Characterization of PVA-Enzyme Coated Indicator Electrodes GA coated again with PVC-KTpClPB-o-NPOE SEM-EDS, FTIR and XRD analysis

This study aims to characterize the tungsten-urea analyte indicator electrode. The method used is biosensor potentiometry with urease enzyme immobilization technique. This indicator electrode was coated with PVA-enzyme coated with glutaraldehyde (GA) 2.9% coated with PVC-KTpClPB- o-NPOE with o-NPOE variation of 61% and 66%. Characterization of coated indicator electrodes using SEM-EDS, FTIR and XRD analysis. A1-4 61% indicator electrode sample coated PVA-enzyme 1x coated with glutaraldehyde (GA) 2.9% 1x coated PVC-KTpClPB- o-NPOE 1x, with o-NPOE 61%. A3-4 61% indicator electrode sample coated PVA-enzyme 3x coated with glutaraldehyde (GA) 2.9% 1x coated PVC-KTpClPB- o-NPOE 1x, with o-NPOE 61%. Likewise, the reasoning of samples A1-4 66% and A3-4 66%. There are four indicator electrodes made with the notation A1-4 61%, A1-4 66%, A3-4 61% and A3-4 66%. The best results were obtained at the indicator electrode sample A1-4 61%, contributing to the urea sensor of the potentiometer cell

An ion selective electrode (ISE) has been used (Huang, 2014) with 2-nitrophenyloctyl ether (NPOE) and mixed in poly(vinyl chloride) (PVC). The obtained sensitivity is 19.7 mV/decade with a range of 5.10-7-10-2M. According to (Rahman, 2008) the optimum sensitivity is 59 mV/decade, for a reaction to be reversible (in practice the difference is typically between 70-100 mV).
The immobilization technique in the construction of the biosensor involves the urease enzyme and a polymer consisting of PVC for the urea bioser (Ulianas, Heng and Ahmad, 2011). Poly(vinylchloride) (PVC) is a polymer matrix commonly used in ISE (Mir, Lugo, Tahirbegi and Josep Samitier, 2014).
The indicator electrodes were made by using the potentiometric biosensor of the urease enzyme immobilization technique in two notations B1-4 2.9% GA and B3-4 2.9% GA. Then analyzed by SEM-EDS. From the two samples above, it was continued to manufacture four indicator electrodes with notation A1-4 61%, A3-4 61% and A1-4 66%, A3-4 66%. Then the four were analyzed by SEM-EDS, FTIR and XRD.

EDS and SEM analysis results
Analysis of indicator electrodes B1-4 and B3-4 using EDS and SEM has not been able to ensure the best indicator electrode samples. For strong conclusions, further FTIR and XRD analyzes are needed. After UV-Vis and SEM-EDS analysis, samples of indicator electrodes B1-4 and B3-4 without o-NPOE were further analyzed by cell potentiometer, to characterize their sensitivity and detection range. The best results were obtained at the indicator electrode B1-4. However, samples B1-4 and B3-4 continued to the next step in the manufacture of indicator electrodes A1-4 61%, A3-4 61%, A1-4 66% and A3-4 66%, the results of the SEM analysis can be seen in Figure 1 and EDS Table 1. SEM-EDS analysis for indicator electrodes having o-NPOE can be seen in table 2. The weight percent of tungsten A1-4 61% is 91.91% and the weight percent of tungsten A3-4 61% is 95.98%. The weight percent of tungsten A1-4 66% was 84.93% and the weight percent of tungsten A3-4 66% was 79.81%. The largest weight percentage of tungsten was at the best 61% o-NPOE content at the indicator electrodes A1-4 61% and A3-4 61%. A good SEM morphological analysis of the membrane was also found at the indicator electrodes A1-4 61% and A3-4 61%, the pores slightly increased the weight percent of tungsten. At the indicator electrodes A1-4 66% and A3-4 66% the number of pores reduces the weight percent of tungsten. Morphology of indicator electrodes A1-4 61% EDS analysis peak intensity 4.3 keV weight percent tungsten 91.91%; morphology of indicator electrodes A1-4 66% EDS analysis peak intensity 2.5 keV weight percent tungsten 84.93%; morphology of indicator electrode A3-4 61% EDS analysis peak intensity 4.3 keV weight percent tungsten 95.98%; morphology indicator electrode A3-4 66% EDS analysis peak intensity 4.5 keV weight percent tungsten 79.81 %. This confirmed the high purity of the prepared tungsten (Shawky, 2021).
Although the dielectric constant = 24 of o-NPOE is the highest value, it does not significantly affect the membrane potentiometric detection limit in the case of drugs .
The observed absorption bands at 745 cm-1 and 1081 cm-1 associated with the C-Cl and B-C stretches, respectively confirmed the presence of the lipophilic additive KTpClPB. The presence of PVC as an inert membrane matrix was confirmed by the gauche absorption band observed in the 669 cm-1 region (Badakhshan, 2019). The ratio of plasticizer/PVC plays a major role to obtain optimal response. o-NPOE was chosen as a plasticizer because of the good solubility of the membrane components and high dielectric constant. Meanwhile, NaTPB is used as a lipophilic additive because of its important role in increasing the sensitivity and selectivity of the electrode and reducing anionic interference (Alharthi, S.S., Fallatah, A.M. and Al-Saidi, H.M., 2021). The lipophilic additive in this study was KTpClPB.
UV-Vis spectroscopy is the most useful and reliable technique for confirming the main characterization of the size, shape and stability of the nanostructures of metal oxides synthesized in liquid suspension. According to the analysis (Shawky, 2021;Al-Mohaimeed, et al, 2021) the increase in the absorption peak with respect to the wavelength has an effect on the increase in % Transmittance of the wave number.
According to (Alharthi, S.S., Fallatah, A.M. and Al-Saidi, H.M., 2021), the increase in % Transmittance with respect to the wavelength of the FTIR, was followed by an increase in the peak intensity with respect to the atomic elements of the EDS. If you observe Figure 2 of the FTIR spectrum pattern, compared to Table 2 of the high peak intensity of EDS, there is only one best sample, namely A1-4 61%. It can be seen in Table 3. the following is the relationship between the composition of o-NPOE in PVC with weight percent and peak intensity height and the pattern of the FTIR spectrum.  Research experiments have been carried out with UV-Vis analysis, the absorbance spectrum pattern of PVC-KTpClPB-o-NPOE at o-NPOE 61% two absorption peaks at 250 nm and 337 nm; at o-NPOE 66% three absorption peaks of 262, 320 and 390 nm. Meanwhile, the best PVA-Enzyme-GA absorbance spectrum pattern was at GA 2.9%, with a peak absorbance height of 300 nm. There is an increase in the absorbance peak with the addition of the concentration of o_NPOE , and an increase in the absorbance of ionopores with the addition of metal salts (Golcs et al., 2018).

XRD Characterization Results using o-NPOE
XRD is an analytical method for estimating and measuring different crystal forms in the tested samples [Shawky, 2021]. (Alarfaj, N.A. and El-Tohamy, M. F., 2020) have used the characterization of UV-Vis, FT-IR, XRD, and EDX spectroscopic methods in determining the calibration curve of the potentiometric system of the o-NPOE modified coated wire membrane sensor. There was a change in the XRD spectrum pattern (Hakim et al, 2021) of KTpClPB as shown in Figure 4.  (El-Naby, E.H., 2019) CE NaTPB ionophore based polymer membrane sensor with incorporation of anionic additives; potassium tetrakis(pchlorophenyl)borate (KTpClPB) produces an excellent "CE NaTPB/KTpClPB" sensor. High sensitivity with a response slope closer to the ideal Nernstian value and a wider linear range and anionic additives cause a dramatic increase with the o-NPOE plasticiser in the lower limit of detection 5.10-5 M (with a DOP limit of detection of 7.5.10-7 M), also improves the interfacial ion exchange kinetics. (Kaur, Chhibber andMittal, 2017, 2017), Response time is an important parameter to evaluate the working efficiency of the electrode, the best content of o-NPOE in PVC is 61%.