New sensor arrays and sampling systems for a modular electronic nose

The electronic nose (EN) is an instrumented chemical sensor array with pattern recognition. ENs with open architectures, such as the MOSES II system, can be readily modified to accommodate a wide range of samples, sensors, and methods. Three specific ways to make the EN more versatile and improve the analytical capability have been developed, installed on the MOSES II system, and evaluated. First, the array of quartz crystal microbalance (QMB) and SnO2 heated metal oxide (MOX) sensors has been expanded to include amperometric gas sensors (AGS). This expands the chemical independence of the sensor responses, increases the analytical chemical information produced by the array, and improves the capability for qualitative and quantitative analysis with the EN. Second, we have incorporated a membrane separator into the sampling system which improves analysis capability especially on sensors that are sensitive to water vapor. Third, we have incorporated a heated noble metal filament into the inlet that thermally decomposes or reacts either gas, liquid, or solid samples to generate gaseous molecules that are derivatives of the sample and may be more/less reactive on the sensors. The filament often produces improved sensitivity and selectivity for specific analytes. Examples are presented of identification of cheeses and explosives, and the detection of bacterial growth. The data illustrate how each of these instrument modifications and newly developed methods can improve the EN by adding either sensors with complementary information or methods of sample pretreatment that enhance analytical performance.