ATI/Unicam 929 A.A. Spectrometer

A. Sample Solutions

A.1 In a clean, dry beaker, obtain a quantity (about 5-10 mL) of certified Zinc chloride solution available in the laboratory to perform the following calibration procedures. (Refer to Section F if Zn standard is unavailable.)

A.2 From the zinc reagent certification notebook, obtain the certification data for the stock solution (date prepared; date standardized; measured concentration); enter in your Lab Notebook and in the Instrument Calibration Record Book.

A.3 Pipet 1.0 mL of stock Zinc chloride solution (Appendix A) into a 250 mL volumetric flask and dilute to volume with deionized water. (Refer to this solution as the "High standard". Pipet 50.0 mL of the High standard into a 100 mL volumetric flask, and dilute to volume. (Refer to this as the "Low standard".)

A.4 In addition to the above solutions, about 100 mL of deionized water will be required as a "blank" solution.

A.5 For Flow Rate Calibration, a 10 mL (or larger) graduated cylinder, with 0.1 mL divisions, will be required to aspirate blank solution.

 

B. Instrument Set-up Procedures

B.1 Start-up

B.1.1 Turn on Exhaust Fan; make sure that the acetylene tank main valve is closed; and that the air valve is closed.

B.1.2 Verify that the Zinc hollow cathode lamp is in one of the four turret positions, and record the specific turret position for later input.

B.1.3 Turn on the AA instrument (front panel switch) and the computer (power distribution strip)

 

B.2 Computer Operation to Open up SOLAAR Operating System

[Note: whenever the procedure selects a screen item, the action taken is to move the mouse pointer to the item and click once with the left mouse switch. Alternatives will be mentioned in the text.

B.2.1 From the [Program Manager] Window, select [SOLAAR AA SYSTEM] ICON (mouse select & double-click)

B.2.2 From next screen, select [SOLAAR] ICON (mouse select & double-click)

The next screen is the "SOLAAR" working window for the AA Spectrometer. All of the operating parameter windows may be cascaded on the screen. Any of these windows can be pulled to the top of the cascade by moving the mouse pointer to the top bar and clicking on it. Any of the operating windows can be removed from the screen and "iconized" down at the bottom of the screen for easy retrieval by clicking on the (down arrow) in the upper right corner of the window.

B.3 Setting Up the SOLAAR System for Calibration

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.

B.3.1 Move the mouse pointer to the Commands Bar at the top of the screen, and select the [WINDOW] command; from the drop-down menu, select the [Tidy Up] button. (This procedure "iconizes" all of the cascaded operating windows previously on the screen, and places them at the bottom of the screen for selected retrieval.)

B.3.2 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 calibration procedure [55ZNCAL.PAR]; move the pointer and select [OK]. (This file installs all the pre-determined operating parameters.)

B.3.3 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 the file entitled [55ZNCAL.TSK]; move the pointer and select [OK]. (This file will be loaded and all the pre-determined analytical sequence parameters will be installed.)

B.3.4 If the SPECTROMETER window is displayed, click on that window; if not, bring up the SPECTROMETER window by clicking on the [SPECTROMETER] ICON from the bottom of the screen (mouse select & double-click). Move the pointer to the Top Commands Bar and select the [SPECTROMETER] command; the drop-down menu will display selections; select [Parameters]; then select [Lamps].

 

 

B.3.5 From the displayed Lamps window, determine that the zinc lamp is assigned to the correct position in the turret. If not, select the [DEFINE] button and select the Zn symbol from the displayed periodic table for the specific turret position. If the lamp assignment is correct, the lamp can now be turned on by placing an "X" in the status box. (Because the deuterium lamp is also required for this determination, an "X" should also be placed in its status box.) To change the status box contents, move the pointer to the box, and click once. If the respective status boxes already have an "X", select the [CLOSE] button, and proceed to the next step. When the status blocks are set appropriately, select the [CLOSE] button, and proceed to the next step.

NOTE: Information displayed in the [SPECTROMETER] windows is required for completing the Calibration Record Sheet. You should examine the sample record sheets at the end of this section, and make a record of required items before moving to the next step in the procedure.

B.3.6 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 [55ZNCAL.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.)

B.3.7 From the Top Commands Bar select [ACTIONS]; then select [SET UP OPTICS]. The system responds with a Screen Command "Move Turret to Position No. N". If the turret is already in position, select the [OK] button; if not, open the hinged door on the front of the instrument and manually rotate the turret to the correct position; close the door; and select the [OK] button.

B.3.8 Bleed off any fuel remaining in the lines by depressing the RED [OFF] button on the instrument front panel for ~ 15 to 30 seconds, until a "click" is heard, then observe the acetylene tank output gauge drop to zero; release the RED button. (NOTE: Be sure that the acetylene tank main valve and the air valve are both closed, before bleeding lines.)

B.3.9 Ignite the flame. (For acetylene-air flames) Open the air valve (~30 psi); open the main valve on the acetylene tank (the output valve should already be open); if necessary adjust the acetylene output pressure to ~8-10 psi.

If the Ignite button on the spectrometer is flashing, it is safe to ignite the flame. Be sure the safety cover is over the flame box. Depress the ignite button until the flame ignites (a few seconds); if necessary, adjust the fuel flow rate to ~20, or until a desirable flame quality is observed, using the control knob on the right front of the instrument, while observing the flow rate gauge.

B.3.10 Check the waste bottle. If the waste level is close to the discharge tubing, dispose of the waste before continuing.

B.3.11 If the lamps have warmed up for a few minutes, check the [SPECTROMETER] window displayed on the screen to see if the proper wavelength has been selected for the element and the absorbance and photomultiplier voltage values are reasonable. After aspirating deionized water (blank) for about 5 seconds, select the [0.0] ICON from the Icon Bar near the top of the screen. This will automatically zero the output absorbance reading. Air can be aspirated into the sample chamber in place of solution between subsequent analyses.

NOTE:

a. Wear safety goggles when operating the AA spectrometer.

b. Always turn on air before fuel; turn off fuel before turning off air.

c. The drain tube from the burner must be above the water level in the collection vessel.

C. Calibration Procedure

C.1.1 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 the Icon Bar near the top of the screen. This will automatically zero the output absorbance reading, requiring about 30 sec.

C.1.2 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 turret should already be in position, so select the [OK] button.

C.1.3 Follow the directions subsequently displayed on the screen. However, do NOT respond immediately when the first command appears: "Aspirate air or DI water to set Zero Absorbance". Instead, use this period to Calibrate the Solution Flow Rate: Fill the graduated cylinder with blank solution and place the aspirator tubing close to the bottom. Observe the loss of solution and measure the time (in seconds) required to aspirate exactly 5.00 mL. Re-fill the graduated cylinder, if necessary, and repeat the flow rate measurement twice. Record results in the Calibration Record Book and Calibration Report Sheet, as well as your Lab Notebook.

C.1.4 Continue aspirating blank solution from, and indicate the action that the spectrometer can begin to make optical measurements by selecting the [OK] button (mouse select or hit the "ENTER" key on the keyboard). The computer will respond by collecting absorbance data for three 4-second time intervals, and record these as "Blank Absorbance" data.

C.1.5 The computer requests that you aspirate [Sample 1], followed by a request to [Aspirate air or DI water to set Zero Absorbance]. This is followed by a request for [Sample 2]. In each case, transfer the aspiration tubing to the proper solution after wiping off with a tissue. Sample 1 should be the "Low Standard Zinc Solution"; Sample 2 should be the "High Standard Zinc Solution".

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

C.1.6 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.

C.1.7 Print out your results. From the Top Bar, select [FILE]; select [PRINT] from the drop-down menu; then select [ANALYSIS RESULTS].

C.1.8 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 provided and placed in drive A.

C.1.9 The final action is to select the [FINISHED] button from the Top Bar.

C.1.10 To begin a new run, Go To C.1.1.

 

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.

 

D. Error Messages

The computer control system for the ATI/Unicam 839 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 simply acknowledges that you are aware of it.

Some error messages can not be passed until the error is corrected or the run is aborted. 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 C.1.1. If the system doesn't allow a re-start, inform the instructor, who will re-initialize the operating system.

E. Report

Enter into your Lab Notebook and the A.A. Spectrometer Calibration Record Book:

a. Date, Time, Operator

b. Instrument I.D.#: (ATI/Unicam 929 AA; DH-413)

c. Stock Solution Preparation Date and certified concentration

d. Specific instrument settings as required

e. Individual and average absorbances and standard deviations for blank solutions and for High and Low standards. NOTE that the blank readings before the High Standard solution readings are identical to the blank readings after the Low Standard solution readings, and should be entered as such on the Calibration Record sheet. Also enter Net Absorbances and Absorbance Ratio for Low/High Standards.

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F. Preparation of Zinc Chloride Stock Solution (If Needed)

Weigh out accurately 1.0423 g of pure, dry ZnCl₂ (F.Wt=136.29), and transfer to a 250 mL beaker. Dissolve with about 100 mL dilute HCl and transfer to a 1000.0 mL volumetric flask and dilute to volume with deionized water.

Label flask with the preparation date and preparer. Record weighing data and concentration calculations in Zinc Standard Notebook and in your Lab Notebook; date and sign both Notebooks.

 

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