Lineback. J. A,. Gross, D. L.. Ill. Geol. Suru. Enuiron. Geol. Note, 58,25 pp (1972). Matsumura, F.. Patil, K . C., Boush, G. M.. Nature. 230. 325-6 (1971). Maxwell, J. A., “Rock and Mineral Analysis,” Wiley, New York. N.Y., pp 430-33, 438-40 (1968). Metcalf, R. L., Sangha. G. K., Kapoor, I. P.. Environ. Sci. Technol., 5 , 709-13 (1971). Mortimer, C. H., Lirnnol. Oceanogr., 16,387-404 (1971). Mount. D.. Statement-Pesticides Committee, Second Session of Conf. in the Matter of Pollution of Lake Michigan and Its Tributary Basin, Federal Water Quality Administration, Chicago, Ill., pp 693-777 (1969). O’Connor. R. C., Armstrong, D. E., Fifteenth Conf. Great Lakes Res., Madison, Wis., Abstracts with Programs for 1972. 118. 1972. Powers, C. F., Robertson, A , . J . Fisheries Res Bd. Canada, 25, 1181-97 (1968).
Rao, P . N., Minear, R. A , , Ill. Inst. Technol. Res. Inst., Chicago, Ill.. private communication. 1972. Reinert, R. E.. Bur. Sport Fisheries and Wildlife, U.S. Department of the Interior, Ann Arbor. Mich.. private communication. 1972. . Reinert. R. E., Pesticides MonitorinpJ., 3, 233-40 (1970). Schacht. R.. Ill. Environ. Protec. Agency, Chicago. Ill., private communication. 1972. Shimp, N.F.. Leland. H. V.. White. W. A,. Ill. Geol. Surc. Enciron. Geol. .Vote. 32, 19 pp (1970). Shimp. N. F.. Schleicher. J . A , . Ruch. R. R., Heck, D. B., Leland, H. v., ibid.. 11, 25 pp (1971).
Receiced f o r recieu .Vocember 30. 1972. Accepted Ma? 14. 1973. Research sponsored b? ‘VSF Grant G K ,5587 and Regional Project Ai.C. 96.
Rapid Gas Chromatographic Method for Determination of Residual Methanol in Sewage Michael E. Fox Canada Centre for Inland Waters, Burlington, Ont., Canada
Described is a rapid and specific method for the determination of low concentrations of methanol over the range 0.5-100 ppm in sewage or other aqueous solutions. The method involves the use of direct aqueous injection gas chromatography on a porous polymer column. No preconcentration or extraction is required. The analysis time of approximately one minute per sample makes the procedure especially suited to process control applications. Pilot plant studies on the biological denitrification of waste waters are currently in progress a t the Canada Centre for Inland Waters, Burlington, Ont. (Dawson et al., 1972). An analytical method for residual methanol, which is added as a supplementary carbon source, was required. The use of methanol as an easily assimilable supplementary carbon and energy source for the biological denitrification of municipal and industrial waste waters appears to be justified on a technical and economical basis (Smith et al., 1972). Advanced waste water treatment systems, such as denitrification, are likely to find increasing acceptance and use in the control of eutrophication of lakes and rivers. Although many substrates have been used as a carbon and energy source, research in denitrification technology in the last five years has established methanol as the prime contender for this role (Christensen and Harremoes, 1972). Efficient and economical control of the denitrification process calls for a rapid, sensitive, and specific method for the analysis of residual methanol in plant streams and final effluent. Analytical procedures now in use or reported in the literature are not entirely suitable with respect to convenience or specificity. In pilot plant studies at the National Environmental Research Centre, Advanced Waste Treatment Research Laboratory in Cincinnati (Smith et al., 1972), a somewhat lengthy procedure was used which involved manual steam distillation of the sample before proceeding to a colorimetric AutoAnalyzer method (Bricker and Vail, 1950). Moore and Schroeder (1970) used gas liq838
Environmental S c i e n c e & Technology
uid chromatography with a Porapak Q column, but no details were given on the specificity, sensitivity, or convenience of the method. Until recently, the pilot plant study a t the Canada Centre for Inland Waters has used total dissolved organic carbon as an approximate indication of residual available carbon (Dawson et al., 1972).
Analytical Considerations A specific analytical method for methanol in the 0.5100 ppm range in sewage was sought which, in addition to being quantitative, would avoid any time-consuming and error-producing cleanup, preconcentration, or extraction techniques. The restrictions appeared to indicate direct aqueous injection gas chromatography as the method of choice. The selection of column packing material and length along with the inlet configuration and other variable operating parameters were made so as t o minimize problems especially associated with direct aqueous injection techniques. A porous polymer column packing material was chosen to avoid the liquid phase stripping effects of water. The active sites on the column packing and tube walls were partially deactivated with phosphoric acid (Mahadeven and Stenroos, 1967) to prevent tailing of water and methanol. A removable glass sleeve in the injection port served to retain inorganic material and organic compounds not volatilized at the operating temperatures. Trace components are not easily quantified when appearing on the tail of an overload solvent peak and tend to broaden when eluted before a peak due to solvent in large excess (Deans, 1971). For this work, an analytically useful compromise between these two situations was made possible by the very small magnitude of the signal produced by water in a flame ionization detector in comparison to the signal produced by similar amounts of most organic compounds. Careful choice of operating conditions allowed the water signal to appear as a very low flat-topped mound of about 50 sec duration with the methanol appearing as a sharp spike superimposed on the water base.
Experimental Apparatus. A MicroTek GC Model 220 equipped with a removable glass demisting sleeve and hydrogen flame ionization detector was used for the study. The single column was 0.5 meter X 3.175 mm 0.d. stainless steel packed with Tenax GC 60/80 mesh, batch 04900, Enka N.V., Holland, modified as follows: The U-shaped column was packed and then saturated with 85% phosphoric acid and allowed to stand for 4 hr. Excess phosphoric acid was then removed by displacement with about 50 ml of glass-distilled water. The column was then dried with a stream of dry nitrogen. GC Operating Conditions Inlet temperature, 225°C Column temperature, 70°C isothermal Detector temperature, 225°C Carrier gas, Nz (Linde, U.H.P.) a t 25 ml/min Detector gases, air (Linde Zero gas) at 280 ml/min Hz (Linde, U.H.P.) a t 40 ml/min Sensitivity, :3.2-256 X 10-l’ amps = full-scale deflection on a 1-mV recorder for typical concentrations in the range 0.5-100 ppm CH30H in sewage Results and Discussion Specific Nature of Response. A number, of low-molecular-weight organic compounds which might be expected to possess similar retention times to methanol, Fisher Pesticide Grade, Lot 785958, on the Tenax column were tested for interference (Table I). Of particular interest were formaldehyde, BDH Reagent Grade, 3741% solution (+11-14% methanol), and formic acid, BDH 98-100% A.R. Grade, which might be postulated as possible products arising from the oxidation of methanol. None of these compounds produced an interfering peak with methanol. Methane, which is probably the only one of these compounds likely to be found in sewage samples a t significant concentrations, is completely eluted before methanol. Formaldehyde in concentrated solutions produces a broad tailing peak eluting after methanol. This broad peak may be due to polymerization of formaldehyde molecules. At ppm concentrations, formaldehyde does not produce a detectable peak under the experimental conditions. It should be noted however, that most commercially available solutions of formaldehyde contain 10-15% of methanol added as a stabilizer. For this reason formalhhyde should not be used to preserve samples for methanol analysis by gc. Other organic compounds of higher molecular weight which may be present in sewage are, for the most part, retained as a deposit in the removable glass injection port sleeve, or in some cases are eluted over such a prolonged time interval that no displacement from the base line is detectable. The column may be purged of such materials from time to time by raising the oven temperature to 250°C and cooling slowly to 70°C. This has not been necessary in this work, and no other measurable peak than the methanol peak has been observed despite the injection of hundreds of sewage effluent samples. Under less aerobic conditions methane might be produced but under extended aerobic biological oxidation, the virtually complete disappearance of very low-molecular-weight organic compounds is supported by other observers (Murphy et al., 1971). Sample Preservation. Although the samples were passed through a 0.45 membrane filter after collection to remove suspended material, the bacterial degradation of the residual methanol continued with further storage of the sample. A typical sample originating from pilot plant denitrification columns with a residual methanol concentration of 30 ppm would lose the remainder of the residual
Table I. Retention Time of Some Low-Molecular-Weight Organic Compounds Relative to Methanol Compound
Retention time (CH30H = 1)
Methane Ethane Propane Methanol n-Bu tane Acetaldehyde Ethanol Propionaldehyde Acetone Formaldehyde Formic acid Methylamine
0.2 0.3
0.5 1 .o 1.3
1.5 2.7 6.7 8.0
-a -b -0
= N o peak observed in diiute (pprn) solutions; RT = 2.3 in concentrated solutions. No peak observed under experimental conditions
Table II. Sample Preservation by Acidification to pH 2 CH30H ppm Sample
To reactor
From denitrification, Column 21 From denitrification, Column.=2 To reactor From denitrification, Column = I From denitrification, Column - 2
PH
0 hr
5 hr
7-8
35
29
125 hr
0
7-a
21
19
0
7-8
16
13
0
2
35
-
34
2
19
-
19
2
16
-
16
Table I I I . Accuracy of Measurements on Sewage Effluent Sample No. 3A with Different Amounts of Methanol Added CH30H added, PPm
0 4
6 13 19
CH30H found PPm
10 14 16 24 30.5
CH30H recovered PPm
0 4 6 14 20.5
methanol in three to five days after filtration and storage a t room temperature (Table 11). Standard solutions of methanol in distilled water showed no change in concentration after storage under identical conditions. A microscopic examination of a filtered sewage effluent sample showed large numbers of bacteria to be present. Acidification of the sample a t the time of collection to about pH 2 with hydrochloric acid, Fisher Reagent Grade. was found to inhibit completely further loss of residual methanol (Table 11). Linear Concentration Range. Detector response to methanol was linear over the chosen range of 0.5-100 ppm CH30H. A plot of seven concentrations of methanol in distilled water ranging from 0.6-96 ppm vs. their corresponding peak heights produced a straight line with an intercept a t the origin. The range was chosen to cover the concentrations likely to be found at the various treatment stages of the denitrification process. The linear range may be extended a t either end, although a decrease in precision will be observed a t levels below 0.5 ppm. Methanol feedstock solutions of about 25,000 ppm were found to be best analyzed by dilution to about 25 ppm. Accuracy and Precision. The accuracy of the method was determined by making measurements on spiked sewage samples a t various concentrations of methanol (Table 111). Volume 7, Number 9, September 1973 839
c
I
,I
s-
i
L
7 ~
Figure 1. Reproducibility of peak height measurements Analyses in triplicate of three sewage effluent samples and one standard methanol solution
The precision of the method was determined from replicate analyses (10) of a sewage effluent sample at the 50ppm level of methanol. At this level the standard deviation was 1.2 and the coefficient of variation 2.4% using peak heights. The corresponding figures using peak areas were 0.8 std dev and 1.6% coefficient of variation. These figures are close to the generally accepted optimum performance of a microliter syringe in the hands of a n experienced operator. The use of peak heights was considered satisfactory for quantitative measurements. Figure 1 illustrates the repeatability on three sewage samples and one standard. Recommended Procedure Pass the sample (25 ml or less) through a 0.45-p membrane filter immediately after collection. Acidify to approximately p H 2 with reagent grade hydrochloric acid ( p H indicating test sticks may be used). Store the sample a t room temperature in clean stoppered glass or polyethylene bottles until the analysis can be performed. With the gas chromatographic parameters set u p as indicated above, inject several 5-11. quantities of distilled water until a small almost flat-topped water response is obtained (Figure 2). The first distilled water injection of a new set of analyses often produces a small positive peak. Inject 5 pl. samples of sewage effluent etc. A new injection may be made as soon as the pen returns to the initial baseline (Fig. 2 ) . Calibrate the analyses by injecting 5 pl. each of a series of standards of methanol in distilled water of appropriate concentrations. Measure peak heights using the top of the water "mound" following the methanol peak as the peak base line.
840
Environmental Science & Technology
~~
~~~
. _
Figure 2. Typical set of analyses Eight sewage effluent samples and appropriate standards
Inject 5 pl. of distilled water between samples occasionally to ensure that ghosting does not occur. After approximately 100-200 samples the removable glass injection port sleeve should be removed and carefully cleaned with chromic acid followed by distilled water. The glass sleeve should then be replaced and the gc oven heated u p to 250°C for 30 min and then slowly cooled to 70°C. Increased size of the water 'base' or ghosting when distilled water is injected are indications of the need to clean the glass sleeve. Acknoccledgment The author thanks R. N.Dawson of the Environmental Protection Service. Environment Canada, for suggesting the work and providing samples from the joint E.P.S.McMaster University pilot plant denitrification studies and also P. M . Sutton for providing treated samples and information on pilot plant denitrification studies and practices. Literature Cited Bricker, C. E . , Yail, \V.A , , Ana/. Chem., 22. 5 , 720-2 (1950). Christensen, M. H., Harremoes. P., "Biological Denitrification in \\'ater Treatment." Rep. 2-72, Dept. of Sanitary Engineering, Technical Cniversity of Denmark (1972). Dawson. R. N., Murphy. K . L.. Sutton, P. M., North West Region, Environmental Protection Service, 1002s Jasper Avenue. Edmonton, Alta T5J 2x9, private communication, 1972. Deans, D. R., Anal. Chem., -13,14,2026-9 (1971). Mahadeven, V.,Stenroos, L., ibid.. 39, 13, 1652-4 (1967). Moore, S. F., Schroeder. E . D.. Water Research, 4, 10. 685-94 (1970). Murphy, K. L., Sedivy, M . J.. Yigers, G. A , . Proc. 6th Canadian Symposium on R a t e r Pollution Research, pp 80-93. 1971. Smith, J. M., Masse, A . M.. Feige. h', A , , Kamphake, L. J.. Enciron. Sci. Technol., 6 , :3,260-7 (1972).
Receiced for reciew Decem ber 18, 1972. Accepted :May 21. 197.3.
