Class: BE-210
Group: R4
Members: Vesal Dini, Rebecca Lintner, Rupesh Patel, Mark Phong, Penelope Siraj
Date: April 30, 1997
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Abstract:
Currently 95% of all concentration analysis in the health sciences utilize spectrophotometry; this represents over three million determinations in the United States alone. Spectrophotometry is also utilized in air pollution and water pollution analysis to determine sulfur dioxide and phosphate concentrations, respectively. Thus the ability to accurately determine the concentrations of specific metallic and organic ions is important in numerous fields of science, research and medicine. In this experiment a comparison was made of two techniques of spectrophotometry: atomic absorption vs. flame photometry using potassium ions and sodium ions. The purpose of the comparison was to observe if one technique of testing would yield a more accurate and a reproducible calibration curve used for the determination of the concentration of the ions from the absorbance values given by the spectrophotometer.

In order to compare the data from both the absorption and the emission tests, plots of absorbance vs. concentration were made. The reproducibility of the data was tested by comparing the percent standard deviation that existed in the slopes of the graphs. For the absorption test the percent deviation in the slope for K+ was 5.06% and for Na+ it was 6.49%. The percent deviation in the slope of the graph for the emission test for K+ was 2.83% and for Na+ it was 3.19%. This is a significant difference in the percent deviation of the two methods, and thus it can be concluded that atomic emission spectroscopy produces more reproducible data. The accuracy of the testing methods was completed by calculating the concentration of an "unknown" using the calibration curve and comparing the results to the actual concentration. The average accuracy for K+ was: Absorption = 4.36% and Emission = 3.01%. The average accuracy of two trials for Na+ was: Absorption = 16.50% and Emission = 23.75%. The test for potassium shows that emission is more accurate then absorption. The sodium tests were inconclusive.

Atomic emission spectroscopy produced more precise, and thus, more reproducible data. The results from sodium testing led to no conclusion, while the potassium results showed that emission was, on average, more accurate.