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G. N. ZEHENTBAUER, Department of Food Science & Nutrition, University of Minnesota, 1334 Eckles Avenue, St. Paul, MN 55108 and G. A. REINECCIUS.

The need to produce low calorie food, which tastes and smells like the full calorie one, has been an unsolved problem for many years. Recently, a new mass spectral technique called real time mouth and nose space analysis has been developed to finally address the process of flavor release during the eating process. However, this technique suffers from relatively low sensitivity ( 1 - 10 ug/L) and lacks the capability to distinguish between odorants with the same molecular weight.

Therefore, our objective was to investigate systematically the parameters, which effect ionization of organic compounds in order to improve sensitivity and selectivity.

A commercially available APCI-probe was modified to introduce gaseous samples through an enlarged sample tube (0.53 mm ID) by an externally connected vacuum pump. To simulate human breath, a vessel, which allowed to evaporate known amounts of odorants in a controlled environment of known relative humidity has been developed.

Our results showed that the sensitivity of our instrument was directly dependent on the flow rate of the introduced gaseous samples. Maximum sensitivity could be achieved at a minimum flow rate of 70 mL/min. An increase in auxiliary gas pressure led to a decrease of peak broadening and increased resolution. Further, by using model systems containing only a few odorants in a human breath-like environment, it could be shown that depending on the amount of water used as ionization gas either compound specific fragmentation or cluster formation could be induced.

The results suggest that in a complex mixture, we often cannot use molecular ion to monitor compound concentration. The ability to control fragmentation (or cluster formation) offers a means of increasing sensitivity and facilitate identification.