CHE 230 - Lab #7
Aluminum by UV-VIS Spectroscopy
Objectives:
Use standard methods to prepare and analyze Jennings water samples for aluminum.
Prepare a calibration curve or Beer’s Law plot of aluminum standards.
Quantify the aluminum content (both total and dissolved) in your water samples.
Tools/Skills:
Syringe filtration
Digestion
Standard preparation
Calibration curve
Procedure:
Sample preparation
Total aluminum – mix and measure out 50.0 mL of sample to be digested
Soluble (dissolved) aluminum – filter >50.0 mL of sample using a 0.45 um syringe filter (Method 3500Al B, 1d); measure out 50.0 mL of filtered sample to be digested
Digest both samples using Method 3030 E Nitric Acid Digestion
Standards
Work out the math for a series (4-6) standards in the range of 0-300 ug/L
By dilution of a 5.00 ug/mL stock standard
To a final volume of 20.0 mL
Standards will be prepared and analyzed based on the procedure from Method 3500-Al B, Section 4a
Volume scale will be adjusted according to the table below:
Adjusted
Original vol (mL)
vol (mL)
Stock standard
x
x
water to
25
10
ascorbic acid soln
1
0.4
0.02N H2SO4
1
0.4
buffer soln
10
4
working dye
5
2
dilute to
50
20
Note: “x” based on M1V1 calculations
Samples
Sample volumes are adjusted to 10.0 mL
Three samples tested:
1. Titration with methyl orange to pink color (record volume for titration; can discard sample)
2. One sample with added EDTA (serves as blank by complexing Al)
3. One sample without EDTA
Samples will be prepared and analyzed based on the procedure from Method 3500-Al B, Section 4b
Volume scale will be adjusted according to the table below:
Original vol (mL)
sample
0.02N H2SO4
EDTA
ascorbic acid
buffer soln
working dye
dilute to
25
titration vol + 1mL
1 *
1
10
5
50
Adjusted
vol (mL)
10
titration vol + 0.4mL
0.4
0.4
4
2
20
*Note: only one of the samples will contain EDTA; you will have a pair of analyses for
each sample
Analyze the quality control sample (single replicate) using the sample procedure (true value will
be provided during post-lab)
Analysis Notes
Use DI water to “zero” the instrument; do not blank with your “0” standard
Make sure your sample absorbances are in the range of your standard absorbances
You may need to dilute your samples to get them in range
Perform 3-4 analysis replicates (replication of analysis procedure—not sample prep—for each sample
(total Al, dissolved Al)
Note: these are not “true” replicates
Reference:
Andrew D. Eaton, Lenore S. Clesceri, Eugene W. Rice and Arnold E. Greenberg. Standard Methods for the
Examination of Water and Wastewater, 21st ed. American Public Health Association. 2005.
Post-Lab/Discussion:
1. Create a calibration curve by plotting absorbance versus concentration for your standards.
o Include the equation of the line and R2 value on your graph.
o Calculate your sample concentrations from the calibration curve.
Consider any dilution steps in your calculation.
Present your results as the average ± 95% confidence interval.
2. What color were your solutions? How does that color compare with the wavelength of analysis (535
nm)? Why are they the same/different?
3. What is the difference between “dissolved” aluminum and “total” aluminum? What trend should be
observed for the dissolved and total content of a given sample?
4. You performed 3 or 4 “analysis replicates,” which are not “true” replicates. What does this kind of
replicate allow us to assess (statistically)? Describe how to perform a “true” replicate.
5. Compile class data for the aluminum results and discuss any trends (especially with respect to sample
location).
6. Comment on the accuracy and precision of your results.
**This lab will be written up as a formal report.**
***The “best” report will be submitted to Jennings.***
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