A N A L Y T I C A L CHEMISTRY
134 The color reaction with diborane and pentaborane was examined also. S o color was obtained with diborane in the conditions of analysis, probably because of the known ( 5 )rapid rate of hydrolysis of diborane in contact with water. With pentaborane a transitory red color was obtained which almost immediately changed to yellow. Absorption between 430 and 500 nip was negligible in the concentration range used for decaborane. Of these boranes the method thus seems restricted t o decaborane. The reaction of decaborane Tyith N,N-diethylnicotinamide appears to be fundamentally similar to that reported by Hill and Johnston ( 1 ) using quinoline. It has an additional advantage t o
the biochemist, over the quinoline method, in that it is directly applicable to aqueous solutions. LITERATURE CITED
(1) Hill, W. H., and Johnston, hl. S.,. 4 ~ . 4 CHEM. ~. 28, 1300 (1955). (2) Keller, W. E., and Johnston, H. L., J . Ckcrn. Phys. 20, 1749 (1952). (3) Schlesinger, H. I., and Burg, 8.B., Chern. Reus. 31, 1 (1942). (4) Stock, .4.,“Hydrides of Boron and Silicon,” Cornell University Press, Ithaoa, N. Y . , 1933. ( 5 ) Stock, A., and Kuss, E., Ber. 47, 810 (1914). RECEIVED for review September 9. 1955. Bccepted October 13, 1955.
Quantitative Determination of Ethylene Glycol in Water EILEEN R. HESS, CHARLES
B. JORDAN, and HALKEY K. ROSS
Paint and Chemical Laboratory Division, Aberdeen Proving Ground,
A rapid and accurate procedure suitable for large numbers of determinations of ethylene glycol in water has been developed. It is especially useful where greater accuracy than a hydrometer determination is necessary. This procedure can be applied to the determination of glycerol, any vicinal glycol or ketone, ahydroxyaldehyde, ketone, or acid in water, as long as the reaction rates of each substance are within practical limits.
Md.
time which expires from the moment the first drop of acid mixture reaches the sample until the white precipitate appears. A black background will aid in recognizing the appearance of this precipitate. If the precipitate forms in less than 23.5 seconds, dilute a portion of the sample tenfold by volume and repeat the test on this mixture. If the precipitate still forms in less than 23.5 seconds, dilute another portion of the sample one hundredfold by volume and repeat the test on this mixture. I n order t o obtain maximum accuracy, the mixture tested should contain from 0.10 to l . O O ~ oglycol. One of the above dilution ratios will insure this range. NOMOGRAPH
A
RAPID and accurate procedure which utilizes only standard
laboratory equipment has been developed for quantitatively determining ethylene glycol in water. The procedure is hased on the well-known periodate scission of vicinal glycols originally proposed by Malaprade (b), followed by formation of the insoluble silver iodate. The qualitative procedure for the determination of glycols in alkyd resins ( I ) involves the standard reaction, which may be written as follows:
R CHOH
I
R CHOH
A4nomograph has been constructed to facilitate the calculation of glycol percentages. The data obtained on the mixtures containing 0.10 to 1.00% glycol, as shown in Table I, are plotted a8
Table I. Data Establishing Relationship between Ethylene Glycol Concentration and Reaction Time Ethylene Glycol, Weight % 0.0998 0 1995 0 2993 0 3990 0 4988 0 5986 0 6983 0 7981 0 8978 0 9976
+ HI04-+2RCHO + HI03 + HzO “03
I
The test depends on the fact that silver iodate is nearly insoluble in dilute nitric acid, nThereas silver periodate, if formed as such, is soluble. During the investigation of glycol in alkyd resin, it was noted that the amount of nitric acid added in the final glycol determination in the procedure was critical, and that, if the glycol concentrations Tvere varied and the concentration of the acid was held constant, the length of time it took the precipitate to form varied, and this time could be accurately reproduced for each glycol concentration By making use of this information, it was found possible to determine any percentage of ethylene glycol from 0.10 to 100% by standardizing the nitric acid concentration in the test and recording the exact length of time it took for the silver iodate precipitate t o appear. PROCEDURE
Place 2.00 =k 0.01 ml. of the ethylene glycol sample t o be tested in a test tube (22 X l i 5 mm.). Add 2.0 ml. of 0.1N aqueous silver nitrate. Pipet into the test tube 5,O ml. of an acid solution containing 80 ml. of concentrated nitric acid and 4.56 grams of periodic acid (HI04 2H20) per liter of solution. Shake thoroughly. By means of an accurate timer, record the length of
Reaction Time, Seconds (Average of 5 t o 10 Runs) 135 81
i
34 30 27 25 23.5
;:$ \ ‘a 40 20 0
0
I
I
01
0.2
I
I
I
I
I
I
I
0 3 04 0.5 0.6 0.7 0 8 09 \ V i 9b ETHYLENE G L Y C O L
I
I
I
1.0
1.1
C2
Figure 1. Plot of reaction time us. per cent of ethylene glycol by weight
V O L U M E 28, N O . 1, J A N U A R Y 1 9 5 6 10 0
135 -10
-I 5
Table 11. Data Illustrating Reproducibility of Method Ethylene G!ycol, Reight % 0.0998
Dilution Ratio (by Volume) 1:l
-2 0
,125
" 35
4- 1 20
0.4988
1:l
0.9976
1:1
4.988
10: 1
9.976
1O:l
24.950
100: 1
49,880
100:l
74.850
1OO:l
99.769
1OO:l
-40
5 - 45
o >
0 -50 w In-
'_I
IS
1:l
e30
w
w r
-14:
0.2495
10'-
-m
ii5
-70
t -90 -90 - 1 00
IPI ! I
Figure 2. Nomograph for rapid computation of per cent of ethylene glycol from observed reaction time
shown in Figure 1. Using this graph, the empirical equation 63 1OD obtained from this data is G = where G is the per cent
e,
of ethylene glycol by weight, D is the dilution ratio by weight, and T is the time of reaction in seconds. The nomograph s h o m in Figure 2 was constructed from this equation. 4 sample solution is shown in Figure 2, wherein a 10 to 1 dilution required 25 seconds; the concentration of the original sample is then read from the middle scale as 9.5% of ethylene glycol by weight. The procedure as set up requires a volumetric dilution of 100 to 1 for concentrations above 10% glycol. Because of the difference in density between ethylene glycol and water, an error is introduced by the volumetric dilution of solutions. I n less than 10% solutions, this error is not significant; hoB-ever, in the higher concentrations this error becomes appreciable. The mark for a 100 t o 1 dilution on the nomograph has therefore been modified to correct for a 50% solution, thus minimizing the error introduced by volumetric dilution. Theoretically, the most accurate procedure would involve dilution by weight. HoFever, the time required t o make such a dilution would detract from the usefulness of the procedure. DISCUSSION
Tables I1 and I11 are representative of the reproducibility and accuracy that may be obtained by the method. -4s can be seen in Table 111,the maximum error based on ethylene glycol present is 1.083y0 and this error is found with the most concentrated glycol solution. This makes the procedure especially useful when results on large numbers of samples are needed and when greater accuracy is needed than is given by a hydrometer. Accuracy is dependent upon laboratory technique. If a nomograph is used to read the results, a 30-inch scale for the per cent ethylene glycol is recommended. Any substance which reduces the periodate radical to the iodate radical, or which gives a precipitate with silver nitrate in acid eolution, interferes with the procedure.
Representative Reaction Times, Sec. 130. 0 139. 3 140 4 133. 8 68.0 67.4 69.2 68.6 38.9 39.3 39.3 39.2 23.5 23.5 23.7 23.5 39.6 40.0 38.9 39.5 23.7 23.5 23.7 23.4 67.5 68.2 69.0 68.0 38.1 38.2 38.4 38.5 27.6 27.7 27.8 28.0 22.2 22.2 22.1 22.1
Table 111. Comparison of Known Per Cents of Ethylene Glycol with Values Computed from Observed Reaction Time Known .-iverage Computed % Ethylene Reaction Value' Ethylene Glycol Glycol. Time, of Using Equation Xeight yo Sec. 63.100 %G = 63.10D/T1.3: Error 63 10 0.1020 +0.0022 0,0998 135.0 -0.0005 0.2490 83 10 0.2495 68.3 +0.0162 0.5150 63 10 0.4988 39.2 +0.0031 1.007 63 10 23.5 0.9976 +0.082 39,s 627 0 5,070 4.988 -0.161 23.8 624 0 9.815 9.976 -0,494 24.456 68.2 6174 24.950 +0.420 38.4 ?985 50.300 49.880 t0.015 74.865 27.8 74.860 3834 22.2 -1.083 98,677 5727 99.760 a I n conducting tests for this table, this value was obtained by weighing initial a n d final volume of mixtures in order t o obtain dilution ratio b y weight, and multiplying this ratio by constant, 63.10.
The procedure can be applied t o the determination of glycerol, any vicinal glycol, or-hydroxyaldehyde, a-hydroxyketone, vicinal ketone, or a-hydroxy acid in water, as long as the reaction rates of each substance are within practical limits. Ethylene glycol, c. P., was used as received from Eimer and Amend, and contained 0.24% moisture determined by the Karl Fischer method. All solutions were prepared and tests were conducted a t 73" F. As can be expected, temperature variations affect the reaction rate. The procedure may be used a t other constant temperatures, provided different sets of constants are determined for the basic equation for each temperature. LITERATURE CITED (1) Jordan, C. B., AXAL.CHEM.26, 1657 (1954). (2) Malaprade, L., Compt. rend. 186, 382 (1928). RECEIVED for review August 20, 195.5. Accepted October 15, 1955.
