidence of structural differences in certain glycogens has been found in amylolysis studies (7) and more recently through the reaction with concanavalin4 (&. The thermographic differences among the glycogens occur a t temperatures where the dominant thermal reaction is transglucosidation (9) involving the hydroxyl groups (3, 6). Of interest too is the suggestion that the glycogen concanavalin-A reaction involves the hydroxyl groups as well as the inner branches of the glycogen molecule (4). Thus, the thermographic changes may, in part, be a reflection of the stereochemistry of transglucosidation. A logical extension of the work reported here would be a more detailed examination of the glycogen and amylopectin series of polysaccharides. Another polysaccharide composed of continuous chains of a-anhydroglucopyranose units is Constantinea jforidean starch, which exhibits thermographic contours (Figure 2,A) reminiscent of starch thermograms. This result is in accord with other chemical and physical evidences (8). The polysaccharides described so far have predominantly the a-anhydroglucose linkages. The corresponding @-linked polymers manifest endothermic reactions a t comparatively higher temperatures. For example, cellulose
1096
ANALYTICAL CHEMISTRY
-
0
I- _100
Figure 1. A. B.
1-
0
L _ _ . 1 L L . - I 300 400 500 600 TEMPERATURE, 'C.
200
100
C. D.
Figure 2.
i
200
360
Hog roundworm glycogen Ascaris glycogen
I
C.
. I
400 500 600 TEMPERATURE. OC
Thermal properties of polyg lucosans A. 8.
700
Thermograms of glycogens
Rabbit liver glycogen Guinea pig liver glycogen
I__-
-2'
CY-
I -
700
.L- .J 800
and /3-linked
Constantinea floridean starch Euglenaceae paramylon Soluble laminarin
with the p-1,4-anhydroglucose linkages gives a thermogram with a sharp endotherm a t 340" C. (9). The Euglenaceae paramylon, a reserve carbohydrate believed to consist of P-1,a-linked glucose radicals (6), displays a thermogram (Figure 2, B ) with a sharp endotherm a t 315" C. On the other hand, laminarin, which is considered to have paramylonlike linkages, gives a thermal curve (C) with endotherms in the 280' t o 295" C. region. Therefore, from thermal analysis alone there seems to be no
obvious relationship between paramylon and laminarin. Similar conclusions have been derived from x-ray data (6). Hygroscopicity is an important characteristic of the polysaccharides, closely related to macromolecular structure (19). The effect of moisture on differential thermographic feature is exemplified most strikingly in the thermograms (Figure 3) obtained from a sample of commercial rice starch. A is a thermogram from a sample vacuum dried a t 100" C., and B that from a sample humidified in air a t 100%
planer spacings and intensities with that of the original A-pattern. As heat treatment a t high temperatures undoubtedly causes molecular rearrangement @), the results observed here demonstrate the limitations occasionally encountered when diffused and often difficultly reproducible x-ray diffraction patterns are used to interpret polymer thermograms. ACKNOWLEDGMENT
The author wishes to thank Fred Smith, W. A. P. Black, and B. J. D. Meeuse for their generous material assistance. LITERATURE CITED
\I/ , 1\/' 100
,
(1) Abdel-Akher, M., Hamilton, J. K.,
,
.
200
,
,
,
500
TEMPERATURE, Figure 3. A. B. C.
D.
.
,
.
40@
300
Montgomery, R., Smith, F., J. Am. Chem. SOC.74,4970 (1952). (2) ~, Abdel-Akher, M.. Smith F., Zbid., 73, 994 (1951). ' (3) Brimhall, B., Znd. Eng. Chem. 36, 72 (1944). (4)
6 3
"C.
Effect of moisture on rice starch thermograms Rice starch vacuum dried Rice starch humidified Rice starch preheated to 130°C. Rice starch preheated to 130'C. and humidifled
relative humidity. Both curves have endothermic peaks a t 130", 275", and 310" C. Humidification alters only the magnitude of the 130" C. endotherm. A sample preheated to 130" C. and then analyzed shows thermogram C with a peak a t 165" C. This peak is shifted t o 115" C. (D)if the sample is first preheated to 130" C. and then humidified. These results suggest that the original 130' C. endotherm is not entirely due to the loss of residual moisture and that the dehydration-
hydration process is not completely reversible. Analogous results have been recorded with other polysaccharides. It is clear from the studies outlined here t h a t differential thermal analysis provides a new means for studying the dehydration-hydration process. I n comparison with other polysaccharides studied (9, IO), the diffused x-ray powder diffraction patterns of the humidified preheated rice starches are nearly identical both in their inter-
(5) (6)
,- - _-, . ( 7 ) Manners, D. J., Ann. Repts. Progr. Chem. (Chem. SOC. London) 50, (1953). (8) Meeuse, B. J. D., Kreger, D. R., Biochim. Biophys. Acta 13, 593 (1954). (9) Morita, H., ANAL. CHEM. 28, 64 (1956). (10) Morita, H., J. Am. Chem. SOC.78, ' 1397 (1956). (11) Morita, H., Rice, H. M., ANAL CHEW27,336 (1955). (12) Northcote, D. H., Biochim. Biophys. Acta 1 1 , 471 (1953).
RECEIVEDfor review May 18, 1956. Accepted January 18, 1957. Presented in part a t the Symposium on Thermogravimetry and Differential Thermal Analysis, 129th Meeting, ,4CS, Dallas, Tex. -4pril 1956. Contribution 320, Chemistry Division Science Service.
Rapid Quantitative Determination of Hydroquinone CHARLES B. JORDAN Coating & Chemical Laboratory, Aberdeen Proving Ground,
F A rapid and accurate method which utilizes only standard laboratory equipment and available inexpensive chemicals, has been developed for quantitatively determining hydroquinone. It is a simple titration procedure and is used for rapid analyses when large numbers of samples are being examined.
H
Md.
is used extensively in many fields of chemistry, as a photographic developer, dye intermediate, medicine, antioxidant, and in many other applications. Xumerous procedures for its determination have been developed, several in recent years (1-7). Most procedures involve ordinary or electrometric titrations using YDROQUINONE
titrating reagents such as iodine, bromine, alkaline periodates or dichromates, compounds of cerium, iridium, vanadium, and various organic compounds. No quantitative procedure could be found in the literature which used ferric chloride as a titrating reagent for the determination of hydroquinone, even though ferric chloVOL. 29, NO. 7, JULY 1957
1097
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