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Absorption Atomic Spectroscopy Abstract: The purpose of this experiment was to detect and quantify the amount of chromium in a sample of fly ash. The absorbance and concentration (respectively) of the three standards of chromium concentration were first determined (1ppm: 0.020 0.003, 0.002%, 3ppm: 0.054 0.001, 0.007%, 5ppm: 0.071 0.002, 0.011%). Our unknown and blank were then measured (Unknown: 0.052 0.003, blank: 0.003 0.001). We then were able to graph absorbance versus concentration of our standards, and from our linear regression line we the used the formula to determine our concentration of chromium in fly ash (0.00701%) Introduction: The principle studied in this experiment was to show that nearly all metals on the periodic can be analyzed via atomic absorption spectroscopy. Also, this experiment set out to teach us how to determine what standards are appropriate to use for our unknown based on experimental research and data (found in the Perkin Elmer Standard Conditions manual). A monochromator was used because many optical characteristics of a material are dependent on color. In this particular experiment, the absorbance of the unknown is what indicated our concentration, which was dependent on the absorbance measured from the standards. Procedure: 1. Sample preparation: a. Starting with 4.5298 grams of fly ash in a flask, we added 50 mL of 1/1 nitric acid. b. The mixture was then heated, to a gentle boil for approximately 40 minutes. c. After heating, the mixture was cooled and filtered, and the filtrate was collected. The mixture was diluted to 100 mL in a flask. d. We also created a blank by added 50 mL of 1/1 nitric acid and diluted with 50 mL of deionized water. 2. Preparation of standards: a. Our chosen metal was chromium. After consulting with the manual, we made 3 standards consisting of 1ppm, 5ppm, and 10ppm. The chromium standard we used was 1000ppm: i. 100 mL x 10 ppm = X mL x 1000ppm = 1.0 mL chromium standard (eq. 1) ii. 100 mL x 5 ppm = X mL x 1000ppm = 0.5 mL chromium standard (eq. 2) iii. 100 mL x 1 ppm = X mL x 1000ppm = 0.1 mL chromium standard (eq. 3) b. Later after the experiment was run once, we found that our sample of fly ash mixture was somewhere between 1ppm and 5ppm, so we went back into the lab and created a 3ppm standard to test 100 i. mL x 3 ppm = X mL x 1000ppm = 0.3 mL chromium standard (eq. 4) 3. AA Analysis: a. After learning how to use the machine, we set our wavelength (357.9nm) and flow rate (fuel = 6, air = 5). The lamp current was 7.2 mAmps and slit width was 7 angstroms. b. We first aspirated with nitric acid, then deionized water, and then our standards, starting from 1ppm to 10ppm. Then we aspirated our sample and our blank, and recorded our absorbances. Trial 1 Trial 2 1ppm 0.018 0.022 3ppm 0.053 0.055 5ppm 0.069 0.072 10ppm 0.099 unknown 0.050 0.054 blank 0.002 0.004 Table 1 Results and Discussion: Avg 0.020 0.003 0.054 0.001 0.071 0.002 0.099 0.052 0.003 0.003 0.001 Sample calc to determine percent of chromium in fly ash (3mg Cr/L)(0.10L)= 0.3mg Cr (eq. 5) (0.0003g Cr/ 4.5298g Fly Ash) x 100 = 0.006% ~ 0.01% Standard Concentration 1ppm 0.002% 3ppm 0.007% 5ppm 0.011% Table 2 Graph of absorbance vs. concentration Absorbance 1ppm 3ppm 5ppm Table 3 Concentration 0.020 0.003 0.002% 0.054 0.001 0.007% 0.071 0.002 0.011% Absorbance v. Concentration y = 0.0017x - 2E-05 R2 = 0.9842 0.012% 0.010% Concentration 0.008% 0.006% 0.004% 0.002% 0.000% 0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 0.080 Absorbance Calculation to determine concentration of unknown: (eq. 6) y = 0.0017x 2E-05 y = 0.0017 (0.053) 2E-05 y = 0.0000701 0.0000701 x 100 = 0.00701% This result seems correct and accurate in that our measurement for 3ppm had an absorbance of 0.054 0.001 and a concentration of 0.007%. The absorbance and concentration of the three standards of chromium concentration were determined to be 1ppm: 0.020 0.003, 0.002%, 3ppm: 0.054 0.001, 0.007%, 5ppm: 0.071 0.002, 0.011%. Our unknown and blank were then measured to be: Unknown: 0.052 0.003, blank: 0.003 0.001. We then were able to graph absorbance versus concentration of our standards, and from our linear regression line we the used the formula to determine our concentration of chromium in fly ash (0.00701%). Our error in absorbance could possible be due to a multitude of things, including but not limited to, an inaccuracy in the machine, inaccuracy in standards (human error), inaccuracy in wavelength chosen, or the machine was not properly aspirated with nitric acid and water before each sample was aspirated.

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