National Metrology Laboratory

Sepang, Malaysia

National Metrology Laboratory

Sepang, Malaysia
Time filter
Source Type

Abdul Kadir H.,National Metrology Laboratory | Abas F.,University Putra Malaysia | Mediani A.,University Putra Malaysia | Ismail I.S.,University Putra Malaysia | Lajis N.H.,University Putra Malaysia
International Food Research Journal | Year: 2017

The aim of the present work was to compare and choose the best method to extract incurred pesticide residues from green tea. Accelerated solvent extraction (ASE) with in-cell cleanup and the quick, easy, cheap, effective rugged and safe (QuEChERS) methods were tested on green tea samples with incurred beta-endosulfan pesticide. The extracts were analyzed by GC-MS/MS and the recovery and the precision of both methods were compared. The average recovery using ASE with the in-cell cleanup method was in the range of 89 to 92% which is better than that obtained using a QuEChERS method. Both the ASE with in-cell cleanup and the QuEChERS methods provided good precision with RSDs in the range of 12 to 15% and 17 to 18%, respectively. This finding indicates that the ASE method with the in-cell cleanup is more suitable for the accurate determination of pesticides incurred in tea. © All Rights Reserved.

Song H.W.,Korea Research Institute of Standards and Science | Salazar M.,Korean University of Science and Technology | Salazar M.,National Metrology Laboratory | Kim S.M.,Korea Research Institute of Standards and Science | Woo S.-Y.,Korea Research Institute of Standards and Science
Mapan - Journal of Metrology Society of India | Year: 2017

The capacitance diaphragm gauge (CDG) is one of the most accurate transfer standards for use in atmospheric to medium vacuum regions. Currently, it is practical to cover a wide range of measurements with the least amount of equipment possible. In this study, one CDG with a metal membrane and two CDGs with a ceramic membrane are characterized through calibrations using a reference standard, in this case a force-balanced piston gauge system, through repeated measurements ranging from about 500 Pa to 13.3 kPa, below 10% of their full capacities (133 kPa). Performance characterizations such as repeatability, long-term instability and zero-pressure instability assessments were conducted. According to repeatability and long-term instability measurements of 133 kPa CDGs tested below 10% of their full-scale (FS) capacities, the metal membrane CDG was found to be somewhat superior compared to the ceramic membrane CDG due to the inherent material stiffness of this type of CDG. However, the difference was negligible, and both membrane-type CDGs could be used at 3 kPa (about 2% of the FS). The responses to heater effects and the results of the zero-pressure instability tests were also evaluated and presented. As shown from these results, the zero-pressure instability is major concerns for the metal membrane CDG, while it has little effect for the ceramic membrane CDG. CDGs in either case have their own advantages and can be used depending on the user’s discretion. © 2017 Metrology Society of India

Ahmed M.D.,International Islamic University Malaysia | Taher M.,International Islamic University Malaysia | Maimusa A.H.,Vector Control Unit | Rezali M.F.,National Metrology Laboratory | Mustafa Mahmud M.I.A.-D.,International Islamic University Malaysia
Natural Product Sciences | Year: 2017

An antimicrobial compound has been isolated from the leaves of Glochidion superbum. The compound was determined as methyl 3, 4, 5-trihydroxybenzoate (methyl gallate), based on ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR) and mass spectroscopy (MS) analysis. The isolated compound exhibited potent antimicrobial activity against three clinical isolates of methicillin resistant Staphylococcus aureus (MRSA) by qualitative agar disc diffusion method and quantitative broth dilution method. Agar disc diffusion was done in a dose-dependent manner for each bacterial isolate at disc potencies of 25, 50, 100, and 150 µg/disc. The zones of inhibition were on average equal to 12.27, 14.20, 15.43, and 24.17 mm respectively. The inhibition zones were compared with that of vancomycin disc at 30 µg as a reference standard. The MIC and MBC values were 50 µg/mL and 100 µg/mL respectively. The results of anti MRSA activity were analyzed using one-way ANOVA with Turkey’s HSD and Duncan test. In conclusion, methyl gallate which was isolated from G. superbum showed the inhibition activity against methicillin resistant S. aureus. © 2017, Korean Society of Pharmacognosy. All rights reserved.

Ibrahim M.A.,National Metrology Laboratory
Proceedings - 5th International Conference on Electrical Engineering and Informatics: Bridging the Knowledge between Academic, Industry, and Community, ICEEI 2015 | Year: 2015

Embedded systems (ES) become available anywhere and anytime as an established part of our daily routine. Developers of these systems face significant challenges in code and information security. Whereas, software tampering is one of these challenges, code integrity detection is one of the main approaches used to defeat it. Checking code integrity achieves tamper proofing by method of identification of unauthorized alteration to recognize any tampered code is executed or tampered data are used. Our research objective is to propose an applicable framework for tampering detection in ES and this paper introduces the exploratory outcomes so far. © 2015 IEEE.

Taher M.,International Islamic University Malaysia | Susanti D.,International Islamic University Malaysia | Rezali M.F.,National Metrology Laboratory | Zohri F.S.A.,International Islamic University Malaysia | And 3 more authors.
Asian Pacific Journal of Tropical Medicine | Year: 2012

Objective: To study the chemical constituents of stembark of Garcinia malaccensis (G. malaccensis) together with apoptotic, antimicrobial and antioxidant activities. Methods: Purification and structure elucidation were carried out by chromatographic and spectroscopic techniques, respectively. MTT and trypan blue exclusion methods were performed to study the cytotoxic activity. Antibacterial activity was conducted by disc diffusion and microdilution methods, whereas antioxidant activities were done by ferric thiocyanate method and DPPH radical scavenging. Results: The phytochemical study led to the isolation of α,β-mangostin and cycloart-24-en-3β-ol. α-Mangostin exhibited cytotoxic activity against HSC-3 cells with an IC 50 of 0.33 μM. β- and α-mangostin showed activity against K562 cells with IC 50 of 0.40 μM and 0.48 μM, respectively. α-Mangostin was active against Gram-positive bacteria, Staphylococcus aureus (S. aureus) and Bacilus anthracis (B. anthracis) with inhibition zone and MIC value of (19 mm; 0.025 mg/mL) and (20 mm; 0.013 mg/mL), respectively. In antioxidant assay, α-mangostin exhibited activity as an inhibitor of lipid peroxidation. Conclusions: G. malaccensis presence α- and β-mangostin and cycloart-24-en-3β-ol. β-Mangostin was found very active against HSC-3 cells and K562. The results suggest that mangostins derivatives have the potential to inhibit the growth of cancer cells by inducing apoptosis. In addition, α-and β-mangostin was found inhibit the growth of Gram-positive pathogenic bacteria and also showed the activity as an inhibitor of lipid peroxidation. © 2012 Hainan Medical College.

Hussain F.,National Metrology Laboratory | Othman M.Y.H.,National University of Malaysia | Sopian K.,National University of Malaysia | Yatim B.,National University of Malaysia | And 2 more authors.
Renewable and Sustainable Energy Reviews | Year: 2013

Abstract Recently, photovoltaic/thermal (PV/T) solar collectors are popular technologies towards harvesting solar energy. A PV/T collector is a combination of photovoltaic and solar thermal components integrated into one system that capable of producing both electrical and thermal energy simultaneously. The concept and design of a PV/T collector are being developed in order to improve the electrical efficiency of a photovoltaic module at high temperature. This paper elaborates literatures of the design developed and the performances of a PV/T air base collector. Early research works in this area until recently are focusing on their design characteristics and results. This report also covers research works on future development of a PV/T collector as a building integrated photovoltaic/thermal (BIPVT) system. It clearly shows that, by appropriate architectural design and configuration, the future of a PV/T collector can be encouraging as an alternative application in the residential, industrial and commercial buildings. © 2013 Elsevier Ltd.

Abdullah M.N.,National University of Malaysia | Abdullah M.N.,National Metrology Laboratory | Shaari S.,National Metrology Laboratory | Ehsan A.A.,National Metrology Laboratory | And 2 more authors.
Physics Procedia | Year: 2011

Four wave mixing (FWM) is one of the non linear optical phenomena in optical fibre, in the presence of high optical field. Even though FWM has negative impact towards dense wavelength division multiplexing (DWDM) system, nevertheless, this phenomenon is also one of the alternative resources in deriving new signals to be adapted in the current and future telecommunication network. The main objective of this research is to study the generation FWM through photonic crystal fibre (PCF) at telecommunication operating wavelength. It covers the structure and manipulation of instrument's configuration to generate FWM through PCF, by applying Fibre Ring Laser (FRL) approach. However, the PCF has zero dispersion at 1040 nm, while the range of signals is around 1550 nm. A system which combines FRL locked with few units of fibre Bragg grating (FBG) and a PCF are used to facilitate the generation of the harmonic signals. Suitable FBGs specifications were identified to match with the output spectrum. Experiments were performed to further analyse the dynamics in generating FWM, including the generated wavelength formations. The results obtained, shows that the agreement between theory and experiments results on positions of multi wavelengths signal due to FWM is 0.3 % on average with expanded uncertainty of 4.9 % at k=2. © 2011 Published by Elsevier B.V.

Ahmad W.A.,University of Technology Malaysia | Yusof N.Z.,University of Technology Malaysia | Nordin N.,University of Technology Malaysia | Zakaria Z.A.,University of Technology Malaysia | Rezali M.F.,National Metrology Laboratory
Applied Biochemistry and Biotechnology | Year: 2012

The present work highlighted the production of violacein by the locally isolated Chromobacterium violaceum (GenBank accession no. HM132057) in various agricultural waste materials (sugarcane bagasse, solid pineapple waste, molasses, brown sugar), as an alternative to the conventional rich medium. The highest yield for pigment production (0.82 g L-1) was obtained using free cells when grown in 3 g of sugarcane bagasse supplemented with 10% (v/v) of L-tryptophan. A much lower yield (0.15 g L-1) was obtained when the cells were grown either in rich medium (nutrient broth) or immobilized onto sugarcane bagasse. Violacein showed similar chemical properties as other natural pigments based on the UV-Vis, Fourier transform infrared spectroscopy, thin-layer chromatography, nuclear magnetic resonance, and mass spectrometry analysis. The pigment is highly soluble in acetone and methanol, insoluble in water or non-polar organic solvents, and showed good stability between pH 5-9, 25-100 °C, in the presence of light metal ions and oxidant such as H2O2. However, violacein would be slowly degraded upon exposure to light. This is the first report on the use of cheap and easily available agricultural wastes as growth medium for violacein-producing C. violaceum. © Springer Science+Business Media, LLC 2012.

Kadir H.A.,National Metrology Laboratory | Kadir H.A.,University Putra Malaysia | Abas F.,University Putra Malaysia | Zakaria O.,National Metrology Laboratory | And 2 more authors.
Analytical Methods | Year: 2015

A fast, simple and easily automated method was developed for the simultaneous determination of pesticide residues in tea using accelerated solvent extraction (ASE) with in-cell cleanup and gas chromatography-tandem mass spectrometry (GC-MS/MS). This method integrates extraction and cleanup processes into a single step, by adding a clean-up sorbent along with the sample into the extraction cell. The efficiency of this method was characterized in terms of its recovery (with values ranging from 90 to 98%), repeatability along with intermediate precision (showing relative standard deviations less than 15%), and sensitivity (providing detection limits between 0.001 and 0.007 μg g-1). The concentration range of the pesticide residues found in the sample is from 0.008 to 0.161 μg g-1. The relative expanded uncertainty achieved for this method ranged from 24% to 34%. The results indicate that the proposed method is easy and reliable for the determination of pesticide residues in tea, and it is suitable for use in routine analysis. This journal is © The Royal Society of Chemistry.

Sirat H.M.,University of Technology Malaysia | Rezali M.F.,University of Technology Malaysia | Rezali M.F.,National Metrology Laboratory | Ujang Z.,Environment and Bioprocess Technology Center
Journal of Agricultural and Food Chemistry | Year: 2010

Phytochemical and bioactivity studies of the leaves and stem barks of Tibouchina semidecandra L. have been carried out. The ethyl acetate extract of the leaves yielded four flavonoid compounds, identified as quercetin, quercetin 3-O-α-L-(2'-O-acetyl) arabinofuranoside, avicularin, and quercitrin, while the stem barks gave one ellagitannin, identified as 3,3'-O-dimethyl ellagic acid 4-O-α-Lrhamnopyranoside. Evaluation of the antioxidative activity on the crude extracts and pure compounds by electron spin resonance (ESR) and ultraviolet-visible (UV-vis) spectrophotometric assays showed that the pure isolated polyphenols and the EtOAc extract possessed strong antioxidative capabilities. Quercetin was found to be the most active radical scavenger in DPPHUV and ESR methods with SC50 values of 0.7 μM ± 1.4 and 0.7 μM ± 0.6 μM, respectively, in the antioxidant assay. A combination of quercetin and quercitrin was tested for synergistic antioxidative capacity;, however, there was no significant improvement observed. Quercetin also exhibited strong antityrosinase activity with a percent inhibition of 95.0% equivalent to the positive control, kojic acid, in the tyrosinase inhibition assay. © 2010 American Chemical Society.

Loading National Metrology Laboratory collaborators
Loading National Metrology Laboratory collaborators