Determination of Moisture in Sugar Solutions with the Karl Fischer Reagent F. W. ZERBAN, N e w York Sugar
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Trade Laboratory, N e w fork, ~
N. Y.,
Apparatus and procedure are described for determining moisture in sugar solutions with the Karl Fischer reagent. Data on reprerentativo analyses are given, with comparisons between refractometric determinations and Karl Firchor titrations.
AND
LOUIS SATTLER, Brooklyn College,
Brooklyn,
N. Y.
Table 1. Standardizations of tho Solutions Standard Methanol 118. Karl Wher Reagent ELF, Reagent Standard Methanol 1 MI. of AlcoholI CI 111. of K.F. MI.
come into wide use for the water in a variety of products. I n a recent article, Johnson (4) gives an extensive bibliography. This reagent, which is commercially available (8), consists of a solution of iodine and sulfur dioxide in a mixture of anhydrous methanol and pyridine. It is extremely sensitive to atmospheric moisture, and consequently titrations with i t must be carried out in a completely closed system, especially where minute quantities of wrtter are being determined. Furthermore, the necessity for stirring the reaction mixture during the titration introduces an extra difficulty into the design of a suitable apparatus. The equipment described below is rugged and overcomes all the manipulative difficulties.
-
MI.
IO.1"
?$.45
. , l . * "
13.60
41.05
Water Cmm 0.1020 0.1145 0.1241
3305 0. u.3294
40-1!!
0.3313
-
AT.
0.3304
Titration of Known Weights of Water Standard Methanol 1\11, of K.F. K.F. Backto Standard Net 1 k r . 01 n . ~=. Reagent Titration Methanol K.F. Gram of Water
MZ.
M1. 26.90 29.75 31.95
1.16
3.50 2.50 2.30
25.74 28.92 31.19
0.83 0.76
0.003963 0.003959 0.0039is A". 0.003967
Water Eouivdent of Standard Methanol
APPARATUS
Two 50-ml. automatic burets (Scientific Glass Apparatus Co. J-740) are so modified that the lower ends of the barrels of the Fresenius stomaeke are enlareed and formed into the outer parts being admitted into the flask from the burets. The male 18/9 joints fit into the burets which are provided with stopcock plugs with tips 16.5 cm. long. Stirring is accomplished by means of a piece of iron bolt 2.81 em. (1.125 inches) long and 0.47 cm. inch) in diameter, fitting snugly and sealed into a, piece of Pyrex tubing, the center of which has been blown out into a small bulb. An Alnioo horseshoe Imagnet (Fisher Scientific Co. 12-012), mounted on a motor prcided with a rheostat, is placed under the flask.
electrodes sealedkta a tube with a male 614135 joint Lnd conn w t d io the brush p o m uf the titrinietrr. T h e Uask is eoverrd with a bell-sl.nprd dome. the Inwr part of which is a fcrnalescniihnll G s I M mint. From 11.c t ~ ui n t l w d m w 1m~icv1two mn!c ~. semihall l8/9 joints set a t suffi&ntly differingheikhts t o permit free rotation of the buret stopcocks. I n addition, the .dome is provided with a check valve (Scientific Glass Apparatus Co. J4880 B) to permit venting of the apparatus whenever liquid is I
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PROCEDURE ,
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i n optratwn, tne apparatiis IS a~scmuien, m u a mcasurca amount of Iixrl I'iseher rcngrnt is niii into rhc Rnsk. Tlw stirrer iq rturreL nncl . . . .-~~standard 111cthanuI is raoidlv added from the other buret until the solution. which ari&naliv had the appearance of tincture of iodine, tu& t o a li&-t reddish brown.--The methanal is then added slowly and finaily dropwise until the mrl noint, rea.ched. With t,hP)Fisher Scientific Co.'s titrimeter ___r_ ._....._i.a _._ . employing a polarized platinum-platinum electrode pair, this in indicated by the closing of the "maaio eye" (8). Fresh Karl Fiseher reaient turns t
