Page 432 - Tandem Techniques

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compounds were used extensively as additives to increase the octane rating of gasolines to prevent
mixture detonation (as opposed to explosion) but their use was banned some years ago. However, they
are still used as boiler and turbine fuel additives and as they are considered environmentally
hazardous, they need to be monitored carefully in the various areas in which they are used. The LC/AS
tandem instrument incorporating the laser-excited atomic fluorescence spectrometer would appear ideal
for this type of assay.

The same tandem instrument was also used for the determination of some organotin compounds. The
tin measurements were carried out by resonance (300 nm excitation wavelength/300 nm detection
wavelength) and non-resonance (300 nm excitation wavelength/317 nm detection wavelength). The
detection limit for non-resonance operation was found to be about 12 ng/ml of tin, which was an order
better than that observed for resonance, i.e., 150 ng/ml of tin.

The LC/AAS Tandem Instrument Utilizing the Graphite Furnace Interface

The graphite furnace is a fairly obvious alternative interface to the flame for tandem LC/AS systems,
and the off-line use of the furnace as an adjunct to a liquid chromatograph has been reported by a
number of workers [18-20]. More recently, Nygren et al. [21] described an on-line LC/AAS tandem
instrument that utilized a graphite furnace interface, in a relatively simple manner. A diagram of the
critical part of the interface apparatus is shown in Figure 10.7 The thermo interface consisted of a
graphite tube made from glassy carbon, 28 mm long, 1/8 in. O.D. and 1.5 mm I.D.. The cuvette was
made from pyrolytically coated high-density graphite, 18 mm long, 4.5 mm I.D., and was side-heated
with integrated electrical contacts. The injection hole in the tube was enlarged to 3.1 mm, to
accommodate the interface. The column was connected to the interface by means of 25-30 cm of fused
quartz capillary (0.32 mm I.D.). The upper part of the interface consisted of a 1/16 in. length of stainless
steel tubing (15 cm long and 0.04 in I.D.), covered by a coiled, porcelain-insulated resistance wire and
could be heated to 200°C.