2090 Anal. Chem. 1982, 54 , 2090-2094

Interferences in Automated Phenol Red Method for Determination of Bromide in Water

Chrls L. Basel and James D. Defreese"

Department of Chemjstry, The Unlversity of Kansas, Lawrence, Kansas 66045

Donald 0. Whittemore"

Kansas Geological Survey, The University of Kansas, Lawrence, Kansas 66045

The phenol red method for the determlnatlon of bromide In water has been automated by segmdnted flow analysls. Samples can be analyzed at a rate of 20 samples/h wlth a method detection Ilmlt, deflned as the cdncentratlon glvlng a signal about three times the standard deviation of replicate analyte determlnatlbns In reagent water, of 10 pg/L. Samples studled Include oil-field brines, hallte solutlon brlnes, ground- waters contaminated wlth these brines, and fresh groundwa- ters. Chlorlde and bicarbonate cause slgnlflcant positive in- terferences at levels as low as 100 mg/L and 50 mg/L, re- spectlvely. Ammonia gives a negatlve Interference that is Important at levels as low as 0.05 mg/L. An ionic strength buffer Is used to suppress a posltlve lonlc strength Interter- ence, correction curves are used to compensate for the chloride Interference, the blcarbonate Interference Is mlni- mlzed by acldlficatlon, and the ammonia Interference is elim- inated by Its removal by Ion exchange. Reactlon product studles are used to suggest a plauslble mode of chlorlde in- terference.

The concentration ratio of bromide to chloride has been established as indicative of the source of sodium chloride contamination of natural waters (1, 2). At a given chloride concentration, this ratio is larger for oil-field brines or waters polluted by oil-field brines than it is for halite solution brines or waters contaminated by halite solution brines. A rapid, accurate method for the determination of bromide was needed for further study and application of this phenomenon.

Colorimetric methods were examined because they are well-suited for automation by continuous flow techniques such as segmented flow analysis (SFA) or flow injection analysis (FIA). An SFA automated method based on the catalytic effect of bromide on the oxidation of iodine to iodate by potassium permanganate in sulfuric acid solution (3) exhibits an unacceptable sensitivity to chloride ( 4 , 5 ) which precludes its use for the saline samples of interest here. The standard phenol red method (6) indicated sufficient accuracy, precision, and sensitivity for our studies. This method has also been shown to be amenable to automation by SFA (7). Preliminary results of the automation of the phenol red method via FIA are encouraging but are not discussed in this paper. A fluorescein method for bromide that may have a low sensitivity to chloride and a low detection limit is presently being in- vestigated by others (8).

The latest edition of ref 6 mentions that interferences to the phenol red method may be present in saline or polluted waters (6), but it does not identify them. Various levels of chloride have repeatedly been stated not to interfere in the phenol red method (7, 9, lo) , although one report (11) has warned of a possible interference depending on reaction time

0003-2700/82/0354-2090$01 2510

and concentration. Chloride was of major concern here be- cause it may be found in high concentrations in oil-field brines, halite solution brines, and freshwaters polluted with either of these.

Ammonia, which is often found in oil-field brines and freshwaters, has been mentioned as an interference in the phenol red method (9,10,12), but no quantitative data have been published. Bicarbonate is often a major constituent in groundwaters. Reports of its tendency to interfere have been conflicting (9, 11, 13).

Other potential interferents are iodide (7,9,12), nitrite (12, 13), ferric iron (13), and manganese (13). These either exhibit negligible effects (5, 13) or are normally found at such low concentrations in natural waters that they are not important to our studies.

In this paper, the automation of the phenol red method for the determination of bromide in natural waters is described. Chloride, ammonia, and bicarbonate interferences are quan- tified and compensation procedures are presented. Studies of the chemistry of the phenol red method to indicate the actual products of the reaction and the mode of chloride interference are also discussed.

EXPERIMENTAL SECTION Apparatus. A Technicon AutoAnalyzer I1 consisting of an

autosampler, proportioning pump, appropriate analytical cartridge, spectrophotometer, and strip chart recorder was utilized for the automation of the phenol red method by SFA, the interference studies, and the ammonia and chloride determinations. A Per- kin-Elmer 555 UV-visible spectrophotometer was used to acquire spectra of reactants and products of the reaction.

Reagents. All reagents were analytical reagent grade. Water for solution preparation and sample dilution was deionized and distilled.

M and 4.6 X lo-, M, respectively. The ionic strength/pH 4.6 buffer contained 2.1 M acetic acid, 2.0 M sodium acetate, 1.5 M sodium nitrate, 0.4 M magnesium sulfate, and 2 mL/L Brij-35 surfactant. A 6 M sodium nitrate solution was used to recharge the ion exchange column.

A "dilute" pH buffer that provides a relative reagent concen- tration in the flow stream similar to that in the manual method (6) was used for several studies. It contained 0.35 M acetic acid, 0.34 M sodium acetate, and 2 mL/L Brij-35 surfactant.

For the spectral studies, the buffer, chloramine-T, and phenol red solutions were prepared as for the manual method (6). A 6.1 X 10" M bromophenol blue solution was also used.

For the interference studies, the following reagents were used to prepare stock solutions: NH4C1 for NH,, Ultrex NaCl for C1, NaHCO, for HC03, NaN03 for Na and NO3, Na2S04 for SO4, MgSO, for Mg, and Ca(N03),.4H20 for Ca. Bromide standards were prepared from KBr.

Automated System. A schematic diagram of the SFA system for bromide determination is shown in Figure 1. Pump tube diameters (flow rates) and reagent concentrations were chosen such that the reagent concentrations in the flow stream were

The phenol red and chloramine-?' solutions were 3.9 X

0 1982 American Chemical Society

ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982 2091

FROM DEBUBBLER

Figure 1. Schematic diagram of segmented flow analysis system for determination of bromide.

similar to those in the manual method reaction mixture (6). However, the buffer was increased in capacity and ionic strength to minimize interferences due to variable buffer capacities and ionic strengths of the mmples. A 20-per-hour adjustable cam was modified to increase the wash cycle time by cutting off one section of both sample positions. This reduced carryover.

The sample is first pumped into a debubbler to remove the bubble introduced whlen the sample probe changes from sample to wash and vice versa. This debubbling process eliminates base line oscillation, a problem also noted by others ( 4 ) . Next, the sample enters an ion exchange column (Dowex 50WX8) to remove ammonium ion. After this column, the segmenting air bubbles are introduced. Next, buffer, phenol red, and chloramine-T solutions are introduced in sequence and mixed by coils. After the chloramine-T introduction, additional coils delay the ab- sorbance measurement by 8 min, a time chosen because the maximum net absorb,snce above the base line is nearly reached at this time. At longer times, the base line absorbance becomes too large to be zeroed on the recorder. The solution is then debubbled and enters the spectrophotometer flow cell where the absorbance is measured at 590 nm with an 8-nm band-pass.

General Procedure. Chloride and ammonia were determined by Technicon methods which use a modified Volhard procedure (14) and the Berthelot reaction (15), respectively.

For the bromide determination, the recorder is zeroed with the sampler in the wash cycle. The highest standard is then sampled several times to set full scale. A series of standards is placed first on the sample carousel, followed by samples with water inter- spersed every seven to eight samples. Approximately every hour, the ion exchange column is recharged by sampling two aliquots of the 6 M sodium nitrate solution. This highly concentrated solution causes extreme base line noise and depression due to ammonia release. Therefore, two aliquots of water are sampled immediately before anid after the sodium nitrate. Standards are run at approximately 1.5-h intervals.

RESULTS AND DISCUSSION System Characterization. Bromide standards were run

in both ascending and descending order with respect to con- centration. The calibration curves are alpproximately collinear with an average equation of peak heiglht (arb units) = (60.70 f 0.34) [Br-] + (0.06 f 0.25), with an SEE (standard error of estimate) = 0.46, and r (correlation coefficient) = 0.99991, over a range of 0.026-1.5 mg/L bromide.

The detection limit, defined as that concentration giving a signal equal to the Students t value for a one-tailed test a t the 99% confidence ltsvel with N - 1 degrees of freedom times the standard deviation of repetitive determinations of bromide in a 25 gg/L standard (16), is 10 gg/L. This is also the concentration giving signal greater than the blank measure by three times the standard deviation of the blank determi- nations (17 ) . Therefore, the phenol red method is suitable for the determination of bromide in most groundwater and surface water.

Precision was meamred by determining the bromide con- centration of each of 26 samples nine times during a 4-day period. These samples consisted of fresh and saline ground-

Table I. on the Determination of Bromide (0.50 mg/L) by the Phenol Red Method

Effect of Major Constituents of Natural Waters

measd [bromide], mg/L dilute ionic strength/ concn,

constituent mg/L pH buffera pH buffera

Na 700 NO3 500 Mg 3 50

1500 700

so 4 Ca c1 1000 HCO, 1000 . I

"3 0.1

0.61 0.53 0.60 0.65 0.62 0.87

>1 .50b 0.37c

0.49 0.49 0.49 0.48 0.49 0.58 1.08 0.43

a See text for composition, Off scale. These values were determined with the ion exchange column removed.

waters and brines with bromide concentrations ranging from 0.14 to 1.1 mg/L, after any necessary dilution. Percent relative standard deviations ( % RSD) ranged from approximately 1 % at the higher concentration to 8% at the lower concentration.

An indication of the accuracy of the method was obtained by spiking samples with 0.25 mg/L Br-. The samples con- sisted of fresh and saline groundwaters and brines, with bromide concentrations ranging from approximately 0.15 to 1.0 mg/L. The average recovery was 98.4 rfr. 4.9% with a range of 91.2 to 106%.

Identification of Interferents. For identification of potentially serious interferences, bromide concentrations were repeatedly determined in solutions that were spiked with 0.5 mg/L bromide and that contained the common major cations and anions found in freshwater and/or saline water. The major constituent concentrations used are near the maximum found in freshwaters or saline waters diluted to bring the bromide concentration within the range of the method and/or to reduce the chloride interference. The results are given in Table I.

Use of the dilute pH buffer gave a positive interference from all major constituents added except ammonia, which, as ex- pected, gave a serious negative interference. The positive interferences were roughly linear with increasing ionic strength of the added constituents. By use of the manual method (6), these interferences were found to be important a t 8 min but not a t 20 min for all positive interferents except chloride and bicarbonate. The chloride interference was greater at 20 min than at 8 min. Use of the ionic strength/pH buffer decreased the positive interferences to insignificant levels except for chloride and bicarbonate, both of which still caused substantial positive interferences. Therefore, chloride, ammonia, and bicarbonate were selected for further, more detailed studies.

Chloride Interference. The extent of the chloride in- terference is shown in Figure 2. A significant positive in- terference is seen for chloride levels as low as 100 mg/L. The curves in Figure 2 were obtained by adding known amounts of chloride to bromide standards and measuring the bromide concentration, which is the sum of the actual bromide and the apparent bromide due to chloride. The actual bromide concentration in the solution is then subtracted from the measured bromide concentration to give the error (correction) due to chloride.

These curves can be used to correct for the chloride in- terference. The chloride and bromide in the sample are de- termined in separate measurements. The appropriate cor- rection is then related to the measured bromide by the cor- rection curve (or interpolation between curves) corresponding to the chloride concentration in the sample. The correction is then subtracted from the measured bromide concentration

2092 ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982

1 1- ,

0 i---- 'L m

L

2 L o W ?

0 .25 5 .75 1 7.2,' 1.5

Measured Br-, mg/L

Flgure 2. Error in the determination of bromide caused by chloride: (A) 2000 mg/L CI-; (B) 1000 mg/L CI-; (C) 500 mg/L CI-; (D) 200 mg/L CI-; (E) 100 mg/L CI-.

Table 11. Effect of the Chloride Correction on the Determination of Bromide in 0.50 mg/L Bromide Standards Spiked with Chloride and in Natural Waters

mg'L measd [bromide], mg/L in bromide standards uncorrected correctedu

50 0.50 0.50 100 0.52 0.50 500 0.55 0.50

1000 0.60 0.50 2000 0.64 0.50

measd [bromide],

mg/L [chloride], uncor- cor-

OFBl 1/100 285 1.13 1.07 F1 + OFB2 1/100 277 1.00 0.94 HSBl 1/100 1930 0.34 0.23 F2 t HSB2 10/100 948 0.24 0.18 F3 none 25 0.14 0.14

a Correction derived from data shown in Figure 2. OFB = oil-field brine; F = fresh groundwater; HSB =

sampleb dilutionC mg/Ld rected rected'

halite solution brine. mide determination, given in ref 14.

Dilution of sample prior to bro- Determined separately by method

to give the actual bromide concentration. The effect of the correction can be seen in Table 11. The correction works quite well for standards. For natural water samples the correction is good to within a few percent or better as indicated by the recovery study.

A much higher chloride interference was seen when the dilute pH buffer was used. This indicates that the chloride interference consists of both an ionic strength component (eliminated with ionic strength/pH buffer) and an effect in- trinsic to chloride.

A plot of apparent bromide due to chloride vs. chloride for chloride standards should not be used as a correction curve, as it has been for the catalytic oxidation method (4), because the correction depends on both the chloride and actual bromide concentrations. This may be more easily seen by replotting the data of Figure 2 as measured bromide vs. chloride. Curves drawn through the points with the same actual bromide exhibit increasing slopes for each increment in actual bromide.

To compensate for a chloride interference in seawater, a set chloride level has been added to bromide standards (11). However, this would not give an accurate measurement here

Table 111. Effect of Ion Exchange on the Determination of Bromide and Ammonia in Bromide Standards Spiked with 0.5 mg/L Ammonia and in Natural Waters

measd concns, mg/L without ion

exchange with ion exchange [bromide], mg/L in standard ammonia bromide ammonia bromide

0.05 0.50 <O.OOu 0.00 0.05 0.10 0.50 <O.OO 0.00 0.10 0.25 0.49 ~ 0 . 0 0 0.00 0.25 0.50 0.50 <O.OO 0.00 0.50 1.00 0.50 0.26 0.00 1.00 1.50 0.50 0.68 0.00 1.49

measd concns, mg/L

exchange exchange without ion with ion

dilu- ammo- bro- ammo- bro- sample6 tionC nia mide nia mide

OFBl 1/100 0.15 0.81 0.00 1.08 F1 + OFB2 1/100 0.36 0.36 0.00 0.92 HSB 1 1/100 0.04 0.22 0.01 0.24 F2 + HSB2 10/100 0.05 0.14 0.01 0.19 F3 none 0.06 0.10 0.00 0.15

OFB = oil-field brine; F = fresh groundwater; HSB = halite solution brine.

a Signal depressed below base line.

Dilution of sample prior to determinations.

because the chloride varies greatly in groundwater and surface water. In addition, because the specific qualitative and quantitative properties of the chloride correction curves de- pend on the design of the analytical system, they need to be generated for the instrumentation used.

A faster measurement time might minimize the chloride interference because of its slower rate of reaction (11) com- pared to bromide, but the sensitivity for bromide would also decrease.

Ammonia Interference. The extent of the ammonia in- terference was examined by adding known amounts of am- monia to bromide standards and determining the bromide concentration, without using the ion exchange column. The results for a series of bromide standards spiked with 0.50 mg/L ammonia are shown in Table 111. Plots of measured bromide vs. actual bromide for different levels of ammonia are a series of straight lines parallel to the bromide calibration curve with no ammonia present. For 1.0 mg/L bromide, the measured bromide concentrations are 0.90 and 0.26 mg/L for ammonia additions of 0.10 and 0.50 mg/L, respectively. A significant negative interference occurs for ammonia levels as low as 0.05

The ammonia interference may be due to a decrease in oxidant and/or brominating species concentration during the formation of chloramines, bromamines, and/or nitrogen by the reduction of hypochlorite (9), bromine, or any hypobromite (18) formed in the reaction. I t is unlikely that halamines react in the phenol red method in a manner similar to bromide as has been suggested (13) because signals for standards with ammonia-to-bromide ratios of approximately one are de- pressed below base line. This indicates decreased formation of halogenated phenol red products.

Ion exchange has been reported to be an efficient method of ammonia removal (18) and was effective in this study as shown in Table 111. Ammonia removal is essentially complete and a corresponding increase in measured bromide concen- tration is seen in all cases.

Bicarbonate Interference. The effect of bicarbonate was determined by adding 0.5 mg/L bromide to bicarbonate standards and measuring the bromide concentration, which

ANALYTICAL CHEMISTRY, VOL. 54, NO. 12, OCTOBER 1982 2093

is the sum of the actual bromide and the apparent bromide due to the presence of bicarbonate. A significant interference is seen for bicarbonate levels as low as 50 mg/L. A plot of the data is linear wiith an equation of measured bromide concentration (mg/L) = (6.2 f 0.3) X [bicarbonate] (mg/L) + (0.50 f 0.02), with an SEE = 0.03 and r = 0.995, over a range of 0 to LOO0 mg/L bicarbonate. The effect of bicarbonate in the presence of no bromide gave a similar trend, suggesting that this is not an interactive effect as it is for chloride. A plot of error due to bicarbonate (measured bromide minus actual bromide) vs. bicarbonate can be used as a correction curve.

That this interference is due to a pH change caused by the bicarbonate (9) was suggested when it was noted that the use of the dilute pH buffer resulted in a much greater bicarbonate interference than the use of the ionic sitrength/pH buffer. A pH of 4.6 is within the transition interval of the major reaction product bromophenol blue where a small increase in pH causes a large increase in absorbance at 590 nm. Even the increased capacity of the ionic ,3trength/pH buffer is not sufficient to buffer against small pH changes for samples with high bi- carbonate levels. Acidification of standards spiked with bi- carbonate to a pH of approximately 4.6 with dilute nitric acid prior to bromide determination reduced the bicarbonate in- terference to an insignificant level. As with chloride, addition of bicarbonate to the bromide standards is not a suitable compensation technilque because, unlike seawater ( I I ) , bi- carbonate is quite variable in the samples studied.

For solutions with high bicarbonate concentrations, it may be advisable to use a buffer of pH 6.0 where the absorbance of bromophenol blue ici insensitive to changes in pH. However, the overall consequences such as the (effect on other inter- ferences and on the reaction rate have not yet been evaluated fully.

Reaction Product Studies. A studly of the chemistry of the phenol red method was undertaken when it was noted that the color produced by the reaction with bromide standards was visually the same as that for chlorfde standards and for the distilled, deionized water blank. Tlhe generally accepted reactions in the determination of bromide by the phenol red method are the oxidakion of bromide to bromine by chlor- amine-T, followed by electrophilic substiitution of the bromine on phenol red (PR) to produce bromophenol blue (BPB):

H3C.C6H4-SO2NC1- 4- 2H' + 2Br- ~ r l

H3C.C6H4.SOzh~Hz + Br, + C1- (1)

O+&&OH 4Br, + oQa OH = Br B r + 4H' + 46,- & so;

BPB

bS0 - PR

To indicate whether the reaction product was actually BPB, we acquired spectra of BPB and PR in pH 4.6 acetate buffer. By use of the manual method procedure (6), spectra of reaction products for bromide, chloride, and combination bromide- chloride standards, for various samplerr, and for water were also recorded and compared to those of BPB and PR. The wavelengths of maximum absorbance are listed in Table IV. The values suggest either that the absorbance maximum of BPB is shifted slightly toward a shorter wavelength due to solvent or solute effects or, more likely, that the reaction product is not exclusively BPB.

If the reaction product is not exclusively BPB, other products may be partiidly or totally chlorinated compounds, such as 3,3'-dichlorophenolsulfonephthalein (chlorophenol red), 3,3'-dibromo-5,5'- dichlorophenolsulfonephthalein (bro- mochlorophenol blue), or 3,3',5,5'-tetrachlorophenolsulfone-

Table IV. Wavelengths of Maximum Absorbance for Solutions of Bromophenol Blue (BPB), Phenol Red (PR), and Products of the Reaction of Standards, Distilled Deionized Water, and Natural Water Samples

wavelengths, nm

solution A, h*

BPBa 590 384 PRa 429 0.5 mg/L bromide 588 440 0.5 mg/L bromide + 588 44 0

800 mg/L chloride 588 440 distilled/deionized water 588 43 8 natural waters samples 588 436

800 mg/L chloride

a In pH 4.6 buffer prepared as described in ref 6.

phthalein (chlorophenol blue) or a partially brominated compound such as 3,3'-dibromophenolsulfonephthalein (bromophenol red) (10,19,20). Chlorophenol red absorbs near 575 nm, but when used in place of phenol red, the wavelength of maximum absorbance shifts toward 590 nm as the reaction proceeds. This is probably due to further halogenation. Bromochlorophenol blue and chlorophenol blue are reported to absorb in the same wavelength region as BPB in this pH range (10, 19, 20).

Phenol red derivatives with additional halogenation on the sulfonated phenyl ring have been reported (19). Some of these derivatives would absorb in the same region as BPB, but their formation in the phenol red reaction is unlikely.

The blue color produced by the blank may be explained as follows. When chloramine-T dissociates in an aqueous solution at pH 4.6, predominantly hypochlorous acid is formed (21). H3C*CCH4*S02NHCl+ H20 *

H3C.C6H4*SO2NHZ + HOCl (3)

Hypochlorous acid, or other chlorine containing substances in equilibrium with it and capable of electrophilic aromatic substitution, may chlorinate PR. Indeed, using 5% chlorine water instead of chloramine-T with a blank solution produced a similar color to that seen with chloramine-T, contrary to an earlier report (22). Chlorination would be expected to occur at the positions ortho to the hydroxy groups of PR as bro- mination does. Species responsible for this chlorination may be HOCl, H,OCl+, and/or C12 (23, 24).

The chloride interference may be explained by the reaction of HOC1/H20Cl+ with C1- to produce Clz, a stronger chlori- nating agent than HOC1/H20C1+.

HOCl + C1- + H+ ~ ' t Cl, + HzO (4) The use of a different oxidizing agent for bromide that

would not itself lead to chlorination of PR or oxidation of chloride should eliminate the absorbing blank and the chloride interference. Such studies are presently being conducted.

CONCLUSION The effect of the compensation for and the removal of

interferences in the bromide determination is to improve the accuracy of measured bromide-to-chloride ratios in surface and groundwaters. This allows better differentiation of the source(s) of salinity contaminating water resources.

LITERATURE CITED (1) Whittemore, Donald 0.; Pollock, Livia M. "Determination of Salinity

Sources in Water Resources of Kansas by Minor Alkali Metal and Halide Chemistry"; Kansas Water Resources Research Institute: Manhattan, KS, 1979, Contribution No. 208.

(2) Whittemore, D. 0.; Basel, C. L.; Gaile, 0. K.; Waugh. T. C. "Geochemical Identification of Saltwater Sources in the Smoky Hill River Valley, McPherson, Saline, and Dickinson Counties, Kansas";

2094 Anal. Chem. 1982, 54 , 2094-2097

Prepared for the US. Army Corps of Engineers by the Kansas Geo- logical Survey, The Unlversity of Kansas, Lawrence, KS, 1981.

(3) Wen, G. S.; Fishman, M. J.; Hedley, A. G. Ana/yst (London) 1980,

(4) Moxon, R. E. D.; Dlxon, E. J. J . Aufom. Chem. 1980, 2, 139-142. (5) Whlttemore, Donald O., Kansas Geological Survey, The University of

Kansas, Lawrence, KS, 1980, unpublished work. (6) "Standard Methods for the Examination of Water and Wastewater",

15th ed.; American Publlc Health Association: Washington, DC, 1981; Part 405.

(7) Archlmbaud, M.; Bertrand, M. R. Chim. Anal. (Paris) 1970, 52,

(8) Marti, V. C.; Arozarena, C. E. "Automated Colorimetric Determination of Bromide in Water"; Paper No. 734, Plttsburgh Conference on Ana- lyticai Chemistry and Applied Spectroscopy, Atlantic City, NJ, March 1981.

(9) Stenger, V. A.; Kolthoff, I. M. J. Am. Chem. SOC. 1935, 57, 831-833.

(10) Wrlght, E. R.; Smlth, R. A.; Messick, B. G. I n "Colorlmetric Determlna- tion of Nonmetals", 2nd ed.; Boltz, David F., Howell, James A,, Eds.; Wiiey-Intersclence: New York, 1978; Chapter 2.

(11) PBron, A.; Courtot-Coupez, J. Analusis 1978, 6, 389-394. (12) Houghton, G. U. J. SOC. Chem. Ind., London 1948, 65, 277-280. (13) Soilo, Frank W.; Larson, Thurston E.; McGurk, Florence F. Environ.

Sci. Technol. 1971, 5, 240-248. (14) "Chloride in Water and Wastewater"; Industrial Method No. 99-70W/

B; Technicon Industrial Systems: Tarrytown, NY, 1974, (15) "Ammonia in Water and Wastewater"; Industrial Method No. 98-7OW;

Technlcon Industrlai Systems: Tarrytown, NY, 1973. (18) Glaser, John A.; Foerst, Denis L.; McKee, Gerald D.; Quave, Steven

A.; Budde, William L. Environ. Sci. Technol. 1981, 75, 1428-1435.

f05, 857-862.

531-533.

(17) Anal. Chem. 1980, 52, 2242-2249. (18) Zitomer,Jred; Lambert, Jack L. Anal. Chem. 1983, 35, 1731-1734. (19) BBnyai, Eva I n "Indicators"; Blshop, Edmund, Ed.; Pergarnon Press:

Oxford, 1972; Chapter 3. (20) "Standard Ultraviolet Spectra Collection"; Sadtler Research Laborator-

ies, 1980; UV Spectra Nos. 10519, 11434, and 25806. (21) Vogel, Arthur I. "A Text-Book of Quantitative Inorganic Analysis", 3rd

ed.; Longmans, Green and Co. Ltd.: London, 1961; p 392. (22) Goldman, Eugene; Bytes, David J. Am. Water Works Assoc. 1959,

(23) Breslow, Ronakl "Organic Reaction Mechanisms", 2nd ed.; W. A. Ben- jamln: New York, 1969; p 150.

(24) March, Jerry "Advanced Organic Chemistry: Reactions, Mechanisms, and Structure", 2nd ed.; McGraw-Hill: New York, 1977; pp 482-485.

57, 1051-1053.

RECEIVED for review May 14, 1982. Accepted July 19, 1982. Presented in part at the 17th Midwest Regional American Chemical Society Meeting, Columbia, MO, Nov 1981 and in part a t the 184th National American Chemical Society Meeting, Kansas City, MO, Sept 1982. Taken in part from the thesis of C.L.B., submitted to the Department of Chem- istry in partial fulfillment of the requirements for the Masters degree. This research was funded by the Kansas Geological Survey. Financial support from an NSF equipment grant (CHE 78-03307) toward the purchase of the Perkin-Elmer UV-visible spectrophotometer is gratefully acknowledged.

Comparison of Highly Lipophilic Crown Ether Carboxylic Acids for Transport of Alkali Metal Cations from Aqueous Solutions into Chloroform

Witold A. Charewlcz,' Owl Suk Heo, and Richard A. Bartsch" Department of Chemistry, Texas Tech University, Lubbock, Texas 79409

A new type of llpophlllc crown ether carboxylic acld, sym- bls[4(5)-tert-butylbenro]-l6-crown-5-oxyacetlc acid (6) Is prepared and compared with P-(sym-dibenzo-16-crown-5- oxy)decanolc acid (5) In the competitive extraction and transport of elkall metal catlons from aqueous solutlons Into chloroform. Although the overall complexatlon behavlor of 5 and 6 for alkall metal cations In solvent extractlon and In llquld membrane transport Is qulte slmllar, 6 exhlblts complete ex- cluslon of LI' and enhanced Na+/K+ selectlvity.

The synthesis of novel and specific organic complexing agents often leads to the development of new separation systems for aqueous ions. For example, the preparation and introduction of highly lipophilic hydroxy oximes led to the current utilization of these compounds as commercial ex- tractants for the hydrometallurgy of nonferrous metals ( I ) .

The potential of crown ethers (macrocyclic polyethers) as the next generation of specific extracting agents for metal ions (2-4) has been markedly enhanced by the introduction of crown ethers which bear pendant ionizable groups (5-9). In such molecules, the combination of ion binding cavities possessing fiied dimensions with ionizable groups creates novel bifunctional complexing agents.

'Visiting Research Professor from the Institute of Inorganic Re- search Chemistry and Metallurgy of Rare Elements, Technical University of Wroclaw, 50-370 Wroclaw, Poland.

In earlier studies (10-12), we have examined the solvent extraction of alkali and alkaline earth metal cations from water into chloroform by crown ether carboxylic acids 1. These

XIC OZH

- n = 1; Y = CH,CH,, CH,CH,CH,, CH,CH,OCH,CH,,

n = 2; Y = CH,CH,OCH,CH, CH,CH,OCH,CH,OCH,CH,

complexing agents exhibit extraction efficiencies and selec- tivities which surpass both those of a closely related, nonionizable crown ether and of phenoxyacetic acid. It was also demonstrated that metal ion extraction does not involve concomitant transfer of the aqueous phase anion into the organic medium. This latter factor is of immense importance to potential practical applications of these ionizable crown ethers for metal ion extraction from aqueous solutions (10).

In assessing the influence of the bridging group Y in 1 and the number of methylene groups which join the crown ether and the carboxylic acid portions of the molecules, it was noted that the carboxylate forms of these complexing agents were of insufficient lipophilicity to remain completely in the organic phase. Therefore, a second generation of more lipophilic crown ether carboxylic acids 2-5 was synthesized (9) and used for alkali metal extraction (13). Loss of the carboxylate forms

0003-2700/82/0354-2094$01.25/0 0 1982 American Chemical Society