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. 2015 Jul 28:5:12462.
doi: 10.1038/srep12462.

Potentiometric detection of chemical vapors using molecularly imprinted polymers as receptors

Rongning Liang  1 , Lusi Chen  2 , Wei Qin  1
Affiliations

Potentiometric detection of chemical vapors using molecularly imprinted polymers as receptors

Rongning Liang et al. Sci Rep. .

Abstract

Ion-selective electrode (ISE) based potentiometric gas sensors have shown to be promising analytical tools for detection of chemical vapors. However, such sensors are only capable of detecting those vapors which can be converted into ionic species in solution. This paper describes for the first time a polymer membrane ISE based potentiometric sensing system for sensitive and selective determination of neutral vapors in the gas phase. A molecularly imprinted polymer (MIP) is incorporated into the ISE membrane and used as the receptor for selective adsorption of the analyte vapor from the gas phase into the sensing membrane phase. An indicator ion with a structure similar to that of the vapor molecule is employed to indicate the change in the MIP binding sites in the membrane induced by the molecular recognition of the vapor. The toluene vapor is used as a model and benzoic acid is chosen as its indicator. Coupled to an apparatus manifold for preparation of vapor samples, the proposed ISE can be utilized to determine volatile toluene in the gas phase and allows potentiometric detection down to parts per million levels. This work demonstrates the possibility of developing a general sensing principle for detection of neutral vapors using ISEs.

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Figures

Figure 1
Figure 1. Experimental setup for potentiometric detection of the toluene vapor.
Figure 2
Figure 2. Schematic representation of the sensing mechanism of the proposed potentiometric vapor detection system based on MIP as receptor.
Figure 3
Figure 3. Equilibrium binding isotherms of the toluene MIP and NIP towards benzoic acid in methanol.
The binding assays were carried out by incubating 50 mg of the MIP or NIP in 3 mL of the methanol solution containing 2 ~ 10 mM benzoic acid. The binding amount is defined as the amount of the indicator which is bound by the MIP or NIP per unit weight. Error bars represent one standard deviation for three measurements.
Figure 4
Figure 4. Potential responses of the toluene MIP based ISE to toluene vapors at different concentrations using benzoic acid as the indicator.
Inset shows the plot of the initial slope of the EMF change versus the concentration of the toluene vapor in the range of 10–150 ppm. Experimental conditions: membrane composition (in wt%), PVC (33), o-NPOE (50), TDMACl (1.5), PEG 600 (12.5) and MIP (3); detection background, 0.03 M PBS of pH 8.0; the indicator, 0.2 mM benzoic acid; incubation time, 30 min. Error bars represent one standard deviation for three measurements.
Figure 5
Figure 5. Potentiometric selectivity of the proposed vapor sensing system towards the toluene vapor (■) over p-xylene (◻), naphthalene (▲) and ethyl acetate (▼) vapors.
The initial slope of the EMF change is used for qualification. Other conditions are as given in Fig. 4. Error bars represent one standard deviation for three measurements.
Figure 6
Figure 6. Potential responses to the toluene vapor in the concentration range of 10–150 ppm for the MIP (■), NIP (◻) and blank (▲) membranes.
The initial slope of the EMF change is used for qualification. Other conditions are as given in Fig. 4. Error bars represent one standard deviation for three measurements.
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