RESULTS A N D DISCUSSION
Table I. Results of Potentiometric Determinations and TLC Determinations for Tertiary Amine in Tertiary Amine Oxide Samples
Potentiometric 0 557,
0 70% 0 62yc 1 03yc
TLC 0 54% 0 77% 0 69% 1 00%
tion of dichlorofluorescein in methanol and placed under the ultraviolet lamp. An outline of the tertiary amine spot is made with a pencil and an area of the spot is obtained by measuring and multiplying the height by width. The average area of the spots representing the various concentrations are taken and plotted, using the appropriate relationship. Sample Procedure. A 5-gram sample of the tertiary amine oxide is weighed into a 10-ml. volumetric flask and made u p to volume with isopropanol. The sample is thoroughly mixed and a 5+1. aliquot of the solution is spotted onto a small T L C plate. The same procedure that is used to prepare the standard curve is then followed. After the chromatogram is developed, the plate is sprayed with the indicator. The area of the tertiary amine spot is determined and the weight of unreacted tertiary amine is obtained from the standard curve.
Figure 1 shows the separation obtained between the tertiary amine and the tertiary amine oxide. The standard curve obtained is shown in Figure 2. tb Four different dimethyl “coco” amine oxide samples were analyzed for unreacted starting tertiary amine. The anresults obtained were compared to re- $ . sults obtained using a potentiometric determination ( 7 ) , and compared quite -0I ” favorably (Table I). When used in a process control, a 1.0quantitative determination by thin layer chromatography has several advantages over other methods. Since it does not necessitate elaborate equip0.2ment, its cost is nominal. It is possible onJ o t v ’ 8.0 ” 10.0 ‘ “ to obtain very good precision and not E sacrifice time. An experienced operator can perform 25 to 30 determinations Figure 2. Standard curve in an hour. Also, a small corner of a work bench is sufficient to handle all (6) LIangold, H. K., Kanimereck, R., Ibid., 39, 202 (1962). necessary equipment. (7) LIetcalfe, L. D., AKAL. CHEM. 34, 1849 (1962). LITERATURE CITED (8) Purdy, S. J., Truter, E. Y.,Analyst 87, 802 (1962). (1) Feigl, F., Amoral, J. R., Mikrochim (9) T’annier, S . H., Stanley, W. L., J . A d a . 1958 337--41. Assoc. Ofic. ilgr. Chemzsts 41, 432 (2) Glynn, E., Analyst 72, 248 (1947). (1958). (3) Hefendehl, F. W., Planta Medica JOHN R PELKA 8 , 65 (1960). LINCOLN I). METCALFE (4) Kirchner, J. G., hliller, J. M., Rice, Armour Industrial Chemical Co. R. G., J . Agr. Food Chem. 2, 1031 (1954). 8401 W. 47th St. (5) Mangold, H. K., J . Am. Oil Chemists2 McCook, Ill. 60529 S O C .38, 708 (1961). I
E
Determination of Van Slyke Factors by Gas Chromatography SIR: Van Slyke factors (VSF) have been determined successfully for many years ( I , 3, 6-8). However, a solution of more than one gas requires the use of gas-free reagents to induce suitable reactions and thus to eliminate the vapor pressure of one or more of the gas components. Even for a solution of one gas, partial pressure must be determined in the presence of water where small pressure changes are difficult to measure; also, by separate experiment, the amount of gas that becomes redissolved during a pressure measurement must be determined and an appropriate correction must be applied to the data. Ramsey (6) applied gas chromatography to the analysis of gas-containing solutions by connecting a gas chromatograph (GC) to a Van Slyke extraction apparatus. The net response of two estractions was taken to represent the release of all dissolved gas. This innovation results in greater sensitivity and allows the experimenter to analyze for a particular gas in a gas mixture. Gordon and Adams ( 2 ) of Argonne S a tional Laboratory have used this equipment for gas analysis where they multiply the GC peak area of the first extrac604
0
ANALYTICAL CHEMISTRY
tion by the appropriate VSF, as determined in the conventional manner (1, ?, 6-8), to calculate the response of all the gas in the sample. This communication extends previous work by relating the two GC peak areas obtained by two successive extractions from a sample in such a way as to enable calculation of Van Slyke factors, Henry’s constant, and Bunsen’s solubility coefficient. If one successively extracts a sample and analyzes the gases on a G C until all the gas is removed from the liquid sample, the sum of the peak areas for any gaseous components can be represented as m
A =
Ea< i=l
where ai is the area related to the i t h extraction of the gaseous component in question. With Henry’s law and the assumption of ideal gas-solution behavior it can be shown that a1
az
=
=
(A
Ak
(2)
- ai)k
(3)
where k is the fraction of gas molecules removed from the liquid phase into the gas phase during the extraction process; this ratio is related to the VSF applicable to the experimental conditions employed. Equations 2 and 3 can be solved simultaneously for k and A; this solution yields k
A
-
a2)/a1
(4)
= al”(a1
- az)
(5)
=
(a1
EXPERIMENTAL
A Perkin-Elmer vapor fractometer, Model l54-DG, was connected to a Thomas Van Slyke apparatus by a four-way valve arrangement (Figure 1). All parts of the apparatus were either glass or copper. For COz analysis, a 0.25-inch diameter, 2-meter, silica gel (50-mesh) column was operated a t 110’ C. Helium was used as carrier gas a t an input pressure of 7.0 pounds per sq. inch to obtain an exit flow rate of 50 cubic em. per minute. The thermal conductivity detector was operated a t 8.0 volts and the output signal was fed into a 5-mv. recorder with a chart speed of 4 inches per minute. For oxygen analysis a 0.25-inch Apparatus.
diameter, 2-meter, 13 X Linde molecular sieve (30-mesh) column was operated a t 21' C. Helium was used as carrier gas at an input pressure of 3.0 pounds per sq. inch to obtain an exit flow rate of 40 cubic cm. per niinut'e. The thermal conductivity detector was operated a t 8.0 volts and the signal was fed into a 1-mv. recorder with a chart speed of 4 inches per minute. Samples to be analyzed were prepared in an aeration vessel as shown in Figure 1; during the process the temperature \vas maintained constant within =t0.5" C. The vessel was completely filled with conductivity water and the capillary stem was inserted.. .ifter the purge gas, C 0 2 for one and O2 for another series of analyses, had bubbled through the water with an input pressure of 770 mm. Hg a t a rate of 100 cubic cm. per minute for 30 minutes, the aerat,ion vessel was inverted, and the capillary stem was removed so that a small amount of water could flow out. A 100-ml. syringe containing 5 ml. of mercury to fill void space was fitted t,o the standard taper joint of the aeration vessel, and the purge gas pushed 80 ml. of solution into the syringe. I n this manner a leak-proof transfer was accomplished. This syringe was inverted and placed in the standard taper joint of the Van Slyke extraction head. liquid sample was introduced into the apparatus and extracted. The enclosed volume of carrier gas between the valve system and the Van Slyke head was expanded into the extraction chamber. The mercury was raised,
V
To Gor Chromotqrophy
Inlet Tube TeflonNylond
Von Slyke Extraction Bulb
AERATION VES& GAS ANALYSIS TRAIN Figure 1 . Apparatus for determining Van Slyke factors by gas chromatography
thus pumping the gas from the extraction chamber, and the glass valve closed. Then the valve system was opened placing the gas into the chromatograph. This procedure was adopted to minimize the absorption of gas during the transfer
Table 1.
al,
Extraction of C 0 2 and A, A /y,
operation. A series of liquid samples was drawn from each single syringe filling. Two successive gas extractions were performed on each liquid sample introduced to obtain area values al and a2.
02 from HzO
square inches square inches square inches [k-l]Bxptl C O Z : T = (297.0 f 0.5) OK.; GC attenuation setting, 128 3.432 0.205 3.650 1.825 1.0636 2.00 3 422 0 189 3.622 1.811 1,0585 2.00 3.569 3 415 0 147 1.0449 1.785 2.00 3 915 0 560 6.534 1.1045 1,719 3.80 8.193 7 230 0 850 1.1332 1.725 4.75 8.695 7.675 0,900 1.1328 1.739 5.00 9.495 1.415 11.158 1.1752 1.703 6.55 10.005 1.631 11.954 1.1948 1.684 7.10 11.363 1.935 13.695 1.2052 1.738 7.88 11.530 2,268 14,353 1.2448 1.679 8.55 16,592 13.025 2.800 1.2738 1.676 9.90 14,200 3.485 18.818 1,3253 1.654 11.38 1.728 Av. A / v f0.036 Deviation of mean at 95% confidence level 0 2 : T = (294.0 f 0.5) OK. : GC attenuation setting, 256 1.365 1 358 0 00743 0.6825 1.0051 2.00 0 7080 1.416 1 408 0 00839 1.0056 2 00 1- . 3. .7.7 1 368 0 00873 0 . SSS5 1.0073 2 00 1 406 1.412 0 00627 0.7060 1,0042 2 00 2.346 2 332 0 01439 0.7002 1.0060 3 35 3.778 3 740 0 03758 0.7128 1.0101 5 30 4.512 4 457 0 05462 0.6941 1.0123 6 50 5.185 5 125 0 05913 0,7054 1 0117 7.35 6.155 6 090 0 06390 0.7258 1 0106 8.48 6.515 6 435 0 07876 0.6857 1.0124 9.50 6.900 6 780 0 11753 0,6831 1 0176 10.10 7.130 7 025 0 10371 1.0149 0.6956 10.25 7.758 7 635 0 12074 1.0161 0,6805 11.40 0.697 Av. A / v 2~0.008 Deviation of mean at 95% confidence level v , ml.
square inches
a21
Modified Swogelok Fitting with 1/8" Copper Tubing Soldered of A
-
[k-llexptl
[k-'I
oaied
[k-'lenlcd
[k-'1caicd
1.0359 1.0359 1.0359 1.0717 1.0907 1.0961 1,1304 1.1433 1.1620 1.1787 1.2738 1.2556
2.67 x 2.19 x 0.86 x 3.11 x 3.89 x 3.34 x 3.96 x 4.50 x 3.71 X 5.60 X 4.91 x 5.55 x
1.0014 1.0014 1,0014 1.0014 1.0024 1.0040 1.0050 1,0057 1.0068 1.0078 1.0085 1.0086 1.0099
0.37 x 0.41 X 0.58 x 0.28 x 0.36 X 0.60 X 0.72 X 0.59 X 0.37 x 0.45 x 0.90 x 0.62 x 0.61 X
10-2
10-2
lo-*
10-2
10-2 lo-? lo-* lo-?
10-2 10-2
~~
VOL. 37, NO. 4, APRIL 1965
665
RESULTS A N D DISCUSSION
The results of two test series are shown in Table I. Area values al and a2 for the first and second gas extractions, respectively, were experimentally determined; values for k-’ and the total area A were then obtained by employing Equations 4 and 5 . T o indicate the precision of the experiment, the quantity A/v-Le., the total area per unit sample volume-was calculated; its value should be a constant for each test series. A small trend is indicated by the data for C 0 2 which may reflect the readsorption of a soluble gas during the transfer process; however, no such effect appears in the data for 02. For comparison purposes values for k-1 based on known values of Henry’s constant K or Bunsen’s solubility coefficient (absorption coefficient) a reported in the literature (4) can be calculated. An existing relationship between these quantities is readily obtainable. First, application of Henry’s law yields
[w] cv
=
n
PPV
-l
= (cv
n)M
(6)
where p is the partial pressure of gas; the concentration (moles per unit volume) of gas dissolved in the liquid before extraction; v , the liquid-sample volume; n the molar quantity of extracted gas; p the density of sample liquid (approximately 1 gram cm.-)) ; and M, the mass per mole of sample liquid (approximately 18.02 gram mole-‘ for aqueous sample). Furthermore, from Equation 2
Finally, by application of the ideal gas law for the extracted gas
is obtained, where V is the volume of the extraction chamber (49.2 cubic cm. for apparatus used in this investigation), R , the gas constant [6.236 X l o 4 (mm. Hg) cubic em. mole-’ ( O K . ) - ’ ] ; and T , the absolute temperature of the extracted gas. From Equations 6, 7, and 8 follows:
original volume, (V - v ) , to the new volume, v’, will result in some redissolution of extracted gas in the solvent brought to enclose this new volume; thus, a molar quantity n’ will be contained in the compressed volume. Application of the ideal gas law for an isothermic compression process yields
From Equations 7 , 8 , and 12 one obtains
-’C
VSF T o introduce Bunsen’s solubility coefficient (absorption coefficient) a, its correlation to Henry’s constant K by the equation a = - pRTo
MK
p
=
iv ’ kvRT ~
(13)
The VSF applicable to the case of employing the GC techniques to the analysis of gas-containing solutions can also be expressed in terms of the ratio k . The GC peak area al is related to the molar quantity n of extracted gas by
n
= yal
(14)
should be noted, where To is the standard temperature of 273’ K. Then from Equations 9 and 10 the formula
where y is the GC calibration coefficient obtained from a separate experiment. From Equations 7 and 14
is obtained. Values of k-’ calculated on the basis of Equation 11 are also shown in Table I ; these appear to be in good agreement with the reported experimental data. It is possible also to use the suggested GC method to obtain the VSF for subsequent application to a standard Van Slyke gas determination, where the pressure p’ that the extracted gas exerts in a known volume v’ is measured. Compression of the extracted gas from its
SOLUBILITY OF GASES I N WATER
C,
k = -n cv
(7)
can be implied.
Table II. GC Calibration Factors and Solubility GC attenuating setting 128 GC calibration factor y, mole/sq. inches 1.904 X Deviation of mean at 959” confidence level f0.014 X Temperature T*, OK. 297.0 f 0 . 5 Pressure p ’ , mm. Hg 770 3.29 X Solubility cs, mole/liter Deviation of mean at, 95y0 confidence level f 0 . 0 7 X loF2
Table 111.
Data
256
If the GC response has been calibrated for the gases in question, the data obtained and shown in Table I can be used to calculate the solubility of the gas in H20 as well as Henry’s constant K and Bunsen’s solubility coefficient (absorption coefficient) a under the conditions prevailing in the experiment. Calibration factors y were obtained by introducing pure gas into the apparatus at known pressure p c , temperature Tc, and volume vc-i.e., a known amount n of gas-and measuring the total GC peak area Ac; If the gas is assumed to be ideal
1.984 X f0.038 X 294.0 f 0 . 5 770 1.38 X 10.03 X
Values of the calibration factor y determined for COz and O2 with their deviation of the mean quoted at the 95% confidence level are shown in Table 11. From Equations 2 and 13
Henry’s Constant and Bunsen’s Absorption Coefficient
(Comparison of Present Data and Literature Values)
con Present data
0 2
Literature value
Present data
Henry’s constant K , mm. Hg 1.30 x 1 0 6 1.21 x i o 8 3.10 x 107 Deviation of mean at 95% confidence level f 0 . 0 3 X loe f 0 . 0 7 x 107 Bunsek’s absorption coefficient a 7.27 X 10-l 7.81 X 10-l 3.06 X Deviation of mean at 95yGconfidence level f O . 16 X lo-‘ f0.07 X
606
ANALYTICAL CHEMISTRY
Literature value 3.11 x 107 3.04 X
is found. By substitution of the average values of A/v taken from Table I, the concentration c of the solution analyzed was calculated and the results are shown in Table 11; because the test samples were saturated solutions of gas in water a t the temperature T* and under the gas pressure p* indicated in Table 11, the quoted concentration c in Table I represents the value for the solubility c,
obtained at temperature T* and under pressure p * , and the value of Henry's constant K a n 8 Bunsen's solubility coefficient (absorption coefficient) CY can be calculated from the formulae
Data obtained from this investigation are compared to literature (4) in Table 111. CONCLUSIONS
The present method is valid for determining Van Slyke factors and for determining the amount of gas dissolved in a
liquid employing gas chromatography. This technique can be applied to a solution containing more than one gas if the gases in question can be resolved. Furthermore, the method described should be applicable for determining the partial pressure of components of some organicaqueous and some organic-organic systems. ACKNOWLEDGMENT
The author thanks Hermann J. Donnert, U. S. Army Nuclear Defense Laboratory, for the extensive critique and constructive suggestions; these efforts have substantially contributed to improve the presentation of this work.
LITERATURE CITED
(1) Adams, G. E., Anderson, A. R., Van
Slyke Factors for Hydrogen, Oxygen, Carbon Dioxide and Carbon Monoxide, ANL-5991 (1959'1. (2) Anderson; A. R., Hart, E. J., J . Phys. Chem. 6 6 , 70 (1962). ( 3 ) DOLIlas, E., Ibid., 68, 169 (1964). (4) H an book of Chemistry and Physics, 44th Ed.. DD. 1706-1709 Chem. Rubber Co., Clevdand, Ohio, 1961. (5) Ramsey, J. H., Sczence 129, 900
3
(19.59). \----, (6) \'an Slyke, D. D., Harington, C. It., J . Bid. Chem. 61, 575 (1924). (7) Van Slyke, D. I)., Neill, J. M., Ibid., p. 523. (8)Van Slvke. D. D.. Stadie. W. C.. ' Zbid., 49,"l (1921). ' RONALD A. SASE
U. S. Army Yuclear Defense Laboratory Edgewood Arsenal, Md.
Polarographic Reduction of Tin(lV) in the Presence of 3-Mercaptopropionic Acid SIR: The polarographic analysis of tin(1V) is ordinarily carried out in chloride (3) or pyrogallol supporting electrolytes (6). I n both solutions, the acidity must be closely controlled within rather narrow limits to obtain wellformed polarographic waves. I n addition, polarograms of the tin (1V)-pyrogallol chelate show a dip in the limiting" current at negative potentials which could be a complicating factor in simultaneous analyses (6). I n this respect, tin(1V) is readily reduced from perchlorate, tartrate, citrate, and ammoniacal solutions in the presence of 3-mercaptopropionic acid. The polarographic waves are well formed and appear suitable for analytical applications in the supporting electrolytes investigated. I n addition, the acidity in perchlorate solution may be varied over a rather wide range, and the polarograms do not show a limiting current dip.
3.40 seconds, the flow rate was 4.34 mg./ second. Chemicals. All inorganic chemicals were of reagent grade. T h e stock tin(1V) solution was prepared from sodium stannate dihydrate (J. T. Baker Co.) by dissolving t h e solid material in 0.1M sodium hydroxide solution. 3-Mercaptopropionic acid (Matheson Coleman & Bell or Evans Chemetics material) was used as received. Procedure. A known volume of supporting electrolyte was deaerated by nitrogen bubbling. Sufficient 3mercaptopropionic acid was added so t h a t t h e final solution concentration was 0 . 2 M , then the tin(1V) aliquot
RESULTS A N D DISCUSSION
EXPERIMENTAL
Apparatus. All polarograms were recorded o n a Sargent Model XXI instrument. T h e saturated calomel electrode contained a flowing junction which served to separate the solution under investigation from the reference electrode ( 1 ) . The flowing junct;on was filled with 0.1M sodium nitrate when perchlorate was the supporting electrolyte. The temperature was maintained at 25' C. by means of a thermostated water bath. T o minimize convection effects caused by vibrations, the water bath containing the cell and electrode assembly was placed on a heavy slab. The slab was then placed on a rubber inner tube, which served as a shock mount. The drop-time was
was added. This sequence of addition was followed to minimize possible air oxidation of the mercaptan and to avoid hydrolysis of the tin(1V). When tin(1V) was added before the mercaptic acid in perchlorate solutions, a temporary opalescence-caused by formation of hydrolytic tin(1V)-was sometimes observed. Hydrolysis was even more marked in the ammonia buffer solution under these conditions. After the nitrogen bubbling step, polarograms were obtained in the usual manner. Addition of 3-mercaptopropionic acid to the 2M ammonia buffer so that the final concentration of complexing agent was 0.2M caused the p H to change from 9.5 to 9.3. For the more acidic solutions, the p H was not decreased significantly on adding a comparable amount of the mercaptic acid.
-0 2
-06 VOLTS
-1
0
SCE
Figure 1. Polarogram of tin(lV) in presence of 3-mercaptopropionic acid A.
B.
0.1 M Perchloric acid, p H = 1.0 0.1M Perchloric acid, p H = 1.0, 0.2M 3-mercaptopropionic acid, 2.00 X 10-4M tin(1VI
The polarographic reduction of the tin(IV)-3-mercaptopropionic acid complex was investigated in perchlorate, citrate, tartrate, ammoniacal, phosphate, and sodium hydroxide supporting electrolytes. Ordinarily, polarographic reduction of tin(1V) in these solutions produces kinetically hindered waves with limiting currents considerably less than predicted for solutions of these concentrations (3). However, in the presence of 3-mercaptopropionic acid, the usual two reduction waves for tin(1V) mere obtained in all supporting electrolytes except the last two. Typical polarographic waves are shown for supporting electrolytes composed of 0.1M perchloric acid (Figure 1, curve B ) , 0.1.11 tartaric acid (Figure 2, curve C), and 2M ammonium hydroxide, 21M ammonium chloride buffer (Figure VOL. 3 7 , N O . 4, APRIL 1965
607
