Many ICP nebulizers generate a 'vacuum' when in operation, and No-Break Nebulizers are no exception, due to a pressure difference that is created by gas flow at the nebulizer's gas orifice. Since the pressure in the region immediately outside the gas orifice of an ICP nebulizer is very close to atmospheric pressure, the nebulizer 'vacuum' is manifested at the intake end of the nebulizer's sample passage.

This effect can be used to aspirate liquid samples at rates governed by the relation attributed to the scientists Hagen and Poiseuille : this states that the volume of a homogeneous fluid passing through a narrow tube per unit time is directly proportional to the pressure difference between its ends and to the fourth power of its internal radius, and inversely proportional to its length and to the viscosity of the fluid. Using the term (dV/dt) for flow rate, the mathematical expression is :

     

Typical levels of vacuum generated by concentric ICP nebulizers are 2 to 7 psi; this quantity is represented by the 'delta-p' term in the equation above. Its magnitude depends upon the pressure of the nebulizer gas, typically rising to a maximum at an applied pressure of 2 to 4 bars. Since the gas flow through an ICP nebulizer is usually constrained by plasma settings to be within the range 0,5 to 1,5 litres/min., the factors that independently regulate nebulizer aspiration are the internal diameter of the sample tube and its length.

No-Break Nebulizers are available in versions that are suited to all types of ICP instruments and through a range of aspirated uptakes from low ( 10 - 100 ul/min. ), to medium ( 50 to 400 ul/min. ) and high uptakes ( 600 ul/min. up to more than 2 ml/min. )

By using the Selection Table in this site and with a choice of the right overall sample tubing length and ID,
a very wide range of aspirated uptakes can be selected.

Above is a typical curve relating aspiration of an ICP nebulizer to its applied pressure.

Curves such as this can be quickly measured with EPOND's  XENA  electronic uptake meter.

This curve closely resembles the shape of the curve relating nebulizer vacuum to applied pressure,
since it is essentially the 'vacuum' that causes the aspiration.
The presence of primary aerosol in the nebulizer's gas orifice alters this 'vacuum' though ...
and the temperature near the tip of a nebulizer will drop when solvent aerosol evaporates
  -  a complete physical analysis is thus quite difficult.

The essential points are that :

(a) aspiration of sample can give a simpler and more stable generation of aerosol, and that

(b) primary aerosol generated at uptakes less than ~ 30 ul/min. is so fine that it can often be injected directly into the injector of an ICP torch.

You can see the publication on this - the ' TISIS ', by J-L. Todoli and J-M. Mermet : JAAS (2002), Vol. 17, pp.345-351