Agilent 1100 HPLC was applied for OTCs speciation
separation. All stainless-steel parts of the HPLC system were
replaced by polyether ether ketone (PEEK) components to
reduce the possible contaminations. A piece of PEEK tubing
was used to connect the analytical column to the PFA
Nebulizer of the ICP-MS. The mobile phase of the HPLC was
CH3CN:H2O-CH3
COOH (65:23:12, V/V), 0.05% TEA, and
pH 3.0. There were 65% CH3CN and 12% CH3
COOH in
mobile phase
[11]
, and the total volume ratio of the organic
solvent was 77%. The high ratio organic solvent could lead to
the instability of inductively coupled plasma discharge. The
carbon particles, in particular, could build up on the orifice of
the plasma torch when CH
3CN and CH3COOH decomposed.
O2/Ar mixed gas (80% Ar) was mixed with the make-up gas
by a mass-flow controller and led to postnebulization, which
converted organic carbon to CO2
during the plasma discharge,
to avoid carbon buildup on the cones. However, if O
2
/Ar
mixed gas was added excessively, the extra power of the
inductively coupled plasma had to be used for the dissociation
of O2
molecules, and the measurement sensitivity of the
instrument could be greatly reduced. Moreover, the excessive
and high temperature O2
that passed from the inductively
coupled plasma could damage the cones. Therefore, 30%
O2
/Ar mixed gas was added to the make-up gas, which not
only reduced the carbon buildup on the cones but also
YU Zhen-Hua et al. / Chinese Journal of Analytical Chemistry, 2011, 39(4): 544–547
protected the cones. To reduce solvent loading on the plasma,
the double-pass spray-chamber was peltier cooled to –5 °C.
The high RF power (1500 W) helped the samples to
decompose completely