STEP BY STEP AAS INSTRUCTIONS

STEP BY STEP AAS INSTRUCTIONS - Iron (Fe)

Courtesy of Josephine Axt
GMU PhD Student- 1997

Turn on AAS, computer, and printer.
Double click on inst.exe icon.
The Lab Benchtop window will open - do not proceed until the 5100 icon underneath the AAS icon is highlighted.
While you're waiting for the icon to light up, open your acetylene tank and air line. Acetylene pressure should be at 14 psi (this is marked on the gauge in black) and air pressure should be about 45-50 psi (neither air pressure nor acetylene pressure should vary much between sessions, but it's important to always check it, especially after changing tanks). The gauge that reads pressure in the tank is the gauge on the right. The gauge on the left reads how much fuel is in the tank. NOTE: when first opened, the acetylene tank, will usually read above 15 psi (red zone). Don't adjust the pressure right away, because 93% of the time, after about 10 minutes, it will have sunk to 14.1 psi always check the pressure after you light the flame. NOTE: the acetylene tank should be replaced when the fuel level drops below 75 psi (using the scale on the inside of the circle on the left hand gauge). Since contaminants sink to the bottom of the tank, it is not advisable to drain a tank to absolute empty .
Under "Windows" at the top of the page, scroll down and open the Element Parameter file. This file is your method file; you can't run an element unless you have defined a method.
The Element Parameter file will ask you whether you want a previously defined file, or a new one (so it is possible to use the same method for different sample runs). In the Element Parameter file, you have three pages to fill out - M ain, Calib, and Options.

Main - specify the element (standard wavelength and slit width will automatically appear), select an appropriate sampling time (default is 5 sec), make sure the flame sensor is on, and confirm that the fuel is acetylene and the oxidant is air. "Time average" and "AA" remain as is.

Calib (Calibration) - enter the concentration of your standards and how you want to refer to them (i.e. Sl, or standard 1, or whatever). The most important thing to do is to make sure that if, for example, you have a 10 ppm standard, the standa rd units are set at mg/L. To change standard and sample units you just double click on the line. It is possible to have standard units and sample units different. You decide the number of significant digits (up to the machine's precision level of course) by entering "5.0" as a standard, or "5.00", etc. Last, click on Nonlinear to change the type of standard curve that will be drawn; absorbance vs. concentration for Fe is only linear up to about 10 mg/L.

Options - highlight the printing options you prefer and type in any comments about your samples. This page prints out at the beginning of your run automatically.
Save your Element Parameter file. The computer will always use the Element Parameter file most recently opened when you begin running samples. Close your newly named file.
You should be back at the Lab Benchtop. Now you will open four files that you will need to manually run your samples. Under Windows, scroll down and select "Flame Control", "Manual Control", "Display Calibration", and "D isplay Data".
OK, but before you begin running samples, you need to adjust the lamp, and then optimize the burner head position, the fuel, and the nebulizer.
NOTE: For fe, you must use the longer burner head with the BLACK PIN. When running samples that use acetylene and air, you use the longer burner head with the black pin, but for any elements that require the hotter N20 flame, you use the shorter burne r head with the red pin. I know from experience that the AAS will not light if you mix up the burner heads!
Adjust the lamp by first opening "Adjust Lamp" under Windows (see, there really is logic to all this; before you know it you won't need this sheet!). If you have created your Element Parameter file (as you should have by now) the AAS has already selected the Fe lamp. Your lamp current should read 25 or 30, and your lamp energy should be in the 60's or 70's [in the past lamp energy has fluctuated, and Perkin Elmer maintains that even at a low lamp energy precise sample measurements are possible, but if lamp energy drops dramatically it is probably a sign something is wrong - call Perkin Elmer!]. Now, open the lid covering the lamps, and maximize the absorbance bar by 1) moving the whole lamp forward and backward and 2) turning the two knobs you will see near the
back end of the lamp, which adjust the lamp's position.
Optimize the vertical position of the burner head by first lowering the burner head with the large right hand knob next to the nebulizer. Then open "Continuous Graphics" under Windows and Autozero by clicking on "Autozero" under < B>Continuous. Raise the burner head until you get a reading, that is, when your .000 goes up, to .004, then .018, etc. Lower the burner head until you have .000 again, then lower it one quarter of a turn more.
Now it's time to light the AAS. Don't close your Continuous Graphics window, just click on the Flame Control window. After opening your air and acetylene lines (air comes through a line from a compressor next door, acetylene is in a tank) click on the flame icon to light the flame. By the way, the exhaust system should be turned ON now!!

Adjust the fuel and oxidant levels by using the Fuel Up/Down and Oxidant Up/Down keys on the keyboard (towards the right on the top line of F keys). For iron, I have found that a fuel of 2 and an oxidant of 8 - 10 works well. Basically, you wa nt a lean flame (meaning the blue line on the burner head at the bottom of the flame is about 1/8" high). You don't want a rich flame, which is the result of a high fuel level.
To adjust the burner head horizontally and diagonally, go back to the Continuous Graphics window. While aspirating a standard (you'll probably want to make more of the standard you choose to aspirate, since a lot of liquid can be used up in thi s step) turn the large shiny left hand knob (horizontal) in both directions until you reach maximum absorbance. Repeat this process with the inside-the-compartment-to-the-right-of-the-burner-head shiny knob (diagonal). Some people like to readjust the ver tical knob at this point, to fine tune it. I don't, but try it yourself and see what you prefer.
The nebulizer is also adjusted using the Continuous Graphics window. Loosen the lock on the nebulzier by turning the "locking ring" counterclockwise. This will allow you to adjust the sample flow rate by twisting the "knob ring"; the knob ring being the ring which the nebulizer tube directly connects into (the locking ring is immediately behind the knob ring, touching the knob ring in fact when it is completely tightened). When the nebulizer tube is no longer locked (i.e. the locking ring has b een loosened) you can adjust the rate at which the tube sucks samples by twisting the knob ring. Now, put the nebulizer tube in a standard, and turn the circular knob ring until bubbles come OUT of the tube in your standard; then turn the circular knob ring in the other direction until you reach a maximum absorbance on your Continuous Graphics window.
NOTE: it is my experience that the nebulizer sucking rate does not change much at all in between running samples. When you have a good rate, I recommend not messing with it unless you're having problems. NOTE: it is also my experience that sucki ng rate doesn't effect absorbance that much, so I usually fill a volumetric flask up to the very top and visually watch the rate at which the level of solution drops. Once you have adjusted the nebulizer using absorbance a few times, you will get a fe el as to what is a good rate for the solution to drop in the neck of the volumetric flask. NOTE. Remember to always "relock" the locking ring after making an adjustment!!

Now you can close the Continuous Graphics window. Then, click on the Manual Sampling window, where you will want to double click on the line above the "save data on/off" icon, to name the file where your sample data will b e stored. If you do not name a file and thereby cause the "save data on/off" icon to be highlighted, your data will not be saved!!!
Now you're ready to begin running your standards/samples. You will always begin a sample run by running a standard curve. Simply put the nebulizer tube in your first standard (your "zero" standard") and scroll down under Calibration to autozero . When the READ icon stops being highlighted, that means the AAS is finished reading that standard, so you will remove the tube, wipe it with a ChemWipe, put it in your second standard, and scroll down to your next standard . Repeat this process until all your standards have been analyzed. NOTE: some people think the neb tube should always be placed in distilled water in between samples, to flush the tube. I have tried it with and without the de-ionized water and found that if you let the nebulizer tub e sit in your standard for one second before its analyzed, then you don't need to do the distilled water wash every time. I tell the AAS to delay analyzing the standard/sample after I hit READ by typing in 1.0 second Delay in the Elem ent Parameter file, Main section. Experiment yourself!
You have to use the mouse to analyze standards (and the nebulizer tube must be in the standard before you click on autozero, Sl, S2, etc.) but to analyze samples you can either use the mouse to click on the large READ icon on the Manual Cont rol screen or the keyboard (in the middle, top row). After your first standard curve is run, rinse with de-ionized water and then put the nebulizer tube in your first sample, hit READ (mouse or keyboard), and then keep the tube in the sample un til the READ icon is no longer lit up. Rinse with de-ionized water, then put the tube in your next sample, hit READ, wait, etc. I recommend running a standard curve after every 10 to 15 samples. In between every sample, I always wipe the neb ulizer tube with a ChemWipe.
The Display Data window will show you the concentration of your most recent sample/standard. The Manual Control window will keep track of the total number of samples/standards you've run. To view your most recent standard curve, click on the Display Calibration window. To edit a standard curve, click on Edit Calibration.
When you've finished running all your samples/standards, you turn off the flame (using keyboard or Flame Control window), close the acetylene/air lines, and bleed the gases remaining in the lines (click on bleed gases in Flame Control window).
To save your data file in, for example, ASCII, so that you can transfer the information into a spreadsheet, go to the Data Benchtop. Then scroll down to Reformat Data. A window will open that will allow you to call up your data fi le (double click on the data line), and then choose various options for what you want saved in your ASCII file. The options are too numerous to list here; most are pretty straightforward, but for a detailed listing consult the manual. Once you've made your choices, simply click on Execute Reformat.
To view your ASCII file, exit the software. At the C prompt, type x. Scroll up using the arrow keys until you find Data - AAS. Hit return twice and you will see a listing of all the Data files. Then follow the commands at t he bottom of the page: hit V to view the document, C to copy it onto a disk, etc.

Link to the experiment

Last update: February 18, 1998.