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the plastic end cap (i.e., all glass). They are typically used with glass concentric nebulizers and use only two ‘O rings’ to
connect the nebulizer to the spray chamber. I have found that the plastic end cap may cause longer washout times, carry over
problems, and is a very large connection surface where connection problems can occur. Using a glass concentric nebulizer and
all glass spray chamber a precision of between 0.2 and 0.5% RSD should be observed. If an all glass system gives a precision of
1% RSD or greater, then there is most likely a connection problem or the nebulizer gas flow rate is too high (look for spitting
when checking the nebulizer free flow and do not be afraid to lower the gas pressure {argon sample flow} to the nebulizer).
Peristalic Pump Tubing
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and the pressure can be set to give a steady mist when the pump in running. The problem is that the pump tubing stretches
and either the pressure is not enough to drive the solution through the tubing or you over tighten and get a pulsating mist
spray. This is a problem that each analyst has to be aware of and solve through experimentation. This problem is particularly
troublesome for ICP-MS users because the argon flow changes as the tubing stretches. This causes a relative increase in the
sensitivity of the higher atomic number elements.
Maintenance
I prefer glass components because of their ease of operation and cleaning. It is always best to start the day with a clean
nebulizer, spray chamber, and torch. Cleaning the torch daily will also extend its life. There are many cleaning solutions that
can be used. Some of our analysts prefer 1:1 nitric acid/water and others prefer sulfuric acid and hydrogen peroxide.
Another common cleaning solution is 1:1 HCl/nitric. All of these solutions will work depending upon the nature of the
contaminants. The sulfuric/peroxide is generally a severe approach and needed only if organics such as grease are suspected.
Be advised that ultrasonic baths are great for cleaning. However, NEVER use them to clean a glass concentric nebulizer.
Glass concentric nebulizers are cleaned by leaching and occasionally by applying a backpressure with water to remove lodged
particles. The use of a cleaning wire or ultrasonic bath is a sure way to destroy the nebulizer.
In summary, when it comes to ICP introduction systems there is no substitute for experience. Relatively speaking,
introduction systems are simple but they are not easy to maintain and they are challenging to operate to their maximum
potential.
Nebulizers, Spray Chambers and Torches 5
There has been a tremendous activity in the area of sample introduction over the past 30 years since ICP has been
commercially available. The objective of this section is to acquaint the reader with the basic options available to the ICP
operator for the introduction of ‘liquid’ samples.
Some of the considerations in selecting an introduction system include dissolved solids content, suspended solids presence,
presence of HF or caustic, detection limit requirements, precision requirements, sample load requirements, sample size
limitations, and operating budget. In the last section, the concentric nebulizer and all glass introduction systems were given
top billing but they may not work at all for your application. The analyst is left with the task of choosing the best introduction
components after taking into account the appropriate considerations.
Nebulizers
Pneumatic Nebulizers
The term “pneumatic” is defined as ‘of or relating to or using air or a similar gas’. The word “nebulizer” is derived from the
Latin “nebula” meaning mist and is defined as ‘an instrument for converting a liquid into a fine spray’. Therefore, a pneumatic
nebulizer is literally an instrument for converting a liquid into a fine spray that uses a gas as the driving force.
Some of the most popular ICP pneumatic nebulizers are:
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