Lab Report (atomic Absorption Spectroscopy) 1t2m1t
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Experiment 1 Title: Atomic Absorption Spectroscopy Introduction Atomic-absorption spectroscopy (AAS) is a technique used for analysis of major, minor, and trace elements in foodstuffs (Chemicool.com, 2016). A liquid sample containing the metal analyte is aspirated into an air-acetylene flame, causing evaporation of the solvent and vaporization of the free metal atoms (Chemicool.com, 2016). This process is called as atomization. The common emission source that emits radiation characteristic of a particular metal is a ‘hollow cathode lamp’. A monochromator is used to select the specific wavelength of light. In this experiment, flame atomization will be used to determine iron in the solution. Spectroscopic measurements are easily performed with liquid samples (Chemicool.com, 2016). Flame atomic absorption spectroscopy (FAAS) can only analyze ions or atoms in solution (Chemicool.com, 2016). Therefore, the preparation of sample either in a known or unknown sample should be done in solution form in order to allow FAAS to analyze the sample accurately and precisely (Chemicool.com, 2016). The objective of the experiment is to determine the amount of iron present in a given food sample. The known iron sample is prepare with different concentration from 2.5ppm to 10ppm, they are used to design the calibration such that the unknown sample concentration locates somewhere in the middle of set range. Materials and apparatus The materials used in the experiment were 100 ppm Fe standard, reagent-grade water, 2 % (v/v) nitric acid, unknown solid sample, 0.1 % (w/w) 1, 10-phenanthroline monohydrate, 10 % (w/w) hydroxylamine hydrochloride, 0.01 M, pH 4 acetate buffer and 50 % (w/w) sodium hydroxide (NaOH). The apparatus and instruments that used are hotplate, beakers, plastic tubes, 0.45μm filter paper, measuring cylinder, volumetric flask, watch glass, atomic absorption spectrometer, pestle and mortar, pipette.
Methodology A) Preparation of Unknown A solid unknown would be provided by the instructor. The sample was digested by dissolving approximately 0.1 g in 10 mL of nitric acid (conc.), to which 30 mL of hydrochloric acid (conc.) was added in a beaker. A graduated cylinder was used to deliver the correct acid volumes. These steps were done in the fume hood. The beaker was warmed on a hotplate with a watch glass on top. The reaction was watched carefully, the heat was turned down when the reaction became violent. There should be no solid at the bottom of the beaker once the digestion was completed. The mixture was let cool and then it was added slowly to a 100 mL volumetric flask containing approximately 30 mL of reagent-grade water. The beaker was rinsed with reagent-grade water several times to ensure that all materials were transferred. It was then diluted to the mark with reagent-grade water and mixed well. The unknown solution was transferred to a plastic bottle and saved. B) Investigation of Instrumental Parameters and Calibration Design First, 5 ppm iron standard was prepared. 5 mL of the provided 100 ppm iron standard was pipetted into a 100 mL volumetric flask and diluted to the mark with 2 % nitric acid. Second, test solution of unknown was prepared. 0.1 mL of the unknown solution prepared in Part A was pipetted into a 100 mL volumetric flask and diluted to the mark with 2 % nitric acid. Then, the absorbance of the two prepared solutions was recorded using 2 % nitric acid as the blank. C) Final Calibration Design The recommended linear range of response for atomic spectroscopic measurements of iron was 2.5 to 10 ppm. A set of four standards that span this range was designed with even concentration spacing. Aliquot volume of the 100 ppm iron standard was rounded to fit the available pipettes. The results from the 5 ppm iron standard were used to predict the absorbance range corresponding to 2.5 to 10 ppm iron. This information was used together
with the measured absorbance of the unknown solution based on a 10 mL aliquot volume that would produce an absorbance that you would predict to fall in the middle of the 2.5 to 10 ppm calibration range. Result Table 1.0 Absorbance data of 0.1g wheat flour Concentration of Standards Replicate 1 (ppm)
Absorbance Replicate 2
Replicate 3
Mean
Standard Deviation
Blank
0.001
-0.000
0.002
0.001
0.0011
2.5
0.095
0.093
0.089
0.092
0.0027
5.0
0.199
0.200
0.199
0.199
0.0004
7.5
0.277
0.280
0.279
0.279
0.0016
10.0
0.359
0.364
0.363
0.362
0.0027
Unknown Sample
0.058
0.023
0.015
0.032
0.0226
Table 1.1 (0.1g wheat flour) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Absorbance 0.001 0.092 0.199 0.279 0.362
Graph 1.0 The concentration versus absorbance of standard curve
Calculation y = absorbance, x = concentration, c = 0
Absorbance readings of sample:
y = mx + c
0.058, 0.023, 0.015
y = 0.0364x + 0
Mean absorbance of sample: 0.032
Intercept: 0.0
Standard deviation of sample: 0.0226
Slope: 0.0364 Correlation Coefficient: 0.9973 Concentration of sample:
M1V1 = M2V2
y = 0.0364x
M1 × 0.1ml = 0.8791ppm × 100ml
Absorbance, y = 0.032
M1 = 879.1ppm =879.1mg/kg =0.8791mg/g
0.032 = 0.0364x
∴ Every 1g of the sample contains 0.8791mg
x = 0.8791ppm
of iron.
Table 1.2 (0.5g wheat flour) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Calculation y = absorbance, x = concentration, c = 0
Absorbance 0.001 0.087 0.204 0.300 0.304
Absorbance readings of sample:
y = mx + c
0.006, 0.000, 0.001
y = 0.0328x + 0
Mean absorbance of sample: 0.003
Intercept : 0.0
Standard deviation of sample: 0.0031
Slope : 0.0328 Correlation Coefficient : 0.9442 Concentration of sample :
M1V1 = M2V2
y = 0.0328x
M1 × 0.1ml = 0.0914ppm × 100ml
Absorbance, y = 0.003
M1 = 91.4ppm = 91.4mg/kg = 0.0914mg/g
0.003 = 0.0328x
∴ Every 1g of the sample contains 0.0914mg of iron.
x = 0.0914ppm
Table 1.3 (Cream cracker) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Calculation y = absorbance, x = concentration, c = 0
Absorbance -0.000 0.096 0.189 0.265 0.359
Absorbance readings of sample:
y = mx + c
0.032, 0.029, 0.026
y = 0.0355x + 0
Mean absorbance of sample: 0.029
Intercept : 0.0
Standard deviation of sample: 0.003
Slope : 0.0355 Correlation Coefficient : 0.9986 Concentration of sample :
M1V1 = M2V2
y = 0.0355x
M1 × 0.1ml = 0.8169ppm × 100ml
Absorbance, y = 0.029
M1 = 816.9ppm =816.9mg/kg =0.8169mg/g
0.029 = 0.0355x
∴ Every 1g of the sample contains 0.8169mg
x = 0.8169ppm
of iron.
Table 1.4 (Coco powder) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Absorbance 0.001 0.107 0.214 0.301 0.362
Calculation y = absorbance, x = concentration, c = 0
Absorbance readings of sample:
y = mx + c
0.012, 0.013, 0.008
y = 0.0366x + 0
Mean absorbance of sample: 0.011
Intercept : 0.0
Standard deviation of sample: 0.0028
Slope : 0.0366 Correlation Coefficient : 0.9889
Concentration of sample :
M1V1 = M2V2
y = 0.0366x
M1 × 0.1ml = 0.301ppm × 100ml
Absorbance, y = 0.011
M1 = 301ppm = 301mg/kg = 0.301mg/g
0.011 = 0.0366x
∴ Every 1g of the sample contains 0.301mg of iron.
x = 0.301ppm
Table 1.5 (Milk powder)
Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Absorbance 0.001 0.101 0.205 0.296 0.380
Calculation y = absorbance, x = concentration, c = 0
Absorbance readings of sample:
y = mx + c
0.003, 0.004, 0.001
y = 0.0381x + 0
Mean absorbance of sample: 0.003
Intercept : 0.0
Standard deviation of sample: 0.0013
Slope : 0.0381 Correlation Coefficient : 0.9982 Concentration of sample :
M1V1 = M2V2
y = 0.0381x
M1 × 0.1ml = 0.341ppm × 100ml
Absorbance, y = 0.0013
M1 = 341ppm = 341mg/kg = 0.341mg/g
0.0013 = 0.0381x
∴ Every 1g of the sample contains 0.341mg of iron.
x = 0.0341ppm
Discussion Atomic Absorption Spectroscopy is a type of spectrometry that is used to determine the concentration of a specific element in a sample, using a combination of a known absorption spectra and measured absorbance to determine analyte concentration, using the Beer-Lambert Law to correlate absorption and concentration (Melville, 2014). This works because each element has characteristic absorption spectra, relating to the specific, quantized transitions of electrons to excited states (Melville, 2014). The Beer-Lambert law (or Beer's law) is the linear relationship between absorbance and concentration of an absorbing species (Hplc.chem.shu.edu, 2016). The Beer-Lambert law is necessary in order to compare its absorbance with that of the sample solution of unknown concentration. The relationship between the absorbance of a solution and the concentration of the absorbing species is known as Beer’s law, which written as A=abc. If absorption measurements are conducted by same spectrometer, the cells should have the same pathlengths (b), the absorptivity(a) and the cell thickness(b) (Food chemicals codex, 1981). The concentration of the sample solution is directly proportional to the absorbance of the sample solution. Based on the graph, the calibration curve is more accurate to the plotted data points. The graph had generated a regression of R² = 0.996932. The R2 value obtained was higher than the acceptable R2 value which is 0.9973. This mean that the regression of R² model has a good fit. The y-intercept of the trendline is near-zero. The trendline followed trivially from the Beer-Lambert Law, which stated that A = kbC. If C = 0, A must obviously also equal to 0 (Melville, J. 2014). Among all the sample products, wheat flour contained a highest concentration of iron in every 1g of the sample, which is 0.8791mg of iron per gram. The advantages of AAS is high sample throughput, easy to use and has a high precision. The concentration of sample is calculated by using the equation y = mx + c from the plotted graph. FAAS calculation had showed a slight higher value by comparing with two concentration of unknown sample.
Conclusion The objective of this experiment which is to determine the concentration of iron ions, Fe2+ in the iron pill achieved. The concentration of unknown iron sample is fall between the ranges of standard calibration from 2.5ppm to 10ppm. The trendlines produced is a direct correlation between concentration and absorption, hence it means that the linear fit is obey to Beer-Lambert law.The high values of the correlation coefficients (0.9973) obtained demonstrate good linear correlation of the absorbance with trace element concentrations. The higher the concentration of iron pill, the higher the absorbance. The absorbance of the unknown sample is 0.8791 mg/L. Every 1g of the sample contains 0.8791 mg of iron.
Reference 1. Hplc.chem.shu.edu.
(2016).
Beer-Lambert
Law.
[online]
Available
at:
http://hplc.chem.shu.edu/NEW/Undergrad/Molec_Spectr/Lambert.html [Accessed 8 July 2017]. 2. Food chemicals codex. (1981). Washington, D.C.: National Academy Press [Accessed 8 July 2017] 3. Chemicool.com. (2016). Definition of atomic_absorption_spectroscopy_aas - Chemistry Dictionary.
[online]
Available
at:
http://www.chemicool.com/definition/atomic_absorption_spectroscopy_aas.html [Accessed 8 July 2017]. 4. Melville, J. (2014). Atomic Absorption Spectroscopy of Metal Alloys. [online] California: UC
Berkeley
College
of
Chemistry.
Available
at:
https://www.ocf.berkeley.edu/~jmlvll/lab-reports/AASalloy/AASalloy.pdf [Accessed 8 July 2017].
Methodology A) Preparation of Unknown A solid unknown would be provided by the instructor. The sample was digested by dissolving approximately 0.1 g in 10 mL of nitric acid (conc.), to which 30 mL of hydrochloric acid (conc.) was added in a beaker. A graduated cylinder was used to deliver the correct acid volumes. These steps were done in the fume hood. The beaker was warmed on a hotplate with a watch glass on top. The reaction was watched carefully, the heat was turned down when the reaction became violent. There should be no solid at the bottom of the beaker once the digestion was completed. The mixture was let cool and then it was added slowly to a 100 mL volumetric flask containing approximately 30 mL of reagent-grade water. The beaker was rinsed with reagent-grade water several times to ensure that all materials were transferred. It was then diluted to the mark with reagent-grade water and mixed well. The unknown solution was transferred to a plastic bottle and saved. B) Investigation of Instrumental Parameters and Calibration Design First, 5 ppm iron standard was prepared. 5 mL of the provided 100 ppm iron standard was pipetted into a 100 mL volumetric flask and diluted to the mark with 2 % nitric acid. Second, test solution of unknown was prepared. 0.1 mL of the unknown solution prepared in Part A was pipetted into a 100 mL volumetric flask and diluted to the mark with 2 % nitric acid. Then, the absorbance of the two prepared solutions was recorded using 2 % nitric acid as the blank. C) Final Calibration Design The recommended linear range of response for atomic spectroscopic measurements of iron was 2.5 to 10 ppm. A set of four standards that span this range was designed with even concentration spacing. Aliquot volume of the 100 ppm iron standard was rounded to fit the available pipettes. The results from the 5 ppm iron standard were used to predict the absorbance range corresponding to 2.5 to 10 ppm iron. This information was used together
with the measured absorbance of the unknown solution based on a 10 mL aliquot volume that would produce an absorbance that you would predict to fall in the middle of the 2.5 to 10 ppm calibration range. Result Table 1.0 Absorbance data of 0.1g wheat flour Concentration of Standards Replicate 1 (ppm)
Absorbance Replicate 2
Replicate 3
Mean
Standard Deviation
Blank
0.001
-0.000
0.002
0.001
0.0011
2.5
0.095
0.093
0.089
0.092
0.0027
5.0
0.199
0.200
0.199
0.199
0.0004
7.5
0.277
0.280
0.279
0.279
0.0016
10.0
0.359
0.364
0.363
0.362
0.0027
Unknown Sample
0.058
0.023
0.015
0.032
0.0226
Table 1.1 (0.1g wheat flour) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Absorbance 0.001 0.092 0.199 0.279 0.362
Graph 1.0 The concentration versus absorbance of standard curve
Calculation y = absorbance, x = concentration, c = 0
Absorbance readings of sample:
y = mx + c
0.058, 0.023, 0.015
y = 0.0364x + 0
Mean absorbance of sample: 0.032
Intercept: 0.0
Standard deviation of sample: 0.0226
Slope: 0.0364 Correlation Coefficient: 0.9973 Concentration of sample:
M1V1 = M2V2
y = 0.0364x
M1 × 0.1ml = 0.8791ppm × 100ml
Absorbance, y = 0.032
M1 = 879.1ppm =879.1mg/kg =0.8791mg/g
0.032 = 0.0364x
∴ Every 1g of the sample contains 0.8791mg
x = 0.8791ppm
of iron.
Table 1.2 (0.5g wheat flour) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Calculation y = absorbance, x = concentration, c = 0
Absorbance 0.001 0.087 0.204 0.300 0.304
Absorbance readings of sample:
y = mx + c
0.006, 0.000, 0.001
y = 0.0328x + 0
Mean absorbance of sample: 0.003
Intercept : 0.0
Standard deviation of sample: 0.0031
Slope : 0.0328 Correlation Coefficient : 0.9442 Concentration of sample :
M1V1 = M2V2
y = 0.0328x
M1 × 0.1ml = 0.0914ppm × 100ml
Absorbance, y = 0.003
M1 = 91.4ppm = 91.4mg/kg = 0.0914mg/g
0.003 = 0.0328x
∴ Every 1g of the sample contains 0.0914mg of iron.
x = 0.0914ppm
Table 1.3 (Cream cracker) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Calculation y = absorbance, x = concentration, c = 0
Absorbance -0.000 0.096 0.189 0.265 0.359
Absorbance readings of sample:
y = mx + c
0.032, 0.029, 0.026
y = 0.0355x + 0
Mean absorbance of sample: 0.029
Intercept : 0.0
Standard deviation of sample: 0.003
Slope : 0.0355 Correlation Coefficient : 0.9986 Concentration of sample :
M1V1 = M2V2
y = 0.0355x
M1 × 0.1ml = 0.8169ppm × 100ml
Absorbance, y = 0.029
M1 = 816.9ppm =816.9mg/kg =0.8169mg/g
0.029 = 0.0355x
∴ Every 1g of the sample contains 0.8169mg
x = 0.8169ppm
of iron.
Table 1.4 (Coco powder) Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Absorbance 0.001 0.107 0.214 0.301 0.362
Calculation y = absorbance, x = concentration, c = 0
Absorbance readings of sample:
y = mx + c
0.012, 0.013, 0.008
y = 0.0366x + 0
Mean absorbance of sample: 0.011
Intercept : 0.0
Standard deviation of sample: 0.0028
Slope : 0.0366 Correlation Coefficient : 0.9889
Concentration of sample :
M1V1 = M2V2
y = 0.0366x
M1 × 0.1ml = 0.301ppm × 100ml
Absorbance, y = 0.011
M1 = 301ppm = 301mg/kg = 0.301mg/g
0.011 = 0.0366x
∴ Every 1g of the sample contains 0.301mg of iron.
x = 0.301ppm
Table 1.5 (Milk powder)
Standard Blank 1 2 3 4
Concentration (mg/L) 0.0 2.5 5.0 7.5 10.0
Absorbance 0.001 0.101 0.205 0.296 0.380
Calculation y = absorbance, x = concentration, c = 0
Absorbance readings of sample:
y = mx + c
0.003, 0.004, 0.001
y = 0.0381x + 0
Mean absorbance of sample: 0.003
Intercept : 0.0
Standard deviation of sample: 0.0013
Slope : 0.0381 Correlation Coefficient : 0.9982 Concentration of sample :
M1V1 = M2V2
y = 0.0381x
M1 × 0.1ml = 0.341ppm × 100ml
Absorbance, y = 0.0013
M1 = 341ppm = 341mg/kg = 0.341mg/g
0.0013 = 0.0381x
∴ Every 1g of the sample contains 0.341mg of iron.
x = 0.0341ppm
Discussion Atomic Absorption Spectroscopy is a type of spectrometry that is used to determine the concentration of a specific element in a sample, using a combination of a known absorption spectra and measured absorbance to determine analyte concentration, using the Beer-Lambert Law to correlate absorption and concentration (Melville, 2014). This works because each element has characteristic absorption spectra, relating to the specific, quantized transitions of electrons to excited states (Melville, 2014). The Beer-Lambert law (or Beer's law) is the linear relationship between absorbance and concentration of an absorbing species (Hplc.chem.shu.edu, 2016). The Beer-Lambert law is necessary in order to compare its absorbance with that of the sample solution of unknown concentration. The relationship between the absorbance of a solution and the concentration of the absorbing species is known as Beer’s law, which written as A=abc. If absorption measurements are conducted by same spectrometer, the cells should have the same pathlengths (b), the absorptivity(a) and the cell thickness(b) (Food chemicals codex, 1981). The concentration of the sample solution is directly proportional to the absorbance of the sample solution. Based on the graph, the calibration curve is more accurate to the plotted data points. The graph had generated a regression of R² = 0.996932. The R2 value obtained was higher than the acceptable R2 value which is 0.9973. This mean that the regression of R² model has a good fit. The y-intercept of the trendline is near-zero. The trendline followed trivially from the Beer-Lambert Law, which stated that A = kbC. If C = 0, A must obviously also equal to 0 (Melville, J. 2014). Among all the sample products, wheat flour contained a highest concentration of iron in every 1g of the sample, which is 0.8791mg of iron per gram. The advantages of AAS is high sample throughput, easy to use and has a high precision. The concentration of sample is calculated by using the equation y = mx + c from the plotted graph. FAAS calculation had showed a slight higher value by comparing with two concentration of unknown sample.
Conclusion The objective of this experiment which is to determine the concentration of iron ions, Fe2+ in the iron pill achieved. The concentration of unknown iron sample is fall between the ranges of standard calibration from 2.5ppm to 10ppm. The trendlines produced is a direct correlation between concentration and absorption, hence it means that the linear fit is obey to Beer-Lambert law.The high values of the correlation coefficients (0.9973) obtained demonstrate good linear correlation of the absorbance with trace element concentrations. The higher the concentration of iron pill, the higher the absorbance. The absorbance of the unknown sample is 0.8791 mg/L. Every 1g of the sample contains 0.8791 mg of iron.
Reference 1. Hplc.chem.shu.edu.
(2016).
Beer-Lambert
Law.
[online]
Available
at:
http://hplc.chem.shu.edu/NEW/Undergrad/Molec_Spectr/Lambert.html [Accessed 8 July 2017]. 2. Food chemicals codex. (1981). Washington, D.C.: National Academy Press [Accessed 8 July 2017] 3. Chemicool.com. (2016). Definition of atomic_absorption_spectroscopy_aas - Chemistry Dictionary.
[online]
Available
at:
http://www.chemicool.com/definition/atomic_absorption_spectroscopy_aas.html [Accessed 8 July 2017]. 4. Melville, J. (2014). Atomic Absorption Spectroscopy of Metal Alloys. [online] California: UC
Berkeley
College
of
Chemistry.
Available
at:
https://www.ocf.berkeley.edu/~jmlvll/lab-reports/AASalloy/AASalloy.pdf [Accessed 8 July 2017].
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