Lab #7 - Al by UV-VIS

advertisement
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.***
Download
Related flashcards
Create flashcards