dIW b y
WALTER A. WOLF Cobat. Unlv.nlty Hornllton, New York
The Investigation of the Purity and Stability of Nicotinamide and Flavin Coenzymes Phyllis R. Brown University of Rhode Island Kingston, Rhode Island 02881 As a laboratory assignment for an advanced analytical laboratory, we investigated the purity of commercial samples of nicotinamide and flavin nucleotides and the stability of these compounds on storage. These compounds are important in enzyme reactions and they are used in clinical laboratories for the measurement of many biological substances. Each student was assigned one of the following compounds: NAD, NADP, NADPH, NADH, FAD, and FMN. For mid semester, a research proposal including a literature search and planned procedures had to be submitted and approved. Instead of a final examination, a paper in the form acceptahle t o a good analytical journal was required. The students continued this project after the end of the semester and were able to obtain enough data to present three papers a t the Pittshurgh Conference on Analytical Chemistry and Applied Spectroscopy last March. They prepared their own abstracts, slides, and presentations. Further details are available from the author upon request.
Desk-Computer Fitting of a Two-Exponential Function V. MenBndez a n d A. U. Acufia Institute de Quhnica ~ k c "Rocasolano." a C.S.I.C Serrano, 1 1 9 , ~ a d r i d - 6Spain , In our Photophysics Laboratory it is often necessary t o check the exponential behavior of emission decays when more than one emitter could be presumed. A similar problem may be found studying first-order simultaneous chemical reactions. The usual procedure of plotting the logarithm of magnitude versus time has a limited discrimination capacity and its range of utility must be confined to cases where the two decay constants are widely different. This shortcoming can be overcome by means of numerical analysis using a modern desk calculator. A program to find the best, in the least-square sense, parameters for C; and hi to fit the experimental data to the function y=
1
Z
i=,
Ci exp (kit)
was developed. The procedure is that described by Hildebrand (I).I t has enabled us to detect double exponential behavior with decay constants differing by about 50%when data of 1% accuracy was used. The program is written in Basic to be run in a HewlettPackard 9830 calculator. I t is used routinely by our graduate students. Listing of the program along with instructions for use are available on request.
'Hildehrand, F. B., "Introduction to Numerical Analysis," McGraw Hill, New York, 1956,p. 378. 98 / Journal of ChemlcalEducation
An Interesting and Inexpensive Solubility Product Experiment for Introductory Chemistry Francis P. Gasparro WPIIPS~P) C0llPjiP WP~~PS ~P~, Masrnchusells 02181 The studv of the sulubilitv eauilibria of silver acetate is a popular and important introdu&ory laboratory experiment which illustrates the principles of solubility product, ion pairs, common ion effect, and ionic ~trength.'.~Given the high cost of silver compounds and current tight budgets, many instructors are likely to consider an alternate compound or abandon the experiment altogether. After an unsuccessful search for a suitable substitute which would demonstrate the principles mentioned above, we decided to redesien the exneriment as a class oroiect. In contrast to . Bell's procedure,' each student in our twelve lab sections prepared one of a series of eight saturated solutions of silver acetate in sodium acetate. A lab section worked a t one of four ionic stren~ths.therebv ensurina three inde~endent sets of data at each ionic strength. A Tinear ~ e a s t ' s ~ u a r e s analysis of the experimental data was used to calculate values for K,, and [AgOAc(aq)], the concentration of the ion pair, a t each ionic strength. As expected, K , was found to increase as the ionic strength increased, whde [AgOAc(aq)] remained constant.
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Averaee Class Results. 22°C Ionic Strength moles/l 2.0 1.0 0.25
KSP class 6.7 x 10W3
5.5 x 4.1 x
[AgOAc(aq)l
literature"oles/l' .
..
5.0 x 3.5 x
8.8 x 9.0 x 10-3 9.1 x
Cooies of a Basic oroeram used to oerform the calculations(suitab1e for &dent use), the laboratory instructions, and a c o m ~ l e t esummarv of results mav be obtained from the author:
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Bell. J. A,. "Chemical Princioles in Practice." Addison-Wesley. .. New York, 1967,p. 113. Ramette. R. W.. J. CHEM. EDUC.. 43.299 (1966). Caleul&d using solubility data ( 1 k j from ~eidell,A,, "Solubilities of Inorganic and Metal-Organic Compounds," Volume I, 4th ed. (1958). 'Literature value, 1.05 X 10W malesfl; MacDaugall, F. H., and Topol, L. E., J Phys. Chem., 56,1090 (1952). Editor's Note: This column is devoted to brief announcements of new ideas in chemical education. These consist of succinct statements of the key ideas of the authors along with possible infarmation on obtaining further material related to the subject upon request. Authors who wish to suhmit articles for consideration for publication should send the manuscripts (one double-spaced, typewritten page) and the supporting materials to Dr. Walter A. Wolf, Editor, Chem Ed Compacts, Department of Chemistry, Colgate University, Hamilton, New York 13346.
