AAS IntroAtomic Absorption Spectroscopy (AAS) is an analytical laboratory technique that converts the analyte of study into a gaseous state for quantitative determination of the chemical species using the Beer-Lambert Law1. AAS relies on the quantum principle that the ground state energy of an atom absorbs a discrete amount of electromagnetic radiation before it is excited to a higher state energy. This radiation is absorbed in the form of a wavelength with each element corresponding to its own wavelength, thus giving AAS a great degree of selectivity1. This is doneby exciting the free atoms via optical radiation using a special hollow-cathode lamp containing the element of interest, allowing for the precision required for the excitation wavelength2. Another advantage of using AAS is it’s easy use and relatively inexpensive cost when compared to other types of high precision spectroscopy. However, AAS also contains its disadvantages. Since AAS relies on the nebulization of the analyte, only solutions can be analyzed. In addition, AAS has less sensitivity than a graphite furnace which allows for analysis of smaller samples between 5-60 μL whereas AAS requires samples in the range of 1-3 mL2. AAS can only be used for quantitative analysis of an element, whereas atomic emission or atomic fluorescence are quantitative and qualitative instruments. The first step in analyzing a chemical’s atomic components is to atomize the sample1. Forthis lab, the sample was atomized via a high temperature flame that was generated via a mixture of compressed air and fuel, specifically an air-acetylene flame at a temperature of about 2,300 °C1. Once the liquid sample is decomposed into its atomic constituents, the hollow cathode lamp is shined and allowed to pass through a collimating lens at the sample’s corresponding absorptionwavelength. The absorption of light by the atomic components is then used to determine the sample’s concentration once it passes through a monochromator (wavelength selector). This isbecause the absorption of the light from the hollow-cathode lamp is linearly proportional to the sample concentration via the Beer-Lambert relationship shown in Figure A4 up to a range of ~0.1to ~0.8 units, another disadvantage of AAS as our least concentrated standard had an absorbance below 0.12. A general scheme for the setup and instrumentation is illustrated in Figure B below5.Figure A. Beer-Lambert Law visual representation of incident light and relationship to concentration4Figure B. Atomic Absorption Spectrometer Block Diagram5 For this experiment, we were interested in using the atomic absorption spectrometer in order to better understand the effectiveness of releasing agents towards overcoming matrix effects and chemical interferences. This will be done by first completing a routine AAS analysis on trace amounts of the metal calcium in millipore water containing diluted HCl. These resultswill then be compared with calcium solutions consisting of various added reagents that were suspended in a solution of either millipore water or diluted HCl. This should allow for the determination of the effects of additional metals and pH on measured absorbance values for calcium. Out of all of the reagents listed below in the methods section, we hypothesize that the samples containing PO43- and Al3+ will have the greatest matrix effects and will lead to a decreasein measured Ca2+ absorbance, with PO43- causing the most effect. In addition, we predict that samples containing the solvent HCl or the releasing agents Sr2+, LaCl3, or Na2EDTA will indicatea mitigation of any matrix effects induced by PO43- and Al on the Ca2+ metal. Methods A SOLAAR atomic absorption spectrometer was used in the experiment, to determine thechemical interference of different ions on calcium and unknown concentrations of calcium. For each solution atomized, the spectrometer took three samples, each were recorded. The average value was used to calculated the absorbance of the solution. All solutions were forced through a Millipore water filter before be atomized by the spectrometer. For part I & II, a series of 20 mL solutions with known calcium concentrations (0 ppm, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm) in Millipore water containing 2% 12M HCl were used to create to a calibration curve with an R2 value greater than .95. Calibration curves after the samples were taken for both parts in theexperiment; the second calibration was performed after the samples due to the sensitivity of the machine. In Part I, a calibration curve was used to determine the calcium concentrations of unknowns A, B and C. The unknown concentrations were calculated using Beer’s Law, c = A/(l*ε). In Part II, 10 20 mL solutions were created to determine the interference of variouschemicals, all solution contained a 30 ppm concentration of calcium. Again Beer’s Law was usedto calculate the unknown concentration of calcium in the solution2. Solution 1 –Millipore water (control)Solution 2 – +100 ppm Al in Millipore waterSolution 3 – +100 ppm Al in diluted HCl solution.Solution 4 – +500 ppm PO43- in Millipore waterSolution 5 – +100 ppm Al + 2000 ppm Sr in HCl solutionSolution 6 – +500 ppm PO43- + 2000 ppm Sr in Millipore waterSolution 7 – +100 ppm Al + 1% w/v Na2EDTA in HCl solutionSolution 8 – +500 ppm PO43- + 1% w/v Na2EDTA in Millipore waterSolution 9 – +100 ppm Al +.5% w/v LaCl3 in Millipore waterSolution 10 – +500 ppm PO43- +.5% w/v LaCl3 in Millipore waterResultsPart IGraph 1. Calibration Curve Part I. Calibration measurements from day 1, ε = the slope of the curve for Beer’s Law. ε = .0008688 (± 1.741E-5), R2 = .9866.Sample 1 Sample 2 Sample 3 Average Ca (ppm)Unknown A 0.00891 0.00748 0.00955 0.008647 9.952 (±.02)Unknown B 0.00460 0.00471 0.00482 0.004710 5.421 (±.02)Unknown C 0.00057 0.00053 0.00048 0.000527 0.6062 (±.02)Table 1. Calculated concentrations of Unknowns. The AAS samples of each solution, were used to calculate the unknown’s Ca concentration using the slope from the calibration curve as ε with a y-intercept of zero. concentration of A = .008647/ .0008688 = 9.952268 ppmPart IIGraph 2. Calibration Curve Part II. ε = .0069 (±1.349E-4) with an R2 of .989, calibration curve for part 2 using the standards described in the methods.Our calibration curve only contains nine data points instead of ten as we ran out of our 20ppm standard. Also, 30 ppm standard for the second calibration only has