Hardware manual

Technical Information 6
Agilent 7500 Series ICP-MS Hardware Manual 6-5
pressure has to be 500 to 600 kPa (72 to 87 psi), giving about 1.2 L/min carrier
gas flow. A 1.0 L/min carrier gas flow rate is recommended and the make- up
gas has to be added to the carrier gas to achieve optimal conditions.
The recommended sample uptake rate is about 0.4 mL/min, which requires a
0.1 rps peristaltic pump speed. Higher peristaltic pump speeds may increase
sensitivity for lighter masses, but lose sensitivity for heavier masses and
increase oxide ions; sensitivity for mid masses may not be affected as much.
Refer to the Ion Lens section later in this chapter.
When a memory problem is severe, cleaning is required.
Concentric Nebulizer (CN)
The concentric nebulizer is one of the most popular nebulizers. This nebulizer
is made of quartz.
The sample is introduced into a small capillary tube by the peristaltic pump.
The carrier gas, which comes out around the capillary, nebulizes the sample.
The sample can also be introduced by self- aspiration.
Because of its inert material, the CN resists almost all chemicals, except HF
and higher concentrations of alkaline solutions. It especially offers good
resistivity against aqua regia. A disadvantage of the CN is the possibility of
clogging at the tip of the nebulizer when higher concentrations of dissolved
solids are introduced. Other problems are the fragility of glass and higher
boron background from Pyrex glass.
A typical carrier gas pressure is about 200 to 300 kPa (29 to 44 psi) at 1.2
L/min carrier gas flow rate. The Ar gas supply pressure has to be set to 700
kPa (100 psi). The behavior of the sample uptake rate is similar to that of the
BN.
When the signal is unstable, the capillary may be blocked by particles from a
dirty sample. In this case, to clean the capillary, you place the tip of the CN in
pure water and reverse the flow of the peristaltic pump so that the peristaltic
pump aspirates water from the nebulizer. Do not use a wire - the capillary can
be broken easily. When all other methods have failed, as a last resort a small
wire could be used to try to free the blockage.