Analysis of Trihalomethanes in Soft Drinks An Instrumental Analysis Experiment Rlchard C. Graham1 and John K. R o b e r t m Science Research Laboratory. U.S. Military Academy. West Point. NY 10996 Environmentalists. scientists. government officials. and most consumers have been concerned about the quality of the environment around us. One of the classes of compounds that is ubiquitous in drinking water supplies is that of the trihalomethanes (THM's) including chloroform, hromoform, dichlorobromomethane, etc. The occurrence of these compounds is well documented and recognized ( 1 4 . Several sources of organic compounds for THM production have tannic acid been implicated including humic material (5-9), (lo), some nitrogen compounds ( 1 0 , and recently such suhstances as Anabaena cylindrica (12) and also other algae (13,141. With the extensive number of potential precursors, it is not so surprising that THM's occur so freely in chlorinated water supplies. In addition to the practice of chlorinating water supplied to customers for consumption, chlorination has been extended to the secondary treatment of wastewater efflwnrs from manufacturing and sewage treatment farilities. The benefits of the practice have been seen through the reduction of pathogens destroyed by the chlorination process. Asnart of the Instrumental Methods of Chemical Analvsis course taught at theU.S. Military Academy, eachcadet must conduct an indenendent ~ r o i e cnear t the end of the semester. One of the most pop;la;analytical techniques has been the analvsis of various substrates for the trihalomethanes. The technique has heen applied to the following situations: a. Swimming pool waters b. Water treatment and water distribution systems c. Soft Drinks d. In-home water purifiers e. Purification of water in canteens using iodine tablets. This naner . will onlv describe in detail the analvsis of THM's in soft drinks. A varietv of methods have been oronosed for the determination of tbtal trihalomethanes (TTHM), but the two methods oromuleated bv the US. Environmental Protection Ageky (USEPA) aie the purge and trap method (15-17) and the liauid-liauid extraction method (18-21). The puree and trap method intails bubbling an inert gas such as hit&gen through a sample to he analyzed and trapping the effluent on a column, such as TFKAX. XAl) rrsins, or artivated charcoal, which is maintained at amhient ur cuhambient temperature. At the conclusion of the purge cycle, the trapped volatiles are thermally desorhed and analyzed by passing the effluent to a gas chromatograph.
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All samples were taken in 41-mL glass vials (Pierce Co.) to' which several small crystals of sodium thiosulfate had been added to inhibit further production of THM's. The vial is
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rapped with a Teflon-fared rilirme septum. For thc analysis ofsoft drinks, the minimization of et'rrrvescence is critiral 50 that the hut~blingdoes not prmuiturely purge some of the THM's from the soh drink. To minimize this problem, tu,o experimental stevi were taken: thr first was to r o d the soft drink to below room temperature and the second was to transfer the soft drink to the glass vial using a 5-mL glass syringe with a stainless steel needle. The needle is used to puncture the cooled soft drink can to withdraw the soda. This soda is then injected into the glass vial through the Teflon septum. Once the glass vial was full, 2 mL was withdrawn through the septum with the syringe and 1 mL of chromatographic-grade pentane was then added. The vial is vieorouslv shaken for 3 min after which the lavers are allowed to separate. One microliter of the pentane iayer is then injected onto a gas chromatograph. A Hewlett-Packard 5736 gas chromatograph with an electron capture detector was used for all determinations. The column was 20-ft X l/s-in.0.d. stainless steel column packed with 20% OV-101 on 801 100 mesh Gaschrom Q maintained at an isothermal temperature of 120 "C. The injector port and detector are maintained at 150 OC and 300 "C, respectively. UHP nitrogen was used as a carrier gas a t a flow rate of 30 mL/min. ?ypical retention times were pentane 1.4 min, chloroform 2.6 min, dibromochloromethane 5.6 min. and hromoform 8.5 min. Chromatograms were recorded and peaks integrated using a Hewlett-Packard 3380 recording integrator. One of the most critical portions of the experimenbis the preparation of the standards to be used in the determination of the trihalomethanes. Because of the volatile nature of the THM's, fresh working standards must be prepared every day the determination is performed. A concentrated stock standard of each of the four THM's in methanol is prepared from the reagent-grade trihalomethane by addingapproximately 9.8 mL of methanol to a 10-mL volumetric flask. Any methanol that mav have wetted the neck of the flask is allowed toevaporate.Tht. flask and methanol are ureighed t ~ l 0.1 mg. Twodrops of'theTHhl an, added from a syringe and the flask is quickly reweighed to0.1 mg.'l'heTH\I should be added directly to the mrthanol and not allowed ti, contact the side of the flask.'I'heaolution is then dilutrd to the mark with methanol. The concentration or the T H Y is ralculated from the weight of the THM added and the total volume of the solution. One should not use the units of ppm, or pph in this instance since the density of the methanol solution is quite different from the density of an aqueous solution. A similar stock standard is prepared for each of the THM's to he determined. The stock standards are rather stable and can be kept reliablv for un to four weeks. u r efor a multicomponent secondary The ~ ~ A ~ r o c e dcaik dilution mixture to he prepared in methanol alcohol such that a 20-pL injection of the multicomponent standard in 100 mL of the water free of THM's will generate a calihration standard whose response is close th that of the unknown. However, we have found that for the students it is easier to prepare a multicomponent stock solution in water for each component by diluting 1 mL of each of the stock solutions to 250 mL with THM-free water. The concentraVolume 65
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tion of this stock standard should be approximately 100 mgl L. This gives a solution from which the working standards are thenmenared hv further dilution to concenGations that will braccet the conEentration of THM's in the samples to be analyzed. The bracketing concentrations should be approximately f20% of the analytical concentration. A convenient set of dilutions to use for the final workine standards is 4.16. 42, and 85 fiL of the multicomponent standard, each diluted to 100 mL. For some of the analyses that are done in connection with this technique, i t was also useful to determine the amount of free chlorine that is present. The chlorine is determined with the method cited in Standard Methods for Examination of Water and Wastewater (23). KMn04 standards are used in lieu of chlorine because of the difficulty to prepare stable chlorine standards. The free chlorine reacts with Nfl-diethyl-p-phenylenediamine to produce a magenta-colored species.
ComDarlson of Results of Analvsls of SamDlesa
Olympic p w l intramural pod instructional pool
1.93 5.67 7.96
0.97 3.03 2.96
0.01 0.11 0.09
0.02 0.05 0.33
Lusk Reservoir chlorination tank settling pond drinking fountain sink Bartlett Hall
0.00 7.37 4.50 1.30 0.70
0.00 0.00 5.20 0.90 0.00
0.00 8.20 5.10 4.00 3.40
0.00 0.00 0.00 1.20 1.70
4.00 1.20 3.9
5.00 0.00 0.00
3.80 6.00 0.00
cola "A" cola " W Cola "C"
15.8 14.0 53.9
0.000 0.113 0.109 0.096 0.105
A l l ~oncentaflons are glven in pglL.
" = na analyzed.
of 100 mg/L for the CHCIBr* and the CHCI3 and 200 mg/L for the CHBr3. Dilutions of 4, 16, 42, and 84 FL of the dilution mixture to 100 mL with THM-free water will eive working standards that have concentrations of 5,20,30, and 100ugIL for theCHCIBr?and theCHCI7and 10,40,l00, and 200 rg1L for the CHRr,. These working standards are not stable and should br made fresh every hour. The multicomponent dilution mixture should be prepared fresh e\,ery day. The stock solutions of the I'HM in methanol are stahle for up to 4 weeks if kept at 4 OC. The amount of THM's in other solutions is compared with the amount of THM in the soft drinks in the table. The recommended maximum limit of total trihalomethanes in drinkine water is 100 u e L . I t is noted that none of the samplelreported exreedrhat limit; however, the soft drinks have the hiehest content of rhloroform. Amone" the different samples, the colas have chloroform as the predominant THM. This table also indicates that the distance from the chlorination treatment facility has a dramatic effect on the ronrentration ofTHMSsin thenamole. Theorder of samoles in terms of distance from source to :ampling location is i u s k Reservoir, chlorination tank, settling pond, drinking fountain in barracks, and sink in Bartlett Hall. Perhaps one of the most striking results indicated in the table is the relatively low concentration of THM's in the swimmingpools. One would expect with the high concentration of chlorine in such a pool that [THM] would he rather high. Although not analyzed, one could speculate that the total organic content of the pool is very low and therefore insufficient organic material is present to react with the amount of chlorine present.
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The absorbance of the solution is then measured a t 515 nm. The total amount of free available chlorine may be found by initially reading the absorbance and then adding a small amount of KI crystals or solution and reading the absorbance again. The total free chlorine is then calculated using the formula in reference 23. Results and Dlscusslon
This technique has oroven to be verv instructive for the cadets a t the Military Academy. TWO-potentialproblems may detract from obtaining acceptable results. The first is the problem in obtaining pentane of sufficient purity to use as an extracting medium. Even the very best pentane can be very quickly contaminated by poor lab practice. Leaving a bottle of pentane uncapped will ensure that the pentane will remove organics from the laboratory air in sufficient quantity to interfere with peaks in the chromatogram. The other problem is that it appears that some of the plastics may he leached from the cap and cap liner of the bottle. The second ~ r o b l e mis the oreoaration of the standards used for quantitation. A stock standard solution is prepared by dilution of weighed amounts of each of the trihalomethanes to be quantitated. Water free of THM's must he used to prepare all of the analytical standards. THM-free water may be prepared by bubbling pure Np through the water or by passing it through a granulated carbon bed. A water preparation system such as the Millipore Milli-Q or the Barnstead Nanopure systems may be used. Working standards are then prepared by serial dilution of the stock standard. Great care must he taken in the dilution, since a small error in the measured volume can make a significant difference in the actual concentrations. Two v mL. When droos of the THM will be a ~ ~ r o x i m a t e l0.2 dil;ted to 10 mL, the apprdximate concentration of the CHCh and the CHCIBr7 will be 30 me/L and for the CHBra t i f 1mL of each of these will be60 mg/L. ~ u b s e q i e ndilution stock methyl alcohol solutions will produce a multicomponent dilution mixture that has an approximate concentration 736
Journal of Chemical Education
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Conclusion
The USEPA method of determining trihalomethanes by liquid-liquid extraction is quite versatile and in particular in this report has been applied to the analysis of the trihalomethanes in soft drinks. Valid results may be obtained by careful anolication of the analvtical techniaue. Care must be taken to&ure that T H M ' S ~ ; ~ not lost through \.olatility of the THM's because of the effervescence of the suft drink. For analysis of aqueous samples, the presence of NazSzO3in the vials is necessarv to ~ r e c l u d efurther oroduction of THM's. Llteralure Cited
1. Rook, J. J. Wafer Treat.Exom. 197423.234. 2. Folq,P.D.;Missingham,G.A.J.Am. Water Works Assoc. 1976.68.195. 3. Health and Welfare Canada. "National Survey for Halamethanes in Drinking Water", Repwt No. 77-EHO~9.1977. 4. Symons,J.M.:Bellar.T.A.;Carswell, J.K.:DeMareo. J.;Kropp,K.L.;Robeck,G.G.; Seeger. D.
R.; Slocum. C. J.; Smith,B. L.:Steuens,A. A. J.Am. Woter WorkaAa8oe.
1375.67.634.
6. Rwk. J. J. J . Am. Wolrr Works Assoc. 1976.68.168. 6. Rook. J. J. J . Am. Water Works Assoc. 1977.69.478.
7. Sfevens,A.A,: S1ocum.C. J.;Seeger,D.R.; Roheck.G.G. J. Am. Wotw Works Assor. 1976.68.615. 8. Young, J. S.; Singer. P. C. J, Am. W d a r Worka Assoc. 1979. 71.87. 9. 0liver.B. O.:Lawrence. J . J . A m . Water Works Arroe. 1979. 71. 161. LO. Youseffi. M.: Zenehelrkv. S. T.: Faust. S. D.J. E n o r o n . S n . Health, Port A 1978.13, 629. 11. Morris. J. C.: Baum. G.Water Chloiinoiion: Enuiron. Impmi Health E i i . Pror. Coni. 1977.1978.2, 29. 12. Briley, K. F.: Williams. R. F.: Longley. K. E.: Sorber, C. A. Water Chlo~inotion: Enuiron. Impocl Heolth E l i . Proc. Con/ 1978.1979.3.512. 13. Hoehn. R. C.; Randall, C. W.: Goade, R. P.: Shaffer. P. T. B. Water Chlolinnfion: Enuiron. Impocl Heolth Ei1.Proc. Canf. 1978, 1919.3.519. 14. 0liver.B. G.:Shindler, D. B.Enu.Sci. Tech. 1980,14,1502. 15. Bellsr.T.T.;Lichtonherp.J . J . J A m Wotsr Workr Asroc. 1974.66. 739.
IS%%p 185. Brdtmann, N.V.,Jr. J . Am. Wolar Work8 Assac. 1975,67,558. Kissinger. L. D.; Fritz, d. S. J . Am. Water Workr Aaaoe. 1916.68.435. Mieure, J. P. J . Am. Water Works Assac. 1971.69.60. Richard, J.J.: Junk, G. A. J. Am. Water WorheA8sac. 1977,69,62. "The Analysis of Trihalomethanes in Drinking Wafer by Liquid Extraction": US Environmental Pmtoctian Aeeney. Environmental Monitorinn and Support Laboratory, Cineirnafi.OH.9~~bt. 1977. 23. Standard ~ ~ t h o lor d * the ~ ~01 warprand ~ Wnstswol~r, ~ 15th ed.; Ameri~ can Public Health Asroe.: Washington, DC. 1980: p 262.
18. 19. 20. 21. 22.
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