Page 446 - Tandem Techniques

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The all-quartz main body consisted of an optical tube (12 cm long, 11 mm O.D. and 9 mm I.D.), which
was positioned in the optical path of the AA spectrometer. The thermospray nebulizer jet was situated
in a side tube, joining the analytical flame tube, and around which was wound a heater coil. Between
the heater and the analytical flame tube were two T junctions, 2.5 cm apart, the first carrying hydrogen
gas and the downstream port oxygen. The combustion chamber-thermospray assembly met the
analytical flame tube at an angle of 45°. The arrangement had a somewhat complex routine to produce
'smooth' ignition.

It was shown that arsenic pentoxide was derivatized, and no signal was observed in the absence of the
post-thermospray hydrogen or in the absence of the cool diffusion flame, which confirmed the nature of
the thermochemically mediated arsine-generation mechanism. It was shown that the solvents used with
both reversed phase and normal phase separations were compatible with the interface, and the system
was relatively insensitive to small changes in the operating conditions. The system was used to
successfully separate a mixture of arsenobetaine, arsenocholine and tetramethyarsonium.

The interface was shown not to denigrate the separation obtained from the column, and that a very
useful sensitivity was obtained. The absolute limits for the arsenic compounds, arsenobetaine,
arsenocholine and tetramethyarsonium, were claimed to be, 13.3, 14.5 and 7.6 ng respectively.
Inherently, this' arrangement has also the advantage of both a low purchase cost and low operating
costs, and this makes it an attractive choice for routine analysis.

The Moving Wheel Liquid Chromatography Helium Microwave Induced Plasma Interface

This interface involves a 'wheel' transport system, used in conjunction with an atmospheric pressure
helium plasma interface, specifically designed for halogen-selective detection. The device was
described by Zhang et al.[32] and the layout of their apparatus is shown in Figure 10.18.