Direct Spectrophotometric Titrations with Bromate-Bromide Solutions PHILIP B. SWEETSER AND CLARK E. BRICKER Department of Chemistry, Princeton University, Princeton, N . J . The use of a standard bromate-bromide solution for analytical determinations has received much attention. Because the end point of these titrations is usually determined indirectly or by means of an irreversible indicator, a more satisfactory method is desirable. No entirely uniform procedure has been suggested for the various applications of this standard solution. Direct spectrophotometric titrations with bromate-bromide solutions were investigated and a simple bromometric procedure for addition
T
HE addition of bromine to olefinic compounds has been extensively used as a method for the quantitative measurement of unsaturation. Wilson has recently surveyed bromination methods of mearmring unsaturation in motor spirit (26). A review of general methods for the determination of unsaturation is given by Volmar and Wagner ( 2 1 ) . Bromination methods differ principally in the reagent used and the procedure for determining the end point. Bromine solutions in various solvents have been used frequently for the determination of unsaturation, although these solutions are not too stable. The most widely uscd brominating reagent has been the bromate-bromide solution first proposed by Francis (8) and used with various modifications (6, 12, 16, 16). The bromate-bromide solutions are stable and may be prepared directly from pure potassium bromate without the need of subsequent Rtandardization. Bromine is liberated upon the addition of the bromate-bromide solution to an acid solution according to the reaction:
and substitution reactions as well as for some inorganic applications was developed. A spectrophotometric end point utilizing the absorption of the tribromide ion eliminates indicator errors and side reactions. By choosing a suitable wave length, this procedure can be applied with equal accuracy to 0.25 iV to 0.001 N bromate-bromide solutions. A single spectrophotometric titration has been applied to the simultaneous determination of arsenic(II1) and antimony(II1) in a mixture of these substances.
in chloroform was used by Uhrig and Levin ( 2 0 ) . Ilolthoff and Bovey ( I S ) determined the end point amperometrically, using a rotating platinum electrode, in the titration of styrene with a bromate-bromide solution. DuBois and Skoog (6) found that direct titrations with bromate-bromide solutions were possible using mercuric chloride as catalyst, and the end point of these titrations was determined by the “dead-stop” electrometric technique. Direct titrations with bromine in carbon tetrachloride were made by Braae ( 2 ) , using mercuric chloride and the Foulk and Bawden dead-stop end point. Bromate-bromide solutions have also been widely used in the bromine substitution reaction for the quantitative determination of phenols and aromatic amines. The end-point procedures of these substitution reactions are similar to those used in the addi-. tion reactions. The most general procedure involves the addition of an excess of the bromate-bromide solution and the determination of the excess bromine by the iodide-thiosulfate procedure or the arsenious acid method. TheFe procedures have Bra6H+ 5Br- = 3Br2 3Hz0 (1) been used with various modifications (6, 9, 14, 18, 1 9 ) for the In the method of Francis (8) and of Johnson and Clark ( I I ) , an determination of phenols, phenolic ethers, amines, and similar compounds. excess of the bromate-bromide solution was added t o the olefin and the excess bromine determined iodometrically, using the The Johnson and Clark type of procedure ( 1 1 ) for addition reactions and the similar Day and Taggart method for substitustarch-iodine end point. Witter et al. ( 2 5 )used a spectrophotomtion reactions ( 5 ) not only are time-consuming but often give eter a t a wave length of 430 mp to determine the iodine liberated by’the exces bromine. A visual end point of the bromine color erroneous results due to side chain substitution, or oxidation by the excess bromine. Further errors may result from the decomposition of the addition product during the back-titration ( 1 7 ) . Wilson ($2) has pointed out that low results in addition reactions may be caused by the presence of small amounts of peroxides, which may be expected in most olefins These peroxides are capable of reacting with an acid solution of sodium iodide, liberating rn much as 3 moles of iodine per mole of the peroxidized hydrocarbon. The direct procedures of Kolthoff ( I S ) ,Braae ( Z ) , and others have greatly reduced the chance of oxidation and substitution due to excess bromine, and have lonered the error due to the peroxide effect. Many bromination reactions tend to be rather slow in the region of the end point, even in the presence of a catalyst, which would make the electrometric procedure rather time-consuming. WAVE LENGTH, MLI, In the inorganic field, bromate solutions have Figure 1. Absorption Spectrum of Bromine-Bromide Solution found extensive use as oxidants, especially in the 1 X IO-’ M bromine i n solvent ayetem with volume ratio of 10 glacial acetic acid, determination of antimony in lead and alloys by 40 methtEnol. 4 potaasium bromide (40%), and 2.4 hydrochloric acid (concentrated)
+
+
+
1107
ANALYTICAL CHEMISTRY
1108
the Gyory method (IO), and also for the determination of arsenic, tin, and other reducing agents. The main limitation of these methods is the determination of the end point. Although methyl orange and other dyes have been used as irreversible indicators, these indicators are inclined t o fade prematurely unless the bromate solution is added slowly. SPECTROPHOTOMETRIC DETERMIh-ATIOS O F EKD POINT
Iodine and bromine both shoiv a large molar extinction in benzene a t a wave length of 295 mp ( 4 , 12). The molar extinction coefficient,of t.he triiodide ion in an aqueous potassium iodideperchloric acid medium has been reported as 2.64 X lo4and 4.00 X 104 a t 352 and 287.5 mp, respectively ( 1 ) . The absorption spectrum for the tribroniide ion in a rnethanol-acet#ic acid solvent was found t o have a maximum a t 270 mp and a molar extinctmionof 1.1 X 10' (see Figure 1). With a solvent cont,aining 1 tmo2% of bromide ioiis, it, is possible to determine spectrophotometrically the end point of the bromate-bromide titration using the absorption of thc tribromide ion. The tribromide ion is formed at the end point of the t,itrations by the conihinat,ion of Equations I and 11. Brf
+ Br-
= Bra-
I1
The molar extinct'ion of the tribromide ion is slightly dependent upon the concentration of the bromide ion and the solvent used, but because the concentration of the bromide ion is essentially constant throughout' a titration, t,he graph of the absorbancy us. niilliliters of bromate-bromide reagent, added will be a straightline plot. Since the tribromide ion has such a high molar extinction, it is not necessary t o operate at, the wave length of maximum absorption. Kave lengt,hs from 360 t o 270 mp were found t'o give linear plot,s of absorbancy versus concentration of tribromide ion. Alt8houghthc sensit,ivity of det,ect,ingtribromide ion is considerably lower Lvith wave lengths from 310 t o 360 nip than a t the n-ave lengt,h of maximum absorption, these wave lengt8hsare preferable in titrations using 0.1 t o 0.25 S bromate-bromide solutions, where it, is convenient to add measurable amounts of titrant he>-ondt,he end point without having too high an absorbancy. Photometric t,itrations with bromate-bromide solutions using the tribroniidc ion absorption offer a very versatile, rapid, and sensitive met#hod for the end-point determination in bot,h the organic and inorganic fields. For react.ions in which the compound under consideration is sensitive tmoexcess bromine, the end point may be determined kvith only a slight excess of bromine present. For brominations that are slow in the region of the end point, a higher wave length may be used, so t8hata considerable excess of bromine may be added. The end point is then determined from the ext,rapolation of t8hegraph of the absorbancy us. milliliters of reagent added. The photometric procedure also offers a very convenient tool for st,udJ-ing the effect of excess bromine and t,he rates of tmhereactions during the various stage? of the bromination. APPARATUS
The Beckman llodel DU spectrophotometer a a s used for the titrations with bromate-bromide solutions. The adaptation of the instrument for use in spectrophotometric titrations, the titration cell, and the 10-ml. microburet have been described ( 3 ) . REAGENTS
The standard bromate-bromide solution (0.25005 n') w-as prepared by dissolving 6.9605 grams of potassium bromate and 24.8 grams of potassium bromide in water and diluting the resulting solution to 1liter. A 0.1000 N solution was also prepared directly, while the 0.0125 N , 0.0100 LV, and 0.0009954 S solutions were prepared by diluting either t h e standard 0.25 S or 0.10 S bromate-bromide solutions. The 10-hendecenoic acid, oleic acid, and 1-octene were commercial samples and no attempt was made t o purify them. The
allyl alcohol was dried over magnesium sulfate and distilled. tlir fraction between 96.i" and 96.9" C. was used for the reported titrations. The refractive index of this fraction was n D = 1.41066 a t 25" C. The 3-phenyl-4-nitrocyclohexene(melting point 103") and the cholesteryl acetate (melting point 112.5") were prepared in this laboratory by W. C. TT'ildman and A. F. Wagner, reepectively. The phenol, o-cresol, and aniline were vacuum distilled; the phenol and o-cresol were dried in a vacuum desiccatoi overnight An antimony solution (ea. 0.10 N ) was prepared from the metal by dissolving antimony powder in concentrated sulfuric acid and diluting the resulting solution with 1.2 N hydrochloric acid. The solution was standardized with the 0.10 A- bromatebromide solution, using methyl orange as an indicator. The arsenious acid solution was prepared by the usual procedure from reagent grade arsenious oxide. A 20% aqueous solution of zinc sulfate and a 15% methanolic solution of mercuric chloride were prepared for use as catalysts PROCEDURE
Addition Reactions. The Beckman DU a a s allowed to aim u p for 5 to 10 minutes before the titrations were started. The wave length for the titrations was selected on the basis of the normality of the brominating reagent and the rate of the reaction, so that measurable amounts of reagent in excess of the end point could be added without having abnormally high or 1ov absorbancy readings. Figure 1 includes the wave-length ranges found most suitable for titrations with various concentrations of bromate-bromide solutions when a 70- to 80-ml. volume of solution was employed. After the titration cell was positioned in the cell compartment, a known quantity of the olefin solution and the solvent system were added. The solvent was prepared 1)y mixing 50 ml. of glacial acetic acid, 20 ml. of methanol, 1.2 ml. oi concentrated hydrochloric acid, and 2 ml. of 4070 potassium bromide.
;i
10-
oe2
06-
m
a 04-
02r
"",
L_
L
_ I -
I O
14
18
22
26
-
-
30
l
-
t
34
-
1-J
1
38
42
46
50
M L OF 0 O O I N KBRO,-KBR
Figure 2. Titration of 0.76 Mg. of Cholesterjl 4cetate with 0.001 V Bromate-Bromide Solution Wave length 294 mp
In some of the slower bromination reactions it was found ciehiiable to use a catalyst to increase the rate of addition of bromine. The addition of 10 ml. of the mercuric chloride solution to the solvent was suitable as a catalyst for titrations involving the more concentrated bromate-bromide solutions (0.25 to 0.10 S) where wave lengths above 320 mp could be employed for determining the end point. At uave lengths below 320 mp, solutions containing mercuric chloride showed such large absorption that it was impossible to adjust the galvanometer to a zero reading. The molar extinction of the tribromide ion is also reduced considerably by the mercuric chloride (owing t o a decrease in the free bromide ion concentration in the solution). For some of the more dilute titrations, the use of zinc sulfate as a catalyst, which was studied by Lewis and Bradstreet (16),was employed. This reagent does not shoy appreciable absorption a t wave lengths ot 294 to 360 nip and does not Ion-er the molar extinction of the tribromide ion. The excess nater present in the solution due to the addition of the zinc sulfate may account, in some cases, for the increased rate of bromination. The solution n a s qtirred for 1 t o 2 minutes m-ith a fitream of
V O L U M E 2 4 , NO. 7, J U L Y 1 9 5 2 Table I. Material
1109
Addition Titrations with Bromate-Bromide Solutions
Wt. Ranges of Sample
Total Volume of Solution
No. of Determinations
G.
MZ.
0 OOQQ-0,0058
0 083-0.168
% 13
5 4
0.240-0.143 0.035-0.073 0.025-0.056
80 80 85
Wave Length M p
7
360 310 360 360 340
3-Plirny1-4-nitrocyclohexene Cholesteryl acetate
0.0043-0.0106
45
8
320
0.0067-0.0219
80
4
295
Cholesteryl aretate
0 00045-0 00116
50
6
294
IO-Hendrcrnoic acid 10-Hendecenoic acid Oleic acid 1-Octene 411vl alcohol
fi
nitrogeri ( 3 ) ,and the galvanometer was set on zero by adjusting the slit Tvidth of the spectrophotometer. The bromate-bromide solution \vas then added from the microburet until the solution showed a slight excess of bromine, whereupon small aliquots of t8hetit,rant Tvere added and the absorbancy was taken 1 minute after each addition of the reagent. Although there was a detectable loss of bromine from a solut,ion which was subjected t,o stirring for a considerable period of time, this loss was negligible R-hen the concentration of the excess bromine n-as low, and when the absorlxincy readings were taken approximately 1 niinut,e after each addit>ion of the reagent. The end point was determined by plotting the absorbancy us. milliliters of reagent added, as is shown in Figure 2; the absorbancy prior t o the end point was mentially zero in all cases. No volume correction was required in any of the titrations, although volumes as Ion- as 50 ml. n'ew usrd i i i some cases.
The act,u:il experimental conditions which were found most suitalde for each of the compounds determined hy this addition procedure are included in Table I. Substitution Reactions. Compounds that can be determined by a bromine substitution react,ion fall into three general classes, which differ mainly in the rate of bromination and the sensitivity of the compound t o excess bromine. The first type includes those which show a slow rat,e of bromination (substit,ution), but are not sensitive t o exceFs bromine. I n the second type arp substanccs which have moderate t o fast, rates of bromination and arc not, sensitive t o an excess of bromine, Compounds of the last t'>-pchave a normal or fast rate of hroniinat,ion, but are sensitivc, to a miall excess of bromine, owing to further subst,itution of t,he side ohain, oxidation, or decomposition of the compound. If compounds of the first type are titrated by t,he general procedure descrihed under addit,ion react,ions, the slow rate of the react,ion will requirc mch a large excess of bromine t,hat,ext,rapolation of t h r curvc of absorbance us. milliliters back t o the end point will
O 0.5
d
I
f 0.4
m
O
2t
04'k
Figure 3.
(A)
-
Catalyst Used
_
z
-
p
.v
None 0.250 Sone 0.0125 None 0.250 None 0 250 I O ml. 0.250 15% HgCIz 5 ml. 0.0125 20% ZnSOa 7 ml 0.0125 ?n% zn%oA -8 ml. 0 0009554 20% ZnSOl
AP. Bromine KO.Found
Bromine No. Calcd.
Ar. Deviation from Mean "c
84.65
86.85
0 22
84.22 54.88 137.44 272.7
86.85 56.6 142.5 275.0
0 13 0.11 0.46 0 17
7 8 63
78 65
0 31
37 32
37.28
0 55
37 54
37 28
0 27
be subjected to dilution errors and possible deviations from Beer's law. The time of such a tit,ration would also be undesirahle. These disadvant,ages were eliminated by using the follon-ing procedure for the determinat'ion of phenol, which can he considered a typical .'Type I" compound, as the final stage of the substitution of the t,hird bromine is a slovi process.
DETERUIXATIOS OF PHEXOL: A 100-ml. portion of a solvelit which consisted of 60 parts of methanol, 80 parts of water, 6 parts of hydrochloric acid (12 IV), and 4 parts of 40% potassium bromide was added t o the titration cell; methanol was used to prevent bhe precipitation of tribromophenol. Then 1.00 ml. of standard 0.1 S bromate-bromide solution was added. .It a m-ave lengt'h of 330 mp, the galvanometer was arbitrarily set a t 0.200 by adjusting the sensitivity and/or slit width. Aftel, a 2.00-ml. aliquot of an aqueous phenol solution was added, the resulting mixture was titrabed with a standard bromate-bromide solution. When the apparent absorbancy approached a value of 0.10, four t o six constant-sized aliquots of the bromate-bromitlc solution were added and readings were taken approximately 1 minute after each addition. To determine the end point, it v a s first necessary to correct the initial 0.200 absorbancy value for a dilut,ion effect. This was done by adding 100 ml. of the solvent to the titration cell, adding 1.00 ml. of the 0.1 iV bromate-bromide solution, and adjusting the galvanometer to 0.200 as in the above procedure. This solution was then titrated with water, and the absorbancy of t h e solut'ion was taken after every 0.5-ml. t o 1.0-1111. addition. These data give a dilution base line as shown in Figure 3, A . This base line may then become a permanent part of the graph used for all titrations in which t h e above conditions (same excess of bromine, wave length, and initial volume) are followed. The end point' of the titration is the point a t which the base line, A , and the titrat'ion curve, B, int'ersect. DETERRlIS.4TIOS O F C O M P O C K D S O F SECOXD TYPE. These compounds (aniline is a t'ypical example) were determined in the same manner as t h e addition react,ion, except that the solvent described for the determination of phenol was used. DETERMIS.4TIOK O F CO?dPOUSDS OF THIRD TYPE. BeiTiUSe these compounds are very sensitive to excess hromine. it is necessarv to use a wave length whereby small concentritions of bromine ea; be accurately determined. Accordingly, a nave length of 300 mp or less is recommended for these determinations. At these lower wave lengths, the brominated compounds may show some absorption. Thus, in the determination of o-cresol, the specI trophotometer was adjusted so t h a t the solution being titrated showed zero absorption about 1 to 2 nil. prior to the predicted end point. Then allsorbancy readings were made after each 0.5-nil. addition of standard bromate-bromide solution. h s boon as the absorbancy was observed to increase rapidly with the addition of bromate, four t o six readings were taken after 0.02- to 0.04-nil portions of the titrant were added. The end point was then determined from the plot of the observed data, as is shown in Figure 4. The -01vent system described for the determination of phenol was used.
Titration of Phenol with 0.100 iVBromate-Bromide Solution Wave length 330 m
KBrOz-KBr Solution
Inorganic Reactions. I n the titration of trivalent arsenic or antimony, a solution 2 t o 3 S in sulfuric acid and 1.5% in potassium bromide was used as a solvent. The procedure was othet-
ANALYTICAL CHEMISTRY
1110
and agree closely with results givea by other workers on commercial samples (2, r). TitraVol of No. of Wave KBrOl-KBr Sample Sample Av. tions with dilute bromate-bromide solutions are Error Compound Soh. Detns. Length Soln. Taken Found possible by this method; the titration of 1.1 M1. M P N Mo. Mo. % t o 0.49 mg. of cholesteryl acetate with a 0.001 Phenol 100 9 330 0.100 7.789 7.803 0.18 Aniline 80 5 350 0.100 8.980 8.992 0.13 N solution shows a very good accuracy. The o-Cresol 80 5 300 0.100 20.86 20.88 0.11 actual titration curve for a 0.7-mg. mmple of cholesteryl acetate is shown in Figure 2; this Table 111. Results of Analyses of Arsenic and Antimony Solution type of curve is typical of all the addition reacVol. of No of Wave KBrOa-KBr Sample Sample Av. tions studied. . aterial Soln. Detna. Length Soh. Taken Found Error Results of the substitution reactions with broMI. M p N Mo. -v8. % Antimony 80 8 330 0.100 31.91 31.90 0.03 mate-bromide solutions, using the spectrophoto80 6 296 0.010 3.196 3.200 0.13 metric end point, are given in Table II. TitraArsenic 80 3 330 0.100 22.34 22.37 0.15 80 3 296 0,010 2.237 2.240 0.13 tions with samplns of 7 to 21 mg. of phenol, aniline, and 0-cresol show an average error of only 1 to 2 p a r b per thouTable IV. Simultaneous Determination of Arsenic and Antimony Mixtures sand. This is a decided improvement Table 11.
Substitution Titrations with Bromate-Bromide Solutions
Wave Length Vol. of Soln. M p
326 326 326
MZ. 80 80 8o
KBrOa-KBr Soln. N 0.100
0.100 0.100
Arsenic Taken
Arsenic Found
Error
Antimony Taken
Antimony Found
Error
G.
G.
%
G.
G
%
0.11 1.18 1 01
0 01286 0.01286 0 01286
0 01288 0 01266 0 01268
0.15 1.71 1 40
0 00914 0 00913 0 01014 0.01026 0 00892 0 00883
wise the same ~LIin the addition reactions and gives a titration curve similar to that shown in Figure 2. Hydrochloric acid solutions could be used in the titrations; however, in the case of antimony, the convenience of such a titration is slightly reduced because of the rather high absorbancy of the chloro complex of trivalent antimony. Thus, the titration curve will start a t a high absorbancy, decrease as bromate-bromide solution is added (converting the antimony into the less absorbing pent,avalent form), and increase after the end point due to the absorbancy of the tribromide ion. More readings will be required with antimony titrations in hydrochloric acid solutions than in sulfuric acid medium, where the first portion of the curve shows zero absorbancy. Low concentrations of hydrochloric acid in the presence of 2 to 3 N sulfuric acid can be tolerated because such solutions also show zero absorbancy during the first portion of the titration. It is possible to make use of the absorbancy shown by the antimonious chloro complex to estimate both arsenic and antimony in a mixture from BL single titration. I n a 6 to 7 N hydrochloric acid solution of antimony and arsenic, the arsenic is first oxidized to the Dentavalent form. followed bv the oxidation of the antimony. -4s the two oxidation statea of arsenic do not show appreciable absorption a t the wave length used (325 mp), the resulting plot of absorbancy us. milliliters of bromate-bromide solution added will have two breaks (see Figure 5). The first portion of the curve corresponds to the amount of bromate used in the oxidation of arsenic, and the second portion to that used in the oxidation of the antimony.
Day Taggart Over the method (6), especially in the case of o-cresol and other compounds of this type, where the results are often 10 to 15% high (19) because of further
0.7
0.6
05
0.4
'
03.
0.21
6.2
Figure 4.
6.4
7.6
6.8 7.0 7.2 7.4 YL. OF 0.IOON. KBn4-KBR
6.6
7.8
Titration of o-Cresol with 0.100 N BromateBromide Solution Wave length 300 mp
I I fI
8 I
I I
RESULTS
I
The results of the addition reactions are given in Table I. The bromine numbers are reproducibk and independent of the weight of the sample. An average deviation from the mean of approximately 0.28% was obtained for all titrations in Table I, using bromate-bromide solutions from 0.25 N to 0.001 N . The low resuIts indicated in the case of 10-hendecenoic acid, oleic acid, and 1-octene are undoubtedly due to impurities in the samples
9I
I
II L
As l111l 4A s W
3: SB(III) 1
1.0
Figure 5.
1.5
sl(v)
,
2.0 2.5 3.0 3.5 ML. OF 0.IOON. KBaOj- KBR
Titration of Arsenic(II1)-Antimony(II1) 6 N in ACI, wave length 326 mp
t
4.0
4.5
Solution
1111
V O L U M E 2 4 , N O . 7, J U L Y 1 9 5 2 reactions of the excess bromine with the organic compound. In the inorganic field, the accuracy and convenience of the spectrophotometric end point are considerably better than the usual visual method employing methyl orange. For example, when 2- to 30-mg. samples of either arsenic or antimony were titrated, the analyses were accurate to within 2 parts per thousand. The actual results of these inorganic applications are shown in Table 111. Analyses of mixtures of arsenic and antimony which n-ere determined by a single photometric titration are shown in Table IV. Although the accuracy from these simultaneous determinations is only about 1%, this method oflers a very fast and convenient technique for the analyses of arsenic. and antimony mixtures.
determination. Further use of the ultraviolet region of the spectrum for determining successive end points is being investigated at the present time. LITERATURE CITED
Awtrey, A. D., and Connick, R. E., J . Am. C h a . Soc., 73, 1842 (1951).
Braae, B., ~ A L CHmf.. . 21, 1461 (1949). Bricker, C. E., and Sweetser. P. H., Ihid., 24, 409 (1952). Custer, J. J., and h-atelson, S., Ibid., 21, 1005 (1949). Day, A. R., and Taggart, IT. 'I'. I n, d . Eng. Chem., 20, 545 (1928).
DuBois, H. D., and Skoog, D. A , rlN.iL. CHEM.,20, 624 (1948). Duyckaerts, G., Bull. SOC. roy. sci. Libge, 18, 152 (1948). Francis, A. IT., I n d . Eng. Chrm., 18, 821 (1926). Francis, A. W., and Hill, A . J., ANAL.CHEM.,13, 357 (1941). Gyory, S., Z.anal. Chem., 32, 415 (1893). Johnson, H. L.. and Clark, R. d.,ANAL.CHEM.,19, 869 (194i). Keefer, R. >I., and Andrews, L. J., J . Am. Chem. Soc., 72, 4677
SUMMARY .&ED COhLLUSIONS
The use of spectrophotometric titrations with bromate-bromide solutions for the determination of olefins by addition of phenols and aminev by substitution, and of inorganic ions by oxidation, was investigated. The spectrophotoinetiic end point in these bronionictric methods is equally useful in the determination of large and small amounts of substances that can be determined by addition, substitution, or oxidation with bromine. These methods should find application in the plastic. natural oil, pharmaceutical, and various inorganic fields. -1method for the simultaneous determination of arsenic and antimony has been developed. With favorable conditions (separation of oxidation potentials, stability of complexes, etc. ), the accuracy of the determination of each component in tt mixture should he aa good as for a single
(1950).
Kolthoff, I. M., and Bovey, F. -I., ANAL.CHEM.,19, 499 (1947). Koppeschaar, TI'. F., 2. anal. Chem., 15, 233 (1876). Lewis, J. B., and Bradstreet, R. B., ANAL.CHEM.,12, :JSi (1940).
Lucas, H. J., and Pressman, D., Ibid., 10, 140 (193s). Petrova, L. N., Zliur. Priklad. Khinz., 22, 122 (1949). Ruderman, I. W., ANAL.CHEM.,18, 753 (1946). Sprung, M. M., Ibid., 13, 35 (1941). Uhrig, K., and Levin, H., Ibid., 13, 90 (1941). Volmar, AI. h'f., and Kagner, Bztll. soc. chim., (5) 2, 826 (1935). Wilson, G. E., J . Inst. Petroleum. 36, 25 (1950). Witter, R. F., Newcomb, E. H., and Stotz, E., J . Biol. Chem., 185, 537 (1950).
RECEIVED for review
December 17, 1951
Accepted M a y 15, 1952.
Reaction of Sodium Nitrite and Sulfamic Acid Indirect Gravimetric Determination of Nitrites ROBERT C. BRASTED School of Chemistry, University of Minnesota, Minneapolis, Minn.
S
EVERAL nicthods foi the estimation of nitrites have been
The research was carried out to deterniine the nature of the gaseous products when an excess of sulfamic acid reacts with a soluble nitrite, and to develop an indirect gravimetric determination of nitrites. Uitrogen oxides, represented bj nitmgen trioxide, to the extent of nearly 1 0 7 ~ are formed with nitrogen when sulfamic acid reacts with nitrite. The percentage of nitrogen trioxide decreases with decrease in nitrite concentration. An apparatussuitable for the analysis of nitrogen(I1) oxide and nitrogen(1V)oxide mixtures is described. Nitrites over a concentration range of
