Page 412 - Tandem Techniques

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nozzle/skimmer alignment and loss due to turbulence. Consequently, the skimmers were designed to
provide an undisturbed path from their point of generation, until they were in the ion source of the mass
spectrometer. The body of the momentum separator was made of stainless steel and the nozzles and
skimmers were machined from 6010 grade aluminum. The separation between the nozzle and the first
skimmer was about 10 mm and was adjustable by the use of shims. The first skimmer had a 100°
exterior angle and a 95° interior angle with a 0.5 mm orifice. The second skimmer had a 45° exterior
angle and a 30° interior angle and a 1 mm orifice. The distance between the two skimmers was also
about 10 mm and was also adjustable. Both interlock chambers were pumped with mechanical vane
(hot oil) pumps, having a capacity of 21.6 m /h. The interface was found to be easy to operate, the
3
skimmer provided little turbulence and it had an overall high transport efficiency. The device was tested
by using the normal phase separation of the cis and trans isomers of retinol acetate. The column was
packed with 5 µm silica gel and the solutes eluted isocratically with a mixture of 95% n-hexane and 5%
diethyl ether at a flow rate of 1 ml/min. The total mass of sample injected was 50 ng and the separation
did not appear to be impaired by the interface and the sensitivity that is achieved, compares well with
other types of interface. Another example of the use of the interface was for the separation of aliphatic
fatty acids using a reversed phase column with gradient development from 80% methanol and 20%
water (containing 3% acetic acid) and 100% methanol. There is some indication of peak tailing,
although whether that arises from the column or the interface was not clear. This particular example
demonstrated that the nebulizer functioned well with aqueous solution containing up to 20% of water. It
was not reported whether or not higher water contents work equally as well. The EI spectra exhibited a
significant molecular ion for all solutes and was in complete agreement with reference spectra for the
respective compound. There was no evidence of thermal degradation occurring in the interface, despite
the relatively high temperature of the ion source (viz. 240°C).

Cappiello and Famiglini [48] developed the technique further, and designed a micro-flow particle beam
interface. They started with the particle beam interface manufactured by Hewlett-Packard, which was
similar in form to