L1-AL Y T I C AL EDI T I O S
118
acids. Since the test approaches so closely in sensitireiiess to pure stannous chloride, little or no tin can be lost by precipitation in the column. Discussion of Results
Except for interferences by a fern anions, this test for tin is specific, and can be used on the original solution with only a slight loss in sensitiveness. Among the cations, Cr7-T and NiTf are probably the most undesirable, since their color seems to obscure a faint mercuric chloride reartion. The metals occurring below hydrogen in the e. m. f. series are completely precipitated in the upper layers of the lead and, beyond increasing the amount of lead chloride that may go into the filtrate, are without effect. One milligram of tin in the presence of several hundred milligrams of copper, silver, etc., is easily detected. Even the combination of mercuric and stannic chlorides causes no complications. The mercury is completely precipitated in the upper layers of the column without any perceptible formation of mercurous chloride. Among the anions there are several that seriously interfere with the test. Iodides pass into the filtrate and react with
Yo1. 2 ,
so. 1
the mercuric chloride to form red mercuric iodide, which completely masks the presence of mercurous chloride. S i trates, chromates, chlorates, and other anions of oxidizing acids prevent the formation of stannous salts, particularly in solutions of high acidity. It was found possible, however, to detect 1 nig of tin in the presence of 2 millimols of sodium nitrate by keeping the acidity below 0.3 -1-and using cold solutions. Certain anions, as oxalate and phosphate, although they form insoluble salts with Pb'-, have no interfering action Even sulfate and sulfide do not seriously interfere. Ferrocyanide and ferricyanide, on the other hand, must not be present, since they produce turbid filtrates, green to blue in color. All of these interferences may be obviated by first evaporating the solution to dryness with an excess of hydrochloric acid. By this treatment these interfering anions are either expelled or destroyed, and in this way the test becomes available for solutions in general. Literature Cited (1) Treadwell, Hela. Chim. A c t a , 6, 816 (1922). ( 2 ) Treadwell and Hall. "Analytical Chemistry," To]. I, p , 254 11916)
Application of Burgess-Parr Sulfur Photometer to Rapid Determination of Sulfur in Foods and Biological Material' Edward W. Toepfer2 and Paul W. Boutwell BELOITCOLLEGE, BBLOIT, \VIS.
This paper describes a rapid routine method for deHE need for a rapid, ter to the determination of termining the total sulfur content of foods and biosulfur in foods and biological accurate method for the logical material. material, with the view to determination of total For the oxidation of materials of suitable character finding an accurate method sulfur in foods and biological up to 1 gram the Burgess-Parr sulfur bomb may be for routine work and one material is evident to all who safely used with the complete retention of the prodsuitable for experiments in have experienced the difficulucts. This method has advantages in ease and speed sulfur metabolism. t i e s of t h e u s u a l o f f i c i a l over the official sodium peroxide fusion. The application of the Burmethod. S t o c k h o l m a n d Oxidation with strong perchloric acid is applicable gess-Parr sulfur bomb and Koch (8) pointed out that in to biological material of all types, and is particularly photometer to the determinathe fusion of the sample with useful for large samples of low sulfur content. tion of sulfur in foods is suga mixture of sodium peroxide The sulfur in the oxidized sample may be quickly gested in the directions ( 2 ) acand sodium carbonate there determined by the use of the Burgess-Parr sulfur phocompanying the instrument, is some loss of sulfur. These tometer, which depends upon the formation of colloidal There is little in the literature writers developed a satisfacbarium sulfate. The conditions for operation must be to suggest that this method as tory method for the determicarefully controlled. applied to foods and biologination of total sulfur in which cal material has been tested the oxidation is effected by the use of 30 per cent hydrdgen peroxide, followed by fuming to any extent. Latshaw ( 5 ) and LeClerc and Dubois (6)used nitric acid and bromine water. Barlow ( I ) earlier called the Burgess-Parr bomb in place of the official sodium peroxattention to the loss of sulfur in the usual dry fusion methods, ide fusion with success, but they followed i t with the usual and also in the wet methods of oxidation which he studied, gravimetric determination of the sulfur. As these investiand developed a combustion method for the Oxidation of gators point out, the utility of the bomb is limited b y its the sample, which, although reliable, is not suitable for rapid capacity and when the sulfur content is low it is often imroutine work. Many modifications have been suggested possible to oxidize a sample large enough to insure a sufficient both for the preliminary oxidation and for the final determi- weight of barium sulfate for a satisfactory determination. nation of the sulfur. S o attempt will be made to give a We have found that samples up to 1 gram can be safely oxicomplete review of this literature. It was the purpose of dized in the special 5.08-em. fusion cup furnished by the the work here reported to study the application of the Bur- makers. When a low sulfur content makes necessary the gess-Parr sulfur bomb and the Burgess-Parr sulfur photome- use of larger samples, it has seemed better to resort to another method of oxidation. The development of a larger bomb Presented before t h e Division of Agri1 Received October 2 , 1929 cultural and Food Chemistry a t t h e 78th Meeting of the American Chemical to handle safely from 2 to 3 grams of material would be very Society, Minneapolis, Minn , September 9 t o 13, 1929 desirable. The use of the bomb has much to its advantage. 2 This paper is p a r t of a thesis presented by Edward m' Toepfer a t It is easily assembled. The charge may be electrically igReloit College for the degree of master of science
T
I S D I ; S T R I d L A S D E,\-GIXEERISG CHE;IIISTRY
January 15, 1930
nited, and i t is usually quickly and completely oxidized with the complete retention of the products. If oxidation does not seem complete because of the physical condition of the sample, which makes difficult its proper incorporation with the oxidizing mixture, the contents of the bomb can be further fused over a flame. The oxidized mass is easily prepared for the sulfur determination either by the usual gravimetric method or by the use of the sulfur photometer to be described. For the oxidation of large samples we have found that the method of LeMatte, Boinet, and Kahane (Y), using fuming nitric acid and strong perchloric acid, is satisfactory. The oxidation is fairly rapid and easily controlled and there is no appreciable loss of sulfur by volatilization when the rates of oxidation and of boiling are properly controlled. This was shown by Wolesensky ( I O ) , who checked and improved this method in applying it to the determination of the sulfur content of rubber. Table I-Photometer D e t e r m i n a t i o n s S h o w i n g Recovery of Added Sulfur t o a Solution of Known Sulfur C o n t e n t
SULFUR IN ORIGINAL
SOLUTION Gram 0 00085 0 00085 0 00085
o
00085 0 00085 0 00085
TOTAL
SULFUR ADDED
SULFUR PRESEXT
Gram 0 0010
Gram 0 OOlS5 0 00205 0 00225 0 00245 o 00265
0.0012 0 0014 0 0016 0 001s 0 0020
0 00285
TOTAL SVLFUR
FOUND Gram
0 00186 0 00202 0 00222 0 00243 0 00267 0.00283
ERROR
119
first three are proteins fairly high in sulfur but difficult of oxidation. This is particularly true of the commercial casein because of its hard, horny character. Oxidation in the bomb of large samples of this material would often be incomplete unless the ignited charge was subsequently fused over a flame. The last three represent samples so low in sulfur that a sufficiently large sample could not be well oxidized in the bomb. These samples were oxidized by the perchloric acid method. Table 11-Analytical
Results (Corrected for Sulfur Added i n Reagents)
SUBSTANCE TAKEN Oxidized Oxidized in bomb by HCIOi
Grams
Grtrvimetric
Grams
SUI.FUR
P e r cent
Photometric
Per rent
BEEF SERUM ALBUMIN ( D R Y , COMMERCIAL)
1,6277
0.7656 0.7634 0.7574 0.6249 0.5085
.... .... ....
....
1.116 1.153 0.978 1.093 1.134
.... .... ....
....
....
0,992 1.052 1,082 1.039 0.983
1,5320 1.2376 1.2847
1,2617
1.039
1.166 1.094 1.083 1.060 1.067 1.014 1.045 1.057 1.059
COMMERCIAL C A S E I N
Gram
+a oonoi -0 -0 -0
001103
00003 00002 on002 0.00002
+o
-
0,9978
1.1037 1.1602 1,1316 1.0211 1,1382
0,5500 0.5454 0.5i04
....
Following the oxidation of the material by whatever method employed, the gravimetric determination of the oxidized sulfur is long and subject to the difficulties of occlusion, loss by filtration, and loss by solution. The method is not adapted to rapid routine work. For these reasons research has been extended to other methods. Dennis and Reed (3) developed a nephelometric method for small quantities of sulfur in blood and urine based on the preparation of a colloidal barium sulfate in a 5 per cent gelatin solution and a comparison of this with a standard prepared a t the same time as the sample. Kahn and Leibhoff (4) produced a color upon the diazotization of benzidine sulfate in the presence of phenol and then used a colorimetric method. Kakefield (9) produced a color from benzidine sulfate with hydrogen peroxide and ferric chloride which is then compared with a standard. Other rapid methods adapted to small quantities of sulfur, which need not be rexiewed here, have been developed. We have used the Burgess-Parr sulfur photometer as developed for the rapid determination of sulfur in coal for the determination of sulfur in foods and biological material. The use of this instrument depends upon the production of colloidal barium sulfate in a solution similar to the one used in the gravimetric determinations. There is no preparation of a standard solution for each determination, as the readings are directly converted into grams of sulfur by comparison with the values on a curre obtained by the standardization of the instrument with a known solution of potassium sulfate. The method is extremely simple and rapid and reliable under carefully controlled conditions. I n conjunction with the perchloric acid method of oxidation it has provided a useful routine method for the determination of total sulfur in the urine. Experimental
I n testing the method a fairly wide range of materials have been analyzed. The materials selected for this report are dried beef serum albumin, dried egg albumin, commercial casein, silk noils, peanut husks, and Jack bean meal. The
.... .... ....
.... .... .... ....
0.613 0.635
0.636 0.600 0.619 0.618
....
....
... ... ...
....
.... ....
,..
0.7120
.... ....
, . .
... ...
0.5474
... ... ... ... ... 0:6i6.
0.617 0.654 0.618 0.638 0,625.
0.617
EGG ALBUMIN ( D R Y , COMKERCIAL)
0.6451 0.6466
0.6414
.... .... ....
.... ....
1.0560
....
2.0000
1.438 1.462 1,462
1,360 1.447
....
SILK
....
JACK
....
2.3578
....
2,0121
...
NOILS
0.142 0.147
....
BEAN
MEAL
....
0.167 0.161
P E A h ’ U T HUSKS
....
....
0.201 0.201
OSIDATIOKOF SahrPLE IS SULFURBom-The procedure for the bomb oxidation follows the directions ( 2 ) furnished by the makers of bhe bonib. Potassium perchlorate was used as the accelerator. Special sulfur-free sodium peroxide was employed. The charge was electrically ignited. Care should be taken because of the danger involved in the possible blowing of a gasket in a worn fusion cup. The 5.08-cm. fusion cup should be used with samples of about 1 gram. Larger samples mere used in some cases, but i t was not always sure that oxidation was complete. After cooling, the fusion mass was completely dissolved in boiling water. The solution and washings were acidified with concentrated hydrochloric acid and boiled to destroy any excess of sodium, peroxide and t o remove completely all carbon dioxide. The solution was then neutralized with ammonium hydroxide and acidified with concentrated hj,drochloric acid, using, 1 cc. in excess. The solution was filtered and made up to a volume of 250 cc. From t’his solution aliquots were taken for the sulfate determination, either gravimetrically or by means of the photometer. For the gravimetric determinat’ion i t was often necessary to use the entire solution. Blanks were run on the reagents, using the “true blank” method of St’ockholmand Koch (8). To the hydrochloric acid solu-. tion of the blank prepared as in the case of the regular samples, 50 cc. of a standard solution of potassium sulfate con-.
120
5’01. 2, No. 1
A S d L YTZCd L EDZTZ0.L-
taining 0.050 gram of sulfur were added. The total sulfur content of the solution was determined by weighing the barium sulfate. A number of determinations were made and good checks were obtained showing 0.00037 gram of sulfur in the reagents for the bomb oxidation. OXIDATIOX O F SAhIPLE K I T H PERCHLORIC ,km-The OXidation with perchloric acid was carried out in a 300-cc. Pyrex Kjeldahl flask by the addition of 12 cc. of fuming nitric acid (sp. gr. 1.50) to a relatively large sample, usually from 1 to 2 grams and alloning the solution of the sample t o take place at room temperature. After the first action had apparently ceased the solution was warmed gently until no more fumes of nitrogen dioxide came off. Then 7 cc. of 70 per cent perchloric acid were added and the solution boiled gently until white fumes appeared. At this point the solution should he colorless or nearly so. If not, more perchloric acid was added and the heating continued as before. The excess of nitric and perchloric acids n-as destroyed by the addition of 25 cc. of sodium chloride solutions containing 3 grams of salt and the chlorine which n-as liberated was boiled off. The solution n-as neutralized by the addition of concentrated ammonium hydroxide and then evaporated to dryness. The dry white salt was ignited a t a low heat and the residue dissolved in water containing 1 cc. of concentrated hydrochloric acid. This solution was then used for the gravimetric determinations or made up to a suitable volume and aliquots were taken for the sulfur deterniination, either gravimetrically or by the photometric method. Blank determinations on t,he reagents for the perchloric acid method of oxidation showed 0.00046 gram of sulfur.
taneously prepared. If a solution contains too srnall an amount of sulfur for a satisfactory reading a known amount of sulfur may be added from a standard solution of potassium sulfate and the total sulfur determined. The accuracy of this procedure was established as follows: h samp!e of beef serum albumin was oxidized in the bomb and prepared for the sulfur determination as usual. The sulfur content of this solution iwis determined and aliquots, known to contain 0.00085 gram of sulfur, an amount too small for a satisfactory photometer reading, were taken. To these aliquots w r e added knonn amounts of sulfur from a standard solution of potassium sulfate. each cubic centimeter of xyhich contained 0.0001 gram of sulfur. The amount of sulfur recovered by the photometer determinations was noted. The results checked satisfactorily, as is shown by reference to Table I. This addition of a known amount of sulfur and its coilstant recovery also shon. the reliability of the sulfur photometer as a method of sulfur determination. Experimental Results
Table I1 gives the analytical results corrected for the sulfur in each blank. The photometer d u e s represent the average of several concordant readings on aliquots of t h e same sample. Table I11 s h o w the results on the dried beef serum albumin. Discussion
The results on beef serum albumin and casein obtained by the photometer were checked by the usual gravimetric method. Considering the small quantities of sulfur inGRAVIMETRIC PHOTOMETRIC volved, the results agree closely and substantiate the reDeviation from Sulfur Deviation from Sulfur mean mean liability of the photometric method. The results on the beef serum albumin in Table I11 show that the deviation Per cent Per cent from the mean in the photometric determinations is slightly O X I D A T I O N Ih B O M B 1.116 +0.038 less than in the grayimetrie determinations. When it is 1.039 - 0 046 1.153 +0.075 1.166 TO.081 necessary to deal with large samples of low sulfur content, 0.973 -0.100 1.094 +o 009 1.093 f0.015 1.083 - 0 002 as is the case ivith most foods and biological materials, these 1.134 +0.056 - 0 025 1.060 results would faror the use of the photometer for accuracy 0.992 -0,086 1.06i - 0 018 Mean 1.078 ..... 1,085 ... as well as for speed and convenience. The average results O X I D A T I O N BY PERCHLORIC ACID following the perchloric acid oxidation of the beef serum 1.052 + O . 013 1.014 -0.030 albumin, both by the gravimetric and by the photometric 1,082 i0.043 1.045 +0.001 1.039 0.000 1.057 4-0.013 methods, are slightly lower than the corresponding results 0,983 -0.056 1.059 +0.015 following the oxidation in the bomb. This may be due to Mean 1.039 ..... 1.044 ..... the possible loss of sulfur during the perchloric acid oxidation, as pointed out by Kolesensky ( I O ) . Unpublished DETERMINATION OF SCLFURBY SULFURPHOTOMETER- results obtained in this laboratory bear out the experience I n carrying out the determinations with the photometer of Kolesensky that when materials of a low sulfur content it is necessary t o follow carefully the directions for its are involved the loss in a carefully controlled oxidation does use ( 2 ) . not appreciably affect the results. The solution for the determination must contain about When the bomb method cannot be used the ease of opera3 grams of sodium chloride per 100 cc. and have a definite tion of the perchloric acid method and its general applicaacidity with hydrochloric acid in order to insure the uni- bility favor its use. I t is particularly useful when it is necesform precipitation of the colloidal barium sulfate upon d i i c h sary to oxidize large samples of low sulfur content and those the determination depends. R e have regulated the acidity not physically suited to ready oxidation in the bomb. This of solutions t o a pH of 3 to 3.8, shown by Dennis and Reed is shown in the case of the silk, the peanut husks, and the ( 3 ) to be desirable for the determination of sulfates in the Jack bean meal. They represent substances too low in presence of phosphates. Each operator should standardize sulfur to be readily determined by the usual gravimetric the instrument for himself, using a standard solution of po- method 15-ithout the oxidation of very large samples. These tassium sulfate. It is important t h a t the sulfur content materials were easily handled by the perchloric acid oxidaof the solution be kept near the limits of 0.002 to 0.003 gram tion, followed by the photometric determination of sulfur. of sulfur per 100 cc. Above or below this limit the turbidity The results on these three materials were obtained on alireadings become less reliable. K h e n the proper conditions quots of the oxidation mixture to which had been added of operation are observed the end point is sharp and is quickly known amounts of sulfur as potassium sulfate. This met’hod read, with excellent checks. The results are directly trans- was also applied to the photometric determination of the lated from depths of solution into grams of sulfur without sulfur in t h e smaller samples of casein oxidized by the bomb making a cornparatiye determination upon a standard siniul- met hod. Table 111-Results on Beef S e r u m A l b u m i n
~~
January 15, 1930
I S D I ' S T R I A I , A S D E S G I S E E R I S G CHEMISTRY Literature Cited
(1) Barlow, J . .4m. Chem. Soc., 26, 341 (19041. (2) Burgess-Parr Co, hfoline, Ill., Booklet 108. (3) Dennis and Reed, J. Biol. C h e m . , 71, 205 (1926). (4) Kahn and Leibhoff, I b i d . , 80, 623 (1928). ( 5 ) Latshaw, J . Assocn. 0 3 c i a l Agv. Chem., 5, 136 (1921).
121
(6) LeClerc and Dubois, J . .4m Chem SOL , 26, 1105 (1904). (7) LeMatte, Boinet,and Kahane, J . p h w m . c h i m . , 5, 325, 361 (1927); Compt. r e n d . soc. b i d . 96, 1211 (1927). ( 8 ) Stockholm and Koch, J. A m . Chem. Joc., 45, 1953 (1923). (9) R-akefield, J. B i d . C h e m . , 81, 713 11029). (10) \X-olesensk>-, I N D . E X G . C H E X , , 20, 12.34 (1928).
Determination of Dextrose in the Presence of Levulose' D. T. Englis and W. J. Byer G S I V E R S I T Y OF
ILLISOIS, V R B A S A , ILL.
A study has been made of the iodometric oxidation of S 9T I S F X C T 0 R Y for dextrose. Within certain dextrose and a dextrose-levulose mixture to establish method for the deterlimits the rate of oxidation of the best conditions for the determination of the former both sugars is favored by inmination of either dexin the presence of the latter in the proportions found in crease in alkalinity. trose or levulobe in a mixture artichoke and chicory sirups. It was found that these of the two has always been Recently Levy and Doisy conditions are fulfilled by using a sodium carbonatedesirable for the analysis of (8)hare made a very interestborate buffer of pH 10.6 and about three times the calhoney and certain other food ing and iniportant study of culated amount of iodine, which gives an apparent products. Such an estimathe effect of borates upon the stoichiometric oxidation of dextrose to gluconic acid in tion is of special importance oxidation of dextrose and the presence of four times the amount of levulose in in the investigations now in other sugars bv various rea20 minutes at 26-27' C. A further study will be made progress looking toward a gents. The rate of oxidation to determine the application of the method to chicory commercial production of of many sugars ty iodine in and artichoke extracts. levulose. sodium carbonate-bicarbonBorates did not seem to exert a selective inhibition on A double temperature ate and sodium carbonatethe oxidation of levulose. polarization has been emborate buffered solutions was The rate of oxidation of the dextrose and dextroseployed for levulose, but the found not to be concerned levulose mixtures beyond the apparent stoichiometric experimental error is great with alkalinity alone, but the point is shown for the borate buffer and for 1.5 per cent for dilute solutions. This borate had a specific inhibisodium carbonate. is also true of the combined tory effect. Although a slight reduction a n d polarization oxidation of lwulose was aumethods for the two sugars. A direct chemical method parent, even in the presence of borates, the statement was has been proposed by K G s ( 0 ) . This procedure involves made that the levulose may not have been pure. Hinton and the use of Ost's ( I O ) copper bicarbonate solution as the Macara ( 5 ) have previously remarked that oxidation of levuoxidizing agent, and it is stated that under suitable tem- lose was negligible when borax n-as employed as the alkali, but perature conditions le1 d o s e is oxidized, while dextrose, they n-ere not favorably disposed towards its use because of mannose, galactose, lactose. and sucrose are not affected. the slower rate of oxidation of the dextrose. It appeared to T!iis method has been studied by the carbohydrate laboratory the writers, however, that t h e borates might hare a preferenof the Bureau of Standards ( 7 ) )but details of the modifica- tial inhibitory action on t'he oxidation of l e n l o s e and that tion adopted have not appeared. Another plan of analysis conditions might be found under Tvhich dextrose could be is possible. Since the total dextrose and levulose can be more accurately determined in its presence by the iodometestimated with considerable accuracy b y the copper reduc- ric method and the method made applicable to levulose sirups. tion method, if a good direct method for dextrose were availPlan of Experiment able the levulose could be calculated by difference. I n 1 8 9 i Roinijn (11) called attention to the fact that dextrose was Since the proportion of dextrose to levulose in the sirups apparently stoichiometrically oxidized to gluconic acid by from the hydrolysis of extracts of artichoke and chicory alkaline iodine solutions while levulose was scarcely affected. is in a ratio of 1 to 3 or 4, the experiments were designed for Many articles have since appeared in which the effect of a mixture of this character. The general analytical protemperature. time, alkalinity, concentration of iodine and cedure used by Levy and Doisy was folloTvetl. Their resugar, and other factors haT7-e been studied. A detailed dis- sults indicated that' a sodium carbonate-borate buffer, 0.15 cussion is not necessary here as the earlier work is well re- and 0.05 molar, respectively, gave very nearly stoichiometric viewed in the later publications ( 1 , 3, d , 5 ) . oxidation of dextrose in 60 minutes. Since this is about There are some differences of opinion as to whether the the maximum interval to be allowed for convenience of dereaction with dextrose is stoichiometric or can be made ap- termination, this buffer concentration (pH 10.6) was selected parently so and whether or not fructose is affected by the for a comparison of the dextrose alone with tiext;rose-.levulose reagent. Many of those differences can be attributed to the (1:4) mixture. varying conditions of experimentation and others to the uncerFurthermore, since Cajori ( 3 ) states that an alkalinity tain purity of the sugars studied. On the whole the evidence equivalent to 1 to 1.5 per cent of sodium carbonate proseems rather conclusive that a small amount of levulose is duces no enolization of dextrose and that under his condioxidized but that the rate is yery slon- in comparison to that tions of determination no levulose was oxidized, experiments 1 ReceiLed July 1 6 , 1929. were also run in the absence of borates a t the higher alkalinity.
A
