V O L U M E 2 6 , N O . 3, M A R C H 1 9 5 4 types of interferences, and of the quantitative methods was carried o u t by Edward Bennett, David Brown, Paul Farrington, George Holzman, Thomas Lee, and John Sease, F i t h the cooperation of John Brocknian and Franklin Hepner. Paul Farrington was lurgely responsible for the procedures for the analysis of the iron group elements, George Holzman for those of the alkaline earth group. Anthony Briglio. ,Jr., for the inclusion of aluminum, and JVarren Schlinger for the inclusion of silver and potassium. Thomas Lee carried much of the responsibility for the final revision of the system of analysis and for the preparation of the final report. LITERATURE CITED (1)
I1ennett, E. L., Gould, C . W., Swift, E. €I., and Siemann. C.,
-1N.kL. (?HEX., 19, 1035 (1917). ( 2 ) Bennett, E. L., and Siemann, C . , Ibid., 21, 1582 (1949j. (3) Elek, d.,and Harte, R. A , , ISD. ESG. CHEM.,-1s.i~. ED., 9, 502 (1937). (4) Elek. d.,and Hill, D. IT., J . A m Chem. Scc., 55, 2550 (1933).
543 Farrington, P. S.,Kiemann, C., and Swift, E. H., ANAL.CHEM., 21, 1423 (1939).
Gould, C. W., Jr., Holaman, G., and Niemann, C., Ibid., 19, 204 (1947); 20,361 (1948).
Shaffer, P. H., Jr., Farrington, P. S.,and Niemann, C., Ibid., 19,492 (1947).
Swift, E. H., and X’iemann, C., Office of Scientific Research and Development, O.S.R.D. Rept. N o . 3693, Parts I and I1 (May 29, 1944); S o . 5430, Part I11 (.lug. 10, 1945); N o . 5075, Appendices (May 17, 1945). Ter Jleulin, H., and Heslinga, J., “Neue hlethoden der organisch-chemischen -Analyse,” Leipsig, Akad. Verlagsgesellschaft. 1927. RECEIVED for review d u g u s t
24, 1933. Accepted October 19, 1953. Material supplementary t o this article has been deposited as Document number 4171 with the AD1 ;iuxiliary Publications Project, Photoduplication Service, Library of Congress, Washington 25, D . C. h copy may be secured b y citing the Document number and by remitting 831.25 for photoprints, or $9.00 for 35-mm. microfilm. Advance payment is required. Make checks or money orders payable t o : Chief, Photoduplication Service. Library of Congress.
Determination of Mercury in the Atmosphere Submicroanalytical Determination of Mercuric Ion in Bromine and Chlorine Water Based on Its Catalytic Action SMILJKO AISPERGER and IVO MURATI Institute of Inorganic, Analytical, and Physical Chemistry, FdCUky of Pharmacy, University of Zagreb, Croatia, Yugoslavia
The reaction of potassium ferrocyani
THE
significance of catalytic action in submicroanalysis has been only recently recognized, though the underlying principle was known long ago. A comprehensive r e v i m b y West (11) refers to 145 publications. Continuing earlier investigations on the kinetics of the reaction of potassium ferrocyanide and nitrosobenzene in aqueous solution (1-3) the catalytic influence of mercuric ions was particularly studied. The reaction proceeds according to Equations 1, 2, and “
CS-
+ €120
HCS
+ OH-
(3)
T h e concentration of the violet complex a t a fived time depends on the concentration of mercuric ions in the solution; it is therefore possible to determine the concentration of mercuric ions by meawring the extinction of the violet complex Using a calibration curve very small amount;: of mercuric ions could be determined in distilled nater, doKn to concentrations of the order of 10-7 mole per liter. The catalytic action of mercuric ions can be influenced by various foreign substances Disturbanceq, arising from a negative salt effect, occur a t higher ionic strengths. The negative salt effect agrees with Bronsted’s theory, since the charges of ferrocyanide and mercuric ions have opposite signs. In performing determinations of mercuric vapor- in the atniosphere all theqe difficulties could be overcome by using a method for trapping mercury vapor first developed by lloldawskij (8)and checked by Stock and Cucuel (10). According to the latter authors, this method coniists in mixing the atmosphere containing mercury with bromine vapor and absorbing the mixture in bromine water. I n this lvay mercury i- converted into mercuric bromide and its solution, after evaporation of excess bromine, contains practically no foreign ions, which is not the case with the usual absorbent.. Stock an 1 Cucuel found Moldawskij’s method convenient. Stock and Cucuel further d e w i b e another method of trapping mercury vapor by condensation in traps immersed in freezing mixtures such as liquid air or liquid nitrogen. This method is considered as one of the best, but it is not so widely practicable. T h e condensate in the traps is subsequently dissolved in chlorine water and, after removal of excess chlorine on a water bath, here again are obtained aqueous solutions of mercuric ion9 free of foreign electrolytes. The catalytic action of mercuric ions in such solutions can be measured without disturbance. Thus the determination of mercury in the atmosphere is reduced to the determination of mercuric ions in bromine or chlorine
ANALYTICAL CHEMISTRY
544
water. This study is concerned with the possibility of determining mercuric ions in bromine or chlorine water by a method devised in this laboratory.
tion, E?o,was estimated. Its value \vas taken as a measure for the intensity of the catalytic action. PROCEDURE
EXPERlMENTAL
Materials. Sitrosobenzene was prepared according to Bamberger ( 4 ) ; 0.G66 gram was dissolved in 1 liter of water a t 70' C. (melting point of nitrosobenzene, 68" C.). The resulting faint green solution was used as a stock Polution. It can be stored for a few days; then it becomes turbid and can no longer be used. The molar concentrations given in the text refer to the monomeric form. Potassium ferrocyanide trihydrate was Merck's analytical grade. All glassware used was Jena or Pyrex brand. Apparatus. A Unicam S.P. 500 quartz spectrophotometer was used for the spectrophotometric measurements (slit width: 0.01 to 0.02 mm.; corresponding spectral band width, 12 to 18 A.; glass cells, 10 mm.). I n part of the work an AC Model Fisher electrophotometer (green filter 525; cylindrical cells 22.6 mm.) was used instead of tLe Unicam spectrophotometer.
0.15
$0.10
-e
: ._ I
L
Y
0.05
I
1
P 3 Hs++Concentration,
5
x
Time, Days 10 20 30
Samples were therefore analyzed the day they were collected, otherwise substantial errors could be expected. When mercuric solutions were kept in the vessels no longer than 2 days, as in the course of the experiments, no difficulties were encountered in reusing the same vessels, provided they were cleaned with sulfuric acid-dichromate solution and thoroughly rinsed with distilled water. Excess bromine was removed on a water bath until no odor of bromine could be detected. T o the solution obtained in this manner, the necessary amount of nitrosobenzene solution was added and p H adjusted to 3.5 by addition of a few drops of 0.3s sodium hydrovide or hydrochloric acid. Then the solution was placed into a water thermostat kept a t 20" f 0.05' C. A volume of potassium ferrocyanide solution, small in comparison to the volume of the above mentioned solution, was placed into the same thermostat. After both solutions had reached it temperature of 20" C. they n-ere mixed. Solutions of potassium ferrocyanide were also prepared immediately before use by dilution of a 0.2M solution. The extinction, &a, iyas measured 30 minutes after mixing against a standard treated the same way. The reaction mixture had to be protected throughout against ultraviolet and generallv against intense light, since ultraviolet light exerts the same catalytic effect as mercuric ions. 17ellowlight of moderate intensity is permissible, for ferrocyanide solutions practically do not absorb above 405 mH (1). The determination may be performed in faint daylight (shaded windows). It was found that the catalytic effect depends exclusively on the concentration of mercuric ions, no matter whether the anion was bromide or chloride. Accordingly, mercuric chloride was used for establishing the calibration curves. Figure 1 shows the results of such a serie~of 32 measurements. The catalytic effect begins to he noticeable at a concentration of 1 X lo-' mole per liter. STATISTICAL TREATMENT OF RESULTS
10-5
Figure 1. Relation of Extinction to Concentration
x.
% 16.7 21.7 42.5
I
4 Mole/Liter
Curve 1. Dependence of extinction of [Fe(CN)r(CeHaNO)] - - - after 30 minutes (Ern) o n concentration of mercuric ion added. Curves 2,3 and 4,5 are 95% confidence limits tor m = 1 and m = 2, respectively 0.
Calibration Curve. rlii aqueous solution of mercuric chloride or mercuric bromide of known concentration was added to pure bromine water. The final concentrations of mercuric ion ranged from 10-7 to mole per liter. Such extremely dilute solutions of mercuric salts had to he prepared just before use, since the salts are slowly adsorbed on the glass of vessels. Stock (9) gives the following figures shoning the extent of the adsorption of mercuric ions from approuimately 6 X 10-7A11mercuric chloride solutions:
Measured values Values calculated from Equation 4
Series I ( 3 2 Analyses). The plot of log E30 against log C H ~ - + gives a straight line up to a concentration of 5 X 10-6 mole pc'r liter of mercuric ion (Figure 2). For higher concentrations the linear relationship does not hold, as previously shown ( 3 ) . B y the method of least squares the following equation of this straight line is obtained:
3 Measurement of Extinction. The extinction was measured a t 528 mH-i.e., a t the maximum of absorption of [Fe(CS)b(CeHIS O ) ]The absorption a t this wave length was considered to be caused by the violet complex alone, since the absorption a t 528 mp from other components in the mixture is practically negligible ( 3 ) . Furthermore, any influence of the components on the absorption xyas compensated for by use of a standard solution. Influence of pH. The velocity of Reactions 1, 2, and 3 must depend on pH, since the dissociation of ferrocyanide changes with the hydrogen ion concentration, as can be seen from the reaction scheme. The maximum velocity is developed a t p H 3.5, and for this reason the reaction was always allowed to proceed a t this pH. The measurements of p H were performed by means of a glass electrode on a Doran pH meter. Concentration of Reagents. Potassium ferrocyanide, 5.0 X l O - * M , and nitrosobenzene, 4.2 X 10-4M, were found to be the most suitable concentrations. The standard solution, a t these concentrations, is stable for more than 30 minutes a t 20" C. Thirty minutes was the interval of time after which the extinc-
+ log E l (
=
+ + 0.687
0.809 (log C ' H ~ + ~ 7 )
(4)
The unknoim concentrations of mercuric ions should be calculated from log Cn,++
=
1.112 log Eao- 4.427
(5)
It must, however, be realized that if by plotting log z against log y a straight line IS obtained indicating the function y = kx", the curve resulting from the least square evaluation gives the best fit not in terms of x and y but in terms of log z and log y. Although the best fit of the substituted variables may not be best for the actual variables, the fit is as good as is readily obtainable by a practical method ( 5 ) . The standard error (8,) of 1: = log CEig++ 7 was calculated, according to Davies ( 6 ) , from the equation
+
.
V O L U M E 26, NO. 3, M A R C H 1 9 5 4 Concn. of Hg++, Mole/Litor 10-
10 -7
545 10 -5
Statistical interpretation of the results leads to the equation log C H ~ += + 1.331 log
(6)
+
i
5
5 0
e
$ 1.5
-
.-c W
I
0
-m rn
- 4.228
The relative standard error in the concentration of mercuric ions, as calculated from Equation 6, for mole per liter of 19.2 and -16.170; mercuric ion and m = 1, amounts to for t n = 2 it amounts to f13.7 and - 12.0%. The corresponding values for 5 x 10-6 mole per liter of mercuric. ion are: +19.7 and -16.470 for tn = 1, and for m = 2, +14.3 and -12.5yo. Series 111(20 Analyses). This was the sole series of measurements carried out b y means of the Fisher electrophotonieter. Procedure and Ptatistical treatment were the same as those used for Series I . The equation
9.0
+
E30
1.0
log CA.++ = 1.102 log Eio - 4.721
1 .o
0.5 7
+ log of Concn. of Hg++,
1.5 Moles/Litor
9.0
Figure 2. Linear Dependence of log Ea0 on log CE,++ Determined by Method of Least Squares Broken lines are 9570 confidence limits
( m = 1)
+
In thi. equation y = log E30 3. b = 0.899 (the dope of the straight line), n = 32, tn is the number o f parallel measurements SX giving the extinction, P = -, j = zyjand s y is the standard
n
error of y with respect to the regression, calculated according to Youtlen ( f 2 ) from the expression
From the standard error s,, the staiidnrd error of the concentration of mercuric ions sc was calculated nccording to the espressioiis f s c = 102+3--7 - CHa++ and - . ~ c = 10~:-sZ-7- C H g + + . T h e relative standard error ( S C ) does not cahanye substantially in the range of concentration!: most favorable for the performing of analyses (1 x 10-6 to 5 X 10-6 mole per liter). I t s value a t 1X mole per liter for tn = 1 is +9.4 and -8.6%, for tn = 2: fG.7 and -6.3%; a t 5 X mole per liter for m = 1 sc nniounts to +9.8 and -8.970, for ti1 = 2 f 7 . t and -6.7%. A fairly constant value for the relative stnndttrti error is to be expected, since scy0 is approximately proportion:rl to s, and s, does not change considerably. From L = log C H ~ + f & 7 follo\$-s: d C l ~ ~ ~ + * , ' d=x In 10CH,+"-i.e., A C H ~ + +A In 1OC",++ X Ax or sc A I n 10C1i~++ X s;, finallysc% A In 10 X 100a, = 2 3 0 . 2 6 ~ ~ . The 957, confidehce limits 1, for L w r e calculated from the kiiiilard errors s Z according to t'he exprewiori I , = x i: 2 . 0 1 . ~ ~ . Tlic, factor 2.04 corresponds to 30 degrecs of freedom ( 7 ) . T h e confitlrnee limits in Figure 2 are calculated for t n = 1. I n Figure are given for m = 1 1 the%'$& confidence limit; of CU,++ (LC~,+L) and 1 ) ) = 2, RS calculated from l c H g + + = IO'=-'. Series I1 (42 Analysesj. The measurements were carried out in :I way analogous to that followed in Series I. hut the standard solution of potassium ferrocyanide and nitrosobenzene, against d i k h the extinctions were estimated, was prepared inimediately tirfoi,c measurement. The procedure w w thus Pimplified although t h p :iwuracy of measurements was reduced a t the same time. Thc cnli1,ration curve no longer starts from the origin but cuts off a *mall intercept on the Ea0 axis, corresponding t o an estinction of 0.007. This is due to the uncatalyzed reaction.
(7)
was obtained, and the errors are mainly an:dogous to t h w e in Series I. Series IV (17 Analyses). IIercuric chloride was added to chlorine water and chlorine evaporated on a water hath until its odor disappeared. The further treatment as the same as already described, for the caqe of bromine water. The concentrations of mercuric chloride varied from lo-' to IO-5 mole per liter. The calibration curve obtained in this instance cwindes JT-ith the one olitiiined \Tit11 bromine water. Series V ( 5 Analyses). Mercuric chloride was added to bromine r a t e r . Bromine was evaporated and to the remaining 5olution chlorine water was added and then chlorine evaporated. The concentrations of mercuric chloride covered the same interval as in Series I and IV. Here again the calibration curve coincides 15-ith that of Series I. I n absorbing mercury vapor? from the atmosphere according to Moldawskij [see Stock and Cucuel (fo)],it was found that one absorption vessel alone, a t a flow speed of 0.8 liter per minute, retained about 95% of the mercury, depending on its concentration. When two absorption vessels in series were used under the same circumstances, the absorption was practically complete. B y means of the described method the atmosphere in the smelting plant of the mercury mine of Idria (Yugoslavia) was analyzed. When necessary, the atmosphere v a s freed from crude dust particles by passing through a Schott G2 sintered-glass filter. Four samples were taken at the same place in front of the furnace, absorbing 50, 25, 23, and 28 liters of air, and the determinat'ion of mercury gave 0.56, 0.43, 0.51, and 0.42 mg. per cuhic meter. It can be seen that the result,s are reproducible enough, taking into account that the sampling took place in a spacious, Fell aerated locality where the concentration vias subjected to fluctuations. Besides, the concentration of mercury in the air depends on the ptage of the smelting process, n-hich could not he esactly the same for each determination. LITER.ATURE CITED
(1) A$pergeY, S.,Trans. Feradau SOC.,48, 617 (1952). ( 2 ) .Ibperger, S . , llurati, I., and eupahin, O., d c t a Pharm. .JugosZac. 3 , 20 (1953). (3) Asperger, S.. llurati, I., arid Cupahin. 0.. ,J. Chern. SOC., 1953,
1041. (4) Bambsrger, E., Ber. deut. diem. Cm., 27, I555 (1891). ( 5 ) Crumpler, T. B., and Yoe, J. H., "Chemical Computations and Erroi,s." p . 221, Yew York, .John TTiley 8: Sons, 1946. (6) Davies, 0. L., "Statistical Methods in Researrh and Production," London. Oliver & Boyd, 1949. (7) Ihi?., p. 270. (8) lloldamski,j, B. L., Zhitr. PriMnd. Khitn., 3 , 955 (1930). Bpi-. de7~t.Chern. Gcs , 71, 550 (1938). (9) Stock, -4., (10) Stock, A , , a n d Cucuel, F., Ih'd., 67B, 122 (1934). (11) West, P. W,, AS.AL. CHEM.,23, 176 (1951). (12) Touden, W. .J.. "Statisticcl JIethods for Chemists," Kew York, John Wiley 8: Sons, 1951. R E C E I V Efor D review .4ilgust 5 , 1953. Accepted N o r e m h e r 16 1053
