Judul: Linearitas dan Limit Deteksi Pasta Karbon Biosensor Arsen dengan Elektrode Pasta Karbon Termodifikasi Zeolit-Fe
Abstrak: Detection of arsenic using biosensor based on enzyme inhibition could be a routine alternative analysis method of aquatic environmental quality. Biosensors were fabricated from carbon paste electrode modified by zeolite-Fe with pyruvate dehydrogenase (PDH) enzyme as bioreceptor which was inhibited its activity by arsenic. Measurement results were compared to atomic absorption spectroscopy (AAS) measurement. Linearity and LOD value of both methods were compared. The results showed optimum performance of biosensor was at pH 7.00, 33 °C, and at PDH concentration of 0.0142 U/mL. The best linearity was around 97.70% in range of 2.50-20 ppb, meanwhile the best LOD achieved as low as 3.78 ppb. Biosensor’s LOD was lower compared to AAS value of LOD measured as low as 6.52 ppb. Paired data test showed that there was no significant difference between the two methods at 95% confidence level. Reproducibility of fabricated biosensor was still low, hence it needs to enhance the biosensor performance
Keyword: limit of detection, linearity, arsenic, biosensor, zeolite-Fe, carbon paste electrode

Judul: Biosensor Arsen(III) Menggunakan Elektrode Pasta Karbon Termodifikasi Partikel Nanozeolit-Fe dan Pengaruh Keberadaan Timbal(II)
Abstrak: Ion detection of arsenic(III) with biosensors using enzyme inhibition principle can be used as a method for detecting arsenic(III) ions in waters. Biosensor is made of carbon paste electrode as modified using zeolite-Fe nanoparticles and the enzyme pyruvate dehydrogenase (PDH) as an agent of biological activity identifier that will be inhibited by the presence of arsenic(III) ions. PDH was immobilized on the surface of the electrode. The optimum condition of enzyme activity was at 33 ᵒC , pH 7, and [PDH] 0.0141 U/mL. The activity of PDH was linear in the range of 0.6-20 ppb arsenic(III) ion concentracions with R2 = 0.9932. Detection limit and quantitation limit were 2.06 and 6.99 ppb, respectively. The electrode was relatively stable for 3 days, with good repeatability at %RSD of 1.98%. The existence Pb(II) ion did not interfere the performance of the ion electrode measurements of As-(III), as the value of Ki,j was <1.
Keyword: Bogor Agricultural University (IPB), ion interference Pb(II), quantitation limit, detection limit, pyruvate dehydrogenase, arsenic

Judul: Penggunaan Teorema Homeomorphy 2-Manifold dan Teorema Euler Poincare pada Torus 𝑇�� dan Simplicial Complex 𝐾��
Abstrak: Two dimensional topological spaces are said to be homeomorphic if they have the same topological invariant, where one of topological invariant used is an Euler characteristic. Homeomorphy 2-Manifold’s Theorem and Euler Poincare’s Theorem are used to distinguish two topological spaces. Homeomorphy 2-Manifold’s Theorem uses Euler characteristic to identify two dimensional topological spaces. Euler Poincare’s Theorem is an alternative way to find Euler characteristic with Betti number, which is topological invariant as well. The objective of this paper is to investigate the homeomorphism of torus 𝑇����� and simplicial complex 𝐾�����. Topological space torus and simplicial complex 𝐾����� have the same Euler characteristic, which is two. Based on Homeomorphy 2-Manifold’s Theorem topological space torus 𝑇����� and simplicial complex 𝐾����� is homeomorphic.
Keyword: simplicial, torus, Euler, homeomorphism, topology