Methyl mercury was determined using a purge and trap GC-ICP-MS
instrument. The purge and trap instrument (Tekmar LSC-2000) was equipped with a 25 mL fritted glass sparger, helium purging gas and
Tenax traps (21059-U Supelco). The purge and trap instrument was
connected on-line to GC (HP 5890) with a heated transfer line (60 °C).
GC was equipped with a capillary column (HP-5: 15 m, 0.32 mm,
0.25 μm (5% phenyl)-methylpolysiloxane) to separate volatile Hg
species. GC was coupled to Thermo Elemental X-series ICP-MS (Thermo
Electron, Winsford, England) with a transfer line shown in Fig. 1. The
transfer line was made of an uncoated fused silica tubing (0.32 mm
i.d.) which was connected to the chromatographic column inside the
GC oven and inserted into the central channel of the ICP-MS torch. A
polyurethane tube with a glass adapter was used to make a gas-tight
connection between the GC and ICP-MS instruments. The argon carrier
gas was introduced into the system via T-piece connection inside the
GC oven and was passed through the polyurethane tube connection to
ICP-MS. The use of a high-velocity argon carrier gas was necessary to
achieve sufficient flow to get the analytes to the plasma and to obtain
good peak shapes. The transfer line could be kept at room-temperature
due to low boiling point (b200 °C) of alkyl Hg species