V O L U M E 25, NO. 11, N O V E M B E R 1 9 5 3 Table I. Determination of Known Amounts of Arsenic Added to Soil‘
1767 whereas the increase in arsenic is 7600 p.p.m. These data indicate that determination of arsenic in soils may be important in finding ore in certain localities.
Arsenic Added.
Arsenic Found, Average, Average, Y Y P.P.M. 1 . 0 , l . O 1 . 0 1.0,1.5 1.1 11 2.5 3, i, 3,’2, 3 2.8 28 5.0 5 , 4, 5, 4, 5 4.6 46 12.0 12, 12, 12, 13, 12 12.1 121 20.0 IS, 20, 18, 17, 16 18 180 40.0 40, 40, 30, 40, 25 35 350 -4nalyses by I(.T. Williams and R. R . Whetatone. U.S. Department of Agriculture. The 0.1-gram eamplea used contained 0.037 of arsenic; this amount would have a negligible effect on the determination of added arsenic.
ACKNOWLEDGMENT
Y
1.0
add 0.5 ml. of 10% stannous chloride solution, and dilute to 10 ml. with water. Add a 2- to 4-gram piece of mossy zinc, and uickly insert the rubber stopper holding the glass pipe of the 8utzeit apparatus. Let stand 1 hour. Remove the mercuric chloride paper and compare with standard artificial spots. Determine the arsenic content of samples containing more than 2000 p.p.m. by transferring a smaller aliquot to the test tube, adding 2 ml. of concentrated hydrochloric acid, and continuing as tiirerted in the procedure,
The author wishes to express his appreciation to L. T. Alexander, U.S. Department of Agriculture, for the use of the sample analyzed by K. T. Williams and R. R. Whetatone (Table I).
Table 11. Increase in Cobalt and Arsenic with Depth in Soils Overlying Cobalt Ore Depth of Sample, Feet 0 2 4 12
Cobalt, P.P.M. 100 400 3 00 800
Arsenic, P.P.M.
B
0 2
70 200
3 00 700
C
0 2
55 100
100 600
Location A
RESULTS
In the ranges of arsenic concentrations of importance for prospecting. the precision and dependability of the field method are shown in Table I. Known quantities of arsenic were added to samples of soils of negligible arsenic content, and arsenic was determined by the field method. These experiments show that the simple field method gives reproducible values close to the true arsenic content and should be useful in outlining anomalies in arsenic content. A series of soil samples was collected at increasing depths from the Blackbird area, Idaho, and analyzed for cobalt and arsenic. Both cobalt content and arsenic content increased with increasing depth. -4s shown in Table 11, the increase in cobalt content from the surface to a depth of 12 feet at location -4is 700 p.p.m.,
400
2000 4000 8000
LITERATURE CITED
Assoc. Offic. Agr. Chemists, “1Iethods of Analysis,” pp, 436-8, 1950.
Comrie, A. D., and Ward, T. J., J .
Inst. Brewing, 34, 530-3
(1928).
Hawkes, H.E., Bull. Geol. Soc. Am., 63, 1260 (1952). Hawkes, H. E., Econ. Geol., 44,706-12 (1949). Henly, A. T., J . Inst. Brewing, 34,608 (1928). Lachele, C. E., ISD. ENG.CHEM.,ANAL.ED.,6,256-85 (1934). Rankama, K., and Sahama, Th. G., “Geochemistry,” p. 738, Chicago, Cniversity of Chicago Press, 1950. Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., pp. 188-9, New York, Interscience Publishers, 1950. RECEIVED f o r review October 22, 1953. Accepted August 3, 1953. Publication authorized by Director, U. S. Geological Survey.
Rapid Accurate Determination of Carbohydrates and Other Substances with the Dichromate Heat-of -Dilution Method HERBERT F. LAUNER AND YOSHIO TOMIMATSU, Testern Regional Research Laboratory, Albany, Cut$.
ASIXPLE
dichromate oxidation technique was recently de- veloped for the determination of moisture in fruits and vegetables (6,8).The oxidation values for such foods were found to be very reproducible (standard deviations, 0.1 to 0.3%), and the oxidation values for standard samples (Xational Bureau of Standards) of glucose and sucrose were close to theory. The technique dispense8 with the usual external heating by utilizing the heat of dilution of concentrated sulfuric acid, and is thus very rapid, requiring a total time of about 5 minutes per weighed specimen. Thus, the technique should find application in the rapid and wcurate determination of certain types of pure organic substances in the presence of water and other nonosidizables, or in the analysis of binary mixtures of pure substances, or as a simple aid in the determination of chemical composition. This report deals with an investigation of the scope and limitations of the technique, as applied to starch, typical sugars, and various other types of organic substances. Application to various types of relluloses, involving special problems, has been described (4). METHOD
-411 operations were performed in watch-glass-covered beakers by using the following procedure.
The test specimen, calculated t o reduce SO%, approximate upper limit, of the dichromate-for example, 0.15 gram of benzoic acid or 2.5 grams of sodium oxalate-was weighed out and 25.00 ml. of 1.835N potassium dichromate was added. (This solution contained 90.00 grams per liter of reagent-grade potassium dichromate crystals, dried overnight a t 100’ to 140” C. The solution was filtered before use, and no other precautions were found necessary in order to secure within 0.05% of nominal roncentration when the solution was standardized against National Bureau of Standards oxidimetric standard potassium dichromate.) Then 10 ml. of concentrated sulfuric acid, reagent grade, d. 1.84, was slowly added (10 to 15 seconds) to the wellstirred solution or mixture. Efficient stirring without splashing, easily accomplished by means of a magnetic stirrer, was required t o avoid reduction of the sulfuric acid. After foaming had moderated, which usually required 15 seconds, 30 ml. more of the acid was rapidly added. After 10 minutes, 150 ml. of water was added and the excess dichromate was titrated whenever convenient. Actually, a 3-minute standing time before titration was found to give maximum yield for typical carbohydrates, aliphatics, and most aromatics, with the exceptions of anthranilic acid and nitrophenol, which gave 0.5% lower yield a t the 3-minute point. However, 10 minutes permitted the most efficient utilization of time in the analysis of series of replicates. Blank determinations gave no reduction in titer. The excess dichromate was determined by electrometric titration of the entire solution without further dilution, using 0.5M ferrous ammonium sulfate (0.2M in sulfuric acid). This solution is not stable and should be standardized against the dichromate
ANALYTICAL CHEMISTRY
1768 Table I.
Results on Starch, Sugars, Aliphaties, and Aromatics Yield, Standard yo of, DeviaTheoretical tions
Substance Starch Glucose Fructose Sucrose 1-Arabinose l-Arabitol a-Methvl mannoside Galact&onic acid.H20 hlethyl galacturonide.2HzO Methyl galacturonide Me e,ster.H?O Trimethyl methyl mannoside ~
Formic acid Oxalic acid (Na salt) Glycolic acid Methanol Glycerol Malonic acid Tartaric acid ( N a salt.2IIz0) Maleic acid Citric acid (Na salt.2HzO) Inositol Benzoic acid Phthalic acid ( K H salt) Anisic acid rlnthranilic acid p-Xitrophenol
99.25 99.60 99.40 99.45 99.65 99.95
100.00 99.85 99,50
100.00
No. of Replicates
0 10 0.15 0.14
8 10 6
0.17
1 :
0.15 0.04 0.10 0.34 0.13 0.08
7
0.06
8 9
99.85 99.60 99.85 99.35 99.30
0.07 0.13
0.15
6 6 10 9 10 10
99 99 98 99 98
0 34 0 16 0.40 0 18 0 35
10 6 6 6 6
30 25 60 05 65
0.07
dry, ashless basis, and gives 72.29 X 0,001 X 1.836 X 150.13 (formula weight of arabinose) = 19.915 equivalents per mole. Since complete oxidation to carbon dioxide corresponds to 20 equivalents per mole, the yield is 19.915/20 = 0.9960, which is expressed in per cent in Table I. The yields are mean values of the indicated numbers of replicates and the standard deviations refer to deviations of individual values from the means. The yields are expressed to the nearest 0.05%, as that was the approsimate combined titrational uncertainty in a mean of sis replicates, exclusive of uncertainties in the moisture and ash determinations. These yields may be compared with others for a variety of substances using external heating methods (1-3, 6, 7 ) .
Table 11. Examples of Incomplete Oxidation Substance
Propionic acid Succinic acid ( N a salt.GH10) Malic acid Lactic acid (Ca salt)
Yield, yo of, Theoretical 35 3 62 60 94 38
72
46
70.6
solution before and after a series of titrations. A simple procedure was to add 5.00 ml. of the dichromate solution to a solution which had just been titrated, and then to retitrate to the same end point. Commercial titrating equipment may be used; the writers prefer a simple arrangement consisting of an inexpensive microammeter (1 pa. per division), a radio potentiometer (500 to 5000 ohms), a 6-volt dry battery, and a tungsten, Nichrome, or calomel electrode versus a positive platinum electrode. Additional details and a discussion of other dichromate methods have been reported ( 5 ) . MATERIALS
The sucrose, sodium oxalate, and benzoic and anisic acids were standard samples from the National Bureau of Standards and were used without corrections for moisture and ash. The fructose was a purified commercial product. The starch was a highly purified material prepared from potatoes by A. L. Potter of this laboratory, and was found to have 0.004% amino nitrogen. Ash was 0.25%. Moisture was determined with a vacuum oven a t 3 mm. of mercury and 100' C. for 5 hours. The rest of the sugars were prepared and purified by R. M. McCready of this laboratory. The other substances were the best obtainable commercially and were used without further purification. Ash and moisture values were in general very low. usually for 16 Ash was determined, after precharring, a t 550' hours. Moisture was determined for the other substances with the Karl Fischer reagent, with the following exceptions: Fructose, nonhygroscopic in any case, was stored for 6 days in vacuo over anhydrous magnesium perchlorate and used without moisture correction. The moisture in arabinose and arabitol was measured with a vacuum oven a t 3 mm. of mercury and 60' C. for 16 hours, that in sodium citrate with a circulating-air oven a t 105' C. for 1 hour, and that in formic acid, by titration. Carbon and hydrogen combustion analyses were made on trimethyl methyl mannoside. A small amount of sodium hydroxide solution was added to the benzoic, anisic, and anthranilic acids before addition of dichromate, as they are not sufficiently soluble in, or easily wetted by, the reagent.
c.,
RESULTS AND DISCUSSION
The results obtained by applying the method to various types of substances are shown in Tables I and 11. The yield values were based upon the assumption that dichromate is reduced to the chromic state (Cr+++),that all carbon is oxidized to carbon dioxide, and that no other valence changes occurred (with the one exception of nitrophenol, whose nitrogen is oxidized from +3 to +5). The following is a typical calculation of yield: 1.0000 gram of &arabinose, containing 0.10% ash and 0.15% moisture, reduced 72.11 ml. of 1.835N dichromate. This becomes 72.29 ml. on the
Standard Deviations 1.2 9 1.2 5 0.8 0.9
2
8 0.15
No. of Replicate8 6 6 6 9 10 6 10 5 6
With nitrogen Glycine Serine Brucine Nicotinic acid Sitrornethane Acetamide
The yields in Table I are all above 99% except for certain aromatics, in which a time effect was noted, indicating that oxidation may not be complete in these particular cases. On the other hand, results slightly under 100% are to be expected, considering the probable systematic errors. In the moisture and ash determinations traces of moisture ('7) and nonoxidizable volatile material may have escaped detection. Volatile substances may be partially lost before oxidation can occur. Methanol, for example, gave variable results, 3 to 7% low, when oxidized as usual in a beaker, but gave essentially quantitative results when a reflus condenser (the only instance in Table I) was used. Finally, results lower than theoretical may be caused by carbon monoxide formation, as noted by others. Christensen and coworkers (2, s),using drastic conditions under which not only carbon monoxide but also oxygen is evolved, found it necessary to oxidize the carbon monoxide mTith a platinum heater to obtain quantitative results. Segal, Tripp, Tripp, and Conrad ( 7 ) found that approximately 1.0% of glucose and sucrose was converted to carbon monoxide under the conditions of their experiments, considerably more than under present conditions, although their results with sodium oxalate were almost identical with that in Table I. The method was tested with known binary mixtures of pure substances (1). As models, mixtures of glucose and sucrose were blended in a series of proportions ranging from 5 to 95%. Upon analysis, the mean departure from the known values, or mean error, was 1.2%. The error is of course higher the smaller the difference between the equivalent weights of the two components, which for glucose and sucrose is only 5%. Two other series of binary mixtures, benzoic-phthalic acids and formic-oxalic acids, gave mean errors of 0.4 and O.l%, respectively. The types of substances listed in Table I1 resist oxidation by dichromate to various extents in the present method, and yields were not improved by use of prewarmed (60" C . ) concentrated sulfuric acid. Methyl groups are slowly oxidized and in combination with carboxyl, as in acetic acid or acetamide, are almost quantitatively stable, although carboxyls in themselves, as in formic, oxalic, and malonic acids, are easily oxidized. If acetic
V O L U M E 25, NO, 1 1 , N O V E M B E R 1 9 5 3 acid is one of the products, it may be sufficiently stable for a quantitative procedure. For example, the odor of acetic acid is easily recognized during the oxidation of rhamnose, a methyl carbohydr:tte, and calculation taking this into account gives a yield of 102.0%. Ethyl alcohol, also, is oxidized within a few per cent of theoretical to acetic acid. llethylene groups are less stable than CH, groups, and their presence in propionic, succinic, and malic acids apparently causes these substances to be less stable than acetic acid. However, the effect of CH2 groups depends entirely upon neighboring groups, for, whereas malonic and citric acids are quantitatively oxidized, malic and succinic acids are resistant to considerably differing degrees, as are lauric and stearic acids. The presence of an OH group apparently renders a carbon atom quantitatively oxidizable, as in the carbohydrates and glycerol, tartaric acid, inositol, and perhaps, most strikingly, glycolic (hydroxyacetic) acid. The difficultly oxidizable CHs group in methanol is rendered quantitatively oxidizable by the OH group. In this respect the CH,O group, and the ether linkare apparently in the same category as the OH age, -C+-C, group, as shown by the results with methyl mannoside, methyl galacturonide, methyl galacturonide methyl ester, and trimethyl methyl mannoside. In fact, it appears possible to generalize t h a t the presence of an oxygen atom of any type, alcohol, carbonyl, carboxyl, ester, and ether renders the particular carbon atom to which it is attached completely oxidizable to carbon dioxide. This general effect of oxygen seems to arise from a specifically engendered oxidizability, rather than merely an oxidative opening wedge, inasmuch as nitromethane, with a partially oxidized carbon atom, is not completely oxidizable to carbon dioxide by the present technique. The effect of amino nitrogen, itself quantitatively nonoxidizable ( 2 , S), vanes greatly. Glycine is more oxidized by the reagent than acetic acid; serine is almost but definitely less than completely oxidized: nicotinic acid, which resembles benzoic acid except that it has nitrogen in place of the meta carbon atom, is, however, practically nonoxidizable. In other positions the NH? group has little or no effect, as in acetamide or anthranilic acid. The f3 nitrogen of p-nitrophenol was quantitatively oxidized to the +5 state by the reagent. The aromatic ring as well as unsaturated structures like malic acid are completely oxidized, although the yields for the aromatics tend to be somewhat l o r e r than those of the aliphatics. CONCLUSIONS
The results indicate that organic substances whose carbon atoms are all individually attached to oxygen atoms, or aromatics,
1769 caz1 be determined with small error in the presence of moisture, ash, and other nonoxidizables, or as pure components in a binary mixture, with the method described, assuming complete oxidation of carbon to carbon dioxide. On the other hand substances reproducibly oxidized to carbon dioxide plus a fairly stable intermediatelike acetic acid can be approximately quantitatively determined by taking this product into account theoretically, or accurately by standardizing the reagent against the pure substance. For samples with one oxidizable component, A:
% A = -
;x
100
For samples with pure components A and B:
where V = volume in liters of dichromate solution of normality N reduced per gram of actual weight of sample, and a and b = equivalents of dichromate reduced per gram of pure components A and B. These values are either theoretical ones deduced from formula or empirical ones determined by experiment, in accordance with the results presented in this paper. ACKNOWLEDGMENT
The authors take pleasure in thanking R. M. hlcCready for his helpful advice and for his contribution of sugars, A. I,. Potter for his contribution of purified starch, and E. A. McComb for the Karl Fischer analyses. LITERATURE CITED
(1) Cardone, J. J., and Compton, J. W., ANAL.CHEM.,24, 1903 (1952);25, 518 (1953). (2) Christensen, B. E., Williams, R. J., and King, A. E., J. Am. Chem. Soc., 59, 293 (1937). (3) Christensen, B. E., Wong, R., and Facer, J. F., IND.ENG.CHEM., ANAL. ED.,12, 364 (1940). (4) Lsuner, H. F.,and Tomimatsu, Y., ANAL.CHEM.,25,1769 (1953). (5) Launer, H.F., and Tomimatsu, Y., Food TechnoE., 6,59 (1952). (6) Moore, W. A,, Kroner, R. C., and Ruchhoft, C. C., ANAL. CHEM..21. 953 (1949). (7) Segal, L.1 Tripp, R. C.,.Tripp, V. W., and Conrad, C. M., Ibid., 21, 712 (1949). (8) Tomimatsu, Y . . and Launer, H. F., Food Technol., 6,281 (1952). RECEIVED for review June 1 , 1953. Accepted August 10, 1953. Presented before the Division of Cellulose Chemistry at the 123rd Meeting ,of the AMERICAN CHEMICAL SOCIETY, Los Angeles, Calif.
Rapid Accurate Determination of Cellulose with the Dichromate Heat-of -Dilution Method B E R B E R T F. LAUNER AND YOSHIO TOMIMATSU Western Regional Research Laboratory, Albany, Calif.
method for the determination of carbohyTdratesheat-of-dilution and certain types of other substances (6) is also apHE
plicable to celluloses. The a-cellulose determination is extensively used (2, 7, 8) in research and industrial control work on paper, rayon, wood pulps, and related products, and a t least three standard (1,IO) methods are in use in this country, whereas total cellulose is routinely determined in cotton (a). In most of these applications, speed and/or precision are essential, and many efforts have been made toward this end. This report presents comparable results with the heat-of-dilution method and another method requiring external heating, applied to identical samples of celluloses, starch, and glucose, with identical reagents.
METHOD
The heat-of-dilution method has been described ( 5 ) . No attempt was made to dissolve the celluloses and precision oxidation wa8 secured in the heterogeneous system. A eriod after the addition of the acid was found to suffice for cellurose, starch, and glucose. The method requiring external heating was essentially that used by Kettering and Conrad (S),in which 0.09 gram of celluof 1 2 sulfuric ~ acid. Then lose, dry basis, is dissolved in 25 20 mi. of water and 10.00ml. of 1.835N dichromate solution are added, and the mixture is boiled under reflux for 1 hour, and and titrated a8 USUal. MATERIALS
The surgical cotton was a commercial product of unknown
