Spectrophotometric Determination of Hydrogen Content in Heavy Water SIR: During the course of a spectrophotometric study of aqueous systems, a method was developed for the rapid determination of the light hydrogen content of heavy water. The method is based on measurement of the intense v3 H D O band a t 16680 A. due to v1 excitation. In this region, D 2 0 absorbs less intensely than the H D O and the absorption by H20 is negligible for very low H concentration. Thus correction for the H20 and DzO absorbance can easily be made for moderately low H concentrations. After these corrections have been rrade, the intensity of the absorption is linearly proportional to the HDO concentration, which is directly related to the H content of the solution. The method is similar, in principle, to the method proposed by Lecomte, Ceccaldi, and Roth ( 2 ) . The purpose of this report is to indicate the validity of the method over a wide range of light hydrogen content and to show its usefulness as a routine method using commercially available spectrophotometers.
+
to prepare the samples and the density using the method described by Kirshenbaum ( 1 ) : Appropriate corrections were made for the oxygen-18 content of the water samples. The spectrophotometric measurements were made with a Cary 14CM Spectrophotometer using 1-em. quartz cells at 25°C. RESULTS A N D DISCUSSION
The near infrared absorption bands of HDO are shown in Table I. The band v 3 a t 16.680 A. (6000 assigned to v1 cm.-l) was used for spectrophotometric determinations. The statistical value of the equilibrium constant for the reaction
+
H2O
+ Dz0 = 2 H D 0
Near Infrared Spectra of H20, DzO, and HDO (cm.-l)
2v,
+
vi'+
2 va v1
v1
VI"+
+
v3
v3
HzO
DZO
HDO
10.210 81310
7500 6130
6,880
5040
8150 7380 7090 6000
Table II. H Content in D 2 0 Samples Containing 0 to 1670 H
Average measured absorbance" 0 146 0 458 0 603 0 827 0 989 1,125 1 339 1 485
Atom __ Expt.b 1 35
4 6 8 10 11 14 16
50 00 40 21 76 32 13
%HCalc.c I 4 5 8 10 11 14 16
34 50 96 43 18 73 32 15
\Ieasured absorbance corrected for
reference D,O (99.6% D).
Atom 7 HE^^^ determined by using Equation 2 Atom c2 Hczie calculated on basis of sample preparation with 99.6Vc DZO and 100C, HZO
1866
=
where
Table I.
ANALYTICAL CHEMISTRY
atom % of light hydrogen of total hydrogen atoms A l = absorbance of a hypothetical 1-em. layer of HDO us. D20 A 2 = absorbance of a 1-cm. layer of H20 US. D20 for 4amples containing greater than 62 atom % H - for samples containing less than 62 atom % H [ .4, = the observed absorbance for a 1-cm. layer of sample us. D,O corrected for the HDO present in the reference D20
%H
*
j
=
+
The i- sign in Equation 2 derives from the fact that the 16,680 A. absorbance has a maximum at 62%. The mlueq of .I1 and dZ have been determined experimentally and the values are indicated by Equations 3 and 4.
AHDO-
Ai
A2
=
AA20
-
10
30
40
sa
w
m
so
so
IW
(1)
is about 4.0. The quantitative relationship between the equilibrium represented by Equation 1 and the measured HDO absorbance can be calculated in terms of the H content of the sample. Equation 2 gives this relationship
%H
ID
ATOM PERCENT HYDROGEN
EXPERIMENTAL
The heavy water contained about 0.4 atom % hydrogen. The exact composition of samples was calculated from the weight of H20 and DzO used
0
do20 =
5 27
(3)
AD20
2 25
(4)
Figure 1 graphically represents the esperimental and theoretical relation-
Figure 1 . Absorbance of D 2 0 - H z 0 mixtures as a function of atom per cent hydrogen at 16680 A. and 25°C.
ship between the absorbance and the H content of the sample. The solid line corresponds to the results calculated from Equation 2 and the circles correspond to the experimentally determined values. In general, the agreement is quite satisfactory and is indicative of the reproducibility and theoretical validity of the method. One of the principal advantages of Equation 2 is that it eliminates errors due to interpolation. The results for DzO samples containing up to 16% H are recorded in Table 11. Table I11 indicates the results of samples containing 20 to 75% H. Since the absorbance us. H content curve has a maximum a t 62%, the error in the H content is larger in this region. Samples having d m values greater than 2.25 may require a slightly
Table 111. H Content in D z O Samples Containing 20 to 7570 H
Average measured absorbance" 1 2 2 3 3 3 3
80 15 58 10 26 34 27
Atom yo H Expt. Calcd: 20 25 33 46 53 67 73
3 5 0 2 0 4 4
20 25 33 46 52 68 73
5 4 4 7 5 1 6
a Absorbance measurements were made using 0 1-em. cells and then corrected to absorbance value for 1 0-cm cell
modified procedure because of the form of Equation 2. For unknown samples in this region it is necessary to determine the absorbance 'of the sample, followed by a similar determination on a carefully diluted sample using HzO of normal deuterium content to ascertain whether the samples were greater or less than 62%) H. I t is also possible to determine the H content of samples containing greater than 90% HzO or more correctly the D content of HzO samples by means of Equation 5 using HzO ,as the reference sample.
(5)
where %D
All
-4,'
= = =
atom % of heavy hydrogen of the total hydrogen atoms absorbance of a hypothetical 1-cm. layer of H D O us. HzO 10.0 times the measured absorbance of a 0.1-cm. layer of sample water
The values of A I 1 and ilZhave been determined experimentally and are given in Equations 4 and 6 Ai' = AHDO- A H 2 0 = 3 52 (6) The results of samples containing 2 to 10% D using Equation 5 are shown in Table IV. I n conclusion, it is possible to rapidly and routinely determine the H content of small samples of water using a spectrophotometric method based on measurement of the absorbance of the H D O band at 16,680 A4.
D Content in Samples Containing 2 to 10% D
Table IV.
70
A,' 0 183 0 318 0 610
5%
Dcaiod
2 69
4 82
2 49 4 98
9 98
9 96
LITERATURE CITED
(1) Kirshenbaum, "Physical Properties and Analysis of Heavy Water," pp.
27-62, McGraw-Hill, Xew York (1951). (2) Leconite, L., Ceccaldi, M., Roth, E., J . Chzm. Phys. 40, 166 (1953). GILBERTGORDOK HIDEOYAMATERA Department of Chemistry University of Maryland College Park, Md. WORK supported by grants from the Atomic Energy Commission and the National Science Foundation.
Spectrophotometric Determination of Cerium with Thenoyltrifluoroacetone after Cupferron-Chloroform Extraction SIR: A previous papw ( 2 ) described a method for the spectrophotometric determination of cerium with thenoyltrifluoroacetone (TTA). However, the interference study was not very extensive, and elimination of interfering elements was not discussed. Further study of interference has shown that the proposed method is reasonably selective. The most serious drawback in the method is the interference of iron. Maganese also has been found to interfere. I n the present work, iron, together with several other metals, have been removed by cupferronchloroform extraction. -4 method is described for the determination of cerium in the presence of small amounts of manganese. EXPERIMENTAL
Apparatus. Absorbance measurements were made with a Hitachi EPU-2-4 spectrophotometer, using 1cm. cells. A shaking machine with a time switch was used for TTAxylene extractions. Reagents. Cupfenon solution, 6 grams in 100 ml. of water, was prepared fresh daily. Sodium bromate solution, 1M. TT.1 solution, 0.5.11, 45 grams in 400 ml. of xylene (Dojindo & Co., Ltd., Kumamoto-shi, Japan). Ammonium hydrogen fluoride-nitric acid solution, 0.1M in SH4HF2 and 0 . 2 X in nitric acid was stored in a polyethylene bottle. Standard cerium solution, 1.00 mg. of Ce(II1) per ml., was prepared as described previously ( 2 ) .
Procedure. Cupferron-Chloroform Extraction. Transfer the sample solution containing 10 to 100 pg. of cerium(II1) to a small (50 to 60 ml.) separatory funnel. Adjust the amount of sulfuric acid to 15 meq. and dilute to 10 ml. with water. Add 2.0 ml. of 6% w./v. cupferron solution and mix. Add 15 ml. of chloroform and shake the system for 1 minute. Drain off and discard the organic phase. Add 1.0 ml. of cupferron solution and mix. Shake the solution with 10 ml. of chloroform for 1 minute. Discard the organic phase. Wash the aqueous phase by shaking it for 30 seconds with 10 ml. of chloroform and discard the organic phase. Transfer the aqueous phase to a small quartz dish and evaporate just to fumes of sulfuric acid. T o decompose residual organic matter, add 1 ml. of 30% hydrogen peroxide, and heat gently. Evaporate the solution until white fumes appear. TTA-Xylene Extraction. Transfer the residue to a small separatory funnel with a total volume of 10 ml. of water. Add 3 ml. of 1.11 sodium bromate solution and allow to stand for 5 to 10 minutes. Add 10.0 ml. of 0.5M T T A solution and shake the system for 10 to 15 minutes. Allow the funnel to stand for about 5 minutes to allow water droplets to separate from the organic phase. Drain off and discard the aqueous phase. Filter the organic phase through a small plug of glass wool into a 1-cm. cell. Measure the absorbance of the solution a t 440 mp or 450 mp using the reagent blank or xylene as the reference. Procedure in the Presence of Manganese. Take two aliquots of the sample and carry out the cupferron-chloro-
form and TTA-xylene extractions in duplicate. Measure the absorbance (AI) of one organic phase. T o another organic phase in a separatory funnel add 10 ml. of ammonium hydrogen fluoride-nitric acid solution. Shake the system for 3 minutes. Allow the funnel to stand for about 5 minutes. Drain off and discard the aqueous phase. Filter the organic phase through a small plug of glass wool into a 1-cm. cell. Measure the absorbance (A2) of the solution a t 440 mp or 450 mp against the reagent blank or xylene. From the calibration curve determine the amount of cerium that corresponds to (A1 - A). Calibration Curve. Take, for example, 0, 20, 40, 70, and 100 pg. of cerium and proceed as described in TTA-xylene extraction. Run a blank through the entire procedure. RESULTS AND DISCUSSION
Interference Study. A brief study on interference was reported (a). Additional data on interference are given in Table I. The present study was made under the experimental conditions described in TTA-Xylene Extraction. hlore than 10 mg. of the diverse ion was not tested. The oxidation state of metals in Table I refers to that before addition of bromate. The relative standard deviations for 8 determinations of 50 pg. of cerium were 3.2 and 3.3y0at 440 and 450 mp, respectively. Thus, a t the 95y0 confidence limits, the allowable limits for the average of VOL. 36, NO. 9, AUGUST 1964
8
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