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off at 3500. The membrane was washed with water, methanol, and then water again, followed by
washes with 30%, 50% and 70% (v/v) aqueous dioxane and finally pure dioxane. The activation and
modification procedure was similar to that used for agarose beads [49]. 0.5 g of the membrane was
suspended in 10 ml of dioxane containing 0.28 g of carbonyldiimidazole and the mixture stirred for 15
minutes at room temperature. The membrane was then washed with 50 ml of dioxane, followed by 50
ml of 0.3M sodium borate (pH 10). After washing, the membrane was suspended in 20 ml of borate
buffer containing 3.25 g of hexanediamine, and the reaction allowed to proceed overnight at 4°C. After
the reaction was complete, the membrane was washed exhaustively with water before use. It is seen that
the preparation of the membrane is a complicated and tedious procedure, but for certain analyses may
well be worth the effort expended. The publication does not indicate the life that could be expected
from an average membrane. The interface is used with a jet separator (Ryharge separator), that
concentrates the extracted materials in the helium purge gas. The output of the jet separator passes
directly to the ion trap mass spectrometer. The layout of the total apparatus is depicted diagramatically
in Figure 5.33.

Figure 5.33
The Membrane Separator/Mass
Spectrometer Tandem System

The tandem instrument was used to determine the concentration of a number of different aldehydes in
aqueous solution, and it was found that the limit of detection or benzaldehyde was about 10 ppm. A
detection limit of 10 ppm is not particularly high, but the system acts as a continuous analyzer and has
some unique characteristics that might make it useful as a water pollution monitor.