able." Method B-extractable material (total BIAS), composed of surfactant BIAS and polyglycol BIAS, persists longer and results from the slower degradation of free polyglycol material which may be recovered in the C H C b extract of method C. This method may be useful for biodegradability testing and other laboratory tests and may, after some additional work, be useful for determination of nonionic surfactants,and their degradation products in environmental samples.
LITERATURE CITED (1) C. D. Frazee, Q. W. Osborn, andR. 0. Crisler, J. Am. Oil. Chem. SOC.,41, 808 (1964). (2) R. Wickbold, Tenside, 8, 61 (1971). (3) R. Wickbold, Tenside, 9, 173 (1972). (4) R. Wickbold, Tenside, 11, 137 (1974). (5) N. T. Crabb and H. E. Perslnger, J. Am. Oil Chem. SOC., 41, 752 (1964). (8)E. S.Lashen, F. A. Blakenship, K. A. Booman, and J. Dupr6, J. Am. Oil Chem. SOC., 43, 371 (1966). (7) S. J. Patterson, E.C. Hunt, and K. B. E. Tucker, J. Proc. lnst. Sewage Purif., London, Paper 2, 190 (1966). (8) S.J. Patterson, C. C. Scott, and K. B. E. Tucker, J. Am. 011 Chem. Soc., 44, 407 (1967). (9) S.J. Patterson, C. C. Scott, and K. 8. E. Tucker, J. Am. Oii Chem. SOC., 47, 37 (1970).
(10) L. Rudling and P. Solyom, WaterRes., 8, 115 (1974). ( 1 1) C. Borstlap and C. Kortland, Fette, Seifen, Anstrichm., 69, 736, (1967). (12) G. F. Longman, Talanta, 22, 621 (1975). (13) R. S. Tobin, F. I. Onuska, B. G. Brownlee, D. H. J. Anthony, and M. E. Comba, Wafer Res., 10, 529 (1976). (14) R. S.Tobin, F. I. Onuska, D. H. J. Anthony, and M.E. Comba Ambio, 5,30 (1976). (15) O.E.C.D. Expert Group on the Biodegradability of Nonionic Synthetic Detergents, "Determination of the Biodegradability of Synthetic Detergents", O.E.C.D. Publications, Paris, France, 1976, in press. (16) R. B. Dean and W. J. Dixon, Anal. Chem., 23, 636 (1951). (17) L. C. Craig and D. Cralg in "Technique of Organic Chemistry, Vol. Hi, R I, Separation and Purification", A. Weissberger, Ed., Interscience, New York, N.Y., 1956, pp 149-391. (16) R. S.Tobin, F. I. Onuska, D. H.J. Anthony, M. E. Comba, and 8. Brownlee, Proc. Can. Fed. Bioi. SOC.,18, 45, abstract (1975). (19) R. S.Tobin and D. H. J. Anthony, "Testing the Biodegradabilityof Nonionic Surfactants by the O.E.C.D. Dynamic Simulation Test", Canada Centre for Inland Waters, Unpublished Manuscript (Sept. 1975);# (20) United States International Trade Commission, Synthetic Organic Chemicals, United States Production and Sales of Synthetic Surface-Active Agents-l973", US. Government Printing Office, Washington, D.C., 1975.
RECEIVEDfor review July 26,1976. Accepted November 22, 1976.
Determination of Ammonia and Methylamines in Aqueous Solutions by Ion Chromatography Spiros A. Bouyoucos Michigan Division Analytical Laboratories, The Dow Chemical Company, Midland, Mich. 48640
An ion chromatographic technique is described for the determination of ammonia, monomethylamine(MMA), dimethylamine (DMA), and trimethylamine (TMA) at high concentrations. The procedure dlscussed involveselimination of deviations from the linearity in the conductimetric detector by converting the incompletely protonated bases, formed in the strlpper column, to the chloride salts. This was achieved by introducing a short column of chiorlde-formresin between the stripper and the conductivity detector. The dramatic improvement of the linearlty enables the determination of weak bases, such as ammonia and methylamines at much higher concentrations.
The principle of separation and determination of inorganic and organic cations and anions by ion chromatography has been described by Small, Stevens, and Bauman ( I ) . The technique involves separating the species of interest on an ion-exchange separating column, followed by removal of the background elements in the eluant with a stripper column. Thus, the ions of interest leave the stripper column in a background of deionized water and they are monitored by the conductivitylmeterlrecorder combination. Ion chromatography is particularly useful for the determination of ammonia and amines in water. A difficulty with this application, however, is the nonlinear detector response for these weak bases, particularly a t concentrations above 100 parts-per-million. It was reasoned that this behavior is due to incomplete protonation or dissociation of the free bases formed in the stripper column, and the equilibria involved are concentration dependent. This paper shows the above to be the case and describes a technique that eliminates the non-
linearity problem for weak bases and enhances the detector response for ammonia. T h e technique involves conversion of the hydroxides to highly dissociated chloride salts, thus enabling the determination of weak bases a t higher concentrations by ion chromatography. Results are presented for the determination of ammonia, MMA, DMA, and TMA together in aqueous solutions.
EXPERIMENTAL Apparatus. Separating Column. Two 9 X 250 mm glass columns
packed with surface-sulfonated styrene divinylbenzene (SS-SDVB), 230-325 mesh and about 0.018 mequiv/g capacity were used. Stripping Column. One 9 X 250 mm glass column packed with AG 1 X 10 anion-exchange resin, 200400 mesh in the hydroxide form was employed. Chloride Form Column. A 2.8 X 120mm glass column, packed with AG-X10 anion-exchange resin, 200-400 mesh in the chloride form was used. Eluant. Hydrochloric acid, 0.01 N, in distilled deionized water at about 3.8 mL/min flow rate was used. A schematic of the system used to determine the amines is shown in Figure 1. Reagents and Procedure. Experimental samples containing 300-600 ppm ammonia, 150-450 ppm MMA, and 10-50 ppm DMA and TMA and standards were prepared using reagent grade materials. The amine content in the standards was verified by potentiometric titrations using 0.1 N HC1. Volatilization of amines in both the experimental and standard samples was avoided by acidifying the sample with nitric acid. A typical chromatogram obtained from a 50-gL injection of an experimental sample is shown in Figure 2.
RESULTS AND DISCUSSION Deviations from linearity were observed as expected for ammonia and MMA. For DMA and TMA which were present ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH' 1977
401
Table I. Recovery of Ammonium, MMA, DMA, and TMA Using the Chloride Form Column NH4+
CHzNH2
(CHdz"
(CHddH
Added, Found, Recovery, Added, Found, Recovery, Added, Found, Recovery, Added, Found, Recovery, Sample
%
%
%
%
%
%
%
YO
A
9.9 6.1 11.6 9.5 5.7
9.8 6.1 11.9 9.6 5.6
99.0 100.0 103.0 101.0 98.0
6.5 9.2 3.8 3.6 7.8
6.4 9.3 3.7 3.5 7.6
98.0 101.0 97.0 97.0 97.0
1.0 2.4
1.0
B C D E
%
%
%
1.4 2.4 1.4
100
1.5 2.3 1.4 1.7
1.6
93 104 100 94
96
1.0
1.0
100
YO
100 96 93
2.3
1.5
1.4
0.8 2.5
0.8 2.4
Pump
Injection Valve
Separating Coiumn
R'OH'
Stripper Column
AG
1.X10, 200.400 Mesh Chlorlde Form
Conductivity Cell Recorder Waste
Figure 1. Analytical system used for analysis of ammonia and methylamine PPM NH:
90
Figure 3. Linearity of ammonia before (a)and after (b) the conversion of the base to chloride salt
80 NH;
I
70
80
60 70 60 I
6 I" r $
-7 50
t
'
/
1
It-
,
Nr /
/
/'
, lbl la)
4c
30 Nai
h
20
10
0
0
2
4
6
8
10 12 Minwes
14
16
18
20
Figure 2. Typical chromatogram of an experimental sample at low concentrations, the linearity was satisfactory. Peak height response vs. concentration curves for standards of each compound are shown in Figures 3a-6a. The linearity appears to be a direct function of the pKb for the base. Ammonia, being the weakest base, pKb = 4.75 exhibits the greatest deviation from linearity, followed by TMA, PKb = 4.20; MMA, pKb = 3.37; and DMA, pKb = 3.22 (2,3). 402
ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
20
40
1
I
60
80
l 100
I
1
120 140 PPM TMA
1
I
I
l
160
180
200
220
>
0
Figure 4. Linearity of TMA before (a)and after (b) the conversion of the
base to chloride salt This behavior appears to be due to formation, in the stripper column, of free bases which because of either incomplete hydration (protonation) or incomplete dissociation do not exhibit maximum conductivity. These deviations were eliminated by converting the bases to chloride salts. A short ionexchange column of chloride-form resin was introduced between the stripper column and the conductivity cell to convert any bases to chloride salts. The improvement of the linearity
PPM M M A
!I__[
Linearity of MMA before (a)and after (b)the conversion of the base to chloride salt Figure 5.
80
Lc
70
-
60
-
50
-
I 0
Figure 7. Shift of the peak height vs. concentration for NH4+ to higher sensitivity
30
40-
1
L
30
-
20
10
0
0
20
40
60
PPM NH:
80
100 120 140 PPM DMA
160
180
200
220
240
Linearity of DMA before (a)and after (b) the conversion of the base to chloride salt Figure 6.
was dramatic. Curves of peak height vs. concentration for standards obtained with this system are shown in Figures 3b-6b. Recovery data for the experimental samples analyzed, also by this technique, are summarized in Table I. Figure 7 shows that a shift occurred in the peak height vs. concentration curve for NH4+ after about 50% of the stripper was converted to the chloride form, which resulted in abnormally high values for NH4+. The same shift also was observed for MMA, DMA, and TMA. This problem could not be solved by using a longer chloride form column. However, by frequent regeneration of
the stripper column with 1.0 N sodium hydroxide, this problem was eliminated. It was also observed that the efficiency of the chloride form column slowly decreases because it is converted to the hydroxide form by the hydroxide salts. The same effect is observed if any sodium hydroxide is left in the stripper column after it is regenerated as a result of improper washing. Under normal circumstances the chloride form column was regenerated with 1.0 N hydrochloric acid for about 15 min every 20 to 25 runs.
ACKNOWLEDGMENT The author is thankful to W. B. Crummett, D. Armentrout, R. Kagel, and T. Stevens for their contribution to the completion of this work. LITERATURE CITED (1) H. Small, T. S. Stevens, and W. C. Bauman, Anal. Chern., 47, 1801 (1975). (2) Fisher & Fisher, "Organic Chemistry", 3rd ed., 1956, p 226. (3) W. Rieman Ill and H. F. Walton "Ion Exchange in Analytical Chemistry", 1st ed., Pergamon Press, Oxford, England, 1970, p 163.
RECEIVEDfor review September 13,1976. Accepted December 13, 1976.
ANALYTICAL CHEMISTRY, VOL. 49, NO. 3, MARCH 1977
403
