AA

Tue, 06/04/2013 - 11:05 -- sewm02

 

Atomic Absorption Spectrometer Operating Procedure

1. Turn on the atomic absorption spectrometer (AA) using the main power switch located on the front right-hand side of the instrument. Allow the AA to warm up until the front screen reads, “Recall method y/n?” Sign in your name, time, and the element being analyzed in the AA user’s logbook.

2. Turn on the computer next to the AA, if it is not already on.

3. Double click the AA WinLab Analyst(2) icon located on the desktop. The software will connect with the AA. If a white error box appears, click ignore and continue.

4. The Perkin Elmer AA WinLab window will appear. Check that the technique in the bottom left hand corner reads “Flame”. Click on the green Ehrlenmeyer icon (basic system procedure).

5. The open method window will appear. Select the method for the element to be analyzed. For example, if copper is being analyzed select the copper method. Press OK.

6. The manual analysis window opens. This provides you with wavelength and slit width information. If you need to edit this wavelength or any other component of the method, select the method editor icon on the toolbar. The method editor window will appear. The wavelength can be changed by selecting from the pull down menu or by entering the new wavelength in the box. Ensure this is an acceptable wavelength for the element. If you are unsure, the value can be checked for the element by looking up the element in the Analytical Methods for Atomic Absorption Spectrometry book. Close the window when editing is complete.

7. Select the lamps icon on the toolbar. A list of several lamps should appear. Choose the lamp that is appropriate for your analysis by clicking under the set up column next to the lamp. The dot should turn green and a window stating “setting up lamp” should appear. When finished peaking wavelength, close the window.

8. Check that the vent above the AA is turned on and working. The “on” switch for this vent is the same “on” switch for the main fume hood between rooms 206 & 208.

9. Open the flame status window by selecting the flame icon on the toolbar. Turn on the gasses. For the compressed air, open the small valve upstream (to the left) of the regulator/filter assembly located on the workbench behind the AA. For the acetylene, turn the knob on the top of the tank all the way on. Make sure the pressure of the compressed is just under 60 psi and that the pressure of the acetylene is just under 15 psi. To obtain this information, read the left gauge on the acetylene tank regulator and gauge on the regulator for the compressed air. Should these values be ABOVE 15 or 60 psi, adjust the flow by turning the knob on the front of the regulator for the acetylene (looks like a T) and the knob above the regulator for the compressed air. Once adjusted, turn both gasses off (shut valves) and bleed the gasses from the AA by clicking on the bleed gasses icon in the flame window. When the gasses have been bled from the system, turn on the gasses, repeating the above procedure and make sure that the pressures are just below the designated values.

10. Record the starting psi of the acetylene tank in the AA logbook. Read the right-hand gauge on the tank to obtain this information. This tells you how much gas is left in the tank. If the pressure in the acetylene tank approaches 85 psi contact Jim Weekley for tank replacement. Operating the AA with acetylene pressure below 85 psi is forbidden due to safety concerns outlined in the AA technical manual.

11. Adjust the flow of the gasses coming into the AA by clicking on the adjust flame icon in the flame window. Manually turn the two knobs on the front of the AA until the scales above them read 4 for the compressed air (oxidant) and 2.5 for the acetylene (fuel). The bottom of the ball should be resting above the desired value.

12. Be sure to check that there is a black check mark on a green background in the flame status box. If so then everything is running fine. If it is a black X with a red status box, click on it to see what the error is. The solution to the error can be found by looking it up in the hardware/software guide for the AA. Periodically check the indicator box to make sure that everything is okay with the system.

13. Before igniting the flame, make sure that the capillary tube in the front of the AA is placed into a container that is FULL of distilled water. Also make sure that the waste container under the AA is not in danger of becoming full. A full waste container causes backup of waste into the AA, which will require professional assistance to get the AA working properly again. Contact Jim Weekley before the waste container is completely full so it can be emptied. Have all standards and samples prepared prior to igniting the flame to minimize the amount of acetylene used.

14. Ignite the flame by pressing the “on/off” icon located on the flame status box.

15. Allow the burner to warm up for 5 to 10 minutes. The AA will draw in the distilled water and clean the AA. Always ensure the AA capillary is in a beaker of distilled water when the flame is on and a sample is not being analyzed.

16. Begin analysis of your sample by first making a calibration curve as follows:

a. Before analyzing, ensure that the standard concentrations prepared are within the linear range for the element being analyzed. The maximum value for the linear range for the standard can be obtained by selecting the recommended conditions in the analysis menu, or using the Analytical Methods for Atomic Absorption Spectrometry book.

b. Open the calibration curve window by selecting the calibration icon on the toolbar.

c. You must manually enter the concentrations of your standards by opening the method editor. Select the Cal. Tab on the bottom of the window. Make sure that the calibration equation says calculated intercept-linear. Select the standard concs tab on the side of the window. Enter the values of the standard concentrations in the table, and close the window.

d. With the capillary tube immersed in the distilled water, click on Analyzed Blank.

e. Immerse the capillary tube in the standard solution indicated in the conc box next to the Analyze Standard icon in the manual analysis window. Then select Analyze Standard. Repeat this step until all standard solutions have been analyzed. Analyze standards in the order they appear in the manual analysis window. The software will automatically plot the calibration curve, which will appear in the calibration window. The absorbance values for each standard will appear in the results window, and it is a good idea to record these values in your lab notebook. The blank should be analyzed before each standard, by aspirating the distilled water and selecting Analyze Blank.

f. To print the calibration curve, go to File in the toolbar, print → window image. You will need to record the slope, intercept, and correlation coefficient displayed in the calibration window in your lab notebook.

17. Prior to analyzing a sample, you must analyze a blank. This will rinse the previous sample from the AA.

18. Place the capillary tube into your sample and allow the AA to draw up a portion of the sample. Select Analyze Sample icon. This reading takes about 20 seconds.

19. A concentration reading in ppm (mg/L) will appear in the results window. Record this reading in your lab notebook.

20. Analyze as many samples as needed by repeating steps 19-21.

21. If you need to analyze another element in the sample, open a new method (under file, select open → method). Select the element to be analyzed and repeat steps 18-22.

22. After all of your samples have been analyzed, place the capillary tube into the distilled water for 5 minutes to clean out the AA.

23. Turn off the flame by clicking the “on/off” icon in the flame status window.

24. Record the final acetylene tank pressure in the logbook. Shut the valve on top of the acetylene tank and shut the valve upstream (to the left) of the compressed air regulator/filter assembly.

25. Bleed the gasses from the AA by clicking the bleed gasses icon in the flame status window. An “X” will appear in the status box. This is because the gasses are turned off.

26. Save any changes necessary by going under file and save as.

27. Turn off the AA main power switch.

28. Exit the AA WinLab software. Log off of the computer.

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