Flame AA Burner Maintenance

Answer

This Information Applies To: All Agilent Atomic Absorption Spectrometry Systems (AA50, AA55, AA240, AA280)

Issue: This article describes when and how to clean an AA burner.

Background

For optimum and safe performance, burners (see Figure 1) should be cleaned after each day of use. Particularly if the solutions being analyzed have a high solids content or a rich nitrous oxide-acetylene flame has been used. If not cleaned regularly, hard deposits that are difficult to remove may build up and inhibit performance.

Warnings: Hot Surface and Explosion Hazard Parts in and near the burner compartment become very hot during operation. To prevent severe burns, always allow parts to cool down, or wear heat-resistant gloves before touching. The burner is correctly assembled, sealed, and pressure-tested during manufacture. To prevent gas leaks and flashbacks, which may cause death, injury or property damage, the burner must never be disassembled, modified, or mistreated. The correct procedure must always be used to clean the burner slot because the use of a burner with an oversized slot can cause a flashback.

Tip: It is impossible to determine with the naked eye whether a burner is clean. Even a low-power inspection lens will fail to show low levels of contamination. The best way is to use a binocular microscope, which allows you to look down inside the burner slot.

Figure 1 - Burner

Steps to follow:

To remove the burner

Figure 2 -  1. Chimney  2. Flame Shield  3. Front panel

1. Remove the chimney, flame shield and front panel from the sample compartment. (refer Figure 2)
   
   
2. Remove the burner by holding the upper and lower ratchet together and lifting the burner vertical.

To clean the burner

Warning: Always wear Personal Protective Equipment when cleaning the burner

1. Invert the burner over a container with dilute (up to 5%) nitric acid, so that only the slot (top portion of the burner) is submerged in the acid. Leave to stand for several minutes or up to overnight to soften excess deposits. Do not submerge the entire burner in solution.
   
   
2. Rinse with distilled water and place the burner inverted in an ultrasonic bath containing dilute laboratory detergent (such as Decon 90) for approximately 10 minutes.
   
   
3. Rinse with distilled water and allow to dry completely.

   Tip: To speed up drying, dry the burner with a paper or lint-free towel, and then use compressed oil-free or inert gas.

4. Insert a non-metallic business card or the Agilent burner cleaning and alignment strip into the burner slot and pour a small amount of metal polishing fluid (such as 'Brasso') on each side just above the burner slot.
   
   
5. Slide the card up and down in the burner slot (perpendicular to the top) to remove any deposits that may be present within the slot. Never use a metal strip as it will scratch the surface and promote the rapid build-up of carbon or other solids.
   
   
6. If the deposits are baked on hard, their removal may require some effort, and several cards may be required. Another option is to use a wooden or plastic spatula, which is slightly thinner than the dimension of the burner slot.
   
   
7. Thoroughly rinse the burner, preferably in the ultrasonic bath again, to remove all traces of the polish.
   
   
8. Dry the burner and inspect it under the microscope.
   
   
9. If necessary, repeat some or all of the previous steps until the burner slot is clean.
   
   

10. Soaking the burner in nitric acid and using an ultrasonic bath effectively removes soft chemical deposits inside the slot. The removal of hard carbon deposits usually requires more significant physical effort.

    Caution: If the width of the slot exceeds 0.47 mm (0.0185 in) for a nitrous-oxide/acetylene burner or 0.54 mm (0.021 in) for an air/acetylene burner, the burner cannot be refurbished and must be replaced with a new one. The damage or corrosion on the internal burner surface and slot can be caused prolonged exposure to high acid concentration solutions and/or acid vapor, because often, after the analysis is completed the flame is immediately turned off. Then, small drops from the last sample/solution will remain on the internal burner surface.

In addition to the preceding cleaning procedure, the following extra step can improve burner life time: After the last sample has been completed and before turning off the flame, aspirate a blank or cleaning solution (2–5% HNO3) for 2–3 minutes. This will remove all excess of sample/standard solutions remaining on the burner surface in the form of small drops.

The burner is now ready to use.

Learn how to effectively maintain your Agilent Atomic Absorption Spectrometry System: Guidelines for Troubleshooting and Maintenance of AA Systems