Gas chromatography has been used to monitor the rapid photodegradation which dilute solutions of Fe(III)-nitrilotriacetate undergo when exposed to sunlight. Iminodiacetate is produced in essentially stoichiometric amounts and is only very slowly photodegraded to glycine under the same conditions. The resulting accumulation of iminodiacetate in natural water systems with continuing input of nitrilotriacetate, which these observations suggest, is of environmental concern because of the possible carcinogenic activity of Nnitroso iminodiacetic acid.

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11. of sample to 25 ml by the CoAPDC method provides a net concentration factor of 40. By adjustment of sample volume and the nitric acid solution volume, concentration factors as high as 400 can be obtained. ACKNOWLEDGMENTThe authors thank J. M. Edmond of Massachusetts Institute of Technology and Michael Orren of Woods Hole Oceanographic Institute for the discussion of their experimental results prior to publication. We appreciate the critical review of the manuscript by G. W. Fuhs of the New York State Department of Health. We gratefully acknowledge the technical assistance of C. P. Snyder and Kaiwen Wang in performing anodic stripping voltammetry.LITERATURE CITED

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Students are introduced to screening and sequential experimentation using simulations and experimentation. The work begins with spreadsheet simulations and practice with the experimental design software. Students learn how to use the graphical output, normal quantile plots, to recognize the specific factors that affect the result of an experiment. In the laboratory, students make a preliminary investigation of the effect of six variables (flame observation height, flame stoichiometry, acetic acid, lamp current, wavelength, and slit width) on the atomic absorption signal for silver. This requires only sixteen experiments. Two or three active variables and an interaction of two variables are typically observed. Following this 26-2 fractional factorial design experiment, students investigate the effect of two active variables in more detail. This typically requires 16 to 25 experiments. The complexity of the system becomes apparent when flame observation height and percentage of acetic acid are studied. Most, but not all, of the observations are consistent with descriptive material that would be found in a typical instrumental methods text.