Optode Membrane for Determination of Nicotine via Generation of Its Bromoethane Derivative

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Abstract
A plasticized poly(vinyl chloride) optode membrane incorporated with a valinomycin ionophore, a H+-selective chromoionophore (ETH 5294), and a lipophilic potassium tetrakis(4-chlorophenyl)borate was used as a reversible sensing device for the indirect optical determination of nicotine. Nicotine was extracted from a tobacco product (1−5 g) and converted to its bromoethane derivative (NBD+Br-) by reacting with a solution of bromoethane in ethanol. NBD+Br- in a solution of 0.05 M boric acid−Borax buffer and 0.2 mM Triton X-100 was extracted into the bulk of the membrane and subsequently caused changes in optical absorption of the sensing layer. The response slope, dynamic working range, detection limit, sensitivity, selectivity, effects of buffer solution and neutral surfactant Triton X-100, and lifetime were discussed in detail. The response was pH dependent. At pH 8.5, the detection range was extended from 0.4 μM to 1 mM. Typical response times (t95) of the samples were 2−4 min. The optode method was successfully used to detect nicotine in a tobacco sample from the market (average content 0.720%; RSD 0.044%; n = 11). The interference of K+ on the optode method can be prevented by the pre-extraction procedure. Malic acid and citrate showed no interferences. The recovery of nicotine as NBD+ was 84−119% in the range 0.035−5% nicotine. The result was satisfactory compared with an AOAC UV standard method.