Colorimetric Analysis for Salicylate in Urine: An Experiment for Nursing Chemistry In addition to lending itself to an experiment suitable for students with nontechnical majors,' the iron-salicylate system also provides a chemistry experiment suitable for students majoring in nursing. An adaptation of the method of Routh, e t aL2 for the analysis of salicylate in blood was used in the experiment herein described with excellent results. The students were provided with two stoek solutions. The first was a 1%solution of Fe(N03)39Hz0which also contained 5 ml of cone. HN08 per liter of solution. The second solution was a standard aqueous solution of sodium salicylate, which contained 10 mg salicylatelllMml(10 mg%).This solution was prepared by dissolving 0.116 gsodium salicylate in 11of distilled water. Each student was provided with four disposable 2.5-ml syringes and seven inexpensive euvets (A.H. Thomas Cat. No. 8493-R10). Each student was then able to prepare his own Beer-Lamhert plot. One milliliter of the iron nitrate solution was placed in each of five cuvets. The following amounts of salicylate solution were placed in the five successive cuvets: 0.5 ml, 1.0 ml, 1.5ml, 2.0 ml, and 2.5 ml. Distilled water was added to each cuvet to bring the total volume in each to 4.0 ml. A separate syringe was used with each stock salution and the distilled water. A sixth cuvet was filled with distilled water to provide a blank. The percent transmittance (%T)of each of the five standard solutions was read at 535 nm an a Spectronic 20, and then graphed versus the concentration of the solutions on semilog graph paper. The concentrations of the solutions were provided to the students. The students were then required to determine the unknown concentration of salicylate in a urine sample. The fourth syringe was used to measure this solution. 1ml of the iron nitrate solution, 1ml of water, and 2 ml of the sample to he analyzed were added by syringe to a seventh cuvet, and the %T was determined. The concentration of salicylate in the sample was then found by comparison to the standard graph. The "unknowns" weresalicylatesolutions varying in concentration from approximately 2.5 to 5.0 mg1100 ml after dilution. Martius yellow was added to simulate the color of urine. The concentrations and volumes sueeested eive readines in the ranre 15-70 %T. which is the most accurate and most readable portion of the transmittance scz; The lynnearity of the ~ e e r - ~ & h e rplots t was excellent, The laboratory can easily he completed in a two-hour laboratory period, including time for explanation of procedures. This experiment was very successful. The formation of the purple complex is dramatic and helps to make quantitative colorimetric analysis come alive. The clinical applications are also of interest to nursing students. The most successful aspect, however, was the use of syringes to measure and deliver the solutions. For many of the students, this was the first experience with theuse of syringes, and they thoroughly enjoyed it. It helped tomitigate theuseof semilog graph paper! The principal sources of error were failure to mix the solutions in the euvets and failure to remove air bubbles from the filled svrinees. In summary, this system is a practical and valuahle one to use as an example of colorimetric analysis, and its clinical and medical aspects are of special interest to nursing ~ t u d e n t s . ~ 'Hoops, S. C., J. CHEM. EDUC.,51,782(1974). ZRouth, J. I., Paul, W. D.,Arrendondo, E., and Dryer, R. L., Clin. Chem., 2,432(1956). 3Copies of student handouts for the experiment a;e available upon request to the authors Saint Mary's College N o r t r e Dame, Indiana 46556
34 1 Journal Of Chemical Education
Margaret A. Cavanaugh Mark A. Barnbenek
