Hardware manual

Technical Information 6
Agilent 7500 Series ICP-MS Hardware Manual 6-3
When the ASX500 Autosampler is used, it takes about 25 seconds for the
sample exchange and 15 - 30 seconds for stabilizing the signal. Use 30 seconds
on fast pump followed by 20 - 40 seconds stabilization time when the ASX500
is used.
The inner diameter of the sample transfer tube (Teflon) is 0.5 mm. A tube
smaller than 0.5 mm i.d. can cause the generation of bubbles in samples. This
problem may occur due to highly pressurized tap water that contains gases
(drinking water samples). It degasses when depressurized. In this case, the
sample has to be degassed prior to introduction.
The orange/red Tygon tubing (0.19 mm i.d.) is used for the internal standard
solution. The sample uptake rate at 0.1 rps is about 20 µL/min. When the
internal standard solution is added to the sample by the peristaltic pump, the
concentration of the internal standard is diluted about 20 times. Therefore, a 1
ppm internal standard solution in 5% (v/v) HNO
3
is recommended.
When orange/red Tygon tubing (0.19 mm i.d.) is used, some adsorption can
occur on the walls of the tubing. Some elements such as Au, Ag, Pd and Pt are
adsorbed onto the Tygon and it takes a long time to get stable signals. Alkali,
alkali- earth, and transition metals are not adsorbed. This adsorption may
occur with the white/black (1.02 mm i.d.) tubing as well, but the sample
uptake rate is much larger than with the orange/red tubing making the
adsorption negligible. In order to minimize this problem, HNO
3
has to be
added to the samples and standard solutions; a concentration of at least 1%
(v/v) HNO
3
is required and preferably 5% (v/v) HNO
3
.
Self- aspiration is a good way to avoid contamination from the peristaltic
pump tube and the adsorption problem, when an autosampler is not used and
the sample volume is sufficient. The concentric nebulizer, the crossflow
nebulizer and the micro flow nebulizer will self- aspirate, but not the
Babington nebulizer. It must be noted that self- aspiration may cause the
NOTE
The orange/red tube (0.19 mm i.d.) is very soft and easily stretched. This sometimes causes
a instability of the sample uptake rate when the peristaltic pump speed is varied drastically:
the tube stretches at higher peristaltic pump speeds and does not recover to its original
length immediately when the peristaltic pump speed is reduced to 0.1 rps. If the higher
pump speed is not used, it takes about 2 minutes for sample exchange at 0.1 rps.
When the internal standard is added to a sample by means of the peristaltic pump, the
maximum peristaltic pump speed should be 0.3 rps. When this fast pump speed is applied in
order to reduce sample exchange time, a longer stabilization time is required. Use 0.3 rps
fast pump for 50 sec and 50 sec stabilization time.