ANALYTICAL CHEMISTRY
1388 Table I.
0,1000-gram sample has been dissolved and diluted t o 100 ml., as 1 p.p.m. is then equivalent t o 0.1% of indium in the alloy.
D a t a for Working Curve
Indium Concentration, P.P.M. 0.0 25.0 75.0
Intensity,
100.0
Average of 5 Readings
DISCUS S I 0 3
3 2 2R. 1 76 6 101 I
A series of samples containing various concentrations of indium and the other elements mentioned earlier in the paper was prepared. These solutions were then analyzed by this procedure. Table I1 gives the results obtained. I n order to calculate the precision of the procedure, the standard deviation of the readings used to obtain the working curve was calculated. A value of 0.33 p.p.m. was obtained using the readings from four working rurvea (approximately 100 readings). The samples all fall within the 3u limit indicating that the procedure is accurate to within = t O . l % indium. The sensitivity of the method may be increased by increasing the slit width; however, if this is done the effect of copper must be re-examined. The minimum detectable amount of indium for an oxy-hydrogen burner appears t o he approxim:ttely 0.2 p.p.m.
T a h l e 11. Results on P r e p a r e d S a m p l e s
X U
1 2 3 4 5
Lj
& 9
10 11
Cu 822 935 850 930 820
AI
930
68 100 30 73 57 100
850 900 845 910 830
.iO
46 63 60 45
Added, Zn 25 27 30 0 $0 0 38 0 52 0 0
P.P.Al. Ph Fe 2 0 3 0.2 0 0 0 3
0
0 2
0 0 6
1 0
2 0
0.5
n
0 0 0
In 86.0 8 0 67.0 11.0 35.0 2.0 8.8 80.8 29.5 28.0 70.0
Re. ported, P.P.11 In 86 1 8.1 66.0 10.8 34.5 2.3 8.8 81.3 29.0 28.0 69.5
Error -0 +O --I -0
1 1
0 2 -0.5
+O.R
0 0 +0.5 -0.5 0.0 -0.3
LITERATURE C I T E D
(1) Boycks. E. C . , Ph.D. thesis, University of Wisconsin, in prepara-
function of concentration from 0 to 100 p,p.m., it was found that the range for this relat,ionship was at least 0 to 1000 p.p.m. for a n indium solution to 1vhic.h no other elements had been added. Analysis of Samples. Ai0.1000-gram sample of alloy is dissolved in a small amount of nitric acid, and the solution is boiled and diluted t,o 100 nil. The emission of this solution is determined on the flame photometer and the concentration of the indium in the alloy is determined by interpolation from the n-orking curve. The calculation of per cent indium is easy if a
tion.
R.,A p p l . Spectroscopy, 2, 11-13 (1952). Jefferson. J. H., Ph.D. thesis, University of Wisconsin, 1961. (4) Saltman, If-., and Sachtrieb, S . H., ;~K.LL. CHEY.,23, 1503-5 (1 951).
(2) Hauaer, H. (3)
R E C E I ~ Efor O review February 27. 1954, Accepted N a y 5 , 1954. The work described was supported in part by the Research Committee of the Graduate School froin funds supplied by the Wisconsin Alumni Research Foundatioli.
Absorption Spectrum of Aqueous Yonochloramine Solutions JACOB KLEINBERGI, M E L V I N TECOTZKY, and L. F. AUDRIETH Department
ol Chemistry and
Chemical Engineering, University o f Illinois, Urbana,
OSOCHLOKBMISE, SH2C1, a n intermediate in the formation of hydrazine in the Raschig synthesis, is commonly determined iodomet~rically. Inasmuch as i t is conceivable that aqueous chloramine solutions might, on standing, give deconipositioii products which would interfere wit,h iodometric analysis, the present study was undertaken to determine the fearibility of :rnalyris for monochloramine hy spectrophotometric‘ means. Xccordiiig to lletcxlf ( e ) ,aqueous solutions of nionochloramine give a maximum absorption a t 2450 -%. and have a molecular estinction, E, of 416 at this wave length. Moreover, on the assuniption that iodometric analysis gives a true measure of chloramine content, the molecular extinction (in solutions containing :iretate or phosphate buffer) remains essentially constant over an extended period of time. Hon-ever, Uetcalf states that when the titers of monochloraniine solutions fall to about one half their original values (no quantitative data are given), extinctioiis no longer correspond to the iodometric titers. The authors have definitely established the adherence to Beer’s law a t the wave length of inasimum absorption of buffered aqueous solutions of monochloramine in the concentration range of 5 X to 3 x 10-3x1, the concent,ration of the chloi~aniine tieing calculated by iodometric analysis. Conformity to I3ec.1,’~ lan. is observed even in solutions which had been permitted to stand for 136 hours. RIoreover, possible products of the decomposition of aqueous monochloramine solutions-e.g., hydrazine, hydroxylamine, nitrate, and nitrit,e ions-do not absorb to any extent a t the wave length of maximum absorption by monochloramine. The results, therefore, demonstrate that nioriochloramine may be determined spectrophotometrically. 1 Present address, Department of Chemistry, University of Kansas. Lan-wnce, Kian.
111. EXPERI\IESTA L
The Spectrophotometer. -4Cary recording spectrophotometer, Model 11, was employed for the spectrophotometric studies. T h e following instrument settings were used: slit control switch at 10, chart range 0 t o 2.4 and Hi-Lo knob at the Lo positio?; The chart drive gears were kept at “60 driving, 60 driven, which gave a chart speed of 10 seconds per division. The large scanning gear was employed and provided a scanning rate of 5 A. per second. One-centimeter cells of fused silica were used in all measurement*.
\
0
I
I
I
I
I
I
V O L U M E 26, NO. 8, A U G U S T 1 9 5 4
1389
PH-11.08 T z - 2 5 - C I NlTlAL CONCENTRATION 0 310.5 X 10-5 A - 245.5 X 10-5
-
ILSO-
0.50r
o.2"
0 0
12.5
Figure 2.
25
325 50 T I M E I N HOURS
62.5
essentially constant, as did the value for the molecular extinction after corrections had been made for decomposition. The stabilities of monochloramine solutions of various concent,rations buffered a t pH 11 were investigated. The initial monochloramine concentration ranged from 64.5 X 10-5 to 310.5 X 10-5M. The experimental data for the three most concentrated solutions are shown in Figure 2, where the absorbances a t 2430 Ai.are plotted against time. After 6 days, approximately 30% decomposition had occurred in each of the solutions. .It the same time each of the solutions was being examined spectrophotometrically, the oxidizing power (assumed to be a measure of the monochloramine content) was determined iodonietrically. -4plot of absorbance a t 2430 -4.against concentration of monochloramine (as determined by iodometric titration) is shown in Figure 3. I t is evident that each series of points falls fairly well on a straight line passing through the origin. This demonstrates the adherence of monochloramine solutions to Beer's law over the range of concentrations examined, and the validity of the iodometric procedure as a means for determining the concentration of monochloramine. The average molecular extinction for monochloramine in aqueous solution a t the wave length of maximum TWP found to be 458. :ib;;orption, 2430
75
Decomposition of -4queous Chloramiiie Solutions
Preparation of Monochloramine Solutions. reagents anti glassware were precooled in a refrigerator; the preparation of the monochloramine solutions was carried out at 0" C. To a 500-nil. separatory funnel immersed in the ice bath, the reagents were added in the following order: 100 grams of ice, 100 nil. of 0.5.1T sodium hypochlorite solution, 100 ml. of reagent grade dit,thyl etFer, and slightly more than 100 ml. of 0.5N aqueous mimonia. The resulting mixture was shaken gently and the aqueous layer was removed and discarded. To the ether layer rrmaining i n the funnel there were added 100 nil. of cold distilled n-ater; tht. nionorhloramine was extracted into the aqueous phase. The concentration of the monochloramine in the aqueous solution was then determined iodometrically using starch :is a n indicator.
P H I 11.08 X = 2430 TIME I N HOURS
a-0
- I6 - 22.5 v - 46.5 0 - 70.5
4 0
p/
V
A - 136.5
W
m
0: 0.75
0.
SPECTROPHOTO\IETRIC DATA
The ahsorption spectrum of monochloramine is characterized by one well defined peak with a maximum a t 2430 &I. (Figure 1). With 1-em. cells this niaximum appears in monochloramine solutions as dilute as 5 X 10-4JI. -4stud3- was made of the effect of varying the p H of monochloramine solutions between values of 9 and 11 on the position of the absorption maximum and the value for the molecular extinction. T o obtain solut,ions of appropriate p H values, buffer systems consisting of boric acid, potassium chloride, and sodium hydroxide weTe employed ( 1 ) . Aliquots of an aqueous nionochloramine solution were diluted n-ith buffer to approsinlately the desired concentration and then the exact concentration was determined iodonietric;illy. Buffers of p H 8.89, 9.81, and 11.08 were used. Each solution was examined spectrophotometrically with time, -the appropriate buffer solution serving as a blank in each instance. The initial monochloramine concentration in each buffer was 3.1 X 10-sAITand the ahsorption maximum appeared a t 2430 A. in each case, the molecular extinction values falling in the range 450 to 460. After about 5 hours the solutions were again ex.amined spectrophotometrically and the monochloramine content was determined iodometrically. The solutions had decomposed to some extent, the greatest loss in monochloramine being observed in the solution of p H 8.89, where the monochloramine conto 2.8 X 10-3JT. cent'ration had dropped from 3.1 X However, the data indicated that over relatively short periods of -time there is little difference in the stabilities of monochlor.amine solutions maintained a t various p H values in the range 0 ito 11. The position of the absorption maximum remained
x' i
0.25
00
50
MOLAR CONCENTRATION X 10.5
Figure 3.
Conformity of Aqueous Chloramine Solutions to Beer's Law
Spectrophotometric examination of water solutions of hydrazine hydrate, hydroxylamine sulfate, sodium nitrate, and sodium nitrite showed that these substances, all possible products of the decomposition of aqueous chloramine solutions, do not absorl) to any degree a t 2430 A,, the wave length at which absorption by monochloramine solutions is n maximuni. ACKNOWLEDGMENT
The authors are indebted t o Gary Ehrlich for technical assistance. LITERATURE CITED
(1) Conway, B. E., "Electrochemical Data," S e w T o r k , E:l;evier Press, 1952. (2) Metcalf, R7. S., J . Chem. Soc., 1942, 148. RECEIVEDfor review February 23, 19.54, Accepted M a y 21, 1954. This investigation was carried out under t h e sponsorship of t h e Office of Ordnanre Research as one phase of a fundamental study of the synthesis of hydrazine. Contract S o . DA-11-022-ORD-828.
