Effect of the polymer matrix on the response of optical sensors for dissolved aliphatic amines based on the chromoreactand ETHT 4001

The absorbance-based chromoreactand 4-(N, N-dioctylamino)-4'-trifluoroacetylazobenzene (ETHT 4001) has been investigated in different polymer matrices for the optical sensing of dissolved aliphatic amines. Sensor layers composed of ETHT 4001 and different polymer materials generally show a decrease in absorbance at around 500 nm and an increase in absorbance at around 420 nm wavelength upon exposure to dissolved aliphatic amines. This change in absorbance is caused by a conversion of the trifluoroacetyl group of the reactand into a hemiaminal or a zwitterion. Several polymer materials have been screened for their use in optical amine sensing, such as plasticized poly(vinyl chloride) (PVC), copolymers of acrylates, polybutadiene (PBD), and silicone. The choice of the polymer affects the sensitivity of the sensor layer, which is generally in the mM range for 1-butylamine, and the response time, which lies in the range of 10-30 min. Furthermore, the polarity of the polymer matrix has a strong influence on the diol formation caused by conditioning in water, and on the absorbance maximum of the solvatochromic reactand. However, the selectivity of the sensor layers for primary, secondary and tertiary amines is nearly unaffected by the polymer matrix. Thus, while it is possible to vary sensitivity towards amines and humidity by choosing the appropriate polymer matrix, it is not possible to modify the sensor's selectivity within different amines. (C) 2000 Elsevier Science B.V. All rights reserved.