introducing a n aerosol of the analyte into the flame. By reducing the size of the burner orifice, particularly with slot burners, the transport efficiency of aerosol into the flame is also reduced causing a loss of analytical sensitivity. A recent application in the construction of burners is the use of a configuration of stainless steel capillary tubes (9);
this allows the advantages of large quenching distance with flexibility of geometric shape to be employed. A feature of the design is that a considerably lower working temperature is reached for the burner head and, with proper choice of capillary diameter, burners can be constructed which provide safety factors not found in many commercial burners.
(9) K. M. Aldous, R. F. Browner, R. M. Dagnall, and T. S. West, ANAL.CHEM.,42, 939 (1970).
RECEIVED for review June 14,1971. Accepted August 9,1971.
I CORRESPONDENCE
I
Solubility Product of Silver Tetraphenylborate in Water and Methanol trode, 0.01M tetraethylammonium perchlorate in methanol SIR: In connection with the calculation of the medium being used as electrode between the two half cells. All emf activity coefficients of silver ion WySAg+, between water and measurements were made with a Corning Model 10 p H organic solvents, S, including methanol, the values of the solubility product of silver tetraphenylborate, K S P ~ g ~ ( ~ s ~ smeter ) r , o n the millivolt scale. Ultraviolet spectra were recorded by a Cary Model 15 in the various solvents must be known. Unfortunately, spectrophotometer a t sensitivity 4. All experiments were considerable uncertainty exists in the literature o n the value performed a t 25 1 "C. of KSPAgB(CsHs)4 in water, and, to a lesser extent, in methanol. Reagents. Methanol was Matheson Spectroquality Grade F r o m potentiometric titrations of sodium tetraphenylborate distilled once over magnesium turnings. The water content with silver nitrate Parker ( I ) reported values of pKS'AgB(CsHa)r was 0.01 by Karl Fischer titration. Conductivity water = 11.7 in water and 13.5 in methanol (corrected to zero was used throughout this work. Sodium bromide, iodide, and carbonate were Mallinckrodt AR Grade, recrystallized ionic strength), but in a later publication ( 2 ) questioned the from water. Sodium tetraphenylborate was Aldrich puriss. reliability of the value in water. By measuring aAg+in product, recrystallized three times according to Popov (6) suspensions of silver tetraphenylborate in aqueous solutions from a 6 0 z ethyl ether-40z cyclohexane mixture. When 10-Ll0-2M in sodium tetraphenylborate potentiometrically the purified salt, mixed with sodium carbonate (see below) with a silver wire electrode, both Havif (3) and Popovych ( 4 ) was heated at 600 "C, a negative test for halides was obtained found a value of 13.4. I n the present study we repeated with silver nitrate after acidification with dilute nitric acid. Popovych's experiments and found p K S p ~ g ~ ( ~=a 14.3 ~s)4 Sometimes solutions 0.02M in sodium tetraphenylborate 0.2 in water. These values of P K ~ ~ A ~ Bin( cwater ~ H ~all ) ~are prepared from the purified salt were slightly turbid. They much smaller than is to be expected o n the basis of the were filtered through a 10-nm porosity Millipore filter medium activity coefficients log = $1.2 and log (Millipore Filter Corp., Bedford, Mass.). The resulting W M clear solutions showed n o appreciable decomposition as y B ( C $ H & ) ~ - = -4.3 between water and methanol ( M ) deduced from the ultraviolet spectra, even upon standing for reported by Popovych ( 4 ) (corrected to the molar scale) and 2 weeks, provided the solutions were deaerated with nitrogen. using the value of P K ~ ~ A ~ B (=c ~14.4 H ~in ) ~methanol found Similar observations were made by Popovych (7). Silver in the present study. A value of p K S P ~ K ~ in ( ~ water s ~ a ) of 4 bromide and iodide were prepared in methanol by a prothe order of 17.5 is predicted. cedure similar to that of Popovych (8) by metathesis of silver Therefore, it was decided to estimate the values of nitrate with sodium tetraphenylborate. A slight excess P K ~ ~ A ~ B in ( c water ~ H ~ and ) ~ methanol by using the chemical ( 2 7 3 of the former was used. The product was washed exchange method by determining the equilibrium between well with methanol. All silver salts were dried in vacuo at silver tetraphenylborate and sodium iodide in water or sodium 50 "C for 3 hr. Preparation, drying, and storage of the silver bromide in methanol. Conversely, the exchange between salts were carried out in the dark. Procedure. In the chemical exchange method, 20 ml of sodium tetraphenylborate and silver iodide in water or silver the sodium halide or tetraphenylborate solution in water o r bromide in methanol was studied. The resulting values of methanol was deaerated with nitrogen and 1-1.5 grams of pKSPAgB(C6Hs)4 in methanol were verified independently by the finely divided silver salt added. To the aqueous solutions measuring potentiometrically aAe- in solutions containing saturated with silver iodide containing sodium tetraphenylvarious concentrations of sodium tetraphenylborate which borate, 100 to 150 mg of silver tetraphenylborate was added were saturated with silver tetraphenylborate. as seed. The suspensions were shaken for 5 days. When
*
*
EXPERIMENTAL
Apparatus. The potentiometric cell and 0.01M AgNOB/Ag reference electrode in methanol were the same as those described for p H measurements with the glass electrode in acetonitrile (5). A clean silver wire served as indicator elec(1) R. Alexander, E. KO, Y . Mac, and A. J. Parker, J . Amer. Cliem. Soc., 89. 3703 (1967). (2) R.'Alexander'and A. J. Parker, ibid.,p 5549. (3) J. Havii, Collect. Czech. Ckem. Commu~7.,24, 1954 (1959). (4) 0. Popovych, ANAL.CHEM.,38, 558 (1966). (5) I. M. Kolthoff and M. K. Chantooni, Jr., J . Amer. Clzem. SOC., 87, 4428 (1965). 194
the suspensions were shaken 5 days without seeding, apparent values of ~ K S P ~ ~of~ 16-16.5 ( C ~ ~were ~ ) obtained. ~ In order t o remove tetraphenylborate, which interferes in the potentiometric titration of bromide in methanol or in water, the methanol suspensions were filtered through a fine porosity sintered glass filter. To 5-ml aliquots of the methanol filtrate were added a few drops of saturated sodium carbonate solution in water and the mixture was taken to dryness in a platinum crucible under a heat lamp, and the crucible and -.
(6) A. I. Popov and R. Humphrey, ibid.,81, 2043 (1959). (7) 0. Popovych sndR. Friedman,J. Phys. Chem., 70,1671 (1966). (8) 0. Popovych, ANAL.CHEM.,38, 117 (1966).
ANALYTICAL CHEMISTRY, VOL. 44, NO. 1, JANUARY 1972
Table I. Exchange Experiments in Methanol
0.00930 0.0186
7.33 >c 1.47 x 10-3
0.37 x 1 . 0 x 10-4
0.0113 0,0226
1.35 x 10-3 2.95 x:
0.77 x 10-4 2.25 X
NaB(C6Hda 4-AgBr 8.60 x 7.0 x 1 . 7 1 x 10-2 1.37 x 10-4 NaBr AgB(CGH5)4 1.27 x 10-3 LOO x 10-2 2.72 X 1.99 X
+
1 . 2 X 10' 1 . 5 X 10'
14.4 14.3
0.70
8.7
14.5
0.60
8.8
14.5
0.78 0.74
0.72 0.62
0.77 0.72
Table 11. Exchange Experiments in Water Initial CPinB(C6Hs)r or C N ~ M I,
[B(GHj)*-] spectrophot., M
0.00740 0.00817 0.0155
4.63 x 10-4 5.1 x 10-4 1.17 x 10-3
0.0107 0.0214
5 . 4 8 x 10-4 1.07 x 10-3
+
NaB(C6Hd4 AgI 6.94 x 10-3 7.66 x 10-3 1.43 x NaI -t AgB(C6Hj)r 1.01 x 10-2 2.03 X
0.066 0.067 0.082
17.2 17.2 17.1
0.054 0.053
17.3 17.3
Table 111. Potentiometric Determination of KBPAaBiC,Ir,)l a value of KdXaBr= 0.10 (IO) was used to calculate the broin Methanol CXaB(CsHs)p E,a n1V aAg' fB(C6Hs)aK ' P A ~ B ( C ~ H ~ ) ~mide ion concentration. Values of pKS'.kgBr in methanol and pKSPAgIin water equal to 15.5 ( Z I ) and 16.0 ( I I ) , re0.88 3 . 5 X 1.57 X -540 2.5 X spectively, were used. Values of pKSi)A.B(c6~ia)r equal t o 1 . 6 X 10-l2 3.92 x 10-3 -552 0.83 5 . 2 x 4 . 3 X 10-l:j 9.80 X -586 0.78 3 . 3 X 14.4 and 17.2 were found in methanol and water, respectively. p K S P ~ r ~ (= ~ 614.4 ~ 5 )zka 0 . 1 Results of potentiometric measurements in sodium tetraa cs. 0.010 M AgNOs/Ag in methanol. phenylborate solutions saturated with silver tetraphenylborate in methanol are presented in Table 111. A mean value of p K S P ~ g ~ ( (of . 6 14.4 ~ s ) rwas obtained in agreement with that contents were heated in a muffle furnace a t 600 "C for 2 hr obtained by the exchange method. Incomplete dissociation a n d cooled. The residue was taken up in 10 ml of 0.1M of silver nitrate in the 0.01M AgNOJAg reference cell in nitric acid, 40 ml of methanol were added, a n d the solution methanol was taken into consideration, Kdanso3in methanol was titrated potentiometrically for bromide with silver nitrate. being reported t o be 1.3 x lop2( 1 2 ) . The aqueous suspensions were filtered through a Millipore In the potentiometric titration in water of 10-3M sodium 50-nm porosity filter and the filtrates were a n a l y ~ e dfor tetraphenylborate spectrophotometrically from 260-280 nm, tetraphenylborate with silver nitrate Havif (3) observed after subtracting the iodide absorbance, which amounted to hardly any change in potential at the silver electrode from less than 1 0 % of the total. Spectra of solutions of known 0-90 % neutralization. In the present study, the potential sodium tetraphenylborate concentrations were run the same of the silver electrode in sodium tetraphenylborate solutions day as the samples. The following absorbance indices of saturated with silver tetraphenylborate which were shaken tetraphenylborate was found, in agreement with those of for 5 days gave only fair theoretical Nernstian response. Popovych (7), 3.4 X lo3, 2.1 X l o 3 , and 3.8 X lo2 a t 260, The following values of pKSPwere found in solutions 1.91 X 270, and 280 nm, while for iodide we found a value of 3 X 5.22 x 1.11 X and 2.73 X 10-?Min sodium 101 a t 260 nm. At 270 nm the longer wavelengths, the abtetraphenylborate: 14.1, 14.4, 14.1, and 14.2,. Probably sorption of iodide is negligible. the reason for the abnormal behavior is that a silver-silver I n the potentiometric method, 20-40 ml of the aqueous or methanol solution of sodium tetraphenylborate were detetraphenylborate electrode is not wetted by water. In aerated with nitrogen, 1.5-2 grams of finely ground silver equilibrium mixtures of silver iodide-silver tetraphenyltetraphenylborate added, a n d the suspensions shaken for 5 borate-sodium iodide and tetraphenylborate the silver elecdays as above. The silver ion activity in these suspensions trode indicates the calculated silver ion activity. was determined potentiometrically with the silver electrode I. M. KOLTHOFF' (below) without filtering. M. K. CHANTOONI, JR. RESULTS AND DISCUSSION School of Chemistry Results of experiments on the exchange between silver University of Minnesota halides and sodium tetraphenylborate and between silver Minneapolis, Minn. 55455 tetraphenylborate a n d halides in methanol and water, respectively, are summarized in Tables I and 11. Activity RECEIVED for review September 7,1971. Accepted October 27, coefficients in methanol were calculated using the following 1971. This work was supported by Grant GP-20605 from a. values in the partially extended DebyF-Hiickel reaction: the National Science Foundation. B(CsH5)?-, 12 A ; Br-, 3 A; and Na+, 4 A (9). I n water the To whom correspondence should be sent. limiting Debye-Huckel law was valid. I n water, sodium iodide and tetraphenylborate and in methanol, sodium (10) R. Jervis, D. Muir, J. Butler, and A. Gordon, J . Amer. Chem. SOC.,75, 2855 (1953). iodide can be regarded as completely dissociated under our (11) P. Buckley and H. Hartley, Phil. Mag., 8, 320 (1959). experimental conditions. For sodium bromide in methanol (12) G. Charlot and B. Trimillon "Chemical Reactions in Solvents and Melts," Pergamon Press, London, U.K., 1969. (9) J. Kielland, J . Amer. Ckem. SOC.,59, 1675 (1937). ~~~
ANALYTICAL CHEMISTRY, VOL. 44, NO. 1, JANUARY 1972
195
