An amperometric biosensor for the indirect determination of Hg(II) has been developed based on inhibition of urease (EC 3.5.1.5) immobilized into alginate–chitosan polyelectrolyte complexes membrane. The biosensor response was monitored by following the reduction peak of hydrolyzed urea at around -0.15 V. The amperometric biosensor has a dynamic range 40–90 ppb Hg(II) with limit of detection of 66.45 ppb toward Hg(II) ions, repeatability (CV) value of 0.86% and only Ag(I) as the main potential interference. The sensor shows a stable and reproducible response for more than 2 weeks when it stored dry at 4 °C. The analytical results of Hg(II)-spiked water sample showed a good agreement with those obtained by atomic absorption spectrometry method, suggesting that the developed method may be applied in the determination of Hg(II) in the water samples.

A study of alginate-chitosan membrane synthesize was done. The membrane was prepared by mixing alginate hydrosol and chitosan hydrosol at mass ratio of 1:1 and pH of 5.28 approximately. Then it was applied for matrix immobilization of urease and bromothymol blue (BTB) by entrapment technique. The physical, chemical, thermal properties of alginate–chitosan membrane and their impact on immobilized urease activity were investigated. The polymer products were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM). It’s showed that alginate-chitosan membrane was formed by electrostatic interaction.  The obtained membran has better mechanical properties than original alginat and chitosan membranes. The immobilization urease into alginate-chitosan membrane retained the catalytic activity of the enzyme, as confirmed by color change of BTB indicator after membrane was immersed in substrate solution (urea). Therefore, alginate-chitosan membrane has good characteristics as matrix of enzyme immobilization.

Determination of alcohol content in food and beverage is needed for halal verification. Ethanol content in various food and beverage traditional products from fermentation was determined using the gas chromatography method with ethanol as standart and n-buthanol as internal standart. As comparison, measurement using alcohol meter were conducted. The GC measurement result were also compared with alcohol content printed on the packaging (value declared by the producer). The result showed that linear range in ethanol concentration was 1-10% with correlation coefficient (r) of  0.9984, indicated that GC has excellent linearity. Limit of detection was  0,5 ng, coefficient  variance (CV) was  ≤ 2%,  accuracy (K) was ≤ 5% and recovery was > 2%, indicated that  GC method has high sensitivity, accuracy, validity and recovery. Alcohol content in beer samples listed in the packaging was confirmed with GC measurement results. Anova test results showed  that the GC methods with  alcohol meter methods did not differ significantly so that the GC and alcohol meter methods can be used as a good alternative in determining the ethanol content in fermented foods and beverages as a support in halal verification.

PEC of the alginate-chitosan membrane as supporting material for immobilizing urease was produced. This study aimed to develop a supporting material for enzyme immobilization that has high stability, a fast response time and an easy and relatively inexpensive preparation procedure. An alginatechitosan PEC membrane was produced by reacting alginate hydrosol and chitosan (1:1 in mass) at pH 5.28, followed by mixing and drying at room temperature. The FTIR spectra, XRD patterns and SEM assay confirmed that alginate-chitosan PEC was obtained. The color change of the BTB indicator proved that urease was trapped in the cavities of the alginate-chitosan PEC membrane while the immobilized urease still showed catalytic activity. Thus, the membrane of alginate-chitosan PEC has good characteristics as a matrix for urease immobilization.

Synthesis of alginate-chitosan polyelectrolyte membrane and the determination of the physical-mechanical properties were carried out. Alginate-chitosan polyelectrolyte complex membrane can be made by mixing hydrosol alginate and chitosan hydrosol with a ratio of 1: 1 at pH 5.28. Membranes of alginate-chitosan polyelectrolyte complexes produced have physical-mechanical properties including load, elongation and elasticity, water absorption and resistance better than the constituent polymers. The results of FTIR spectroscopy analysis showed that there was an electrostatic interaction between alginate and chitosan through protonated amine groups of chitosan and carboxylic groups from alginate. Surface analyses by SEM showed that morphology of alginate-chitosan polyelectrolyte complex membrane was different with single membrane morphology