Determination of Submicrogram Levels of Phenol in Water P. D. Goulden, Peter Brooksbank, and M. B. Day Department of the Environment, Canada Centre for lniand Waters, 867 Lakeshore Road, P. 0. Box 5050, Burlington, Ontario
The determination of phenolic compounds in water is an important part of water quality measurement. The levels of phenols and phenolic compounds give an indication of the presence of pollution from industrial sources such as petroleum products and insecticide, herbicide, fungicide, and pesticide residues. The presence, even in concentration of 1 ppb, of some phenols in drinking water supplies may lead, on chlorination, to the formation of objectionably tasting and odoriferous chlorophenols. The “Guidelines for Water Quality Objectives and Standards” ( I ) gives the “acceptable limit” and the “objective” for drinking water purposes as 2.0 pg/l. phenol and “not detectable,” respectively. Available manual determinations have a limit of detection of l pg/l. phenol ( 2 ) ,while automated methods report limits of detection of 2 pg/l. ( 3 ) . However, to monitor waters for phenols effectively and to attain the required water quality, there is a need for an automated method with a limit of detection that is an order of magnitude smaller than that currently available. The commonly used analytical methods, e.g., those described in “Standard Methods for the Examination of Water and Wastewater” ( 2 ) , involve separation of the phenolic compounds by steam distillation and their determination colorimetrically with 4-aminoantipyrine (4AAP). This reagent is known not to react with certain para-substituted phenols but the significance of this characteristic in water quality measurement has not been determined. At present, other reagents are available for phenol measurements, in particular, 3-methyl-2-benzothiazolinone hydrazone (MBTH) ( 4 ) which couples under oxidative conditions with phenols to yield a dye. The reaction is inherently more sensitive than that with 4AAP; besides the MBTH reacts with a broader spectrum of phenols than does 4AAP. In particular, it reacts with some of the parasubstituted phenols that do not react with 4AAP. In earlier work on the determination of cyanides ( 5 ) , we have developed continuous distillation equipment that permits the distillation of comparatively large sample flows in an automated system. This technique has now been applied to the determination of phenol. In the cyanide determination, since the HCN evolved is easily separated from the steam, there is concentration in the distillation step itself. This is more difficult to accomplish in the phenol distillation. The method found most convenient is to distil and condense a large sample flow and then, after the color formation step, to concentrate the dye by extraction into a small solvent flow. This technique has been used with both 4AAP and MBTH, a t a (1) Department of the Environment, Inland Waters Directorate, Ottawa,
Ontario, “Guidelines for Water Quality Objectives and Standards-A Preliminary Report,” Tech. Bull., 67, 31 (1972). ( 2 ) American Public Health Association, American Water Works Association, and Water Pollution Control Federation, “Standard Methods for the Examination of Water and Wastewater,” 13th edition, February 1971. (3) W . J. Traversy, “Methods for Chemical Analysis of Waters and
Wastewaters,” Inland Waters Branch, Dept. of Fisheries and Forestry, Ottawa, Canada, 1971. (4) H. 0. Friestad, D. E. Ott, and F. A. Gunther, Anal. Chem., 41, 1750 (1969).
Goulden, B. K. Afghan, and P. Brooksbank, Anal. Chem., 44, 1845 (1972).
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sample rate of 10 per hour. The limit of detection for the two methods is 0.2 pg/l. phenol. The step that separates the phenols from interfering substances is a single distillation, hence the method is applicable only to those relatively “clean” waters for which this single distillation constitutes a satisfactory “clean-up” procedure.
EXPERIMENTAL Apparatus. The manifold used for the 4AAP colorimetric method is shown in Figure 1 and that for the colorimetric method with MBTH, in Figure 2. The distillation process is identical for the two reagents. The sampler is an “Industrial Sampler” (Technicon), modified as previously described ( 6 ) to control the amount of air taken into the system during the sample arm transfer. The pump is a 20channel proportioning pump (Carlo Erba); the colorimeter and recorder are standard AutoAnalyzer equipment (Technicon). The distillation tube is made of borosilicate glass and is 18-mm i.d., 60 cm long, wrapped with asbestos and then with 22-gauge wire, to give a resistance of about 24 ohms. Approximately 100 V ac are applied to this heating wire through a variable transformer. Details of the distillation tube and of the condenser system are shown in Figure 3. The extractor consists of 3-mm i.d. glass tubing about 90 cm long, bent into a U and filled with thin strips of Teflon (DuPont) twisted together. The separator is a T-piece of glass tubing, 3-mm i d . , as shown in Figure 4. Inside the arm, through which the aqueous-air-solvent mixture is fed, a piece of Teflon measuring 1.5 mm X 0.8 mm X 10 cm, is inserted and held in place along the bottom of the tube with a spiral made of 26-gauge Chrome1 wire. All connections are made by using glass tubing and Teflon or Acidflex sleeving. To avoid air bubbles forming in the solvent during the measurement, the manifold is arranged so that there is approximately 10 cm of chloroform positive pressure on the colorimeter flow-cell. To facilitate rapid removal of water droplets that occasionally separate in the flowcell, the colorimeter is mounted at a 45” angle to the horizontal. Reagents. 4-Aminoantipyrine Colorimetric Method (4AAP). Aqueous, 10% (v/v) sulfuric acid is used. The buffered 4AAP is prepared by dissolving 25 g of potassium bicarbonate, 26 g of boric acid, and 45 g of potassium hydroxide in 1000 ml of water and adding 2 g of 4-aminoantipyrine. The aqueous potassium persulfate solution is 2.5% (w/v); the p H of this solution is adjusted to about 11 with potassium hydroxide. The 4AAP and potassium persulfate solutions are prepared fresh on each day of use. The wash water is treated with copper sulfate solution in the same proportions as the samples. Phenol standard solutions are prepared from a stock solution of 1000 mg/l. phenol, preserved with copper sulfate, and stored in a refrigerator. The standard solutions of phenol, containing up to 10 pg/l. phenol are prepared immediately before use or may be prepared by adding the stock phenol aliquot to water-plus-copper sulfate at 4 “C and storing them in glass bottles or volumetric flasks in a refrigerator. 3-Methy1-2-bentothiazolinone Hydrazone (MBTH) Colorimetric Method. The aqueous MBTH solution is 0.05% (w/v). It is stable for up to a week if stored in a refrigerator. The following solutions were prepared: aqueous, 1% (w/v) ethylenediaminetetraacetic acid from its disodium salt; aqueous sulfuric acid, 2% (v/v); ceric ammonium sulfate by dissolving 1% (w/v) of ceric ammonium sulfate [Ce(NH4)4(SO4)42H2O]in a 1.5% (v/v) solution of sulfuric acid in water; the buffer solution, by dissolving 70 g of potassium hydroxide, 30 g of borax, and 50 g of monosodium phosphate, in that order, in water and diluting the solution to 1000 ml with water. The phenol standards are prepared according to the procedure given in the 4AAP method. Goulden and P. Brooksbank, “An Automated Solvent Extraction Method for the Determination of Trace Metals in Natural Waters by Atomic Absorption Spectrophotmetry.” Paper No. 206, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, March 1973.
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ANALYTICAL CHEMISTRY, VOL. 45, NO. 14, DECEMBER 1973
CONDENSER
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Figure 2. Manifold for M B T H determination
Procedure. The system is set in operation using distilled water through the resample and colorimetric reagent lines. The power to the distillation tube is turned on and adjusted to give the desired
distillation rate. The reagents are then added. Standard phenol solutions are run over the range required, generally 0.5 to 10 Fg/L phenol, to prepare a calibration curve.
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Separator RESULTS AND DISCUSSION
Distillation. Approximately 80% of the sample flow is distilled in the method. This amount is used because it is practical as well as close to the recommended 100% distillate in the manual “Standard Methods for the Examination of Water and Wastewater” ( 2 ) and it can be achieved without incurring problems of tube fouling from the dissolved solids in the samples. Variations of 10% in the amount distilled do not have any effect on the concentration of the distillate. When 60% of a phenol standard was distilled, there was some concentration in the distillate. This effect was not seen in the natural water samples investigated (waters from Lake Ontario), as described below; this 80% distillation procedure gave results that were not significantly different from the “Standard Methods” ( 2 )procedure that distils 100%of the sample. Colorimetric Determination. 4-Aminoantipyrine. The purpose of the work with 4AAP was to optimize this classical reaction a t the large flow rates desired so that a smooth base line could be obtained to allow amplification of the signal. The reaction of phenols with 4AAP is affected by a number of factors; a discussion of these is given by Faust and Lorentz ( 7 ) . In the present work, the effects of reagent concentration, pH, and temperature were determined. There was optimum sensitivity (over the range 0-10 fig/. phenol) when the 4AAP concentra(7) S D. Faust and F. G. Lorentz, Proceedings of the 11th Ontario Industrial Waste Conference, June 1964, pp 173-201
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tion was 0.2%. When the potassium persulfate concentration reached 2.5%, there was a levelling-off in sensitivity. The pH-sensitivity curve was a t an optimum and almost flat between pH 10.5 and 11; a pH of 10.8 f 0.5 was chosen as being the easiest to maintain for an even base line. A reaction temperature a t 34 “C gives the optimum response; within reason, the length of time during which the reaction is kept a t this temperature has little effect. 3-Methyl-2-benzothiazolinone Hydrazone. Because of the inherently greater sensitivity of the reaction with MBTH than with 4AAP, it was not necessary to optimize conditions as carefully to obtain the same sensitivity. Essentially, the conditions described by Friestad et al. ( 4 ) were used in the color-forming reactions, modified for the large distillation volume. Two changes were made: it was necessary to add the EDTA very early in the system to avoid precipitation of cerium hydroxide on neutralization; and the buffer was changed to facilitate obtaining a final p H of 7.3-7.6 and thus an optimum intensity of color. Solvent Extraction. In this step, approximately 9 ml/ min aqueous phase are extracted with 0.5 ml/min chloroform. In both the extraction and separation, use was made of the ability of chloroform to wet Teflon. This solvent flows in a thin stream on the surface of the Teflon, giving good extraction and good separation. [After this technique of separation had been developed, some hydrophobic filter paper (Technicon Corp.) was made available to us. This paper used with a continuous filter (Technicon Corp.) gives a positive separation of the solvent and aqueous phase. This may be a preferred method of separation.] The MBTH dye was very readily extracted by chloroform; one extractor was required for essentially 100% extraction, whereas two extractors were required for 4AAP method. Comparison of Methods. Samples of natural waters were analyzed by both the automated 4AAP method and by the manual distillation-chloroform extraction method using 4AAP given in “Standard Methods.” Ten samples from the St. Lawrence River, 30 samples from Lake Ontario, and 10 samples from Hamilton Harbour were analyzed. The phenol levels ranged from 0 to 15 fig/l. No significant differences were found between the results from these two methods. From the comparatively few natural water samples ana-
A N A L Y T I C A L CHEMISTRY, VOL. 45, NO. 14, DECEMBEiR 1973
lyzed to date by both the 4AAP and MBTH methods, no conclusions can be drawn as to the usefulness of MBTH in reacting with, e.g., para-substituted phenols. The analysis of approximately 60 samples from Lake Ontario, containing from 0 to 15 kg/l. phenol, showed no statistically significant difference between the results from the 4AAP and MBTH methods. However, the parallel measurements demonstrate the operating advantages when using MBTH: its relative insensitivity to p H change and its more intense color formation as compared to the 4AAP with the same levels of phenol. Detection Limits and Precision. For both the 4AAP and MBTH methods, the detection limit, defined as that level which gives a signal of twice the background noise, was 0.2 kg/l. At a concentration of 5 pg/l. phenol, based on 11 replicate determinations, the coefficient of variation of the 4AAP method was 3.6% and that of the MBTH method, 2.4%. Interferences. In the present work, no study was made of the effect of interfering substances. According to the literature (2, 4 ) , steam distillation from acidic solution removes interfering substances with the exception of aliphatic aldehydes and is a satisfactory “clean-up” procedure for most natural water samples. A single distillation does not suffice to remove all interferences from some industrial waters, and those waters which experience has
shown to require it, should be treated by a preliminary manual distillation and solvent extraction step as described in “Standard Methods.” Studies were made of the distillation procedure used, to confirm that there is a minimum entrainment, i. e., nonvolatile substances added in the sample are not recovered in the distillate. This is considered a satisfactory demonstration of the efficiency of the process in removing interfering substances. Phenol Concentration. For some methods of phenol determination, it is preferable to concentrate the phenols in an aqueous solution, e.g., if analysis is to be made by fluorescence measurement. Our early work was designed to concentrate the phenol before the colorimetric step. This could be done by passing the steam-phenol stream through a packed column concurrently with sodium hydroxide solution. The phenol is absorbed in the alkaline liquid stream and the gas stream, ie., the steam plus air that exits from the column, contains no phenol. A concentration factor of about five could be achieved by this means. For the colorimetric determination, however, it was more convenient to obtain the concentration by organic solvent extraction. Received for review April 20, 1973. Accepted July 18, 1973.
Cation Exchange Studies of Ti4’, V5+,Fe3+,Nb5+,and U022’ in Formic, Oxalic, Tartaric, and Citric Acid Media Mohsin Qureshi, K. G. Varshney, and R. C. Kaushik Z. H. College of Engineering and Technology and Department of Chemistry, Aligarh Muslim University, Aligarh (U.P) lndia
The separation of titanium, vanadium, iron, niobium, and uranium from interfering elements has received consideration, owing to their increased use in the industrial field. Cation exchange resins have been extensively used for these separations for the last 15 years and a number of interesting results have been obtained (1-4). In the sorption studies of Zr4+ and Nb5+ on Dowex-50 in organic solvent-HC1-aqueous solution systems, Kawashima and Bono ( 5 ) observed that the reaction between the resin and the metal ion in mixed solvents is greatly influenced by the organic solvents. Complex formation of the metals with organic compounds has been advantageously used to achieve difficult separations. Thus, a cation exchange separation method for uranium in dimethyl sulfoxide (6) has been described. Another method for separating uranium from other elements has been developed in tetrahydrofu(1) H. Kusagawa and J. Shimokawa, Dai-2-Kai Genshjryoku, symposium, Holumshu 3, 59 (1958). (2) A. I . Athavale, M . N. Nadkarni, and Ch. Venkateswarlu, Anal. Chim. Acta. 23,438 (1960) (3) K. Tonasaki and M. Otomo, J. Chem. SOC.Jap.. Pure Chem. Sect., 80,41 (1959). (4) Y . S. Kim and H. Zeitlein. Anal. Chem.. 43, 1390 (1971) (5) T. Kawashirna and Y . Bono, Nagoya Kogyo Gijutsu Shikensho Hokoku. 13, 269 (1964) (6) G . E. Janauer, J. Korkisch, and S. A. Hubbard, Taianta. 18, 772 (1971).
ran-nitric acid media containing trioctyl phosphine oxide (7). Carboxylic acid media have shown great potential for the separation of metal ions which are otherwise very difficult to separate. Fridman and Yudina (8) extracted and separated Nb5+ and Ti4+ from oxalic acid solution using cation exchanger KY-2 in the protonated form. Similarly, lanthanides have been separated in 4.75% NH4 citrate (9, 10). Also, tartaric acid, citric acid, and formic acid (1116) have proved to be very effective for metal ion separations. However, a selective study of the metal ions mentioned above in carboxylic acid media is lacking. It was, therefore, decided to take only the five metal ions and de(7) M. M. Khater and J. Korkisch, Talanta, 18, 1001 (1971). (8) I . D. Fridman and I: N. Yudina. Zh. Prikl. Khim. (Leningrad), 32, 1914 (1959). (9) B. H. Ketelie and G. E. Boyd, J . Amer. Chem. Soc.. 69, 2800 (1947). (10) S. A. Brooksbank and G. W. Leddicotte. J . Phys. Chem., 57, 819 (1953). (11) T. Shiokawa and A. Sato, Nippon Kinzoku Gakkaishi, Ser. 6, 15, 284 (1951); Chem. Abstr., 47, 8578 (1953). (12) M. Marhoul, Chem. Prum., 11, 102 (1961); Anal. Abstr., 8, 3194 (1961) . (13) P. Radhakrishna. Ana/. Chim. Acta. 6, 351 (1952) (14) W. E. Brown and W. M. Reiman. J. Amer. Chem. Soc.. 74, 1278 (1952). (15) M . Qureshi and K. Husain, Ana/. Chem.. 43, 447 (1971). (16) M. Qureshi and W. Husain, Talanta, 18, 399 (1971).
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