Paul Gunston
Carlos VargasThis Information Applies To: Agilent VGA 77 Accessory
Issue: The Agilent Vapor Generation Accessories use high concentrations of HCl and require thorough cleaning to maintain optimum working condition.
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Warning: The Vapor Generation Accessories uses high concentrations of HCl. Continual exposure to HCl fumes may damage skin and lungs. Wear appropriate PPE when handling and cleaning the VGA components. Always maintain an efficient exhaust system during VGA determinations
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The Vapor Generation Accessory 77 (VGA 77) is a vapor generation system for Atomic Absorption (AA) and the VGA 77P is for Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) applications. Unless otherwise specified, in this article both the VGA 77 and VGA 77P will be referred to as VGA 77.
Figure 1. Vapor Generation Accessory 77 (VGA 77)
The working life of the absorption cell and the gas/liquid separator will depend on the type of analytical programs carried out. Clean immediately if contamination is suspected during conditioning, or whenever the system has been left unused for some time.
At some stage, the glass will start to turn white indicating the onset of devitrification. Initially, devitrification will not degrade the analytical performance, but eventually the devitrified area will extend over most of the cell at which point it may be necessary to discard the cell. If devitrification is excessive, the cell will eventually crack spontaneously or fail through thermal shock.
Whether the cell becomes devitrified or not, and even with meticulous cleaning, the inside surface may deteriorate to the extent that the analytical signal will be suppressed. Regularly monitor the performance of the cell using absorbance measurements obtained from standard solutions. Discard the cell when the results of this monitoring become unacceptable. Sometimes, the center section of the cell may gradually soften in the flame and sag. If uncorrected, it will prevent the alignment of the cell with the optical path. When sagging is first noticed, turn the cell over so that it will return to its normal shape the next time it is heated.
Cleaning Procedures:
Always clean up any spilt liquids immediately. The front of the Spectrometer, the burner/torch compartment and, the VGA 77 should be cleaned daily with a soft cloth. If there are spills, use a cloth dampened with distilled water and appropriate PPE.
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This section applies to the VGA 77 on Atomic Absorption instruments only
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Always clean the absorption cell (Figure 2) thoroughly immediately after use, when contamination is suspected while conditioning the system, or whenever the system has been left unused for some time. The cell is fragile and must be handled with appropriate care.
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Warning: The cell is heated when in use. Always turn off the flame and allow the cell to cool before attempting to remove it from the sample compartment.
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Disconnect the black fluoro-elastomer tubing from the cell inlet.
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Release the spring clips and remove the absorption cell from the cell support.
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Soak the absorption cell in dilute nitric acid for at least 30 minutes.
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Rinse thoroughly with distilled water and allow it to air dry in a dust-free location.
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If the cell has been exposed to contamination with potassium iodide, soak the cell in sodium hydroxide solution (0.5% w/v) for at least 30 minutes. Wash thoroughly with dilute hydrochloric acid and then wash thoroughly with distilled water. Allow to air dry in a dust-free location.
Caution: Do not leave the cell in the sodium hydroxide for too long as this solution may accelerate cell devitrification. Avoid handling the central part of the quartz cell with bare hands after it has been cleaned or while it is in use.
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Disconnect the tubing from the vapor outlet of the separator (Figure 3), and the sample inlet.
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Carefully remove the rubber mounting strap holding the separator in place.
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Disconnect the drain tubing from the drain in the bottom of the module. You may now lift the separator out of the module.
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Disconnect the tubing from the inert gas inlet of the separator.
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If the separator has been exposed to solutions containing potassium iodide, soak the separator in sodium hydroxide solution (0.5% w/v) for at least 30 minutes. Wash thoroughly with dilute hydrochloric acid and then wash thoroughly with distilled water. Allow to air dry in a dust-free location.
Tips: If the separator has not been exposed to potassium iodide solutions, it may be treated in the same way as the absorption cell. To avoid KI contamination, it is recommended that you dedicate a separate module to the analysis of those elements requiring prereduction with KI (i.e., As or Sb). -
Refit the separator into its mounting bracket, secure it with the retaining strap and reconnect all tubing. If the system is not to be used for some time, the separator should be filled with distilled water.
The fluoro-elastomer tubing connecting the gas/liquid separator to the absorption cell is susceptible to contamination with potassium iodide. Agilent recommends using a dedicated separate module for the analysis of those elements requiring prereduction with KI (i.e., As or Sb). If there is no KI contamination, the tubing can be cleaned by flushing it well with distilled water. If there is KI contamination, remove traces of KI as follows:
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Disconnect and remove the tubing.
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Soak the tubes in sodium hydroxide solution (0.5% w/v). Wash thoroughly with dilute hydrochloric acid and then wash thoroughly with distilled water.
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Allow the tubes to air dry in a dust-free location.
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Reconnect the tubing.
Check tubing daily and look for the following signs of wear:
- Loss of elasticity and stretching. Roll the tubing between your fingers. Stretched tubing will feel oval or flat in shape and will not reshape quickly after being pinched. Tubing in good condition will feel round and reshape quickly.
- Cracks in the tubing, which can cause liquid on the outside or bubbles in the tubing.
- Visible sample deposit blocking or partially blocking the tubing
When the system is not being used, the pressure bar should be released, the pump tubes removed from around the rollers and released from the retaining bracket to minimize wear. Spray the outside of the tubes and the surface of the pump rollers with silicone lubricant to reduce mechanical wear.
An alternative method of removing iodine from the tubing and gas/liquid separator is to pump a freshly prepared 1% w/v sodium thiosulfate solution through the system for 5–10 minutes. Remove the thiosulfate by pumping distilled water through the system for 5–10 minutes.
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Learn how to effectively maintain your Agilent Vapor Gas generator:
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