Use of dinitrosaiicyiic acid reagent for determination of reducing sugar

Table I.

Reduction of Thallium(lll) to Thallium(1)

Reductor Cadmium

Detns.
5
5

K O . of

7
a

Bismuth

4 4 4 3 2 5
4 4

Silver

Taken 32.0 53.1 106.4 212.8 32.0 53.1 106.5 212.8 32.0 53.1

T1, Mg. Found, av. 31.9 5'2.9 106,3 212.7 32.0 53.1 106.4 213.1 32.0 53.0 106.5 106.5 212.8 213.1

Std. Dev. 0.22 0.33 0.20 0.40
0.10

0.17 0.25 0.39 0.11 0.10 0.14 0.44

miumrod (Fisher Scientific Co.) were i' washed with ll hydrochloric acid and then with 1N sulfuric acid. Bismuth. The chunk metal (Fisher scientific Co.) was crushed and the coarse pieces were sorted out. Silver. Granular silver (G. Frederick Smith Chemical Co.). The columns were washed nith 1K sulfuric acid and kept filled n i t h 0.01N sulfuric acid when not in use.
PROCEDURE

Measured aliquotsof the standard thallium solution were treated to give sulfuric acid concentrations from 0.1 to l.O*V and total volumes of 50 to 100 ml. Each solution was uassed through the

was added 40 nil. of 6-Y hydrochloric acid. The thallium(1) lyas titrated potentiometrically with 0.1000A7 potassium bromate using the Fisher Titrimeter with a platinum-calomel electrode pair* Blanks were run on thereductors with the above procedure, but substituting 50 nil, of l,oLvsulfuric acid for the thallium solution. The correction, in terms of milliliters of 0.1s potassium bromate, was 0.02 ml. for the bismuth, 0.03 ml. for the silver, and 0.05 ml. for the cadmium reductor. After the blank correction was deducted, the results shown in Table I were obtained.
DISCUSSION

small but may vary from lot to lot,depending upon the purity. The results obtained with silver compared favorably n ith those obtained a i t h bismuth or cadmium. Upon addition of hydrochloric acid, a precipitate of silver chloride is obtained. Although the results do not indicate any loss of thallium chloride by coprecipitation with the silver chloride, the use of the bismuth or cadmium reductors is considered more convenient. K he n bismuth or cadmium is used, thallium(1) chloride, formed upon addition of hydrochloric acid, disappears as the titration proceeds. I n the ease of silver, the silver chloride remains, and there is no visible rridence that the thallium chloride has been completely oxidized. This is not a criticism of the reduction by silver, but rather a limitation of the bromate method, which requires theaddition of hydrochloric acid. Other reductors studied were lead, aluminum, zinc, amalgams of zinc, cadmium, lead, and bismuth. S o n e of these proved satisfactory. Sickel reduced the thallium quantitatively but the blanks nere high and erratic. A better grade of nickel metal nould probably serve satisfactorily.
LITERATURE CITED

(1) Anderson, J. R. A,, rlx.4~. CHEBI.2 5 , 108 (1953). (2) Zintl,E., Rienacker, G., 2. anorg Chem. 153, 276 (1926). RECEIVED revieTY January 17, 1958. for Accepted October 27, 1958.

\Tit11 jo-ml. portions of 0.1N sulfuric acid. To the solution and washings

bismuth, cadmium, or silver. The blank corrections for these metals are

Use of DinitrosaIicyIic Acid Reagent for Determination of Reducing Sugar
GAIL LORENZ MILLER
Pioneering Research Division,Quarfermasfer Research and Engineering Center, Natick, Mass.

b Rochelle salt, normally present in the dinitrosalicylic acid reagent for reducing sugar, interferes with the protective action of the sulfite, but i s essential to color stability. The difficulty may be resolved either b y eliminating Rochelle salt from the reagent and adding it to the mixture of reducing sugar and reagent after thecolor i s developed, or b y adding known amounts of glucose to the samples of reducing sugar to compensate for the losses sustained in the presence of the Rochelle salt. The optimal composition of a modified dinitrosalicylic acid reagent is given.
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ANALYTICAL CHEMISTRY

*T

HE D I N T R O S A L I C Y L I C ACID REAGENT,

developed b y Sumner and coworker (11-14 for the determination of...