Fig xA Real time on mobile color analysis system for

The optical Furosemide for MA detection has been developed by entrapping a bisazo dye in plasticized poly vinyl chloride (PVC) [15] and [16]. The dye, (4-[4-(4-trifluoroacetylphenylazo)-1-naphthylazo]-N,N-dioctylaniline), was prepared by using a diazotization procedure lasting more than 5 h. It was then dissolved with plasticizer and PVC in tetrahydrofuran before being spin coated on rotating polyester foil. This sensor was originally reported as a detector for amphetamine, which causes its color to change from blue to red, with a detection limit of 0.1 mmol L−1 [16]. However, it was suggested that because of MA's higher lipophilicity and the sensor response would be improved by a factor of 1.2. It was also suggested that the sensor responded to simple aliphatic amines with between 10 and 100 times less sensitivity than the amphetamine response.
Fluorescence chemosensors have also previously been developed for MA [17] and [18]. These fluorine-based sensors were synthesized using a complicated Suzuki-Miyaura cross-coupling reaction lasting 72 h. The resultant polymers needed a further 2 days of purification revealing a yield of 33–85% [17] and [18]. Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(2,1,3-benzothiadiazole-4,7-diyl)] revealed the best selectivity and sensitivity to MA vapor with a detection limit of 180 ppb [18].