Operation
82 Agilent 55B AA Spectrometer User’s Guide
Figure 37. Thimble location. The locking ring is between the thimble and the nebulizer block
High vacuum setting
For samples with relatively low levels of dissolved solids, optimum performance is
achieved with the nebulizer in high vacuum mode. Here the capillary is set to give
the maximum pressure drop (vacuum) at the capillary tip. This setting uses
narrow-bore plastic capillary tubing (0.38 mm ID).
A nebulizer set up in this way will show minimum variation in uptake rate with
variation in liquid level in the sample tubes. The nebulizer may, however, be more
susceptible to clogging by salts deposited from the sample.
To set the nebulizer in high vacuum mode:
1 Take one length of the narrow-bore (0.38 mm ID) plastic capillary tubing
supplied with your nebulizer.
2 Fit the flared end of this tubing to the nebulizer capillary - trying to fit the other
end will damage the tubing.
3 Set up the instrument to measure absorbance using an easily atomized
element (such as copper) in an air-acetylene flame.
Since the uptake rate will be low, the initial sensitivity will be less than normal.
4 Set the instrument in continuous read mode.
5 Zero the instrument by pressing the Alt and Read keys together.
6 Loosen the locking ring and turn the ring and thimble fully clockwise.
7 Observe the absorbance while nebulizing a suitable standard solution.
8 Slowly and carefully turn the thimble counter-clockwise until the absorbance
reaches a maximum.
9 Hold the thimble so it cannot turn, then turn the locking ring until it is firmly
against the spray chamber body, locking the thimble in place.
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