SOP for Operation of Atomic Absorption Spectrometer (ChemTech, Model CTA 3000)

OBJECTIVE

This document outlines the procedure for the operation of the Atomic Absorption Spectrophotometer from ChemTech Company (Model CTA 3000).

SCOPE

Atomic absorption spectrometry (AAS) is a technique in which free gaseous atoms absorb electromagnetic radiation at a specific wavelength to produce a measurable signal. AAS is an important sensitive method that is suitable for the determination of selected elements at the trace and partly at the ultra-trace level.

RESPONSIBILITIES

It is the responsibility of the QC Executive.

ACCOUNTABILITY

Manager – Quality Control

PRECAUTIONS

• Wait to leave until closing the acetylene tank when not in use. Acetylene is explosive and quite dangerous.
• To shut off the flame in an emergency-push the red button on the right front of the instrument.
• The pressure of the acetylene gas cylinder must never fall below 4 bar.
• When the flame is ignited, to protect the furnace, insert the steel plate which separates the furnace from the flame.
• The water traps should be filled with water so that excess amounts of water overflow into waste containers.

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OPERATING PROCEDURE

• Turn on the instrument (The power switch at the right hand of the instrument is only turned on when we wish to use the furnace), computer and verify ventilation.
• Double-click on the “AAWin” program located on the desktop.

• From the drop-down menu select the “online” item and press OK. The program will proceed through a checking process. Please wait until you finish the checking process. This usually takes a few minutes.
• An element selection window will appear. Select the working lamp and click on finish.
• The “AAWin” window will open. Open the “instrument” menu and select the “measure method” item. The “set measurement method” dialog box opens. Select the method you wish to use then click on Execute. Wait for the system to locate the selected atomizer in the path of light. This usually takes a few minutes. After finishing this procedure, close the “set measurement method” dialog box.
• Optimize atomizer position using “instrument” menu-burner parameters. The position of the atomizer should be adjusted carefully so that the whole energy of the hollow cathode lamp reaches the detector. The path of light can be checked by a piece of white paper.
• After adjusting the position of the atomizer, click on the “Lamp” icon and then click next. Press the “search peak” button. The “wavelength scanning/peak searching” dialog box opens. Click the “search peak” button and wait. This usually takes a few minutes. After appearing in the spectrum, close the “wavelength scanning/peak searching” dialog box.
• Click on the “Energy” icon. The “Energy” dialog box opens. Click on “Auto-balance”. The energy of the lamp should be about 100 %.
• Click on the “Sample” icon and enter calibration and sample information.

The above-mentioned steps are identical for all measurement modes. The next steps for every measurement mode are explained in the following sections:

Flame:

• Switch on the air compressor, which is below the bench
• Open the acetylene gas valve.
• Click on the “Fire” icon. The flame will ignite.
• Click on the “Meas” icon. The measure window will be opened in the upper right corner of the screen.
• Place the suction tube in the blank and click on the “Zero” button.
• Place the suction tube in your standard solution. Watch the Absorbance vs. time on the screen. When the Abs level has stabilized, click on the “start” button. If you are using multiple standards start with the least concentrated standard.
• The resulting calibration curve should be visible in the calibration window.
• Place the suction tube in DI water between standard solutions and samples.
•  When analyses are complete, aspirate DI water for a few minutes.
• Finally, close the main acetylene tank valve and air supply valve.

Furnace:

• Open the “instrument” menu and select the “Heating program” item. Define the heating program.
• Insert the graphite tube in its location on the furnace (The hole of the tube should be at the top). Check the path of light. The light should be passed through the graphite tube and reach the detector.
• Open the argon gas valve. Click on the “tube” icon to fix the furnace.
• Open the cooling water valve.
• Click on the “burn” icon to clean the graphite tube, if necessary.
• Click on the “Meas” icon. The measure window will be opened in the upper right corner of the screen.
• Inject the bank into the graphite tube using a micropipette and click on the start to run the heating program. When the heating program is finished, Click on the “Zero” button.
• Inject standard solutions into a graphite tube using a micropipette and click on start to run the heating program.
• Once analyses are complete, close the main argon tank valve and the cooling water valve.

Hydride generation:

• Insert quartz T-atomizer (quartz cell) on the burner head.
• Set up a Hydride Vapor Generator (HVG-CTA 2290) and connect it to a quartz T-atomizer.
• Adjust the position of the atomizer.
• Connect the quartz cell to the power supplier (Voltage = 120). Wait until the quartz cell.
• Open the argon gas valve. Adjust the argon gas pressure to optimum. Most systems operate at 0.7 L/min. At 25 PSI, the flow is approximately 0.7 L/min.
• Click on the “Meas” icon. The measure window will be opened in the upper right corner of the screen.
• Switch on the Hydride Vapor Generator. Turn on both the sample and drain pumps.
• Place the sample, acid, and reducing agent pump tubing in the corresponding solution. Watch the Absorbance vs. time on the screen. When the Abs level has stabilized, click on the “start” button.
• Place the suction tube in DI water between standard solutions and samples.

• Once analyses are complete, transfer all samples and reagent pump tubing to a DI water reservoir for rinsing.
• After the tubing has been flushed with DI water, remove the tubing from the rinsing vessel and allow the system to pump dry for a minute before shutting off the pump.
• To maximize the life of the pump tubing, unclamp the tubing blocks and release the tension on the pump tubing after use.

ABBREVIATIONS

QC – Quality Control

ANNEXURE

Nil

REVISION HISTORY

Nil

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