Application of Volume Change Characteristics of a Sulfonated low Cross-linked Styrene Resin CALVIN CALMON Research Laborutory, Permutit Co., New York, N. Y . The volume of sulfonated polystyrene resins depends on the cross linking of the resin, the cation in the ex-
change position, and the type and concentration of the solution in equilibrium with the resin. The above properties are utilized in the application of the low cross-linked exchangers as a'new analytical tool. The initial results show that these resins may be used for determining concentrations of certain solutions, ionic species of given valences, and reaction end points where changes in concentration or in valence take place. A single bead of resin may be used for repeated analyses. If the resin is used in a column, only a few minutes are needed for an analysis. The method requires only one standardization, and, therefore, may find numerous applications.
S
OME of the swelling and devuelling characteristics of sulfo-
nated polystyrene resins cross-linked with divinylbenzene have been reported by various investigators (i-7). Most of tho woi k has been done with the higher cross-linked resins, with monovalent ions, or in a nailow iange of concentration. This papei deals only with a sulfonated styrene resin cross-linked with 1% divinylbenzene (Permutit QX). The cations studied had valences from 1 to 4 and the concentrations of sodium chloride and hydrorhloric acid fiolutions mere from 0.005 to 2.5 II'. Applications investigated were to determine whether this type of resin could be used as an indicator of caoncentrations and as an endpoint indicator in rractioris irivolvirig concentration or valmce ChXl I Kc's
sodium chloride solution of a particular strength was passed through and the minimum volume observed. Equilibrium was obtained in less than a minute and with a volume of solution less than 100 ml. When the next strength of solution was through, there was no difference in the results, whet=; was passed after the weaker solution or whether the first solution was rinsed out of the bed with distilled F-ater. Single Sphere Method. The single sphere method consisted of placing a single bead in a concave slide and measuring its maximum swollen volume under a microscope. The diameter of the spheres, when in the monovalent cation form sxvollen in distilled water, ranged from 1.0 to 1.7 mm. When the maximum volume was obtained, the bead was treated several times with a strong solution of the specific cation. The solution was removed with a filter paper and the sphere washed with distilled water until free of soluble electrolytes. The treatments were repeated until several checks were obtained. This was not confined to a single sphere, as often four or five spheres were used for an experiment with a particular cation. For the effect of concentration of a certain Eolution on the volume of the spherefi, the bead was allowed t o come to equilibrium with the given solution by repeated additions of fresh solution and removal of the old solution by adsorption with filter paper. Usually, with dilute solution, longer periods of contact were necessary.. Often 15 or more analyses mere made with a single sphere. RESULTS
Table I gives the data for the volume ratio obtained for the cations studied, by both the column bed and single sphere methods. It is evident that with a feq- exceptions, the volumes of the resin depend upon the valence of the cation. All monovalent ions have a volume ratio of 1.0. In the case of the divalent ions, the single sphere method gave an average volume ratio of 0.47 or a shrinkage of about 53%. I n the column bed method, the average volume ratio (disregarding zinc and ferrous ions
EXI'EHIMENTAL
Volume Measurements. The volume of the resin was studied by two methods: in a column bed and by a single sphere. The column bed method consisted of placing the wetted beads which were in the hydrogen form in a calibrated 10-ml. buret with funnel attachment. The wet bed volume in distilled water was about 5 ml. and the material was kept a t the zero point of the buret by a Pvlonel metal xreen with 50-mesh openings. To backwash the bed, distilled yater was introduced at the tip of the buret, so that the bed WBF raised into the funnel and then settled by draining the water. To determine the effect of the cation, the bed was treated with a soluble salt of the particular cation. The solution was usuall>r concent,rated and the initial rate of salt introduction m-as rapid. The bed was then rinsed free of the excess solution and the backwashed-and-drained volume was noted. This often required several washings and backwashings. The treatment with solution was then repeated but with a lower flow rate, and fin:dly allowed to stand in contact with the solution for 0.5 hour. The bed was again rinsed with distilled water and, when free of soluble electrolytes, the volume was checked once more by backwashing and draining. When a constant bed volume waits obtained after several treatments, it was recorded as thc volume of the bed for that particular ion. When exchange for another ion was desired, the bed R-as treated with 1 to 1 hydrorhloric acid solution in wat,er and then washed free of acid until the original volume in the hydrogen state was obtained. The bed was then treated with the next ion in question. For a study of the effect of concentration of solution on t'he bed in B given salt form, the bed was first converted to the particular cation, such as sodium and hydrogen, and then the various strengths of the acid or salt solutions were passed through until the minimum volume was observed. Thus, for a sodium chloride solution, the hrd was in the sodium form when the
Table I. Effect of Cation on Volume of Sulfonated 1% Cross-Linked Styrene Resin (Permutit QX) (Volume of resin in hydrogen state taken a s 1; other results give ratio of their volume t o material in H state)
Cation
H+ Li Sa
K+ Rb++ cs
Bed method
1.0 1.0 1.0 1.0
1.0
..
1:0
1.0 1.0
LIg + Ca++ %n++ Cd:,' Fe co++ Xi++ Cu++ Mn++
0.49
0.46 0.44 0.50 0.47 0.46 0.43 0.45 0.48 0.47
f
1456
1.0
1.0 1.0 1.0
1.0
a
Volume Ratio Sphere method 1.0
0.54 0.54 0.62 0.47 0.63 0.55 0.59
0.51
Sr+'
0.37
0.34
Ba++ Pb-+
0.18 0.19
0.17 0.23
AI+++ Fe'++
0.26
p++++;
O,l9
..
0.22 0.16 0.17 0.17
Th+++ Average value
0.11
0.09a
0.21
V O L U M E 2 4 , NO. 9, S E P T E M B E R 1 9 5 2
1457
where slight gelatinous precipitates formed, resulting in a drag effect between the glass and the spheres) is 0.53, which nearly coincides with the value obtained from the single sphere method. A higher volume ratio would be expected for the column bed method because there may be some free space between the bed and the wall of the glass tube A tube of larger diameter may decrease the difference betn-een the two methods. For strontium, barium, and lead the volume ratios are reduced, no doubt because of the inqolubility of their sulfonates. The trivalent ions showed an average volume ratio of 0.22 for the bed method and 0.18 for the sphere method. In the case of thorium, reproducible results were obtained in the column bed method, but with the sphere method, three of the six spheres tested showed volume ratios of 0.06 and the other three were 0.12. The reaxon for this variation cannot yet be explained, but it may be due to the technique used or variatiom in the structure of the spheres. When the log of the average volume ratio obtained by the two methods is plotted against the valence, a straight line seems to be the result. Therefore, with the exception of a few ionsi.e , those M ith limited sulfonate solubility or those showing hydro\idt, precipitation-the volume ratio depends on the valence of the cation; the higher the valence. the lower the volume ratio Since volume ratios which were dependent on the valence of the cations were obtained, it would seem that we may look upon the resin as a nintrix with active groups of -SOaattached to various points along the matrix. When the -SOdgroup has a monovalent cation, water can come between these active groups and expand the matrix to its maximum permiwible limits, n hich are dependent upon the cross-linking and on the electrolyte content of the solution. When the change from a monovalent cation to a divalent ration is made, only the alternate spaces between active groups art' free for water to enter and cause swelling t o a new limit. This limit may be approximately 50% of the original volume; however, the actual volume of the resin may be neglected, as the swelling of the 1% cross-linked resin is many times the original dry volume. The single sphere method showed the resin particle to swell 25 times the dry state when placed in water. Similarly, when the valence of the cation is increased to three, then only one third of the spare8 are free for water to enter and t o expand the resin. However, the results obtained would indicate that a greater reduction in the volume ratio takes place than that expected from the picture formulated. With the quadrivalent cation every fourth space bhould be available for expansion. However, the reduction in volume is still greater than expected, indicating a possibility that some active groups are somewhat under the electrostatic attraction of the multivalent ion, thus preventing the expansion possible with the free spaces available. Another possible mechanism is that with the multivalrnt ions, the water of hydration is also reduced, so that a reduction in ewelling due both to the unavailability of free spaces for expansion
Table 11. Effect of Hjdrochloric .4cid and Sodium Chloride Concentrations on Volume Ratio of a Sulfonated 1% Cross-Linked Styrene Resin Normality of
NaCl or HC1 Solution 0 0 0.005 0.01 0.02 0 05
0 1 0.5 1 0 2.0 2 5 5 0 10 0
NaCl Solution Bed Sphere method method 1.0 1.0 0.95 0.94 0.89 0.88 0.77 0.82 0.72 0.72 0.64 0.63 0.45 0.38 0 40
:
0 29
:
HCl Solution Bed Sphere' method method 1.0
1.0
o:s9 0.83 0.73 0.65 0.47 0.42
o:i1 0.89 0.68
0.36
0:26 0.20
0.63 0.45 0.43
and the reduction in the water content of the cation itself i R ohtainrd. Effect of Concentration. Table I1 shows the effect of the volume ratios of the resin by both the single sphere and the c*olumnbed methods for sodium chloride and hydrochlorir acid solutions when in contact with the refiin in the sodium and hydrogen states, respectively. The plot obtained from the log of the concentration versus the bed volume is a straight line for cwnc.entrations to 1 N . From the data in Table I1 it is evident that the single sphere and the column bed method are not too far apart, and that there is little difference between sodium cnhloiide and hydrochloric acid solutions. This agrees with the ('onvlusions of Rome investigator,=t o whom reference has been made (1,d).
Table 111. AnalyrsiF of Boiler W a t e r s hy Red Volume Clethod Volume Ratio of Bed 0.80 0.75 0.75
Sample 1 2 3 4
0.70
Concentration. CaCOa From BY Table I1 analysin t 100 1108 I850 1700 I850 1830 2798 moo .P.P.51. .-~
--
.
,,, /L
Lliffertrwe -0.7 t 8 ii rl 1
- 8 r, ._-
The shrinkage in bed volume for Hulfuric acid was less than expected, possibly indicating the prrsenrx. of the bisulfate ion. In the case of acetic acid, slight shrinkage was observed up to a concentration of 2 N ; this indicates that the phenomenon depends on the ionic strength of the Polution in question. APPLICATIONS
In view of the reproducibility of results and ease of handling, it appears t,hat these characteristic volume changes may be utilized as a tool in analysis nf strong electrolytes. The first investigation on its use as an analytical tool was applied to boiler waters, where the cations were monovalent and the concentrxt,ion varied from 22 t o 60 meq. per liter. \Then these solutions were passed through sodium beds a t their maximum volume in distilled water, the maximum shrinkage of the bed volumes was noted for each solution. The conrentration of each was then determined from t.he plotted data of Table 11. The agreement between the analyfiis by chemical means (alkalinity, chloride, sulfate, phosphate, etc.) and the ratio bed volume method, which required less than 1minute in nprrat'ion, varied from 0.7 to 8.9% as can be seen from the check i n Table 111. The method is a t present being refined by the use of l o n r i mms-linked rwins, so as t o make it more accurate. The determination of the conrrsntration of divalent ions in natural waters by the column bed mr:thod was also investigated. The bed volume ratios were determined for a bed through which were passed aliquots of a known calcium solution, the quantity being equal to the capacity of the bed. After each portion of solution the bed was rinsed with distilled water. Thus a curve was prepared which gave the degree of shrinkage with the passage of a given quantity of calcium salt. When a given quantity of natural water, containing a calcium and magnesium content less than the capacity of t,he bed, was passed through the bed, followed by backwashing and rinsing with distilled water, a shrinkage took place due to the exchange from the monvalrnt to the divalent ions. The correlation bet)ween the concentration obtained from the prepared curve was found to he within 4% of the value determined by chemical analysis. With the above facts one can readily see that the volume ratio method may be used as an indicator of breakthrough reactions where a change takes place either in concentrations or in the valence of the cations involved. Thus, the authors have deter-
ANALYTICAL CHEMISTRY
1458 Table IV. Low Cross-Linked Resin as Indicator of Calcium-Magnesium Breakthrough i n a Softening Unit [lo% effluent,from 200 ml. bed of a cation exchanger, used for softening a water containing 425 p.p.m. (as CaCOa) total hardness, passed through a 5ml. bed of 1% cross-linked sulfonated polystyrene resin1 % of Run (Breakthrough Softness of Water Effluent Taken at 8 Drops (Drops of Standard Volume through Softenof Standard Soap per 40 M1. of Ratio of Soap) Effluent ) i i l g Unit, Liters Bed 0.0 0 0 1.0 (Distill.ed water) 1 3 0.94a 2 6 0.90 9 28 0.90 16 50 0.88 72 23 0.90 26 2 81 0.89 29 90 2 0.87 93 30 5 0.86 32 100 5 0.85 32.2 >8 0.81 32 3 0.73 >8 32 4 .. 0.54 >8 [’ Initial drop due to change frotn distilled water to efflrirnt containing 425 p.p,m, (as CaCOa) of electrolvtee.
mined the breskthrougli point of calcium and magnesium in a water-softening unit by the change in volunics of the sodium resin {Table IV). Further work is being continued with the 1 yocross-linked resin At the same time resins vr.ith lower cross linking are being prepared, as incressed magnification of volume changes with thew resins may be obtained and thus the method described may hecome a more accurate analytical tool. Other applications of the ion exchange lo\\- cross-linked resins as analytical tools may be in determining the water content of organic solvents and solutions, and studying of the valences of various ions in electrolytic solutions as evident from the volume ratio? of the ferrous and ferric ions given in Table I. A4sin many cases anions are involved, low cross-linked anion exchange resins are also under investigation. The resins may also be of value for ionic separations through density variation of their resin forms. Thus a k n o m quantity of solution containing a mixture of trivalent chromiuni and divalent cobalt w a s pasqed c l o d y through a hydrogrn bed of
the resin. The totai rtmount of electrol~tes passed through the bed was equal t o the capacity of the bed. I t was noted that the upper portion of the bed was dark while the lower portion was light. indicating the chromium t o be on top of the bed and the cobalt on the lower portion. On baclwashing the bed, the dark portion settled on the bottom and the cobalt portion appeared on the top, because of their density differences. By backwashing at different rates, the two layers could be collected in different vessels. Thus recovery and separation of certain ions map be accomplished. SUMMARY
1. The n e t volumP of 1% rross-linked sulfonated polystyrene resins (Permutit QX) depeuds on the valence of the cation in the exchange position of the resin. The higher the valence, the smaller the volume euvept for a fen cationq irhich form insoluble sulfonates 2. The net volume of the above resin varies with the concentration. The higher the concentration. the smaller the wet volume 3. The volume change. of Ion cross-linked sulfonated polvRtyrene resin mitv be utilizeti as an analvtical tool. 4CKNOWLEDGMENT
The author xishe&to thank William Wood and Jan Wilga for prepaiing the Permntit QX resine. LITERATURE CITED
Baunian, J%-. C., presented at Gordon Research Conference on Ion Exchange, July 1949. (2) Baunian, W. C., and Eichhorn, ,J., 6.Am. Chem. SOC.,69, 2830 (1)
(1947).
(3) Boyd, G. E., and Larson, Q. V., presented at Gordon Research
Conference on Ion Exchange, July 1949. Gregor, H. P., J. Am. Chem. Soc., 70, 1293 (1948). Gregor, H. P., et aE.,J . Colloid Cheni., 6 , 2 0 , 2 4 5 , 3 0 4 , 3 2 3 (1951). (6) Honda, RZ., J . 4 m . ( ‘ h e m . SOC.,73, 2943 (1951). (7) Pepper, K. W., Paisley, H. &I.. and Young, h l . A., J . Applied (4) (5)
Chem., 1951, 12%. R E C L I V Kfor D rt,\iew, April 3 , 1952.
Ai.rrp:id .Irinr 2, 1962.
Audio-Frequency Conduct omet er ROBERT €3. FISCHER AND D4LE J . FISHER’ lnrliann Cinirersity, Bloominpton, l n t l .
S
INCE its introductlon in 1875 b j Iiohlrausch (31, a Whrat-
stone bridge has generally been used to measure conductivity by means of the resistance of a conductivity cell coniisting of two electrodes immersed in the test solution. There have been many modifications of the basic method, but tht- undrilying principle of the bridge method is unchanged. If a Wheatstone bridge is adjusted to null with a conventional potentiometer control as one aim of the bridge, the angular position a t null of this control a< expressed in usual dial diviqions is normally not a linear function of the cell resistance 01 of thc cell conductivity. Likewise, the output voltage of the biidge under unbalanced conditions ic not a linear function of either cell resistance or cell conductivity hut is a parabolic function of the resistance of an arm. Srveial attempt? t o obtain a linear relationship between dial or meter reading and cell resistance and/or cell conductivity have been made with soine success. Specially wound potentiometers have been found useful in the Wheatstone null adjustment method, particularly over the middle range of the potentiometer, The nonlinear output voltage of the unI
Present address, Oak RIdge National Laboraalry Oak Ridge. Tenn
balsnccd Ijridge has l x e n distorted into a linear relationshlp between cell rehistance and a meter reading by reliance upon the nonlinear transfer characteristic of a specific electron tube ( 1 ) . Probably the most useful circuit reported to achieve the desired linear relationshipi i i that of the Serfass conductance bridge. This manually operated instrument uses a special type of nulladjuyting TTheat~tontbridge circuit and provides dial readings that may he ]inearl\ related to either cell resistance or cell conductance by electrically transposing the unknown and qtandard arnir of the Wheat&one bridge The audio-frequency conductomete~described 111 this report makes use of a common cathorlca difference amplifier. The difference amplifier is effectively a two-tube circuit ( 2 , 4 ) which, undcr conditions of ordinary operation, yields an output voltage that is a linear function of the amplified difference between two input voltages. This output voltage is substantially independent of power ‘upply voltage vaIiations, provided that the two tubes ale matched A double triode such as the Type 6SK7 is generally euitable Pentodes permit greater amplification, although this did not seem necessary in this application.
