Supplementary materials - ISE
Optimization and in-line potentiometric monitoring of enhanced photocatalytic degradation kinetics of Gemifloxacin using TiO2 nanoparticles/H2O2
Fawzia Ibrahima, Medhat A. Al-Ghobashyb,c,*, Mohamed K. Abd El-Rahmanb and Ibrahim F. Abo-Elmagda
a Analytical Chemistry Department, Faculty of Pharmacy, Mansoura University, Egypt
b Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Egypt
c Bioanalysis Research Group, Faculty of Pharmacy, Cairo University, Egypt
*Correspondence:
Dr. Medhat A. Al-Ghobashy, Analytical Chemistry Department, Faculty of Pharmacy, Cairo University, Cairo 11562, Egypt
E-mail:
Figure S1: Diagram of GEM ISE sensors showing the profile of the potential in mV vs time in min. The chemical structure of GEM showing the ionic centers is displayed.
I. GEM ISE prepared and used at pH 10
I.1 Sensor fabrication
In a glass Petri dishes (~5-cm diameter), 0.4 mL of 2-NPOE was thoroughly mixed with 190 mg PVC and 10 mg of TDMAC for sensor II. The mixture was dissolved in 6 mL THF by stirring using a glass rod. The Petri dish was then covered with a Whatman No. 3 filter paper and left to stand overnight to allow solvent evaporation at room temperature. A master membrane with a thickness of ~0.1 mm was obtained. From the prepared membrane, a disk (about 8-mm diameter) was cut using a cork borer and was then fixed using THF to a transposable PVC tip that was clipped into the end of the electrode glass part.
Equal volumes of 10 mM GEM in phosphate buffer of pH 10.0 and 10 mM potassium chloride in distilled water were mixed and used as an internal reference solution. Ag/AgCl-wire (1 mm diameter) was used as an internal reference electrode. The sensor was conditioned by soaking in a 10mM stock standard solution of GEM in phosphate buffer of pH 10.0 for 24 h and storing in the same solutions when not in use.
I.2. Sensor calibration
The proposed sensor was conjugated with double junction Ag/AgCl-reference electrode, calibrated by being immersed in GEM solutions ranged from 10 µM to 10mM and allowed to equilibrate while stirring until constant reading of the potentiometer. Then the electromotive forces (e.m.f) were recorded within ± 1 mV. Calibration graph was plotted relating the recorded electrode potentials obtained by the proposed sensor vs log molar concentrations of GEM and was washed with distilled water before and after each run till reaching a constant potential.
Figure S2: A: Profile of the potential in mV versus log concentrations of GEM in (M) obtained with the sensor, B: Profile of the potential in mV versus time in min obtained with the sensor
I.3 Application
GEM possesses a carboxylate moiety (Figure S1) with a pKa of 7.76, thus it behaves as anion in basic medium and therefore GEM ISE must exhibit anion exchange capacity. This was achieved by utilizing TDMAC as a lipophilic anionic exchanger where the membrane was initially conditioned by soaking in 10-3 M GEM solution to replace the original exchangeable counter ion (Br-) of the ion exchanger with acetate. The membrane showed a Nernstian response over a concentration range of 0.1mM-10mM with anionic slope of -33.2 mV/concentration decade.
Upon studying the pH effect on the sensor; below pH 8.0 there was a slight gradual decrease in the potential with increasing the pH without a well-defined constant region, this could be explained that below pH 8.0 the medium is not basic enough to cause complete dissociation and ionization of the carboxylate group of GEM (pKa value ~ 7.76). Alternatively, it was apparent that the sensor response was fairly constant in solutions of a pH values 10.0 - 12.0, i.e. in these pH ranges the ionisable COO- group of GEMS is completely dissociated and sensed. Keeping in mind the reduced anionic Nernstian Slope and slow response time of this fabricated tridodecylmethyl ammonium chloride based membrane sensor, therefore, it was not qualified for monitoring GEM photodegradation process.
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