c127.1 Expt 6 & 11 Report
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Transcript of c127.1 Expt 6 & 11 Report
Experiment No.6Atomic Absorption Spectroscopy (AAS)
CHEM 127.1 - MADDuro, Marlon
Espiritu, KevinSotelo, Tiffany
INTRODUCTION
Basics
• One of the most common methods used for analyzing metals in a sample
• Uses absorption of emitted light from free atoms
• Used for qualitative and quantitative analysis– Requires standards of known concentration
for quantitative analysis
Basics
• Involves atomization at very high temperatures
• The light emitted from sample give a line spectrum– AAS detects the emission from first half of
excitation process (during absorption and before transition to excited state)
Notes
• Very selective – elements have different sets of energy levels
• Follows Beer-Lambert law– Limited by quality of monochromator– Bandwidth of absorbing species must be
broader than light source– Fixed by narrowing radiation sources
Basic Parts
1. Lamp2. Atomizer3. Nebulizer4. Monochromator5. Photomultiplier tube (PMT)
Lamp
• Hollow Cathode Lamp (HCL)– Most common lamps– Provides constant yet intense light line for
element of interest– Cathode is made of same element analyzed
and contains low pressure inert gas– Light from HCL goes through glass
transparent to UV-Vis region– Generates very narrow spectral lines
Lamp
Lamp
• Electrodeless Discharge Lamp (EDL)– Contains small amount of analyte in form of
salt/metal– Narrower spectral lines
• Deuterium (D2)– Used for background correction– Limited wavelength range (190-320nm)
• Continuum sources
Atomizers
• Flame• Destroys analyte ions and complexes• Involves the following processes:
– Desolvation, vaporization, atomization, ionization
• Creates elemental form of element of interest
• Used for liquid or dissolved samples
Flame Atomizer
Nebulizer
• Controls flow rate of sample• Mixes fuel and oxidant – pressure
generated sucks sample through tube– Fuel is usually acetylene
• Creates an aerosol of the sample• aerosol + fuel + oxidant
– heterogeneous mixture that goes to the burner– Leftover sample goes to glass waste container
Monochromator
• Filters specific bands for the element of interest for entry to the PMT
• The line from the light source (usually HCL) is isolated
• Allows light not absorbed by sample to pass through
Photomultiplier Tube
• The light is detected by the PMT• PMT readings comes from presence of
analyte in flame• The elemental form of the analyte absorbs
light and the corresponding decrease in the PMT reading is transformed into analytical data
Apparatus
Procedure• Fit the specific light source lamp to the lamp housing,
and switch on the instrument.• Light the source lamp, adjust the wavelength dial of the
spectroscope to the wavelength of the analytical line specified, and set at an appropriate current value and slit-width.
• Using the supporting gas and combustible gas specified, ignite the mixture of these gases, adjust the gas flow rate and pressure, and make the zero adjustment after nebulizing the solvent into the flame.
• Nebulize the test solution or the standard solution or control solution prepared by the method prescribed elsewhere, and measure the absorbance.
Analysis
• Calibration curve Method– Preparation of a standard curve, followed by
measurement of the adsorbance of the unknown.• Standard Addition method
– To equal volumes of more than 2 of different test solutions, add the standard solution so that the stepwise increasing amounts of the object element are contained in the solutions, and add the solvent to make a definite volume.
Standard Addition Method
• Beer-Lambert Law: A = kC• Unknown: A0 = kCx
• Unknown + standard:
T
ss
T
xx
VVC
VVC
kA
Standard Addition Method• Dividing A by A0:
• Working Equation:
Tx
ssxx
0 VCVCVC
AA
sx
ssxx
s
T
0 CCVCVC
CV
AA
sxs
x
s
T
0V
C1
CV
CV
AAy
DETERMINATION OF TRACE LEVELS OF COPPER AND LEAD IN VEGETABLE SAMPLES USING THE ATOMIC ABSORPTION SPECTROPHOTOMETER
Experiment:
Copper (Cu)
• A micronutrient needed for the absorption and transport of iron in the blood stream.
• RDA: 900 μg / day• Main sources are shellfish, beans and
mushrooms.• Also found in vegetables in trace amounts.
Experimental
• Preparation of stock solutions– 0.5 g of Cu(s) dissolved in 1:1 nitric acid– Diluted to 250 mL in a vol. flask– Take 5 mL aliquot and dilute to 100 mL– Stock solution: 100 ppm Cu
Experimental
• Preparation of standard solutions– 5 100-mL vol. flasks (1-5)– 0.50,1.25, 2.50, 5.00 mL of the stock solution
added to flasks 1-4– Flask 5 is reagent blank.
Experimental
• Preparation of sample– From 1 kg of vegetables, dried for two weeks– 2 g of dried leaves used.– Digested in conc. HNO3 for 20 min– 10 mL d. H2O added and filtered while
washing out the filter paper into 50-mL vol. flask
Experimental
• Analysis of vegetable sample– Absorbance of standardd sol’n and each
sample recorded using the AAS using the setting for Cu.
– Solution was diluted 1:5 if absorbance is too high.
– Three trials performed
Experimental
• Standard addition– 10 mL digested solution in 5 50-mL vol. flasks– 0.00, 1.00, 2.50, 5.00, 10.00 ppm of added
standards then diluted to the mark.– Absorbance of each solution measured.– Plot of A/Ao versus Vs made.
Calibration Curve
Standardppm Cu
A A'
blank 0.0 0.0123 0.0000
1 1.0 0.1937 0.1814
2 2.5 0.3685 0.3562
3 5.0 0.6789 0.6666
4* 10.0 1.1751 1.1628
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50
0.1
0.2
0.3
0.4
0.5
0.6
0.7
R² = 0.994078942520581
ppm Cu
A'
Analysis of Vegetables
Sample A A'ppm Cu
sol’n sample
1 0.0498 0.0375 0.09945 2.486
2 0.0475 0.0352 0.08177 2.044
3 0.0475 0.0352 0.08177 2.044
Average 0.08767 2.192
Sample A A'ppm Cu
sol’n sample
1 0.1219 0.1096 0.6536 16.34
2 0.1278 0.1155 0.6989 17.47
3 0.1134 0.1011 0.5883 14.71
Average 0.6469 16.17
kangkong
kamote tops
0.1301130.02456 - 0.0375
g 2.00
mL 50.0ppm 0.09945
Sample computations:
A’ = 0.0375Vs = 50.0 mLwsample = 2.00 g
Solution: ppm Cu =
= 0.099449 ppm Cu
Sample:
ppm Cu =
= 2.486 ppm Cu
Standard Addition
SolutionSample 1 Sample 2 Sample 3
Vs (mL) A y A y A y
1 0.00 0.0119 0.5000 0.0127 0.5000 0.0133 0.5000
2 0.50 0.1619 6.803 0.1632 6.425 0.1612 6.060
3 1.25 0.3350 14.08 0.3311 13.04 0.3282 12.34
4 2.50 0.6165 25.90 0.6147 24.20 0.6148 23.11
5 5.00 1.0865 45.65 1.0820 42.60 1.0820 40.68
slope 8.908 8.307 7.940
y-int 2.106 1.984 1.848
r 0.997 0.997 0.998
ppm CuSolution 0.1123 0.1204 0.1259
Sample 14.03 15.05 15.74
kangkong
Standard Addition
SolutionSample 1 Sample 2 Sample 3
Vs (mL) A y A y A y
1 0.00 0.0272 0.5000 0.0261 0.5000 0.0276 0.50002 0.50 0.1696 3.118 0.1679 3.216 0.1733 3.1393 1.25 0.3308 6.081 0.3315 6.3506 0.3317 6.0094 2.50 0.6200 11.40 0.6191 11.86 0.6202 11.265 5.00 1.1073 20.35 1.1078 21.22 1.1088 20.09
slope 3.934 4.105 3.875
y-int 1.013 1.035 1.025
r 0.999 0.999 0.999
ppm CuSolution 0.2542 0.2436 0.2581
Sample 31.78 30.45 32.26
kamote tops
Standard AdditionSample computations:Slope = 8.908 ppm-1
Solution: Cx = 1/(8.908 ppm-1) = 0.1123 ppm
Sample: ppm Cu =
2.00g50.0mL
10.0mL50.0mL0.1123ppm
=14.03 ppm Cu
Average ppm Cu in kangkong: 14.94 ppm (1.494 mg per 100 g)Average ppm Cu in kamote tops: 31.49 ppm (3.149 mg per 100 g)
Experiment No.11Nuclear Magnetic Resonance (NMR)
Spectroscopy
CHEM 127.1 - MADGroups 5 and 6
INSTRUMENTATION
Wide-Line NMR
• Wide-line NMR1. Electromagnet2. Oscillator3. Modulation and lock-in detection4. Signal acquisition
Pulse NMR
1. Programmable Pulse Generator2. Transmitter3. Probe circuit4. Reciever
NMR Spectrometer
NMR Spectrophotometer
Video Clip
Sample Quality Affects Spectra
• Low NMR sample quality increases every peak’s width, making it hard to resolve small couplings and frequency differences.
Factors Affecting Sample Quality
• NMR spectra are strongly affected by both the sample contents and the NMR tube. These factors include:
Boundaries Between Materials Cause Problems
• We shim to make the field more uniform across the sample, but sample factors can limit shimming’s effectiveness.
• Every material gets magnetized in a magnetic field, and the strength of its response is its magnetic susceptibility (χ). To ensure field uniformity, one must minimize such interfaces.
Sample Height
• Sample should at least exceed the detection region.
• “Three fingers” rule
• Solid particles must be absent in the sample.
NMR Tube Straightness (Camber) and Concentricity
• A tube is held at the top, but the sample must be aligned precisely in the center of the probe for maximum performance.
• The centers of the inner and outer surfaces of the tube may not coincide well.
• Poor positioning of the sample in the coil and nonuniformity of the glass wall thickness create shimming problems.
NMR Tube Cleaning
• Rinse 1x with sample’s solvent• Rinse 5-10x with non- chlorinated solvent, e.g.
acteone &/or H2O• Rinse 1x with D2O• Store inverted on a lab wipe• Dry with stream of N2• If absolutely necessary, dry flat in oven ≤ 125
°C, ≤ 45 min• NEVER STORE IN AN OVEN!
Processing of NMR
RESULTS
Compound 1
Compound 1
Methyl 4-(2-hydroxyethyl)benzenesulfonate (1). C9H12O4S, 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 2.42 (s, 3 H) 2.58 (br. s, 1 H) 3.77 (t, J=4.76 Hz, 2 H) 4.09 (t, J=4.40 Hz, 15 H) 7.33 (d, J=8.06 Hz, 15 H) 7.77 (d, J=8.43 Hz, 15 H).
S
O
O
OCH3
OH
Compound 2
Compound 2
Biphenyl-4,4'-diyldimethanediyl dimethanesulfonate (2). C16H18O6S2, 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 2.45 (s, 6 H) 4.17 (s, 4 H) 7.33 (d, J=7.69 Hz, 4 H) 7.72 (d, J=8.06 Hz, 4 H).
O
OS
O
CH3O
S
CH3
OO