Separation of Phenolic Compounds by Anion Exchange Resin in Copper(I I) Chloride-Organic Solvent Medium Kil Sang Lee, Dai Woon Lee, and Yong Soon Chung Department of Chemistry and Natural Science Research Institute, Yonsei Unioersity, Seoul, Korea
THESEPARATION of phenolic compounds by resin is known t o be closely related with the treatment of industrial waste water. The adsorption behavior of some phenols on strongly basic anion exchange resin has been previously studied ( 1 , 2 ) . Separation of each component from the phenolic compounds was not achieved by them. It is thought that the elution mechanism of phenolic compounds including aliphatic and aromatic hydroxy acids, is due t o differences of molecular adsorption and dissociation of phenol (3-7). The differential complexing is also reported as an elution mechanism (8, 9). The separation of some aromatic acids from a column of Dowex 1-X8 (chloride form) in FeC13-organic solvent medium was studied in our previous work (10). The primary object of the present study was t o investigate the applicability of a cupric chloride-organic solvent medium as a n eluent for the separation of some phenolic compounds. The group which has small dissociation constants such as m-amirophenol, guaiacol, and pyrocatechol was adsorbed weakly on the resin, while salicylic and p-aminosalicylic acid were adsorbed strongly because of their ionization. Among the phenolic compounds, pyrocatechol, homopyrocatechol, and salicylaldehyde can form complexes with Cu(I1) ion in the eluent so that these compounds are eluted more quickly than the others. The effects of p H and organic solvent were found t o be very important factors in the elution behavior.
Table I. Analyses of Phenolic Compounds Anal. wavelength, Loaded, Recovered, Phenolic compound nm mg mg Pyrocatechol 356 0.444 0.434 Resorcinol 358 0.443 0.444 Guaiacol 368 0.489 0.479 Homopyrocatechol 352 0.500 0.477 Phloroglucinol 374 0.660 0.653 374 0.465 0.453 m-Aminophenol m-Methoxyphenol 365 0.489 0.479 p-Aminosalicylic acid 375 0.600 0.571 Salicylaldehyde 550 0.480 0.468 Salicylic acid 530 0.555 0.557 Table 11. Volume Distribution Coefficients (D,) of Phenols in Various Concentrations of CuC12 Flow rate: 0.5-0.7 ml/min; resin bed: 0.8 X 18.5 cm Phenol Salicyl- ResPyro- Guaia- aldeorEluent, pH 1.3 catechol col hyde cinol 4.13 4.76 5 52 13.3 0.025MCuC13-45% MeOH 12.1 5.31 0,05MCuC1~-45zMeOH 1.10 4.56 12.0 0.10MCuCl~-45%MeOH 1.00 4.12 4.23
EXPERIMENTAL
Materials. The strongly basic anion exchanger Dowex 1-X8 (chloride form, 200- to 400-mesh) was used for determination of the distribution coefficients and separation experiments. The resin was air dried, placed in a n oven (60 "C) overnight and then stored in a vacuum desiccator. Stock solutions of the phenolic compounds (0.02M), eluents, and other reagents were prepared using reagent grade chemicals and ion-free water or alcohol. The cupric chloride-organic solvent eluent was prepared; the cupric chloride was expressed as molarity and the amount of organic solvent as percentage by volume. The pH of the eluent was controlled by the addition of hydrochloric acid. Ion Exchange Column. For the column method, Dowex 1-X8, C1- form was placed in a borosilicate glass column (25 x 0.8 cm in diam.) furnished with Teflon (Du Pont) fittings (1) R. E. Anderson and R. D. Hansen, Ind. Eng. Chem., 47, 71 (1955). ( 2 ) M. G. Chasanov, R. Kunin, and F. X. McGarvey, ibid., 48,305 ( 1956). (3) V. I. Demidov, Isuetn. Metal. 35, 13 (1962). (4) J. L. Lash and J. Cohen, Drug Stand., 28, 65 (1960). ( 5 ) N. E. Skelly and W. B. Crummett, ANAL.CHEM.,35, 1680 (1963). (6) J. Hamekoski and M. Hyle, Suomen Kemistilehti B , 35, 162 (1962). (7) C. Davies, R. D. Hartley and G. J. Lawson, J. Chrornatogr., 18, 47 (1965). (8) K. S . Lee and 0. Samuelson, Anal. Chim. Acta, 37, 359 (1967). (9) U. B. Larsson, T. Isaksson, and 0. Samuelson, Acta Chem. S c a d . , 20, 1965 (1966). (10) K . S . Lee, D. W. Lee, and E. K. Lee, ANAL.CHEM.,42, 554 (1970). 396
and a porous Teflon (Du Pont) bottom. The column was washed thoroughly with aqueous organic solvent using a Beckman Accu-Flo pump, and then the resin bed was adjusted to 18.5 cm. Volume Distribution Coefficient ( D J . For determination of the D,value, 0.2 ml of the stock solution of each phenolic compound was added to the column and then forced into the resin bed using nitrogen gas. A supply of the appropriate eluent was then connected to the column. The flow rate during the elution was 0.5-0.8 ml per minute. The volume distribution coefficients were calculated from the peak elution volume of the phenolic compounds (10). The phenolic compounds were determined by UV spectrophotometry. The phenolic compounds in CuClrorganic solvent medium produced yellowish green color as a result of reaction with a reagent. The reagent was prepared as follows; 3.2 grams of mercuric acetate, 1.0 gram of sodium nitrite dissolved in 20 ml of concd acetic acid and diluted to 1 liter with deionized water. Salicylaldehyde and salicylic acid were analyzed using ferric chloride solution. The analytical wavelength for phenolic compounds and the analyses of the compounds in the elution experiment are illustrated in Table I. RESULTS AND DISCUSSION
Phenolic Compound-Cu(I1) Complexes. Phenolic compounds such as pyrocatechol, homopyrocatechol, guaiacol, and salicylaldehyde formed Cu(I1)-phenolic compound complexes with cupric ion in the acidic medium (11). On the ~~
~
(11) L. G. Van Uitert and W. C. Fernelius, J . Amer. Chem. SOC.,769 375 (1954).
ANALYTICAL CHEMISTRY, VOL. 45, NO. 2, FEBRUARY 1973
Table 111. Volume Distribution Coefficients (D,) of Phenols in Various Concentrations of MeOH Flow rate: 0.5-0.7 ml/min; resin bed: 0.8 X 18.5 cm Phenol Homo4 mAminoPYroPyroSalicyl- Methoxy- Resor- Salicylic salicylic m-Amino- cateacid acid phenol chol c:atecho1 Guaiacol aldehyde phenol cinol Eluent PH 1.22 8.96 9.83 0.05M CuClz1.3 0.27 1.01 18.9 21.5 ... (10.0) (7.78) (27.1) (31.5) 30% MeOH 3.5 (0.84) ... ... ... 1.10 4.56 5.31 0 ,OSM CUC121.3 0.17 0.79 15.3 18.7 7.89 12.1 45% MeOH 3.5 (0.90) ... ... (4.99) (4.34)G (12.8)a (24. 5)' (3 .27) (8.00) (13.3) ... (30.8) 7.61 4.60 6.50 0.18 8.31 7.81 13.4 0.10M KCl1.3 45% MeOH 0.58 1.98 2.30 4.45 6.06 5.63 9.29 0.17 0.47 0.05M CUClz1.3 60% MeOH 3.5 (10.8) D yvalues at pH 2.3. Table IV. Effect of Various Organic Solvents on Volume Distribution Coefficient Flow rate: 0.5-0.7 ml/min; resin bed: 0.8 X 18.5 cm Homomm-Amino- PyroPhloropyroSalicyl- Methoxyphenol catechol Resorcinol glucinol catechol Guaiacol aldehyde phenol 0.05 0.63 3.86 5.20 0.36 1.44 1.55 2.94 ( 0 .26)a (4 34) (1.65) (1.65) 0.06 0.90 4.99 11.4 0.31 1.28 1.01 2.41 (0.30) (5.20) (12.1) (1.60) (0.79) (2.41) 0.07 1.10 8.64 18.8 ... 2.90 3.80 6.60 (0.33) (9.93) (3.05) (2.62) (7.35) 0.17 1.10 12.1 21.4 0.79 4.56 5.31 7.89 (0 .90) (13.3) (21.4) (4.99) (3.27) (8.00) 0.21 1.01 8.68 11.2 0.79 2.41 3.70 6.06 (0.58) (9.29) (13.9) (3.37) (3.16) (7.89) 8 . 88b 0 .56b ... 2. 95b 4. 62b 0.22 1 ,19b (1.87) (11 . I ) (ii'.i) (2.84) (2.51) (6.28) ... (19.2) ... ... (8.00) (7.35) (12.1) (0.58)
Eluent, pH 1.3 0,05M CuClz45% MeKO 0.05M CuClz45% PrOH 0.05M CuClz4 5 z EtOH 0.05M CuClz45% MeOH 0.05M CuClz30% MezCO 0.05M CUC1230% PrOH 0.05M CuClz30% EtOH 0.05M CUC120.27 30% MeOH (0.84) D, values at pH 3.5 Resin bed: 0.8 X 52.5 crn.
t
1.22
21.5 (31.5)
48.3 (52.6)
other hand, resorcinol, rn-methoxyphenol, m-aminophenol, and phloroglucinol did not form complexes in the eluent medium, which is generally accounted for by their structures. In the slightly acidic medium (above pH 4) salicylic and p aminosalicylic acid form complexes with cupric ion. This result was obtained by the spectrophotometric investigation and was further supported from the distribution data (Table 111). Volume Distribution Coefficient. Volume distribution coefficients of phenolic compounds in the various media were measured to determine the elution behavior and to find out the optimum conditions of separation. To determine the optimum concentration of cupric chloride for the separation, D, values of several phenolic compounds in various concentrations were measured and are shown in Table 11. Pyrocatechol has a very small D,value, because of the formation of complex with Cu(I1); the influence of cupric ion concentration on D, value in pyrocatechol was negligible beyond O.O5M, while it was remarkable in guaiacol and salicylaldehyde. Resorcinol which does not form a complex with Cu(I1) was also negligible. Cupric chloride O.O5M, was adopted as the optimum concentration in this experiment. This was because there was great differences of D,values among phenolic compounds at that molarity (see Table 11). In the elu-
1.01
8.96 (10.0)
9.83 (7.78)
Phloroglucinol 48.3 (52.6) 21.4 (21.4) 12.7
p -Amino
Salicylic acid 4.66 (9.61) 2.62 (12.8) 14.3 (18.9) 15.3 (30.8)
salicylic acid 5.09 4.77 16.2 18.7
18.9 (27.1)
tion volume, overlapping above 0.01M and tailing phenomenon below 0.025Mwere found. The effect of methanol on the volume distribution coefficient was also studied (Table 111). The concentration of cupric chloride was fixed at 0.05M and the percentage of methanol was varied from 30 to 60%. It was observed that the D,values of all phenolic compounds decreased when there were increases in methanol percentage. The results suggest that the decrease of D, value by addition of methanol is related to the decrease of dielectric constant of the eluent, dissociation of phenolic compound, and the interaction of resin and solvent. It was observed that the effect of methanol on D,value was equal with all phenolic compounds. Homopyrocatechol, pyrocatechol, and m-aminophenol showed small differences of D, value which can be explained by the fact that these are eluted very quickly. Another important factor which influenced D ,value was the pH of the eluent. D,values of phenolic compounds except salicylaldehyde increased, when pH values increased from 1.3 to 3.5 (Table 111). This influence is likely due to dissociation of the phenolic compound, though some of them have very low dissociation constants. In salicylaldehyde, D,values were decreased which may be explained by the fact that the Cu(I1)-salicylaldehyde complex was enhanced with
ANALYTICAL CHEMISTRY, VOL. 45, NO. 2 , FEBRUARY 1973
397
1
0.05M CUCIZ45% PrOH
.-.-._.-.
I
p
cn m
Em
Y
fj .3
*4
m
K
a
4: .2
.I
.o
.O 0
Do
50
0
150
ELUATE VOLUME, ml
I
rate: 0.5-0.6 ml/min
I
200
300.
500
ELUATE VOLUME, rnl
Figure 1. Separation of pyrocatechol-salicylaldehydesalicylic acid mixture by elution with 0.05M CuC12-45 % EtOH Column: 0.8 X 18.5 cm; flow
100
I
1
Figure 3. Separation of a mixture of phenols Eluent: 0 . 0 5 M C ~ C 1 ~ - 3 0 MeOH Pyrocatechol (P), Guaiacol (G), rn-Methoxyphenol (M), Phloroglucinol (Ph 11) - X- X-: Pyrocatechol (P), Salicylaldehyde (S), Resorcinol (R), Phloroglucinol (Ph 11) Column: 0.8 X 18.5 cm; flow rate: 0.5-0.6 ml/min. -0-0-0:
rn- AhllNOPHENOL
.8
.6
w
2
8
.4
m
a
.2
.O 0
100 200 ELUATE VOLUME, rnl
300
Figure 2. Separation of a mixture of m-aminophenolm-methoxyphenol-resorcinol by elution with 0.05M CuCI2-3O % PrOH Column: 0.8 X 52.5 cm; flow rate: 0.8-1.0 ml/min
increasing pH of the eluent; the absorbance of the complex increased when there were increases of pH. On the other hand, homopyrocatechol and pyrocatechol had low D,values because of complexation. The effect of pH was not significant to their elution and therefore data were not included in Table 111. The D ,value of m-aminophenol was very small in acidic medium but there were increases in D, values as pH increased. This result can be evidenced further from other results. At pH 1.3, m-aminophenol was eluted from 5 ml to 15 ml in 30z-MeOH medium; at pH 6.5 from 20 ml to 100 ml; at pH 12 it was not eluted till 400 ml of eluate. The small D,value of m-aminophenol in 0.05M CuC12-MeOH can be explained by the fact that in acidic medium it can not be adsorbed on the resin because of its low dissociation. The 398
effect of pH on D,values was also determined in resorcinol. When it was loaded on the column (0.8 x 5.2 cm), at pH 1.1, it took from 42 ml to 234 ml in 10% methanol; at pH 7.4, from 72 ml to 240 ml; at pH 9.5, from 120 ml to 260 ml. It was shown that the loading pH condition was also a factor for the separation work. In salicylic acid which has a very high dissociation constant, a large variation was observed with changes of pH values. It was suspected that this effect is due to dissociation because salicylic acid did not form a complex in 0.05M CuC12-45% MeOH medium (pH 1.3). D, values in two different media, 0.1M KC1-45% MeOH (pH 1.3) and 0.05M CuC12-45% MeOH (pH 1.3) were compared with each other to point out the effectiveness of using a copper-containing eluent (Table 111). The differences in D,of homopyrocatechol, pyrocatechol, and salicylaldehyde were due to their complexing with Cu(I1). In addition, the tailing phenomenon in KCl-MeOH medium was seriously more than that in a C u C k M e O H medium. Therefore this phenomenon must be considered in separation work. The effect of various organic solvents on D, was studied in 0.05M CuC12-organic solvent media. It was observed that the addition of these organic solvents to the eluent decreased the sorption of the phenolic compound. This was also true for methanol. The solvents were listed in the order of their effect on the D, values (Table IV); Methanol-ethanol-1-propanol-acetone for the group of m-aminophenol, pyrocatechol, resorcinol, and phloroglucinol; and methanolethanol-acetone-1-propanol for the group of homapyrocatechol, guaiacol, salicylaldehyde, rn-methoxyphenol, salicylic, and p-aminosalicylic acid. The decreasing order of D, was in accord with the decreasing order of the dielectric constant of the organic solvent in the latter group. In the former group, the relationship between D, value and the dielectric constant of the medium was also seen except for acetone and 1-propanol. The results suggested that the sorption of phenolic compounds was influenced by the dielectric constant of the medium and the interaction between
ANALYTICAL CHEMISTRY, VOL. 45, NO. 2, FEBRUARY 1973
organic solvent and phenolic compound or resin. This information should be considered in future separations. Based on overall results, it is assumed that the factors affecting the adsorption and elution behavior of the weakly acidic phenolic components are as follows ; the dissociation of the phenols which varies with the pH of the medium, differential complexing of Cu(I1)-phenolic compound, the dielectric constant which can be changed with the addition of an organic solvent, the molecular adsorptivities of the phenolic compounds on the resin, and the interaction between organic solvent and resin or phenols. Separation of Mixtures. The elution order of phenolic compounds in 0.05M CuCls-organic solvent media is: maminophenol .-,homopyrocatechol + pyrocatechol e guaiacol + salicylaldehyde + m-methoxyphenol + resorcinol + salicylic acid + p-aminosalicylic acid e phloroglucinol (Tables I11 and IV). The results obtained in this experiment show that it is possible to separate each phenolic component from the mixture. To determine the optimum condition for the separation, the range of elution volume must be considered, because of the overlapping of the elution. In the copper-containing eluent media, the following phenolic components can be separated from the mixture; 1. Pyrocatechol (or m-aminophenol) H salicylaldehyde t) salicylic acid. [0.8 x 18.5 cm, 0.05M CuC12-45z EtOH (pH 1.3), 0.5-0.6 ml/min] 2. Pyrocatechol (or homopyrocatechol, m-aminophenol) tt guaiacol (or salicylaldehyde) t--) m-methoxyphenol (or resorcinol) (--f phloroglucinol. [0.8 x 18.5 cm, 0.05MCuC12-30z MeOH (pH 1.3)] 3. m-Aminophenol t--f m-methoxyphenol ++ resorcinol. [0.8 X 52.5 cm, 0.05M CuC12-30% PrOH (pH 1.3), 0.71.O ml/min]
4. Guaiacol ++ resorcinol t-f salicylic acid. [0.8 x 18.5 cm, 0.05M CuC12-45z MeOH (pH 1.3), 0.5-0.6 ml/min] 5. m-Aminophenol ++ p-aminosalicylic acid. [0.8 x 18.5 cm, 0.05M CuC12-45% acetone (pH 1.3), 0.5-0.7 ml/min]. In eluents without Cu(II), several components can also be separated, but the tailing phenomenon should be borne in mind and considered. It is as follows;
-
6. m-Aminophenol homopyrocatechol (or pyrocatechol, salicylaldehyde, m-methoxyphenol, resorcinol) tf phloroglucinol. [0.8 x 18.5 cm, 0.1M KC1-45z MeOH (pH 131 7. Guaiacol tf m-methoxyphenol (or resorcinol). (0.8 X 18.5 cm, 30% MeOH-H20) 8. Salicylaldehyde t-f resorcinol. (0.8 X 18.5 cm, 45% MeOH-H20). Consequently, it is emphasized that copper-containing eluents were very effective in separation work. Elution curves for the separation of the mixtures are illustrated in Figures 1, 2, and 3. Phloroglucinol which is adsorbed strongly on the resin can be eluted quickly, if there were a change of the eluent as soon as the other phenols are eluted (Figure 3). ACKNOWLEDGMENT
It is a pleasure to acknowledge the financial assistance of Tae Sun Park, the President of Yonsei University, and the technical assistance of J. H. Yu.
RECEIVED for review June 12, 1972. Accepted September 19,1972.
Analysis of Solution Samples by Microwave Induced Plasma Excitation F. E. Lichte and R. K. Skogerboe Department of Chemistry, Colorado State Unicersity, Fort Collins, Colo. 80521 REPORTSFROM VARIOUS LABORATORIES have dealt with the analytical applicability of the low power, microwave induced argon plasma as a spectrometric excitation source (1-8). Many of these reports have emphasized the fact that relatively small quantities of sample can be introduced into the plasma per unit time. Excessive introduction rates extinguish the (1) H. E. Taylor, J. H. Gibson, and R. K. Skogerboe, ANAL. CHEM., 42, 876 (1970). (2) Zbid., p 1569. ( 3 ) F. E. Lichte and R. K. Skogerboe, ibid., 44,1321 (1972). (4) Zbid., p 1480. (5) K. F. Fallgatter, V. Svoboda, and J. D. Winefordner, Appl. Spectrosc., 25, 347 (1971). (6) S. Murayarna, H. Matsuno, and M. Yamamoto, Spectrochim. Acta, 23B, 513 (1968). (7) M. Yarnarnoto and S. Murayarna, Spectrochim. Acta, 23A, 773 (1967). (8) H. Kawaguchi, M. Hasegawa, and A. Mizuike, Specrrochim. Acta, 27B, 205 (1972).
plasma. This factor has consequently limited the general analytical utility and has precluded the direct analysis of solution samples unless the aqueous phase is largely removed prior to the plasma (5,8) or higher power in conjunction with specially designed coupling cavities is used (6-9). Another factor referred to in the literature which presents a problem involves the general difficulty in tuning the cavityplasma system to minimize the voltage-to-standing wave ratio ( I O ) . While such tuning is certainly not impossible, it is tedious and subject to significant variations from time to time. A design change in the Evensen cavity (11) which (9) H. Goto, K. Hirokawa, and M. Suzuki, Fresenius’ 2. Anal. Chem., 225,130 (1967). (10) J. M. Mansfield, M. P. Bratzel, Jr., M. D. Norgordon, D. N. Knapp, K. E. Zacha, and J. D. Winefordner, Spectrochim. Acta, 23B, 389 (1968). (11) F. C. Fehsenfeld, K. M. Evensen, and H. P. Broida, Rec. Sci. Imtrum., 36, 294 (1965). The cavity referred to is No. 5 in this
reference.
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