Microcosm
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Using an Aquarium To Teach Undergraduate Analytid Chemistrv J
Kenneth D. Hughes School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta, GA 30332-0400
The need for individuals who a r e competent in both wet chemical and instrumental measurements is i n creasing, as several authors of articles in the JOURNAL have indicated (1-3). But there is a lack of individuals who are trained in classical titrimetric and gravimetric techniques because of the shift away from traditional wet chemistry in many university teaching laboratories. Industries suffering from this predicament include those involved in advanced materials and composites. Two reasons for the move away from traditional wet chemistry are the increasing number of analytical techniques that must be covered in a fixed amount of course time and the lack of enthusiasm expressed by undergraduates for courses that concentrate strictly on classical techniques. Although the problem of the a m o u n t of m a t e r i a l included i n courses can be addressed with only minor difficulties, the reason for the lack of enthusiasm is difficult to ascertain. We believe t h a t in many cases a lack of appreciation, understanding, and historical awareness of classical analysis is at the root of the problem. Students who are exposed to chemistry outside of the classroom, through co-op work in government and i n dustrial laboratories, seem to have a 0003-2700/93/0365-883A/$04.00/0 0 1993 American Chemical Society
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better understanding of the impor tance of experimental protocols and the need to master basic laboratory skills, such as weighing, pipetting, and diluting. Unfortunately, not all students can participate in these types of programs. Students who lack a practical understanding of and appreciation for laboratory techniques usually leave the laboratory poorly trained. Inade quate training early in a student’s career sets the stage for future unhappiness because the main difficulty encountered in instrumental analysis is usually poor technique in sample preparation. The importance of real-world chemistry in undergraduate chemistry curricula, with respect to motivating students, has been discussed (4, 5). In the past, a number of methods have been used to promote students’ interest in chemistry in general and to specifically increase interest in
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8 the laboratory portion of the curriculum. Unusual samples have been brought into the laboratory, and field trips have been incorporated into courses. Biological samples such as blood and urine are complex and interesting but unfortunately are no longer appropriate for teaching lab0 ratories because of possible health hazards. Sample-collecting field trips are often difficult to conduct because of logistics and the number of students. An alternative is to use environmental samples from selfcontained laboratory ecosystems. In the fall of 1992, we set up a saltwater aquarium with coral reef fish to serve as such a laboratory ecosystem. Experiments based on aquarium samples were incorporated into the first part of a two-quarter analytical chemistry curriculum. The course is
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REPORT taken by junior and senior chemistry, biology, and textile students, and by some engineering students. Our objectives are to motivate students to understand traditional wet chemistry techniques by using “natural” or real- world samples for lab0 ratory analysis; to show that solving scientific problems drives the devel opment of new instrumentation with improved capabilities; and, most important, to provide visible evidence of chemistry’s role in the environment and biological processes. Students monitored the aquarium four days a week and determined the concentrations of ammonia and nitrite, nitrate, and phosphate ions using spectrophotometry; sulfate ions using gravimetry; and calcium and magnesium ions using EDTA titrations. They also determined dissolved oxygen, salinity, and alkalinity using redox and potentiometric methods. The content of the traditional classroom lectures given in conjuction with the laboratory did not have to be changed. This curriculum incorporates analysis of natural samples with both classical and instrumental methods and provides each student with a continuing sense of discovery. Students are trained in the techniques of pipetting, weighing, dilution, and spectrophotometric calibration. The aquarium has been popular with students and the general public, as evidenced by articles in the student newspaper and various city newspapers (6). Why a marine aquarium? The marine ecosystem is a unique environment that encompasses many well-documented dynamic chemical and biological systems. The box below provides a partial list of inorganic species present in seawater and the context in which they are de-
.aboratory venue! Beer’s law and -the nitrogen cyclc Ammonidammonium ion Nitrite ion Nitrate ion ’lectrochemistr, ---I Alk
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c termined. The term “venue” is in keeping with Atlanta’s participation in the 1996 summer Olympics and refers to the various analytical sections within the lab. These elements are important in the biology of the ecosystem. The current technology and application of analytical chemis try to the field of oceanography was covered in a recent REPORT (7). Researchers a t the Smithsonian Institution’s Marine Systems Laboratory have tried t o reproduce the marine ecosystem in the laboratory. The aquariums, called microcosms, range from 30 t o 750,000 gal and have been successfully maintained for the past decade (8). The general public’s interest in freshwater and marine aquariums dates back thousands of years and crosses all cultural boundaries. The aquarium hobby is one of the largest hobby industries in the world, with yearly sales of more than $1billion (9). Even in t h e economically depressed former Soviet republics, en thusiasm for aquariums is strong; individuals spend o n e - t h i r d of a month’s s a l a r y on a small g l a s s aquarium (10).In the United States, attendance a t public aquariums has been tremendous. The environment is an important national concern, and recent media coverage h a s elicited a strong response from university a n d high school students. Coral reefs, rain forests, bioremediation of toxic waste sites, and oil spills are frequently in the news, and students are familiar with these topics. Unfortunately, the media do not always convey chemical concepts accurately. The aquarium provides a hands-on approach to un-
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derstanding the chemically related events mentioned in the news. The marine environment was cho sen because it provides a complex aqueous system t h a t is interesting and visually exciting to students. The reef environment of the Grand Cayman Islands pictured above and on p. 886 A attests to the beauty and uniqueness of this ecosystem. Aquar iums are relatively inexpensive, can be obtained in a range of sizes and shapes, require little maintenance, and provide strong tangible evidence of chemistry’s role in the environment. The wet chemical and instrumental techniques presented in undergraduate teaching laboratories are easily applied to tracking the dynamic biological and chemical cycles in an aquarium. The idea is not limited to saltwater systems. Freshwater aquariums can provide the same h a n d s - o n approach; a r a i n forest aqueous system is just one topic that could be studied in conjunction with the use of freshwater tanks (11,12). Closed laboratory ecosystems can be maintained indefinitely; at the beginning of each quarter students can alter existing chemical and biological cycles or initiate new ones by applying experimental water treatment techniques. Examples include adding ozone, adding peroxide in combination with exposure to UV light, or adding adsorbates such as activated carbon to the tank. Flow patterns (strength and direction), as well as temperature and lighting, can also measurably affect the chemical cycles. The aquarium We are using a 300-gal marine tank that is 8 ft long, 2 ft wide, and 2.5 ft
high (Figure 1). Water is removed from the aquarium by a gravity feed system (i.e., a hole in the bottom of the tank) and returned to the aquarium through two inlet holes, also in the bottom of the tank, after cycling through the filtration unit. The tank is lit by four metal halide lights; each is controlled by a n individual timer set to simulate the sun's movement. Flow in the system is provided by two 2000 gal/h pumps at opposite sides of the tank. The pumps alternate between on and off every 60 s; providing a limited amount of "tidal" action for the fish. The aquarium includes fish from the Damsel family. If healthy when purchased, they have very long lifetimes in enclosed environments, are exceptionally tolerant to chemical changes, and are omnivorous, inexpensive, and make a n eye-catching display. They a r e also extremely plentiful in the ocean, and thus their collection has a minimum impact on the environment. The aquarium is housed in a small room with large glass windows that allow everyone to see it even when class is not in session. The aquarium and the display of current laboratory data have been of interest to students and visitors alike. The aquarium design is flexible, which allows different types of experiments to be conducted. It is important that students routinely have individual access to the ecosystem. At one end of the tank is a tap that students can use for easily removing samples without c o n t a m i n a t i n g them. At the other end of the tank are nine 1-in. bulkheads with ball valves. The valves enable students to incorporate additional flow patterns into the tank, pipe water to nearby locations for on-line experiments, and insert up to nine different ionselective electrodes, temperature probes, and other measuring devices. Laboratory curriculum The aquarium was used in the fall of 1992 by four laboratory sections containing 12 students each. I n each section, teams of three students rotated through the four different venues shown in the box. In many undergraduate laboratory formats, discussion about experiments among students is discouraged because of the need for individual grading. Isolating individuals is not done in real laboratories (51, and having students work together gives the lab more of a real - world feel. In the aquarium- based laboratory format, students are active members
of three different groups-the team of three, the laboratory section, and the entire class. Each team works in each venue for two consecutive weeks and then rotates to the next set of experiments. Team members work together to prepare standards and reagents needed for t h e analyses, and they work independently to perform t h e analyses using samples they personally remove from t h e aquarium. Students in each section are encouraged to discuss their findings from earlier laboratory periods and to provide guidance to others
who are completing experiments in a new chemical venue for t h e f i r s t time. As part of the entire class, the students are responsible for obtaining the best possible data to maintain the ecosystem and for charting the chemical trends as the ecosystem progresses through its natural cycle. The most important element of the laboratory is the feeling of discovery that students experience throughout the academic quarter. Because the aquarium ecosystem is dynamic, it is difficult to predict proper dilutions and calibration standards for many
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Figure 1. Photo and schematic of aquarium. ANALYTICAL CHEMISTRY, VOL. 65, NO. 20, OCTOBER 15, 1993
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REPORT of the assays. This results in a constantly changing laboratory manual. S t u d e n t s m u s t decide on correct standards and the appropriate dilutions. The composition of the synthetic sea salt used in the aquarium is not published, and thus the composition of elements in the aquarium water is not readily predictable. The instructor acts more as a consultant or mentor to the students than as an authority figure who holds secret the correct value for the weekly analysis. This learning experience can only be achieved when students have adequate laboratory time to conduct and repeat the experiments. Four major laboratory reports, handed in when the teams rotated to a new venue, were required for the academic quarter. The reports included an in-depth discussion of the biological system being analyzed as well a s detailed coverage of t h e chemical procedures and statistical treatment of the data. In addition to the laboratory reports, a final paper was required that summarized and analyzed the results obtained during the quarter. It included a discussion of procedures, with emphasis on why each step in the procedure was performed; a summary of the chemical and biological cycles relevant to the aquarium ecosystem; a detailed discussion of the class data, including the trends observed over the quarter and how each individual’s data fit into the trends; and suggestions for future experiments and tank modifications. Usually the initial laboratory session in t h e rotation did not go smoothly because students were not prepared for t h e different experi-
ments required in the 6 - h period. However, the next laboratory session in which the experiments were repeated went smoothly because each student had practiced and worked out problems with the procedures. During the second laboratory period students revealed a level of confidence not seen earlier, primarily because they had learned to manage their time and to work together as a group as well as independently. Students seemed t o enjoy t h e second session more and even had time to contemplate the reason for experimental steps and to modify the procedures if desired. I believe this is the response we need to obtain in all teaching laboratories. The venues
The experiments conducted in this course were derived from Standard Methods For the Examination of Water and Wastewater (13).This text concurrently describes classical and instrumental techniques for the determin a t i o n of inorganic a n d organic species. There are many more experiments and interrelated chemical cycles in addition to the ones in the laboratory venues. that could be investigated. The data presented in the next sections a r e derived from the fall 1992 academic quarter. Estimates for the error associated with the data in each chemical venue are difficult to ascertain and are not addressed. Beer’s law and the nitrogen cycle. The components of the nitrogen cycle include complex n i t r o g e n containing organic species, ammonia/ammonium ion, nitrite and nitrate ions, and nitrogen gas. Bacterial
colonies in the aquarium (Figure 2) are an integral part of the nitrogen cycle because they mediate this oxidative pathway (14).Bacteria colonize all surfaces in the aquarium, including the limestone rock and the plastic filter media. The nitrogen cycle is initiated when fish and food are introduced into the aquarium. Heterotrophic bacteria quickly become es tablished and decompose complex organic compounds to ammonia/ ammonium ion. Simultaneously, fish excrete ammonia a s a metabolic waste product. Ammonia is extremely toxic to marine animals and must be quickly eliminated from t h e aquarium. In marine aquariums, t h e ammonia/ ammonium ion equilibrium is criti cally important to the health of the livestock. Students discovered in one of their first homework problems that, a s t h e pH of t h e system i n creases, t h e ammonia/ammonium ion equilibrium shifts to produce increased levels of ammonia, exacerbating t h e problem. Temperature also affects the equilibrium, but to a much smaller extent. There are a number of ways to remove ammonia, such as heavily aerating the tank and establishing bacteria that oxidize ammonia to nitrite ion (Nitrosomonas) and then to nitrate ion (Nitrobacter). These bacteria can be added to the tank, or the small number of bacteria added when new fish are put in the tank can be encouraged to populate the aquarium filter. Although encouraging bacterial growth requires only t h a t the substrate have a large surface area, oxygen, and a constant flow of aquarium water (ammonia source), up to 12 weeks may be required to establish these colonies. Nitrite ion and ammonia are extremely toxic to marine organisms and must be kept a t very low levels (< 1ppm). Toxicity of the nitrate ion is organism - depend e n t a n d can extend over a wide range (15,16).In our system, nitrate ion levels slowly increase over time as there is no aerobic bacterial pathway by which this species can be eliminated. Nitrate ion may be removed by replacing the tank water, removing algae, or c r e a t i n g a n anaerobic chamber in which additional microbes reduce the ion to nitrogen gas. Recently, we used spectrophotometry to monitor the increase in ammonia with the standard Nessler assay. assay requires the use of HgI, sF The for color formation and thus could pose a waste disposal problem. Other 5 valid methods for ammonia determi-
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Figure 2. d r o g e n - mefabullring udcteria.
Figure 3. Trends in ammonia and nitrite ion concentrations. nation include using a commercially available ammonia- selective electrode or using a method based on a phenate reaction (13)of ammonia, phenol, and hypochlorite ion that is catalyzed by a manganese salt and can also be measured with a spectrophotometer. Flow injection analysis (FIA) can also be used (13).Nitrite and nitrate ions are monitored (nitrate is reduced to nitrite first) as a colored azo product of the anion. Nitrate ion may be reduced by using a column of copper sulfate - t r e a t e d cadmium granules or by using hydrazine. Titanium chloride may be used, but it reduces the nitrate ion one step further to ammonia. The data taken over the 12-week quarter are presented in Figure 3. As fish and food are slowly introduced into the “sterile” tank, ammonia levels begin to build. Nitrite ion levels increase gradually after food is intro duced because significant concentra tions of a”onia/ammonium ion are required to stimulate the colonization of the Nitrosomonas bacteria. The first dip in ammonia levels is caused by a 48-h period in which no food was added to the tank. This shows
t h a t a n association exists between ammonia levels and the metabolic activity of the heterotrophic bacteria and fish. The third peak is the result of a change in t h e flow pattern of aquarium water through the filter. By changing the flow, surfaces that have not been colonized extensively with bacteria are exposed. As a result, t h e ammonia levels increase dramatically. Eventually both t h e ammonia and nitrite ion levels fall to undetectable levels as both colonies of bacteria become established. The educational importance of this venue is t h a t it demonstrates complex dynamic chemical cycles and shows t h a t the cycles are mediated by bacteria. Microbial- and enzyme mediated chemical reactions are be coming increasingly important in modern synthesis and environmental cleanup efforts (17). The aquarium provides a n ideal focal point for discussing current topics in this field. In addition, a plot of fish death versus time (not shown) correlates well with t h e rise and fall of ammonia and nitrite ion levels in t h e tank. Thus the connection between nitrogen levels and fish stress is clearly made. Students are also introduced t o spectrophotometry, calibration curves and linear regression, pipet ting, and volumetric calculations. Electrochemistry and ecosystem stability. Potentiometric methods and redox titrations are used to monitor dissolved oxygen (DO) levels, salinity, and the buffer capacity of the aquarium. Salinity is a critical parameter in the closed ecosystem. Temperature changes, evaporation, a n d removal a n d replacement of samples of aquarium water affect salinity, which m u s t be monitored daily to avoid undue stress on the aquarium inhabitants. Salinity can be monitored by numerous methods, including conductivity, refractive index, and chemical analysis. In our
case, chloride ion concentration is determined by silver nitrate (argentometric) titration and differential plotting of potential changes measured a t a silver electrode. An empirical calculation relates chloride ion concentration to salinity (13). DO can be monitored electrochemically by a Clark electrode or by a n iodide/iodine - based redox titration. These methods are discussed in most instrumental and quantitative analysis texts. We have chosen the Winkler method and have used both amperometric (dead- stop) and visual (starch) indicators for end-point detection. DO is a component of t h e system with obvious importance to living organisms. DO levels are affected by temperature and salinity changes, and thus the health of all organisms is dependent on these interrelated aquarium characteristics. Tables describing the relationship among the three physical character istics can be found in Reference 13. As a r e s u l t of fish metabolism, acidic organic compounds in addition to ammonia a r e released into t h e aquarium water. Organic acids affect t h e carbonate buffer equilibrium that serves to stabilize the pH in the marine environment. As the buffer capacity of t h e system decreases, rapid changes in pH are possible and the health of the organisms in the system may be compromised. Alkalinity (buffer capacity) is monitored as CaCO, concentration with a glass/ reference electrode pair and titration with a strong acid. The electrochemical data from the 1992 quarter are presented i n F i g u r e 4. S t u d e n t s learn about redox chemistry, titrations, and potentiometry with glass and silver electrodes and see a demonstration of buffer capacity. What better way to supplement lecture discussions of buffer capacity than to study organisms that require a buffered environment for survival? Gravimetry and the sulfur cycle. Sulfur in the marine aquarium is present as sulfate ion (a major component of seawater) and H2S resulting from anaerobic bacterial activity. Gravimetry is used to monitor sulfate ion levels, which should fluctuate only with deviations in salinity. Gravimetric analysis is based on precipitation of BaSO, in acid solution after the addition of BaC1,. This e x p e r i m e n t is common i n m a n y quantitative analysis laboratories and is discussed in detail in many texts. H,S is a n unwanted component in the ecosystem because it is highly toxic to marine organisms and to nitrifying bacteria. The aquarium
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REPORT was maintained so that the possibility of anaerobic locations and H,S production were minimized. As a result H,S was not monitored. This section provides additional experi ence with analytical balances and pipetting and covers the topics of basic solubility and precipitation theory.
Titrimetry and reef structure. Coral reefs a r e composed of limestone deposits, which form when coral and other organisms fix calcium. Calcium ion is therefore a critical component in all coral reef environments. Magnesium ion is also present at part-per- thousand levels and has significance in many important biochemical pathways, such as photosynthesis. Calcium and magnesium ion levels within the aquarium are monitored by EDTA complexometric titration. These ions are also used to determine water hardness and are routinely measured in most freshwater analysis laboratories. Therefore this section of the laboratory is very important. Phosphate ion is monitored by spectrophotometry using a reaction involving ammonium molybdate, stannous chloride, and phosphorus. Phosphate ion analysis was con-
Figure 4. Trends in temperature, salinity, dissolved oxygen, and alkalinity. 888 A
ducted on tank samples before and after sulfuric and nitric acid hydrolysis. Both orthophosphates (dissolved phosphate) a n d t o t a l phosphate (which includes organically bound phosphorus) were determined. Phosphate ion is important to the coral reef environment and our closed ecosystem because it is one inorganic species t h a t promotes microalgal growth. Large amounts of algae are responsible for eutrophication i n freshwater systems and for smothering coral heads in marine environments. As food is introduced into the tank, phosphate ion levels increase; at about 1ppm phosphate ion, increases in the algal level are noticeable. Calcium and magnesium ion data from this venue are provided in Figure 5 . Only fluctuations in phosphate ion levels above that resulting from evaporation should be observed because there are no calcium -fixing organisms in the ecosystem. In this section students are provided with additional experience in titration, pipetting, and spectrophotometry. A review of pH -controlled solubility is inherent in the analysis of calcium and magnesium ions, and therefore students are provided with further continuity between lecture topics and the laboratory. The instrumental laboratory Although we concentrate primarily on analysis by classical a n d wet chemical techniques, the aquarium ecosystem provides unique opportunities to eliminate some of the inadequacies of many instrumental labor a t o r y curricula. To remove t h e “black box” concept of analytical instruments, many undergraduate laboratories have been developed to provide excellent rapid tutorial training on instrument functions. Because of limited time, however, unknown solutions are often prepared by teaching assistants (or obtained from the stock room) and given to students to analyze on the various instruments. I n other cases, commercial items (e.g., steel and vitamins) are provided for analysis. Although using these items is a step in the right direction, it does little to convey the scientific basis behind current instrument capabilities and the need for further development of new instrument systems. Because students have little interest in the samples traditionally used for teaching instrumental methods, the importance of these analytical techniques and their ability to rapidly provide excellent information are lost on many students. Unfortu-
ANALYTICAL CHEMISTRY, VOL. 65, NO. 20, OCTOBER 15,1993
Figure 5. Trends in calcium and magnesium ion concentrations.
nately, this impression can be longlasting. We are developing experiments that will demonstrate the true strength and practical importance of modern instrumentation, Some appropriate instrumental methods include ion chromatography, GC/MS, FIA, capillary electrophoresis, atomic absorption and emission techniques, LC, and voltammetry. Many possibilities also exist for simultaneous investigation of wet chemical and instrumental methods, which would provide continuity throughout the analytical curriculum. One example is the comparison of atomic absorption and emission techniques with EDTA titrations of inorganic species. Table I demonstrates the numerous possibilities for comparing detection limits and uncertainties. A wide range of organic compounds can also be found in the aquarium water and on the adsorbate material located in the filtration unit. These compounds-from simple organic components to vitamins, proteins, a n d peptides-provide many possibilities for conducting interesting investigations with sophisticated analytical instrumentation. Undergraduate research The aquarium provides a unique system by which undergraduates can conduct individual research projects. Students are using GC/MS to identify organic compounds removed from the aquarium water by activated carbon while other students use a number of different analytical techniques to examine metal accumulation in algae. The research they complete is publishable and of general interest to aquarium hobbyists and perhaps commercial fisheries. The aquarium has also been the basis for independent projects in other courses. In one instance, a textile student used the data taken during
elements in seawater :oncentral
water aquaria can greatly aid high school chemistry discussions and increase students’ interest. Mass and molar relationships can be related through the mixing of synthetic sea salt. This exercise drives home the point of producing a synthetic environment suitable for marine life forms from packaged chemical reagents. Acid-base titrations can be performed easily with samples taken from the aquarium. In many cases, spectrophotometric equipment is not available in high schools; however, this should not be a problem. All of the chemical measurements described above can be made from commercially available test strips or easy-to-use test kits. Preparation of simple colorimetric standards with detection by visual comparison provides acceptable analytical results at t h e high school level. Test kits for nitrogen determinations can cost as little as a few cents per measurement and oxygen analysis can be done for $1. A smaller t a n k used in conjunction with these test kits could be an effective way to introduce high school students to environmental chemistry. Setup for small aquariums can be less t h a n $100. The livestock could be given to t h e students for continued examination (or pleasure) at home at the end of each school year.
the fall 1992 quarter to complete a multivariate analysis project in a chemometrics course. We anticipate that many other situations will arise in which students will want to study the aquarium.
Summary A marine aquarium is a unique focal point for the training and education of undergraduate chemistry, biology, and engineering students. Basic wet chemical and instrumental techniques are easily incorporated into the laboratory curriculum to investigate and monitor the dynamic chemical and biological cycles within the aquarium. Best of all, student r e sponse to the laboratory and the analytical techniques has been positive. Whether their demonstrated enthusiasm will translate into an increase in the number of individuals interested in chemistry remains to be seen. At t h e very least, students leave the analytical curriculum with a n understanding of the importance of chemistry’s role in the environment and all biological systems.
The aquarium in high school chemistry The high school chemistry curriculum usually includes an introduction to the periodic table, acid-base and salt identification, conversion factors, and other basic general chemist r y principles. Marine and fresh-
Special thanks go to Robert Brag (laboratory coordinator and research scientist), Jerry 0’ Brien (building engineer), Jerry Cloninger and Don Woodward (glass shop), and Ken Williams (machine shop). I acknowledge members of my research group (Melinda Armstrong, Kevin Crawford, Beth DeBry, Beth Haywood, Diana Maniak, and Jeff Moore) for agreeing to this unusual teaching assignment. Financial sup-
port was provided by the School of Chemistry and Biochemistry. Jack Kent of Kent Marine, Marietta, GA, and Jorge Medina, Pisces Pets, Jonesboro, GA, also provided assistance.
References (1) Beck 11, C. M. Anal. Chem. 1991,63, 993 A-1003 A. (2) Kallmann, S.Anal. Chem. 1984,56, 1020 A- 1128 A. (3) Dulski, T.R.Anal. Chem. 1991,63, 65 R-86 R. (4)Richard, L. H.; Hawkes, S. J.; Spencer, J. N.; Bodner, G. M. J. Chem. Ed. 1992,69,175-86. ( 5 ) Walters, J. P. Anal. Chem. 1991,63, 977 A-985 A; 1077 A-1087 A; 1179 A1191 A. (6) The Technique, Jan. 15, 1993; Chicago Tribune, Feb. 14, 1993; The Record, Hackensack, NJ, March 1, 1993. ( 7 ) Johnson, K. S.; Coale, K. H.; Jannasch, H. W. Anal. Chem. 1992,64, 1065 A- 1074 A. (8) Adey, W. H.; Loveland, K. Dynamic Aquaria; Academic Press: San Diego, CA, 1991. (9) Feddern, H. A. Freshwater and Marine
Aquarium 1992,15,3.
(10) Blagoveshchensky, V.Aquarium Fish 1993,5, 66. 11) Goulding, M. Sci. Amer. 1993,266, 114-20. 12) Harris, T. M. J. Chem. Ed. 1993,4 , 340-41. 13) Standard Methods For the Examination of Water and Wastewater, 18th ed.; American Public Health Assn.: Washington, DC, 1993. 14) Brock, T. D.; Madigan, M. T. Biology of Microorganisms, 5th ed.; Prentice Hall: Englewood Cliffs, NJ, 1988. (15) Moe, M. A,, Jr. The Marine Aquarium Reference; Green Turtle Publications: Plantation, FL, 1992. (16) Spotte, S. Marine Aquarium Keeping; John Wiley and Sons: New York, 1973. (17) Zitomer, D. H.; Speece, R. E. Enuirun. Sci. Technol. 1993,2,227-44. (18) Handbook of Chemistry and Physics, 64th ed.; CRC Press: Boca Raton, FL, 1984.
Kenneth D.Hughes received his B.S.degree from Muhlenburg College (PA) in 1985 and his Ph.D. from Purdue University under the direction of Fred E. Lytle in 1989. After two years of postdoctoral studies at the University of Illinois-Urbana with Paul Bohn, he joined the faculty at the Georgia Institute of Technology. His research interests include the use of waveguide excitation for the investigation of molecular orientation in planar membrane models and analytical applications of luser-immobilization techniques in microbiology.
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