This procedure assumes the instrument has been set up by the Instructor (i.e., the flame is ignited; exhaust fan is on; source lamps are on; the optics/electronics have the proper settings; and the computer screen displays the operating menu.). Otherwise, see Start-Up Procedure in Appendix 6.

1.0 [Note: whenever the procedure selects a screen item, the action taken is to move the mouse pointer to the item and click once on the left mouse switch. Alternatives will be mentioned in the text, (e.g., double-click.)]

1.1 Bring the previously prepared solutions (preceding section) of the sample(s) and standard additions to the AA instrument. Have a beaker of deionized water available as the "blank".

1.2 From the operating menu displayed on the computer screen, move the pointer to the left side of the Top Commands Bar, and select the [FILE] command; from the drop-down menu, select the [LOAD] command; from the drop-down menu displayed, select [Analysis Parameters]; from the list of files, select the file entitled "55MNSTAD.PAR"; move the pointer and select [OK]. (This file installs all the pre-determined operating parameters.)

1.3 Move the pointer to the left side of the Top Commands Bar, and select the [FILE] command; from the drop-down menu, select the [LOAD] command; then select [Sequence Parameters]; from the list of files select file entitled "55MNSTAD.TSK"; move the pointer and select [OK]. (This file will be loaded and all the pre-determined analytical sequence parameters will be installed.)

To prepare the screen for operation of the spectrometer for several analyses:

move the pointer to the Top Commands Bar and select the [WINDOW] command; from the drop-down menu select [Load Positions]; from the displayed files select [55MNSTAD.FMT]; select [OK]. Again move the pointer to the Top Bar and select the [WINDOW] command; from the drop-down menu select [Arrange Icons]. (This last action will move all the iconized windows to the area of the screen left open by the preceding selections.)

1.4 When ready to begin the analysis procedure, the plastic sampling tube (for

aspiration of solution) should be aspirating only air. Place the tubing in the blank

solution; wait about 5 seconds; move the pointer and select the [0.0] ICON from

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the Icon Bar near the top of the screen. This will automatically zero the output absorbance reading, requiring about 30 sec.

1.5 Move the pointer to the Top Bar and select [ACTIONS]; then select [ANALYZE]

from the drop-down menu. The system responds with a Screen Command "Move Turret to Position No. 'N'". The Mn lamp should already be in position, so select the [OK] button; if in doubt, check with the instructor.

1.6 Follow the directions subsequently displayed on the screen. For example, when "Aspirate Blank" appears, place the aspirator tubing into the blank solution (well below the surface), and indicate the action is completed by selecting the [OK] button (mouse select or hit the "ENTER" key on the keyboard).

Between each sample selected for aspiration, wipe the tubing off with a clean tissue, to avoid cross-contamination.

For the standard addition procedure the computer will ask for [Blank], [Sample 1], [Std Addn 1], [Std Addn 2], [Blank], [Sample 2],.. etc, up to four samples. You may select [STOP] to terminate these requests after two samples, or you may re-run the same samples. For improved precision, the AA procedure may perform three repeated measurements on each solution. Continue aspirating each sample solution until all replicate determinations have been completed.

Throughout the analysis procedure, three windows displayed on the screen will provide a real-time status of the experimental results. The [SIGNAL] window displays absorbance measurements as they are done; the [CALIBRATION GRAPH] displays the up-dated calibration curve, with sample absorbance values; and the [SPECTROMETER] window displays the lamp and absorbance values at all times.

1.7 When the pre-determined procedure has been completed, the computer will output a message "Analysis is Complete". Your response is to select the [OK] button. Then remove the aspiration tube from the last solution; wipe it off; and allow only air to be aspirated.

1.8 Print out your results and calibration graph: From the Top Bar, select [FILE]; select [PRINT] from the drop-down menu; then select [ANALYSIS RESULTS]; then select [PRINT], [CALIBRATION GRAPH]. Be sure to put your name on print-outs immediately. NOTE: Only the data points for Sample 2 are plotted; the Sample 1 calibration line may be included if similar.

1.9 Optional. You may save all data, results and parameters in a diskette file by selecting [FILE], [SAVE], [A], specifying which information you want saved and specifying a file name. For this, a diskette must be placed in drive A.

 

 

1.10 The final action is to select the [FINISHED] button from the Top Bar.

1.11 To begin a new standard addition experiment, Go To 1.4.

2.0 Error Messages

The computer control system for the ATI/Unicam 929 spectrometer will provide error messages if an unexpected procedural step is taken, or if an analytical error is detected. Usually, you can move forward by simply selecting the [OK] button. This doesn't fix the error, but acknowledges that you are aware of it.

Some error messages can not be passed until the error is corrected or the run is aborted. For example, if you try to aspirate standards out of the expected order of ascending concentration, the system will inform you of the error; you can try again, but if you continue to add samples out of order, you will continue to get an error message and the procedure will not ever be completed.

When an irretrievable procedural error has been made, the run can be aborted by selecting the [STOP] button from the top bar. The computer will ask if you want to lose all data to that point; usually your response will be [OK], so that you can start over again. To re-start your analysis procedure, go to step 1.4. If the system doesn't allow a re-start, inform the instructor, who will re-initialize the operating system.

NOTE: To make any of the parameter windows active, either select the ICON, or select the Top Bar of the displayed Window. The Commands related to this selected parameter will then become available at the Right-Hand Side of the Top Command Bar.

3.0 Report

For your Report (see Spectrometry Report section, p. 32), the average %Mn in steel will be required. This average is for Samples 1 and 2. The standard deviation reported will be between samples.

Be sure that all relevant data are recorded in your Lab Notebook. For example: the specific volumetric quantities used for several quantitative dilutions; original sample weights and volumes; and the related calculations of concentrations.

The procedure also obtains three replicate measurements of the blank, allowing calculation of the standard deviation of the blank, which can be used in computing the Detection Limit required in the Report.

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