Table 1. Typical Results in Determination of CPC by Thermometric Titration with Orange II
Concn. of CPC (mrnole/liter) Taken Found 0.500 1.00 1 .oo 1.oo 1.00 1 .oo 2.00 2.00
0.505 1.01 1.00 1.01 0.99 1.04 1.99 2.01
t
c
2*o
,JOLUUE
I ,5Error,
%
OF TITRANT USED
r!I
END POINT
I I
\
1.o 1.0 0 1.0 1 .o 4.0 0.5 0.5
RESULTS AND DISCUSSION
Table I shows data concerning the accuracy attainable in the determination of CPC by thermometric titration with Orange 11. Since the CPC used in this study was free of halide impurities, a silver nitrate thermometric titration was used to verify the concentration of the sample solutions. The results of three titrations of a 5 x 10-4X CPC solution with 0 . W silver nitrate gave an average value of 4.99 x 10-4 i 0.04 x 10-4-11, It appears that in the absence of interfering halide ions, silver nitrate might be the titrant of choice for quaternary ammonium surfactants. However, in most practical situations, halide ion contamination would be expected to be present and thus preclude the use of silver nitrate. The analysis of a sample
I
0
J I
.3
.6
I
1.2 I.5 M I L L I L I T E R S OF TITRANT
Figure 1 .
.9
1.8
2.1
Typical enthalpogram
100 ml. of 1 X 1 O - W CPC titrated with 0.108M Orange II
by the use of both Orange I1 and silver nitrate could serve as-a measure of halide ion contamination. Preliminary work with other quaternary ammonium surfactants of varying chain length and polar groups indicates that thermometric titration with Orange I1 may be used for rapid and accurate analysis. Additional work is planned to determine the effects on this procedure of nonionic surfactants, amine salts, and inert materials usually present in preparations containing quaternary ammonium surfactants.
LITERATURE CITED
(1) Jordan, J., Pei, P. T., Javick, R. A., ANAL.CHEhf.35,1534 (1963). (2) Raffa, R., Stern, 1cI. J., College of
Pharmacy, Columbia University, New York, N. Y., unpublished data, 1965. (3) Zografii, G., Patel, P., Weiner,' N. D., J . Pfiarm. Sci. 53.544 (1964).
NORhlAN D. WEINER ALVIN FELMEISTER Of
College of Pharmacy ~ Columbia ~ New York, X. Y. 10023
~
i
Simultaneous Polarographic Estimation of M a ior Constituents in Lead-Tin and Lead-Tin-Indium Alloys SIR: Kolthoff and Johnson (8) observed that the diffusion current for the stannic-stannous polarographic reduction wave, in 4N HC1 and in the presence of a small amount of tetraphenylarsonium chloride (TPXC), is equal to one-half of the total diffusion current for tin. I n addition, they observed that the stannic-stannous halfwave potential is shifted to more negative values and its diffusion current is unaffected by the presence of moderate quantities of lead. While investigating procedures for the analysis of lead-tin and lead-tin-indium alloys as a part of a quality assurance program, it was felt that the observations made by Kolthoff and Johnson could be applied to the simultaneous estimation of each of the major constituents in a lead-tin or a lead-tin-indium solder. A well defined polarogram showing three reduction waves is obtained corresponding to the Sn+4-Sn+2, the Sn+" 516
ANALYTICAL CHEMISTRY
SnO, Pb+LPb0, and the In+"InO reductions. This offers a direct estimation of tin and indium and an indirect determination of lead. EXPERIMENTAL
Apparatus. A Sargent Model XXI Polarograph was used in conjunction with a water-jacketed (25.0' =t0.1' C.), mercury pool-DME polarographic cell in the recording of all current-voltage curves. T h e capillary characteristic for the D l I E was 2.03 mg.2'3 sec.-*/2 as measured in distilled water and open circuit. During initial investigations, a conventional SCE-DJIE cell was used in the recording of polarograms from which halfwave potentials were calculated; this cell possessed a cell resistance of 70 ohms as measured with an industrial Model RC conductivity bridge. When desirable, the potentials were measured a t the beginning and end of each polarogram with a Rubicon potentiometer.
Sample Preparation. Most of the samples investigated were of t h e nonflux variety; however, when samples also contained flus, they were melted in a small test tube under an argon atmosphere and manually moved away from the molten flux. This procedure was performed a t least three times before the samples were washed with xylene. dll samples were then machined and the turnings washed with xylene before weighing. Unknown Solution Preparation. The requisite amount (see subsequent discussion), weighed t o t h e nearest 0.1 mg., of unknown or standard solder sample Tvas placed in a 250-ml. Erlenmeyer flask. Concentrated HC1, 80 ml., and concentrated H S O s , 2 ml., were added and the flask a n d contents were heated until the resulting solution was colorless (or until the solution volume was approximately 50 ml.). The solution was cooled, quantitatively transferred to a 100 ml. volumetric flask, and diluted to the mark.
~
Polarographic Test Solution Preparation. T o each 100-ml. volumetric
flaqk, 20.0 ml. of unknown solution, 10 ml. of TP.IC (0.4 gram/liter), 20 ml. of concentrated HCl, 20 ml. of ethanol, and a known amount (see subqequent discussion, of standard lead nitrate (1.000 gram/100 ml.) were added; t h e solution is mixed, cooled, and diluted t o t h e mark. Polarographic Procedure. Each solution is polarographed, after a 7-minute degassing period with argon, utilizing normal procedures.
Table I.
Sn, mg./100 ml.
-Eli2, mv.
mg./100 ml.
-E112,b mv.
mg./100 ml.
20.0 20.0 20.0 20.0 20.0 20.0
c
221 268 311 335 361
18.8 31.3 43.8 56.3 68.8 81.3
499 507 499 508 501 501
15.0 15.0 15.0 15.0 15.0 15.0
a b
RESULTS AND DISCUSSION
l l i u r a (8) has described a polarographic procedure for the analysis of lead-tin solders utilizing a 4M ammonium bromide supporting electrolyte. Preliminary investigation of this system indicated an indirect determination of residual current' because the stannicstannous half-wave potential occurs near the anodic dissolution of mercury; however, Kolthoff and Johnson ( 2 ) have shown that TPXC, in a slightly different supporting electrolyte system, enhances this evaluation. They reported some of the variables which must be considered in these systems, such as the usable concentration of TPXC, the effect of the HC1 concentration, the need for the ethanol, the advantageous shift of the stannic-stannous reduction potential, and the equality of the diffuz'+ion currents of the stannic-stannous and stannous-tin reduction waves. However, during this investigation it was noted that several factors must be controlled closely to obtain the desired results. In order that the half-wave potential of the stannic-stannous reduction is sufficiently negative to easily measure the residual current, the lead-tin ratio should be at least 2: 1 in this supporting electrolyte medium (Table I). I n addition, the tin concentrat'ion in the polarographic test solution should be 0.001 to 0.00231. When the tin concentrations fall below 0.001.11, the effect of lead on the stannic-stannous half-wave potential is not nearly so great, and larger lead-tin ratios are needed to obtain satisfactory residual current measurements; because many of the samples investigated here require a standard addition of lead, this is not desirable. Purging time was critical. Incomplete removal of oxygen increased the tin and lowered the lead results. During this investigation a purging cell was not used; however, purging times of 6 to 8 minutes were satisfactory. Preliminary measurements were made with a conventional SCE-DME polarographic cell which had been thermostated at 25" f 0.1' C. Upon continual use of this cell with the solutions described here, the lead analyses became erratic and nonreproducible; this prob-
Effect of Lead Concentration on Half-Wave Potentials of Sn+LSn+* and ln+3-ln' Reduction Waves"
c
Pb,
In,
-Eli*,
mv.
63 1 640 638 646 642 644
SCE-DNE polarographic cell used in these measurements. Half-wave potential for Sn+2-Sn", Pb +2-Pbo reduction wave. Not conveniently measured.
Table II. Effect of Lead-Tin Ratio on Lead and Tin Calibration Factors
Pb/Sn ratio
mg. Sn/pa.
mg. Pb/pa.
2.34 2 82 2 82 3 13 3 44 4 07
2.11 2 13 2 13 2 10 2 10 2 07
2.83 2 80 2 86 2 86 2 85 2 96
lem was eliminated by the use of a mercury pool-DME cell. Although it was not completely investigated, these results were attributed to lead chloride saturation in the supporting electrolyte media. At low and high lead-tin ratios, the milligram of lead per microampere and milligram of tin per microampere calibration factors become concentrationdependent (Table 11). Such a condition does not lead to reliable analysis on samples where the conditions are not essentially identical to those of the standard solutions. Normal polarographic accuracy, il%, is obtained
% Pb
=
x
{ [(idSnC'-Sno,Pbt2-Pbo-idSn+eSn+2)Cca. factor, mg. Pb/pa.]
Table 111.
when the lead-tin ratio varies between 2.2 and 4.0. For general analysis, when the percentages of tin and lead are completely unknown, a preliminary determination may be needed so the correct amount of lead is added to the polarographic test solution. The evaluation of the percentage of indium is not affected by either the tin or lead in solution except for the residual current of the indium reduction wave; it is hindered somewhat by the limiting current of the Sn+2-Sn', Pb+2-Pb' reduction wave. This difficulty is easily eliminated by the use of the midpoint correction technique (1). The evaluations of the percentages of tin and indium mere made utilizing the diffusion currents of the indium and the stannic-stannous reduction waves and their corresponding calibration factors. However, because of the experimental conditions necessary for adequate tin analysis (the standard addition of lead to the polarographic test solution), the evaluation of the percent'age of lead in the original sample is somewhat more involved. The procedure followed in this investigation is summarized in Equation 1.
- mg. P b added)
X
500 ---____ sample wt., mg.
(1)
Analysis of Several Standard Lead-Tin and Lead-Tin-Indium Solders
detns.
Pb/Sn ratio
Pb
Sn
In
Total
43.7/56. 3/OQ
3
2.8
43.1
...
/37.6/24.9" 40.2/29.8/30.0" 30.1/49.8/20.1"
1 1 2
2.3 2.6 3.4
36.8 37.3 38.6 31.6
56.8 57.2 57.0 37.7 38.5 29.8 49.1
99.9 100.5 100.6 100.0 100.7 98 4 100.5
No. of
% Pb/o/o Sn/70 In
Per cent
... ... 25.5 24.9 30.0 19.8
a Standard solders prepared by melting and mixing requisite weights of reagent grade metal under an argon atmosphere. Melts machined and turnings washed with xylene.
VOL. 38 NO. 3, MARCH 1966
517
Table I11 summarizes the analysis of several standard solder samples. Utilizing the procedure suggested, a series of 44 samples, presumably 37.5% lead, 37.5% tin, and 25.070 indium were analyzed; the results were 37.2 0.7% lead, 37.8 0.4% tin and 25.2 + 0.2% indium. Several other lead-tin solders, where the lead content varied from 40 to 60%, gave similar results.
*
*
ACKNOWLEDGMENT
Appreciation is extended to Joseph
0. Frye, this laboratory, for preparation of standard solders used in this investigation, LITERATURE CITED
(1) Elving, P. J., Van Atta, R. E., ANAL. CHEM.26, 295 (1954).
(2) Kolthoff, I. M., Johnson, R. A., Zbid., 23, 574 (1951). (3) Miura, Y., Bunseki Kagaku 7, 779
(1958).
D.E.SELLERS I).J. ROTH
Mound Laboratory hlonsanto Research Corp. hliamisburg, Ohio Mound Laboratory is operated by blonsanto Research Corp. for the U. S. Atomic Energy Commission under Contract No. AT-33-1-GEN-53.
Separation of Alkaline Earth Elements by Anion Exchange SIR: Ion exchange has been used for the separation of the alkaline earths by other methods (2-5). The results obtained by the authors in the investigation of the anion exchange equilibria of alkaline earths in the presence of 2,6pyridinedicarbosylic acid suggested that this system might prove convenient for the separation of these elements (1). It would also be of interest to observe the correlation between batch equilibrium studies and the elution behavior. I n the previous study (1) the distribution coefficients, defined as
I
=
K D
Moles of metal ion per kg. of dry resin Moles of metal ion per liter of solution were measured as a function of the concentration of ammonium 2,6pyridinedicarboxylate (Figure 1). At high concentrations of complexing agent all of the distribution coefficients are low. At low concentrations of complexing agent, strontium and calcium have large distribution coefficients, while those of magnesium and barium are low. This suggests that this system should allow the separation of calcium or strontium from magnesium or barium. EXPERIMENTAL
The ion exchange resin used was Dowex 1, 50-100 mesh with 8% crosslinkage. This form was used since it was the same as the form used in the distribution studies. The elution experiments were performed using a resin column 37.6 cm. long in a glass tube of 5.2-mm. diameter. The density of the
Table I.
Experiment 15 1‘ 2b
a
b
Element hk Ca Ba
2b Sr Eluent change at 75.5 mi. Eluent change at 56.0 ml.
51 8
. . . . . . .. I
0.00 I 0.01 LIGAND MOLARITY
ANALYTICAL CHEMISTRY
, , , ,\
I 0.I
I
Figure 1 . Plot of the log of the distribution coefficient of metal ions as a function of the log of the molarity of 2,6-pyridinedicarboxylic acid
column was 0.492 gram per ml. and the fractional interstitial volume was 0.53. The resin was used in the 2,6-pyridinedicarboxylate form. The metals were added to the column by placing 0.2-ml. aliquots of 0.25df solutions of the metal chlorides on top of the resin column. Elution was carried out with the appropriate concentration of ammonium 2,6-pyridinedicarboxylate a t a rate of approximately 0.5 ml. per minute. The pH values of the eluting solutions ranged from about 7.1 for the most dilute to 7.6 for the most concentrated. The titration data ( I ) indicate that the distribution coefficient between pH 7 and 10 is constant. Above a p H of 10, hydroxide ion might compete for resin sites; below a p H of 7, hydrogen ion will compete for the ligand. The elution was monitored in most cases by a conductance cell a t the bottom of the column. The conductance cell was one arm of a conductance
Quantitative Data on Separations
Taken, mmole 0.100 0.050 0.050 0.050
.
Found, mmole 0.103 0.050 0.050 0.047
Eluent vol. range 0 to 75.5ml. 78.7 to 100.5 ml. 0 to 56.0 ml. 61.0 to 96.6
bridge, the off-balance of which was plotted on a recorder. Effluent samples were analyzed by flame photometry. The samples were ignited in platinum crucibles. The metal oxide was dissolved in 3.ON HC1 and again evaporated to dryness. The metal chloride residue was then dissolved and analyzed for metal content by flame photometry. ; iBeckman DU, with the flame photometer attachment, was used. The reagents were prepared and analyzed as given previously (1). RESULTS AND DISCUSSION
I n one experiment a misture of magnesium chloride and calcium chloride was placed on the top of the column and then the magnesium was removed with 2.0 x 10-3.11 ammonium 2,6 - pyridinedicarboxylate (Figure 2). The calcium remained on the column. Then, a 1.0 x 10-1M eluent was used and the calcium was removed (Figure 2 ) . This complete separation can be explained on the basis of the distribution coefficient difference for magnesium and f calcium a t 2.0 x 1 0 - ~ ~complexing agent. A similar experiment was carried out using a mixture of barium and strontium (Figure 3). The same complete separation was obtained. A quantitative representation of the
