Experiment 5: Pre-Lab Talk

Sample Analysis Using Atomic Absorption Spectroscopy (AAS) 1Pre-Lab TalkThompson Rivers University

BC ILN112

OutlineAnalysis of Iron by Atomic Absorption Spectroscopy (AAS) What we want you to learn from this experimentLab IntroductionStandard and Sample PreparationDilution of the Fe Unknown Submitting Your Samples to the BC-ILNUsing the Atomic Absorption SpectrophotometerTreatment of Data & Results

BC ILN23

Analysis of Iron by AASWhat we want you to learn from this experiment:The general principles of Atomic Absorption Spectroscopy (AAS) as an analytical technique Prepare a sample for quantitative analysisIdentify the main parts of the flame AAS and understand their purpose Explain why the lamp wavelength is set at 372 nm Determine whether or not a particular element is present in a solution through the presence or absence of a signal from an atomic absorption transitionContinued

BC ILN34

Analysis of Iron by AASWhat we want you to learn from this experiment:Prepare standard solutions containing known amounts of an element using a Mohr pipet and volumetric flasksUse experimental data to construct a calibration curve, perform dilution calculations, and calculate the amount of an unknown element in a sample Assess experimental results to determine accuracy and suggest reasons for any discrepancy or experimental error

BC ILN45

AAS TheoryAAS is an instrumental method of quantitative and qualitative analysis Uses an Atomic Absorption Spectrophotometer Uses the characteristic absorption spectrum associated with each element, such as iron Identifies elements present in a wide variety of substances, such as a commercially available multivitamin which contains a wide variety of chemical species including minerals considered to be beneficial to human health

Lab Introduction

BC ILN56

AAS Block Diagram

Lab Introduction BC ILN6SampleAAS requires an aqueous sample of adequate volume to ensure there will be enough to perform several runsManualThe samples can also be ran manually by inserting the aspirator tube directly into the sample by the operator Auto-SamplerComputer operated and programmed to run specific samples, loaded in auto-sampler tubes placed into the auto-sampler racks, in a specific order

7

Lab IntroductionTheoryDuring AAS analysis, an aqueous sample is sprayed into a flame which supplies the energy to dissociate a sample into ground state atomsThis is known as Sample Atomization

BC ILN7Atomic Absorption Spectroscopy8

Lab Introduction BC ILN8

9

Lab IntroductionTheory

The absorbance of the sample is directly proportional to the concentration of analyte atoms in the sample

BC ILN9Preparation of Unknown Fe (Multivitamin) SolutionObtain a multivitamin tablet and record the brand name and mass of iron per tabletPlace the tablet in a 150 mL beaker and add 20 mL of 6.0 M hydrochloric acid (HCl)Swirl gently and let stand while preparing the standardsTo be continued

10

BC ILN10Fe Standard SolutionsUse five 100 mL volumetric flasks and a Mohr pipet to prepare a series of solutions containing approx. 1, 2, 3, 4 and 5 mL of 500 mg/L calibrating stock solutionRead and record the actual volume used accurately to two decimal places in your data bookFill each flask to the mark with deionized waterInvert the flask several times to ensure thorough mixing

Preparation of Standards 11

BC ILN11Fe (Multivitamin) Solution Continued from beforeHeat the 150 mL beaker on a hotplate in the fumehood, swirling periodically and note observationsPrepare a fluted filter paper and gravity filtration apparatusGravity filter the solution into a 100 mL volumetric flaskRinse and fill to the mark with deionized water

Preparation of Unknown 12

BC ILN12DilutionObtain 40 mL of the prepared unknown Fe solutionUse a 25 mL volumetric pipet to dilute exactly 25.00 mL of unknown Fe solution into a 100 mL volumetric flaskFill to the mark with deionized water

Dilution of Fe Solution13

BC ILN13Prepare your labeled autosampler tubes for submission to the BC-ILN Your instructor will supply you with autosampler tubes with caps and a rack to put them in for submissionLabel the tubes and organized them in the rack providedSubmitting Your Samples14

3 cm

BC ILN14During your scheduled instrument timeGo to your computer station get connected to the BC-ILN Ask your instructor to show you how to operate the Atomic Absorption SpectrophotometerRunning Your Samples15

BC ILN15Running Your Samples16

BC ILN1617

Treatment of DataGraphing the Results Figure 2. Calibration Curve for Iron prepared using a Varian AAS model 55B

Label Axis with UnitsTitle Calibration CurveLabel Unknown Values

BC ILN17

Data-Book

18

Presentation of ResultsPage No.DateExperimentTitleBrand InformationObservationsNeat TablesStock Solution

BC ILN18